The function of meiofauna and the importance of their biodiversity in contrasting southern European deep-sea environments

Aims and objectives

The overall aim of this study is to identify the role of meiofauna in the C flow through benthic deep-sea sediments of the Mediterranean in relation to their biodiversity. In order to unravel the link between meiofaunal biodiversity and function, it is essential to reveal the interactions in the benthic food web and the trophic position of different meiofauna taxa and functional groups at different locations with contrasting food input. Only in this way we can contribute to the understanding of deep-sea ecosystem functioning, and to the conservation of deep-sea ecosystems in a changing environment. In order to achieve this overall aim we identified five specific objectives which fit into 5 of the 6 main objectives of the BIOFUN project:

1. The description of the biodiversity of the meiofauna, especially Nematoda. Interpretation of the biodiversity in a geographical and bathymetrical context in relation to environmental factors and geological barriers. The bathyal (and abyssal) biodiversity of the meiofauna in contrasting deep-sea environments will be studied. Furthermore, the biogeography of some dominant meiobenthic taxa will be investigated.

2. To allocate the Carbon flux to meiofauna in an experimental approach

3. To investigate the trophic interactions in the meiofauna undertaking stable isotope and fatty acid analyses  

4. To make the link between biodiversity and functioning in meiobenthic communities  

5. To contribute to ecotrophic models

Analyses

1. Biodiversity and biogeography analysis

Samples for biodiversity analysis will be collected at three geographical locations (East and West Med basin and Atlantic Galicia Basin) and at minimum two water depths (between 1000 and 3000 m). Additional locations for biogeographical analysis will be sampled along a trans-Mediterranean transect. At these three sites the biodiversity of meiofauna, and in particular nematodes as dominant taxon of the metazoan meiofauna (representing > 90 %) will be analyzed up to species level. Since most of the deep-sea nematodes are new to science and since the dominant genera are characterized by a high species richness, all species within the most dominant genera present at all locations will be taxonomically identified in order to study the spatial turn-over and biogeographical patterns within these dominant genera. Samples from the same locations will be analyzed for molecular analysis by UNIVPM in order to allow a comparison of biodiversity patterns based on molecular and morphological data. Meiofauna biodiversity data will also be collected by HCMR and UNIVPM. Integration of these data in a larger dataset will extend the geographical range and available taxonomic information.

Working on board R/V Belgica, in the NE Atlantic, June 2008. © Ellen Pape 

2. Natural biomarker analysis

At each site meiofauna samples will be collected for analysis of natural biomarkers. Different meiofauna taxa will be analyzed separately. Nematodes will be analyzed in bulk but also sorted according to body size, depth in the sediment, morphology of the buccal cavity and other functional criteria. Additional samples for overall sediment biomarker composition will be processed, while biomarker composition of sediment trap material will be available too (CEFREM). For all these components of the BBL, stable isotope ratios will be investigated in addition to lipid composition (in collaboration with NIOO).

3. Enrichment experiments

During these experiments ¹³C or¹⁵N labelled benthic bacteria or epipelic diatoms (preferentially collected from sediment traps) will be added to the sediment and incubated for several days. In this way food pulse events are simulated which allows to follow up the uptake of label (food) by different meiofauna taxa (selectivity) and to quantify the carbon flow from these different nutritional sources to particular taxa or groups (Middelburg et al, 2000) Label incorporation will be measured by stable isotope analysis of selected meiofauna taxa. During the experiments changes respiration and SCOC will be monitored (in collaboration NIOO). Experiments will be performed in situ by means of ROV or lander technology. However, nematodes communities have proved to persist for longer time (several weeks) in mesocoms conditions if retrieved quickly from water depths above 2500 m (personal observations) and kept in lab conditions of atmospheric pressure, and in situ temperature and oxygen. Therefore parallel to some of the in situ experiments, lab mesocosm studies will be performed, allowing long term uptake.