Precting the effects of climate change on the community structure of the bristol channel

Populations of 81 fish and 15 macro-crustaceans living in Bridgwater Bay in the outer Severn Estuary, England have been monitored monthly since 1980. These time series provide a near-complete record of abundance for the estuarine macrofauna of the Bay. The abundance of the majority of species remained stable until 1989 when notable changes began to be observed. There has also been an almost linear increase in species richness since 1980 resulting in greater food web complexity. Studies of individual species show that for many these changes can be related to climatic variables such as water temperature and the North Atlantic Oscillation. For example, Atlantic prawn, Palaemon serratus, sole, Solea solea and bass, Dicentrarchus labrax have increased in abundance with increasing water temperature while sea snail Liparis liparis and dab, Limanda limanda have declined. Other factors, such as the closure of cooling water intakes and improvements in water quality may also have allowed some species enhanced population growth. The net effect of all these changes has been a marked increase in fish and crustacean standing crop. The changing structure and dynamics of the Bridgwater Bay food web over the last 25 years is described and used as the basis to predict future community structure under different climatic regimes.