Egg production rate and interannual variations of Paracalanus parvus (Copepoda: Calanoida)

Abstract

Weekly to biweekly measurements of the in situ egg production rate (EPR) of a dominant warm-water copepod (Paracalanus parvus) were made from August 2009 to July 2010 at a coastal station, along with analysis of environmental and food conditions. In addition, the results of a 10-year survey of abundance and environmental parameters are presented. The EPR ranged from <1 to 24 eggs female&#8211 1 d&#8211 1 with a mean of 4 eggs female&#8211 1 d&#8211 1. The calculated female growth rate was highest in August at 0.26 d&#8211 1, coinciding with the highest EPR, but growth was very low in winter (<0.01 d&#8211 1). Estimated copepod production followed similar seasonal patterns to those of EPR and female growth rate, and annual mean production was estimated to be low at 44.3 mgC m&#8211 3 yr&#8211 1. The EPR, weight-specific female growth, and production of P. parvus were all strongly related to water temperature, but little associated with Chl-a concentration. However, large ariabilities were noted in the summer (>20℃) values of these relationships, with a negative relationship between EPR and salinity. This seemed to be related to local input, which may provide heterotrophic food via terrigenous materials. Observed high abundances during times of extremely low female growth and low EPR suggest that the populations might be sustained by supplements from offshore, where their growth condition onditions. In addition, the results of a 10-year survey of abundance and environmental parameters are presented. The EPR ranged from <1 to 24 eggs female&#8211 1 d&#8211 1 with a mean of 4 eggs female&#8211 1 d&#8211 1. The calculated female growth rate was highest in August at 0.26 d&#8211 1, coinciding with the highest EPR, but growth was very low in winter (<0.01 d&#8211 1). Estimated copepod production followed similar seasonal patterns to those of EPR and female growth rate, and annual mean production was estimated to be low at 44.3 mgC m&#8211 3 yr&#8211 1. The EPR, weight-specific female growth, and production of P. parvus were all strongly related to water temperature, but little associated with Chl-a concentration. However, large variabilities were noted in the summer (>20℃) values of these relationships, with a negative relationship between EPR and salinity. This seemed to be related to local input, which may provide heterotrophic food via terrigenous materials. Observed high abundances during times of extremely low female growth and low EPR suggest that the populations might be sustained by supplements from offshore, where their growth condition