San Andres Archipelago Coral Reefs

Category: Marine and Oceanic Biomes.

Geographic Location: Caribbean Sea.

Summary: This group of coralline formations supports coral reef, mangrove, seagrass bed, algae, and forest habitats; it is protected in some measure by a system of conservation areas.

The San Andres Archipelago contains one of the most representative coral reefs in the Caribbean Sea, based on its development and complexity, which derive primarily from the strong marine current present in the archipelago and its distance from the mainland. While the total above-water surface area of the islands and immediate offshore waters of the archipelago is less than 45 square miles (116 square kilometers), it is the fundamental component of the vast Seaflower Biosphere Reserve of approximately 135,136 square miles (350,000 square kilometers). Under the dominion of Colombia, the full official name of the archipelago notes the three main islands: San Andres, Providencia, and Santa Catalina. The archipelago lies in the western Caribbean Sea, within 150 miles (240 kilometers) of Nicaragua and 480 miles (770 kilometers) from the Colombian mainland.

The average water surface temperature in the archipelago is 82 degrees F (28 degrees C), with a tropical dry climate. The mean air temperature is 81 degrees F (27 degrees C), moderated by the tradewinds. Besides the main islands, the archipelago also includes the atolls of Albuquerque, Courtown, Roncador, Quitasueño, and Serrana; and the reef banks of Serranilla, Bajo Alicia, and Bajo Nuevo. All of these areas are coralline structures created over old volcanoes in the early Cenozoic period. The same geologic, biologic, oceanographic, and meteorological processes have modeled the structures so the geomorphological and ecological features are common to all.

The archipelago has well-developed peripheral or barrier coral reefs in the marine current, generally on the side facing the current, and, offshore, wide pre-coral reef terraces. On the protected side, a more extensive barrier coral reef is present next to a lagoon terrace and a sedimentary shallow plane. In the lagoon basin, the depth can reach 66 feet (20 meters); nevertheless, columnar coral species can reach the surface. In protected sites, segments of barrier coral reef can be found where the lagoon basin is open or semi-open.

All of these coral reefs were modeled by sea-level oscillations during the cycles of ice age and thaw during the Pleistocene; by erosion and accretion processes in the modern era, or Holocene; and by long-term climate and current meteorological perturbations such as hurricanes.

Biodiversity

The coral species composition and morphology in the archipelago are generally determined by how open or closed a particular section of the lagoon basin is. The bottom can be dominated by seagrasses, algae, or coralline structures, depending on these factors, which in turn are shaped by three main elements: the marine current energy, the depth, and the presence of islands. The coralline formations in the archipelago are affected by marine current intensity that varies on a scale of 1–5; the average depth range is 33–39 feet (10–12 meters); and only two formations have islands that can influence the coral reefs with runoff, sediments, and nutrients that go to the lagoons. These factors have led these formations to hold from 6 percent to 28.5 percent coverage of coral species.

Six hermatypic, or stony, species associations are present in the archipelago, listed from more tolerant to marine current to less tolerant: red fouling algae (Porolithon pachydermum); fire coral (Millepora complanata) and colonial zoanthids (Palythoa spp.); elkhorn coral (Millepora palmata) and brain coral (Diplora sfrigosa); staghorn coral (Acropora cervicornis); finger coral (Porites porites); and boulder star corals (Montastraea spp.). A total of 57 hermatypic coral species are present here, together with incrusting calcareous algae. Several coral species present in the archipelago, such as column and cathedral corals, are absent in the continental reefs.

The islands and atolls provide habitat for 460 acres (186 hectares) of mangrove ecosystem, and for 18 resident and 76 migratory bird species, respectively, two of them endemic (found only here) and endangered, as well as many endemic subspecies. Four species of marine tortoises (Caretta caretta, Chelonia mydas, Dermochelys coriacea, and Eretmochelys imbricata) are present around the coral reefs, using the ecosystems for feeding and nesting. The relict forests of the islands are also important hot spots of biodiversity, with more than 360 species (roughly 75 percent native and 25 percent introduced); they also provide habitat for some endemic reptiles.

Besides the coral reef ecosystem, 4,942 acres (2,000 hectares) of seagrass beds occur within the archipelago, predominantly around the main islands. These, together with the coral formations, represent habitat for at least 270 species of fish, two of them endemic. In the coral reefs, the families Pomacentridae, Labridae, and Scaridae are dominant. The fish community tends to vary more based on reef types than on the structure of coral formations.

Environmental Threats

The main pressures on these ecosystems are represented by legal and illegal industrial fishing, including fishing of queen conch (Strombus gigas), Caribbean spiny lobster (Panulirus argus), spotted spiny lobster (Panulirus guttatus), and purple land crab (Gecarcinus ruricola). Artisanal fishing is relatively low-impact. Climate change, too, presents stark challenges to the coral reefs here, with heavier damage expected from storms, and especially from the rise in average seawater temperature, to which corals are particularly sensitive. Their zooxanthellae symbionts tend to disperse when seawater temperatures reach certain limits, exposing the coral polyps to predators, such as the crown of thorns starfish, and to disease; this is typically accompanied by the phenomenon of coral bleaching.

In part to protect the coral reefs from human damage, the Old Providence Natural National Park and the San Andres Archipelago Marine Protected Area were established. Along with the Seaflower Biosphere Reserve—which encompasses one-tenth of the Caribbean Sea—these reserves are policed to prevent overfishing and destructive recreational and tourist activities, as well as to monitor the health and balance of the marine and terrestrial species here. In 2017, the Colombian government began a program to restore the region’s coral refers that had been damaged by human activity and climate change. The government enlisted the help of local fishermen to “plant” and cultivate coral in nurseries. By 2018, eight such nurseries had been established.

Bibliography

Díaz, J. M. “Marine Biodiversity in Colombia: Achievements, Status of Knowledge, and Challenges.” Gayana 67, no. 2 (2003).

Mejía, Luz Stella and Jaime Garzón-Ferreira. “Estructura de Comunidades de Peces Arrecifales en Cuatro Atolones del Archipiélago de San Andrés y Providencia (Caribe sur Occidental).” Revista de Biologia Tropical 48, no. 4 (2000).

Moloney, Anastasia. “Colombia’s Island Fishermen Dive into Battle to Protect Coral Reefs.” Reuters , 12 Nov. 2018, www.reuters.com/article/us-colombia-environment-climatechange/colombias-island-fishermen-dive-into-battle-to-protect-coral-reefs-idUSKCN1NH142. Accessed 1 Sept. 2022.

Natural National Parks of Colombia. “Nature and Science Old Providence.” http://www.parquesnacionales.gov.co/PNN/portel/libreria/php/decide.php?patron=02.02021503&f‗patron=02.020215.