Introduction

R/V Pelagia Cruise BIOSYS / HERMES-D

INTRODUCTION

During the cruise aspects of the ecology and biology of cold water coral reefs in the NE Atlantic Ocean will be studied. On the SE slopes of the Rockall Bank� (350 nautical miles WNW from Ireland) mounds occur which can reach heights of up to 350 m with their tops at ca 500-600 m below sea level. These mounds harbor an unexpectedly rich and diverse bottom community of living stony corals, sponges, bryozoa, hydroids, crabs, fishes etc. resembling an oasis in the desert (oligotrophic ocean). The question is where these organisms get their nutrition from (basis of the food web) and why these communities are so diverse. After all, these organisms live here in utter dankness between 500 and ca 800 m depth, where there is no primary production of algae directly available as food (energy). Primary production drives the productivity in shallow water tropical coral reefs (tropical corals and sponges live in symbiosis with algae, which require light for the synthesis of organic matter). In the dark, organisms basically depend on organic matter which reaches them through the water column (transport), and/or they depend on gas or other compounds which seep from the bottom (eg methane). The diversity of organisms on deep water coral reefs is surprisingly high. This suggests that there are special environmental conditions, which support these deep water coral reef communities. Study of the food web complexity (who eats what, and who eats who) should reveal the basis of the food web of these systems. The availability of food for the benthic community and food preferences by corals will be investigated besides trophic relations between different organisms of the benthic community. Detailed studies will be made of the associations between invertebrates and microorganisms. Coral and sponge associated microorganisms produce biomass/organic compounds, which may become available to their hosts in addition to the food particles which corals/sponges capture/filter from the passing water. Corals offer food, a place to live in and on (dead coral skeleton provides a hard substratum for settlement of other organisms and shelter) and corals are therefore considered to play a key role in the food web, the diversity and the functioning of deep water coral reefs.�
For analyses and experiments we collect bottom water and material from the bottom with so called boxcores. A boxcore grabs a small intact piece of the bottom (0.2 m2 each time) and is subsequently hauled on deck of the research vessel. The distribution of living coral communities is inventoried by under water video. To measure environmental conditions and biological activity in situ we use stand alone tripod landers on the bottom. Landers are equipped with sediment traps, current velocity meters, water clarity transmission meters, incubation chambers, water sampling devices etc. and will provide us with crucial information about the variations in environmental conditions of these deep water coral reefs.