Can Copepods Feed on Kelp Detritus? A Laboratory Study With Calanus finmarchicus

Abstract

Kelp forests are dynamic coastal habitats that generate large amounts of carbon-rich detritus. The fate of this detritus is largely unknown and considered a missing link in global carbon budgets. Kelp detritus can serve as food for benthic invertebrates and pelagic invertebrate larvae, but we know close to nothing about the role of kelp detritus as food for other zooplankton. We conducted feeding experiments to test if the highly abundant pelagic copepod Calanus finmarchicus can feed on fragments of two dominant kelp species, Saccharina latissima and Laminaria hyperborea. A series of experiments including particle ingestion, fecal pellet production, and DNA tracing tended to support the hypothesis that C. finmarchicus can feed on kelp particles of both species, but at a reduced rate relative to when on a regular phytoplankton diet. Moreover, the results provide initial evidence that L. hyperborea contains substances that are toxic to copepods, an observation that warrants further research. Pelagic copepods consuming kelp detritus would constitute a largely undescribed pathway of carbon from benthic primary producers to the pelagic food web, and a trajectory for deep-sea carbon sequestration. We hope these preliminary results will inspire future studies on the role of pelagic filter feeders in carbon transport and turnover from macroalgae habitats.