Project title: The ecological function of mosses in high-arctic Greenland lakes
Period: 2010 – 2014
Funding: The Danish National Research Foundation
Objectives
The overall objective of the project is to describe the ecological function of aquatic mosses in high-arctic
lakes with low nutrient availability and short food chain. More specifically we will determine growth and
photosynthetic rates of mosses in different water depth in lakes, and test the hypothesis that mosses
constitute a significant food resource for benthic animals in high-arctic lakes. Moreover, we will test a
reconstruction method previously used for estimating growth rates of high-arctic aquatic mosses in order
to describe the influence of climate variations.
Background
Aquatic mosses are often the only kind of macrophytes in high-arctic lakes. Despite the low nutrient
availability and short ice free periods the mosses often create massive stands on the lake bed even in
deeper lakes. The mosses most likely constitute an important component in the overall ecology of the lakes
as primary producers and food resource for secondary producers, and thereby as important organisms in
carbon and nutrient cycling.
We expect that the growth of mosses is controlled by light, temperature and nutrient
concentration in the lakes but it is unknown to what extent each of these factors are important. Laboratory
experiments of growth on arctic aquatic mosses in relation to phosphorous and nitrogen concentrations in
the water revealed a surprisingly high extension growth on >5 cm during 2 months incubation at optimal
light, nutrient and temperature conditions (Riis et al. 2010). Previous studies of the mosses growth using
reconstruction techniques only showed annual growth of about 1 cm (Sand-Jensen et al. 1998). Both the
laboratory experiment and the reconstruction method have, however, limitation when determining growth
rates of mosses in the lakes. Regarding the laboratory experiment it is always uncertain when extrapolating
data from the laboratory to the field conditions, because many additional factors can influence growth in
the field compared to controlled laboratory experiments. Regarding the reconstruction method it is also
connected with uncertainties. The reconstruction technique is based on differences in the size and density
of leaves on the moss plants’ stems (Riis and Sand-Jensen 1997, Sand-Jensen et al. 1999). In a temperate
lake we know that this growth pattern reflects temporal differences during a year such that leaves are
longer and denser in summer compared to winter (Riis and Sand-Jensen 1997). Therefore, the annual
growth in the temperate lake could be identified on individual moss plants (Riis and Sand-Jensen 1997,
Sand-Jensen et al. 1999). For using the reconstruction technique in high-arctic lakes it is, however, also
important to directly relate the growth pattern to annual growth measured on moss individuals incubated
in the lakes. In the proposed study we will measure moss growth and growth pattern in situ over a year in
high-arctic lakes, which allows us to test the reconstruction technique as well as to determine in-situ
growth rate and relate it to physical and chemical conditions in the lake.
Grazing on moss plants in lakes is traditionally assumed to be of marginal importance. However,
because food resources are scarce in high-arctic lakes it is likely that moss is an important food resource for
benthic invertebrates. For example moss parts in the guts of the arctic tadpole shrimp Lepidurus arcticus
have been found (Christoffersen 2001). There are only few studies that quantify the grazing on moss and
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their periphyton. Here we will test the hypothesis that mosses in high-arctic lakes constitute a significant
food resource for benthic invertebrates.
Overall the project will contribute to evaluate the importance of aquatic mosses in the carbon and
nutrient cycling in high-arctic lakes as well as develop an easy and inexpensive method to study moss
growth over extended periods. These aspects are important when evaluating the ecosystem structure and
function in high-arctic lakes now and in the future. The consequences of climate change on the
phytoplankton in high-arctic lakes have recently been described (Christoffersen et al. 2008), but because
the ecology of the mosses are only poorly known it has so far been impossible to predict the effect of
climate change on the ecological role of high-arctic aquatic mosses.
Referencer
Christoffersen, K. (2001). Predation on Daphnia pulex by Lepidurus arcticus. Hydrobiologia 442: 223-229.
Christoffersen, K. S., Amsinck, S. L., Landkildehus, F., Lauridsen, T. L., & Jeppesen, E. (2008). Lake flora and fauna in
relation to Ice-melt, water temperature and chemistry at Zackenberg. In: High-arctic ecosystem dynamics in a
changing climate. Ten years of monitoring and research at Zackenberg. Eds. H. Meltofte, Christensen, T. R., Elberling,
B., M. C. Forchhammer & M. Rasch. Advances in Ecological Research, 40, Academic Press. pp. 371-390
Riis, T., Sand-Jensen, K. (1997) Growth reconstruction and photosynthesis of aquatic mosses: influence of light,
temperature and carbon dioxide at depth. Journal of Ecology, 85, 359-37
Riis, T., Olesen, B., Katborg, K. K., & Christoffersen K. S., (2010). Growth of an aquatic bryophyte (Warnstorfia fluitans
(Hedw.) Loeske) from a High Arctic lake: effect of nutrient concentration. Arctic, 63, 100-106.
Sand-Jensen, K., Riis, T., Markager, S., Vincent, W.F. (1999) Slow growth and decomposition of mosses in Arctic lakes.
Canadian Journal of Fisheries and Aquatic Sciences, 56, 388-93.
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