Quantification of intraspecific and interspecific competition in fish species of the Aegean Sea

Competition shapes species coexistence and community assembly, playing a central role in maintaining biodiversity and ecosystem resilience. Here, we used an asymmetric competition index that quantifies the possible competitive effect of a species on any other, using southern Aegean Sea nekton biomass from the Mediterranean International Trawl Survey dataset, combined with data on six traits relevant to trophic ecology and spawning. We modeled the effect of selected haul-level covariates on the competition index, and we indicated competition variation across depth and habitats. Most species experienced stronger inter- than intra-specific competition. Both the higher-than-expected significance of interspecific competition (in comparison to intraspecific that is generally anticipated to be higher) and the existence of an extensive network of multiple competitive interactions indicated, are associated with high biodiversity, combined to the absence of dominance by one or a few species in the community (no species is disproportionally highly abundant in comparison to others); the latter may be relevant to community stability and resilience. The quantification of competition across marine ecosystems can help predict how fish communities will respond to future resource availability and environmental conditions.