Macrobenthos of the Tortoli Lagoon: A Peculiar Case of High Benthic Biodiversity among Mediterranean Lagoons

Coastal lagoons and brackish ponds are extremely dynamic and temporary ecosystems that follow natural changes throughout their geological history. The correct management of the lagoons ensures their integrity and proper functioning. For this reason, their ecological status should be surveyed for assessing the most appropriate strategies of use. In the present study, historical datasets collected in 2003-2004 are used to investigate the spatiotemporal variation in the species composition and community structure of the macrobenthos of the Tortol Lagoon (Sardinia, Italy) and to assess their relationship with key environmental variables. Owing to the presence of a riverine runoff at a site and confined areas at some distance from the sea inlet, we hypothesize the marked spatiotemporal changes of the macrobenthic community consistent with the high environmental variability typical of coastal lagoons. The results show a surprisingly high benthic biodiversity for a medium-sized lagoon (250 ha), with 101 species unevenly distributed across the lagoon. The environmental variables did not explain the zonation of the macrobenthic community as that typically found along a lagoonal gradient, due to a marked marine influence. The sampling sites were in fact discriminated by the species distribution according to their ecological affinity; in particular, the most distinctive characteristics of the Tortol Lagoon emerged from the strictly marine species that represented the most abundant group, consistently with the high marinization of the lagoon. Our results show that the Tortol Lagoon constitutes a peculiar ecosystem within Mediterranean lagoons, departing from the classic confinement theory.