Seasonality of Oithona similis and Calanus helgolandicus reproduction and abundance: Contrasting responses to environmental variation at a shelf site
Journal of Plankton Research
Oxford University Press
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Reason for embargo
Under embargo until 06 May 2019 in compliance with publisher policy.
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.
L.E.C. was funded by the Natural Environment Research Council (NERC) Great Western Four+ Doctoral Training Partnership. We would like to acknowledge the NERC National Capability in supporting the Western Channel Observatory L4 time series. Further funding came from the Natural Environment Research Council and Department for Environment, Food and Rural Affairs (Grant no. NE/L003279/1, Marine Ecosystems Research Programme). Non-linear system identification components of this work were supported by J.T.B. in a personal scientific capacity.
This is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this record
Vol. 40, Issue 3, pp. 295 - 310