Effects of HABs and a dystrophic event on zooplankton community structure in a Mediterranean lagoon (W Greece)

Abstract

This study reports on the spatiotemporal distributions of zooplankton assemblages during two harmful algal blooms (ΗΑΒs) and a dystrophic crisis in Papas lagoon (W Greece, E Mediterranean), a water body with a long history of eutrophication phenomena. The main focus is placed on the impact of toxic microalgae on the metazooplankton community structure under contrasting environmental conditions including an anoxic event. Towards this aim, we recorded environmental parameters and sampled different size components of plankton communities (microalgae, microzooplankton and mesozooplankton) over the course of a year, in order to assess the metazooplankton assemblages (using nMDS, PERMANOVA and CCA) within a more comprehensive framework, considering lower trophic levels. HABs had a detrimental impact on all key holoplankton and meroplankton taxa regardless of environmental conditions, while their co-occurrence with anoxia resulted in the collapse of zooplankton populations. Recovery of zooplankton abundances after the compounded effects of HABs and anoxia was significantly slower in relation to the sole impact of HABs. Concerning holoplankton, dominance of egg-spawning calanoid copepods (Acartia clausi, Paracartia latisetosa) prior to the compounded extreme events shifted to smaller egg-carrying harpacticoids (Euterpina acutifrons) and cyclopoids (Oithona nana) in the recovered assemblages while in meroplankton, bivalvia larvae were largely replaced by cirripedia nauplii. These results suggested that the cumulative effects of HABs and dystrophic crises may significantly alter the taxonomic composition and size-structure of metazooplankton communities with possible harmful consequences for ecosystem functioning and fish and shellfish recruitment.