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State of Saldanha Bay & Langebaan Lagoon 2011 Benthic macrofauna in 2004, 2008, 2009 and 2010. SIMPER analysis revealed that a large suite of species (83 species) were responsible for much of the difference (90%) found between Langebaan Lagoon and Saldanha Bay in 2011. Opportunistic species such as the mud prawn (Upogebia capensis), the amphipod (Ampelisca spinimana) and the polychaete (Polydora) were found in higher abundance in Saldanha Bay compared to Langebaan Lagoon, while two Ostracod species and the amphipod, Ampelisca palmata were found in greater abundance in the Lagoon compared to Saldanha Bay. The polychaetes Notomastus latericeus and Marphysa depressa were found exclusively within the Lagoon. Figure 7.2. Dendrogram representing the similarity of sites (Bray Curtis Similarity) based on the benthic macrofaunal community composition sampled at Small Bay (SB), Big Bay (BB), Salamander Bay (S), Donkergat (D) and Langebaan Lagoon (LL) in 2011. The 30% level of similarity is indicated by the slice. Clusters of sites significantly similar are represented by the red dotted lines (SIMPROF). A further distinction of two groupings of sites within Saldanha Bay could be seen at the 30% level of similarity. The first grouping (A) included all Small Bay sites (with the exception of the Yacht Club basin and Multi-purpose Quay), all sites in Salamander Bay and Donkergat and sites along the Ore Terminal within Big Bay. These sites are all characterised by moderate to high levels of trace metal contamination and a relatively moderate to low mud component. The depth at these sites varies between 2.8 and 16 m. The second grouping (B) contained sites from the middle and southern sections of Big Bay. These sites were characterised by low trace metal concentrations and relatively moderate mud components. The cluster analysis also allowed us to identify sampling sites that are ‘outliers’, meaning that they have a very different species composition to other samples taken from the same area and thus do not fit into any groups. Species composition may differ at these sites due to anthropogenic impacts (such as pollution discharge) or certain environmental variables (e.g. a sudden increase in depth or change in the size of sediment particles). As was observed in all surveys since 2008, the site SB1 is an obvious outlier, most likely due to the fact that it had very low species abundance and 134 ANCHOR e n v i r o n m en t a l
State of Saldanha Bay & Langebaan Lagoon 2011 Benthic macrofauna diversity (only 2 species in 2008, 4 species in 2009 and 2010, and 5 species 2011). As was evident in previous surveys, this site is characterized by very high levels of organic pollution and high trace metal concentrations. At the 30% level of similarity, the site at the Multi-purpose Quay (SB14) was a clear outlier. SB14 is dominated by two species, the deposit feeding bivalve Tellina gilchristi and the scavenging dog whelk Nassarius vinctus. Both are relatively small species and are likely to be opportunistic. Interestingly the site at the Multi-purpose Quay was most similar to the B grouping (central and southern Big Bay). The sediment analysis revealed that the Multi-purpose Quay had the second highest levels of trace metal contamination while the sites in the central and southern sections of the Bay had the lowest concentrations of trace metals (Figure 5.29). Figure 5.14, which shows the distribution of mud in the Bay, revealed that in 2011 the sites positioned centrally within Big Bay and at the Multi-purpose quay all had a relatively large mud fraction. The accumulation of mud at these sites is mostly likely due to the higher depth, while at the Multi-purpose quay it is most likely due to a combination of depth and shelter. This correlation suggests that the benthic macrofaunal communities in Saldanha Bay are more influenced by particle size composition than by the level of trace metal contamination. The cluster and SIMPROF analysis revealed 5 statistically similar groups of sites indicated by the red lines on the dendrogram (Figure 7.2). These groups were displayed geographically using GIS, which revealed a clear spatial pattern (Figure 7.5). Sites in the first group (A1 - orange) were all positioned in the northern reaches of Small Bay. This is the least disturbed area within Small Bay (as revealed by the levels of trace metal contamination and the distribution of mud) and the flushing of fine sediments and contaminants seems to be comparatively the best in this section of Small Bay. Sites in the second group (A2 - red) were all positioned around the Ore Terminal and in close proximity to the mussel farms. Historically these areas have shown a high level of disturbance due to a combination of dredging events, mariculture activities and reduced circulation. Sites from Donkergat and Salamander Bay comprised the third group (A3 - pink). This area had a similar particle size composition (Figure 5.14) and depth range to that found in the Lagoon (Table 7.1), however, the trace-metal contamination at this site was high (Figure 5.29). Sites from the central areas of Big Bay comprised the fourth group (B – green) and sites from the Lagoon comprised the fifth group (C - blue) (Figure 7.5). The benthic macrofaunal communities at all Small Bay, Salamander Bay and Donkergat sites (A1, 2 and 3) were characterised by the mud prawn Upogebia capensis and a polychaete species belonging to the genus Polydora (Table 7.2). Upogebia capensis, an opportunistic species, is typically found in sheltered bays where it creates burrows in fine muddy substrate. The mud prawn, which is common at most sites in Small Bay, has been dominant within Small Bay since the early nineties. Their initial increase in Small Bay was attributed to a reduction in water movement resulting from the construction of the iron ore terminal and the Marcus Island causeway (Jackson and McGibbon 1991). The dominance of these species in these areas suggests that these sites are in the early phases of recovery or that the sites are subject to ongoing unpredictable environmental variations. 135 ANCHOR e n v i r o n m en t a l
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