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Marine Seaweed Invasions: the Ecology of Introduced Fucus evanescens
Stockholm University, Faculty of Science, Department of Botany.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biological invasions are an important issue of global change and an increased understanding of invasion processes is of crucial importance for both conservation managers and international trade. In this thesis, I have studied the invasion of the brown seaweed Fucus evanescens, to investigate the fate and effect of a perennial, habitat-forming seaweed introduced to a coastal ecosystem. A long-term study of the spread of F. evanescens in Öresund (southern Sweden) showed that the species was able to expand its range quickly during the first 20 years after the introduction, but that the expansion has been slow during the subsequent 30 years. Both in Öresund and in Skagerrak, the species is largely restricted to sites where native fucoids are scarce. Laboratory experiments showed that the restricted spread of F. evanescens cannot be explained by the investigated abiotic factors (wave exposure and salinity), although salinity restricts the species from spreading into the Baltic Sea. Neither did I find evidence for that herbivores or epibiota provide biotic resistance to the invader. On the contrary, F. evanescens was less consumed by native herbivores, both compared to the native fucoids and to F. evanescens populations in its native range, and little overgrown by epiphytes. Instead, the restricted spread may be due to competition from native seaweeds, probably by pre-occupation of space, and the establishment has probably been facilitated by disturbance.

The studies provided little support for a general enemy release in introduced seaweeds. The low herbivore consumption of F. evanescens in Sweden could not be explained by release from specialist herbivores. Instead, high levels of chemical anti-herbivore defence metabolites (phlorotannins) could explain the pattern of herbivore preference for different fucoids. Likewise, the low epibiotic colonisation of F. evanescens plants could be explained by high resistance to epibiotic survival. This shows that colonisation of invading seaweeds by native herbivores and epibionts depends on properties of the invading species. The large differences between fucoid species in their quality as food and habitat for epibionts and herbivores imply that invasions of such habitat-forming species may have a considerable effect on a number of other species in shallow coastal areas. However, since F. evanescens did not exclude other fucoids in its new range, its effect on the recipient biota is probably small.

Place, publisher, year, edition, pages
Stockholm: Botaniska institutionen , 2004. , 44 p.
Keyword [en]
biological invasions, marine, seaweed, algae, herbivory, enemy release hypothesis, phlorotannins, anti-fouling, Fucus evanescens
National Category
Ecology
Identifiers
URN: urn:nbn:se:su:diva-132ISBN: 91-7265-870-3 (print)OAI: oai:DiVA.org:su-132DiVA: diva2:189873
Public defence
2004-05-28, föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-05-06 Created: 2004-05-06Bibliographically approved
List of papers
1. Establishment of the exotic species Fucus evanescens C. Ag. (Phaeophyceae) in Öresund, Southern Sweden
Open this publication in new window or tab >>Establishment of the exotic species Fucus evanescens C. Ag. (Phaeophyceae) in Öresund, Southern Sweden
2002 (English)In: Botanica Marina, ISSN 0006-8055, E-ISSN 1437-4323, Vol. 45, no 6, 510-517 p.Article in journal (Refereed) Published
Abstract [en]

The spread and establishment of the exotic species Fucus evanescens in öresund, Southern Sweden was documented through inventories in 1966–72 and 2000. The species spread fast from the first known introduction in 1955, colonising harbours along the coast. After this expansion the further spread has been limited and the species is still largely confined to harbour areas, where it occurs in the same depth zone as its native relatives, F. vesiculosus, F. serratus and Ascophyllum nodosum. It is more common in the northern part of the area and has not expanded into the Baltic Sea proper. Tests of the attachment strength of F. evanescens plants suggest that the restriction to harbours is not due to the direct effects of wave exposure on adults. In the laboratory, reproductive success of F. evanescens decreased from 99% in 24 psu to 12% in 10 psu and at lower salinity reproduction failed. Growth of embryonic recruits was similarly affected by salinity. Hence, low salinity explains the limited success of F. evanescens in southern Öresund, where the salinity is low and fluctuating, and its failure to colonise the Baltic Sea proper.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-22994 (URN)
Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2017-12-13Bibliographically approved
2. Invasion of a habitat-forming seaweed: effects on associated biota
Open this publication in new window or tab >>Invasion of a habitat-forming seaweed: effects on associated biota
2004 (English)In: Biological Invasions, ISSN 1387-3547, E-ISSN 1573-1464, Vol. 6, no 2, 141-150 p.Article in journal (Refereed) Published
Abstract [en]

Fucus evanescens is a brown alga of arctic origin that has invaded European coasts. The epiphytic community of F. evanescens in southern Sweden was compared with that of the native Fucus vesiculosus, to examine to what extent an invading seaweed can modify local biodiversity. F. evanescens was much less fouled than F. vesiculosus, supporting both less biomass and fewer species of epiphytes. Multivariate analysis of the most common epiphyte taxa showed that the epiphytic community composition of F. evanescens was not entirely separated from that of F. vesiculosus, but host species contributed significantly to explain the variation in community composition. The biomass of free-living invertebrates was also lower on F. evanescens, although the pattern differed between taxonomic groups. While the biomass of amphipods was lower on F. evanescens, there was no significant difference in biomass of isopods or gastropods between the Fucus species. The good correlation between biomass of epiphytes and free-living animals suggests that the epiphytes play an important role in providing a suitable habitat for many species of free-living epifauna. The study shows that the invasion of F. evanescens affects the environmental conditions for many species associated with the Fucus community but that the direct effect on biodiversity is probably low.

Keyword
epifauna, epiphytes, Fucus evanescens, Fucus vesiculosus, host specificity, introduced species, invasion
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-22995 (URN)10.1023/B:BINV.0000022132.00398.14 (DOI)
Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2017-12-13Bibliographically approved
3. Evaluation of the enemy release hypothesis for an invading seaweed
Open this publication in new window or tab >>Evaluation of the enemy release hypothesis for an invading seaweed
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-22996 (URN)
Note
Part of urn:nbn:se:su:diva-132Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2010-01-13Bibliographically approved
4. Chemical settlement inhibition versus post-settlement mortality as an explanation for differential fouling of two congeneric seaweeds
Open this publication in new window or tab >>Chemical settlement inhibition versus post-settlement mortality as an explanation for differential fouling of two congeneric seaweeds
2004 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 138, no 2, 223-230 p.Article in journal (Refereed) Published
Abstract [en]

It has been proposed that seaweed secondary metabolites, e.g. brown algal phlorotannins, may have an ecologically important function as a chemical defence against epiphytes, by acting against colonisation of epiphytic organisms. We tested whether the low epiphytic abundance on the invasive brown seaweed Fucus evanescens, compared to the congeneric F. vesiculosus, is due to a more effective chemical defence against epiphyte colonisation. A field survey of the distribution of the common fouling organism Balanus improvisus (Cirripedia) showed that the abundance was consistently lower on F. evanescens than on F. vesiculosus. However, contrary to expectations, results from experimental studies indicated that F. vesiculosus has a more effective anti-settlement defence than F. evanescens. In settlement experiments with intact fronds of the two Fucus species, both species deterred settlement by barnacle larvae, but settlement was lower on F. vesiculosus both in choice and no-choice experiments. Phlorotannins from F. vesiculosus also had a stronger negative effect on larval settlement and were active at a lower concentration than those from F. evanescens. The results show that Fucus phlorotannins have the potential to inhibit settlement of invertebrate larvae, but that settlement inhibition cannot explain the lower abundance of the barnacle Balanus improvisus on F. evanescens compared to F. vesiculosus. Assessment of barnacle survival in the laboratory and in the field showed that this pattern could instead be attributed to a higher mortality of newly settled barnacles. Observation suggests that the increased mortality was due to detachment of young barnacles from the seaweed surface. This shows that the antifouling mechanism of F. evanescens acts on post-settlement stages of B. improvisus.

Keyword
Antifouling, Balanus improvisus, Epiphytes, Fucus, Phlorotannins
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-22997 (URN)10.1007/s00442-003-1427-9 (DOI)
Available from: 2004-05-06 Created: 2004-05-06 Last updated: 2017-12-13Bibliographically approved

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