Abstract
A survey of six common grouper (Serranidae) species was conducted on both the western protected and eastern unprotected reefs around Chumbe Island, Zanzibar. Species, estimated maturity, and habitat were recorded using standardized categories. Fundamental niche and general habitat preference were extrapolated based on observed realized niche and qualified based on substrate, depth, slope position, and general reef region. Taking habitat preference into account, abundance and biomass density of serranid populations were compared between locations on the reef in order to best account for how habitat influences distribution and population health. The results of this study provide depth to previous research on the protected reef and indicate noteworthy shifts in population composition between 2014 and 2018 that favour species with less specified habitat preference, such as Aethaloperca rogaa and Cephalopholis argus. Surveys of Chumbe’s nearby unprotected eastern reef indicate low levels of species abundance, which this study hypothesizes is the result of inappropriate habitat structure, increased fishing pressure, and decreased population health within the MPA. Ultimately, this study suggests that MPAs do not protect all species equally, and habitat preference must be taken into account when assessing MPA effectiveness at protecting different species. Indeed, especially as serranid habitat faces continued degradation, serranid conservation will depend even more on protection of each species’ preferred habitat in coral systems. As such, assessing serranid populations as a whole fails to capture the changes in population distribution and composition that is occurring between species, which may be more indicative of shifts and disturbances in the ecosystem.
Highlights
Coral reefs offer many ecosystem services, many of which operate in a synergistic relationship with one another
In order to best account for the rapid changes occurring on coral reefs in the face of climate change, this study aims to identify habitat preferences of six common species of grouper in order to inform best management strategies in the face of external pressures that cannot be eliminated by the boundaries of a no-take area (NTA)
A total of 362 individuals were observed around Chumbe Island, the majority of which were recorded within the marine protected area (MPA)
Summary
Coral reefs offer many ecosystem services, many of which operate in a synergistic relationship with one another. In Zanzibar, the rapid growth of coastal populations has resulted in unsustainable exploitation of the productive fishing grounds offered by nearby coral reefs. This overexploitation has diminished reef biodiversity, and sapped these systems of the bountiful fisheries that attracted coastal populations to fish them in the first place. The presence of groupers on a reef indicates (1) that the reef is not overexploited, (2) that the coral is healthy and complex, (3) that lower trophic levels are being balanced by natural predation (Hackradt et al, 2014; Kelly and Ruhl, 2011), and (4) that the reef likely supports high abundances and biodiversity of marine life and offers noteworthy, stable
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