Small-scale spatial heterogeneity and seasonal variation in a population of a cave-dwelling Mediterranean mysid

Ribes, M.; Coma, R.; Zabala, M.; Gili, JM
J Plank Res
Seasonal changes in small-scale spatial distribution patterns of abundance and composition of Hemimysis speluncola Ledoyer (1963) (Crustacea, Mysidacea) were studied in a population of cave-dwelling mysids off the Medes Islands (NW Mediterranean Sea). The distribution pattern was characterized all year round by marked spatial segregation of juveniles, which occupied areas closer to the cave entrance, while adults were concentrated mainly in the innermost part of the cave. The small-scale spatial heterogeneity observed appears to be regulated by biological factors, particularly social and reproductive behaviour. Nevertheless, a certain adaptation of the distribution of the swarms to hydrodynamic factors suggests that physical factors may also play a role. The heterogeneous aggregation pattern recorded would clearly appear to be an adaptive strategy by the population to enable it to thrive within its habitat. That adaptation is designed to reduce predation mortality, enhance mating efficiency and regulate the population generally. Marked seasonal fluctuations in the density and composition of the population were recorded, with high density levels in winter and throughout the spring. Two methods were employed to quantify the population: hauls with plankton nets towed by divers and collection of faecal pellets. The patterns observed using both these methods were similar, although the latter method yielded total density values that were an order of magnitude greater.
Mysid, Mediterranean
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