| 1. |
- Eggertsen, Maria, 1981-, et al.
(author)
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Different environmental variables predict distribution and cover of the introduced red seaweed Eucheuma denticulatum in two geographical locations
- 2021
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In: Biological Invasions. - : Springer. - 1387-3547 .- 1573-1464. ; 23, s. 1049-1067
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Journal article (peer-reviewed)abstract
- In this study we examined abiotic and biotic factors that could potentially influence the presence of a non-indigenous seaweed, Eucheuma denticulatum, in two locations, one outside (Kane’ohe Bay, Hawai’i, USA) and one within (Mafia Island, Tanzania) its natural geographical range. We hypothesized that the availability of hard substrate and the amount of wave exposure would explain distribution patterns, and that higher abundance of herbivorous fishes in Tanzania would exert stronger top–down control than in Hawai’i. To address these hypotheses, we surveyed E. denticulatum in sites subjected to different environmental conditions and used generalized linear mixed models (GLMM) to identify predictors of E. denticulatum presence. We also estimated grazing intensity on E. denticulatum by surveying the type and the amount of grazing scars. Finally, we used molecular tools to distinguish between indigenous and non-indigenous strains of E. denticulatum on Mafia Island. In Kane’ohe Bay, the likelihood of finding E. denticulatum increased with wave exposure, whereas on Mafia Island, the likelihood increased with cover of coral rubble, and decreased with distance from areas of introduction (AOI), but this decrease was less pronounced in the presence of coral rubble. Grazing intensity was higher in Kane’ohe Bay than on Mafia Island. However, we still suggest that efforts to reduce non-indigenous E. denticulatum should include protection of important herbivores in both sites because of the high levels of grazing close to AOI. Moreover, we recommend that areas with hard substrate and high structural complexity should be avoided when farming non-indigenous strains of E. denticulatum.
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| 2. |
- Eggertsen, Maria, 1981-, et al.
(author)
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Different environmental variables predict distribution of the introduced red seaweed Eucheuma denticulatum in two geographical locations
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Other publication (other academic/artistic)abstract
- In this study we examined abiotic and biotic factors that could potentially influence the presence of a non-indigenous seaweed, Eucheuma denticulatum, in two locations, one outside (Kane’ohe Bay, Hawai’i, USA) and one within (Mafia Island, Tanzania) its natural geographical range. We hypothesized that the availability of hard substrate and the amount of wave exposure would explain distribution patterns, and that higher abundance of herbivorous fishes in Tanzania would exert stronger top-down control than in Hawai’i. To address these hypotheses, we surveyed E. denticulatum in sites subjected to different environmental conditions and used generalized linear mixed models (GLMM) to identify predictors of E. denticulatum presence. We also estimated grazing intensity on E. denticulatum by surveying the type and the amount of grazing scars. Finally, we used molecular tools to distinguish between indigenous and non-indigenous strains of E. denticulatum on Mafia Island. In Kane’ohe Bay, the likelihood of finding E. denticulatum increased with wave exposure, whereas on Mafia Island, the likelihood increased with cover of coral rubble, and decreased with distance from areas of introduction (AOI), but this decrease was less pronounced in the presence of coral rubble. Grazing intensity was higher in Kane’ohe Bay than on Mafia Island. However, we still suggest that efforts to reduce non-indigenous E. denticulatum should include protection of important herbivores in both sites, because of the high amount of grazing damages close to AOI. Moreover, we recommend that areas with hard substrate and high structural complexity should be avoided when farming non-indigenous strains of E. denticulatum.
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| 3. |
- Florén, Karl, et al.
(author)
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Kartering av bentiska naturvärden i Bottniska Viken
- 2018
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Reports (other academic/artistic)abstract
- Som en del i Havs- och vattenmyndighetens kartläggning av havsbotten längs svenska kusten har bentiska ekosystemkomponenter och naturvärden karterats på översiktlig nivå i Bottniska viken. Karteringen utfördes med hjälp av rumslig modellering baserad dels på befintliga biologiska fältdata, dels på biologiska data från kompletterande undersökningar samt på heltäckande lager över fysiska, kemiska och antropogena variabler. Totalt skapades 17 heltäckande kartor över vegetation och epifauna, sju kartor över infauna samt en karta över sammanlagda bentiska naturvärden.
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| 4. |
- Florén, Karl, et al.
(author)
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Kartering av marina naturvärden i Västerbottens län
- 2018
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Reports (other academic/artistic)abstract
- Som en del i Havs- och vattenmyndighetens kartläggning av havsbotten längs svenska kusten har bentiska ekosystemkomponenter och naturvärden karterats i hög upplösning i Västerbottens län. Karteringen utfördes med hjälp av rumslig modellering baserad dels på befintliga biologiska fältdata, dels på biologiska data från kompletterande undersökningar samt på heltäckande lager över fysiska, kemiska och antropogena variabler. Totalt skapades 11 heltäckande kartor över vegetation och epifauna, fem kartor över infauna, en karta över sikyngel, en karta över Helcom Underwater Biotopes (HUB) samt en karta över bentiska naturvärden.
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| 5. |
- Fulton, Christopher J., et al.
(author)
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Form and function of tropical macroalgal reefs in the Anthropocene
- 2019
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In: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 33:6, s. 989-999
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Research review (peer-reviewed)abstract
- Tropical reefs have been subjected to a range of anthropogenic pressures such as global climate change, overfishing and eutrophication that have raised questions about the prominence of macroalgae on tropical reefs, whether they pose a threat to biodiversity, and how they may influence the function of tropical marine ecosystems. We synthesise current understanding of the structure and function of tropical macroalgal reefs and how they may support various ecosystem goods and services. We then forecast how key stressors may alter the role of macroalgal reefs in tropical seascapes of the Anthropocene. High levels of primary productivity from tropical canopy macroalgae, which rivals that of other key producers (e.g., corals and turf algae), can be widely dispersed across tropical seascapes to provide a boost of secondary productivity in a range of biomes that include coral reefs, and support periodic harvests of macroalgal biomass for industrial and agricultural uses. Complex macroalgal reefs that comprise a mixture of canopy and understorey taxa can also provide key habitats for a diverse community of epifauna, as well as juvenile and adult fishes that are the basis for important tropical fisheries. Key macroalgal taxa (e.g., Sargassum) that form complex macroalgal reefs are likely to be sensitive to future climate change. Increases in maximum sea temperature, in particular, could depress biomass production and/or drive phenological shifts in canopy formation that will affect their capacity to support tropical marine ecosystems. Macroalgal reefs can support a suite of tropical marine ecosystem functions when embedded within an interconnected mosaic of habitat types. Habitat connectivity is, therefore, essential if we are to maintain tropical marine biodiversity alongside key ecosystem goods and services. Consequently, complex macroalgal reefs should be treated as a key ecological asset in strategies for the conservation and management of diverse tropical seascapes. A plain language summary is available for this article.
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| 6. |
- Fulton, Christopher J., et al.
(author)
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Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes
- 2020
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In: Fish and Fisheries. - : Wiley. - 1467-2960 .- 1467-2979. ; 21:4, s. 700-717
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Journal article (peer-reviewed)abstract
- Canopy-forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life-history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta-analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal-associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life-history stage. Major overlap (40%-43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal-associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal-associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal-associated fish and fisheries.
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| 7. |
- Halling, Christina, et al.
(author)
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The introduction of South East Asian seaweed and its ecological implications; Can native East African Eucheuma denticulatum and Kappaphycus alvarezii be a potential alternative for farming?
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Other publication (other academic/artistic)abstract
- The seaweed farming of eucheumoids in East Africa is solely based on introduced South East Asian (SEA) haplotypes of the carrageenophytes Eucheuma and Kappaphycus. As overexploitation of natural seaweed resources lead to a decline in harvest and export, commercial seaweed farming was started using highly productive SEA strains of the same genus introduced from the Philippines to Zanzibar in 1989. Initially, productivity was high, the sector grew rapidly and seaweed farming soon became an important livelihood. Today, the industry faces various challenges such as decreased productivity and high rates of diseases and epiphytic infestations. Continuous introduction of foreign stock for cultivation vitalization might not be the solution, as escapees of SEA Eucheuma denticulatum have been found spreading into natural environments around Zanzibar with uncertain ecological consequences. We suggest that indigenous haplotypes of E. denticulatum and Kappaphycus alvarezii should be re-evaluated for farming potential, for increasing the genetic diversity and hence resilience within stocks.This study is a first step towards a reassessment of farming potential of East African (EA) haplotypes. Molecularly identified haplotypes of E. denticulatum and K. alvarezii were tested in in-situ farming conditions in Zanzibar, and growth rates, grazing and epiphytes were compared between EA and SEA haplotypes. Results show, except for an overall decreased growth compared to previous studies, that growth rate was site dependent and that SEA Eucheuma haplotypes have a higher growth rate (1.3 ±1.8 - 3.6 ±1.9% per day) compared to EA haplotypes (0.2 ±1.0 - 2.0 ±0.4% per day). No significant differences were found in grazing rate between native and introduced Eucheuma haplotypes, while native Kappaphycus was more prone to grazing. In conclusion the farming potential for native E. denticulatum, is not rejected but underlines that there is an urgent need of continued search for native East African seaweed resources and a further identification of their desirable traits. If successful, this would enable East African seaweed industry to further expansion and secure its ecological and economical sustainability.
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| 8. |
- Tano, Stina A., et al.
(author)
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Extensive spread of farmed seaweeds causes a shift from native to non-native haplotypes in natural seaweed beds
- 2015
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In: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 162:10, s. 1983-1992
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Journal article (peer-reviewed)abstract
- 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.
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| 9. |
- Tano, Stina A., et al.
(author)
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Tropical seaweed beds as important habitats for juvenile fish
- 2017
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In: Marine and Freshwater Research. - 1323-1650 .- 1448-6059. ; 68:10, s. 1921-1934
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Journal article (peer-reviewed)abstract
- Seaweed beds within tropical seascapes have received little attention as potential fish habitat, despite other vegetated habitats, such as seagrass meadows and mangroves, commonly being recognised as important nurseries for numerous fish species. In addition, studies of vegetated habitats rarely investigate fish assemblages across different macrophyte communities. Therefore, the aim of the present study was to investigate the role of tropical seaweed beds as fish habitat, particularly for juvenile fish, by comparing their fish assemblages with those of closely situated seagrass beds. Fish assemblages were assessed by visual census in belt transects, where fish were identified and their length estimated, and habitat variables were estimated for each transect. The abundance of juvenile fish in seaweed beds was twice as high as that in seagrass meadows, whereas there was no difference in total, subadult or adult fish abundance. In addition, the abundance of commercially important and coral reef-associated juveniles was higher in seaweed beds, as was fish species richness. Fish assemblages differed between habitats, with siganids being more common in seagrass meadows and juvenile Labridae and Serranidae more common in seaweed beds. These results highlight that tropical seaweed beds are important juvenile fish habitats and underscore the need to widen the view of the shallow tropical seascape.
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| 10. |
- Tano, Stina, 1983-
(author)
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Seaweed in the tropical seascape : Importance, problems and potential
- 2016
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Doctoral thesis (other academic/artistic)abstract
- 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.
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