Temporal patterns of meiofaunal assemblages associated with key Mediterranean habitat types

The Mediterranean Sea is characterized as a biodiversity and climate change hotspot, highlighting the importance of monitoring and conserving a variety of habitats. Posidonia oceanica , Cymodocea nodosa and Pinna nobilis are ecosystem engineers, offering suitable environments for a plethora of species, but they are classified as threatened or endangered. Well-sorted fine sand also has ecological value but is susceptible to anthropogenic pressure regarding changes in organic matter. Here, we examined temporal patterns in meiofaunal community structure in these habitats, which are possibly linked to temporal changes in abiotic conditions. Sediments of the C. nodosa habitat and the P. nobilis habitat exhibited the highest meiofaunal abundance in both 0-5 and 5-10 cm sediment layers, while the bare sand habitat showed the highest values for all diversity indices for the upper sediment layer. Taxon richness was the highest in the C. nodosa habitat; no difference was observed when P. nobilis was included. Temporal changes in meiofaunal and nematode abundance were observed only for the P. nobilis and the C. nodosa habitats. Ordination (non-metric multidimensional scaling) and hierarchical clustering grouped P. nobilis and C. nodosa habitat samples for both sediment layers, while the P. oceanica habitat samples were separated from the bare sand habitat samples in the upper sediment layer. Organic carbon was the most important abiotic factor influencing meiofaunal communities in both sediment layers. This study highlights that meiofauna can successfully be used for habitat monitoring, as shown by differences in diversity and abundance among habitat types.