| 4.2.2.6 |
Apart
from the rocky bottom of the eastern and
southern subtidal regions of Hong Kong,
the majority of Hong Kong's seabed area
is soft and comprises a mixture of sand
and mud which varies in species composition
from place to place and under differing
degrees of current scour (Morton et al 1996).
The northwestern waters of Hong Kong are
subject to regular deposition of large quantities
of silt from the Pearl River creating, in
many cases, an unstable and inhospitable
environment for seabed organisms. In contrast,
the seabed of the eastern waters of Hong
Kong is generally composed of materials
that are more coarse in nature, and consequently
form a more stable environment for seabed
organisms.
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| 4.2.2.8 |
Over
the past decade, the soft bottom seabed
has been subject to numerous sand dredging,
dredged material disposal and backfilling
(ie of empty sand dredging pits) activities.
Sand dredging has occurred at inter alia,
Outer Deep Bay, the Brothers, East Sha Chau,
North Lantau, Sokos, South Tsing Yi, East
Lamma Channel, Po Toi, and East Tung Lung
Chau (see Paragraph 3.6.1.4 - Minerals,
Aggregates and Energy for a discussion of
remaining sand resources). On at least one
occasion smothering by fine sediments from
dredging activities at the East Tung Lung
Chau Marine Borrow Area resulted in mortality
to gorgonians and hard corals near the Ninepins
(Hodgson 1994). It is also known that the
intensity of trawl activities in Hong Kong
waters has a considerable influence on the
soft seabed environment (Selby and Evans
1997) and a detrimental effect on benthic
fauna (Morton 1996).
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| 4.2.2.9 |
Marine
habitats which are of particular importance
in maintaining the marine ecological natural
capital stock of Hong Kong can be considered
to lie within the following categories:
Areas
which support the highest known marine biodiversity
values for Hong Kong: These areas are considered
to comprise areas which are documented to
provide habitats for supporting high biodiversity
assemblages and/or designated, or considered
for designation as Marine Protected Areas
(eg Marine Parks and Marine Reserves) because
of high biodiversity. Therefore the subtidal
areas of the designated Marine Protected
Areas, including Hoi Ha Wan Marine Park,
Yan Chau Tong Marine Park and Cape d'Aguilar
Marine Reserve, which are discussed under
Paragraphs 3.2.1.9 - 3.2.1.11 - Land Use
and Land Supply are considered to be of
special concern. The Sha Chau and Lung Kwu
Chau Marine Park is not included in this
category because it was designated on the
basis of habitat for Chinese White Dolphin
(Sousa chinensis) rather than the presence
of high biodiversity. It is, however, included
in the category concerning habitat for [rare]
species (see below).
The
potential Marine Parks/Marine Reserves at
Shelter Island, South Lamma, South-west
Lantau, and Ping Chau, also support a rich,
biologically important, marine community
and can be regarded as having the highest
biodiversity values among the Hong Kong
marine areas. The potential marine park
at Shelter Island contains a high diversity
of subtidal hermatypic coral assemblages
(Binnie Consultants Ltd 1995c) and benthic
infaunal communities (Shin and Thompson
1982). The subtidal areas of South Lamma
Island support high abundances of soft corals
(ERM 1998e) and the soft bottom benthic
areas at Sham Wan are reported to contain
high abundance of benthic fauna (ERM 1997b).
Also, the southwestern waters within the
potential South Lamma Marine Park have the
highest sighting frequency of Finless Porpoise
among the Hong Kong marine areas (ERM 1998f).
For the potential Marine Park at Southwest
Lantau, the presence of a rich infaunal
community in the benthic areas (ERM 1997c)
and a relatively high abundance of the coral
reef butterflyfish (Chateodon modestus)
near the Soko Islands (Binnie Consultants
Ltd 1997g) together with a documented utilization
of the marine areas by both the Chinese
White Dolphin and the Finless Porpoise,
provide evidence for the high biodiversity
nature of the area. The subtidal areas of
the potential Ping Chau Marine Reserve provide
a unique seabed configuration which supports
a rich associated fauna of corals (D McCorry
pers comm) and reef building corals (Morton
and Morton 1983).
Areas
which are documented to function as important
marine spawning, nursery or key foraging
habitats: Marine areas which serve as spawning
and nursery grounds for commercially important
species were identified by the AFCD Study
on Fisheries Resources and Fishing Operations
in Hong Kong Waters (ERM 1998a). Critical
spawning areas were found to include eastern,
southern and northeastern waters (Figure
4.2e). Southern waters, Port Shelter
and the northeast New Territories (Figure
4.2e) were found to be important nursery
habitats for commercial fisheries in Hong
Kong.
Areas
which contain marine habitats that are regionally
rare or threatened or provide documented
critical habitat for rare species: Species
which are of special concern are discussed
in the following sections. Key habitats
for marine mammals, turtles, horseshoe crabs,
corals and seagrasses, which are protected
under the Wild Animals Protection Ordinance
(Cap 170) and/or Marine Parks Ordinance
(Cap 476), and/or documented to be rare/threatened
are briefly identified here. All areas are
shown in Figure 4.2e.
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