Short report on the MAR-ECO part of the Arni Fridriksson survey in June 2003 (summarised)
Map showing the location of the stations taken. Click for a larger map
By Thorsteinn Sigurdsson & Astthor Gislason
Photo: Photo: Einar Asgeirsso
The goal of the research cruise was to examine the organisation and tropic structure of the pelagic ecosystem over the Reykjanes Ridge from phytoplankton to fish as apex predators. Special emphasis was placed on describing and quantifying tropic interactions among copepods, euphausiids, chaetognaths and fish along a transect across the Mid-Atlantic Ridge.
The data collected will be used to estimate the biomass at the various trophic levels and the energy flow through the ecosystem. As physical factors influence the primary productivity, distribution and diel migration of species and all results will be interpreted in relation to water mass characteristics and hydrography.
Cruise track. Click for a larger map
The proposed research was carried out on the RV Arni Fridriksson as part of a redfish survey in the Irminger Sea and adjacent areas from 4-30 June 2003. One week of this period was devoted to research relating to the MAR-ECO project.
A multidisciplinary team of sixteen physical oceanographers, biologists and engineers with expertise on taxonomy, biological and technical sampling methods, hydroacoustics etc. as well as mammal experts participated in the cruise.
Technology used for monitoring the trophic interactions in the pelagic ecosystem included Multinet, WP-2, Gloria type pelagic trawl, Euphausiid trawl (Krill trawl), small phytoplankton net, CTD, echo sounder at different frequencies and other equipment. Observations included both intensive studies at five stations, and an overall mapping of water mass characteristics, phytoplankton biomass, zooplankton and nekton abundance. Samples for nutrient measurements were also collected from selected depths.
View of the whale watching tower
Preparing a CTD rosette for water sampling.
Phytoplankton: Sea water samples (1 l) for phytoplankton measurements (chlorophyll a and primary production) were taken from depths of 0, 10, 20, 30, 50, 100, 150 and 200 m with water bottles. The samples were filtered through GF/C filters for chlorophyll measurements. Seawater samples for primary production was also taken at all stations.
Zooplankton: The zooplankton was sampled with a Multinet sampler (0.25m2 opening, 180 (m mesh size) that was towed vertically from the bottom and to the surface. The zooplankton samples are preserved in 4% neutralised formalin. In addition, krill trawl was used (4X4 m, 9 mm mesh size of the cod-end) to collect Euphausiids.
During the whole survey, live zooplankton was collected with a WP2 net (0.25 m2 opening, 180 (m mesh size). The life samples were used for measuring egg production and gut fluoresecence.
Nekton: A GLORIA-type midwater trawl (46X46 m opening) with cod-end lined with 9 mm mesh net was used to sample pelagic fish, cephalopods and large zooplankton. The catch was identified onboard to species for the fishes but the zooplankton was placed in formalin or alcohol. In order to identify food remains, stomach samples were also taken from numerous species throughout the survey area. The stomach content will be analysed later.
Getting ready to fix sample in formalin. Click for a larger picture of the zooplankton sampling
Acoustic measurements: To monitor the distribution and abundance of pelagic fish and macroplankton, acoustic measurements with a Simrad EK500 echo sounder with two transducers (18 & 38 kHz) mounted on a protruding keel was used along with BI500 post-processing system.
Working in the lab on board
Nearly 50 stations were take during the MAR-ECO part of the survey, nine were with the Gloria trawl and nine with the krill trawl. Only small part of all the collected material has been studied as yet. Furthere analyses will take place over the next year. It is hoped that by comparing the results with those from another MAR-ECO project (Z1
Setting out the trawl.
Distribution, abundance's and species composition of zooplankton in cross-frontal and cross-ridge transects of the Mid-Atlantic Ridge) researchers will be able to assess if the trophic structure varies from north to south.
L. lucifera, with male attached