Diel horizontal migration of Mesopodopsis slabberi (Crustacea: Mysidacea) in Algoa Bay, southern Africa

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Abstract
The mysid shrimp Mesopodopsis slabberi (van Beneden), exhibited a diel pattern of onshore-offshore movement off Sundays River beach, South Africa. Shoreward migration at sunset resulted in the presence of relatively high numbers of mysids after dark behind the breaker line (ca 6m water depth) compared to further offshore. At first light, M. slabberi migrated back to deeper water (> 15 m) where it remained during daylight. The nocturnal presence of mysids behind the breakers is interpreted as a response to increased concentration of phytoplankton, principally Anaulus australis Drebes and Schulz, which outwelled from the inner surfzone through rip current activity. Consumption by M. slabberi was estimated to be 51 g C d-1. On an annual basis, this approximated to 70% of total available carbon consumed by the macrofaunal trophic assemblage in the Sundays River surfzone.