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.
37 (September 2021
to November 2021)
24 January 2022
Revision 0
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
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 L Summary of
Environmental Licenses and Permits
Appendix
M Record of ¡§Notification
of Summons and Prosecutions¡¨
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 thirty-seventh 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 September to 30 November 2021.
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 |
|||
Sep 2021 |
Oct 2021 |
Nov 2021 |
||
Air
Quality |
1-hr
TSP at AMS5 |
3,
9, 15, 21, 27 and 30 |
6,
12, 18, 22 and 28 |
3,
9, 15, 19, and 25 |
1-hr
TSP at AMS6 |
Not
applicable.(see remark 2) |
Not
applicable.(see remark 2) |
Not
applicable.(see remark 2) |
|
24-hr
TSP at AMS5
|
2,
8, 14, 20, 24 and 29 |
5,
11, 15, 21 and 27 |
2,
8, 12, 18, 24 and 30 |
|
24-hr
TSP at AMS6 |
Not
applicable.(see remark 2) |
Not
applicable.(see remark 2) |
Not
applicable.(see remark 2) |
|
Noise |
9,
15, 21 and 27 |
6,
12, 18 and 28 |
3, 9, 15 and 25 |
|
Water Quality |
Not
applicable.(see remark 1) |
Not
applicable.(see remark 1) |
Not
applicable.(see remark 1) |
|
Chinese
White Dolphin |
Not
applicable.(see remark 1) |
Not
applicable.(see remark 1) |
Not applicable.(see
remark 1) |
|
Mudflat Monitoring
(Ecology) |
3,
6, 16, and 17 |
-
|
- |
|
Mudflat Monitoring (Sedimentation rate) |
4 |
- |
- |
|
Site Inspection |
1,
8, 15, 24 and 30 |
6,
12, 20 and 29 |
3,
10, 17, 24 and 30 |
Remarks:
1) Water quality monitoring and dolphin monitoring
were temporarily suspended during the reporting period.
2) 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.
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) |
Not
applicable. (see remark 1) |
Not
applicable. (see remark 1) |
Turbidity
level |
Not
applicable. (see remark 1) |
Not
applicable. (see remark 1) |
|
Dissolved
oxygen level (DO) |
Not
applicable. (see remark 1) |
Not
applicable. (see remark 1) |
|
Dolphin Monitoring |
Quarterly
Analysis (Sep 2021 to Nov 2021) |
Not
applicable. (see remark 2) |
Not
applicable. (see remark 2) |
Remarks:
1) Water quality monitoring was temporarily
suspended during the reporting period. Thus, no water quality monitoring
results and exceedances from September 2021 to November 2021 are presented.
2) Dolphin monitoring was temporarily suspended
during the reporting period. Thus, no quarterly analysis of dolphin monitoring
results and exceedances from September 2021 to November 2021 are presented.
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 complaint 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.
Table 1.1 Construction
Activities during Reporting Period
Description of Activities |
Site Area |
Landscape
maintenance works |
SHT East Portal |
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 water quality monitoring programme
and dolphin monitoring programme were temporarily suspended during the
reporting period, since no marine works were scheduled or conducted.
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) |
Sep 2021 |
AMS5 |
29 |
17 - 46 |
352 |
500 |
AMS6 |
- |
- |
360 |
||
Oct 2021 |
AMS5 |
25 |
19 - 31 |
352 |
|
AMS6 |
- |
- |
360 |
||
Nov 2021 |
AMS5 |
33 |
21 - 56 |
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) |
Sep 2021 |
AMS5 |
31 |
12 - 53 |
164 |
260 |
AMS6 |
- |
- |
173 |
||
Oct 2021 |
AMS5 |
53 |
34 - 64 |
164 |
|
AMS6 |
- |
- |
173 |
||
Nov 2021 |
AMS5 |
86 |
58 - 111 |
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) |
Sep 2021 |
NMS5 |
61 |
58 - 63 |
When one documented complaint is received |
75 |
Oct 2021 |
60 |
57 - 63 |
|||
Nov 2021 |
58 |
57 - 60 |
Table 3.9 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 |
810291.169 |
816678.715 |
1.159 |
S2 |
810958.272 |
815831.531 |
0.864 |
810958.266 |
815831.526 |
0.991 |
S3 |
810716.585 |
815953.308 |
1.341 |
810716.589 |
815953.330 |
1.456 |
S4 |
811221.433 |
816151.381 |
0.931 |
811221.452 |
816151.409 |
1.136 |
Table 3.10 Comparison
of Measurement
Comparison of measurement |
Remarks and
Recommendation |
|||
Monitoring Station |
Easting |
Northing (m) |
Surface Level |
|
S1 |
0.009 |
-0.012 |
0.209 |
Level
continuously increased |
S2 |
-0.006 |
-0.005 |
0.127 |
Level continuously increased |
S3 |
0.004 |
0.022 |
0.115 |
Level continuously increased |
S4 |
0.019 |
0.028 |
0.205 |
Level continuously increased |
Table 3.11 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-Sep-2021 |
7.3 |
3.6 |
3.1 |
7.0 |
3.8 |
3.4 |
04-Sep-2021 |
6.5 |
4.4 |
3.4 |
6.4 |
4.6 |
3.5 |
07-Sep-2021 |
5.3 |
4.2 |
9.0 |
5.2 |
3.6 |
9.2 |
09-Sep-2021 |
5.3 |
4.7 |
4.5 |
5.4 |
4.2 |
5.2 |
11-Sep-2021 |
5.2 |
5.1 |
6.1 |
5.3 |
5.4 |
6.1 |
14-Sep-2021 |
5.2 |
4.6 |
4.2 |
5.5 |
5.3 |
3.9 |
16-Sep-2021 |
5.4 |
5.2 |
3.3 |
5.3 |
5.1 |
3.6 |
18-Sep-2021 |
6.4 |
5.2 |
4.8 |
6.2 |
5.5 |
3.2 |
21-Sep-2021 |
6.0 |
5.1 |
6.5 |
6.0 |
4.4 |
6.5 |
23-Sep-2021 |
6.4 |
5.7 |
5.6 |
5.7 |
5.5 |
5.4 |
25-Sep-2021 |
6.5 |
4.7 |
3.2 |
6.8 |
5.2 |
3.2 |
28-Sep-2021 |
6.3 |
5.2 |
1.6 |
6.6 |
4.8 |
1.1 |
30-Sep-2021 |
6.6 |
5.6 |
1.7 |
6.6 |
5.4 |
2.0 |
Average |
6.0 |
4.9 |
4.4 |
6.0 |
4.8 |
4.3 |
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 September 2021 (totally 4 sampling days 3rd
(for ST), 6th (for TC1), 16th (for TC2) and 17th
(for TC3).
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 3rd (for ST), 6th (for TC1), 16th
(for TC2) and 17th (for TC3) September 2021, which were sunny and
hot days.
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 3rd (for
ST), 6th (for TC1), 16th (for TC2) and 17th
(for TC3) September 2021, which were sunny and hot days.
3.6.11
The intertidal soft shore community surveys were conducted in low tide period
on 3rd (for ST), 6th (for TC1), 16th (for TC2)
and 17th (for TC3) September 2021. 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
In total of 10 and 7 individuals of Carcinoscorpius rotundicauda and Tachypleus
tridentatus were found in present survey. The recorded individuals were mainly distributed along the shoreline
in ST and TC3. All of them were observed on similar substratum (fine sand or
soft mud, slightly submerged). Photo records of the observed horseshoe crab are
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
For Carcinoscorpius
rotundicauda, more
individuals (8 ind.) were found in ST with average body size 39.83 mm (prosomal
width ranged 31.26 ¡V 48.81 mm). In TC3, 2 individuals with average body size
38.12 mm (prosomal width ranged 35.56 ¡V 40.67 mm) were found in present survey.
The search record in ST (1.33 ind. hr-1. Person-1) and
TC3 (0.33 ind. hr-1. Person-1) were very low. No Carcinoscorpius
rotundicauda was recorded in TC1 and TC2 in present
survey.
3.6.18
For Tachypleus tridentatus, 7 individuals
with average body size 40.92 mm (prosomal width ranged 37.87 ¡V 44.25 mm) were
found in ST. In TC3, only one individual with body size 38.78 mm (prosomal
width ranged 38.78mm) was found in present survey. The search records in ST
(1.00 ind. hr-1. Person-1) and TC3 (0.17 ind. hr-1.
Person-1) were very low. No Tachypleus tridentatus was found
in TC1 and TC2 in present survey.
3.6.19
No mating pair or large individual (≥100mm) was found
in present survey.
3.6.20
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, 2 mating pairs of Tachypleus
tridentatus with large body sizes (male 150mm and Female 200mm; Male 180mm
and Female 220mm) was 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
mating pairs 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). No mating pair was found in September
2021 (present survey).
3.6.21
No large individuals (prosomal
width >100mm) of Carcinoscorpius rotundicauda and Tachypleus tridentatus was recorded in September 2021
(present survey). 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 were 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. Based 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.
3.6.22
No marked individual of horseshoe
crab was recorded in September 2021
(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 crabs 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.
3.6.23
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
3.6.24 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.
3.6.25 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 (present survey), 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 crab 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 months in Hong Kong in record. As such, hot and shiny weather decreased
horseshoe crab activity.
3.6.26 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
3.6.29 Throughout the monitoring period, the search records of horseshoe crabs
were fluctuated and at moderate ¡V very low level in June (Figures 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 individuals 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 September
2021 (present survey), the number of Carcinoscorpius rotundicauda and Tachypleus
tridentatus gradually decreased to 10 ind. and 7 ind., respectively in
comparing with the September of previous record. The drop of abundance may be
related to the hot weather in September 2021. Throughout the monitoring period,
similar distribution of horseshoe crabs population were found.
3.6.30 The search record of horseshoe crab declined obviously
in all sampling zones during dry season especially December (Figures 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 0-12 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-1person-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 ºC 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.
3.6.31 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 mm - 49.81 mm), it indicated
that breeding and spawning of this species had occurred about 3 years ago along
the coastline of Tung Chung 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).
3.6.32 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 - 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 continued to grow and reach about 55mm. The
population size of Tachypleus tridentatus slightly decreased in ST from
March 2021 to September 2021 and the mean proposal width of them slightly
decreased to about 40.9mm.
3.6.33 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 became increased
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
3.6.34
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.
3.6.35 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 33.97 mm 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 September
2021 (present survey), 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
3.6.36
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.
3.6.37
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 - 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 ¡V 80 mm in prosomal width.
Juveniles reaching this size would gradually migrate to sub-tidal habitats.
3.6.38 As a summary
for horseshoe crab populations in TC3 and ST, there were spawning 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.
3.6.39 In March 2019 to June 2019, 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 September 2021 (present survey), 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 (~31¡V 48mm).
Impact
of the HKLR project
3.6.40
It was
the 36th 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. The survey
results of present survey 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 months in Hong Kong in record. As
such, hot and shiny weather decreased horseshoe crab activity.
Seagrass Beds
3.6.41 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 in ST. In ST, there were three
small sized and three large sized of Halophila ovalis found at tidal
zone 1.5m above C.D nearby mangroves plantation. The larger strand had area
~480m2 in high vegetation coverage (60 ¡V 70%), ~450m2 in
high vegetation coverage (70 ¡V 80%) and ~288m2 in high vegetation
coverage (80 ¡V 90%) At close vicinity, three small sized (~4m2 -45m2)
of Halophila ovalis beds were observed at tidal zone 1.5m above C.D. All
the small sized of Halophila ovalis beds were in moderate to high
vegetation coverage ranging from 50-80%. In TC3, 1 large patch and 2 small
patches of Halophila ovalis were found at tidal zone 1.5m above C.D. The
larger strand had area ~350m2 in high vegetation coverage (70 ¡V
80%), while two small patches with area size in ~30m2 and 64m2
had moderate coverage (50 to 70%).
Another seagrass species Zostera japonica was found at tidal zone
1.5m above C.D nearby mangroves plantation with ~20m2 in moderate to
high vegetation coverage (70 - 80%). 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.
3.6.42 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.
3.6.43 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
3.6.44 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 Mach 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.