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Extensive spread of farmed seaweeds causes a shift from native to non-native haplotypes in natural seaweed beds
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.ORCID iD: 0000-0003-1359-703X
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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Number of Authors: 5
2015 (English)In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 162, no 10, 1983-1992 p.Article in journal (Refereed) Published
Abstract [en]

Seaweed farming has been the cause of introductions of non-indigenous seaweed species and genotypes throughout the world. In Zanzibar, Tanzania, foreign genotypes of Eucheuma denticulatum were introduced for farming purposes in 1989, and in recent years a spread of non-indigenous haplotypes has been reported. The current study aimed to investigate the presence and extent of introduced and native haplotypes of E. denticulatum as well as their relative frequencies, to obtain the severity of the spread of cultivated seaweed and the current state of the native populations. The results show that all investigated sites are dominated by the introduced South-east Asian haplotypes, even where seaweed farming has never occurred. As the frequencies of East African haplotypes are remarkably low, this shows a shift from native to introduced E. denticulatum. This shift may, at least in part, be caused by earlier overharvest of natural seaweed populations, and indicates a cryptic invasion of the introduced haplotypes at the potential cost of the recovery of the native haplotype populations.

Place, publisher, year, edition, pages
2015. Vol. 162, no 10, 1983-1992 p.
National Category
Biological Sciences
Research subject
Marine Ecotoxicology; Marine Ecology
URN: urn:nbn:se:su:diva-122757DOI: 10.1007/s00227-015-2724-7ISI: 000362322200005OAI: diva2:871699
Sida - Swedish International Development Cooperation Agency, SWE2010-052
Available from: 2015-11-16 Created: 2015-11-10 Last updated: 2016-06-30Bibliographically approved
In thesis
1. Seaweed in the tropical seascape: Importance, problems and potential
Open this publication in new window or tab >>Seaweed in the tropical seascape: Importance, problems and potential
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increasing demand for seaweed extracts has led to the introduction of non-native seaweeds for farming purposes in many tropical regions. Such intentional introductions can lead to spread of non-native seaweeds from farming areas, which can become established in and alter the dynamics of the recipient ecosystems. While tropical seaweeds are of great interest for aquaculture, and have received much attention as pests in the coral reef literature, little is known about the problems and potential of natural populations, or the role of natural seaweed beds in the tropical seascape.

This thesis aims to investigate the spread of non-native genetic strains of the tropical macroalga Eucheuma denticulatum, which have been intentionally introduced for seaweed farming purposes in East Africa, and to evaluate the state of the genetically distinct but morphologically similar native populations. Additionally it aims to investigate the ecological role of seaweed beds in terms of the habitat utilization by fish and mobile invertebrate epifauna. The thesis also aims to evaluate the potential of native populations of eucheumoid seaweeds in regard to seaweed farming.

The initial results showed that non-native E. denticulatum is the dominating form of wild eucheumoid, not only in areas in close proximity to seaweed farms, but also in areas where farming has never occurred, while native eucheumoids are now scarce (Paper I). The low frequency of native E. denticulatum in seaweed beds, coupled with a low occurrence of reproductive structures, indicates that the effective population size may be low, which in turn may be a threat under changing environmental conditions. These results, combined with indications that seaweeds may be declining in East Africa, illustrates the need for attaining a better understanding of the ecological role of tropical seaweed habitats. The studies on the faunal communities of seaweed beds showed that they are species rich habitats, with high abundances of juvenile fish and mobile epifauna (Paper II and III), strongly indicating that these habitats should be considered for future seascape studies and management actions. Productivity in East African seaweed farming is decreasing, and as the current cultivation is based on a single non-indigenous haplotype, a more diverse genetic base has been suggested as a means to achieve a more productive and sustainable seaweed farming. Although our results show that East African E. denticulatum has a lower growth rate than the currently used cultivar (Paper IV), the several native haplotypes that are present in wild populations illustrates that, though a demanding endeavour, there is potential for strain selection within native populations.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2016. 49 p.
Seaweed, Macroalgae, Eucheumoids, Non-indigenous, Haplotype, Fish, Nursery, Epifauna, Diversity, Seaweed farming, Zanzibar, East Africa, Tropical
National Category
Research subject
Marine Ecotoxicology
urn:nbn:se:su:diva-129256 (URN)978-91-7649-396-0 (ISBN)
Public defence
2016-06-08, Vivi Täckholm (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 13:00 (English)

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: 2016-05-16 Created: 2016-04-18 Last updated: 2016-05-17Bibliographically approved

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