70 YEARS OBSERVATIONS OF CHANGES IN DISTRIBUTION AND ABUNDANCE OF ZOOPLANKTON AND INTERTIDAL ORGANISMS IN THE WESTERN ENGLISH-CHANNEL IN RELATION TO RISING SEA TEMPERATURE

1. Extensive changes in marine communities in southwest Britain and th e western English Channel have been recorded during the past 70 years. 2. Over the same period there was a climatic warming from the early 1 920s, then a cooling to the early 1980s, with recent resumption of war ming; the change in annual mean temperature was approximately +/-0.5 d egrees C. 3. Marked changes occurred in plankton community structure; the distribution of both plankton and intertidal organisms was affecte d, with latitudinal shifts of up to 120 miles; there were increases or decreases of 2-3 orders of magnitude in abundance. 4. Warm water spec ies increased in abundance and extended their range during periods of warming, while cold-water species declined or retreated; the reverse o ccurred during the period of cooling. 5. Climate change can influence marine communities by a combination of: direct effect on the organisms ; effects mediated by biotic interactions; and indirectly through ocea n currents. 6. From climate models that indicate rises of mean tempera ture of 2 degrees C in the next 50 years, and from the observed change s, we can expect future latitudinal shifts of 200-400 miles in distrib ution of plankton, fish and benthos, with extensive restructuring of p lanktonic, pelagic and benthic communities. 7. Species common now in t he Bay of Biscay will become common in the English Channel; those pres ently restricted to the western English Channel could colonise the cen tral Irish Sea; changes in community structure could lead to lower abu ndances of infaunal benthos and fish. 8. To fully prove the effects of global warming, future changes in the marine biota must exceed those recorded in the 1950s and 1960s.