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.

To understand the changes in the position of the mangrove forest fronts, migration trends of Rhizophora mangle along the coast, were analyzed in response to oceanographic, climatic variability and hydrological coast regulators. Due to the large biological, physical and climatic differences between Pacific and insular Caribbean coasts of Colombia, the working hypothesis proposed differences in migration drivers and mangrove responses between the coasts. Remote sensing and photointerpretation techniques were used to identify and quantify the spatial variation of deltaic forest types on the Pacific coast and open-water forest types in the Caribbean. Regression analysis was used to relate mangrove front changes with river water discharge, ENSO climate variability, and wave height and velocity coming from directions in interaction or not with the coral reef (in open water forest). It was found that in 13 years of observation (2010 to 2023), there were constant changes in the position of the mangrove front in both the Caribbean and the Pacific. Wave heights from directions that do not interact with the coral reef barrier, such as during periods of strong hurricane influence, along with ENSO variability, collectively explained the annual changes in the mangrove front of open waters (R^² = 0.91). Freshwater discharge, which was linked to the size of a protective sediment bar in front of the mangroves, significantly accounted for the annual changes in mangrove coverage (R^² = 0.70). During the period analyzed, the open-coast mangrove front exhibited a progradation of 0.45 to 1.02 yr^⁻¹, while the deltaic mangrove in Bocagrande showed a retreat of 1.13 yr^⁻¹. These findings provide valuable insights for marine spatial planning, supporting mangrove conservation efforts.