Zooplankton production and energy flow : towards a biological model of Southampton Water

Abstract

Growth rates, production and the ecology of calanoid copepods, together with abundance of meroplankton, were examined within Southampton Water, U.K. Estimated biomass values of calanoid copepods are greater in the inner estuary (ie. total range found was between 0.0206 and 17.844mgCm^-3 at Cracknore), and lower at the mouth of the estuary (ie. between 0.0006 and 15.175mgCm^-3 at Calshot). Estimated annual calanoid copepod production rates were typically <290mgCm^-3yr^-1 at the estuary mouth, while mid-estuary rates averaged �530mgCm^-3yr^-1. Estimates of other pelagic and benthic components were also derived to allow a box model of annual carbon production rates of the dominant compartments to be established. Calanoid copepod annual production rates represent around 0.5% of total annual primary production, while estimates of ciliate annual production were 6.2 to 9.3 times greater than the copepod rates. This study therefore confirms the dominance of the microbial community in this area with regard to carbon ingestion and production.

Calanoid copepod weight-specific growth rates were found to vary between 0.008 to 0.378d^-1 when measured in situ at Calshot. Biomass of calanoid copepods was very low in comparison to many other temperate areas, which may be the result of high flushing rates and the relatively lower growth rates. The calanoid production rates are lower than in most other estuarine and neritic areas previously studied. Gelatinous predators within the estuary appear to have strong impacts upon mesozooplankton numbers at times, even though their apparent production and ingestion demands are much less than in many other neritic areas. These impacts are pronounced as a result of the low biomass and production rates of calanoids. Annual gelatinous production rates were higher in the upper estuary, where they reach 27.5mgCm^-3yr^-1 at Cracknore, with annual ingestion demands at the same site reaching 77.2mgCm^-3yr^-1. At the mouth of the estuary gelatinous production ingestion demands are little over 1.6mgCm^-3yr^-1. The gelatinous predators may prey heavily upon meroplanktonic larvae in addition to copepods, the initial weight of such meroplankton is highlighted as a potentially important source for these predators, and as a benthic-pelagic energy-matter pathway.

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