Depicting the novel Eastern Mediterranean food web: a stable isotopes study following Lessepsian fish invasion

Abstract

The introduction of Red Sea species through the Suez Canal has caused dramatic alteration of Eastern Mediterranean marine communities, however changes at the level of trophic interactions remain poorly understood. Capitalizing on this spectacular bioinvasion, we used stable isotope analysis to depict the novel fish food web occurring in the Eastern Mediterranean, off the Lebanese coast. Multivariate analyses were performed on six trophic groups contrasting the δ15N–δ13C ratios of native (MED) versus non-indigenous (Lessepsian-LES) species. Community-wide aspects of trophic structure were explored by means of recently developed quantitative metrics, such as the average distance to centroid and the standard ellipse area. Although the trophic positions of Lessepsian and native species were comparable, native fishes generally showed a greater trophic diversity than Lessepsians, the latter being mainly located in the central region of the available trophic space. We argue that the original trophic niche of native species has widened out due to the shift they have made towards less preferred food items, whilst highly competitive invaders are exploiting more energetic resources. In the absence of historical data, our observations agree with the idea of a rapid change of the Eastern Mediterranean food web, driven by niche displacements through trophic competition.