Remarkable size-spectra stability in a marine system undergoing massive invasion

The Mediterranean Seais an invasion hotspot, with non- indigenousspecies suspected to be a major driver behind community changes. We used size spectra, a reliable index of food web structure, to examine how the influx of Red Sea fishes into the Mediterranean Seahas impacted the indigenousspecies community. This is the first attempt to use changes in the size spectra to reveal the effect of biological invasions. We used data from trawlcatches along Israel9s shoreline spanning 20 years to estimate changes in the community size spectra of both indigenousand non- indigenousspecies. We found that the relative biomass of non- indigenousspecies increased over the 20 years, especially for small and large species, leading to a convergence with the indigenousspecies size spectra. Hence, the biomass of indigenousand non- indigenousspecies has become identical for all size classes, suggesting similar energetic constraints and sensitivities to fishing. However, over this time period the size spectrum of indigenousspecies has remained remarkably constant. This suggests that the wide-scale invasion of non- indigenousspecies into the Mediterranean may have had little impact on the community structure of indigenousspecies.