PLANKTON DYNAMICS AND AURELIA-AURITA PRODUCTION IN 2 CONTRASTING ECOSYSTEMS - COMPARISONS AND CONSEQUENCES

The population dynamics and production of the Scyphomedusa Aurelia aur ita (Lam.) were examined within two contrasting ecosystems on the sout h coast of England; Southampton Water, an open productive estuary, and Horsea Lake, an enclosed, brackish, man-made body of water. Annual A. aurita production in Southampton Water ranged between 31 and 58 mg C m(-3) year(-1) in different years (1990-94); while at Horsea Lake, ann ual production was 76 mg year(-1) in 1994. The potential impact of A. aurita on the mesozooplankton communities was estimated through C m(-3 ) measurements of in situ secondary production and transfer efficiency between the two populations. Using literature-based estimates for mes ozooplankton production, the annual transfer efficiency between the me sozooplankton and A. aurita populations in Southampton Water ranged be tween 9 and 26% in different years, and in Horsea Lake was 73% in 1994 . These data imply that the abundant A. aurita population may have a s ignificant impact on the mesozooplankton community of Horsea Lake, and in turn, the very small A. aurita sizes observed indicate a severely food limited population. The ecological role of A. aurita in Horsea La ke is discussed in View of the very low chi a and mesozooplankton numb ers present. (C) 1997 Academic Press Limited.