Deep-sea metazoan diversity in relation with ecosystem functioning

UNIVPM-DiSMAr

Aims and objectives

Benthic faunal diversity provides an ideal tool for exploring the relationships between biodiversity and ecosystem functioning, and among benthic faunal taxa, nematodes are ideal model for deep-sea investigations. Nematodes are indeed the most abundant metazoans on Earth, but in the deep sea they are even more important accounting for more than 90% of the total abundance of metazoa. This phylum is also characterised by: i) very high species richness (i.e., among the most diverse of marine Phyla); ii) distinct and easily recognisable feeding type and iii) life strategies that make it possible to also identify functional diversity traits.

We identified the following key tasks:

1)      Diversity distribution, community structure, abundance and biomass of metazoan meiofauna and identification of nematodes to species level.

2)      Physico-chemical characteristics of the water column and of the sediment-water interface (down to 20 cm depth).

3)      Biochemical and biogeochemical analyses, quantification of the organic matter bioavailable to consumers in deep-sea sediments

Work plan

Field work: Oceanographic cruises planned in spring-summer of 2008 and 2009. In order to make comparable these data with those collected in other previous occasions from deep-sea sites and hierarchical sampling strategy and sampling at fixed depths will be endorsed. At each sampling site, triplicate deployments of box-corer or multiple corers will be carried out. This hierarchical sampling strategy will provide the opportunity to assess the pattern of spatial variability in meiofaunal, abundance, biomass and diversity. The same sampling strategy will also help to assess spatial variability in the quantity, biochemical composition and bioavailability of meiofaunal food resources.

Analyses: Sediment subsamples will be collected from independent deployments of the box- or multiple corers will be stored at -20°C until the analysis of the quantity and biochemical composition and bioavailability of the sediment organic matter. These sediments will be analysed in terms of chloroplastic pigments (chlorophyll-a and phaeopigments) and of total and enzymatically hydrolyzable protein, carbohydrate and lipid concentrations (spectrophotometrically). The sum of total protein, carbohydrate and lipid C will be reported as the biopolymeric fraction of sedimentary organic C, whereas the sum of the enzymatically digestible fractions of protein, carbohydrate and lipid C will be reported as the bioavailable fraction of biopolymeric C, and will be utilised as an estimate of the bioavailability of organic C for meiofauna.

Additional sediment samples will be used for the meiofaunal study. Sediment cores obtained from separate corer deployments will be sliced into five horizons (0-1, 1-2, 2-3, 3-5, 5-15 cm) and analysed for meiofaunal abundance. Meiofauna will be extracted according to standard protocols and counted and identified to major taxa under stereomicroscope. Replicate sediment samples will be utilised for nematode extraction and analysis. Nematodes will be sorted and identified to genus and, when possible, to species level. A subsample of the nematodes extracted from each core and sediment layer will be utilized for diversity analysis based on molecular tools.