Chlorophyll a to estimate the particulate organic carbon available as food to large zooplankton in the euphotic zone of oceans

In order to optimize the sustained exploitation of marine renewable resources, a major objective of modern biological oceanography is to quantify, model and predict the flux of biogenic carbon (BC) from phytoplankton towards large metazoans. The present paper explains why the concentrations of sestonic particulate organic carbon ([POC]) provide estimates of the BC that can be used as food by large (i.e. meso- and macro-) zooplankton, and can thus be channelled towards large metazoans. Because of this, the wealth of existing [POC] data provide first-order estimates of the BC available to large zooplankton. The paper also derives, from a large set of data from the literature, general relationships between chlorophyll a concentrations ([Chl]) and [POC] in the euphotic zone of oceans. These empirical relationships can be used to compute [POC] from [Chl] and thus obtain from the latter, which is easy to determine in the field or derive from remotely sensed images of ocean colour, estimates of the BC that is available as food to large zooplankton.