Relationships between organic matter and benthic communities in the Atlantic and Mediterranean 

Summary

Bathyal and abyssal ecosystems cover over 60% of the earth’s surface and are thought to be hotspots of marine biodiversity. Deep-sea benthic communities are the ultimate recipients of food produced in overlying surface waters by phytoplankton and play an integral role in the global carbon reservoir. The overall aims of IP 3&4 are (1) to elucidate linkages between organic matter processing and the benthic community (2) to investigate and model trophic linkages and (3) to unravel the links between community composition, trophic structure and biogeochemical cycling. 

The five main objectives of IP 3&4 are:

1. To identify the bathyal and abyssal biodiversity of macro- and megafauna in two contrasting deep-sea environments

2. To elucidate the flow of carbon to archaea, bacteria and macrofauna using in situ enrichments with stable isotopes

3. To investigate trophic linkages within the food-web

4. To link differences in trophic structure and biodiversity to local biogeochemical functioning by quantifying the OM mineralization pathways and reconstructing the carbon sequestration scheme

5. To develop a dynamic mass balance model to describe the flow of bacterial and phytodetritus carbon and nitrogen through the entire food web 

Work Plan

Cruises

NIOZ/NIOO will lead two cruises, one to Galicia Bank, N. Atlantic (Sept/Oct 2008) and another to the Algerian-Balearic Basin (W. Mediterranean, October 2009). The aim is to sample two habitats with differing food availability, productive vs. oligotrophic at 1200, 1900 and 3000 m. Each cruise will: 

1. Map/characterize the seafloor of each area using multibeam.

2. Investigate food availability and the physical characteristics of each area using moorings equipped with sediment traps, data loggers, current meters and instruments to detect optical backscatter and fluorescence. Moorings will be deployed for 12 months.

3. Characterize the food sources available both in the water column (CTD & SAPS) and at the seafloor (multicores).

4. Determine macro and megafaunal biodiversity (Agassiz trawl and boxcores both equipped with video).

5. Benthic landers (ALBEX and the newly developed MOVE!) will be deployed to measure solute fluxes and oxygen microprofiles and to carry out baited camera experiments and in situ pulsechase experiments (Mediterranean only).

6. Long-term deck incubations will be carried out for ex situ pulse-chase experiments.

Analyses

1. Mass fluxes will be determined from sediment trap material.

2. Biodiversity, biomass and abundances of macro and megafauna will be determined from video analyses of boxcores and Agassiz trawl transects in additions to samples obtained from these instruments.

3. Trophic studies will be carried out on collected faunal and food source (e.g. sediments and water) samples using natural abundance stable isotopes (bulk and compound specific), and biomarkers such as lipids and pigments.

4. Solute fluxes and oxygen microprofiles will be measured both in situ and from sediment cores

5. Stable isotope pulse-chase experiments will be carried out with enriched phytodetritus (POM) and dissolved organic matter (DOM). POM and DOM enriched in heavy isotopes (13C and 15 N) will be added to sediment communities. Total community respiration will be measured via 13C in dissolved inorganic carbon. Assimilation and uptake of phytodetritus by infaunal organisms will be determined through measurement of 13C and 15N tissues. Carbon and nitrogen assimilation by bacteria and archaea will be based on appearance of 13C or 15N in microbial biomarkers (13C in phosphor-lipid derived fatty acids for bacteria, 13C in archaeal ether lips and 13C and 15N in Dalanine, a prokaryotic biomarker). This approach allows a direct assessment on the role of the various organisms involved and will be the first study involving all three kingdoms (archaea, bacteria and eukaryotes). To study the trophic significance of heterotrophic bacteria and archaea in a deep-sea ecosystems 13C-glucose will be added to isotopically enrich the osmotrophs (bacteria and archaea). Incorporation of 13C-glucose into archaea and bacterial carbon will be traced with above mentioned biomarkers and subsequent transfer to benthic fauna will be followed through measuring the appearance of 13C of organism tissues.

6. Biodiversity and quanti-qualitative studies on the Protistan community:  living field-obtained cultures will be used to try to obtain PLF specific markers, in order to analyze the role and the importance of protozoa in the foodweb;  DNA  extracted from field samples, coupled with DGGE technique and metagenomics will be used to get an insight of the relative abundance of the major groups, and draw the community fingerprinting.