An unpalatable choice, are Transparent Exopolymer Particles an alternative food source during the winter-spring transition for Acartia clausi in the Belgian Part of the North Sea?

Transparent Exopolymer Particles (TEP), a major class of marine gels, are omnipresent in ocean systems and influence both carbon cycling and particle dynamics. Nevertheless, their trophic role remains poorly understood, particularly regarding consumption by zooplankton. This study examines whether Acartia clausi, a dominant calanoid copepod in the North Sea, feeds on TEP during the winter-spring transition. TEP and EPS concentrations were measured in two-day incubation periods with and without copepods. EPS was assessed via mono- and polysaccharide concentrations, representing labile and structurally complex EPS fractions, respectively. Findings showed two main trends. In Run II (winter), A. clausi marginally significantly reduced TEP concentrations, suggesting potential grazing. In Run III (early spring), TEP increased in copepod treatments, accompanied by declining EPS concentrations, inferring TEP formation through mechanical aggregation of EPS. In Run IV, TEP decreased sharply without corresponding EPS changes, implying direct consumption. Copepods also significantly increased monosaccharide concentrations, possibly due to sloppy feeding. Overall, A. clausi can act as both consumer and facilitator of TEP, depending on context. However, other factors, such as microbial degradation and wave action, may be more important. This duality has implications for biogeochemical modeling and carbon sequestration in coastal systems.