Biodiversità ed ecologia della meiofauna marina in ambiente subtidale delle Maldive, con particolare riferimento ai nematodi

Meiofauna is applied as an important ecological indicator to understand how human activities can affect the natural enviroment. Maldivian atolls in fact are rapidly changing due to the increase of human impact and the effects of climate change, that also lead to a variations of the distribution and diversity of the benthic communities such as meiofauna (Semprucci et al 2014). The aim of the study was to increase the knowledge of the meiofaunal communities of the Maldives, in particular those of the subtidal habitat that are currently almost unknown (Semprucci et al 2013). Previus studies focused their attention on meiofaunal communities of back-reef platform and lagoons, whereas during this study I analysed samples coming from the reef slopes with a particular attention to the outer and inner reefs. Samples were collected in May 2013 from three different atolls: North Malé, South Malé and Felidhoo at different depths, inclinations and habitat, in three replicates at each sampling station. Samples collection was performed by a Scuba diver who pushed a plexiglass corer tube of 2cm in diameter, in to the sediment for 5 cm. The samples were treated with a solution of 7% Mg Cl2 to relax the animals and a solution of formalin to fix and some drops of Bengal Rose to stain them. In laboratory the meiofauna was extracted from samples by sieving them through a 42-500 μm mesh net, followed by flotation and multiple decantation. Samples were then centrifugated in silica gel gradient and subsequently transferred in Delfuss Petri dishes and counted and sorted by taxa under a stereomicroscope and Delfuss petri dish. I performed a multivariate statistical analyses on the data obtained. The similarity analysis (ANOSIM) was performed to check the difference between the meiofaunal communities. The highest level of dissimilarities in the meiofaunal communities were revealed for the factor “habitat” (external or internal reef) (p=0.006), followed by “depths” (p=0.002) while “inclinations” and “atolls” resulted to be less significant (p>0.05). I also calculated the curves of k-dominance for each factor; for the habitats, the external reef proves to be the one with the highest diversity, in the case of atolls the diversity resulted greater at South Malé, and again the diversity is higher at lower dephts and greater inclinations. During the last year, I focused on the deepening of the study one of a dominant group of meiobenthic animals: nematodes. Recently the interest in the use of marine nematodes as bioindicators in ecological assessments has greatly increased (Semprucci et al., 2018). I also proposed to identify the morpho-functional characters of the species of nematodes encountered the Maldives to understand if those can be interpreted as adaptations to different typologies of habitat (Semprucci et al., 2018). For the study of the morpho-functional adaptations we realized permanent slides of nematodes. About 100 nematode specimens were removed randomly from each replicate and transferred into a capsule containing a 5% aqueous Glycerine solution; then latter was then put at 50 °C for 48 hours. Nematodes were transferred into a drop of pure glycerine on a slide within a paraffin ring and finally covered with a cover glass. The specimens were identified using a stereomicroscope that allowed us to classify them at genus level using the pictorial guides of Platt and Warwick (1983, 1988) and Warwick et al. (1998) and the NeMys online identification key (Guilini et al., 2016). The uni and multi-variate analysis conducted on the morfo-functional adaptations highlighted interesting relationship between these traits and the habitat in particular for the amphids and the cuticles (characters that have been little considered till now).