Marine seaweed invasions: Impacts and biotic resistance in native ecosystems
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Marine seaweeds constitute one of the most productive plant systems known on Earth and a rich fauna including juvenile fish and crustaceans is dependent on the habitats they form. Human influence on marine costal ecosystems has resulted in large scale changes to the abundance and distribution of species, where species introductions constitute an obvious part. The aims of this thesis were to 1) explore how non-native seaweeds impact on ecosystem functions (primary production and decomposition), and 2) study how interactions between non-native seaweeds and native communities affect invasion success. I used a combination of laboratory assays, outdoor mesocosms and field experiments.
Paper I and II revealed that the impact on ecosystem functions were substantially different depending on the identity of the invader. The highly successful non-native red alga Heterosiphonia japonica had a large effect on community productivity. Due to the rapid growth of the invader, the primary production increased by more than four times in mixed species communities with the invader compared to communities with only native species. In contrast, the morphologically similar and equally successful non-native red alga Bonnemaisonia hamifera grew slowly and had no effect on community production. But B. hamifera produces a potent defense compound that deters native herbivores and reduces the growth of micro-organisms. As a direct or indirect effect of this chemical defense, the litter from B. hamifera decomposed considerably slower compared to native seaweed litter. Rapid growth and defense against predation are likely important in explaining how the two invaders have become successful in the invaded range. These results show that traits related to invasion success may determine impacts on native communities.
Paper III shows that the rapidly growing invader H. japonica is avoided as food by native herbivores, which likely enables the invader to survive during colder seasons with sub-optimal growth conditions.
In paper IV I found that competition from the native brown alga Fucus vesiculosus decreased growth of the non-native congener Fucus evanescens. Native herbivores caused more damage to the native competitor but it did not relieve F. evanescens from competitive pressure. Several native brown algae grow in the niche of F. evanescens, which may explain why the species only is growing sparingly in the invaded range. The results indicate that competition with native seaweeds have potential to reduce the success of non-native seaweeds in the new range.
In summary, this thesis shows that non-native seaweeds differ strongly in their effect on ecosystem functions. Knowledge of which traits are present among abundant non-native species and how these traits relates to different effects may enable us to gain a better understanding of invasion impacts on native communities. The thesis also highlights that competitive interactions can be of importance for invasion success in seaweed communities.
Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2015. , 27 p.
Plant invasion, exotic species, generalist herbivores, plant-herbivore interactions, enemy-release hypothesis, ecosystem function
Research subject Marine Ecotoxicology
IdentifiersURN: urn:nbn:se:su:diva-116788ISBN: 978-91-7649-176-8OAI: oai:DiVA.org:su-116788DiVA: diva2:808168
2015-06-09, Stora föreläsningssalen, Lilla Frescati, Lilla Frescativägen 5, Stockholm, 13:00 (English)
ProjectsAlien-native trophic interactions: consequences for invasion success and ecosystem effects of invasions
FunderSwedish Research Council Formas, 217-2007-534
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.2015-05-182015-04-272015-05-22Bibliographically approved
List of papers