Serranilla is a protected island of the Seaflower Biosphere Reserve, far from dense human population. These characteristics could help sustain structurally complex coral reefs, often associated with higher biodiversity, abundance, and biomass of reef-associated organisms, including reef fish. However, the multiple threats present in Serranilla, including intense illegal fishing, can impact coral ecosystems generally and also specific key groups, such as the parrotfish, in particular. During the “Seaflower Research Expedition 2017”, we assessed how structural habitat complexity influences reef fish assemblages. In addition, we explored differences in parrotfish species (family: Scaridae) between Serranilla and San Andrés, the most populated island in the Archipelago. On Serranilla, we found that habitat structure, rugosity, and coral cover accounted for up to 66% of variation in reef fish diversity, abundance, and biomass, with values being higher on more complex reefs. Parrotfish species differed between the islands, with larger species supporting higher biomasses at Serranilla, by comparison with San Andrés; however, the abundance, biomass, and lengths of parrotfish species were low in both areas compared with those reported from other protected Caribbean reefs. Our study indicates that despite the evident relationship between structurally complex habitats and reef fish, other threats in Serranilla could be affecting parrotfish populations, such as illegal fishing, a widespread activity in the area.

Insular and coastal territories like those in the Seaflower Biosphere Reserve are exposed to strong winds, waves, storms, and hurricanes. In November 2020, Hurricanes Eta and Iota provided a costly reminder of the risks facing Seaflower’s people and ecosystems. Coral reefs and mangroves are natural shields, reducing wind and wave strength during normal and extreme conditions. These coastal protection ecosystem services (ES) are vital for human safety and well-being, and become more important given the heightened vulnerability of low-lying insular islands to climate change impacts. These ecosystems also provide biodiversity refuge ES for fishes and shellfish, key for food security and resilience to global challenges like hurricanes, sea level rise, and global warming. Despite their importance, these valuable ecosystems are threatened by anthropogenic pressures, jeopardizing the survival and well-being of islanders; their restoration and recovery require improved management and decision-making, and heightened societal awareness of our dependence on marine ecosystems and their potential as climate change adaptation solutions. We identify ES provided by coral reefs and mangroves, interdisciplinary management tools, and recommendations to motivate society and decision-makers to expand efforts for the protection, restoration, and use of these ecosystems as Nature-based Solutions for climate change adaptation and mitigation in Seaflower.