Appendix 8.5 CORAL MAPPING SURVEY
Objectives
The main objectives of this work was to record the species number, locations and sizes of coral colonies along the alignment and within the dredging area of Outfall Option 1., and to identify potential translocation sites on the nearby coastline to facilitate a translocation plan where necessary. The location of the Study Area is in Picnic Bay close to Mo Tat Wan, as shown in Figure A8.5-1.
The survey included three parts:
1) A quantitative dive survey to count and record the coral colonies (hard and soft) in terms of their species, size, abundance, distribution and ecological significance, or species of conservation concern within the dredging area;
2) To capture underwater video transects and benthic cover/ecological attributes of the four major transects; and
3) To identify potential translocation sites.
The present survey also verified the findings from the previous dive survey conducted in 1998.
1) Coral mapping at Outfall Option 1
A transect with scale was deployed along the outfall alignment (Main transect) as indicated on Figure A8.5-1. The Main transect extended for 50 m. The outfall alignment was determined in the field with both landscape features and geographical co-ordinates from a portable Global Positioning System (GPS). The exact location of the Main Transect, however, was determined on site based on a preliminary survey.
Starting from 1m distance on the Main transect, transects parallel to the coastline (Parallel transect) were deployed at 2m intervals. The Parallel transects extended 17m from both sides of the Main transect, thus covering a width of 34m to ensure the dredging area (33m in width) was completely covered.
Within 1m on either side of each Parallel transect, the locations of any coral colonies (both hard and soft) found were recorded with reference to the Parallel transects and Main transect. A specific code was assigned to each colony recorded. Their sizes and the sizes of the boulders on which they colonise were also estimated and recorded.
Results were presented as a map showing the locations of all coral colonies within the dredging area. The total number of coral colonies, their sizes and the sizes of the boulders beneath were also provided according to their assigned codes.
2) Video recording and ecological assessment at Outfall Option 1
Video transects were recorded on the Main transect and three of the Parallel transects.
Each transect was filmed at approximately 40cm above the substrate and at a constant speed in compliance with standard protocols for coral surveys (no more than 10 metres per minute). The video camera was held perpendicular to the substrate to minimise parallelax error and to keep the substrate in focus. The video transects recorded a 40cm swath of seabed
The video for the Main transect showed the zoning of seabed substrate along the outfall alignment, and also the distance of the band in which most corals can be found. Video tapes for the parallel transects showed whether there is any change of coral colony density along the coastline within the dredging area. The video tapes of Parallel transects were also used to rectify the locations of coral colonies recorded in the field.
The present conditions of coral colonies were recorded on site and extracted from the video transects. Information concerning the physical nature of Outfall Option 1 was recorded during the survey. This information consisted of observations regarding the degree of exposure of the site to wave action, the nature of the substrate type and the topographic profile of the site.
In addition to video recording, the benthic cover and ecological attributes of the above 4 major transects were recorded following the Rapid Ecological Assessment (REA) technique.
Video transects were recorded on the Main transect and three of the Parallel transects.
The benthic cover and ecological attributes of the above 4 transects were also recorded following the Rapid Ecological Assessment (REA) technique.
The Rapid Ecological Assessment technique allows qualitative information on the ecological attributes of a habitat to be obtained rapidly without compromising scientific rigour. Following the video footage was taken, an assessment of the benthic cover and taxon abundance was undertaken within 2m either side of each transect filmed.
Two assessment categories, benthic cover and taxonomic groups, would be applied for the transects. For benthic cover, five ecological and seven substratum attributes were assigned to one of seven standard ranked categories.
Table A8.5 - 1 Categories and ranking of Ecological and substratum attributes.
|
Ecological |
Substratum |
|
Hard coral |
Hard substrates |
|
Dead standing coral |
Continuous pavement |
|
Soft coral |
Bedrock/boulders/sand |
|
Sea anemone beds |
Rubble |
|
Macroalgae |
Cobbles |
|
|
Sand with gravel |
|
|
Mud |
|
|
|
|
Rank |
Percentage cover (%) |
|
0 |
None recorded |
|
1 |
1-5 |
|
2 |
6-10 |
|
3 |
11-30 |
|
4 |
31-50 |
|
5 |
51-75 |
|
6 |
76-100 |
An inventory of benthic taxa was also complied for each transect. Taxa were identified on site to the following levels:
· Hard corals
· Soft corals, anemones and conspicuous macroalgae were recorded according to morphological features and to genus level where possible
· Other benthos (such as sponges, ascidians, echinoderms) were recorded to genus level whereever possible or phylum plus growth form
Each taxon was ranked in terms of abundance in the community. These broad categories rank taxa in terms of relative abundance of individuals, rather than the contibution to benthic cover along each transect.
Table A8.5 - 2. Ranking of taxonomic inventory.
|
Rank |
Abundance |
|
0 |
Absent |
|
1 |
Rare |
|
2 |
Uncommon |
|
3 |
Common |
|
4 |
Abundant |
|
5 |
Dominant |
3) Identification of potential translocation sites
Bound dives were conducted along the coastline between Mo Tat Wan and Sok Kwu Wan. Two locations suitable for translocation purpose were identified and recorded on maps.
The conditions of the subtidal habitats, as well as the marine ecological assemblages, especially the present conditions of any exiting coral colonies, in the vicinity of the potential translocation sites were recorded with the provision of video samples.
Information concerning the physical nature of the potential translocation sites was also recorded. This information included the degree of exposure of the sites to wave action, the nature of the substrate types and the topographic profiles of the sites.
Results
1) Coral mapping at Outfall Option 1
The dive surveys were conducted on 11 and 12 May 2002.
Within the surveyed area, bedrock and boulders extended from the coastline to about 25m away. Between 25m to 30m away from the shore, scattered boulders were found on sandy seabed. Outside 30m from the shore, the seabed was sandy and muddy.
A total of 280 coral colonies were recorded
and mapped within the surveyed area. In the sake of presentation, 8 zones, each
of 4m x 34m, were established within the surveyed area (Figure A8.5 - 1). These eight
zones have covered all coral colonies recorded within the surveyed area. The
locations and codes of coral colonies within each zone were shown in Figure A8.5 - 2 to Figure A8.5 - 9. A description
of these coral colonies, in terms of their species, their sizes and the sizes
of the boulders beneath, was
ere
presented in Annex A8.5-A8.5 - 1.Selected photos of the coral
colonies were shown in Annex A8.5-A8.5 - 2.
A summary of the number of colonies from
each genus was ere presented
below in Table A8.5 - 3.
|
Genus |
No. |
|
Favia sp. |
48 |
|
Favites sp. |
54 |
|
Cythastrea sp. |
28 |
|
Platygyra sp. |
69 |
|
Pavona sp. |
5 |
|
Turbinaria sp. |
15 |
|
Hydonphora sp. |
5 |
|
Plesiastrea sp. |
52 |
|
Gonipora sp. |
4 |
Platygyra was the most abundant genus (69 colonies), while Gonipora was the least (4 colonies).
The most abundant colonies of hard corals, Platygyra, Favites, Plesiastrea and Favia recorded in the present survey are all common genus and have been recorded throughout coastal areas in the Eastern waters of Hong Kong.
Table A8.5 - 4. No. of coral colonies in each zone within the surveyed area.
|
Zone |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
|
No. of coral colonies |
43 |
33 |
62 |
49 |
41 |
21 |
23 |
8 |
Zone 3 (from 8m to 12m form the coastline) contained the most coral colonies.
Details of where the coral genera in the surveyed area have been recorded elsewhere in Hong Kong. All the genera have been recorded extensively in Hong Kong and are not considered to be rare in Hong Kong waters.
2) Video recording and ecological assessment at Outfall Option 1
Descriptions of the four transects in terms of substrate composition as well as marine organisms are presented in Table A8.5 - 5 below.
Table A8.5 - 5. Descriptions of the four transects.
|
Transects |
Description |
|
Main |
This transect was laid along the outfall alignment. From 0m to 25m of this transect, the substratum was mainly bedrock and boulders. From 25m to 30m, the seabed was sandy bottom with scattered boulders. Beyond 30m from the coast, the seabed was sandy and muddy. |
|
P1 |
This transect was parallel to the
coastline. The substratum type was dominated by boulders and bedrock. |
|
P2 |
This transect was parallel to the
coastline. The substratum type was dominated by boulders and bedrock. |
|
P3 |
This transect was parallel to the
coastline. The substratum type was dominated by boulders and bedrock. |
The ecological attributes, the substratum attributes, and the taxonomic inventory and the scores of abundance of the taxa for each transect were presented below in the Table A8.5 - 6.
Table A8.5 - 6. Ecological, substratum attributes and taxonomic inventories of the four transects.
|
Substratum attributes |
Main Transect |
Transect P1 |
Transect P2 |
Transect P3 |
|
Hard substrate |
4 |
5 |
4 |
4 |
|
Continuous pavement |
|
|
|
|
|
Bedrock/boulders/sand |
4 |
5 |
5 |
5 |
|
Rubble |
|
|
|
|
|
Cobbles |
|
|
|
|
|
Sand with gravel |
3 |
|
|
|
|
Mud |
3 |
|
|
|
|
|
|
|
|
|
|
Ecological attributes |
Main Transect |
Transect P1 |
Transect P2 |
Transect P3 |
|
Hard coral |
1 |
1 |
1 |
1 |
|
Dead standing coral |
|
|
1 |
|
|
Soft coral |
|
|
|
|
|
Sea anemone beds |
|
|
|
|
|
Macro-algae |
|
|
|
|
|
|
|
|
|
|
|
Taxa |
Main Transect |
Transect P1 |
Transect P2 |
Transect P3 |
|
Sea cucumbers |
1 |
|
1 |
|
|
Sponges |
|
|
|
|
|
Gorgonians |
|
|
|
|
|
Dendronephthya spp. |
|
|
|
|
|
Ascidians |
|
|
|
|
|
|
|
|
|
|
The majority of the substrate on main
transect was found to be sand
and mud in comparison to the other parallel transects. The Main trasect, however,
also had a high percentage of bedrock and boulders as the boulders extended to
about 25m from the coast. The three parallel transect were within the boulder
zone, so all have high percentage of hard substratum and bedrock/boulders.
In terms of the ecological attributes, hard corals were recorded on each transect. In the present survey, no soft corals were recorded within the surveyed area.
As shown in the above table, the abundance
of benthic organisms was low on each of the four transects. The only sessile
organisms recorded other than corals were sea cucmumber on Main Transect and Transect P2, but
both were of category 1, i.e. rare.
3) Identification of potential translocation sites
Two potential site for translocation were identified, namely Translocation Site 1 & Translocation Site 2 (Figure A8.5 - 10).
The results of the bound dives indicate that both sites were suitable for coral translocation as healthy coral colonies were found at both sites. The hard coral coverage, however, was higher in Translocation Site 1. The substratum attributes of Translocation Site 1 was also better as the coverage of mud was smaller. The degree of exposure was also lower in Translocation Site 1 and its topographic profile was smoother. Given the above factors, the Translocation Site 1 is considered better than Translocation Site 2.
Discussion
Conservation value
As stated above, the coral genera are not
considered to be rare in Hong JKong waters as they have been extensively
recorded in other localities. All coral colonies recorded within the surveyed
area at Sok Kwu Wan were all small in size, most having a diameter of less than 25cm. As a result, though the number of coral colonies recorded was not
low (280), the coral colonies located within the surveyed area are all common
species and small in size, and thus not considered to be of high conservation
value.
The substratum of the surveyed area varied.
The seabed of 0m to 25m from the coast appeared to be predominantly bedrock and
boulders, while from 25m to 30, scattered boulders are found on sandy bottom.
Beyond this distance, the substrate appeared to be sand and mud. The ecological
attritbubtes of the Main and the
three Parallel transects were similar. All had low percentage cover (1-5%) of
corals. Other sessile organisms were also rare along all the four transects.
Annex A8.5 - 1. Details of coral colonies recorded in the dive survey. The first number represents the diameter of the coral colonies, while the second number represents the diameter of the boulders beneath. “B” represents bedrock. (FA-Favia; FT-Favites; CY-Cythastrea; PA- Pavona; PY-Platygyra; TUR-Turbinaria; HY-Hydnophora; PLA-Plesiastrea; GON-Goniopora)
|
|
Zone 1 |
|
Zone 2 |
|
Zone 3 |
|
Zone 4 |
|||||
|
Code |
|
Code |
|
Code |
|
Code |
|
|||||
|
1 |
PY (20-25) |
44 |
PLA 15-35 |
77 |
CY (10-30) |
139 |
CY 10-15 |
|||||
|
2 |
CY (15-15) |
45 |
PY 13-13 |
78 |
PLA (30-30) |
140 |
PY 25-35 |
|||||
|
3 |
HY (25-B) |
46 |
FT 5-20 |
79 |
FT (20-B) |
141 |
FT 15-60 |
|||||
|
4 |
PY (25-B) |
47 |
PY 15-15 |
80 |
CY (20-B) |
142 |
CY 35-b |
|||||
|
5 |
FT (35-B) |
48 |
CY 20-100 |
81 |
FT (40-B) |
143 |
CY 20-b |
|||||
|
6 |
FT (80-B) |
49 |
FA 25-b |
82 |
PY (20-40) |
144 |
CY 25-b |
|||||
|
7 |
PY (25-50) |
50 |
FT 10-60 |
83 |
HY (20-50) |
145 |
PY 5-30 |
|||||
|
8 |
PY (30-B) |
51 |
PY 23-35 |
84 |
FT (10-50) |
146 |
HY 10-20 |
|||||
|
9 |
FT (35-B) |
52 |
FA 20-b |
|
85 |
FA (25-40) |
147 |
PLA 15-25 |
||||
|
10 |
PY (20-B) |
53 |
FA 30-b |
|
86 |
PLA (20-20) |
148 |
PY 10-15 |
||||
|
11 |
PY (35-B) |
54 |
FA 15-25 |
87 |
PLA (10-10) |
149 |
PY 10-15 |
|||||
|
12 |
FA (15-B) |
55 |
CY 10-70 |
88 |
TUB (70-B) |
150 |
FT 10-15 |
|||||
|
13 |
FA (20-B) |
56 |
PY 20-b |
|
89 |
FT (30-B) |
151 |
PY 5-10 |
||||
|
14 |
CY (15-B) |
57 |
FT 13-b |
|
90 |
FA (30-50) |
152 |
PY 7-10 |
||||
|
15 |
PY (30-40) |
58 |
PY 25-35 |
91 |
FA (30-50) |
153 |
PLA 10-b |
|||||
|
16 |
FT (25-B) |
59 |
PY 7-35 |
92 |
PLA (20-25) |
154 |
PLA 10-b |
|||||
|
17 |
PY (25-B) |
60 |
FT 13-40 |
93 |
PAV (20-B) |
155 |
TUR(15-20) |
|||||
|
18 |
FA (20-55) |
61 |
PLA 20-50 |
94 |
PLA (40-B) |
156 |
GON(15-b) |
|||||
|
19 |
FT 45-B) |
|
62 |
FA 10-20 |
95 |
PLA (30-40) |
157 |
PY(35-35) |
||||
|
20 |
FT (40-B) |
63 |
PLA 3-40 |
96 |
FA (15-25) |
158 |
PT(40-b) |
|||||
|
21 |
CY (15-B) |
64 |
TUR 14-14 |
97 |
PLA 40-B) |
159 |
CY(5-10) |
|||||
|
22 |
FT (10-B) |
65 |
PY 10-30 |
98 |
PLA (40-B) |
160 |
CY(5-15) |
|||||
|
23 |
PY (20-B) |
66 |
PY 13-30 |
99 |
PY (15-20) |
161 |
CY(25-25) |
|||||
|
24 |
FT (25-50) |
67 |
FA 7-20 |
100 |
FT (30-40) |
162 |
TUR(25-30) |
|||||
|
25 |
PY (50-B) |
68 |
FA 25-b |
|
101 |
CY (30-30) |
163 |
FT(30-45) |
||||
|
26 |
FT (10-B) |
69 |
FA 5-b |
|
102 |
TUB (40-60) |
164 |
PY(25-45) |
||||
|
27 |
HY (20-20) |
70 |
FA 7-b |
|
103 |
FT (20-40 |
|
165 |
FA(15-45) |
|||
|
28 |
PY (55-B) |
71 |
PY 10-b |
|
104 |
FLA 30-0 |
166 |
CY(10-45) |
||||
|
29 |
PY (60-B) |
72 |
PLA 15-b |
105 |
PLA (30-30) |
167 |
CY(20-b) |
|||||
|
30 |
CY (40-B) |
73 |
PY 5-b |
|
106 |
FA (30-50) |
168 |
PLA(15-25) |
||||
|
31 |
PY (40-B) |
74 |
FT 7-b |
|
107 |
PY (20-40) |
169 |
PY 35-b |
||||
|
32 |
FT (30-B) |
75 |
PY 13-b |
|
108 |
PY (40-40) |
170 |
FA 25-b |
||||
|
33 |
FT (30-B) |
76 |
PY 20-b |
|
109 |
FT (20-70) |
171 |
FA 15-20 |
||||
|
34 |
FT (20-B) |
|
|
|
|
110 |
PLA (30-30) |
172 |
FA 10-30 |
|||
|
35 |
FT (30-B) |
|
|
|
|
111 |
PAV (30-40) |
173 |
PLA 20-b |
|||
|
36 |
FT (40-B) |
|
|
|
|
112 |
CY 40-B |
174 |
PLA 20-b |
|||
|
37 |
PY (30-B) |
|
|
|
|
113 |
PY (30-40) |
175 |
PLA 25-b |
|||
|
38 |
FT (30-B) |
|
|
|
|
114 |
FT (30-80) |
176 |
PLA 30-b |
|||
|
39 |
PY (10-B) |
|
|
|
|
115 |
PY (30-B) |
177 |
PLA 25-b |
|||
|
40 |
PY (20-B) |
|
|
|
|
116 |
PY (40-B) |
178 |
PY 25-25 |
|||
|
41 |
PY (50-B) |
|
|
|
|
117 |
PLA (30-B) |
179 |
PLA 5-b |
|||
|
42 |
PY (20-B) |
|
|
|
|
118 |
FT 40-B |
|
180 |
FT 15-b |
||
|
43 |
CY (30-B) |
|
|
|
|
119 |
FA 40-B |
|
181 |
FA 35-b |
||
|
|
|
|
|
|
|
|
|
120 |
PLA 50-70 |
182 |
PY 35-b |
|
|
|
|
|
|
|
|
|
|
121 |
PLA 30-B |
183 |
PY(20-60) |
|
|
|
|
|
|
|
|
|
|
122 |
PY 20-20 |
184 |
TUR(13-13) |
|
|
|
|
|
|
|
|
|
|
123 |
TUB 50-50 |
185 |
FA(40-40) |
|
|
|
|
|
|
|
|
|
|
124 |
PLA 30-30 |
186 |
PY(15-15) |
|
|
|
|
|
|
|
|
|
|
125 |
FA 20-B |
|
187 |
PA 13-35 |
|
|
|
|
|
|
|
|
|
126 |
PLA 20-20 |
|
|
|
|
|
|
|
|
|
|
|
|
127 |
TUB 30-B |
|
|
|
|
|
|
|
|
|
|
|
|
128 |
PLA 30-40 |
|
|
|
|
|
|
|
|
|
|
|
|
129 |
PY 50-B |
|
|
|
|
|
|
|
|
|
|
|
|
130 |
TUB 40-B |
|
|
|
|
|
|
|
|
|
|
|
|
131 |
PY 30-B |
|
|
|
|
|
|
|
|
|
|
|
|
132 |
FT 15-20 |
|
|
|
|
|
|
|
|
|
|
|
|
133 |
FA 30-30 |
|
|
|
|
|
|
|
|
|
|
|
|
134 |
PY 20-B |
|
|
|
|
|
|
|
|
|
|
|
|
135 |
FT 20-30 |
|
|
|
|
|
|
|
|
|
|
|
|
136 |
CY 30-30 |
|
|
|
|
|
|
|
|
|
|
|
|
137 |
FT 30-30 |
|
|
|
|
|
|
|
|
|
|
|
|
138 |
PLA 50-50 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Zone 5 |
|
Zone 6 |
|
Zone 7 |
|
Zone 8 |
|
Code |
|
Code |
|
Code |
|
Code |
|
|
188 |
FA 10-10 |
229 |
PA 25-150 |
250 |
HY 10-10 |
273 |
PLA 15-25 |
|
189 |
TUB 30-B |
230 |
FA 20-30 |
251 |
GON 30-30 |
274 |
PLA 15-30 |
|
190 |
FA 20-20 |
231 |
PY 30-30 |
252 |
TUB 10-10 |
275 |
FA 10-250 |
|
191 |
FA 10-10 |
232 |
FA 35-50 |
253 |
FT 30-30 |
276 |
PLA 10-15 |
|
192 |
PLA 20-20 |
233 |
FA 30-40 |
254 |
GON 20-20 |
277 |
PLA 12-20 |
|
193 |
PY 30-40 |
234 |
GON 25-25 |
255 |
FT 30-30 |
278 |
PLA 15-30 |
|
194 |
PY 30-40 |
235 |
FA 35-60 |
256 |
FA 20-30 |
279 |
PLA 20-40 |
|
195 |
TUB 10-10 |
236 |
FA 40-60 |
257 |
FT 30-40 |
280 |
FA 5-10 |
|
196 |
PY 20-30 |
237 |
FA 15-b |
258 |
FT 10-20 |
|
|
|
197 |
PY 30-50 |
238 |
PLA 25-60 |
259 |
FT 40-40 |
|
|
|
198 |
FA 15-3 |
239 |
FT 25-b |
260 |
CY 15-15 |
|
|
|
199 |
PY 30-60 |
240 |
PY 20-25 |
261 |
TUB 35-35 |
|
|
|
200 |
PLA 40-B |
241 |
CY 5-b |
262 |
CY 30-5 |
|
|
|
201 |
FT 30-B |
242 |
FA 25-30 |
263 |
FT 20-20 |
|
|
|
202 |
FA 10-20 |
243 |
PY 20-25 |
264 |
CY 10-40 |
|
|
|
203 |
FT 15-B |
244 |
PY 15-25 |
265 |
FA 5-20 |
|
|
|
204 |
PY 40-50 |
245 |
FA 25-25 |
266 |
FT 30-40 |
|
|
|
205 |
PLA 20-40 |
246 |
FA 15-80 |
267 |
PLA 10-20 |
|
|
|
206 |
PY 50-60 |
247 |
CY 7-10 |
268 |
FA 30-B |
|
|
|
207 |
FT 10-B |
248 |
FA 30-35 |
269 |
TUB 30-30 |
|
|
|
208 |
FT 30-B |
249 |
PY 7-10 |
270 |
PY 50-50 |
|
|
|
209 |
PLA 30-30 |
|
|
271 |
TUB 40-40 |
|
|
|
210 |
FT 20-20 |
|
|
272 |
FT 35-35 |
|
|
|
211 |
PLA 20-20 |
|
|||||
|
212 |
FT 40-60 |
|
|||||
|
213 |
PY 40-B |
|
|||||
|
214 |
PLA 30-30 |
|
|||||
|
215 |
FA 30-B |
|
|||||
|
216 |
CY 40-B |
|
|||||
|
217 |
PY 40-60 |
|
|||||
|
218 |
FT 60-60 |
|
|||||
|
219 |
PLA 30-B |
|
|||||
|
220 |
PLA 50-80 |
|
|||||
|
221 |
PLA 30-30 |
|
|||||
|
222 |
PLA 30-30 |
|
|||||
|
223 |
FT 20-20 |
|
|||||
|
224 |
FA 10-40 |
|
|||||
|
225 |
FT 20-40 |
|
|||||
|
226 |
PLA 15-15 |
|
|||||
|
227 |
CY 40-40 |
|
|||||
|
228 |
PAV 20-40 |
|
|||||