Unexpected guests at the table: how a non-native ascidian uses food resources and its consequences on ecosystem functioning

GIACHETTI CLARA; SCHWINDT EVANGELINA; ALURRALDE GASTÓN; GIACHETTI CLARA; TATIÁN MARCOS; SCHWINDT EVANGELINA; ALURRALDE GASTÓN; TATIÁN MARCOS; CALCAGNO EMILIA; BATTINI NICOLAS; CALCAGNO EMILIA; BATTINI NICOLAS

Puerto Madryn

Conferencia; X International Conference on Marine Bioinvasions; 2018

Harbors are prone areas for biological invasions since they provide diverse artificial structures that favor colonization by sessile marine organisms, like ascidians. These filter-feeding animals have a key role in pelagic-benthic coupling when reaching high densities: via the uptake of organic matter and the deposition of feces, ascidians fuel one of the major trophic pathways in marine ecosystems. In order to assess ascidian contribution in this pathway, we performed aquaria experiments using a non-native species (Ascidiella aspersa) and a cryptogenic one (Asterocarpa humilis) that flourish in a port area in Puerto Madryn city, Argentina. We evaluated the mass-specific biodeposition rate and the feces quality (C:N ratio) for both species, under two different diets (natural seston and natural seston enriched with phytoplankton). These parameters were related to ascidian densities, which were estimated after a year of deployment of artificial succession plates. Ascidians were the most abundantorganisms of encrusting communities. Ascidiella aspersa predominated, reaching an annual average density of 233 individuals m-2, that is up to five-folds the density reached by A. humilis. The trophic processes varied according to the species and the type of diet: biodeposition rates were similar under natural seston but higher in A. aspersa under natural seston plus phytoplankton. Feces quality of A. aspersa was higher than A. humilis after feeding with natural seston. Besides, the amount of carbon and nitrogen in feces is greater in A.aspersa than in A. humilis for both diets. Considering the densities observed and the estimated trophic processes, A. aspersa would have a major incidence in the flow of particles being able to alter the normal stoichiometry and the trophic pathways in the assessed ecosystem.