Seasonality of Oithona similis and Calanus helgolandicus reproduction and abundance: contrasting responses to environmental variation at a shelf site

L. E. Cornwell, H. S. Findlay, E. S. Fileman, T. J. Smyth, Andrew G. Hirst, J. T. Bruun, A. J. McEvoy, C. E. Widdicombe, C. Castellani, C. Lewis, A. Atkinson*

*Corresponding author for this work

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Abstract

The pelagic copepods Oithona similis and Calanus helgolandicus have overlapping geographic ranges, yet contrast in feeding mode, reproductive strategy and body size. We investigate how these contrasting traits influence the seasonality of copepod abundance and reproductive output under environmental variation, using time series data collected over 25 years at the Western Channel Observatory station, L4. The proportional change in egg production rate (EPR, eggs female−1 d−1) over the annual cycle was ~10-fold and similar for both species, although EPR of O. similis was only ~ 11% that of C. helgolandicus. The timing of EPR maxima for O. similis coincided with increased sea surface temperature (SST) in summer, likely due to a temperature-dependent brooding period. Conversely, EPR of broadcast spawning C. helgolandicus was more strongly related to net heat flux and diatom biomass, both parameters associated with the spring phytoplankton bloom. In both species, female body mass correlated negatively with SST, with a 7.5% reduction in body mass per °C in C. helgolandicus compared to just 2.3% in O. similis. Finally, seasonality of EPR and adult and copepodite abundance was strongly decoupled in both species, suggesting that optimum conditions for reproduction and abundance occurred at different times of the year.
Original languageEnglish
JournalJournal of Plankton Research
Volume40
Issue number3
Pages (from-to)295-310
ISSN0142-7873
DOIs
Publication statusPublished - 2018

Keywords

  • functional trait
  • egg production rate
  • Oithona similis
  • Calanus helgolandicus
  • Western Channel Observatory

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