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Influence of mangrove deforestation on trophic organization of fish assemblages in creek systems
Stockholm University, Faculty of Science, Department of Zoology. (Ecology)
Stockholm University, Faculty of Science, Department of Zoology. (Ecology)
Stockholm University, Faculty of Science, Department of Zoology. (Ecology)ORCID iD: 0000-0001-5535-9086
(English)Manuscript (Other academic)
Abstract [en]

The mangrove biotopes in Tanzania are under increasing pressure from domestic uses and changes in land-use for aquaculture and solar salt farms. To investigate the impacts of man-made activities on trophic structure of mangrove-associated fish species, sampling of fish from various trophic groups was performed in mangrove creeks. Trophic organization and stable isotope signatures (δ 13C and δ 15N) of fish in undisturbed areas of mangrove creeks were compared with clear-cut areas of mangrove as well as with reservoirs for saltworks or fish farms constructed after mangrove clearing. Results showed significantly higher densities, species numbers, diversity (H’) and numbers of trophic groups in undisturbed sites compared to both types of disturbed sites. Overall, omnivorous fish comprised the most abundant feeding guild, with the highest number of individuals found in the cleared sites followed in order by the uncleared sites and the reservoirs. The feeding guild zoobenthivores/piscivores was the most diverse group, with the highest species richness in the undisturbed areas. Multivariate analysis showed that assemblage structure of omnivores in the reservoirs was separated from those in the uncleared and cleared sites, while zoobenthivores/piscivores differed between uncleared sites and the disturbed areas (cleared sites and reservoirs). Stable isotope ratios of δ13C and δ15N values in fish tissue muscles indicate significant diet shifts between undisturbed and disturbed mangrove creek systems, although the effects are species-specific. Our findings suggest that mangrove deforestation combined with land-use changes, such as salt- or fish farm constructions, has a greater impact on the trophic structure of fish in mangrove creeks than mangrove deforestation only. Hence, the extent and severity of disturbance seem to be important in predicting fish assemblage composition.

Keyword [en]
Mangrove, Fish, Functional groups, Anthropogenic disturbance, Tanzania, Western Indian Ocean.
National Category
Fish and Aquacultural Science
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-27398OAI: oai:DiVA.org:su-27398DiVA: diva2:214034
Projects
Sida-SAREC Marine Bilateral Programme between Sweden and Tanzania
Available from: 2009-05-01 Created: 2009-05-01 Last updated: 2014-10-13Bibliographically approved
In thesis
1. Fish community patterns in Tanzanian mangrove creeks
Open this publication in new window or tab >>Fish community patterns in Tanzanian mangrove creeks
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Human beings have exploited the biota of mangrove systems for centuries and fish continue to be one of the main products harvested from these habitats. The assumption of mangroves functioning as recruitment areas for juvenile fish from neighbouring habitats such as seagrass beds and coral reefs is a common argument for conservation and management of mangrove ecosystems. Yet, mangrove systems are increasingly in decline worldwide primarily because of destructive anthropogenic activities. In the present thesis, fish assemblages in various mangrove creeks in Tanzania were investigated. Specifically, it dealt with the distribution, abundance and trophic structure of fishes in space and time as predicted by habitat characteristics and environmental conditions occurring naturally and following human-induced changes of clearing for construction of ponds for salt production and fish farming. In addition, the variation in population density and genetic connectivity of the economically important striped mullet (Mugil cephalus) was examined. In undisturbed creeks the fish abundance and assemblage composition showed inconsistent spatial patterns within and among different creeks that appear to be strongly influenced by species-specific responses to dominant bottom substrate types and to some extent to water depth and clarity. Seasonality had little impact on most fish assemblage variables. The genetic analysis showed mixed demes of Mugil cephalus and significant separation between Zanzibar Island and Tanzania mainland. Anthropogenic effects were found on the structural and functional organisation of fish assemblages resulting in lower densities, species numbers, diversity and number of trophic groups in the reservoirs compared to less disturbed sites. These changes in fish assemblage composition seem to be caused by an increase in salinity and water temperature as well as by the loss of refuge and feeding grounds. The findings in this thesis will contribute to coastal management planning for conservation and suggests integration of various activities (like fish farming and salt production) in order to maximise the economical use of deforested areas.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2009. 38 p.
Keyword
Mangrove ecosystems, fish assemblages, Mugil cephalus, population genetics, spatial and seasonal variability, human disturbance, East Africa
National Category
Natural Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-27168 (URN)978-91-7155-879-4 (ISBN)
Public defence
2009-05-27, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2009-05-06 Created: 2009-04-23 Last updated: 2009-05-05Bibliographically approved

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