Los afloramientos de cianobacterias marinas bentónicas parecen ser recurrentes en varias localidades arrecifales del Caribe colombiano. Sin embargo, su efecto sobre las comunidades locales aún no se han dimensionado. En esta nota documentamos algunas interacciones entre cianobacterias y organismos arrecifales.
Blooms of marine benthic cyanobacteria are recurrent in several locations at the Colombian Caribbean. In these events, cyanobacteria grow over the substrate and benthic organisms although their effect has not been fully assessed. This study evaluated interactions between cyanobacteria and hermatypic corals, in order to identify any deleterious effects that could be related to allelopathic mechanisms. Organic extracts from cyanobacteria collected in San Andres, Old Providence and Rosario islands were tested against embryos of the reef-building coral Orbicella annularis. The indirect effect of cyanobacterial extracts was also assessed by resuspending the extracts in seawater and monitoring polyp retraction and recovery of the coral Madracis mirabilis (=auretenra). Additionally, the effect of direct contact between cyanobacterial extracts and the coral Porites porites was assessed by incorporating cyanobacterial extracts into PhytagelTM gels and placed in direct contact with the coral. After 24, 48 and 72 h of exposure, chromatographic profiles of associated zooxanthellae was evaluated by HPLC. A deleterious effect on the zooxanthellae was evidenced by an increase in pheophytin, a degradation product from chlorophyll. The competitive abilities of algae and cyanobacteria should be considered as a constraint to reef restoration initiatives. Cyanobacteria have the ability to compete with corals due to their growth rates, defenses against herbivory and potentially allelopathic mechanisms.
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.
Hurricanes and tropical storms are major climatic disturbances with potentially catastrophic effects on coastal and marine ecosystems. The impact of these climatic events on coastal communities may vary greatly and depends on the hurricane’s severity, trajectory, and duration. Furthermore, the impact of hurricanes can be patchy, causing extensive damage in some locations, while leaving other subjacent areas intact. In coral reef areas, breakage, dislodgement, and sandblasting may cause extensive coral mortality, and loss of coral cover may increase due to sedimentation and freshwater runoff. After the impact of the climatic event, successional stages in the reef community have been observed, where blooms of ephemeral algae may occupy space made available by the storm impact. We report a bloom of the red alga Trichogloeopsis pedicellata on the west coast of the island of San Andrés, following Hurricane Iota. The survey was carried out in seven locations at different depths: shallow (2–5 m) and deep (8–15 m). Three video transects were recorded at each sampling site, and 15 photo quadrats were analyzed for benthic cover. For the biomass estimate, three to five quadrats of 25 × 25 cm were laid on the substrate, all the algae inside were collected, and their wet biomass was determined. The algal cover reached 100% in some locations, with wet biomass up to 5,264 g/m2, and persisted for several weeks. The bloom was more severe at shallow depths. Apparently, the availability of the substrate due to the detachment of foliose algae triggered the bloom. After a few months, the bloom receded naturally.
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