Recovery and recruitment of the brown mussel, Perna perna (L.), in Transkei: implications for management

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Abstract
The brown mussel Perna perna, has been an important food resource for indigenous inhabitants of the Transkei coast for centuries. The impoverished state of mussel stocks in this region and major differences in low-shore community structure between exploited and protected areas, have been ascribed to the ever-increasing exploitation of this species. In spite of this there has been no effective management of this resource owing to political and logistical problems related to law-enforcement, and misconceptions concerning the resilience of P. perna and the interspecific interactions which govern its recovery. Our present understanding of the ecological impacts of exploitation, and of the potential for recovery, is based on a series of studies and observations made over the last 15 years. These studies have shown that algae usually replace mussels following disturbance and that recovery may take more than eight years. As mussels tend to recruit preferentially into existing mussel beds, exploitation not only affects reproductive output but also reduces the preferred habitat. Recruitment onto both natural and artificial substrata is extremely low, even in marine reserves where standing stock is considerably higher than in exploited areas. Under these conditions stock enhancement in conjunction with rotational cropping may be the best management strategy.