State of the Bay Report 2011-Final.pdf - Anchor Environmental

State of Saldanha Bay & Langebaan Lagoon 2011
Benthic macrofauna
The Small Bay sites (groups A1 and A2) were also characterised by the purple-lipped dog
whelk Nassarius speciosus, the three legged crab (Thaumastoplax spiralis), the amphipod
Hippomedon normalis and the tongue worm (Ochateostoma capense). The carnivorous purplelipped
dog whelk N. speciosus is also an opportunistic species that can tolerate anoxic conditions,
and has been known to occur in high abundance under the mussel rafts in Small Bay (Stenton-Dozey
2001). The three legged crab is a small crab (8 mm) which is found in small temporary burrows or
sharing the burrows of prawns. The northern Small Bay sites were distinguished from those around
the Ore Terminal by the higher abundance of the polychaete Nephtys hombergii, an ostracod and
two polychaete species. N. hombergii, is a burrowing predator that feeds on juvenile molluscs,
crustaceans, other polychaetes, diatoms and detritus. N. hombergii prefers to live in fine grained
sediments, and the abundance of this species generally increases as grain size decreases. This
species is also known to tolerate a low oxygen concentration (Fauchald and Bellan 2009).
The sites around the Ore Terminal and in close proximity to the mussel farms (A2) were
distinguished from northern Small Bay sites by the relatively high abundances of amphipod species,
most notably Ampelisca anomala, Ampelisca spinimana and Paramoera capensis. Ampelisca sp. are
detritivores and are known to be abundant in dredged areas and on fine sand. It is thus not
surprising that they had become dominant at sites in close proximity to the Ore Terminal in Small
Bay and Big Bay given that this area has undergone periodic dredging.
The Salamander Bay and Donkergat sites were distinguished from the Small Bay sites and
Big Bay sites in close proximity to the Ore Terminal by the relatively high abundance of the
opportunistic bivalve Tellina gilchristi, the polychaete Euclymene sp., the predatory crown crab
Hymenosoma obiculare and the bivalve Venerupis corrugata. The small deposit feeding bivalve T.
gilchristi was also a dominant species at the central Big Bay sites in 2011 and in previous surveys
(Anchor Environmental Consultants 2010) and is likely to be an opportunistic species. The crown
crab, which has previously dominated at most of the Small Bay sites (2010), lives in soft sediments,
spending the day buried and coming out at night to feed on small crustaceans (Hill and Forbes 1979).
The central Big Bay sites were characterised by a high abundance of the cumacean, Iphinoe
africana, which is a small detritivorous crustacean. These sites were also dominated by amphipods
(Amphilisca spinimana and Photis longidactylus), polychaetes (Scolaricia dubia and Sabellides
luderitzi), sandworms (Nephyts sphaerocirrata and N. hombergi), dog whelks (Nassarius vinctus and
N. speciosus) and the deposit feeding bivalve T. gilchristi. The deposit feeding polychaete S. dubia
has been found in soft bottom habitats with a fine grained sediment texture and a high percentage
of organic matter (Jayaraj et al. 2008). Sea pens are colonial marine cnidarians which were
historically found widely distributed in Saldanha Bay. These filter-feeding organisms are typical K-
strategists and are thus good indicators of the state of recovery of an area. The sea pen Virgularia
schultzei was found in high abundance at sites at the southern and central reaches of Big Bay (BB25,
BB29 and BB30) in 1991, 2004 and 2009. It was not recorded at these sites in 1999 and 2008 and
was found at a much lower abundance in 2010. The 2011 survey revealed that the abundance of sea
pen had increased since 2010, but not yet to the levels seen in 2009. These three sites are the only
sites within Saldanha Bay where the sea pen has been recorded since 1999. The distribution of the
sea-pen does not correlate with the distribution of mud, but interestingly rather with the levels of
trace metal contamination as all sites have very low levels of contamination. This suggests that this
species has a low tolerance for trace metal contamination. The fluctuations in the numbers of sea
pens at these sites in recent years is indicative of a very patchy distribution. The presence of sea
pens certainly supports the notion that the sites in central Big Bay are at an advanced state of
recovery.
The macrofauna in Langebaan Lagoon was dominated by the amphipod Ampelisca palmata,
two ostracod species, the crown crab (Hymenosoma obiculare), and a polychaete belonging to the
genus Maldanidae. Maldanidae are deposit feeding polychaetes which burrow in soft sediment.
Ostracods are small crustaceans (1-4 mm), commonly known as seed shrimps, that mostly crawl
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