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  • 1.
    Garpe, Kajsa C.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Yahya, Saleh A.S.
    Stockholm University, Faculty of Science, Department of Zoology.
    Lindahl, Ulf
    Stockholm University, Faculty of Science, Department of Zoology.
    Öhman, Marcus C.
    Stockholm University, Faculty of Science, Department of Zoology.
    Long-term effects of the 1998 coral bleaching event on reef fish assemblages2006In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 315, p. 237-247Article in journal (Refereed)
    Abstract [en]

    Coral bleaching events constitute compound disturbances often resulting in coral death as well as successive degradation of the reef framework. The 1997/1998 El Niño Southern Oscillation (ENSO) was the most severe on record and affected coral reefs worldwide. The present study examined the response of fish assemblages in plots of transplanted coral before and after the 1998 bleaching. Multidimensional scaling ordinations (MDS) demonstrate significant changes in assemblage composition related to habitat alteration. Within-site variability increased with disturbance, the increase being most apparent following substrate erosion. The differences in long-term responses as opposed to short-term responses were striking. Six mo after coral death, total abundance as well as taxonomic richness had increased at one of the sites, but not the other, whereas 6 yr later, both measures had decreased significantly at both sites. Functional groups, with documented affiliations with coral, were significantly influenced by the habitat alteration. Herbivore abundance increased as an immediate response to bleaching, but was subsequently decimated in eroded habitat. The loss of structural complexity had major detrimental effects on the entire fish community. In conclusion, we present evidence of severe and long-lasting secondary impacts of a catastrophic bleaching event, with no apparent recovery. The discrepancies between short-term and long-term responses underline the importance of long-term monitoring of fish assemblages following habitat alteration.

  • 2. McClanahan, Tim R.
    et al.
    Muthiga, Nyawira A.
    Maina, Joseph
    Kamukuru, Alboghast T.
    Yahya, Saleh A.S.
    Stockholm University, Faculty of Science, Department of Zoology.
    Changes in northern Tanzania coral reefs during a period of increased fisheries management and climatic disturbance2009In: Aquatic conservation, ISSN 1052-7613, E-ISSN 1099-0755, Vol. 19, no 7, p. 758-771Article in journal (Refereed)
    Abstract [en]

    1. Surveys of coral reefs in northern Tanzania were conducted in 2004/5 with the aim of comparing them over an∼8-year period during a time of increased efforts at fisheries management and the 1998 El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) coral mortality event that caused 45% mortality in northern Tanzania and much of the Indian Ocean.

    2. Changes associated with both management, its absence, and the ENSO were found but changes were generally small and ecological measures indicated stability or improvements over this period, particularly when compared with reports from much of the northern Indian Ocean.

    3. Fisheries management in two areas increased the biomass of fish and benthic communities. A small fisheries closure (0.3 km2) displayed little change in the coral community but ecological conditions declined as measured by sea urchins and fish abundances. This change may be associated with its small size because similar changes were not measured in the large closure (28 km2).

    4. The few sites without any increased management were still degraded and one site had experienced a population explosion of a pest sea urchin, Echinometra mathaei.

    5. The lack of significant changes across this disturbance indicates that these reefs are moderately resilient to climate change and, therefore, a high priority for future conservation actions.

  • 3.
    Wilhelmsson, Dan
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Yahya, Saleh
    Stockholm University, Faculty of Science, Department of Zoology.
    Öhman, Marcus
    Stockholm University, Faculty of Science, Department of Zoology.
    Effects of high-relief structures on cold-temperate fish assemblages: a field experiment2006In: Marine Biology Research, ISSN 1745-1000, E-ISSN 1745-1019, Vol. 2, no 2, p. 136-147Article in journal (Refereed)
    Abstract [en]

    High-relief structures may influence the abundance and diversity of reef-associated fish. We conducted a field experiment to investigate whether the presence of vertical structures (PVC pipes) affects fish communities on artificial reefs. The effect of the height of the structures (1 and 3 m) was also tested. Furthermore, the effects on fish of placing artificial reefs on otherwise featureless bottoms were quantified. Algal and macro-invertebrate colonization of the reefs was also recorded. The experiment was carried out on the west coast of Sweden over a period of 1 year. The vertical structures had a positive effect on fish abundance but not on diversity. The height of the structures did not, however, influence the fish communities. Natural as well as urban vertical structures on the seafloor could have a positive effect on local fish abundance. The positive effects of artificial reefs on total fish abundance and diversity were immediate. Of the 10 species recorded, two, the black goby Gobius niger and the goldsinny wrasse Ctenolabrus rupestris , dominated over the whole survey period. There were significant temporal differences in fish abundance, and diversity increased with time.

  • 4.
    Yahya, Saleh
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Effects of coral bleaching on reef fish communities2008Licentiate thesis, monograph (Other academic)
  • 5.
    Yahya, Saleh A. S.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Zoology. Stockholm University, Faculty of Science, Department of Systems Ecology.
    Öhman, Marcus C.
    Stockholm University, Faculty of Science, Department of Zoology.
    Jiddawi, Narriman
    Andersson, Mathias H.
    Stockholm University, Faculty of Science, Department of Zoology.
    Mgaya, Yunus D.
    Lindahl, Ulf
    Coral bleaching and habitat effects on colonisation of reef fish assemblages: an experimental study2011In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 94, no 1, p. 16-23Article in journal (Refereed)
    Abstract [en]

    Degradation and mortality of corals is increasing worldwide and is expected to have significant effects on coral reef fish; hence studies on these effects are essential. In the present study, a field experiment was set up within Mafia Island Marine Park in Tanzania (East Africa) to examine the effects of bleaching and habitat structure on colonisation of coral reef fish assemblages. Live and bleached staghorn coral Acropora formosa was transplanted onto plots in a site dominated by sand and rubble, and the experimental design comprised of three treatments: live coral, bleached coral and eroded coral rubble. There was an immediate increase (within 24 h) in fish abundance and diversity in the two treatments with standing corals. Overall, live and bleached coral plots showed similar effects, but differed from the eroded coral plots which had a much lower abundance and diversity of fish. In general, fish species diversity changed with time over the study period while fish abundance did not. Multivariate analyses showed that while there were differences in fish assemblage structure between standing corals and the eroded coral treatment, there was neither a difference between live and bleached coral treatments nor any temporal effects on fish assemblage structure. Our findings suggest that physical structure and complexity of habitat have stronger effects on colonisation of reef fish assemblages than changes in coral health (such as bleaching) which do not affect coral structure. This may have important implications for appropriate coral reef management.

  • 6.
    Yahya, Saleh A.S.
    Stockholm University, Faculty of Science, Department of Zoology.
    Habitat structure, degradation and management effects on coral reef fish communities2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Coral reefs are among the most diverse and productive ecosystems on earth, and are critical to the survival of tropical marine ecosystems and sustenance of local human populations. However, coral reefs are quite vulnerable to disturbances, both natural and anthropogenic. This thesis looks at how coral reef communities have responded to climactic disturbances, particularly the 1997-98 El Niño Southern Oscillation (ENSO) and subsequent coral bleaching and mortality that affected much of the Indian Ocean, including the coastal waters of Tanzania, where the study was conducted. In particular, it investigates the effects of coral bleaching, habitat degradation and reef spatial arrangement on reef fish assemblages.

    Habitat structural complexity and spatial arrangement of reefs had an effect on reef fish communities. Fish communities showed patterns in distribution among habitats and between patch and continuous reefs. Fishes preferred live to bleached/dead or eroded coral, but trophic groups reacted differently to patch and continuous reefs. There were slight changes in fish abundance and significant changes in fish diversity on experimental, bleached branching Acropora coral plots over a period of one year. While fish abundance on one site increased shortly after a bleaching event, 6 years later fish abundance had decreased significantly. Conversely, coral reef communities in northern Tanzania had changed little over an 8-year period, with minor changes associated with the 1997-98 ENSO and the presence or absence of fisheries management. The coral reefs in the region were found to show high variability in community structure and responses of associated fish and invertebrate communities.

    The findings of this thesis indicate the importance of habitat structure and spatial arrangement of reefs, the detrimental effects of coral bleaching, and the possibility that some reefs and some (generalist) reef fish taxa may exhibit resilience to climate change.

  • 7.
    Yahya, Saleh A.S.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Öhman, Marcus
    Stockholm University, Faculty of Science, Department of Zoology.
    Jiddawi, Narriman
    Mgaya, Yunus
    Fish assemblages in relation to quality, structure and configuration of staghorn coral reefs at Mafia and Zanzibar islands, TanzaniaManuscript (Other academic)
  • 8.
    Yahya, Saleh A.S.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Muhando, Christopher
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Fish and sea urchin community patterns and habitat effects on Tanzanian coral reefsManuscript (preprint) (Other academic)
1 - 8 of 8
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