Spatial distribution of parrotfishes and groupers in an Okinawan coral reef: size-related associations in relation to habitat characteristics

Parrotfishes (Labridae: Scarini) and groupers (Epinephelidae) are important fish groups that are regarded as the fisheries targets of primary importance in coral reefs. In order to establish ecosystem-based management of these two fish groups, clarifying the spatial distribution relative to habitat characteristics is of central importance. The present study investigated the spatial distributions of 12 parrotfishes species and seven groupers species in relation to environmental characteristics in an Okinawan coral reef. Ten out of the 12 parrotfish species and all seven grouper species showed species-specific spatial distributions. Four substrate types in the inner reefs (branching Acropora, bottlebrush Acropora, dead branching Acropora, and dead bottlebrush Acropora), three substrate types in the exposed reefs (massive coral, other coral, and calcium carbonate substratum), and water depth showed significant associations with the spatial distribution of fishes. Among the 12 parrotfish species, two species (Scarus spinus and S. forsteni) and four species (S. psittacus, S. hypselopterus, S. dimidiatus and S. ghobban) were primarily found in exposed reefs and inner reefs, respectively. Among the seven grouper species, two species (Cephalopholis argus and C. urodeta) and two other species (C. miniata and Epinephelus ongus) were primarily found in exposed reefs and inner reefs, respectively. Size-related spatial distribution was also found for three parrotfish species (Chlorurus microrhinos, Scarus rivulatus and S. hypselopterus), indicating that smaller-sized and larger-sized individuals were respectively found at sites with greater coverage of substrates with fine structure (live bottlebrush Acropora and dead bottlebrush Acropora) and coarse structure (live branching Acropora, dead branching Acropora and calcium carbonate substratum). The present study suggested that the spatial distribution of parrotfishes and groupers is not necessarily associated with the higher coverage of living corals, but positively associated with high substrate complexity. Thus, actual spatial distributional patterns of species should be considered to select candidate sites for protection and conservation for the two fish groups.

The influence of habitat preference on longitudinal population composition and distribution of Groupers (Serranidae) in Chumbe Island Coral Park, Zanzibar, Tanzania

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.

Linking Protection with the Distribution of Grouper and Habitat Quality in Seychelles

Marine protected areas can be designated for a number of reasons, but exactly how they provide benefits is only recently being understood. We assessed the effect of protection on the size and distribution of six common species of grouper in a coral reef ecosystem. Data on live coral cover, coral genus diversity, and coral colony structure type were also compared to give an indication of reef quality between sites. A significant interaction was found forAethaloperca rogaaandCephalopholis nigripinnis, indicating that protected areas held greater numbers of smaller and median sized fish of these species than unprotected areas. Similar but nonsignificant trends were found forCephalopholis miniataandCephalopholis argus. ForAnyperodon leucogrammicus, MPAs held significantly more fish than unprotected sites, but as the increase was equal between size categories there was no interaction. The last speciesEpinephelus fasciatus,which was one of the smallest species, had no significant interaction, similar mean counts between protected and unprotected areas, and no obvious strong favouritism for particular sites with values indicating better reef quality, indicating intraspecies competition. The results of this study indicate that while the MPAs in this study are likely too small to benefit large groupers, the improvements to habitat quality have indirect benefits to groupers, especially at their earlier life stages.