BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

amphipods. Other faunal members include the whelks Burnupena papyracea and
Argobuccinum argus, the starfish Marthasterias glacialis, the crab Plagusia chabrus and
polychaetes. The fish fauna is dominated by the endemic hottentot Pachymetopon
blochii, but also includes twotone fingerfin Chirodactylus brachydactylus, redfinger
Cheilodactylus fasciatus, blacktail Diplodus sargus capensis, galjoen Dichistius
capensis, maned blennies Scartella emarginata, and various klipfish.
The kelps E. maxima and L. pallida are the main primary producers in this system. Sea
urchins Parechinus angulosus feed directly on young kelp (sporelings) but the main
energy conversion pathway is by means of detritus- and particularly filter-feeders feeding
on the detritus derived from the kelp plants. This detritus is also an important food
source for filter-feeders in the rocky and sandy intertidal (Bustamante & Branch 1996b,
Soares et al. 1997). The main filter-feeders in the kelp beds are the mussels and the top
predator on this species is the West Coast rock lobster. The kelps, sea urchins, mussels
and rock lobsters are thus the keystone species in this system.
Intertidal sandy beach communities - The West Coast of South Africa is almost linear,
and virtually all beaches are exposed to strong wave action, and are thus of the
intermediate or reflective type (McLachlan et al.. 1993). Typical of exposed beaches,
they are usually relatively steep and narrow with well-sorted fine to medium-sized
sediments, although some of the steepest beaches can have coarse sands (Branch &
Griffiths 1988).
The entire Benguela region from the Cape Peninsula right up the West Coast to northern
Namibia has a remarkably consistent sandy beach fauna (Field & Griffiths 1991).
Although very few data exist on the species compositions of the Table Bay sandy
beaches (Bloubergstrand and Milnerton Beach), data from other beaches are very likely
to be applicable to them. Lane & Carter (1999) reviewed the composition of the softbottomed
benthic macrofauna (invertebrate animals >1mm in body size) communities of
the West Coast, and the following description of the beach zones and their invertebrate
beach macrofauna is based on their document, supplemented by data from other studies
and reviews (Christie 1976, Bally 1983, 1987, Branch & Griffiths 1988, Jaramillo et al..
1995).
The sandy beach intertidal is divided into the following zones (Figure 4b):
Supralittoral zone - The supralittoral zone is situated above the high water spring mark
(HWS), and receives water input only from large waves at spring high tides or through
sea spray. This zone is characterised by air-breathing crustaceans, particularly the
amphipods Talorchestia capensis and T. quadrispinosa, the giant isopod Tylos
granulatus and the terrestrial isopod Niambia sp. The giant isopod T. granulatus,
however, is very sensitive to disturbance (e.g. driving and walking on the beach) and has
almost completely disappeared from Table Bay beaches (P. Nel, Marine Biological
Research Unit, UCT, pers. comm.) A diverse array of insect species (Coleoptera and
Diptera) can also be found, which are almost all associated with, and feeding on, wrack
or other debris deposited along the drift-line. Oligochaetes can also be abundant, again
particularly under seaweed debris. Community composition depends on the nature and
extent of wrack, in addition to the physical factors structuring beach communities, as
described above.
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