Seasonal and spatial distribution patterns of the congeneric group acartia in the solent-southampton water estuarine system, with special reference to aspects of their fecundity

The mesozooplankton community of the Solent area and its relationship with the mesozooplankton community of Southampton Water is described for the first time. Seasonal distribution patterns followed similar trends, with the mesozooplankton characterised by a spring-summer peak of abundance. During the 1995 spring peak a higher concentration of total mesozooplankton abundance was observed in the east and central Solent with a maximum of 14, 181 ind.m-3 in April and 17, 471 ind.m-3 in May, respectively. This peak of abundance was composed mainly of high concentrations of larval stages such as cirripede nauplii, gastropod and decapod larvae. The spatial distribution observed is assumed to be partly influenced by the hydrographic structure of the area. It is suggested that tidal currents and the presence of a residual gyre in the east Solent could be promoting larval, and also possibly holoplanktonic, species retention.In the upper reaches of Southampton Water at Bury Buoy a similarly timed seasonal abundance pattern was observed but with higher mesozooplankton concentrations up to 25, 471 ind.m-3 (June) were recorded. The Bury Buoy peak of abundance was comprised mainly of a high copepod species abundance together with high concentrations of cirripede nauplii. Copepod species dominated the mesozooplankton community in the whole system for much of the year particularly the congeneric group Acartia, which exhibited seasonal and spatial distribution patterns.Three Acartia species occur in the Solent, Acartia bifilosa, Acartia discaudata and Acartia clausi, while Acartia tonsa and Acartia margalefi are mainly restricted to the upper reaches of Southampton Water, with A. margalefi first recorded in British waters. Within the water system a single discrete peak of maximum abundance was recorded for each Acartia species which appeared in a sequential order with A. bifilosa during May, A. discaudata during May/June, A. margalefi during June, A. clausi during August and A. tonsa during September. The present study reports the first records of egg production rates in Solent-Southampton Water Acartia species, which were observed to be influenced by temperature and salinity.