Publication Abstract

Structure and function are ecosystem properties that underpin the food web descriptor of the European Marine Strategy Framework Directive. The study presented here was designed to investigate whether measurements of phytoplankton and zooplankton standing stock could be used to derive estimates of primary and secondary production and hence energy flow through the pelagic component of the marine ecosystem. As a first step, estimates of primary and zooplankton biomass and production, together with measurements of physical, chemical and biological variables, were obtained during cruises in the Irish and Celtic Seas during 2010 and 2011. Sampling sites ranged from anthropogenically enriched mixed coastal waters to deep seasonally stratified regions of the shelf. Estimates of gross daily phytoplankton production were derived from ¹⁴C uptake experiments, microplankton respiration by oxygen evolution in dark-incubated samples, and crustacean zooplankton production from a chitobiase enzyme-based bioassay.

We will show that there were consistent relationships between primary and secondary production. At all but one seasonally stratifying site, higher secondary production was associated with higher primary production. As examples, regressions of ln-transformed primary production (lnPP) against ln-transformed zooplankton production (lnZP) had R² values of 0.69 for inshore stations (lnZP = 0.94*lnPP – 1.95) and 0.91 for an offshore station (lnZP = 2.81*lnPP – 15.58). These results are discussed in the context of the factors controlling the linkages between primary and secondary production and whether a seasonal and/or regional index of vigour can be developed using primary to secondary production ratios.