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Marine seaweed invasions: Impacts and biotic resistance in native ecosystems
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.
Keyword [en]
Plant invasion, exotic species, generalist herbivores, plant-herbivore interactions, enemy-release hypothesis, ecosystem function
National Category
Ecology
Research subject
Marine Ecotoxicology
Identifiers
URN: urn:nbn:se:su:diva-116788ISBN: 978-91-7649-176-8 (print)OAI: oai:DiVA.org:su-116788DiVA: diva2:808168
Public defence
2015-06-09, Stora föreläsningssalen, Lilla Frescati, Lilla Frescativägen 5, Stockholm, 13:00 (English)
Opponent
Supervisors
Projects
Alien-native trophic interactions: consequences for invasion success and ecosystem effects of invasions
Funder
Swedish Research Council Formas, 217-2007-534
Note

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.

Available from: 2015-05-18 Created: 2015-04-27 Last updated: 2015-05-22Bibliographically approved
List of papers
1. Divergent ecological strategies determine different impacts on community production by two successful non-native seaweeds
Open this publication in new window or tab >>Divergent ecological strategies determine different impacts on community production by two successful non-native seaweeds
2014 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 175, no 3, 937-946 p.Article in journal (Refereed) Published
Abstract [en]

The consequences of plant introductions into ecosystems are frequently reported from terrestrial environments, but little is known about the effects on ecosystem functioning caused by non-native primary producers in marine systems. In this study we explored the effects of the invasion by the two filamentous red algae Heterosiphonia japonica and Bonnemaisonia hamifera on the primary production of seaweed communities by using single and mixed cultures of non-native and native red algae. The experiments were conducted both in the presence and absence of herbivores. Biomass production of the invaded community increased more than four times in mixed cultures with H. japonica, while introduction by B. hamifera had no significant effect. The different impact on community production could be explained by differences in life history strategies between the invaders; H. japonica grew considerably faster than the native seaweeds which directly increased the community production, while B. hamifera showed a relatively slow growth rate and therefore had no effect. From previous studies it is known that B. hamifera produces a highly deterrent, but also costly, chemical defence. The assessment of survival and growth of a native generalist herbivore further corroborated that the biomass produced by B. hamifera constitutes a very low-quality food, whereas the performance of herbivores on a diet of H. japonica was comparable to that on native algal diets. In summary, this study demonstrates that successful invaders belonging to the same functional group (filamentous red algae) may have distinctly different impacts on productivity in the recipient community, depending on their specific life history traits.

Keyword
Plant invasion, Primary production, Ecosystem function, Heterosiphonia japonica, Bonnemaisonia hamifera
National Category
Biological Sciences
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-106319 (URN)10.1007/s00442-014-2938-2 (DOI)000338202600017 ()
Note

AuthorCount:4;

Available from: 2014-08-06 Created: 2014-08-04 Last updated: 2017-12-05Bibliographically approved
2. Decomposition rates differ between two seaweed invaders with different ecophysiological traits
Open this publication in new window or tab >>Decomposition rates differ between two seaweed invaders with different ecophysiological traits
(English)Manuscript (preprint) (Other academic)
Keyword
plant invasion, ecosystem function, Heterosiphonia japonica, Bonnemaisonia hamifera
National Category
Ecology
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-116785 (URN)
Funder
Swedish Research Council Formas, 217-2007-534
Available from: 2015-04-27 Created: 2015-04-27 Last updated: 2016-01-29Bibliographically approved
3. Low feeding preference of native herbivores for the successful non-native seaweed Heterosiphonia japonica
Open this publication in new window or tab >>Low feeding preference of native herbivores for the successful non-native seaweed Heterosiphonia japonica
(English)Manuscript (preprint) (Other academic)
Keyword
Plant invasion, generalist herbivores, plant-herbivore interactions, enemy-release hypothesis, exotic species
National Category
Ecology
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-116786 (URN)
Funder
Swedish Research Council Formas, 217-2007-534Swedish Research Council, 621-2011-5630
Available from: 2015-04-27 Created: 2015-04-27 Last updated: 2016-01-29Bibliographically approved
4. Competition between the non-native Fucus evanescens and the native congener Fucus vesiculosus
Open this publication in new window or tab >>Competition between the non-native Fucus evanescens and the native congener Fucus vesiculosus
(English)Manuscript (preprint) (Other academic)
Keyword
seaweed invasion, exotic species, biotic resistance, plant-herbivore interactions, Littorina obtusata
National Category
Ecology
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-116787 (URN)
Funder
Swedish Research Council Formas, 217-2007-534
Available from: 2015-04-27 Created: 2015-04-27 Last updated: 2016-01-29Bibliographically approved

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