The use of transplanted brown mussels (Perna perna) as indicators of marine health in Richards Bay harbour

M.Sc.Richards Bay Harbour is notably one of the fastest growing, economically important harbours in South Africa. However, this economic growth has lead to increased anthropogenic activities surrounding the harbour, which may result in higher contaminant, including metal, concentrations within the harbour. These contaminants may negatively influence the natural ecosystem functioning within the harbour. Consequently, assessment of the extent and effect of contamination, through continuous biomonitoring of Richards Bay Harbour, is essential. In the present study, the main aim was to assess the marine health in Richards Bay Harbour by studying spatial and temporal variation of bioaccumulation and biological responses within the mussel, Perna perna, using an active biomonitoring (ABM) approach. The ABM approach was preferred over the traditional passive biomonitoring of resident mussels since it eliminates several inherent factors that may mask the mussels’ true responses to the ambient environment. This approach entailed the transplantation of reference mussels from a relatively uncontaminated environment into Richards Bay Harbour, which is known to be contaminated by metals. In order to identify the reference mussel population for transplantation purposes, a study was undertaken to assess metal levels in two other P. perna populations within the same ecoregion as Richards Bay Harbour, namely Dawson’s Rocks and Sheffield Beach. The results showed that most metal concentrations were lower at Sheffield Beach, which consequently lead to the selection of this population as a reference. The effect of size differences on metal bioaccumulation was also assessed using the three latter mentioned mussel populations, which showed that, although local conditions strongly influence the relationship between metal bioaccumulation and size, utilisation of a narrow size range would minimise the size effect on bioaccumulation and should be used for ABM studies.Prof. V. Wepene