The effect of temperature on shell size and growth rate in Krithe praetexta praetexta (Sars)

The effect of temperature on growth rate, shell size and shell shape in Kri the praetexta praetexta (Sars) was studied in four thermocultures. From Jul y 1995 to June 1996, the cultures were kept in a continuously flowing open system pumping water from the intermediate watermass of the Gullmarn fjord, west coast of Sweden. Three cultures were kept at constant temperatures of 5, 10 and 14 degrees C, respectively. The fourth (reference) culture large ly followed the natural variation in temperature. At the termination of the experiment, all living ostracods from a 125 mu m sieve were sampled from t he cultures. Population age structures were analysed for the various thermo cultures of K. praetexta praetexta. These were more shifted towards later o ntogenetic stages with higher temperature, i.e. the ontogenetic development was more rapid in the warmer cultures. An alternative explanation is due t o diapause causing cohorts to accumulate in some ontogenetic stages only wh en the temperature is constant. The differences in shell size of K. praetex ta praetexta among the thermoconstant cultures were not statistically signi ficant.