Temperature-regulated egg production rate, and seasonal and interannual variations in Paracalanus parvus

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Weekly to biweekly measurements of the in situ egg production rate (EPR) of a dominant warm-temperature copepod (Paracalanus parvus) were made from August 2009 to July 2010 at a coastal station, together with analysis of environmental and food conditions. In addition, the results of a 10-year survey of P. parvus abundance and environmental parameters are presented. EPR ranged from <1 to 24 eggs female–1 day–1 with a mean of four eggs female–1 day–1. The calculated female growth rate was highest in August at 0.26 day–1, coinciding with the highest EPR, but growth was very low in winter (<0.01 day–1). The EPR and weight-specific female growth of P. parvus were both strongly related to water temperature, but weakly associated with chlorophyll-a (Chl-a) concentration. However, large variability was noticed in the summer (>20°C) 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 from terrigenous sources. 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 could be better (e.g. higher water temperature). Future warming would contribute to a trend of increasing abundance of this copepod, especially of non-summer populations.

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