The seasonal abundance and production of Oithona nana (Copepoda:Cyclopoida) in Southampton Water

Williams, John Austin; Muxagata, Erik


Recent studies indicate that Oithona spp. contribute significantly to total copepod biomass. Little is known, however, about their ecological significance, particularly in the case of the estuarine Oithona nana. A study comprising three sites within Southampton Water was conducted to evaluate the late-stage copepodite/adult (stages IV–VI) O. nana community, using 120-mm mesh nets. Although present throughout the estuary, there was a striking spatial gradient with O. nana most common in the upper estuary. A clear seasonal pattern was observed with O. nana as the most abundant copepod species from late summer until early winter. It comprised 61% of all copepods recorded, with a biomass of 757.22 mg C m–3. Production estimates of O. nana were derived from the ‘instantaneous-growth’ approach, using appropriate growth equations. The estimated production of O. nana ranged from 1.50 mg C m–3 year–1 within the lower estuary to 146.77 mg C m–3 year–1 in the upper estuary. In the upper estuary, this compares with production rates of 187.47 mg C m–3 year–1 for all Acartia congeners (excluding nauplii), the most common calanoid genus. Throughout the estuary, O. nana annual production represented 18% of total copepod production clearly indicating that, at least in the upper estuary, O. nana production may be directly comparable with calanoid production.

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