Kristine Engel Arendt:
Plankton community structure in a West Greenland fjord - influenced by the Greenland Ice Sheet

Date: 01-10-2011    Supervisor: Per Juel Hansen

Ongoing climate change in the Arctic has received a lot of attention in recent years. Knowledge about the effects on ecosystems, however, is often limited by lack of datasets and poor understanding of basic ecological processes.

Greenlandic fjords are located at the junction between the Greenland Ice Sheet and the ocean. Discharge from the Ice Sheet, runoff from surrounding land and the interaction with large scale circulation systems of the ocean makes Greenlandic fjords sensitive to future climate change and changes would probably alter the function of the fjord food web. Despite this obvious influence of climate change to fjords and there central role for the Inuit culture the fjords of Greenland are in general understudied. Biological studies of species composition, abundances, biomass and basic ecological understanding remains very incomplete.

This PhD thesis describes studies of plankton community structure and its function in West Greenland waters. The focus is laid on the differences between offshore and fjord system and describes how the pelagic food web of the fjord differs from what is in general observed in Arctic offshore areas.

The studies revealed huge differences in plankton community composition and hereby function of the food web in offshore towards fjord system. The biomass of small copepods is surprisingly high in the fjord. Pseudocalanus spp. dominates the inner fjord in spring and high biomasses of Microsetella norvegica (Fig. 1B) enhance the biomass of particular small copepods in summer. Together with high biomasses of rotifers these small zooplankton species seem to be well adapted to the fjord environment. Whereas, the larger copepods Calanus is found at higher biomass offshore than in the fjord. On an annual basis the outer fjord mouth is found to be dominated by the small copepod M. norvegica and copepod biomass peaks as late as in August. Large Calanus copepods are found to be an important grazer on the spring phytoplankton bloom as in other Arctic areas. Though, these studies contradict the traditional emphasis of Calanus as the main grazer on an annual basis. Instead the studies demonstrate that small copepods can be a key component in Arctic fjord environments on an annual basis.

Concentration of suspended sediments is high in the fjord, however, suspended sediments cannot solely explain the spatial distribution of plankton communities. Instead ocean-fjord-glacier interactions through its potential ability to prolong the productive season of the primary producers are suggested as an important driver for the findings.