Experimental results in Lake Mývatn (Iceland) and its relationship to climate change
Version in Spanish and Portuguese
Climate change is one of the most
important threats affecting loss of biodiversity and degradation in natural systems.
Particularly, lakes in the polar region are in the front line of research due
to their vulnerability to the rapid increase of global temperature. These lakes
have the characteristic to show simple food webs with very low trophic levels
due to the presence of few species. This implies that they are good model
systems suitable for experimental manipulations and allow to test general
predictions in relation to climate change.
Recently, members of the Aquatic Ecology group
from the University of Vic-Central University of Catalonia (UVic-UCC), leaded
by Sandra Brucet, have published a paper about food webs in polar region. A
three-month experiment was conducted in Lake Mývatn (Iceland) during the
summer of 2014, together with scientists from Aarhus University (Denmark) belonging
to professor Erik Jeppesen’s group.
The main purpose of the experiment was to
assess the predation role of a small fish (three-spined stickleback, Gasterosteus aculeatus L.) in the food
web of the lake (Fig. 1). This fish species feeds on very small aquatic
organisms called plankton (microscopic algae and animals, phytoplankton and
zooplankton, respectively), whose abundance and size can change as a result of
the predation process. However, it remains unclear whether fish predation
influences the food web of the Arctic lakes, which are nutrient-poor compared
to temperate and tropical ones. Clarifying this question is important because Artic
lakes are expected to experience an increase in temperature and nutrient concentration,
which benefit the abundance of small fish such as sticklebacks.
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Figure
1: Different individuals of
sticklebacks caught in the Lake Mývatn. Can these small
fish dominate the lake?
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The experimental set-up consisted of eight polyethylene
cylinders (a.k.a. enclosures) located in the Western part of the lake (Fig. 2).
We added sticklebacks to half of the enclosures (4 fish per enclosure) and left
the other half with no fish addition (controls). After setting similar chemical
and biological conditions in all cylinders, the experiment was run from the
20th of June to the 20th of August (a total of 61 days). Physicochemical
(phosphorus, nitrogen, temperature, oxygen etc.) and biological (macroinvertebrates,
zooplankton, phytoplankton etc.) parameters were recorded from each enclosure
every two weeks (i.e. in total five samplings).
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Figure
2. Experimental set-up in the
Western part of the Lake Mývatn.
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Our results showed that the small fish plays an
important role in controlling the abundance of other group of organisms by
decreasing zooplankton abundance and size, leading to an increase of the phytoplankton
biomass. However, unexpectedly, the blooming of filamentous cyanobacteria (Anabaena) in all enclosures after the
second sampling period masked the effects of fish predation on the food web. Because
cyanobacteria are toxic and not edible by zooplankton, they reduced the
abundance and size of zooplankton in both enclosures with and without fish. This
suggested that cyanobacteria blooms may
have the potential to interfere with the predation role of sticklebacks in
lakes. Despite the cyanobacterial bloom, an increase in the density of
sticklebacks in Lake Mývatn could have some consequences on the food web
leading to an increased abundance of phytoplankton. Our results can be applied
to other shallow lakes of polar region, where there may be stronger predation
from smaller fish and increased occurrence of cyanobacterial blooms with the
global warming.
Reference: Cañedo-Argüelles, M., Sgarzi, S.,
Arranz, I., Quintana, X.D., Ersoy, Z., Landkildehus, F., Lauridsen, T.,
Jeppesen, E., Brucet, Z. Role of predation in biological communities in
naturally eutrophic subarctic Lake Mývatn, Iceland, Hydrobiologia (2016) 790: 213-223
