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Biodiversity, Conservation Biology, Ecology, Ecosystem Science, Enviroment.

Unraveling the structure and composition of Varadero Reef, a coral reef in the Colombian Caribbean.

 By BFP Staff  Tuesday, June 5, 2018

Valeria Pizarro​, Sara C. Rodríguez, Mateo López-Victoria, Fernando A. Zapata, Sven Zea, Claudia T. Galindo-Martínez, Roberto Iglesias-Prieto, Joseph Pollock, Mónica Medina.
-Ecomares NGO, Cali, Valle, Colombia
-Department of Natural Sciences and Mathematics, Pontifica Universidad Javeriana, Cali, Valle, Colombia
-Department of Biology, Universidad del Valle, Cali, Valle, Colombia
-Centro de Estudios en Ciencias del Mar—CECIMAR, Universidad Nacional de Colombia—Sede Caribe, Santa Marta, Magdalena, Colombia
-Department of Biology, Pennsylvania State University, State College, PA, United States of America.

Coral reefs provide important ecosystem services (Moberg & Folke, 1999), but many currently face unprecedented pressure from multiple natural and anthropogenic stressors (Wilkinson, 2008). Caribbean reefs have been particularly impacted, with coral cover decreasing from an average of 50% to 10% in just four decades (Jackson et al., 2014). Coral cover loss has resulted in a phase shift from coral to macroalgal domination with a concurrent increase in sponge abundance (e.g., Rose & Risk, 1985; Szmant, 2002; Ward-Paige et al., 2005; Chavez-Fonnegra, Zea & Gomez, 2007; Malaio, Turingan & Lin, 2008; Jackson et al., 2014).

Coral reef ecosystems, built mainly by scleractinian corals, typically thrive within a narrow range of environmental conditions characterized by low sedimentation rates, low nutrient availability (i.e., oligotrophic waters), high light penetration, warm waters (e.g., around 28 °C) and salinity between 33 and 36 psu (Kleypas, McManus & Meñez, 1999; Díaz et al., 2000; Sheppard, Davy & Pilling, 2009). Although reefs can be found outside these ranges in “extreme” environmental conditions, such reefs are typically dominated by a low number of resistant specialist species. Some examples include reefs under higher water temperatures in the Persian Gulf and Hawaii (Oliver & Palumbi, 2009; Riegl & Purkis, 2012), reefs under low pH waters in Japan and Papua New Guinea (Fabricius et al., 2011; Inoue et al., 2013), and reefs under high salinity such as those at the Arabian Sea where salinity can exceed 45 psu and temperatures regularly top 34 °C (Rezai et al., 2004).

In 2013, a reef was discovered under unexpected conditions below a thick layer of highly turbid water at the mouth of Cartagena Bay, Colombia (López-Victoria, Rodríguez-Moreno & Zapata, 2015). This reef, known as Varadero, is located south of Tierra Bomba Island, at the mouth of the highly polluted Bay. The man-made “Canal del Dique” dumps industrial and sewage waste as well as discharges of sediment from the Magdalena River into the vicinity of Varadero. With a drainage basin covering 24% of Colombia’s surface area (27.3 million hectares), the Magdalena River feeds approximately 144 × 106 tons of suspended solids into Cartagena Bay each year. This enormous sediment load has contributed to the demise of the Bay’s once vibrant coral reefs (Restrepo et al., 2006). Paradoxically, Varadero Reef has not only survived, but thrived with up to 80% coral cover dominated by large Orbicella spp. colonies, the major reef-building corals in the Caribbean (López-Victoria, Rodríguez-Moreno & Zapata, 2015).

Despite its close proximity to the city of Cartagena, Colombia (>1 million inhabitants), Varadero Reef remained concealed due to the perception that local environmental conditions were incompatible with reef growth. High levels of sedimentation and turbidity have previously been shown to drive coral bleaching and disease that can ultimately lead to coral death (Bruno et al., 2003; Harvell et al., 2007; Pollock et al., 2014). Here we provide a preliminary characterization of Varadero Reef, including its geomorphology (i.e., size, shape and location) and biological diversity (i.e., coral, fish and sponge community composition). We also compare these characteristics with those of a nearby reference reef, Barú Reef, located 4.5 km south of Varadero, in a location much less influenced by runoff from the Canal del Dique and the city of Cartagena.

Current plans to dredge part of Varadero threaten the survival of this reef and could hinder researchers’ ability to gain insights into the factors that have allowed corals to thrive under such unusual conditions. There is, therefore, an urgent need to describe the location and characteristics of Varadero as a first step towards gaining acknowledgement of its existence and garnering inherent legal and environmental protections.

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