| The Cape Metropolitan Area is largely
surrounded by the Atlantic Ocean. Apart from having several hundreds of kilometres of
coastline, the marine environment around the CMA is unique in that it lies at the juncture
of two biogeographic provinces. The area east of Cape Point at the tip of the Cape
Peninsula lies within the warm Agulhas Province and supports a relatively diverse array of
marine species. The area west of Cape Point falls within the Cool Namaqua Province and has
a relatively low biodiversity (Stephenson 1939, 1944, 1948, McQuaid and Branch 1984,
McQuaid et al. 1985, Emanuel et al. 1992, Prochazka, Chotkowski and Buth,
1999). Due to the frequent mixing of
water from both the Agulhas and Benguela systems (Fricke and Thum 1975) organisms
characteristic of each biogeographic province are able to exist here, and thus the Cape
Peninsula displays a higher diversity and endemism of marine life than adjacent areas. For
example, all 24 species of resident rockpool fish that occur within the CMA are endemic to
southern Africa (Prochazka 1994), and of the 259 continental-shelf fish species which
occur in this area, 88% are endemic to southern Africa (Turpie, unpublished data).
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| Contents of CONTEXTUAL INFO on Marine
and Coastal Ecosystems: |
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| Marine habitats |
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| The marine environment of the CMA has a diversity of habitats, from areas
of rocky coast and sandy beaches and dunes, to rocky and sandy sub-tidal areas and the
pelagic zone (water above the reefs and sandflats). Each of these supports a diversity of
marine life (Smith and Heemstra, 1986). |
| Rocky
intertidal zone |
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Of the 307km of coastline falling within the CMA, 56% is made up of rocky
shores. The marine biota inhabiting this rocky intertidal zone are not evenly distributed
along the shore. Several factors contribute to the variable diversity and biomass evident
within rocky intertidal communities, namely:
- Differences in water temperature (McQuaid
and Branch 1984) between the west and east coasts of the Cape Peninsula. While the cold
West Coast supports a high biomass of organisms, it is relatively poor in terms of species
richness relative to the warmer False Bay coast.
- Substratum type (McQuaid et al. 1985)
and exposure to wave action (McQuaid and Branch 1984) influence both biomass and species
richness.
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| Sandy
beaches and dunes |
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Sandy beaches constitute 44% of the coastline of the CMA. Species richness
on these beaches is far lower than on the adjacent rocky shores, primarily due to the
reduced habitat diversity. Dunes occur at the landward extreme of sandy beaches. These
form the sole habitat of several species of specially adapted plants, as well as providing
nesting sites for some shorebirds, notably the Whitefronted Plover (Charadrius
marginatus) and the endemic African Black Oystercatcher (Haematopus moquini).
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| Rocky
and sandy subtidal areas |
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| Subtidal reefs and sandflats occur around the CMA. In water of less than
five metres depth, rocky reef areas are dominated by seaweeds, with the kelp Ecklonia
maxima forming the bulk of the algal biomass. These reefs are home to a vast array of
invertebrate species, including the commercially and recreationally important Abalone (Haliotis
midae) and West Coast Rock Lobster (Jasus lalandii). The reef invertebrates
form the food base for the cryptic (e.g. klipfishes) and larger suprabenthic species of
fish such as Kob (Argyrosomus inodorus) and White Steenbras (Lithognathus
lithognathus). A large proportion of the larger fish species, primarily those
belonging to the Family Sparidae, is also endemic to southern Africa. |
| The pelagic zone |
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| The pelagic zone includes the water above the reefs and sandflats. Here
plankton form the basis of the foodwebs. Fish such as Yellowtail (Seriola lalandii)
and Snoek (Thyrsites atun) are abundant in False Bay at certain times of year,
while the major pelagic fishes of the West Coast of the Cape Peninsula include Maasbanker
(Trachurus trachurus) and Pilchard (Sardinops sagax). The pelagic zone is
also used by whales and dolphins. The most common cetaceans in the areas are the Southern
Right Whale (Balaena glacialis), Common Dolphin (Delphinus delphis) and
Dusky Dolphin (Lagenorhynchus obscurus). Although the dolphins are present here all
year round, the Southern Right Whales are only present from about June to December each
year, when they migrate north from Antarctic waters to breed. Table 1 indicates the percentage of
southern African marine species from a variety of groups that occur in the CMA. This is
generally quite high, ranging from 21 to 83%, and averaging 43%.
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Table 1 |
Percentage
of southern African species of 14 groups of marine organisms recorded from the marine
environment surrounding the CMA. |
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|
GROUP |
% of southern African species recorded from the marine
environment surrounding the CMA |
| Sandy shore
invertebrates |
55 |
| Rocky shore
invertebrates |
31 |
| Octocorals |
34 |
| Amphipods |
71 |
| Crabs |
19 |
| Chitons |
68 |
| Bivalves |
32 |
| Gastropods |
28 |
| Opisthobranchs |
34 |
| Echinoderms |
26 |
| Fish |
|
| Rockpool species* |
44 |
| Shelf species |
21 |
| Sea- &
shorebirds** |
83 |
| Cetaceans |
45 |
|
| * includes only true resident species |
| ** does not include vagrant species |
| (Source: unpublished data, Zoology
Department, UCT) |
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| Marine Conservation |
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| Two major types of Marine Protected Areas (MPA's) are present within the
CMA (See Map 2 in the Terrestrial Ecosystems Context info section)
and Table 2 below). These include areas of complete
protection for marine biota, and areas that protect only selected species or groups of
species. The two complete protection areas, where no marine organism of any variety may be
collected, constitute only approximately two percent of the coastline of the CMA. Both of
these MPA's occur on the False Bay coast of the Cape Peninsula and are composed of rocky
substratum. At present, no complete protection areas are currently demarcated on the
western shores of the CMA, nor for sandy subtidal areas. In addition, the area receiving
complete protection only offers protection to relatively small and sessile animals. Larger
and more mobile organisms are likely to spend a reasonable proportion of their time
outside of the protected area, and are thus vulnerable to harvesting in these adjacent
areas. In the marine protected areas
within the CMA, four major species or groups of species are listed as "critical"
in at least two of the MPA's. These include Abalone (Haliotis spadicea), African
Black Oystercatchers (Haematopus moquini), all the linefish species that occur here
(including the endemic Sparidae), and dune vegetation, which is listed as
"critical" in all the MPA's around the CMA (Attwood et al. 1997).
In many instances, MPA's in the CMA have
been established as single-species reserves to provide protection to spawning stocks of a
given species or to increase catches of that species in adjacent areas, or both. There are
many areas or species in the CMA that are not afforded legal protection in spite of their
special biological, historic and cultural significance.
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Table 2 |
Marine
Protected Areas within the CMA, detailing their location and the type of protection
offered. |
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|
MPA TYPE & NAME |
LOCATION |
NOTES |
| Complete protection areas |
| Miller's Point
Marine Reserve |
3km stretch,
extending 1 nautical mile out to sea, between beacons at Partridge Point and Miller's Point |
No harvesting of
any marine life, with the exception of Snoek |
| Kalk Bay
Marine Reserve |
Kalk Bay station
to St James station |
No harvesting of
any marine life, with the exception of washed-up Redbait |
| Rock lobster sanctuaries |
| Table Bay Rock
Lobster Sanctuary |
For 12 nautical
miles seawards from the high water mark, between Melkbos Point and Die Josie, Chapmans
Peak |
Protection for
the West Coast Rock Lobster only |
| Kommetjie Rock
Lobster Reserve |
Between beacons
situated at Klein Slangkop and Slangkop Point |
Protection for
the West Coast Rock Lobster only |
| Cape of Good
Hope Marine Reserve |
Scarborough to
Dias Point |
Protection for
the West Coast Rock Lobster only |
| Invertebrate sanctuaries |
| Glencairn
Marine Reserve |
Jagger's Walk at
the southern end of Fishoek Beach to Glencairn Beach |
Protection for
invertebrates, but angling is allowed |
| Muizenberg
Marine Reserve |
Muizenberg
station to St James station |
Protection for
invertebrates, but angling is allowed |
| Seabird & seal sanctuaries |
| Robbesteen |
± 10km south of
Melkbos Point breeding colony and seabirds |
Protection of
Cape Fur Seal |
| Boulders
Coastal Park (being incorporated
into the Cape Peninsula National Park) |
South of
Simonstown |
Protection of the
African Penguin |
| Duikerklip |
Near Hout Bay |
Protection of
breeding colonies of Cape Fur Seals and seabirds |
| Krom River |
Between NW
boundary fence and Olifantsbos in Cape Point Nature Reserve |
Protects breeding
African Black Oystercatchers |
| Wolfgat |
1km on northern
shore of False Bay |
Protects unique
cliff-nesting Kelp Gull colony |
|
| (Source: Jackson and Lipshitz, 1984 and
Robinson and de Graaf, 1994) |
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| Health of the marine and coastal
environment |
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| The quality of the water along the CMA coastline is dependent on the
quality of water discharged via sewage and stormwater pipelines from adjacent areas of
land. Stormwater is a significant source of pollution as it is difficult to enforce
compliance with water quality limits outside of wastewater treatment works. Table 3 below presents stormwater quality at selected stormwater
outlets along the CMA coastline. |
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Table 3 |
Bacteriological
levels in stormwater at selected sites along the Atlantic and False Bay Coasts |
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|
| Sampling point |
Samples |
Faecal coliforms/100ml Percentiles |
| |
examined |
80% |
95% |
| Atlantic Coast |
| Three Anchor Bay
Stormwater A |
25 |
2
500 000 |
3
900 000 |
| Three Anchor Bay
Stormwater B |
25 |
1
100 000 |
4
200 000 |
| Rocklands Beach
Stormwater |
6 |
430
000 |
>5
600 000 |
| False Bay Coast |
| Muizenberg
Station Stormwater |
37 |
71
000 |
280
000 |
| Mitchells Plain
West Stormwater Outlet |
24 |
150
000 |
680
000 |
| Mitchells Plain
East Stormwater Outlet |
24 |
170
000 |
1
100 000 |
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| Figure 1 and Figure 2 present the results of bacteriological sampling undertaken
over the past 12 months at 47 samples sites along the CMA coastline (CMCWQC, 1998). |
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| Results are evaluated against the South African Water Quality Guidelines
for Coastal Marine Waters (DWAF, 1992) for counts of faecal coliform per 100 ml. The
results show that a number of sites along False Bay and the Atlantic Coasts exceed the 80%
and 95% limits. These limits are derived using a target value for an indicator organism
(i.e. coliforms) for recreational use. The 80% limit refers to the percentage of samples
that must not have more than 100 counts of faecal coliforms per 100ml. The 95% limit
refers to the percentage of samples that must not have more than 2000 counts of faecal
coliforms per 100ml. |
| Figure
2 |
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| Results
of bacteriological monitoring on the Atlantic Coast of the Cape Metropolitan Area (Source:
CMCWQC, 1998) |
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| The Mussel Watch Programme undertaken by DEATs Sea Fisheries Research
Institute monitors heavy metals, such as cadmium, copper, lead and mercury in mussels at
26 sampling locations in the CMA. Filter-feeders such as mussels tend to accumulate trace
elements, hydrocarbons and pesticides. Since they are sessile, mussels display short-term
variability and long-term trends with respect to water quality. Sampling of mussels has
therefore proven to be helpful in identifying areas of low water quality and changes in
levels of contaminants. Table 4 shows sampling sites where
contaminant levels exceeded the limits set by the South African Bureau of Standards. |
Table 4 |
Sites
where heavy metal levels exceeded South African Bureau of Standards’ limits |
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|
| Sampling site |
Heavy metal |
% samples
exceeding limit |
Year |
| Paarden
Eiland |
Cadmium |
77 |
May ‘94 |
| Green
Point |
Cadmium |
77; 15 |
May ’94; Oct ‘94 |
| Graafs
Pool |
Cadmium |
68 |
May ‘94 |
| Blouberg |
Cadmium |
52 |
May ‘94 |
| Monwabishi |
Cadmium |
51 |
May ‘94 |
| Robben
Island West |
Cadmium |
45 |
May ‘94 |
| Sea
Point |
Cadmium |
40; 25 |
Oct ’94; Oct ‘93 |
| Black
River |
Cadmium |
29 |
May ‘95 |
| Robben
Island East |
Cadmium |
28 |
May ‘94 |
| Robben
Island North |
Cadmium |
22 |
May ‘94 |
| Robben
Island South |
Cadmium |
17 |
May ‘95 |
| Granger
Bay |
Lead |
47; 29 |
Oct ’87; Oct ‘86 |
| Marine
Oil |
Lead |
37 |
May ‘87 |
| Simonstown |
Lead |
36 |
Oct ‘87 |
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| (Source: Sea Fisheries Research Institute,
1995) |
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| Another important indicator of the health of the marine environment is the
exploitation of marine species. Over-exploitation primarily affects species of commercial
and / or recreational importance. The most important of these include the West Coast Rock
Lobster (Jasus lalandii), Abalone (Haliotis midae), Alikreukel (Turbo
sarmaticus), and a range of line fish species, particularly those belonging to the
family Sparidae. Decreases in anglers’ catches of most of these fishes have recently
been demonstrated (Taylor, 1993), indicating decreasing fish stocks and the need to
conserve these endemic species. The
pollution and physical alteration of estuaries has a negative impact on fish stocks as
they are important nursery areas for several species of marine fishes. The Milnerton
Lagoon, Sandvlei and the Eerste River Estuary are amongst the most important estuaries in
the CMA in the terms of their nursery functions. Although adjacent surf zone habitats also
function as nursery areas for several fish species, the availability of suitable nursery
areas in this zone is limited.
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