Abalone, sea urchins and rock lobster: a possible ecological shift that may affect traditional fisheries

Abstract

A possible association between sea urchins Parechinus angulosus and juvenile abalone Haliotis midae has been monitored since 1989 during diving surveys at three sites on the South-Western Cape, South Africa. In 1994, numbers of sea urchins declined dramatically at two sites (Belly's Bay and Mudge Point), with a simultaneous decline in juvenile abalone. This decrease coincided with an apparent influx of rock lobster Jasus lalandii into the kelp beds of these regions. The hypothesis is proposed that predation by rock lobsters caused the previously large population of sea urchins to collapse, resulting in high mortality of juvenile abalone.