Long-term distribution patterns of mobile estuarine invertebrates (Ctenophora, Cnidaria, Crustacea:Decapoda) in relation to hydrological parameters

Abstract

Between 1977 and 1992, semi-quantitative samples of macroinvertebrates were taken at fortnightly intervals from the Thames Estuary (UK) utilising the cooling water intake screens of West Thurrock power station. Samples were taken for 4 h over low water, the abundances of invertebrates recorded in 30 min subsamples and related to water volume filtered. Abundances of the major estuarine species have therefore been recorded every 2 wk for a 16 yr period, together wlth physicochemical parameters such as temperature, salinity and freshwater flow. Annual cycles of distribution were apparent for several species. Carcinus rnaenas exhibited a regular annual cycle, with a peak in autumn followed by a decrease in numbers over winter, relating to seasonal temperature patterns. Conversely, abundance of Crangon crangon was consistently lowest in summer, responding to seasonal changes in salinity, whilst Liocarcinus holsatus, Aurelia aurita and Pleurobrachia pileus were only present in summer samples, with P. pileus often in vast numbers (>l00000 per 500 million I). The estuarine prawn Palaemon longirostris showed no obvious sustained annual pattern, but evidence for a longer cycle of distribution was apparent. During 1989-1992 severe droughts in southeast England severely disrupted annual salinity patterns and coincided with a large increase in the Chinese mitten crab Eriocheir sinensis population. This included the first synchronised migration of adults in the UK. Settlement of young crabs during low-flow periods is suggested as an explanation for this population increase.

Juvenile Chinese mitten crabs (Eriocheir sinensis) in the Thames estuary: distribution, movement and possible interactions with the native crab Carcinus maenas

“…From then until 1991 there were only sporadic sightings of this species (Ingle 1986). During 1991During -1992 there was a marked increase in their abundance at West Thurrock Power Station (Attrill and Thomas 1996a) and indications of a seaward migration of adults occurring in October and November of 1992. It was speculated that the reason for this sudden increase in the population was the decrease in freshwater flows following a drought period in the Thames in 1989-1991, which allowed the establishment of a young population (Attrill and Thomas 1996a).…”

Open Water Processes of the San Francisco Estuary: From Physical Forcing to Biological Responses

“…It was first found in the San Francisco Estuary in 1992 and since that time has increased rapidly in abundance and range, as it did previously in the Thames Estuary (Attrill and Thomas 1996). In contrast to most crabs, the mitten crab is catadromous, rearing in rivers and sloughs upstream and reproducing in brackish water (Halat and Hieb 1996;Rudnick et al 2003).…”

Effects of temperature and the presence of benthic predators on the vertical distribution of the ctenophore Pleurobrachia pileus

“…On the other hand, the adult individuals that overwinter are found closer to the sediment and, hence, less obvious in plankton samples. Nevertheless, much is still unknown concerning the population dynamics of Pleurobrachia, and other authors have observed other overwintering strategies for different Pleurobrachia species and different localities (Milne and Corey 1986;Attrill and Thomas 1996). When the population builds up through intense reproduction in spring, the average size of the individuals decreases, to reach a minimum around August (Greve 1971), and main reproduction is early in the season.…”