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. 44 (June to August 2023)
27 October 2023
Revision 0
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
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
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-fourth 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 June 2023 to 31 Aug 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 |
|||
Jun 2023 |
Jul 2023 |
Aug 2023 |
||
Air
Quality |
1-hr
TSP at AMS5 |
5,
9, 15, 21 and 27 |
3,
7, 13, 19, 25 and 31 |
4,
10, 16, 22, 28 and 31 |
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
|
2,
8, 14, 20, 28 and 30 |
6,
12, 18, 24 and 28 |
3,
9, 15, 21, 25 and 31 |
|
24-hr
TSP at AMS6 |
Not
applicable.(see remark 1) |
Not
applicable.(see remark 1) |
Not
applicable.(see remark 1) |
|
Noise |
5,
15, 21 and 27 |
3,
13, 19, 25 and 31 |
4, 10, 16, 22 and 28 |
|
Water Quality |
2,
5, 7, 9, 12, 14, 16, 19, 21, 23, 26, 28 and 30 |
3,
5, 7, 10, 12, 14, 19, 21, 24, 26, 28 and 31 |
2,
4, 7, 9, 11, 14, 16, 18, 21, 23, 25, 28 and 30 |
|
Chinese
White Dolphin |
5,
6, 12, 19 and 20 |
5,
7, 25 and 26 |
7, 11, 14 and 24 |
|
Mudflat Monitoring
(Ecology) |
2,
3, 4 and 5 |
-
|
- |
|
Mudflat Monitoring (Sedimentation rate) |
30 |
- |
- |
|
Site Inspection |
6,
16, 20 and 30 |
6,
12, 18 and 27 |
4,
9, 15 and 25 |
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.
2) The sedimentation rate monitoring
on 15 June 2023 was rescheduled to 30 June 2023 due to the bad weather
conditions.
3) 24-hr TSP monitoring at EM&A
Station AMS5 ¡V Ma Wan Chung Village on 26 June 2023 was rescheduled to 28 June
2023 due to malfunction of HVS at AMS5 on 26 June 2023.
4) No.8 Storm Signal was in force on
17 July 2023, the water quality monitoring were cancelled due to safety reasons
and no substitute monitoring will be conducted.
5) As Super Typhoon Saola was rather
close to Hong Kong on 1 September 2023, the local weather deteriorated, and
winds strengthened further. 1-hr TSP monitoring at AMS5 on 1 September 2023 was
rescheduled to 31 August 2023.
6)
As Super
Typhoon Saola was rather close to Hong Kong on 1
September 2023, the site inspection on 31 August 2023 was cancelled.
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 (June 2023 to August 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 being blocked by the silt curtains of the
Tung Chung New Town Extension (TCNTE) project. Water quality monitoring has
been temporarily conducted at alternative stations, namely SR4(N3) (Coordinate:
E814779, N818032) until 1 March 2023. Proposal for permanently relocating the
SR4(N2) was approved by EPD on 3 March 2023. The water quality monitoring has
been conducted at stations SR4(N3) since 3 March 2023.
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) |
Jun 2023 |
AMS5 |
36 |
9-109 |
352 |
500 |
AMS6 |
-- |
-- |
360 |
||
Jul 2023 |
AMS5 |
31 |
3-89 |
352 |
|
AMS6 |
-- |
-- |
360 |
||
Aug 2023 |
AMS5 |
17 |
5-47 |
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) |
Jun
2023 |
AMS5 |
25 |
15-42 |
164 |
260 |
AMS6 |
-- |
-- |
173 |
||
Jul
2023 |
AMS5 |
25 |
13-35 |
164 |
|
AMS6 |
-- |
-- |
173 |
||
Aug
2023 |
AMS5 |
25 |
16-36 |
164 |
|
AMS6 |
-- |
-- |
173 |
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) |
Jun 2023 |
NMS5 |
62 |
60-66 |
When one documented complaint is received |
75 |
Jul 2023 |
58 |
56-60 |
|||
Aug 2023 |
56 |
55-58 |
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
Distribution
Table 3.4 Dolphin Encounter Rates
(Sightings Per 100 km of Survey Effort) During Reporting Period (June 2023 to August 2023)
SURVEY AREA |
DOLPHIN MONITORING DATES |
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) |
Primary Lines
Only |
Primary Lines
Only |
||
Northeast Lantau |
Set 1 (5, 6 &
12 Jun 2023) |
0.00 |
0.00 |
Set 2 (19 &
20 Jun 2023) |
0.00 |
0.00 |
|
Set 3 (5 & 7 Jul 2023) |
0.00 |
0.00 |
|
Set 4 (25 &
26 Jul 2023) |
0.00 |
0.00 |
|
Set 5 (7 &
11 Aug 2023) |
0.00 |
0.00 |
|
Set 6 (14 &
24 Aug 2023) |
0.00 |
0.00 |
|
Northwest
Lantau |
Set 1 (5, 6 &
12 Jun 2023) |
0.00 |
0.00 |
Set 2 (19 &
20 Jun 2023) |
0.00 |
0.00 |
|
Set 3 (5 & 7 Jul 2023) |
0.00 |
0.00 |
|
Set 4 (25 &
26 Jul 2023) |
0.00 |
0.00 |
|
Set 5 (7 &
11 Aug 2023) |
1.62 |
1.62 |
|
Set 6 (14 &
24 Aug 2023) |
0.00 |
0.00 |
|
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) |
||
June ¡V August 2023 |
September
¡V November 2011 |
June ¡V August 2023 |
September
¡V November 2011 |
|
Northeast Lantau |
0.0 |
6.00 ¡Ó 5.05 |
0.0 |
22.19 ¡Ó 26.81 |
Northwest Lantau |
0.27 ¡Ó 0.66 |
9.85 ¡Ó 5.85 |
0.27 ¡Ó 0.66 |
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)
|
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) |
6.00 ¡Ó
5.05 |
22.19 ¡Ó 26.81 |
June-August 2013
(HKLR03 Impact) |
0.88 ¡Ó
1.36 |
3.91 ¡Ó
8.36 |
June-August 2014
(HKLR03 Impact) |
0.42 ¡Ó
1.04 |
1.69 ¡Ó
4.15 |
June-August 2015
(HKLR03 Impact) |
0.44 ¡Ó
1.08 |
0.44 ¡Ó
1.08 |
June-August 2016
(HKLR03 Impact) |
0.00 |
0.00 |
June-August 2017
(HKLR03 Impact) |
0.00 |
0.00 |
June-August 2018
(HKLR03 Impact) |
0.00 |
0.00 |
June-August 2019
(HKLR03 Impact) |
0.00 |
0.00 |
June-August 2020
(TMCLKL Post-Construction) |
0.00 |
0.00 |
June-August 2021
(TMCLKL Post-Construction) |
0.00 |
0.00 |
June-August 2022
(HKLR03 Impact) |
0.00 |
0.00 |
June-August 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)
|
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 |
June-August 2013
(HKLR03 Impact) |
6.56 ¡Ó
3.68 |
27.00 ¡Ó 18.71 |
June-August 2014
(HKLR03 Impact) |
4.74 ¡Ó
3.84 |
17.52 ¡Ó 15.12 |
June-August 2015
(HKLR03 Impact) |
2.53 ¡Ó
3.20 |
9.21 ¡Ó 11.57 |
June-August 2016
(HKLR03 Impact) |
1.72 ¡Ó
2.17 |
7.48 ¡Ó 10.98 |
June-August 2017
(HKLR03 Impact) |
2.20 ¡Ó
2.88 |
6.58 ¡Ó
8.12 |
June-August 2018
(HKLR03 Impact) |
1.16 ¡Ó
1.39 |
2.87 ¡Ó
3.32 |
June-August 2019
(HKLR03 Impact) |
0.62 ¡Ó
1.52 |
1.55 ¡Ó
3.80 |
June-August 2020
(TMCLKL Post-Construction) |
0.57 ¡Ó
0.89 |
0.57 ¡Ó
0.89 |
June-August 2021
(TMCLKL Post-Construction) |
0.00 |
0.00 |
June-August 2022
(HKLR03 Impact) |
0.28 ¡Ó 0.67 |
0.28 ¡Ó
0.67 |
June-August 2023
(HKLR03 Impact) |
0.27 ¡Ó
0.66 |
0.27 ¡Ó
0.66 |
Table 3.8 Comparison of average dolphin group
sizes from impact monitoring period (June ¡V August 2023) and baseline
monitoring period (September ¡V November 2011) (Note: ¡Ó denotes the standard deviation of the average group size)
|
Average Dolphin Group
Size |
|
June ¡V August
2023 |
September ¡V November 2011 |
|
Overall |
1.00 (n = 1) |
3.72 ¡Ó 3.13 (n = 66) |
Northeast Lantau |
-- |
3.18 ¡Ó 2.16 (n = 17) |
Northwest Lantau |
1.00 (n = 1) |
3.92 ¡Ó 3.40 (n = 49) |
Table 3.8 Measured
Mudflat Surface Level Results
Baseline Monitoring (September 2012) |
Impact Monitoring (June 2023) |
|||||
Monitoring Station |
Easting (m) |
Northing (m) |
Surface Level (mPD) |
Easting (m) |
Northing (m) |
Surface Level (mPD) |
S1 |
810291.160 |
816678.727 |
0.950 |
810291.182 |
816678.709 |
1.123 |
S2 |
810958.272 |
815831.531 |
0.864 |
810958.271 |
815831.525 |
0.970 |
S3 |
810716.585 |
815953.308 |
1.341 |
810716.586 |
815953.314 |
1.440 |
S4 |
811221.433 |
816151.381 |
0.931 |
811221.447 |
816151.381 |
1.124 |
Table 3.9 Comparison
of Measurement
Comparison of Measurement |
Remarks and Recommendation |
|||
Monitoring
Station |
Easting
(m) |
Northing
(m) |
Surface
Level (mPD) |
|
S1 |
0.022 |
-0.018 |
0.173 |
Level continuously increased |
S2 |
-0.001 |
-0.006 |
0.106 |
Level continuously increased |
S3 |
0.001 |
0.006 |
0.099 |
Level continuously increased |
S4 |
0.014 |
0.000 |
0.193 |
Level continuously increased |
Table 3.10 Impact
Water Quality Monitoring Results (Depth Average) at Station SR3(N)
|
Mid Ebb Tide |
Mid Flood Tide |
||||
DO (mg/L) |
Turbidity (NTU) |
SS (mg/L) |
DO (mg/L) |
Turbidity (NTU) |
SS (mg/L) |
|
2-Jun-2023 |
6.72 |
3.13 |
2.60 |
6.83 |
3.33 |
2.00 |
5-Jun-2023 |
6.54 |
4.43 |
3.53 |
6.07 |
4.08 |
4.10 |
7-Jun-2023 |
6.08 |
4.20 |
5.35 |
5.73 |
3.98 |
5.80 |
9-Jun-2023 |
6.28 |
4.45 |
3.58 |
5.98 |
4.50 |
3.45 |
12-Jun-2023 |
6.40 |
4.33 |
4.63 |
6.64 |
4.50 |
5.20 |
14-Jun-2023 |
6.61 |
4.25 |
4.73 |
6.83 |
4.55 |
4.15 |
16-Jun-2023 |
5.83 |
3.60 |
2.78 |
5.72 |
3.43 |
1.73 |
19-Jun-2023 |
6.55 |
3.80 |
3.70 |
6.17 |
3.73 |
3.35 |
21-Jun-2023 |
6.81 |
3.70 |
2.85 |
6.37 |
3.63 |
3.70 |
23-Jun-2023 |
7.28 |
4.13 |
5.18 |
6.95 |
3.65 |
4.53 |
26-Jun-2023 |
7.08 |
3.78 |
3.28 |
6.84 |
3.63 |
1.93 |
28-Jun-2023 |
6.52 |
3.53 |
4.28 |
6.65 |
3.68 |
4.73 |
30-Jun-2023 |
6.76 |
4.05 |
4.58 |
7.17 |
3.68 |
4.25 |
Average |
6.57 |
3.95 |
3.93 |
6.46 |
3.87 |
3.76 |
|
Mudflat Ecology
Monitoring
3.16.6
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). 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 June
2023 (totally 4 sampling days 2nd (for ST), 3rd (for
TC3), 4th (for TC2) and 5th (for TC1).
3.16.8 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 2nd (for ST), 3rd (for TC3), 4th (for TC2) and 5th (for TC1) June 2023, which were
sunny days.
3.16.12
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.
3.16.13
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)
3.16.16 In total of 27 individuals of Tachypleus tridentatus were found in present survey. The recorded individuals were distributed within areas of ST and TC3. All 27 findings were juvenile specimens. Photo records of previously observed
horseshoe crab is shown in Figure 3.1 of
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.
3.16.17 No Carcinoscorpius
rotundicauda was
recorded in present survey.
3.16.18 For Tachypleus tridentatus, 18 individuals with average body size
59.09 mm (prosomal width ranged 46.21 ¡V 77.25 mm) were found in ST and 9
individuals with average body size 66.6 (prosomal width ranged 46.5-84.13 mm)
were found in TC3 in present survey. The search records in ST (3.0 ind. hr-1.
Person-1) and in TC3 (1.5 ind. Hr-1. Person-1).
3.16.19
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 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 adult individuals (prosomal width >100mm) of Carcinoscorpius
rotundicauda were recorded in September 2022 survey, with one alive, one
dead in TC3 and one dead in TC2.
June 2022, 7 large individuals (prosomal width >100mm) of Carcinoscorpius
rotundicauda was recorded (prosomal width ranged 131.4mm - 140.3mm) in TC3.
In December 2018, one large individual of Carcinoscorpius rotundicauda
was found in TC3 (prosomal width 148.9 mm). In March 2019, 3 large individuals
(prosomal width ranged 220 ¡V 310mm) of Carcinoscorpius
rotundicauda were observed in TC2. In June 2019, there were 3 and 7 large
individuals of Tachypleus tridentatus recorded in ST (prosomal width
ranged 140 ¡V 180mm) and TC3
(prosomal width ranged 150 ¡V 220mm),
respectively. In March 2020, a mating pair of Tachypleus tridentatus was
recorded in TC1 with prosomal width 123 mm and 137mm. Base on their sizes, it
indicated that individuals of prosomal width larger than 100 mm would progress
its nursery stage from intertidal habitat to sub-tidal habitat of Tung Chung
Wan. The photo records of the large horseshoe crab are shown in Figure 3.4 of Appendix O. These large
individuals might move onto intertidal shore occasionally during high tide for
foraging and breeding. Because they should be inhabiting sub-tidal habitat most
of the time. Their records were excluded from the data analysis to avoid mixing
up with juvenile population living on intertidal habitat.
3.16.20
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.
3.16.21
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
3.16.22
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.
3.16.23
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
juvenils 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. In March 2023, total of 12 individuals of
juveniles Carcinoscorpius rotundicauda and Tachypleus tridentatus
were found and recorded. In June 2023, total of 27 individuals of juveniles Tachypleus
tridentatus were found and recorded.
3.16.24 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.
3.16.27 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.
3.16.28 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.
3.16.29 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).
3.16.30 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.
3.16.31
In recent
year, the 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.
3.16.32 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.
3.16.33 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
3.16.34 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.
3.16.35 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.
3.16.36 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.
3.16.37
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 in TC3 and ST was kept as
low-moderate level while their body sizes were mostly in small to medium
range (~56¡V62mm). In September
2022, the population size of both horseshoe crab species in TC3 and ST was kept
as low-moderate level while
their body sizes were mostly in small to medium range (~44-79mm).
3.16.38 It was the 44th 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
3.16.39 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 ~8400m2 in moderate vegetation coverage (40-50%), ~5200m2 in
moderate vegetation coverage (30 - 40%),~1900m2 in
moderate vegetation coverage (20 - 30%) and three ~600 - 200m2 in
low to moderate vegetation coverage (10 - 30%). In TC3, 3 large patches of Halophila
ovalis were found at tidal zone 1.5m above C.D. The
larger strand had area ~2200m2 in moderate vegetation coverage (40 - 70%), ~1900m2 in
moderate vegetation coverage (30 - 60%) and ~800m2 in moderate vegetation
coverage (20-50%). At close vicinity to mangrove, one small sized (35m2) of Zostera japonica beds were
observed at tidal zone 2.0m above C.D in ST. 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 in Annex
III of Appendix O.
3.16.40 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.
3.16.41 According to the
previous results, majority of seagrass bed was confined in ST, the temporal
change of both seagrass species was investigated in details:
Temporal variation of seagrass beds in ST
3.16.42
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.
3.16.43
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.
3.16.44
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
3.16.45
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.
3.16.46
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).
3.16.47
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.
3.16.48
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
3.16.49
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
3.16.50
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.
3.16.51
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.
3.16.52
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.
3.16.53
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. 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 distritrution 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. Seagrass in
December 2022 and September 2022 have decreased compare to June 2022 due to
normal seasonal change. Seagrass in March 2023
have increased compare to previous quarter due to normal seasonal change.
Seagrass in June 2023 have further increased around 20% compared to previous
period.
Impact of the HKLR project
3.16.54
It was the
44th 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. Seagrass in June 2023 have increased compare to previous
quarter due to normal seasonal change.
Intertidal Soft Shore
Communities
Substratum
3.16.55
Table 3.3 of Appendix O 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 TC2, high percentages of ¡¥Gravels and Boulders¡¦ (90%) was
recorded at high tidal level, following by ¡¥Sands¡¦ (5%) and ¡¥Soft mud¡¦ (5%). At
mid tidal level, ¡¥Gravels and Boulders¡¦ was the main substratum
type (70%), following by ¡¥Sands¡¦ (20%) and ¡¥Soft mud¡¦ (10%). At low tidal level, ¡¥Soft mud¡¦
covered 80% , ¡¥Soft mud¡¦ and ¡¥Sands ¡¦ covered 20% of the
transect.
¡P
In TC3, higher percentage of ¡¥Gravels and Boulders¡¦ was
recorded at high tidal level (65%). At mid tidal levels, ¡¥¡¥Gravels and Boulders¡¦ was the
main substratum type (50%), following by ¡¥Soft mud ¡¦ (30%)
and ¡¥Sands¡¦ (20%). At low tidal level, ¡¥Soft mud¡¦ covered 70% of the
transect.
¡P
In ST, ¡¥Gravels and Boulders¡¦ was the
main substratum type (65%) at high tidal level. At mid tidal levels, ¡¥Gravels and Boulders¡¦ and ¡¥Soft
mud¡¦ was the main substratum type (50% and 30%), following by ¡¥Sand¡¦ (20%). At
low tidal level, ¡¥Soft mud¡¦ was the main substratum type (90%) and ¡¥Sands¡¦ covered 10% of the transect.
3.16.56
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
¡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
3.16.59
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.
3.16.60
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 (1,671 - 2,522 ind.)
varied among the four sampling zones while the phyla
distributions were similar. In general, Mollusca was the most dominant phylum (no. of individuals: 1,526 - 2,307 ind.; relative
abundance 83.9 ¡V 91.5%; density 203 - 308 ind. m-2). Other phyla
were much lower in number of individuals. Arthropoda (88- 310 ind.; 4.4 ¡V 13.9%; 12 - 41 ind. m-2) was common phyla relatively. Other phyla
were very low in abundance in all sampling zones.
Dominant species in every sampling zone
3.16.61
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.
3.16.63
In TC2, the substratum
types were mainly ' Gravels and Boulders' at high tidal level. The rock oyster Saccostrea cucullata (136 ind. m-2, 39%) was dominant at
high density. The gastropod Monodonta labio (59 ind. m-2,
17%) was dominant at low to moderate density. ), the Batillaria multiformis (38 ind. m-2, 11%) was dominant at
low
densities. At mid
tidal level (main substratum types ¡¥Soft mud¡¦ and ¡¥Gravels and
Boulders¡¦), rock
oyster Saccostrea cucullata (92 ind. m-2, 29%), gastropods Monodonta
labio (62 ind. m-2, 17%) and Batillaria zonalis (48 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 (43 ind. m-2, 19%) was dominant
at low to moderate densities, the Batillaria multiformis (33 ind. m-2, 15%) were of lower
densities, regarded as common species.
3.16.64
In TC3, the substratum
type was mainly ¡¥Gravels and Boulders¡¦ at high tidal level. The rock oyster Saccostrea
cucullata (144 ind. m-2, 40%) was of dominant species at high density
and the gastropod Monodonta labio (92 ind. m-2, 21%) was of low to moderate
density. At mid tidal level (main substratum types ¡¥Soft mud¡¦), the rock
oyster Saccostrea cucullata (83 ind. m-2, 24%) was of
dominant species at low to moderate density. The
gastropod Monodonta labio (45 ind. m-2, 13%) was at low
density level. At low tidal level, the major substratum type was ¡¥Soft mud¡¦.
The Lunella
granulate 53 ind. m-2, 18%), the Batillaria multiformis (47 ind. m-2, 16%), Batillaria
zonalis (42 ind. m-2, 14%) and the Barbatia virescens (53 ind. m-2, 18%) at lower density.
3.16.66
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 (876 ind.),
gastropods Monodonta labio (468 ind.) and Batillaria multiformis (165 ind.) were the most common species on
gravel and boulders substratum. Batillaria
zonalis (142 ind.) was the most common species on sands and soft
mud substrata.
Biodiversity and abundance of soft shore communities
3.16.67
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.
3.16.68
Among the
sampling zones, the mean species number was varied from 14 - 21 spp. 0.25 m-2
among the four sampling zones. The mean densities of TC3 (336 ind. m-2)
was higher than ST (307 ind. m-2)
followed by TC2 (298 ind. m-2)
and TC1 (223 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 2.27, TC1
was 2.07 and ST were 2.13, followed by while the mean J of TC2 and ST were 0.8,
which were slightly higher than TC3 (0.77) and TC1. This can be due to the relatively non-even taxa distribution.
3.16.69
In the
present survey, no clear trend of mean species number, mean density, H¡¦ and J observed among the tidal level.
Impact of the HKLR
project
¡P The Contractor was reminded to maintain the silt curtains properly
at Portion X.