engleski

Trophic cascades driven by Aurelia sp.1 in a Mediterranean lagoon

In recent decades, much attention has focused on the global increase in gelatinous zooplankton biomass, particularly in temperate ecosystems. Jellyfish, which are voracious consumers, may cause significant alterations in zooplankton abundance and dynamics. A confined environment like Varano Lagoon represents a suitable habitat for invasion and establishment by the scyphomedusa Aurelia sp., which has successfully resided there since 2000. The role of this gelatinous top predator was investigated by analyzing spatial and temporal dynamics of the meso- and micro-zooplankton community and jellyfish abundance. This was complemented by investigation of the composition and abundance of prey found in the jellyfish stomach content. Preliminary data showed seasonal variations in diet revealing that medusae ingest most of the mesozooplankton taxa present in the Varano Lagoon. The selectivity index C suggested null selection toward most prey, except positive selection for harpacticoid copepods and fish eggs. These preliminary results led to conclusion that Aurelia sp. medusae feed on zooplankton prey largely non-selectively and may have an unexpected effect on epibenthic prey. In addition, the exponentially population growth which occurred in late spring not only reduced the zooplankton standing stock, but also caused a structuring effect on zooplankton community, suggesting trophic cascades driven by jellyfish. This phenomenon resulted in food limitation for the gelatinous organisms and led to population collapses in the summer. Population monitoring and ongoing activities on jellyfish trophic ecology (e.g. stable isotopes) will clarify their predatory impact and how jellyfish fit into the lagoon food web.

zooplankton abundance; Varano Lagoon; jellyfish trophic ecology

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