SeaFlower Biosphere Reserve: New Findings and Trends in the Largest Caribbean Marine Protected Area

Seagrass meadows are important for carbon storage, this carbon is known as “blue carbon” and represents a vital ecosystem service. Recently there has been growing interest in connectivity between ecosystems and the potential for connected ecosystems to facilitative ecosystem services. Tropical seagrass meadows are connected to coral reefs, as the reef barrier dissipates waves, which facilitates sediment accumulation and avoid erosion and export. Therefore, coral reefs might enhance the seagrass meadows capacity as a blue carbon sink. We tested this hypothesis through an assessment of blue carbon across a gradient of connected seagrass meadow and coral reef sites. We assessed attributes of seagrass meadows along a transect in addition to classifying the sites as exposed and sheltered. Classification of sites was completed through analyzing wave crest density in photographs and using granulometric evenness index. Organic carbon and organic matter were measured in sediment core samples and within seagrass living biomass (both above and below ground). Lastly, we measured changes in above and below ground traits of seagrass plants across the same sites. Gaps in the reef barrier were linked to high wave disturbance and exposed conditions, whilst barrier continuity to low wave disturbance and sheltered conditions. Organic carbon in sediments was 144 Mg ha^–1 in the most sheltered (with reef barrier) and 91 Mg ha^–1 in the most exposed (without reef barrier) meadows. Sheltered conditions also showed a redistribution of seagrass biomass to a greater quantity of roots compared to rhizomes. Whilst in exposed conditions the opposite occurred, which could be due to increased rhizome biomass have to enhanced anchorage or greater nutrient availability. This study found that coral reefs facilitate blue carbon potential in seagrass meadows indicating that coral reefs support this important ecosystem service. Also, results suggest that loss of coral reef structure due to bleaching and other stressors will likely result in a reduction of the blue carbon storage capacity of adjacent seagrass meadow. Further research should investigate how combined global and regional stresses may impact on the potential for coral reefs to buffer seagrass meadows, and how these stresses affect the functional traits of seagrass plants.

Microorganisms represent nearly 90% of ocean biomass and are fundamental for the functioning and health of marine ecosystems due to their integral contribution to biogeochemical cycles and biological processes. In marine environments, microorganisms exist as microbial communities in the water column, benthonic substrates, and macroorganisms, where they establish symbiotic interactions and fulfill their ecological roles. Such interactions can have a harmful or beneficial impact on the hosts depending on the emergent properties of the communities, their taxonomic structure, and functionality. To evaluate these features, culture independent approaches like metabarcoding have been developed and have hugely contributed to the characterization of marine microbial diversity. The present study was aimed to explore the structure and metabolic functionality of microbial communities associated to marine hosts at the Serrana Bank, a coral atoll part of the Seaflower Biosphere Reserve (Archipelago of San Andrés, Old Providence and Saint Catalina, Colombia). We found a highly diverse microbial assemblage associated with the corals Siderastrea siderea, Colpophyllia natans, and Orbicella annularis, the sponge Haliclona sp. and sediment from Isla de los Pájaros lagoon. However, the coral Porites astreoides had significantly lower bacterial diversity and a different community composition. Proteobacteria was the most abundant phylum within bacterial communities in the evaluated hosts, except in P. astreoides, where Cyanobacteria was the predominant group. Firmicutes, Actinobacteria, Bacteroidetes, Acidobacteria, Chloroflexi, and Gemmatimonadetes were also identified within all microbiomes, but their dominance varied between hosts. Additionally, the most abundant group among the fungi communities associated with O. annularis, S. siderea, and C. natans was Ascomycota, but significant differences between clasess and order were observed among hosts. Finally, functional profiles revealed that the principal microbial functions were focused on membrane transport, carbohydrates, amino acids and energy metabolism, replication, and translation processes. A significant higher metabolic functionality was found in the sponge microbiome in comparison to the coral microbial communities.