Trophic and specific diversity of harpacticoid copepods associated to Posidonia oceanica macrophytodetritus

Extended meadows of living Posidonia oceanica plants in the Mediterranean Sea produce large amounts of detritus of dead seagrass plants that are packed at the bottom of the sea. In spite of their large quantities, these phytodetritus are of low nutritional quality (high C:N:P ratio). However, these detritus are massively colonised by bacterial communities, fungi, diatoms, meiofauna and macrofauna. This leads to the assumption that those associated communities enrich the litter and play an important role in the energy transfer to higher trophic levels like macrofauna and juvenile fish that use these accumulations as nursery and feeding grounds.
In these litter accumulations harpacticoid copepods (Crustacea) are the main meiofauna players (metazoans in the size range of 38µm – 1mm). Their families are characterised by different specialized morphologies (body form and appendages). Nonetheless their morphological differences they are all grazers and seem to feed on similar sources. Ecological theories state that diversity of trophic niches is an essential parameter to explain specific diversity. Therefore subtle trophic niches may occur among species assemblages, linked to the complexity of the phytodetritus.
In order to unravel the ecological function, trophic relations, seasonal fluctuations and habitat interactions in these litter accumulations, a bulk stable isotope analysis (SIA) is conducted. The isotopic composition of C and N of the potential food sources and the most dominant harpacticoid copepod families are measured using an EA-IRMS coupling. The results are run in a SIAR Beyesian mixing model to calculate the approximate contributions of each potential food sources towards the composition of different families of harpacticoid copepods present in the macrophytodetritus.