Meiofauna associated with coral sediments in the Maldivian subtidal habitats (Indian Ocean)

Coral reefs are important hot spots of biodiversity, but despite the problems related to their conservation, studies on meiobenthic biodiversity are scarce. This paper provides a preliminary overview of the meiofauna and nematodes inhabiting coral sediments in the outer reef and lagoon habitats of the Maldives, and investigates their relationships with micro-habitat type. The abundance and community structure of the meiofauna and nematodes reveal significant differences between stations. Coral fragments and rubble from the outer reefs seem to act as a trap for the finest sediment, which might contribute to creating a heterogeneous micro-habitat suitable for both epifaunal (Epsilonematidae and Draconematidae genera) and sediment-dwelling (Tricoma, Richtersia, Ptycholaimellus and Molgolaimus) taxa. On the other side, the lagoon’s sediments are mainly colonized by dwelling taxa, probably due to the low-flow regime that enhances the deposition of organic matter and pelite fractions. A high level of diversity was recorded in both the habitats studied. Among the factors that probably determine the high diversity in the lagoon is the presence of small biogenic structures. These are characterized by a high degree of angularity, which might add more complexity to the habitat. The nematodes reveal an overlap in the taxonomic composition between the Maldives and other geographically distant areas, possibly supporting the existence of iso-communities that are typical of the coral degradation zone. Nematode trophic composition reflects differences in availability of food resources; epigrowth and non-selective deposit feeders are dominant in the lagoon, while selective deposit and epistrate feeders are dominant in the outer reefs.