Top-predator effects of jellyfish Odessia maeotica in Mediterranean salt marshes

Abstract

Jellyfish can act as planktonic top predators, and their effects may cause drastic changes in the plankton structure of marine and freshwater systems. However, the top predator effects may not necessarily be the same in species-poor habitats as they are in species-rich habitats. The present study analyses the effects of the small lacunae jellyfish Odessia maeotica in a speciespoor habitat, Mediterranean salt marshes in the wetlands of Empordà (NE Iberian Peninsula). A field experiment was carried out in March 2008 to assess the direct and indirect effects of O. maeotica on plankton composition. Our results show that the presence of O. maeotica changed the plankton composition through top-down effects. Changes were strong in zooplankton, because O. maeotica can suppress almost the entire trophic level of large zooplankton (> 50 µm). Weak indirect effects on phytoplankton composition were observed as well. When O. maeotica was present, changes in the relative abundance of the phytoplankton species were found, but there was no net increase in phytoplankton biomass. Our results suggest that these weak indirect effects may be the result of trophic cascade effects coupled with the oligotrophic conditions of these salt marshes. Thus, trophic cascade effects lead to an increase in ciliate biomass, and these ciliates would feed on small algae (jellyfish-copepods-ciliates-small algae), while oligotrophic conditions would prevent increases in algal biomass.

Determination of Temporal Spawning Patterns and Hatching Time in Response to Temperature of Atlantic Bluefin Tuna (Thunnus thynnus) in the Western Mediterranean

“…In Balearic waters the zooplankton distribution in the surface layer responds to the annual light cycle: descendent migration and arrival at the surface are synchronised with dawn and dusk, and depth reached at night followed as well the moonlight cycle [55] , zooplankton reach shallower or deeper layers with new moon or full moon respectively. In particular, the abundance of Pelagia noctiluca , top planktonic predators [56] , in the Balearic ABFT spawning ground is relevant and increasing [57] . The nocturnal abundance of P. noctiluca at the sea surface in this region [37] is indicative of the well-known pattern of diel vertical migration of this species [58] – [60] .…”

Predation and competition effects on the size diversity of aquatic communities

“…In the same way, size diversity can be used to analyse variations in the size-based organisation of communities. Size diversity has been applied in the analysis of size based-patterns in ecosystem self-organisation, such as community responses to environmental gradients (Badosa et al 2007a;Schartau et al 2010;Emmrich et al 2011), topdown predation effects (Brucet et al 2010;Compte et al 2010Compte et al , 2012Rudolf 2012;Ye et al 2013) and seasonal dynamics or successional patterns after disturbances Paredes and Montecino 2011).…”

Plankton Taxonomic and Size Diversity of Mediterranean Brackish Ponds in Spring: Influence of Abiotic and Biotic Factors

“…This, together with the fact of not including in our analysis the presence of other predators, that although they were observed in situ (e.g., jellyfish Odessia maeotica, the amphipod Gammarus aequicauda) they could not be sampled properly, may prevent finding significant top-down effects on zooplankton size structure. We cannot ignore the fact that in the Mediterranean brackish ponds both the jellyfish and the amphipod have been found to act as planktonic top predators [86,87] causing changes in lower trophic levels through cascading effects [88,89].…”