TAXONOMIC COMPOSITION AND MORPHO-FUNCTIONAL TRAITS OF NEMATODES IN MALDIVIAN SUBTIDAL HABITATS

Nematodes are one of the most abundant animal phyla in marine bottoms, and show a remarkable diversity in carbonate sediments. The Maldivian Archipelago is experiencing major environmental changes and habitat loss, which requires great attention. Previous studies on meiofauna and nematodes from Maldives have revealed a considerable biodiversity in these sediments that are exclusively carbonate with a highly porous structure, which offers many microhabitats to meiobenthic organisms. Recently, an important relation between the morpho-functional traits of nematodes and the loss of ecosystem functioning has been proven. Thus, the taxonomical structure of the nematode communities of subtidal habitats of Maldives and five morpho-functional traits (cuticle morphology, tail shape, amphid type, structure of buccal cavity, lifestyle) were studied. The Maldivian nematode community included 174 genera in 37 families, mainly represented by Desmodoridae, Chromadoridae and Xyalidae, a faunistic composition in line with that usually found in this type of sediments. As for morpho-functional traits, the most common cuticle morphology was dotted/annulated with or without lateral differentiation (80% of the community).The most common type of amphid was loop-like in 42% of the community, followed by spiral (21%), circular (16%) and slit (11%). The analysis of trophic groups showed the prevalence of epistrate feeders (2A, 54%), followed by selective deposit feeders (1A, 22%), omnivorous (2B, 14%) and non-selective depositories (1B, 11%). As for life strategy, the colonizer-persisters class 3 (c-p 3) made up the 57% of the community, the c-p 2 22%, and c-p 4 20%. Statistical analysis allowed to detect interesting relations between nematode morpho-functional traits, especially amphid type and cuticle morphology, and some environmental features. For instance, a significant presence of nematodes with the peculiar cuticle provided with desmi was found in the outer reefs, likely related to the high abundance of Desmoscolecidae, a family typical of very heterogeneous sediments and highly hydrodynamic habitats just like the outer reefs. Instead, nematodes with a bacteria-coated cuticle were more numerous in the inner reefs: this cuticle occurs in the subfamily Stilbonematinae (fam. Desmodoridae), that is often associated to sediments with low hydrodynamism and hypoxic conditions as are those found in inner reefs. The bladder-like amphid typical of Desmoscolecidae appeared relevant to discriminate the habitat of the outer reef, whereas the pocket-like amphid was definitely more represented in nematodes of the inner reefs. No literature data about the relation amphid -habitat are available, but a correlation of the amphid type with the hydrodynamic regime is likely.