Original Articles

STUDIES ON THE ZOOBENTHOS OF SOME SOUTHERN CAPE COASTAL LAKES. SPATIAL AND TEMPORAL CHANGES IN THE BENTHOS OF SWARTVLEI, SOUTH AFRICA, IN RELATION TO CHANGES IN THE SUBMERGED LITTORAL MACROPHYTE COMMUNITY


Abstract

Major changes in the benthic macro-invertebrate community of the littoral zone of Swartvlei, South Africa, took place between January and April 1978, and the equivalent months of 1980. These changes, which were associated with a collapse of the submerged littoral macrophyte community, took the form of a major decline in total standing stocks. This decline was predominantly influenced by a one to two orders of magnitude reduction of the Musculus virgiliae Barnard population (Pelecypoda, Mytilidae). A simultaneous change in species composition also took place. The mean total invertebrate standing stock over a littoral transect fell from 132,46 ± 178,4 g dry mass m−2 in January 1978 (healthy macrophyte community) to 34,71 ± 15,48 g dry mass m−2 in January 1980 (after the macrophyte die-back), and from 130,73 ± 168,93 g dry mass m−2 in April 1978 to 6,43 ± 1,81 g dry mass m−2 in April 1980. These figures represent a reduction in invertebrate standing stock for the entire lake littoral of 263,25 tonnes dry mass between January 1978 and January 1980, and 280,35 tonnes dry mass between April 1978 and April 1980. Development of epipsammic algal mats subsequent to the die-back of the littoral macrophytes was not sufficient to provide food, and surface area for attachment and shelter from predators and wave action, for the originally predominant suspension-feeding invertebrate community.

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