Many coral reefs have phase shifted from coral to macroalgal dominance. Ocean acidification (OA) due to elevated CO 2 is hypothesised to advantage macroalgae over corals, contributing to these shifts, but the mechanisms affecting coral-macroalgal interactions under OA are unknown. Here, we show that (i) three common macroalgae are more damaging to a common coral when they compete under CO 2 concentrations predicted to occur in 2050 and 2100 than under present-day conditions, (ii) that two macroalgae damage corals via allelopathy, and (iii) that one macroalga is allelopathic under conditions of elevated CO 2 , but not at ambient levels. Lipid-soluble, surface extracts from the macroalga Canistrocarpus (=Dictyota) cervicornis were significantly more damaging to the coral Acropora intermedia growing in the field if these extracts were from thalli grown under elevated vs ambient concentrations of CO 2 . Extracts from the macroalgae Chlorodesmis fastigiata and Amansia glomerata were not more potent when grown under elevated CO 2 . Our results demonstrate increasing OA advantages seaweeds over corals, that algal allelopathy can mediate coral-algal interactions, and that OA may enhance the allelopathy of some macroalgae. Other mechanisms also affect coral-macroalgal interactions under OA, and OA further suppresses the resilience of coral reefs suffering blooms of macroalgae.Coral reefs are one of the most diverse and complex ecosystems on the planet and provide livelihoods, food, and important ecosystem services for hundreds of millions of people 1 . However, a large proportion of reefs worldwide are severely degraded, and many reefs are on a trajectory of decline 2,3 . A symptom of decline is a reduced cover of reef-building corals and an increased abundance of upright macroalgae 4,5 . Understanding the drivers of macroalgal increases and the effects of coral-macroalgal interactions on reef degradation and resilience is of critical importance for the conservation of reef ecosystems [6][7][8] .The drivers of coral loss and macroalgal increase are varied and include herbivore loss through overfishing or disease, decreased water quality associated with nutrient enrichment and sedimentation, coral mortality caused by predators, hurricanes and cyclones, bleaching and diseases, algal colonization associated with coral morality, and a failure of juvenile corals and fishes to recruit once reefs become algal dominated 2,9-12 . Problems arising from human-induced ocean acidification, that occurs as atmospheric CO 2 is absorbed by the ocean and lowers pH 13 , have also been suggested as potential drivers of elevated algal populations on reefs [14][15][16] . Elevated seawater CO 2 concentrations may enhance fleshy algal growth rates 15,17,18 , reduce coral growth and calcification rates 19 , and strengthen space competition between macroalgae and corals, with outcomes that favour macroalgae over corals 14,15,20 . Habitats with naturally elevated CO 2 concentrations show increased fleshy macroalgal abundance 21 and decreased coral...

Abundance of Diadema antillarum (Echinodermata: Echinoidea) in the coasts of Venezuela. Diadema antillarum is a shallow-water sea-urchin from the tropical Atlantic whose populations almost disappeared in 1983-84 because of widespread mortalities which reached 87-100 %. In Venezuela, urchin population densities before the mortality event were comparable to those of other Caribbean regions; however, later abundancies remain unknown. The objectives of this study were to evaluate the recent densities of certain D. antillarum populations along the Venezuelan coasts and compare the densities at the Parque Nacional Mochima before and after the mortality. At each location urchin densities were determined by means of transects using 1m 2quadrats as sampling units. The highest mean densities were observed at the sites on the central coast: Ensenada de Oricao, 0.28 ind/m 2 (2002) and 1.05 ind/m 2 (2003), and Chichiriviche de la Costa, 0.84 ind/m 2 (2002) and 0.74 ind/m 2 (2003). In Mochima, the mean density before the mortality for D. antillarum oscillated between 0.28 and 4 ind/m 2 , after the mortality event the mean density varied between 0.15 ind/m 2 (2000) and 0.47 ind/m 2 (2000). The populations of D. antillarum studied at Parque Nacional Morrocoy and Refugio de Fauna Silvestre Cuare showed highest densities at Playuela (0.43 ind/m 2) and Cayo Sur (0.95 ind/m 2) respectively, whereas other sites showed densities below 0.1 ind/m 2. The density registered at Playuela in 2003 is lower than that reported before the mortality event (0.58-3.64 ind/m 2). The density for Parque Nacional Archipiélago de Los Roques, specifically for the Arrecife de Herradura remained constant between 2002 and 2003 with values between 0.22-0.23 ind/m 2 respectively. To conclude, the sea urchin abundancies observed at most of the Venezuelan coastal sites that we studied were higher than those reported for other areas of the northern Caribbean, even though the values have not yet returned to those preceding the 1984 mass-mortality event, due to the slow recovery of the populations.

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El Niño Southern Oscillation (ENSO) has generated global coral massive bleaching. The aim of this work was to evaluate the massive bleaching of coral reefs in Puerto Cabello, Venezuela derived from ENSO 2010. We evaluated the bleaching of reefs at five localities both at three and five meter depth. The coral cover and densities of colonies were estimated. We recorded living coral cover, number and diameter of bleached and nonbleached colonies of each coral species. The colonies were classified according to the proportion of bleached area. Satellite images (Modis Scar) were analyzed for chlorophyll-a concentration and temperature in August, September, October and November from 2008-2010. Precipitation, wind speed and air temperature information was evaluated in meteorological data for 2009 and 2010. A total of 58.3% of colonies, belonging to 11 hexacoral species, were affected and the greatest responses were observed in Colpophyllia natans, Montastraea annularis and Montastraea faveolata. The most affected localities were closer to the mainland and had a bleached proportion up to 62.73±36.55%, with the highest proportion of affected colonies, whereas the farthest locality showed 20.25±14.00% bleached and the smallest proportion. The salinity in situ varied between 30 and 33ppm and high levels of turbidity were observed. According to the satellite images, in 2010 the surface water temperature reached 31ºC in August, September and October, and resulted higher than those registered in 2008 and 2009. Regionally, chlorophyll values were higher in 2010 than in 2008 and 2009. The meteorological data indicated that precipitation in November 2010 was three times higher than in November 2009. Massive coral bleaching occurred due to a three month period of high temperatures followed by one month of intense ENSO-associated precipitation. However, this latter factor was likely the trigger because of the bleaching gradient observed. Rev. Biol. Trop. 60 (2): 527-538. Epub 2012 June 01.

Predation rate of Coralliophila abbreviata (Neogastropoda: Coralliophilidae) on some coral species at Parque Nacional Morrocoy, Venezuela. Coralliophila abbreviata is a tropical gastropod of the Caribbean Sea. This gastropod is an important corallivore. The objective of this work was to estimate the predation rate of C. abbreviata on some coral species in the coral reefs of Morrocoy National Park, Venezuela. The localities were Cayo Sombrero and Cayo Peraza. We evaluated the rate on five coral species: Montastraea annularis, Colpophyllia natans, Diploria strigosa, Diploria labyrinthiformis and Agaricia agaricites. We used three experimentals treatments. in treatment 1 we marked colonies with buoys that had been predated by C. abbreviata. in treatments ii and iii we used exclusion cages. Treatment ii included the colony with its predators and treatment iii was the control (only the colony). The injuries of the colonies were measured every 4 days for at least a month. The predation rate in treatment i varied depending on the coral species. The highest rate was on C. natans Un factor importante que puede definir la estructura de las comunidades coralinas son los organismos depredadores (coralív-oros), los cuales pueden representar una amenaza potencial para estos sistemas; (Moran 1986; Birkeland y Lucas 1990, Turner 1994, Knowlton 2001) debido a que pueden generar efectos negativos en la diversidad (Baums et al. 2003).Coralliophila abbreviata (Lamarck, 1816) es un molusco depredador de corales, común en las aguas tropicales del Atlántico Occidental; posee una distribución que abarca desde Bermudas hasta Venezuela. Se encuentra en aguas someras y habitualmente permanece en agregaciones mayores a veinte individuos sobre las colonias coralinas (Ward 1965), específicamente en la frontera entre el tejido vivo y el tejido muerto (Lewis 1960). Se ha estimado que C. abbreviata puede consumir 9 cm 2 /día de tejido coralino vivo (Ott y Lewis 1972).Estos moluscos se alimentan de tejido coralino mediante una probóscide que insertan sobre la cavidad celentérica del coral que, a través de una acción enzimática, provoca la fragmentación del epitelio. No posee rádula y el tejido que succiona pasa directamente al esófago mediante una bomba bucal que conduce el alimento hacia su intestino (Soong & Chen 1991). Miller (1981 reporta que C. abbreviata depreda por lo menos 14 especies de corales escleractínidos en el Caribe.En enero de 1996 el Parque Nacional Morrocoy (PNM) sufrió una mortalidad masiva en el sistema arrecifal, Laboy-Nieves et al. (2001) reportaron la muerte del 90% de la cobertura coralina, por lo que la depredación por C. abbreviata podría afectar la recuperación de los arrecifes coralinos en la zona de estudio. Si esta aseveración es correcta, se esperaría encontrar que C. abbreviata presente una tasa de depredación superior o igual, a la estimada por otros investigadores en los arrecifes del Caribe sobre especies coralinas presentes en el área de estudio.En tal sentido, se pretende estimar la tasa de depreda...