Sand and Wave Induced Mortality in Invasive (Mytilus galloprovincialis) and Indigenous (Perna perna Mussels

Sand and wave induced mortality in invasive and indigenous mussels was investigated. Mean daily wave heights were calculated from hourly values, and then used to calculate mean monthly values. Correlation analysis was used to test for significant relationship between monthly mortality of each species and mean monthly values for wave height and sediment amount. Mortality rates of both species at Robberg and Keurbooms fluctuated seasonally during the sampling period. At both sites, M. galloprovincialis mortality attained a clear peak in winter and P. perna showed peaks in autumn and another in winter. Mean monthly mortality was not correlated with sediment amount for either species. Mean monthly wave height increased in late autumn-winter, with a peak in August, and then decreased in spring.