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Spatial and seasonal variation of fish assemblages in mangrove creek systems in Zanzibar (Tanzania)
Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology. Stockholm University, Faculty of Science, Department of Systems Ecology.
Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology.
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2010 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 89, no 4, 277-286 p.Article in journal (Refereed) Published
Abstract [en]

Spatial and seasonal variations of fish assemblage composition were studied in three non-estuarine mangrove creeks of Zanzibar (Tanzania). Fish were collected monthly for one year at three sites (lower, intermediate and upper reaches) in each creek using a seine net (each haul covering 170 m(2)). Density, species number and diversity of fish were all higher at sites with dense cover of macrophytes (seagrass and macroalgae) than over unvegetated sandy sites. In general, fish assemblages mainly comprised juveniles of a few abundant taxa, e.g. Mugil cephalus, Mugilidae spp. and Leiognathus equulus at sites with mud substratum and Germs oyena, Lethrinus harak and Sillago sihama at sites dominated by macrophytes. Multivariate analyses revealed significant separations in fish assemblage composition within the two creeks where the bottom substratum differed among sites. Overall, season seemed to have little effect on density, species number, diversity index (H') and assemblage structure of fish. Water condition variables were also relatively stable across the season, although a short-term fluctuation primarily induced by decreased salinity, occurred during the heavy rains in April and May. Fish assemblage structure was not significantly affected by any of the abiotic factors tested. However, significant regressions were found between the other fish variables and environmental variables, but since these associations were mostly species-specific and generally inconsistent, we suggest that the overall distribution patterns of fish were mainly an effect of particular substrate preferences of fish species rather than contemporary water conditions.

Place, publisher, year, edition, pages
2010. Vol. 89, no 4, 277-286 p.
Keyword [en]
Mangrove creeks, Fish communities, Non-estuarine, Substratum heterogeneity, East Africa
National Category
Fish and Aquacultural Science
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-27395DOI: 10.1016/j.ecss.2010.08.002ISI: 000283002100004OAI: oai:DiVA.org:su-27395DiVA: diva2:214031
Projects
Sida-SAREC Marine Bilateral Programme between Sweden and Tanzania
Available from: 2009-04-30 Created: 2009-04-30 Last updated: 2011-11-24Bibliographically 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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Mwandya, AugustineGullström, MartinAndersson, Mathias H.Öhman, Marcus C.
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