Benthic trophic status and spatiotemporal variability of macrobenthic assemblages in S'Ena Arrubia Lagoon (Sardinia, Italy)

Quantity and nutritional availability of sedimentary organic matter (OM) are among the most important factors affecting benthic fauna dynamics. Despite this, the relative importance of food sources with different nutritional quality on the macrobenthos dynamics has been poorly investigated, especially in naturally eutrophic coastal lagoons. We investigated the spatiotemporal variations in the relationship between the macrobenthic assemblages and the quantity and nutritional quality of OM in a Mediterranean coastal lagoon (S'Ena Arrubia lagoon, Sardinia, Italy). Sampling was carried out at six stations selected at different distances from the sea inlet and with a different degree of confinement, in two dates in winter (February and March) and two dates in summer (June and July) 2021. The PERMANOVA tests showed significant differences among stations, seasons and sampling dates in the benthic assemblages, and the quantity and quality of OM. The DistLM analyses revealed that the photosynthetically produced OM (as total phytopigment contents) and OM freshness (as the protein-to-carbohydrate ratio), as well as the nutritional quality of OM (as the algal fraction of biopolymeric C), played a crucial role in influencing the spatiotemporal distribution of the macrobenthic abundance, taxonomic richness and composition, with the most significant correlations being detected for the deposit-feeders and detritivores, such as Streblospio shrubsolii, Microdeutopus gryllotalpa, Malacoceros fuliginosus and Polydora ciliata. These results suggest that a thorough assessment of the environmental quality of coastal lagoon's sediments should consider jointly macrobenthic metrics and the benthic trophic status, as assessed using complementary biochemical descriptors.