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Effects of seabird nesting colonies on algae and aquatic invertebrates in coastal waters
Stockholm University, Faculty of Science, Department of Botany. (Plant ecology)
Stockholm University, Faculty of Science, Department of Botany. (Plant ecology)
Stockholm University, Faculty of Science, Department of Botany. (Plant ecology)
(English)In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599Article in journal (Refereed) Accepted
Abstract [en]

Seabirds concentrate marine nutrients, from large marine areas, on their nesting islands. The high nutrient load may cause runoff into surrounding waters and affect marine communities in similar ways as reported from marine fertilization experiments. In order to test if cormorant colonies affect algae and invertebrates in surrounding coastal waters, we collected Fucus vesiculosus fronds, its epiphytic algae and associated invertebrate fauna near abandoned and active cormorant nesting islands and reference islands without nesting cormorants in the Stockholm archipelago in the northern Baltic Proper, Sweden. First, we showed, with δ15N analyses, that ornithogenic nitrogen provided a significant nitrogen source for algae and invertebrate consumers near islands with high nest density. Second, the nitrogen and phosphorus content of algae near active cormorant islands with high nest density was elevated and epiphytic algae increased relative to Fucus. Third, 3 of 5 invertebrate taxa (Jaera albifrons, Gammarus spp. and Chironomidae) showed increased biomasses near islands with high nest density, but contrary to earlier fertilization studies only J. albifrons increased in abundance compared to reference islands. We conclude that runoff from seabird colonies has a profound effect on primary producers and some consumers in the surrounding water, but only if the colonies exceed a certain nest density. Thus, seabirds not only affect marine communities via top-town forces as commonly assumed, but also via bottom-up forces by concentrating nutrients around their nesting islands. Consequently, seabird islands can be seen as natural fertilization experiments and give important insights in the effects of eutrophication of marine systems.

Keyword [en]
nitrogen, stable isotopes, bottom-up, eutrophication, Baltic Sea, cormorants
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-43246OAI: oai:DiVA.org:su-43246DiVA: diva2:354918
Available from: 2010-10-06 Created: 2010-10-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. The impact of cormorant nesting colonies on plants and arthropods
Open this publication in new window or tab >>The impact of cormorant nesting colonies on plants and arthropods
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Seabirds concentrate large amounts of marine nutrients on their nesting islands. This nutrient input can have large consequences for island food webs and community structure. The high nutrient load may also cause runoff into surrounding waters and affect marine communities. In my thesis, I studied the effect of cormorant nesting colonies on the stoichiometry, abundance, species richness, and species composition of plants, algae, and invertebrates on land and in costal waters and investigated if differences in the elemental composition or homeostasis can explain differences in the numerical response among invertebrate groups. δ15N analysis indicated that ornithogenic nitrogen provided a significant nitrogen source for plants and arthropods on nesting islands and around high nest density islands also for brackish algae and invertebrates. Furthermore, nutrient runoff created a potential feed-back loop to spiders via chironomids. Cormorant nutrient input changed island vegetation and increased plant P and N content and epiphytic algae:Fucus ratio, but decreased plant species richness and vegetation cover. Invertebrates responded indirectly to these qualitative and quantitative changes in their food source and habitat, but also directly to cormorant subsidies. However not all taxonomic and feeding groups were affected and responses were both positive and negative. Differences in the numerical response among taxonomic groups could not be explained by differences in the level of homeostasis, since, generally, all invertebrates were strongly homeostatic. Similarly, consumer nutrient content was a poor predictor for displayed responses. I conclude that cormorant colonies have strong impacts on island vegetation and some consumer groups. However, even if they can decrease the species richness of some organism groups on their nesting islands, they increase the habitat heterogeneity in an archipelago and thus may increase the regional species diversity.

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University, 2010. 80 p.
Keyword
seabirds, cormorants, islands, nitrogen, phosphorus, plants, arthropods, δ15N, Baltic Sea, ecological stoichiometry, species richness, species composition, numeric response
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-43165 (URN)978-91-7447-147-2 (ISBN)
Public defence
2010-11-05, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Accepted. Paper 4: Manuscript.Available from: 2010-10-14 Created: 2010-10-01 Last updated: 2010-10-18Bibliographically approved

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