The economy of Greenland is to a large extent dependent upon income from fisheries. About 93% of the national income is based on export of fish products, and of this approximately 68% is coming from export of shrimps. To allow a sustainable utilisation of these resources, knowledge about the trophic transfer of energy from the primary producers to shrimps and fish larvae is essential. The Disko Bay (Western Greenland) is one of the most productive areas in Greenland and the target for a large research project on trophic transfer in the pelagic.

The role of bacteria in Arctic pelagic ecosystems has been discussed during the last decade. Arctic bacterial communities may quickly respond to phytoplankton blooms. For instance, in the Disko Bay the most important single event in the productive cycle is the spring phytoplankton bloom which starts in May when the sea-ice breaks up. About 75% of the annual primary production is channelled through the bacterial trophic level. A detailed understanding of the processes that regulate how much of the primary production is channelled directly to higher trophic levels, lost to the aphotic zone during stratification of the water body or regenerated by the pelagic bacteria (and hence refuelling the primary production), is required to be able to properly manage the fishing resources.

The National Environmental Research Institute in Roskilde, Denmark, invited us to participate in a field study which hopefully will develop into a longer project within the Nordic Arctic Research Programme 1999-2003–Rapid Changes in the Arctic. Our main objective was to study the fate of the spring bloom in Disko Bay and in particular the role of appendicularians. These pelagic tunicates are unique in that they can feed on the smallest picoplankton, including bacteria. Furthermore they build a unique mucus house that they leave after it has become fouled with particles. This takes 4–6 hours and the abandoned houses rapidly sink to the bottom, thus forming a significant pathway for organic carbon from surface waters to the benthos. Three researchers from Kristineberg Marine Research Station took part in the project, and two of us planned to work on sedimentation and appendicularians.

Field-work

After a magnificent journey to the Danish field station Arktisk Station on the southern shore of Disko, we started a field sampling programme on 1 June. The vessel was a small traditional fishing cutter with a single cylinder engine and we had to mount winches and rigging to fit our sampling needs. The basic programme consisted of steaming to a 300 m deep station 1 hour south of Godhavn, taking samples for chemistry and biology for 6 hours and then returning to the lab. While sampling we deployed drifting sediment traps which we recovered before steaming back. At the lab, incubations of copepods were set up and we measured egg production, fecal pellet production and grazing rates. As we were part of a bigger team (12 people), a large dataset was created at each sampling occasion. The sampling was then repeated every 2–3 days for one month, but we only participated in the first two weeks.

The weather was favourable most of the time and the midnight sun made it possible to work at any time of the day or night. The spring moved very rapidly while we were there: at our arrival there was meter thick snow around the lab, but with constant sun the ground was bare when we left. Flowers and grasses had just begun growing fast and the ground was markedly warm. We were very successful in our field-work and in particular, the deployment of sediment traps. Unfortunately, we found no appendicularians. Since their occurrence at Disko had never been investigated before, we had relied on colleagues working east of Greenland at the same latitude. They classified our waters as ”Appi paradise with animals big as fists”! This may be so east of Greenland, but not here. During the entire month we only caught one small animal. For comparison, appendicularians can equal or outnumber copepods in boreal waters during summer. My focus and that of Erik consequently moved to the sediment trap part of the study, as well as the rate measurements on copepods.

It is a fantastic experience to work with such large animals as the dominant copepods in Disko Bay. Their lengths range from 3–10 mm, in contrast to our Swedish species which never exceed 8 mm and most of the time are less than 1 mm. Working at 0°C and with a chlorophyll vertical distribution very different from home waters is also very interesting. The spring bloom in these waters starts as soon as the seasonal ice melts and then rapidly depletes surface waters of nutrients. As a consequence, the phytoplankton biomass and production moves deeper and deeper until light becomes limiting. We arrived at the peak of the bloom, with chlorophyll concentrations ranging 10–30 mg m^-3 in the subsurface peak at 25 m. After a month the peak was still there, but with values lower than 2 mg m^-3.

If the appendicularian work can be considered a failure, the sediment trap work was a success. Our deployments are the first of their kind in Disko Bay and we have good data from 10 cruises with replicate traps at 15, 30, 50 and 100 m. A trap consists of a 50 cm long, 6 cm diameter plastic cylinder with a lead weight in the bottom. The trap is attached to a vane with a gimble thereby pointing the trap into any current. The rigs are attached to a rope and the whole array deployed free drifting. It is a matter of intricate balance and design to make the traps hang at the right depth and avoid pumping of the system by surface waves. Thus the system is suspended by 15 small buoys, of which 8 should be allowed to hang below the surface. The good quality of the sedimentation data is entirely dependent on this and we were fortunate in that the design proved usable in the field.