Introduction

Diary

Participants

 

R/V Pelagia Cruise HERMIONE /CoralFISH
	Diary overview
Monday, 26 October	This fish Neocyttus helgae, also called Oreo was caught in our trawl in the Porcupine Bight…
Today is the last working day of the CORALFISH portion of this cruise and a very busy day it turned out to be too. We had to recover all of the landers that were currently in the water, this included both Henko’s and Thom’s landers. A hopper-camera and box core was also on the program for today. But for me there were two main tasks to complete.   The first task was to complete our collection of animals and samples for food web analysis. Nanne has spent the last few months at NIOZ trying to piece together the food webs of various different coldwater coral ecosystems.
Working out the food webs of these systems is important if we are to understand them and manage/protect them appropriately. In order to do this Nanne will measure the stable isotope ratios of the food sources e.g. sediments, plankton and organic material in the water column and the ratios of the tissues of the consumers (animals) we collect from the coral framework. We will measure the isotope ratios of carbon and nitrogen and these increase by about 1 and 3 units, respectively, in a food chain from food source to consumer. In simple terms we can see through these measurements, that ‘you are what you eat’!   So in order to finish our collection we needed to take a plankton tow using a vertical net, we did one tow at 100 m and another at 200 m below the surface of the water. In these tows we found small crustaceans called copepods and a few jellyfish. But one of the most exciting parts of the day had to be the beam trawl which we used to collect the animals living near the live coral. We carried out the trawl between two coral mounds in order to preserve the living coral on top of the mounds. When the net came back up to the surface we could see that it was bulging with a huge catch. Most of the catch included ‘coral rubble’, large pieces of dead coral but we could see on the top of this some very large fish. After spending some time searching through the rubble we found some very nice animals, these included: springy spiral black coral, a few rather fat sea stars (we think some of these eat the corals), lots of squat lobsters, anemones, Bathynectus, a crab that we have been observing in the videos, a carrier crab…these have also been seen in the videos carry sponges or corals with their hind legs, lots of Eunice these are polychaete worms that build tubes through the coral framework, Cidaris a pencil urchin (its spines look like pencils) and a couple of octopi. The fish that we caught included: rat tails, a Mora, Lepidion, Brosme, Gaidropsaurus and a very unusual diamond shaped fish called an Oreo (see the photograph) which has only been reported twice before. Once we sorted through the catch we bagged up the samples and put them in the freezer ready for Nanne to analyse back in the Netherlands.   The final task of the day was to send away the new NIOZ lander ‘Fish observatory’. For most of the day we had been busy preparing this lander, which was deployed in amongst the coral. The main task of this lander is to observe the fish living near the corals over the course of one year. In order to do this a time-lapse bait system was attached to the lander which will release a bait (sardines) every 20 days in order to attract fish so that they may be recorded on the video cameras. Also attached to the lander are a current meter, a fluorometer and a sediment trap, which, will collect the particles sinking through the water for each month of the year; this will enable us to estimate how much food is available to the corals. So, we will wait with baited breath for the cruise next year to retrieve the lander and to see the first long-term observations of fish living in cold water coral systems. Rachel Jeffreys, NIOZ.   Marc Lavalye