Abstract
Marine protected areas (MPAs) have been shown to increase long-term temporal stability of fish communities and enhance ecosystem resilience to anthropogenic disturbance. Yet, the potential ability of MPAs to buffer effects of environmental variability at shorter time scales remains widely unknown. In the tropics, the yearly monsoon cycle is a major natural force affecting marine organisms in tropical regions, and its timing and severity are predicted to change over the coming century, with potentially severe effects on marine organisms, ecosystems and ecosystem services. Here, we assessed the ability of MPAs to buffer effects of monsoon seasonality on seagrass-associated fish communities, using a field survey in two MPAs (no-take zones) and two unprotected (open-access) sites around Zanzibar (Tanzania). We assessed the temporal stability of fish density and community structure within and outside MPAs during three monsoon seasons in 2014–2015, and investigated several possible mechanisms that could regulate temporal stability. Our results show that MPAs did not affect fish density and diversity, but that juvenile fish densities were temporally more stable within MPAs. Second, fish community structure was more stable within MPAs for juvenile and adult fish, but not for subadult fish or the total fish community. Third, the observed effects may be due to a combination of direct and indirect (seagrass-mediated) effects of seasonality and, potentially, fluctuating fishing pressure outside MPAs. In summary, these MPAs may not have the ability to enhance fish density and diversity and to buffer effects of monsoon seasonality on the whole fish community. However, they may increase the temporal stability of certain groups, such as juvenile fish. Consequently, our results question whether MPAs play a general role in the maintenance of biodiversity and ecosystem functioning under changing environmental conditions in tropical seagrass fish communities.
Highlights
Marine protected areas (MPAs) have become one of the key marine conservation strategies worldwide
We investigated whether MPAs can buffer direct and indirect effects of monsoon seasonality on tropical fish communities associated with seagrass beds
We hypothesized that: i) fish communities would be temporally more stable within MPAs than open-access sites in terms of fish density, diversity and community structure; ii) the indirect effects of seasonality would be at least as important as the direct effects; and iii) a higher fish community stability over time within MPAs could be explained by the stabilising effects of protected areas due to increased diversity
Summary
Marine protected areas (MPAs) have become one of the key marine conservation strategies worldwide. There is a pertinent need for more knowledge about the extent to which monsoon seasonality affects tropical fish communities and fish habitats, and the potential ability of MPAs to buffer those seasonal effects, to advance future management of ecosystems and the natural resources that humans depend upon Another factor strongly affecting coastal fish communities in shallow areas is the distribution and abundance of foundation species such as reef-building corals, seagrasses and perennial macroalgae. We hypothesized that: i) fish communities would be temporally more stable within MPAs than open-access sites in terms of fish density, diversity and community structure; ii) the indirect effects of seasonality (those mediated by changes in the seagrass habitat) would be at least as important as the direct effects; and iii) a higher fish community stability over time within MPAs could be explained by the stabilising effects of protected areas due to increased diversity. We tested these hypotheses for the overall fish community, as well as for different age classes: juveniles, subadults and adults
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