Impact of mussel culture on macrobenthic community structure in Saldanha Bay, South Africa

The impact of raft mussel-culture in Saldanha Bay, South Africa on macroben thic community structure (abundance and biomass) was studied. Sampling was conducted in January between 1993 and 1996 to assess: (1) the composition o f macrobenthos below rafts relative to outside the farm; (2) effects of raf t position and age within the farm; and (3) recovery rate of benthos after raft removal. Analyses included ABC plots, hierarchical clustering and spec ies diversity indices. Disturbed communities were found under 78% of raft s ites sampled. The level of disturbance (Warwick Statistics) and the dominan t opportunistic species (Bray-Curtis Similarities) changed from year to yea r, polychaetes and scavenging gastropods being most common. The degree of d isturbance appeared related to raft sites positioned in the middle of the f arm rather than raft age. Whereas ABC plots and hierarchical cluster analys es best identified the disturbance of benthic communities, diversity indice s detected marginal recovery four years after raft removal. Although deposi t feeders dominated all sites, suspension feeders increased in number and b iomass at reference sites. This study presented a "yes/no" scenario that wi ll be addressed in subsequent research in the modelling of culture ecosyste ms. (C) 1999 Elsevier Science Ltd. All rights reserved.