EFFECTS OF TEMPERATURE ON OOCYTE GROWTH IN THE MEDITERRANEAN TEREBELLID EUPOLYMNIA-NUEBULOSA (ANNELIDA, POLYCHAETA)

Eupolymnia nebulosa (Montagu) is a widely distributed terebellid polyc haete that builds its tubes on the coastal shelf in areas with mixed s oft and hard bottoms. From a long-term survey in the Bay of Banyuls, F rance (NW Mediterranean), we found an advancement of the timing of the spawning period coincident with a delayed breakdown of the thermoclin e. We postulate that persistent high temperatures can influence gamete development by stimulating oocyte growth, resulting in earlier spawni ng. During 1992 and 1993, we used a between-individuals experimental a pproach to assess the possible effect of temperature on oocyte growth based on: (1) determination of the growing fraction of the oocyte popu lation (i.e. oocyte net growth); (2) identification of differences in oocyte growth-rate among females; (3) comparison of non-significantly different size-distributions of the growing oocyte fraction (net oocyt e size-distributions) at the beginning of the experiments with those a t the end. No effect of temperature on oocyte growth was detectable at the population level, but a positive individual response to prolonged high temperature was evident. Thus, the lack of a significant respons e by the population to prolonged high temperature does not imply a lac k of individual response. We propose a model of oocyte-growth dynamics based on temperature that incorporates previous observations of exten ded oogenesis and oocyte growth during periods of both increasing and decreasing temperature and on the scattered pattern of oocyte size-dis tributions at the onset of spawning.