The tropical seascape consists of a complex mosaic of interconnected systems like coral reefs, seagrass beds and mangrove forests that support biodiversity and ecosystem services. Over the last decades, human-induced habitat destruction and declines in biodiversity have contributed to an increasing implementation of marine protected areas (MPAs). However, as MPAs primarily focus on excluding impacts of fisheries on target species, particularly in coral reef, we know less of how MPAs affect habitat-forming, benthic species across the whole seascape. Here, we investigated how community- and government-managed MPAs affect the species composition, diversity and cover of benthic sessile organisms along a seascape gradient, from the intertidal to the subtidal reef zone, in 12 sites along the Kenyan coast. Community-managed MPAs with only a few years (≤6 years) of protection had a higher diversity of coral- and seagrass assemblages than fished areas, most likely by facilitating the presence of both early and late successional species. Moreover, MPAs appear to increase total seagrass cover in intertidal and mid lagoon zones, as well as topographic complexity in the reef zone, but have no effects on total coral cover (which was very low in all sites). Finally, using a space-for-time substitution approach, our results suggest that protection may in the long term (>20 years) facilitate a gradual shift in assemblage composition, from dominance of structurally simple and stress-tolerant foundation species in fished areas, to structurally complex and stress-sensitive species. To our knowledge, this study is the first indicating that MPAs can increase biodiversity and cause a shift from structurally simple to complex species in soft-bottom seagrass-dominated systems. In summary, our findings suggest that community-managed MPAs protected for <10 years increase the diversity of benthic communities across the tropical seascape, whereas dominance by structurally complex species with disproportional importance for ecosystem functioning is restricted to government-managed MPAs protected for several decades.

Government-managed marine protected areas (MPAs) can restore small fish stocks, but have been heavily criticized for excluding resource users and creating conflicts. A promising but less studied alternative are community-managed MPAs, where resource users are more involved in MPA design, implementation and enforcement. Here we evaluated effects of government-and community-managed MPAs on the density, size and biomass of seagrass- and coral reef-associated fish, using field surveys in Kenyan coastal lagoons. We also assessed protection effects on the potential monetary value of fish; a variable that increases non-linearly with fish body mass and is particularly important from a fishery perspective. We found that two recently established community MPAs (< 1 km(2) in size, <= 5 years of protection) harbored larger fish and greater total fish biomass than two fished (open access) areas, in both seagrass beds and coral reefs. As expected, protection effects were considerably stronger in the older and larger government MPAs. Importantly, across management and habitat types, the protection effect on the potential monetary value of the fish was much stronger than the effects on fish biomass and size (6.7 vs. 2.6 and 1.3 times higher value in community MPAs than in fished areas, respectively). This strong effect on potential value was partly explained by presence of larger (and therefore more valuable) individual fish, and partly by higher densities of high-value taxa (e.g. rabbitfish). In summary, we show that i) small and recently established community-managed MPAs can, just like larger and older government-managed MPAs, play an important role for local conservation of high-value fish, and that ii) these effects are equally strong in coral reefs as in seagrass beds; an important habitat too rarely included in formal management. Consequently, community-managed MPAs could benefit both coral reef and seagrass ecosystems and provide spillover of valuable fish to nearby fisheries.

Marine ecosystems are under increasing human pressure and therefore in need of effective management. Marine protected areas (MPAs) can reduce the effects of local disturbances on habitat-forming benthic organisms like corals and seagrasses and are well-known to affect species composition. However, we know considerably less about their effects on organisms’ traits (physiological, morphological, and/or behavioural characteristics), which in turn dictate how organisms respond to stressors and influence ecosystem processes and services. We conducted a field survey along the Kenyan coast to assess the effects of MPAs on species and trait composition of seagrass assemblages; an important group of habitat-forming plants in shallow coastal areas that form the basis for multiple ecosystem services. We measured five morphological traits (shoot density, leaf length and width, number of leaves per shoot, and above:below-ground biomass ratio) on multispecies seagrass assemblages within government MPAs, community MPAs, and fished areas in three habitat zones (shallow, mid-lagoon and, reef). Using causal modelling (path analysis) of multivariate data, we found that MPAs influence seagrass species composition and, indirectly, trait composition in mid-lagoon areas. Meanwhile, there were no MPA effects in the shallow intertidal (potentially because of impacts from MPA-related tourism), and weak effects in the reef zone, presumably due to competition from corals. Finally, most of the MPA effects on overall seagrass trait composition were explained by species turnover, rather than phenotypic plasticity. In conclusion, MPAs appear to be an effective conservation tool for seagrass assemblages by reducing local disturbances and favouring seagrass species with certain traits, primarily in mid-lagoon areas. However, the lack of MPA effect in intertidal areas highlights the need for management approaches that regulate human impacts across the whole tropical coastal zone.

Marine ecosystems subjected to human impacts are increasingly managed using marine protected areas (MPAs). MPAs have been suggested to not only benefit harvested species but also to increase ecosystem resilience (resistance to and/or recovery from disturbances), but this hypothesis has to our knowledge never been tested experimentally. Theory suggests that MPA effects on recovery from disturbance should be particularly important for recovery from large (vs. small) disturbances, because large disturbances generally increase the likelihood that local assemblages are pushed into alternative trajectories and do not recover. In this study we experimentally tested the effects of a no-take MPA on the recovery of seagrasses from experimental small-scale disturbance (clearings of two sizes; 0.25 and 1m2) in coastal Kenya. There was a faster seagrass recovery and less sediment erosion within the MPA than in three reference sites. Moreover, small clearings recovered faster than large clearings in terms of sediment erosion, but there was no such size effect on seagrass cover. These MPA effects were relatively weak, dissipated over time and were not detectable after 2 years. In summary, this study supports the hypothesis that MPAs can increase recovery from disturbance, and hence ecosystem resilience, but the relatively weak and dissipating effects emphasize the need for more and large-scale studies critically assessing the relationship between MPAs and ecosystem resilience.