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

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State of Saldanha Bay & Langebaan Lagoon 2011 Benthic macrofauna Figure 7.3 Geographic representation of the results of a PRIMER analysis showing significant clustering of sites based on the similarity of trace metal concentrations (Euclidean Distance). Group A generally had the highest concentrations for all metals and group E the lowest (SIMPER analysis) Figure 7.4 Variation in the percentage mud in sediments in Saldanha Bay and Langebaan Lagoon as indicated by the 2011 survey results. 136 ANCHOR e n v i r o n m en t a l
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 137 ANCHOR e n v i r o n m en t a l
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