Effect of the Benguela temperature anomaly, 1982–1983, on the breeding cycle of Donax serra Röding

Abstract

As part of an environmental monitoring programme for Koeberg nuclear power station near Cape Town, the breeding cycle and population dynamics of the white mussel Donax serra Röding were studied between early 1981 and the end of 1985. There is normally a cyclical pattern of high sexual activity during winter and spring and lesser activity during autumn. During summer, the proportion of sexually active animals is at its lowest and juveniles are at their maximum. During winter, juveniles are at their minimum. However, a major disruption of the pattern occurred at the end of 1982. The proportion of sexually active animals in the population increased dramatically during summer and settlement of larvae did not take place. In addition, there was no settlement of larvae from the abnormal summer breeding event. The normal cycle was resumed towards the end of 1983, with an extensive period of sexual activity followed by a major larval settlement. The period over which the abberations in the breeding cycle occurred, i.e. late 1981 and early 1982, coincides with the Benguela warm event, when surface seawater temperatures were significantly higher than normal. It would appear that the above-average summer water temperatures induced a period of sexual activity akin to that normally observed during winter and spring, while having a deleterious effect on larval survival and settlement. © 1987 Taylor & Francis Group, LLC.