Contract No. HY/2011/03
Hong Kong-Zhuhai-Macao Bridge Hong Kong Link Road
Section between Scenic Hill and Hong Kong Boundary Crossing Facilities
Quarterly EM&A Report No. 42 (December 2022 to February 2023)
2 June 2023
Revision 1
Main Contractor Designer
Contents
Executive Summary
1.4 Construction Works Undertaken During the Reporting Period
2.1 Summary of EM&A Requirements
3....... Environmental Monitoring and Audit
3.1 Implementation of Environmental Measures
3.2 Air Quality Monitoring Results. 6
3.4 Water Quality Monitoring Results
3.5 Dolphin Monitoring Results
3.6 Mudflat Monitoring Results
3.7 Solid and Liquid Waste Management Status
3.8 Environmental Licenses and Permits
4....... Environmental Complaint and Non-compliance
4.2 Summary of Environmental Complaint, Notification of Summons and Successful Prosecution
5....... Comments, Recommendations and Conclusion
Figures
Figure 1.1 Location of the Site
Figure 2.1 Environmental Monitoring Stations
Figure 2.2 Transect Line Layout in Northwest and Northeast Lantau Survey Areas
Appendices
Appendix A Environmental Management Structure
Appendix B Construction Programme
Appendix C Location of Works Areas
Appendix D Event and Action Plan
Appendix E Implementation Schedule of Environmental Mitigation Measures
Appendix F Site Audit Findings and Corrective Actions
Appendix G Air Quality Monitoring Data and Graphical Plots
Appendix H Noise Monitoring Data and Graphical Plots
Appendix I Water Quality Monitoring Data and Graphical Plots
Appendix J Dolphin Monitoring Results
Appendix L Summary of Environmental Licenses and Permits
Appendix N Cumulative Statistics on Complaints
Appendix O Mudflat Monitoring Results
Executive Summary
The Hong Kong-Zhuhai-Macao Bridge (HZMB) Hong Kong Link Road (HKLR) serves to connect the HZMB Main Bridge at the Hong Kong Special Administrative Region (HKSAR) Boundary and the HZMB Hong Kong Boundary Crossing Facilities (HKBCF) located at the north eastern waters of the Hong Kong International Airport (HKIA).
The HKLR project has been separated into two contracts. They are Contract No. HY/2011/03 Hong Kong-Zhuhai-Macao Bridge Hong Kong Link Road-Section between Scenic Hill and Hong Kong Boundary Crossing Facilities (hereafter referred to as the Contract) and Contract No. HY/2011/09 Hong Kong-Zhuhai-Macao Bridge Hong Kong Link Road-Section between HKSAR Boundary and Scenic Hill.
China State Construction Engineering (Hong Kong) Ltd. was awarded by Highways Department as the Contractor to undertake the construction works of Contract No. HY/2011/03. The main works of the Contract include land tunnel at Scenic Hill, tunnel underneath Airport Road and Airport Express Line, reclamation and tunnel to the east coast of the Airport Island, at-grade road connecting to the HKBCF and highway works of the HKBCF within the Airport Island and in the vicinity of the HKLR reclamation. The Contract is part of the HKLR Project and HKBCF Project, these projects are considered to be ¡§Designated Projects¡¨, under Schedule 2 of the Environmental Impact Assessment (EIA) Ordinance (Cap 499) and EIA Reports (Register No. AEIAR-144/2009 and AEIAR-145/2009) were prepared for the Project. The current Environmental Permit (EP) EP-352/2009/D for HKLR and EP-353/2009/K for HKBCF were issued on 22 December 2014 and 11 April 2016, respectively. These documents are available through the EIA Ordinance Register. The construction phase of Contract was commenced on 17 October 2012.
BMT Hong Kong Limited was appointed by the Contractor to implement the Environmental Monitoring & Audit (EM&A) programme for the Contract in accordance with the Updated EM&A Manual for HKLR (Version 1.0) and provided environmental team services to the Contract until 31 July 2020.
This is the forty-second Quarterly EM&A report for the Contract which summarizes the monitoring results and audit findings of the EM&A programme during the reporting period from 1 December 2022 to 28 February 2023.
Environmental Monitoring and Audit Progress
The EM&A programme were undertaken in accordance with the Updated EM&A Manual for HKLR (Version 1.0). A summary of the monitoring activities during this reporting period is presented as below:
Monitoring Activity |
Monitoring Date |
|||
Dec 2022 |
Jan 2023 |
Feb 2023 |
||
Air Quality |
1-hr TSP at AMS5 |
2, 7, 13, 19, 23 and 29 |
4, 10, 16, 20, 26 and 31 |
6, 10, 16, 22 and 28 |
1-hr TSP at AMS6 |
Not applicable.(see remark 1) |
Not applicable.(see remark 1) |
Not applicable.(see remark 1) |
|
24-hr TSP at AMS5 |
1, 6, 12, 16, 22 and 28 |
3, 9, 14, 20, 26 and 31 |
3, 9, 15, 21 and 27 |
|
24-hr TSP at AMS6 |
Not applicable.(see remark 1) |
Not applicable.(see remark 1) |
Not applicable.(see remark 1) |
|
Noise |
7, 13, 19 and 29 |
4, 10, 16, 26 and 31 |
6, 16, 22 and 28 |
|
Water Quality |
2, 5, 7, 9, 12, 14, 16, 19, 21, 23, 26, 28 and 30 |
2, 4, 6, 9, 11, 13, 16, 18, 20, 25, 27 and 30 |
1, 3, 6, 8, 10, 13, 15, 17, 20, 22, 24 and 27 |
|
Chinese White Dolphin |
1, 5, 12 and 14 |
3, 11, 12, 16 and 17 |
3, 8, 14 and 16 |
|
Mudflat Monitoring (Ecology) |
15, 16, 17 and 18 |
- |
- |
|
Mudflat Monitoring (Sedimentation rate) |
1 |
- |
- |
|
Site Inspection |
1, 7, 13, 22 and 30 |
4, 10, 17, 26 and 31 |
7, 17, 23 and 28 |
Remarks:
1) The existing air quality monitoring location AMS6 ¡V Dragonair / CNAC (Group)Building (HKIA) was handed over to Airport Authority Hong Kong on 31 March 2021. 1-hr and 24-hr TSP monitoring at AMS6 was temporarily suspended starting from 1 April 2021. A new alternative air quality monitoring location is still under processing during the reporting period.
The access to the WQM station SR4(N2) (Coordinate: E814688, N817996) is blocked by the silt curtains of the Tung Chung New Town Extension (TCNTE) project. Water quality monitoring was temporarily conducted at alternative stations, namely SR4(N3) (Coordinate: E814779, N818032) in October and November 2022. Alternative monitoring station SR4(N3) (Coordinate: E814779, N818032) is proposed to replace the monitoring station SR4(N2). Proposal for permanently relocating the aforementioned station is in progress.
As confirmed by
the Contractor, the construction site of the Contract No. 2011/03 was closed
and no
construction works were conducted on 22, 23 and 24 January 2023. As such, no
impact water quality
monitoring was scheduled on 23 January 2023.
Breaches of Action and Limit Levels
A summary of environmental exceedances for this reporting period is as follows:
Environmental Monitoring |
Parameters |
Action Level (AL) |
Limit Level (LL) |
Air Quality |
1-hr TSP |
0 |
0 |
24-hr TSP |
0 |
0 |
|
Noise |
Leq (30 min) |
0 |
0 |
Water Quality |
Suspended solids level (SS) |
0 |
0 |
Turbidity level |
0 |
0 |
|
Dissolved oxygen level (DO) |
0 |
0 |
|
Dolphin Monitoring |
Quarterly Analysis (Dec 2022 to Feb 2023) |
0 |
1 |
The Environmental Team investigated all exceedance and found that they was not project related.
All investigation report for exceedance of the Contract has been submitted to ENPO/IEC for comments and/or follow up to identify whether the exceedances occurred related to other HZMB contracts.
Implementation of Mitigation Measures
Site inspections were carried out to monitor the implementation of proper environmental pollution control and mitigation measures for the Project. Potential environmental impacts due to the construction activities were monitored and reviewed.
Complaint Log
There was no complaints received in relation to the environmental impacts during this reporting period.
Notifications of Summons and Prosecutions
There were no notifications of summons or prosecutions received during this reporting period.
Reporting Changes
This report has been developed in compliance with the reporting requirements for the subsequent EM&A reports as required by the Updated EM&A Manual for HKLR (Version 1.0).
The proposal for the change of Action Level and Limit Level for suspended solid and turbidity was approved by EPD on 25 March 2013.
The revised Event and Action Plan for dolphin monitoring was approved by EPD on 6 May 2013.
The original monitoring station at IS(Mf)9 (Coordinate: 813273E, 818850N) was observed inside the perimeter silt curtain of Contract HY/2010/02 on 1 July 2013, as such the original impact water quality monitoring location at IS(Mf)9 was temporarily shifted outside the silt curtain. As advised by the Contractor of HY/2010/02 in August 2013, the perimeter silt curtain was shifted to facilitate safe anchorage zone of construction barges/vessels until end of 2013 subject to construction progress. Therefore, water quality monitoring station IS(Mf)9 was shifted to 813226E and 818708N since 1 July 2013. According to the water quality monitoring team¡¦s observation on 24 March 2014, the original monitoring location of IS(Mf)9 was no longer enclosed by the perimeter silt curtain of Contract HY/2010/02. Thus, the impact water quality monitoring works at the original monitoring location of IS(Mf)9 has been resumed since 24 March 2014.
Transect lines 1, 2, 7, 8, 9 and 11 for dolphin monitoring have been revised due to the obstruction of the permanent structures associated with the construction works of HKLR and the southern viaduct of TM-CLKL, as well as provision of adequate buffer distance from the Airport Restricted Areas. The EPD issued a memo and confirmed that they had no objection on the revised transect lines on 19 August 2015.
The water quality monitoring stations at IS10 (Coordinate: 812577E, 820670N) and SR5 (811489E, 820455N) are located inside Hong Kong International Airport (HKIA) Approach Restricted Areas. The previously granted Vessel's Entry Permit for accessing stations IS10 and SR5 were expired on 31 December 2016. During the permit renewing process, the water quality monitoring location was shifted to IS10(N) (Coordinate: 813060E, 820540N) and SR5(N) (Coordinate: 811430E, 820978N) on 2, 4 and 6 January 2017 temporarily. The permit has been granted by Marine Department on 6 January 2017. Thus, the impact water quality monitoring works at original monitoring location of IS10 and SR5 has been resumed since 9 January 2017.
Transect lines 2, 3, 4, 5, 6 and 7 for dolphin monitoring have been revised and transect line 24 has been added due to the presence of a work zone to the north of the airport platform with intense construction activities in association with the construction of the third runway expansion for the Hong Kong International Airport. The EPD issued a memo and confirmed that they had no objection on the revised transect lines on 28 July 2017. The alternative dolphin transect lines are adopted starting from August¡¦s dolphin monitoring.
A new water quality monitoring team has been employed for carrying out water quality monitoring work for the Contract starting from 23 August 2017. Due to marine work of the Expansion of Hong Kong International Airport into a Three-Runway System (3RS Project), original locations of water quality monitoring stations CS2, SR5 and IS10 are enclosed by works boundary of 3RS Project. Alternative impact water quality monitoring stations, naming as CS2(A), SR5(N) and IS10(N) was approved on 28 July 2017 and were adopted starting from 23 August 2017 to replace the original locations of water quality monitoring for the Contract.
The role and responsibilities as the ET Leader of the Contract was temporarily taken up by Mr Willie Wong instead of Ms Claudine Lee from 25 September 2017 to 31 December 2017.
The topographical condition of the water monitoring stations SR3 (Coordinate: 810525E, 816456N), SR4 (Coordinate: 814760E, 817867N), SR10A (Coordinate: 823741E, 823495N) and SR10B (Coordinate: 823686E, 823213N) cannot be accessed safely for undertaking water quality monitoring. The water quality monitoring has been temporarily conducted at alternative stations, namely SR3(N) (Coordinate 810689E, 816591N), SR4(N) (Coordinate: 814705E, 817859N) and SR10A(N) (Coordinate: 823644E, 823484N) since 1 September 2017. The water quality monitoring at station SR10B was temporarily conducted at Coordinate: 823683E, 823187N on 1, 4, 6, 8 September 2017 and has been temporarily fine-tuned to alternative station SR10B(N2) (Coordinate: 823689E, 823159N) since 11 September 2017. Proposal for permanently relocating the aforementioned stations was approved by EPD on 8 January 2018.
The works area WA5 was handed over to other party on 22 June 2013.
According to latest information received in July 2018, the works area WA7 was handed over to other party on 28 February 2018 instead of 31 January 2018.
Original WQM stations IS8 and SR4(N) are located within the active work area of TCNTE project and the access to the WQM stations IS8 (Coordinate: E814251, N818412) and SR4(N) (Coordinate: E814705, N817859) are blocked by the silt curtains of the Tung Chung New Town Extension (TCNTE) project. Alternative monitoring stations IS8(N) (Coordinate: E814413, N818570) and SR4(N2) (Coordinate: E814688, N817996) are proposed to replace the original monitoring stations IS8 and SR4(N). Proposal for permanently relocating the aforementioned stations was approved by EPD on 20 August 2019. The water quality monitoring has been conducted at stations IS8(N) and SR4(N2) on 21 August 2019.
There were no marine works conducted by Contract No. HY/2011/03 since July 2019. A proposal for temporary suspension of marine related environmental monitoring (water quality monitoring and dolphin monitoring for the Contract No. HY/2011/03) was justified by the ET leader and verified by IEC in mid of September 2019 and it was approved by EPD on 24 September 2019. Water quality monitoring and dolphin monitoring for the Contract will not be conducted starting from 1 October 2019 until marine works (i.e. toe loading removal works) be resumed. As discussed with Contract No. HY/2012/08, they will take up the responsibility from Contract No. HY/2011/03 for the dolphin monitoring works starting from 1 October 2019.
According to information received in January 2020, the works area WA3 and WA4 were handed over to Highways Department on 23 December 2019 and 14 March 2019 respectively.
The role and responsibilities as the IEC of the Contract has been taken up by Mr. Manson Yeung instead of Mr. Ray Yan since 18 May 2020.
Mr. Leslie Leung was Environmental Team Leader of the Contract for July 2020. The role and responsibilities as the Environmental Team Leader of the Contract has been taken up by Ms. Claudine Lee with effective from 1 August 2020.
The existing air quality monitoring location AMS6 ¡V Dragonair / CNAC (Group) Building (HKIA) was handed over to Airport Authority Hong Kong on 31 March 2021. 1-hr and 24-hr TSP monitoring at AMS6 was temporarily suspended starting from 1 April 2021. A new alternative air quality monitoring location is still under processing.
The role and responsibilities as the IEC of the Contract has been taken up by Mr Brian Tam instead of Mr Manson Yeung since 12 April 2021.
The role and responsibilities as the IEC of the Contract has been taken up by Mr Adi Lee instead of Mr Brian Tam since 3 May 2022.
The role and responsibilities as the IEC of the Contract has been taken up by Mr Brian Tam instead of Mr Adi Lee since 25 July 2022.
The role and responsibilities as the ENPO Leader of the Contract has been taken up by Mr Louis Kwan from ANewR Consulting Limited instead of Mr H.Y. Hui from Ramboll Hong Kong Limited Since 1 October 2022.
The role and responsibilities as the IEC of the Contract has been taken up by Mr James Choi from ANewR Consulting Limited instead of Mr Brian Tam from Ramboll Hong Kong Limited since 1 October 2022.
Table 1.1 Construction Activities during Reporting Period
Description of Activities |
Site Area |
Landscape maintenance works |
SHT East Portal |
Removal of Temporary Toe Loading Platform |
Portion X |
Table 2.1 Summary of Impact EM&A Requirements
Environmental Monitoring |
Description |
Monitoring Station |
Frequencies |
Remarks |
Air Quality |
1-hr TSP |
AMS 5 & AMS 6 |
At least 3 times every 6 days |
While the highest dust impact was expected. |
24-hr TSP |
At least once every 6 days |
-- |
||
Noise |
Leq (30mins), |
NMS 5 |
At least once per week |
Daytime on normal weekdays (0700-1900 hrs). |
Water Quality |
¡P Depth ¡P Temperature ¡P Salinity ¡P Dissolved Oxygen (DO) ¡P Suspended Solids (SS) ¡P DO Saturation ¡P Turbidity ¡P pH |
¡P Impact
Stations: ¡P Control/Far
Field Stations: ¡P Sensitive
Receiver Stations: |
Three times per week during mid-ebb and mid-flood tides (within ¡Ó 1.75 hour of the predicted time) |
3 (1 m below water surface, mid-depth and 1 m above sea bed, except where the water depth is less than 6 m, in which case the mid-depth station may be omitted. Should the water depth be less than 3 m, only the mid-depth station will be monitored). |
Dolphin |
Line-transect Methods |
Northeast Lantau survey area and Northwest Lantau survey area |
Twice per month |
-- |
Mudflat |
Horseshoe crabs, seagrass beds, intertidal soft shore communities, sedimentation rates and water quality |
San Tau and Tung Chung Bay |
Once every 3 months |
-- |
Remarks:
1) Original WQM stations IS8 and SR4(N) are located within the active work area of TCNTE project and the access to the WQM stations IS8 (Coordinate: E814251, N818412) and SR4(N) (Coordinate: E814705, N817859) are blocked by the silt curtains of the Tung Chung New Town Extension (TCNTE) project. Alternative monitoring stations IS8(N) (Coordinate: E814413, N818570) and SR4(N2) (Coordinate: E814688, N817996) are proposed to replace the original monitoring stations IS8 and SR4(N). Proposal for permanently relocating the aforementioned stations was approved by EPD on 20 August 2019. The water quality monitoring has been conducted at stations IS8(N) and SR4(N2) on 21 August 2019.
2) The access to the WQM station SR4(N2) (Coordinate: E814688, N817996) is blocked by the silt curtains of the Tung Chung New Town Extension (TCNTE) project. Water quality monitoring was temporarily conducted at alternative stations, namely SR4(N3) (Coordinate: E814779, N818032) in October and November 2022. Alternative monitoring station SR4(N3) (Coordinate: E814779, N818032) is proposed to replace the monitoring station SR4(N2). Proposal for permanently relocating the aforementioned station is in progress.
Table 2.2 Action and Limit Levels for 1-hour TSP, 24-hour TSP and Noise
Environmental Monitoring |
Parameters |
Monitoring Station |
Action Level |
Limit Level |
Air Quality |
1-hr TSP |
AMS 5 |
352 µg/m3 |
500 µg/m3 |
AMS 6 |
360 µg/m3 |
|||
24-hr TSP |
AMS 5 |
164 µg/m3 |
260 µg/m3 |
|
AMS 6 |
173 µg/m3 |
|||
Noise |
Leq (30 min) |
NMS 5 |
When one documented complaint is received |
75 dB(A) |
Table 2.3 Action and Limit Levels for Water Quality
Parameter (unit) |
Water Depth |
Action Level |
Limit Level |
Dissolved Oxygen (mg/L) |
Surface and Middle |
5.0 |
4.2 except 5 for Fish Culture Zone |
Bottom |
4.7 |
3.6 |
|
Turbidity (NTU) |
Depth average |
27.5 or 120% of upstream control station¡¦s turbidity at the same tide of the same day; The action level has been amended to ¡§27.5 and 120% of upstream control station¡¦s turbidity at the same tide of the same day¡¨ since 25 March 2013. |
47.0 or 130% of turbidity at the upstream control station at the same tide of same day; The limit level has been amended to ¡§47.0 and 130% of turbidity at the upstream control station at the same tide of same day¡¨ since 25 March 2013. |
Suspended Solid (SS) (mg/L) |
Depth average |
23.5 or 120% of upstream control station¡¦s SS at the same tide of the same day; The action level has been amended to ¡§23.5 and 120% of upstream control station¡¦s SS at the same tide of the same day¡¨ since 25 March 2013. |
34.4 or 130% of SS at the upstream control station at the same tide of same day and 10mg/L for Water Services Department Seawater Intakes; The limit level has been amended to ¡§34.4 and 130% of SS at the upstream control station at the same tide of same day and 10mg/L for Water Services Department Seawater Intakes¡¨ since 25 March 2013 |
(1) Depth-averaged is calculated by taking the arithmetic means of reading of all three depths.
(2) For DO, non-compliance of the water quality limit occurs when monitoring result is lower that the limit.
(3) For SS & turbidity non-compliance of the water quality limits occur when monitoring result is higher than the limits.
(4) The change to the Action and limit Levels for Water Quality Monitoring for the EM&A works was approved by EPD on 25 March 2013. Therefore, the amended Action and Limit Levels are applied for the water monitoring results obtained on and after 25 March 2013.
Table 2.4 Action and Limit Level for Dolphin Impact Monitoring
|
North Lantau Social Cluster |
|
NEL |
NWL |
|
Action Level |
STG < 70% of baseline & |
STG < 70% of baseline & |
Limit Level |
STG < 40% of baseline & |
Remarks:
(1) STG means quarterly average encounter rate of number of dolphin sightings.
(2) ANI means quarterly average encounter rate of total number of dolphins.
(3) For North Lantau Social Cluster, AL will be triggered if either NEL or NWL fall below the criteria; LL will be triggered if both NEL and NWL fall below the criteria.
Table 2.5 Derived Value of Action Level (AL) and Limit Level (LL)
|
North Lantau Social Cluster |
|
NEL |
NWL |
|
Action Level |
STG < 4.2 & ANI < 15.5 |
STG < 6.9 & ANI < 31.3 |
Limit Level |
(STG < 2.4 & ANI < 8.9) and (STG < 3.9 & ANI < 17.9) |
Remarks:
(1) STG means quarterly average encounter rate of number of dolphin sightings.
(2) ANI means quarterly average encounter rate of total number of dolphins.
(3) For North Lantau Social Cluster, AL will be triggered if either NEL or NWL fall below the criteria; LL will be triggered if both NEL and NWL fall below the criteria.
Table 3.1 Summary of 1-hour TSP Monitoring Results Obtained During the Reporting Period
Reporting Period |
Monitoring Station |
Average (mg/m3) |
Range (mg/m3) |
Action Level (mg/m3) |
Limit Level (mg/m3) |
Dec 2022 |
AMS5 |
82 |
16-180 |
352 |
500 |
AMS6 |
|
|
360 |
||
Jan 2023 |
AMS5 |
61 |
28 - 124 |
352 |
|
AMS6 |
|
|
360 |
||
Feb 2023 |
AMS5 |
52 |
33 - 114 |
352 |
|
AMS6 |
|
|
360 |
Table 3.2 Summary of 24-hour TSP Monitoring Results Obtained During the Reporting Period
Reporting Period |
Monitoring Station |
Average (mg/m3) |
Range (mg/m3) |
Action Level (mg/m3) |
Limit Level (mg/m3) |
Dec 2022 |
AMS5 |
61 |
27 - 92 |
164 |
260 |
AMS6 |
|
|
173 |
||
Jan 2023 |
AMS5 |
62 |
38 - 73 |
164 |
|
AMS6 |
|
|
173 |
||
Feb 2023 |
AMS5 |
70 |
31 - 96 |
164 |
|
AMS6 |
|
|
173 |
Table 3.3 Summary of Construction Noise Monitoring Results Obtained During the Reporting Period
Reporting period |
Monitoring Station |
Average Leq (30 mins), dB(A)* |
Range of Leq (30 mins), dB(A)* |
Action Level |
Limit Level Leq (30 mins), dB(A) |
Dec 2022 |
NMS5 |
58 |
56 - 60 |
When one documented complaint is received |
75 |
Jan 2023 |
62 |
59 - 66 |
|||
Feb 2023 |
61 |
59 - 64 |
SPSE = ((S / E) x 100) / SA%
DPSE = ((D / E) x 100) / SA%
where S = total number of on-effort sightings
D = total number of dolphins from on-effort sightings
E = total number of units of survey effort
SA% = percentage of sea area
Table 3.4 Dolphin Encounter Rates (Sightings Per 100 km of Survey Effort) During Reporting Period (December 2022 to February 2023)
Survey Area |
Dolphin Monitoring Dates |
Encounter rate (STG) |
Encounter rate (ANI) |
Primary Lines Only |
Primary Lines Only |
||
Northeast Lantau |
Set 1 (1 & 5 Dec 2022) |
0.00 |
0.00 |
Set 2 (12 & 14 Dec 2022) |
0.00 |
0.00 |
|
Set 3 (3 & 11 Jan 2023) |
0.00 |
0.00 |
|
Set 4 (12, 16 & 17 Jan 2023) |
0.00 |
0.00 |
|
Set 5 (3 & 8 Feb 2023) |
0.00 |
0.00 |
|
Set 6 (14 & 16 Feb 2023) |
0.00 |
0.00 |
|
Northwest Lantau |
Set 1 (1 & 5 Dec 2022) |
0.00 |
0.00 |
Set 2 (12 & 14 Dec 2022) |
1.93 |
1.93 |
|
Set 3 (3 & 11 Jan 2023) |
0.00 |
0.00 |
|
Set 4 (12, 16 & 17 Jan 2023) |
1.70 |
11.89 |
|
Set 5 (3 & 8 Feb 2023) |
0.00 |
0.00 |
|
Set 6 (14 & 16 Feb 2023) |
1.57 |
6.29 |
Survey Area |
Encounter rate (STG) |
Encounter rate (ANI) |
||
Reporting Period |
Baseline Monitoring Period |
Reporting Period |
Baseline Monitoring Period |
|
Northeast Lantau |
0.0 |
6.00 ¡Ó 5.05 |
0.0 |
22.19 ¡Ó 26.81 |
Northwest Lantau |
0.87 ¡Ó 0.96 |
9.85 ¡Ó 5.85 |
3.35 ¡Ó 4.84 |
44.66 ¡Ó 29.85 |
Notes:
1) The encounter rates deduced from the baseline monitoring period have been
recalculated based only on survey effort and on-effort sighting data made along
the primary transect lines under favourable conditions.
2) ¡Ó denotes the standard deviation of the average encounter rates.
Table 3.6 Comparison of Average Dolphin Encounter Rates in Northeast Lantau Survey Area from All Winter Quarters of Impact Monitoring Period and Baseline Monitoring Period (Sep ¡V Nov 2011)
Monitoring Period |
Encounter rate (STG) |
Encounter rate (ANI) |
September-November 2011 (Baseline) |
6.00 ¡Ó 5.05 |
22.19 ¡Ó 26.81 |
December 2012-February 2013 (HKLR03 Impact) |
3.14 ¡Ó 3.21 |
6.33 ¡Ó 8.64 |
December 2013-February 2014 (HKLR03 Impact) |
0.45 ¡Ó 1.10 |
1.34 ¡Ó 3.29 |
December 2014-February 2015 (HKLR03 Impact) |
0.00 |
0.00 |
December 2015-February 2016 (HKLR03 Impact) |
0.00 |
0.00 |
December 2016-February 2017 (HKLR03 Impact) |
0.00 |
0.00 |
December 2017-February 2018 (HKLR03 Impact) |
0.00 |
0.00 |
December 2018-February 2019 (HKLR03 Impact) |
0.00 |
0.00 |
December 2019-February 2020 (HKLR03 Impact) |
0.00 |
0.00 |
December 2020-February 2021 (TMCLKL Post-Construction) |
0.00 |
0.00 |
December 2021-February 2022 (TMCLKL Post-Construction) |
0.00 |
0.00 |
December 2022-February 2023 (HKLR03 Impact) |
0.00 |
0.00 |
Notes:
1) The encounter rates deduced from the baseline monitoring period have been
recalculated based only on survey effort and on-effort sighting data made along
the primary transect lines under favourable conditions.
2) ¡Ó denotes the standard deviation of the average encounter rates.
Table 3.7 Comparison of Average Dolphin Encounter Rates in Northwest Lantau Survey Area from All Winter Quarters of Impact Monitoring Period and Baseline Monitoring Period (Sep ¡V Nov 2011)
Monitoring Period |
Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort) |
Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort) |
September-November 2011 (Baseline) |
9.85 ¡Ó 5.85 |
44.66 ¡Ó 29.85 |
December 2012-February 2013 (HKLR03 Impact) |
8.36 ¡Ó 5.03 |
35.90 ¡Ó 23.10 |
December 2013-February 2014 (HKLR03 Impact) |
8.21 ¡Ó 2.21 |
32.58 ¡Ó 11.21 |
December 2014-February 2015 (HKLR03 Impact) |
2.91 ¡Ó 2.69 |
11.27 ¡Ó 15.19 |
December 2015-February 2016 (HKLR03 Impact) |
2.64 ¡Ó 1.52 |
10.98 ¡Ó 3.81 |
December 2016-February 2017 (HKLR03 Impact) |
3.80 ¡Ó 3.79 |
14.52 ¡Ó 17.21 |
December 2017-February 2018 (HKLR03 Impact) |
4.75 ¡Ó 2.26 |
15.73 ¡Ó 15.94 |
December 2018-February 2019 (HKLR03 Impact) |
2.40 ¡Ó 1.88 |
7.95 ¡Ó 6.60 |
December 2019-February 2020 (HKLR03 Impact) |
1.96 ¡Ó 2.23 |
8.15 ¡Ó 10.85 |
December 2020-February 2021 (TMCLKL Post-Construction) |
3.01 ¡Ó 2.83 |
8.47 ¡Ó 9.07 |
December 2021-February 2022 (TMCLKL Post-Construction) |
1.63 ¡Ó 1.47 |
3.52 ¡Ó 3.87 |
December 2022-February 2023 (HKLR03 Impact) |
0.87 ¡Ó 0.96 |
3.35 ¡Ó 4.84 |
Notes:
1) The encounter rates deduced from the baseline monitoring period have been recalculated based only on survey effort and on-effort sighting data made along the primary transect lines under favourable conditions.
2) ¡Ó denotes the standard deviation of the average encounter rates.
Table 3.8 Measured Mudflat Surface Level Results
Baseline Monitoring |
Impact Monitoring |
|||||
Monitoring Station |
Easting |
Northing (m) |
Surface Level |
Easting |
Northing (m) |
Surface Level (mPD) |
S1 |
810291.160 |
816678.727 |
0.950 |
810291.187 |
816678.820 |
1.137 |
S2 |
810958.272 |
815831.531 |
0.864 |
810958.274 |
815831.537 |
0.978 |
S3 |
810716.585 |
815953.308 |
1.341 |
810716.586 |
815953.301 |
1.457 |
S4 |
811221.433 |
816151.381 |
0.931 |
811221.439 |
816151.373 |
1.097 |
Table 3.9 Comparison of Measurement
Comparison of measurement |
Remarks and Recommendation |
|||
Monitoring Station |
Easting |
Northing (m) |
Surface Level |
|
S1 |
0.027 |
-0.007 |
0.187 |
Level continuously increased, need attention |
S2 |
0.002 |
0.006 |
0.114 |
Level continuously increased, need attention |
S3 |
0.004 |
-0.007 |
0.116 |
Level continuously increased, need attention |
S4 |
0.006 |
-0.008 |
0.166 |
Level continuously increased, need attention |
Table 3.10 Impact Water Quality Monitoring Results (Depth Average) at Station SR3(N)
Date |
Mid Ebb Tide |
Mid Flood Tide |
||||
DO (mg/L) |
Turbidity (NTU) |
SS (mg/L) |
DO (mg/L) |
Turbidity (NTU) |
SS (mg/L) |
|
02-Dec-2022 |
6.5 |
3.5 |
5.1 |
7.4 |
3.5 |
4.7 |
05-Dec-2022 |
6.5 |
4.0 |
5.9 |
7.3 |
3.6 |
5.7 |
07-Dec-2022 |
6.0 |
3.7 |
2.7 |
6.5 |
3.5 |
2.3 |
09-Dec-2022 |
6.6 |
3.8 |
3.5 |
6.2 |
3.5 |
3.4 |
12-Dec-2022 |
7.0 |
3.7 |
7.0 |
7.3 |
4.4 |
5.6 |
14-Dec-2022 |
6.2 |
2.8 |
8.3 |
6.1 |
2.9 |
7.4 |
16-Dec-2022 |
6.4 |
3.5 |
3.4 |
6.6 |
3.9 |
4.8 |
19-Dec-2022 |
7.0 |
3.7 |
4.4 |
7.2 |
4.5 |
5.9 |
21-Dec-2022 |
6.7 |
3.9 |
3.2 |
7.3 |
4.1 |
3.0 |
23-Dec-2022 |
7.0 |
4.0 |
4.8 |
6.7 |
3.4 |
3.9 |
26-Dec-2022 |
6.9 |
4.2 |
6.2 |
6.6 |
3.9 |
6.5 |
28-Dec-2022 |
6.2 |
4.0 |
5.6 |
6.0 |
3.8 |
4.9 |
30-Dec-2022 |
6.3 |
4.5 |
3.1 |
6.7 |
3.8 |
3.4 |
Average |
6.6 |
3.8 |
4.8 |
6.8 |
3.7 |
4.7 |
Mudflat Ecology Monitoring
3.6.6 In order to collect baseline information of mudflats in the study site, the study site was divided into three sampling zones (labeled as TC1, TC2, TC3) in Tung Chung Bay and one zone in San Tau (labeled as ST) (Figure 2.1 of Appendix O). The horizontal shoreline of sampling zones TC1, TC2, TC3 and ST were about 250 m, 300 m, 300 m and 250 m, respectively (Figure 2.2 of Appendix O). Survey of horseshoe crabs, seagrass beds and intertidal communities were conducted in every sampling zone. The present survey was conducted in December 2022 (totally 4 sampling days 15th (for ST), 16th (for TC3), 17th (for TC2) and 18th (for TC1).
3.6.8 Active search method was adopted for horseshoe crab monitoring by two experienced surveyors in every sampling zone. During the search period, any accessible and potential area would be investigated for any horseshoe crab individuals within 2-3 hour of low tide period (tidal level below 1.2 m above Chart Datum (C.D.)). Once a horseshoe crab individual was found, the species was identified referencing to Li (2008). The prosomal width, inhabiting substratum and respective GPS coordinate were recorded. A photographic record was taken for future investigation. Any grouping behavior of individuals, if found, was recorded. The horseshoe crab surveys were conducted on 15th (for ST), 16th (for TC3), 17th (for TC2) and 18th (for TC1) December 2022, which were fine days.
3.6.9 In June 2017, a big horseshoe crab was tangled by a trash gill net in ST mudflat (Figure 2.3 of Appendix O). It was released to sea once after photo recording. The horseshoe crab of such size should be inhabiting sub-tidal environment while it forages on intertidal shore occasionally during high tide period. If it is tangled by the trash net for few days, it may die due to starvation or overheat during low tide period. These trash gill nets are definitely ¡¥fatal trap¡¦ for the horseshoe crabs and other marine life. Manual clean-up should be implemented as soon as possible by responsible governmental agency units.
3.6.10 Active search method was adopted for seagrass bed monitoring by two experienced surveyors in every sampling zone. During the search period, any accessible and potential area would be investigated for any seagrass beds within 2-3 hours of low tide period. Once seagrass bed was found, the species, estimated area, estimated coverage percentage and respective GPS coordinates were recorded. The seagrass beds surveys were conducted on 15th (for ST), 16th (for TC3), 17th (for TC2) and 18th (for TC1) December 2022, which were fine days.
3.6.11 The intertidal soft shore community surveys were conducted in low tide period on 15th (for ST), 16th (for TC3), 17th (for TC2) and 18th (for TC1) December 2022. In every sampling zone, three 100m horizontal transect lines were laid at high tidal level (H: 2.0m above C.D.), mid tidal level (M: 1.5m above C.D.) and low tidal level (L: 1.0m above C.D.). Along every horizontal transect line; ten random quadrats (0.5 m x 0.5m) were placed.
3.6.12 Inside a quadrat, any visible epifauna was collected and was in-situ identified to the lowest practical taxonomical resolution. Whenever possible a hand core sample (10 cm internal diameter ´ 20 cm depth) of sediments was collected in the quadrat. The core sample was gently washed through a sieve of mesh size 2.0 mm in-situ. Any visible infauna was collected and identified. Finally, the top 5 cm surface sediment was dug for visible infauna in the quadrat regardless of hand core sample was taken.
3.6.13 All collected fauna were released after recording except some tiny individuals that were too small to be identified on site. These tiny individuals were taken to laboratory for identification under dissecting microscope.
H¡¦= -£U ( Ni / N ) ln ( Ni / N ) (Shannon and Weaver, 1963)
J = H¡¦ / ln S, (Pielou, 1966)
3.6.16 No horseshoe crab was recorded during surveys conducted in December 2022. Two horseshoe species were recorded in previous monitoring events, i.e. Carcinoscorpius rotundicauda and Tachypleus tridentatus. Photo records of previously observed horseshoe crab is shown in Figure 3.1 of Appendix O and the present survey result regarding horseshoe crab are presented in Table 3.1 of Appendix O. The complete survey records are presented in Annex II of Appendix O.
3.6.17 In the survey of March 2015, there was one important finding that a mating pair of Carcinoscorpius rotundicauda was found in ST (prosomal width: male 155.1mm, female 138.2mm). It indicated the importance of ST as a breeding ground of horseshoe crab. In June 2017, mating pairs of Carcinoscorpius rotundicauda were found in TC2 (male 175.27 mm, female 143.51 mm) and TC3 (male 182.08 mm, female 145.63 mm) (Figure 3.2 of Appendix O). In December 2017 and June 2018, one mating pair was of Carcinoscorpius rotundicauda was found in TC3 (December 2017: male 127.80 mm, female 144.61 mm; June 2018: male 139 mm, female 149 mm). In June 2019, two mating pairs of Tachypleus tridentatus with large body sizes (male 150mm and Female 200mm; Male 180mm and Female 220mm) were found in TC3. Another mating pair of Tachypleus tridentatus was found in ST (male 140mm and Female 180mm). In March 2020, a pair of Tachypleus tridentatus with large body sizes (male 123mm and Female 137mm was recorded in TC1. Figure 3.2 of Appendix O shows the photographic records of the mating pair found. The recorded mating pairs were found nearly burrowing in soft mud at low tidal level (0.5-1.0 m above C.D.). The smaller male was holding the opisthosoma (abdomen carapace) of larger female from behind. A mating pair was found in TC1 in March 2020, it indicated that breeding of horseshoe crab could be possible along the coast of Tung Chung Wan rather than ST only, as long as suitable substratum was available. Based on the frequency of encounter, the shoreline between TC3 and ST should be more suitable mating ground. Moreover, suitable breeding period was believed in wet season (March ¡V September) because tiny individuals (i.e. newly hatched) were usually recorded in June and September every year (Figure 3.3 of Appendix O). One mating pair was found in June 2022.
3.6.19 No marked individual of horseshoe crab was recorded in December 2022 (Present survey). Some marked individuals were found in the previous surveys of September 2013, March 2014, and September 2014. All of them were released through a conservation programme in charged by Prof. Paul Shin (Department of Biology and Chemistry, The City University of Hong Kong (CityU)). It was a re-introduction trial of artificial bred horseshoe crab juvenile at selected sites. So that the horseshoe crab¡¦s population might be restored in the natural habitat. Through a personal conversation with Prof. Shin, about 100 individuals were released in the sampling zone ST on 20 June 2013. All of them were marked with color tape and internal chip detected by specific chip sensor. There should be second round of release between June and September 2014 since new marked individuals were found in the survey of September 2014.
3.6.20 The artificial bred individuals, if found, would be excluded from the results of present monitoring programme in order to reflect the changes of natural population. However, the mark on their prosoma might have been detached during moulting after a certain period of release. The artificially released individuals were no longer distinguishable from the natural population without the specific chip sensor. The survey data collected would possibly cover both natural population and artificially bred individuals.
Population difference among the sampling zones
3.6.21 Figure 3.5 and 3.6 of Appendix O show the changes of number of individuals, mean prosomal width and search record of horseshoe crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus in respectively in each sampling zone throughout the monitoring period.
3.6.22 To consider the entire monitoring period for TC3 and ST, medium to high search records (i.e. number of individuals) of both species (Carcinoscorpius rotundicauda and Tachypleus tridentatus) were usually found in wet season (June and September). The search record of ST was higher from September 2012 to June 2014 while it was replaced by TC3 from September 2014 to June 2015. The search records were similar between two sampling zones from September 2015 to June 2016. In September 2016, the search record of Carcinoscorpius rotundicauda in ST was much higher than TC3. From March to June 2017, the search records of both species were similar again between two sampling zones. It showed a natural variation of horseshoe crab population in these two zones due to weather condition and tidal effect. No obvious difference of horseshoe crab population was noted between TC3 and ST. In September 2017, the search records of both horseshoe crab species decreased except the Carcinoscorpius rotundicauda in TC3. The survey results were different from previous findings that there were usually higher search records in September. One possible reason was that the serial cyclone hit decreased horseshoe crab activity (totally 4 cyclone records between June and September 2017, to be discussed in 'Seagrass survey' section). From December 2017 to September 2018, the search records of both species increased again to low-moderate level in ST and TC3. From December 2018 to September 2019, the search records of Carcinoscorpius rotundicauda change from very low to low while the change of Tachypleus tridentatus was similar during this period. Relatively higher population fluctuation of Carcinoscorpius rotundicauda was observed in TC3. From March 2020 to September 2020, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were increased to moderate level in ST. However, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were decreased from very low to none in TC3 in this period. From March 2021 to September 2021, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were kept at low-moderate level in both ST and TC3. It is similar to the previous findings of June. It shows another growing phenomenon of horseshoe crabs and it may due to the weather variation of starting of wet season. The survey results were different from previous findings that there were usually higher search records in September. One possible reason was that September of 2021 was one of the hottest month in Hong Kong in record. As such, hot and shiny weather decreased horseshoe crab activity. In December 2021, no juvenile was recorded similar to the some previous in December due to the season. In March 2022, only juveniles recorded in both ST and TC3, no adult specimen was observed. In June 2022, total of 13 individuals of Carcinoscorpius rotundicauda and Tachypleus tridentatus were found, with 6 juveniles, 6 adults and 1 died recorded. In September 2022, total of 7 individuals of were found, with 4 juveniles, 3 adults (1 alive and 2 died) recorded
3.6.23 For TC1, the search record was at low to moderate level throughout the monitoring period. The change of Carcinoscorpius rotundicauda was relatively more variable than that of Tachypleus tridentatus. Relatively, the search record was very low in TC2. There were occasional records of 1 to 4 individuals between March and September throughout the monitoring period. The maximum record was 6 individuals only in June 2016.
Seasonal variation of horseshoe crab population
3.6.27 Throughout the monitoring period, the search records of horseshoe crabs were fluctuated and at moderate ¡V very low level in June (Figure 3.5 and 3.6 of Appendix O). Low ¡V Very low search record was found in June 2013, totally 82 individuals of Tachypleus tridentatus and 0 ind. of Carcinoscorpius rotundicauda were found in TC1, TC3 and ST. Compare with the search record of June 2013, the numbers of Tachypleus tridentatus were gradually decreased in June 2014 and 2015 (55 ind. in 2014 and 18 ind. in 2015); the number of Carcinoscorpius rotundicauda raise to 88 and 66 ind. in June 2014 and 2015 respectively. In June 2016, the search record increased about 3 times compare with June 2015. In total, 182 individuals of Carcinoscorpius rotundicauda and 47 individuals of Tachypleus tridentatus were noted, respectively. Then, the search record was similar to June 2016. The number of recorded Carcinoscorpius rotundicauda (133 ind.) slightly dropped in June 2017. However, that of Tachypleus tridentatus rapidly increased (125 ind.). In June 2018, the search record was low to moderate while the numbers of Tachypleus tridentatus dropped sharply (39 ind.). In June 2019, 10 individuals of Tachypleus tridentatus were observed in TC3 and ST. All of them, however, were large individuals (prosomal width >100mm), their records are excluded from the data analysis to avoid mixing up with the juvenile population living on intertidal habitat. Until September 2020, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus gradually increased to 39 ind. and 28 ind., respectively. In December 2020, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus greatly decreased to 3 ind. and 7 ind., respectively. In March 2022, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus gradually decreased to 7 ind. and 2 ind., respectively in comparing with the March of previous record. The drop of abundance may be related to the unusual cold weather in the beginning of March 2022. Throughout the monitoring period, similar distribution of horseshoe crab population was found.
3.6.28 The search record of horseshoe crab declined obviously in all sampling zones during dry season especially December (Figure 3.5 and 3.6 of Appendix O) throughout the monitoring period. Very low ¡V low search record was found in December from 2012 to 2015 (0-4 ind. of Carcinoscorpius rotundicauda and 0 ¡V 12 ind. of Tachypleus tridentatus). The horseshoe crabs were inactive and burrowed in the sediments during cold weather (<15 ºC). Similar results of low search record in dry season were reported in a previous territory-wide survey of horseshoe crab. For example, the search records in Tung Chung Wan were 0.17 ind. hr-1 person-1 and 0.00 ind. hr-1 person-1 in wet season and dry season respectively (details see Li, 2008). Compare with the search record of December from 2012 to 2015, which of December 2016 were much higher relatively. There were totally 70 individuals of Carcinoscorpius rotundicauda and 24 individuals of Tachypleus tridentatus in TC3 and ST. Since the survey was carried in earlier December with warm and sunny weather (~22 ºC during dawn according to Hong Kong Observatory database, Chek Lap Kok station on 5 December 2016), the horseshoe crab was more active (i.e. move onto intertidal shore during high tide for foraging and breeding) and easier to be found. In contrast, there was no search record in TC1 and TC2 because the survey was conducted in mid December with colder and cloudy weather (~20¢XC during dawn on 19 December). The horseshoe crab activity would decrease gradually with the colder climate. In December of 2017, 2018 and 2019, very low search records were found again as mentioned above. No record of houseshoe crab was recorded in December 2022.
3.6.29 From September 2012 to December 2013, Carcinoscorpius rotundicauda was less common species relative to Tachypleus tridentatus. Only 4 individuals were ever recorded in ST in December 2012. This species had ever been believed of very low density in ST hence the encounter rate was very low. In March 2014, it was found in all sampling zones with higher abundance in ST. Based on its average size (mean prosomal width 39.28 ¡V 49.81 mm), it indicated that breeding and spawning of this species had occurred about 3 years ago along the coastline of Tung Chun Wan. However, these individuals were still small while their walking trails were inconspicuous. Hence there was no search record in previous sampling months. Since March 2014, more individuals were recorded due to larger size and higher activity (i.e. more conspicuous walking trail).
3.6.30 For Tachypleus tridentatus, sharp increase of number of individuals was recorded in ST during the wet season of 2013 (from March to September). According to a personal conversation with Prof. Shin (CityU), his monitoring team had recorded similar increase of horseshoe crab population during wet season. It was believed that the suitable ambient temperature increased its conspicuousness. However similar pattern was not recorded in the following wet seasons. The number of individuals increased in March and June 2014 and followed by a rapid decline in September 2014. Then the number of individuals fluctuated slightly in TC3 and ST until March 2017. Apart from natural mortality, migration from nursery soft shore to subtidal habitat was another possible cause. Since the mean prosomal width of Tachypleus tridentatus continued to grow and reached about 50 mm since March 2014. Then it varied slightly between 35-65 mm from September 2014 to March 2017.Most of the individuals might have reached a suitable size (e.g. prosomal width 50 ¡V 60 mm) strong enough to forage in sub-tidal habitat. In June 2017, the number of individuals increased sharply again in TC3 and ST. Although mating pair of Tachypleus tridentatus was not found in previous surveys, there should be new round of spawning in the wet season of 2016. The individuals might have grown to a more conspicuous size in 2017 accounting for higher search record. In September 2017, moderate numbers of individual were found in TC3 and ST indicating a stable population size. From September 2018 to March 2020, the population size was low while natural mortality was the possible cause. From June 2020 to September 2020, the population size of Tachypleus tridentatus increased to moderate level in ST while the mean proposal width of them conitued to grow and reach about 55mm. The population size of Tachypleus tridentatus slightly decreased in ST from March 2021 to March 2022 and the mean proposal width of them increased to about 77.59mm.
3.6.31 Recently, Carcinoscorpius rotundicauda was a more common horseshoe crab species in Tung Chung Wan. It was recorded in the four sampling zones while the majority of population located in TC3 and ST. Due to potential breeding last year, the number of Tachypleus tridentatus increased in ST. Since TC3 and ST were regarded as important nursery ground for both horseshoe crab species, box plots of prosomal width of two horseshoe crab species were constructed to investigate the changes of population in details.
Box plot of horseshoe crab populations in TC3
3.6.32 Figure 3.7 of Appendix O shows the changes of prosomal width of Carcinoscorpius rotundicauda and Tachypleus tridentatus in TC3. As mentioned above, Carcinoscorpius rotundicauda was rarely found between September 2012 and December 2013 hence the data were lacking. In March 2014, the major size (50% of individual records between upper (top box) and lower quartile (bottom box)) ranged 40 ¡V 60 mm while only few individuals were found. From March 2014 to September 2018, the median prosomal width (middle line of whole box) and major size (whole box) decreased after March of every year. It was due to more small individuals found in June indicating new rounds of spawning. Also there were slight increasing trends of body size from June to March of next year since 2015. It indicated a stable growth of individuals. Focused on larger juveniles (upper whisker), the size range was quite variable (prosomal width 60 ¡V 90 mm) along the sampling months. Juveniles reaching this size might gradually migrate to sub-tidal habitats. In March 2022, 2 Carcinoscorpius rotundicauda with body size (prosomal width 52.21-54.63mm) were found in TC3. The findings were relatively lower than the previous record in March. This can due to the natural variation caused by multi-environmental factors.
3.6.33 For Tachypleus tridentatus, the major size ranged 20-50 mm while the number of individuals fluctuated from September 2012 to June 2014. Then a slight but consistent growing trend was observed from September 2014 to June 2015. The prosomal width increased from 25 ¡V 35 mm to 35 ¡V 65 mm. As mentioned, the large individuals might have reached a suitable size for migrating from the nursery soft shore to subtidal habitat. It accounted for the declined population in TC3. From March to September 2016, slight increasing trend of major size was noticed again. From December 2016 to June 2017, similar increasing trend of major size was noted with much higher number of individuals. It reflected new round of spawning. In September 2017, the major size decreased while the trend was different from previous two years. Such decline might be the cause of serial cyclone hit between June and September 2017 (to be discussed in the 'Seagrass survey' section). From December 2017 to September 2018, increasing trend was noted again. It indicated a stable growth of individuals. From September 2018 to that of next year, the average prosomal widths were decreased from 60mm to 36mm. It indicated new rounds of spawning occurred during September to November 2018. In December 2019, an individual with larger body size (prosomal width 65mm) was found in TC3 which reflected the stable growth of individuals. In March 2020, the average prosomal width (middle line of the whole box) of Tachypleus tridentatus in TC3 was 33.97mm which is smaller than that in December 2019. It was in normal fluctuation. From June 2020 to December 2020, no horseshoe crab was recorded in TC3. In Sep 2021, only one Tachypleus tridentatus with body size (prosomal width 38.78mm) was found in TC3. The decrease in the species population was considered to be related to hot weather in September, which may affect their activity. Across the whole monitoring period, the larger juveniles (upper whisker) usually reached 60 ¡V 80 mm in prosomal width, even 90 mm occasionally. The juveniles reaching this size might gradually migrate to sub-tidal habitats.
Box plot of horseshoe crab populations in ST
3.6.34 Figure 3.8 of Appendix O shows the changes of prosomal width of Carcinoscorpius rotundicauda and Tachypleus tridentatus in ST. As mentioned above, Carcinoscorpius rotundicauda was rarely found between September 2012 and December 2013 hence the data were lacking. From March 2014 to September 2018, the size of major population decreased and more small individuals (i.e. lower whisker) were recorded after June of every year. It indicated new round of spawning. Also there were similar increasing trends of body size from September to June of next year between 2014 and 2017. It indicated a stable growth of individuals. The larger juveniles (i.e. upper whisker usually ranged 60 ¡V 80 mm in prosomal width except one individual (prosomal width 107.04 mm) found in March 2017. It reflected juveniles reaching this size would gradually migrate to sub-tidal habitats.
3.6.35 For Tachypleus tridentatus, a consistent growing trend was observed for the major population from December 2012 to December 2014 regardless of change of search record. The prosomal width increased from 15 ¡V 30 mm to 60 ¡V 70 mm. As mentioned, the large juveniles might have reached a suitable size for migrating from the nursery soft shore to subtidal habitat. From March to September 2015, the size of major population decreased slightly to a prosomal width 40 ¡V 60 mm. At the same time, the number of individuals decreased gradually. It further indicated some of large juveniles might have migrated to sub-tidal habitat, leaving the smaller individuals on shore. There was an overall growth trend. In December 2015, two big individuals (prosomal width 89.27 mm and 98.89 mm) were recorded only while it could not represent the major population. In March 2016, the number of individual was very few in ST that no box plot could be produced. In June 2016, the prosomal width of major population ranged 50 ¡V 70 mm. But it dropped clearly to 30 ¡V 40 mm in September 2016 followed by an increase to 40 ¡V 50 mm in December 2016, 40 ¡V 70 mm in March 2017 and 50 ¡V 60mm in June 2017. Based on overall higher number of small individuals from June 2016 to September 2017, it indicated another round of spawning. From September 2017 to June 2018, the major size range increased slightly from 40 ¡V 50 mm to 45 ¡V 60 mm indicating a continuous growth. In September 2018, decrease of major size was noted again that might reflect new round of spawning. Throughout the monitoring period, the larger juveniles ranged 60-80 mm in prosomal width. Juveniles reaching this size would gradually migrate to sub-tidal habitats.
3.6.36 As a summary for horseshoe crab populations in TC3 and ST, there were spawning ground of Carcinoscorpius rotundicauda from 2014 to 2018 while the spawning time should be in spring. The population size was consistent in these two sampling zones. For Tachypleus tridentatus, small individuals were rarely found in both zones from 2014 to 2015. It was believed no occurrence of successful spawning. The existing individuals (that recorded since 2012) grew to a mature size and migrated to sub-tidal habitat. Hence the number of individuals decreased gradually. From 2016 to 2018, new rounds of spawning were recorded in ST while the population size increased to a moderate level.
3.6.37 In March 2019 to June 2019 and Dec 2021, no horseshoe crab juveniles (prosomal width <100mm) were recorded in TC3 and ST. All recorded horseshoe crabs were large individuals (prosomal width >100mm) or mating pairs which were all excluded from the data analysis. From September 2019 to September 2020, the population size of both horseshoe crab species in ST gradually increased to moderate level while their body sizes were mostly in small to medium range (~23 ¡V 55mm). It indicated the natural stable growth of the horseshoe crab juveniles. In December 2020, the population size of both horseshoe crab species in ST dropped to low level while their body sizes were mostly in small to medium range (~28 ¡V 56mm). It showed the natural mortality and seasonal variation of horseshoe crab. In June 2022, the population size of both horseshoe crab species in ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~51¡V78mm). In September 2022, the population size of both horseshoe crab species inTC3 and ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~56¡V62mm).
Impact of the HKLR project
3.6.38 It was the 42nd survey of the EM&A programme during construction period. Based on the monitoring results, no detectable impact on horseshoe crab was revealed due to HKLR project. The population change was mainly determined by seasonal variation, no abnormal phenomenon of horseshoe crab individual, such as large number of dead individuals on the shore had been reported.
Seagrass Beds
3.6.39 Two seagrass species Halophila ovalis and Zostera japonica were found in present survey. Halophila ovalis was found in TC3 and ST and Zostera japonica was found only in ST. In ST, there were six large sized of Halophila ovalis found at tidal zone 1.5m above C.D nearby mangroves plantation. The larger strand had area ~6600m2 in moderate vegetation coverage (30 - 40%), ~3800m2 in moderate vegetation coverage (30 - 35%),~1000m2 in moderate vegetation coverage (25 - 30%) and three ~600 - 180m2 in low to moderate vegetation coverage (10 - 25%). In TC3, 3 large patches of Halophila ovalis were found at tidal zone 1.5m above C.D. The larger strand had area ~1600m2 in moderate vegetation coverage (40 - 50%), ~1200m2 in moderate vegetation coverage (30 - 45%) and ~480m2 in moderate vegetation coverage (20- 30%). At close vicinity to mangrove, one small sized (5m2) of Zostera japonica beds were observed at tidal zone 2.0m above C.D. Table 3.2 of Appendix O summarizes the results of present seagrass beds survey and the photograph records of the seagrass are shown on Figure 3.9 of Appendix O. The complete record throughout the monitoring period is presented inAnnex III of Appendix O.
3.6.40 Since the commencement of the EM&A monitoring programme, two species of seagrass Halophila ovalis and Zostera japonica were recorded in TC3 and ST (Figure 3.10 of Appendix O). In general, Halophila ovalis was occasionally found in TC3 in few, small to medium patches. But it was commonly found in ST in medium to large seagrass bed. Moreover, it had sometimes grown extensively and had covered significant mudflat area at 0.5 ¡V 2.0 m above C.D. between TC3 and ST. Another seagrass species Zostera japonica was found in ST only. It was relatively lower in vegetation area and co-existed with Halophila ovalis nearby the mangrove strand at 2.0 m above C.D.
3.6.41 According to the previous results, majority of seagrass bed was confined in ST, the temporal change of both seagrass species were investigated in details:
Temporal variation of seagrass beds in ST
3.6.42 Figure 3.11 of Appendix O shows the changes of estimated total area of seagrass beds in ST along the sampling months. For Zostera japonica, it was not recorded in the 1st and 2nd surveys of monitoring programme. Seasonal recruitment of few, small patches (total seagrass area: 10 m2) was found in March 2013 that grew within the large patch of seagrass Halophila ovalis. Then, the patch size increased and merged gradually with the warmer climate from March to June 2013 (15 m2). However the patch size decreased and remained similar from September 2013 (4 m2) to March 2014 (3 m2). In June 2014, the patch size increased obviously again (41 m2) with warmer climate followed by a decrease between September 2014 (2 m2) and December 2014 (5 m2). From March to June 2015, the patch size increased sharply again (90 m2). It might be due to the disappearance of the originally dominant seagrass Halophila ovalis resulting in less competition for substratum and nutrients. From September 2015 to June 2016, it was found coexisting with seagrass Halophila ovalis with steady increasing patch size (from 44 m2 to 115 m2) and variable coverage. In September 2016, the patch size decreased again to (38 m2) followed by an increase to a horizontal strand (105.4 m2) in June 2017. And it did no longer co-exist with Halophila ovalis. Between September 2014 and June 2017, an increasing trend was noticed from September to June of next year followed by a rapid decline in September of next year. It was possibly the causes of heat stress, typhoon and stronger grazing pressure during wet season. However, such increasing trend was not found from September 2017 to March 2021, while no patch of Zostera japonica was found. From June 2021, the species was recorded again in area of 45m2. The recorded area of the seagrass bed in September 2021 survey was slightly decreased to 15m2.
3.6.43 For Halophila ovalis, it was recorded as 3 ¡V 4 medium to large patches (area 18.9- 251.7 m2; vegetation coverage 50 ¡V 80%) beside the mangrove vegetation at tidal level 2 m above C.D. in September 2012. The total seagrass bed area grew steadily from 332.3 m2 in September 2012 to 727.4 m2 in December 2013. Flowers were observed in the largest patch during its flowering period. In March 2014, 31 small to medium patches were newly recorded (variable area 1 ¡V 72 m2 per patch, vegetation coverage 40-80% per patch) in lower tidal zone between 1.0 and 1.5 m above C.D. The total seagrass area increased further to 1350 m2. In June 2014, these small and medium patches grew and extended to each other. These patches were no longer distinguishable and were covering a significant mudflat area of ST. It was generally grouped into 4 large patches (1116 ¡V 2443 m2) of seagrass beds characterized of patchy distribution, variable vegetable coverage (40-80%) and smaller leaves. The total seagrass bed area increased sharply to 7629 m2. In September 2014, the total seagrass area declined sharply to 1111m2. There were only 3-4 small to large patches (6 ¡V 253 m2) at high tidal level and 1 large patch at low tidal level (786 m2). Typhoon or strong water current was a possible cause (Fong, 1998). In September 2014, there were two tropical cyclone records in Hong Kong (7th ¡V 8thSeptember: no cyclone name, maximum signal number 1; 14th ¡V 17th September: Kalmaegi, maximum signal number 8SE) before the seagrass survey dated 21st September 2014. The strong water current caused by the cyclone, Kalmaegi especially, might have given damage to the seagrass beds. In addition, natural heat stress and grazing force were other possible causes reducing seagrass beds area. Besides, very small patches of Halophila ovalis could be found in other mud flat area in addition to the recorded patches. But it was hardly distinguished due to very low coverage (10 ¡V 20%) and small leaves.
3.6.44 In December 2014, all the seagrass patches of Halophila ovalis disappeared in ST. Figure 3.12 of Appendix O shows the difference of the original seagrass beds area nearby the mangrove vegetation at high tidal level between June 2014 and December 2014. Such rapid loss would not be seasonal phenomenon because the seagrass beds at higher tidal level (2.0 m above C.D.) were present and normal in December 2012 and 2013. According to Fong (1998), similar incident had occurred in ST in the past. The original seagrass area had declined significantly during the commencement of the construction and reclamation works for the international airport at Chek Lap Kok in 1992. The seagrass almost disappeared in 1995 and recovered gradually after the completion of reclamation works. Moreover, incident of rapid loss of seagrass area was also recorded in another intertidal mudflat in Lai Chi Wo in 1998 with unknown reason. Hence, Halophila ovalis was regarded as a short- lived and r- strategy seagrass that could colonize areas in short period but disappears quickly under unfavourable conditions (Fong, 1998).
Unfavourable conditions to seagrass Halophila ovalis
3.6.45 Typhoon or strong water current was suggested as one unfavorable condition to Halophila ovalis (Fong, 1998). As mentioned above, there were two tropical cyclone records in Hong Kong in September 2014. The strong water current caused by the cyclones might have given damage to the seagrass beds.
3.6.46 Prolonged light deprivation due to turbid water would be another unfavorable condition. Previous studies reported that Halophila ovalis had little tolerance to light deprivation. During experimental darkness, seagrass biomass declined rapidly after 3-6 days and seagrass died completely after 30 days. The rapid death might be due to shortage of available carbohydrate under limited photosynthesis or accumulation of phytotoxic end products of anaerobic respiration (details see Longstaff et al., 1999). Hence the seagrass bed of this species was susceptible to temporary light deprivation events such as flooding river runoff (Longstaff and Dennison, 1999).
3.6.47 In order to investigate any deterioration of water quality (e.g. more turbid) in ST, the water quality measurement results at two closest monitoring stations SR3 and IS5 of the EM&A programme were obtained from the water quality monitoring team. Based on the results from June to December 2014, the overall water quality was in normal fluctuation except there was one exceedance of suspended solids (SS) at both stations in September. On 10th September 2014, the SS concentrations measured during mid-ebb tide at stations SR3 (27.5 mg/L) and IS5 (34.5 mg/L) exceeded the Action Level (≤ 23.5 mg/L and 120% of upstream control station¡¦s reading) and Limit Level (≤ 34.4 mg/L and 130% of upstream control station¡¦s reading) respectively. The turbidity readings at SR3 and IS5 reached 24.8 ¡V 25.3 NTU and 22.3 ¡V 22.5 NTU, respectively. The temporary turbid water should not be caused by the runoff from upstream rivers. Because there was no rain or slight rain from 1st to 10th September 2014 (daily total rainfall at the Hong Kong International Airport: 0 ¡V 2.1 mm; extracted from the climatological data of Hong Kong Observatory). The effect of upstream runoff on water quality should be neglectable in that period. Moreover the exceedance of water quality was considered unlikely to be related to the contract works of HKLR according to the ¡¥Notifications of Environmental Quality Limits Exceedances¡¦ provided by the respective environmental team. The respective construction of seawall and stone column works, which possibly caused turbid water, was carried out within silt curtain as recommended in the EIA report. Moreover there was no leakage of turbid water, abnormity or malpractice recorded during water sampling. In general, the exceedance of suspended solids concentration was considered to be attributed to other external factors, rather than the contract works.
3.6.48 Based on the weather condition and water quality results in ST, the co-occurrence of cyclone hit and turbid waters in September 2014 might have combined the adverse effects on Halophila ovalis that leaded to disappearance of this short-lived and r-strategy seagrass species. Fortunately Halophila ovalis was a fast-growing species (Vermaat et al., 1995). Previous studies showed that the seagrass bed could be recovered to the original sizes in 2 months through vegetative propagation after experimental clearance (Supanwanid, 1996). Moreover it was reported to recover rapidly in less than 20 days after dugong herbivory (Nakaoka and Aioi, 1999). As mentioned, the disappeared seagrass in ST in 1995 could recover gradually after the completion of reclamation works for international airport (Fong, 1998). The seagrass beds of Halophila ovalis might recolonize in the mudflat of ST through seed reproduction as long as there was no unfavourable condition in the coming months.
Recolonization of seagrass beds
3.6.49 Figure 3.12 of Appendix O shows the recolonization of seagrass bed in ST from December 2014 to June 2017. From March to June 2015, 2 ¡V 3 small patches of Halophila ovalis were newly found co-inhabiting with another seagrass species Zostera japonica. But the total patch area of Halophila ovalis was still very low compare with previous records. The recolonization rate was low while cold weather and insufficient sunlight were possible factors between December 2014 and March 2015. Moreover, it would need to compete with seagrass Zostera japonica for substratum and nutrient, because Zostera japonica had extended and covered the original seagrass bed of Halophila ovalis at certain degree. From June 2015 to March 2016, the total seagrass area of Halophila ovalis had increased rapidly from 6.8 m2 to 230.63 m2. It had recolonized its original patch locations and covered its competitor Zostera japonica. In June 2016, the total seagrass area increased sharply to 4707.3m2. Similar to the previous records of March to June 2014, the original patch area of Halophila ovalis increased further to a horizontally long strand. Another large seagrass beds colonized the lower tidal zone (1.0 ¡V 1.5 m above C.D.). In September 2016, this patch extended much and covered significant soft mud area of ST, resulting in sharp increase of total area (24245 m2). It indicated the second extensive colonization of this r-selected seagrass. In December 2016, this extensive seagrass patch decreased in size and had separated into few, undistinguishable patches. Moreover, the horizontal strand nearby the mangrove vegetation decreased in size. The total seagrass bed decreased to 12550 m2. From March to June 2017, the seagrass bed area remained generally stable (12438- 17046.5 m2) but the vegetation coverage fluctuated (20 ¡V 50% in March 2017 to 80 ¡V 100% in June 2017). The whole recolonization process took about 2.5 years.
Second disappearance of seagrass bed
3.6.50 In September 2017, the whole seagrass bed of Halophila ovalis disappeared again along the shore of TC3 and ST (Figure 3.12 of Appendix O). Similar to the first disappearance of seagrass bed occured between September and December 2014, strong water current (e.g. cyclone) or deteriorated water qualities (e.g. high turbidity) was the possible cause.
3.6.51 Between the survey periods of June and September 2017, there were four tropical cyclone records in Hong Kong (Merbok in 12- 13th, June; Roke in 23rd, Jul.; Hato in22 ¡V 23rd, Aug.; Pakhar in 26 ¡V 27th, Aug.) (Online database of Hong Kong Observatory) All of them reached signal 8 or above, especially Hato with highest signal 10.
3.6.52 According to the water quality monitoring results (July to August 2017) of the two closest monitoring stations SR3 and IS5 of the respective EM&A programme, the overall water quality was in normal fluctuation. There was an exceedance of suspended solids (SS) at SR3 on 12 July 2017. The SS concentration reached 24.7 mg/L during mid-ebb tide, which exceeded the Action Level (≤ 23.5 mg/L). But it was far below the Limit Level (≤ 34.4 mg/L). Since such exceedance was slight and temporary, its effect to seagrass bed should be minimal.
3.6.53 Overall, the disappearance of seagrass beds in ST has believed the cause of serial cyclone hit in July and August 2017. Based on previous findings, the seagrass beds of both species were expected to recolonize in the mudflat as long as the vicinal water quality was normal. The whole recolonization process (from few, small patches to extensive strand) would be gradually lasting at least 2 years. From December 2017 to March 2018, there was still no recolonization of few, small patches of seagrass at the usual location (Figure 3.12 of Appendix O). It was different from the previous round (March 2015 ¡V June 2017). Until June 2018, the new seagrass patches with small-medium size were found at the usual location (seaward side of mangrove plantation at 2.0 m C.D.) again, indicating the recolonization. However, the seagrass bed area decreased sharply to 22.5 m2 in September 2018. Again it was believed that the decrease was due to the hit of the super cyclone in September 2018 (Mangkhuton 16th September, highest signal 10). From December 2018 to June 2019, the seagrass bed area increased from 404 m2 to 1229 m2 while the vegetation coverage is also increased (December 2018: 5¡V 85%; March 2019: 50 ¡V 100% and June 2019: 60 ¡V 100%). Relatively, the whole recolonization process would occur slower than the previous round (more than 2 years). From September 2019 to March 2021, the seagrass bed area in ST slightly decreased from 1200 m2 to 942.05 m2, which were in normal fluctuation. From March 2021 to December 2021, the seagrass bed area in ST decreased from 942.05 m2 to 680m2, which were in normal fluctuation. In March 2022, the seagrass bed area in ST increased significantly to approximately 2040 m2, which believed to be related to more rain in current dry season. It was observed that the brown filemental algae bloom occurred at ST site in March 2022. Distribution of the algae was overlap with seagrass beds, mainly the species Halophila ovalis and the algae was grown over the top of the seagrass. In some areas, the brown filemental algae full covered the seagrass bed, refer to Figure 3.9 of Appendix O. The seagrass was still alive when checked during the field survey. Whether the algae bloom will kill seagrass in longer period time is unknown. The seagrass distribution and health condition should be checked in coming June monitoring. The algae bloom of the brown filemental algae at the seagrass bed is disappeared as observed in June 2022, refer to Figure 3.9 of Appendix O. Seagrass in present survey (September 2022) has decreased compared to June 2022 due to normal seasonal change.
Impact of the HKLR project
3.6.54 It was the 42nd survey of the EM&A programme during construction period. Throughout the monitoring period, the disappearance of seagrass beds was believed the cause of cyclone hits rather than impact of HKLR project. The seagrass bed was recolonizing since there had been a gradual increase in the size and number from December 2018 to June 2019 after the hit of the super cyclone in September 2018. The seagrass bed area decreased from March 2021 to December 2021, which were in normal fluctuation. It is observed that the seagrass Halophila ovalis covered larger area than before. Total seagrass bed area significantly increased from March 2022 to June 2022 and slightly reduced in September 2022.
Intertidal Soft Shore Communities
Substratum
3.6.55 Table 3.3 and Figure 3.13 of Appendix O show the substratum types along the horizontal transect at every tidal level in all sampling zones. The relative distribution of substratum types was estimated by categorizing the substratum types (Gravels & Boulders / Sands / Soft mud) of the ten random quadrats along the horizontal transect. The distribution of substratum types varied among tidal levels and sampling zones:
¡P In TC1, high percentages of ¡¥Gravels and Boulders¡¦ (90%) were recorded at high tidal level. At mid tidal level, ¡¥Gravels and Boulders ¡¦ was the main substratum type (60%), following by ¡¥Soft mud¡¦ (30%). At low tidal level, ¡¥Soft mud¡¦ was the main substratum type (90%), followed by ¡¥Sands¡¦ (5%) and ¡¥Gravels and Boulders¡¦ (5%).
¡P In TC2, high percentages of ¡¥Gravels and Boulders¡¦ (90%) was recorded at high tidal level, following by ¡¥Sands¡¦ and ¡¥Soft mud¡¦ (5%). At mid tidal level, ¡¥Soft mud¡¦ and ¡¥Gravels and Boulders¡¦ was the main substratum type (50% and 30%), following by ¡¥Sands¡¦ (20%). At low tidal level, ¡¥Soft mud¡¦ covered 85% and ¡¥Sands ¡¦ covered 10% of the transect.
¡P In TC3, higher percentage of ¡¥Gravels and Boulders¡¦ was recorded at high tidal level (70%). At mid tidal levels, ¡¥Soft mud¡¦ was the main substratum type (70%), following by ¡¥Gravels and Boulders ¡¦ (20%) and ¡¥Sands¡¦ (10%). At low tidal level, ¡¥Soft mud¡¦ covered 95% of the transect.
¡P In ST, ¡¥Gravels and Boulders¡¦ was the main substratum type (85%) at high tidal level. At mid tidal levels, ¡¥Gravels and Boulders¡¦ and ¡¥Soft mud¡¦ was the main substratum type (60% and 30%), following by ¡¥Sand¡¦ (10%). At low tidal level, ¡¥Soft mud¡¦ was the main substratum type (80%) and ¡¥Sands¡¦ covered 15% of the transect.
3.6.56 There was neither consistent vertical nor horizontal zonation pattern of substratum type in all sampling zones. Such heterogeneous variation should be caused by different hydrology (e.g. wave in different direction and intensity) received by the four sampling zones.
Soft shore communities
3.6.57 Table 3.4 of Appendix O lists the total abundance, density and number of taxon of every phylum in this survey. A total of 8495 individuals were recorded. Mollusca was the most abundant phylum (total abundance 7647 ind., density 255 ind. m-2, relative abundance 90.0%). The second and third were Arthropoda (586ind., 20 ind. m-2, 6.9%) which followed by Annelida (115 ind., 4 ind. m-2, 1.4%) and Sipuncula (77 ind., 3 ind. m-2, 0.9%), respectively. The fifth was Nemertea with total abundance 42 ind., density 1 ind.m-2 and relative abundance 0.5%. The sixth was Cnidania with total abundance 26 ind., density 1 ind.m-2 and relative abundance 0.3%. Platyhelminthes was very low in abundances (density <0 ind. m-2, relative abundance £0.0%). Moreover, the most diverse phylum was Mollusca (32 taxa) followed by Arthropoda (6 taxa). Annelida (3 taxa) and Sipuncula (2 taxa). There was 1 taxon for Nemertea, Cnidaria and Platyhelminthes.The taxonomic resolution and complete list of recorded fauna are shown in Annexes IV and V of Appendix O respectively. As reported in June 2018, taxonomic revision of three potamidid snail species was conducted according to the latest identification key published by Agriculture, Fisheries and Conservation Department (details see AFCD, 2018), the species names of following gastropod species were revised:
¡P Cerithidea cingulata was revised as Pirenella asiatica
¡P Cerithidea djadjariensis was revised as Pirenella incisa
¡P Cerithidea rhizophorarum was revised as Cerithidea moerchii
Moreover, taxonomic revision was conducted on another snail species while the specie name was revised:
¡P Batillaria bornii was revised as Clypeomorus bifasciata
3.6.58 In March 2021, an increased number of sea slugs and their eggs were observed in all sampling zones. It may due to the breeding season of sea slug and the increased of algae on the intertidal.
3.6.59 Table 3.5 of Appendix O shows the number of individuals, relative abundance and density of each phylum in every sampling zone. The total abundance (1,613 - 2,382 ind.) varied among the four sampling zones while the phyla distributions were similar. In general, Mollusca was the most dominant phylum (no. of individuals: 1,476 ¡V 2,192 ind.; relative abundance 84 ¡V 92.5%; density 197 - 292 ind. m-2). Other phyla were much lower in number of individuals. Arthropoda (86 - 293 ind.; 3.7 ¡V 13.6%; 11 - 39 ind. m-2) was common phyla relatively. Other phyla were very low in abundance in all sampling zones.
Dominant species in every sampling zone
3.6.60 Table 3.6 of Appendix O lists the abundant species in every sampling zone. In the present survey, most of the listed abundant species were of high or very high density (>100 ind. m-2), which were regarded as dominant species. Few of the listed species were of low to moderate densities (42 ¡V 95 ind. m-2). Other listed species of lower density (<42 ind. m-2) were regarded as common species.
3.6.62 In TC2, the substratum types were mainly ' Gravels and Boulders' at high tidal level. The rock oyster Saccostrea cucullata (123 ind. m-2, 38%) was dominant at high density. The gastropod Monodonta labio (50 ind. m-2, 15%) was dominant at low to moderate density and Batillaria multiformis (36 ind. m-2, 11%) was of lower density. At mid tidal level (main substratum types ¡¥Soft mud¡¦ and ¡¥Gravels and Boulders¡¦), rock oyster Saccostrea cucullata (90 ind. m-2, 29%), gastropods Monodonta labio (47 ind. m-2, 15%) and Batillaria zonalis (46 ind. m-2, 15%) were dominant at low to moderate densities. Substratum types ¡¥Soft Mud¡¦ were mainly distributed at low tidal level, the Barbatia virescens (45 ind. m-2, 20%) was dominant at low to moderate densities and Lunella granulate (26 ind. m-2, 11%) was of lower densities, regarded as common species.
3.6.63 In TC3, the substratum type was mainly ¡¥Gravels and Boulders¡¦ at high tidal level. The rock oyster Saccostrea cucullata (124 ind. m-2, 43%) was of dominant species at high density and the gastropod Monodonta labio (62 ind. m-2, 22%) was of low to moderate density. At mid tidal level (main substratum types ¡¥Soft mud¡¦), the rock oyster Saccostrea cucullata (114 ind. m-2, 29%) was of dominant species at high density. The gastropod Monodonta labio (60 ind. m-2, 15%) was at low density level. At low tidal level, the major substratum type was ¡¥Soft mud¡¦. The Lunella granulate (41 ind. m-2,16%), the Batillaria multiformis (34 ind. m-2, 13%) and Batillaria zonalis (31 ind. m-2, 12%) at lower density .
3.6.65 In general, there was no consistent zonation pattern of species distribution across all sampling zones and tidal levels. The species distribution was determined by the type of substratum primarily. In general, rock oyster Saccostrea cucullata (855 ind.), gastropods Monodonta labio (448 ind.) and Batillaria multiformis (156 ind.) were the most common species on gravel and boulders substratum. Batillaria zonalis (126 ind.) was the most common species on sands and soft mud substrata.
Biodiversity and abundance of soft shore communities
3.6.66 Table 3.7 of Appendix O shows the mean values of species number, density, and biodiversity index H¡¦and species evenness J of soft shore communities at every tidal level and in every sampling zone. As mentioned above, the differences among sampling zones and tidal levels were determined by the major type of substratum primarily.
3.6.67 Among the sampling zones, the mean species number was varied from 14 - 19 spp. 0.25 m-2 among the four sampling zones. The mean densities of ST (317 ind. m-2) was higher than TC3 (313 ind. m-2) followed by TC2 (287 ind. m-2) and TC1 (215 ind. m-2). The higher densities of TC3 and ST are due to the relatively high number of individuals in each quadrat. The mean H¡¦ for TC2 was 2.23, TC3 was 2.0, TC1 was 2.13 and ST were 2.17, followed by while the mean J of TC2, TC3 and ST were 0.8, which were slightly higher than TC1 (0.77). This can be due to the relatively non-even taxa distribution.
3.6.68 In the present survey, no clear trend of mean species number, mean density, H¡¦ and J observed among the tidal level.
3.6.69 Figures 3.14 to 3.17 of Appendix O show the temporal changes of mean species number, mean density, H¡¦ and J at every tidal level and in every sampling zone along the sampling months. In general, all the biological parameters fluctuated seasonally throughout the monitoring period. Lower mean species number and density were recorded in dry season (December) but the mean H' and J fluctuated within a limited range.
Impact of the HKLR project
3.6.71 It was the 42nd survey of the EM&A programme during the construction period. Based on the results, impacts of the HKLR project were not detected on intertidal soft shore community. Abnormal phenomena (e.g. rapid, consistent or non-seasonal decline of fauna densities and species number) were not recorded.
¡P The Contractor was reminded to maintain the silt curtains properly at Portion X.