ORNITHOGENIC ENRICHMENT OF THE HIGH ARCTIC MARINE COASTAL FOOD WEB

Nitrogen stable isotope ratio (δ15N) is the most commonly used proxy for estimating
ornithogenic enrichment of biota and ecosystems. Elevated δ15N values in the vicinity of a
seabird colony result from the isotopic fractionation of N with progression through the
marine food web of which seabirds are the top predators (feeding on large zooplankton and
fish), and after ammonia volatilization from deposited guano.
Seabirds play a key role in Arctic terrestrial ecosystems by delivering great amount of
organic matter and nutrients of marine origin to the colony surroundings, thus stimulating
development of extraordinarily lush and rich tundra there. Considerable fraction of these
nutrients is trapped by terrestrial ecosystem but the rest returns to the sea, possibly
constituting a locally important resource for the marine coastal food web near the bird
cligs. However, the exact role and importance of the ornithogenic supplies for the marine
nearshore communities remains unknown.
We present results of the studies conducted in the coastal zone beneath bird cligs at
Bjørnøya and Bellsund (Svalbard). Along distance from the cligs (between 50 and 200 m)
and depth (down to 22 m) we (i) tracked changes in seabird-derived resources for marine
producers by measuring sea water chemistry, (ii) followed the flow of the ornithogenic
nutrients concentrated around the colonies by measuring δ15N in the successive trophic
levels of the coastal food web (POM, SOM, and benthic producers and consumers of
digerent feeding modes), and (iii) depicted changes in species composition of planktonic
protists, mesozooplankton, and benthic algae and invertebrates.