Mytilus galloprovincialis (Mollusca: Bivalvia) in a warm-temperate South African estuarine embayment

Abstract

The distribution, population structure, condition and gonad indices, and the attachment strengths of the invasive Mediterranean mussel Mytilus galloprovincialis are described from the Knysna Estuary, South Africa. Mussels were found in the rocky intertidal at the mouth of the estuary and on all man-made hard substrata as far as 12 km from the mouth in 2013. However, mussel beds were found only in the lower reach of the estuary, where mussel densities were as high as 120 per 0.01 m2. When compared to mussels from the embayment regions of the estuary, those at the estuary mouth, where wave action was high, were generally smaller, had significantly lower condition and gonad indices, and greater attachment strength. This suggests that mussels within the sheltered regions of the estuary invest more energy in growth and reproduction, and that this is one reason for their success as an invasive species in the Knysna estuarine embayment.

Keywords: attachment strength, byssus, condition index, gonad index, Knysna Estuary, shell length