Pergamon J. rherm. Biol. Vol. 20, No. l/2, pp. 91-104, 1995 Copyright 0 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0306-4565/95 $9.50 + 0.00 INFLUENCE OF TEMPERATURE ON THE MARINE FAUNA: WHAT CAN BE EXPECTED FROM A CLIMATIC CHANGE M. BHAUD, J. H. CHA, J. C. DUCH&NE and C. NOZAIS Observatoire Ockanologique, Universite P. et M. Curie, Laboratoire Arago, 66650 Banyuls-sur-mer, France Abstract-Temperature is a complex term under which are grouped many different parameters. These elements, together with others such as turbulence and advection, act on specific parts of the life cycle. These parameters however do not provide an explanation of all the changes brought about by exceptional years or a new trend of climate change. Two different relationships between variables subsumed under temperature and a biological event are described, mainly from Polychaeta: macroecological relations based on a large spatial scale e.g. geographic or bathymetric distribution and reproductive period on a latitudinal transect; microecological relations in the detailed control of a life cycle for a given location. It has been shown that short-term perturbations, often on a time scale less than 1 month, may be at the origin of variable reproductive success of the species, affecting either breeding or larval success. The methodological consequence is to disregard mean annual temperature which may suppress or seriously obscure the short deviations of greater importance. For the control of specific distribution area, the importance given to the larval stages is probably overestimated, the existence of so-called pseudopopulations suggests that the survival of larvae is possible in a temperature range greater than that allowing reproduction of the adults. The extensive analysis of a particular life cycle suggests that temperature is not the factor determining the time of reproduction or more generally the timing of biological events. The timing mechanism and its selective advantage are probably based, for the species examined, on the growing conditions during first 3 months of the benthic juvenile life. Key Word Index: Temperature; climate change; polychaetes; regulation; life cycle INTRODUCTION Temperature is generally considered as one of the most important physical variables controlling the life of marine organisms. Geographic and bathymetric boundaries (Allee, 1923; Orton, 1920; Hutchins, 1947; Darlington, 1957; Hedgpeth, 1957), reproduc- tive period and more particularly, the period of larval presence in the plankton (from Garstang, 1894 to Thorson, 1946, 1950), recruitment and turnover pro- cesses of the species with integration of all parts of the life cycle (Sinclair, 1988; Bhaud and Cha, 1992) and metabolism (Mangum, 1970; Mangum and Sassa- man, 1969) have all been considered to be subject to the influence of temperature. Two preliminary remarks must be stated. Tem- perature is an imprecise expression which subsumes varied concepts: a summer, winter or annual mean; a range related to a time period; a decreasing or increasing gradient; a variability around maxima or minima calculated on a given period of time (Fig. 1). This parameter may be recorded at the present time in which case the annual variability can be precisely known, or it may be deduced for past time for which only a mean over a variable period of generally several hundred years, is available. These different views of variability, are a probable source of conflict between biologists and physicists. There are several ways to identify the relationship between climate and biology. The most frequent method consists of examining two temporal parallel series: one for biology, the other for the hydroclimate. A long-term analysis, over a period longer than 50 years, of both plankton and benthos, in the North Atlantic Ocean, displays cycles of different periods: from 3-4 years to 18-20 years (Gray and Christie, 1983). Physical explanations for such periodicities are available (Maximov, 1952; Maximov and Smirnow, 1965). Such data which link quantitative variation of biological elements with variation of primary period- ical factors (Monchadsky, 1958), are very numerous. However, after the analysis of temporal series of benthic populations, Gray and Christie (1983, p. 93) conclude that predicting long-term changes in benthic communities is an unattainable goal due to the extremely long period expected. Cycles may be appar- 91