Effect of temperature on development, growth and reproduction in the marine copepod Pseudocalanus newmani at satiating food condition

Abstract

Post-embryonic development time, somatic growth, egg production rate, survival and sex ratio for the marine calanoid copepod Pseudocalanus newmani from the Pacific coast off southwestern Hokkaido were determined at five temperatures (3, 6, 10, 15 and 20°C) when a mixed algal diet was provided at satiating food condition (0.36 μg C ml -1 ) in the laboratory. At temperatures between 3 and 15°C, the development time from hatching to adult female increased exponentially with decreasing temperature, being 23.3, 33.1, 46.7 and 74.6 days at 15, 10, 6 and 3°C, respectively. Males developed into adults 2-5 days earlier than did the females. At the highest temperature of 20°C, both embryonic and post-embryonic development and egg production of P newmani were suppressed. This inhibitory effect of high temperature is consistent with the vertical distribution range and seasonal abundance cycle of this copepod in the field; it tends to avoid the warm surface layer (>15°C) and scarcely appears in the water column during summer and autumn. Body size of P newmani was not affected by temperature until C1, but increased with decreasing temperature after C2. The weight-specific growth rate (SGR) increased linearly with temperature (T) until 15°C, which is expressed as SGR = 0. 0095T + 0.0462 (r = 0.996). This growth pattern may also indicate high-temperature stress to this copepod, the general pattern of copepod growth being exponential. The weight-specific egg production rate (SER) also increased with temperature (SER = 0. 02T + 0.014, r = 0.99), below 15°C. The proportion of male offspring of P newmani that grew to adulthood was nearly 50% at 3 and 6°C, but decreased with increasing temperature at 10-15°C. This unequal sex ratio may be due to sex change during juvenile development under temperature control. These results suggest that temperature plays an important role in life history traits of P newmani through not only temperature- dependent growth and reproduction, but also through high-temperature inhibition and temperature- controlled sex ratio under sufficient food supply.