Effects of ocean acidification on the potency of macroalgal allelopathy to a common coral.

Many coral reefs have phase shifted from coral to macroalgal dominance. Ocean acidification (OA) due to elevated CO2 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 CO2 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 CO2, 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 CO2. Extracts from the macroalgae Chlorodesmis fastigiata and Amansia glomerata were not more potent when grown under elevated CO2. 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.

Massive bleaching of coral reefs induced by the 2010 ENSO, Puerto Cabello, Venezuela.

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 non-bleached 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 Montastraeafaveolata. 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 31 degree C 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.

Variabilidad temporal de la abundancia de Coralliophila abbreviata y Coralliophila caribaea (Mollusca, Coralliophilidae) en un arrecife coralino del Parque Nacional Morrocoy, Venezuela

Temporary abundance variation of Coralliophila abbreviata and Coralliophila caribaea (Mollusca, Coralliophilidae) in a coral reef at Morrocoy National Park. The mollusks Coralliophila abbreviata and C. caribaea are coral predators in the Caribbean Sea . We evaluated the temporal variability of abundance and size structure of C. abbreviata and C. caribaea in Cayo Sombrero, Morrocoy National Park, Venezuelar (September 2004 - August 2005). The density of C. abbreviata and C. caribaea was evaluated monthly by means of two 50- meter long transects paralell to the coast line, at 3 m and 6 m deep; aditionally, 30 individuals of C. abbreviata were collected to measure size. The densities of C. abbreviata at the shallow transect fluctuated between 1.78 ind/m² in September and 6.26 ind/m² in May. The densities at the deep transect fluctuated between 4.23 ind/m² in January and 7.66 ind/m² in May. The densities of C. caribaea at the shallow transect fluctuated between 0 ind/m2 (except in September) and 0.03 ind/m² (September) and the densities at the deep transect fluctuated between 0 ind/m² (October to March and July) and 0.1 ind/m² (April). Most individuals of C. abbreviata and C. caribaea measured between 12 and 16 mm and between 10 and 15 mm long respectively. Rev. Biol. Trop. 56 (2): 501-511. Epub 2008 June 30.

C. abbreviata y C. caribaea son moluscos coralívoros del Mar Caribe. Evaluamos la variabilidad temporal de la abundancia y los cambios en la estructura de talla de C. abbreviata y C. caribaea en Cayo Sombrero, Venezuela (septiembre 2004-agosto 2005). Se colocaron transectas fijas de 50 metros de longitud a profundidades de tres y seis metros cada una, paralelas a la costa. Se evaluó mensualmente durante un año la densidad de ambos depredadores y se seleccionaron 30 individuos de C. abbreviata para medirlos cada mes. Las densidades de C. abbreviata en la transecta somera fluctuaron entre 1.78 ind/m² en septiembre y 6.26 ind/m² en mayo; las densidades de C. abbreviata en la transecta profunda estuvieron comprendidas entre 4.23 ind/m² en enero y 7.66 ind/m² en mayo. Las densidades de C. caribaea fluctuaron en la transecta somera entre 0 ind/m² (todos los meses menos septiembre) y 0.03 ind/m² (septiembre) mientras que la transecta profunda fluctuó entre 0 ind/m² (octubre a marzo y julio) y 0.1 ind/m² (abril). La mayoría de los individuos de C. abbreviata midieron entre 12 y 16 mm de longitud. El largo de la mayoría de los individuos de C. caribaea estuvo comprendido entre 10 y 15 mm.

[Temporary abundance variation of Coralliophila abbreviata and Coralliophila caribaea (Mollusca, Coralliophilidae) in a coral reef at Morrocoy National Park]. / Variabilidad temporal de la abundancia de Coralliophila abbreviata y Coralliophila caribaea (Mollusca, Coralliophilidae) en un arrecife coralino del Parque Nacional Morrocoy, Venezuela.

The mollusks Coralliophila abbreviata and C. caribaea are coral predators in the Caribbean Sea . We evaluated the temporal variability of abundance and size structure of C. abbreviata and C. caribaea in Cayo Sombrero, Morrocoy National Park, Venezuelar (September 2004 - August 2005). The density of C. abbreviata and C. caribaea was evaluated monthly by means of two 50-meter long transects paralell to the coast line, at 3 m and 6 m deep; aditionally, 30 individuals of C. abbreviata were collected to measure size. The densities of C. abbreviata at the shallow transect fluctuated between 1.78 ind/m2 in September and 6.26 ind/m2 in May. The densities at the deep transect fluctuated between 4.23 ind/m2 in January and 7.66 ind/m2 in May. The densities of C. caribaea at the shallow transect fluctuated between 0 Ind/m2 (except in September) and 0.03 Ind/m2 (September) and the densities at the deep transect fluctuated between 0 Ind/m2 (October to March and July) and 0.1 Ind/m2 (April). Most individuals of C. abbreviata and C. caribaea measured between 12 and 16 mm and between 10 and 15 mm long respectively.

Abundancia de Diadema antillarum (Echinodermata: Echinoidea) en las costas de Venezuela / 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 1 m2-quadrats as sampling units. The highest mean densities were observed at the sites on the central coast: Ensenada de Oricao, 0.28 ind/m2 (2002) and 1.05 ind/m2 (2003), and Chichiriviche de la Costa, 0.84 ind/m2 (2002) and 0.74 ind/m2 (2003). In Mochima, the mean density before the mortality for D. antillarum oscillated between 0.28 and 4 ind/m2, after the mortality event the mean density varied between 0.15 ind/m2 (2000) and 0.47 ind/m2 (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/m2) and Cayo Sur (0.95 ind/m2) respectively, whereas other sites showed densities below 0.1 ind/m2. The density registered at Playuela in 2003 is lower than that reported before the mortality event (0.58-3.64 ind/m2). 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/m2 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.

Diadema antillarum es un erizo de aguas someras del Atlántico tropical cuyas poblaciones fueron diezmadas entre los años 1983-1984 con mortandades de hasta 87-100 %. En Venezuela, las densidades registradas antes de la mortalidad presentaban valores similares a los de otras regiones del Caribe, sin embargo se desconoce las abundancias posteriores al evento. Los objetivos del presente estudio fueron evaluar las densidades recientes de algunas poblaciones de D. antillarum a lo largo de las costas de Venezuela y comparar las densidades de la Bahía de Mochima antes y después de la mortandad. Se utilizaron transectos, y cuadrantes de 1m2 como unidad muestreal. Se registraron las mayores densidades promedio en las localidades del litoral central: Ensenada de Oricao con 0.28 ind/m2 (2002) y 1.05 ind/m2 (2003), y Chichiriviche de la Costa con 0.84 ind/m2 (2002) y 0.74 ind/m2 (2003). En la Bahía de Mochima, la densidad promedio antes de la mortandad de D. antillarum osciló entre 0.28 y 4 ind/m2, luego del evento de mortandad la densidad promedio varió entre 0.15 ind/m2 (2000) y 0.47 ind/m2 (2002). Las poblaciones de D. antillarum estudiadas en el Parque Nacional Morrocoy y Refugio de Fauna Silvestre Cuare presentaron las densidades promedio más altas en Playuela (0.43 ind/m2) y Cayo Sur (0.95 ind/m2), mientras que las demás áreas presentaron densidades inferiores a 0.1 ind/m2. La densidad registrada en Playuela en el 2003 es menor a la informada antes del evento de mortandad (0.58-3.64 ind/m2). La densidad del Parque Nacional Archipiélago Los Roques, específicamente en el Arrecife de Herradura, se mantuvo constante durante 2002-2003, con valores entre 0.22 y 0.23 ind/m2 respectivamente. En conclusión, las abundancias registradas en la mayoría de las localidades evaluadas en Venezuela son superiores a las informadas para áreas al norte del Caribe, aunque todavía no se ha alcanzado los niveles anteriores a la mortalidad de 1984 por el lento incremento de las poblaciones.

[Abundance of Diadema antillarum (Echinodermata: Echinoidea) in the coasts of Venezuela]. / Abundancia de Diadema antillarum (Echinodermata: Echinoidea) en las costas de 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 1 m2-quadrats as sampling units. The highest mean densities were observed at the sites on the central coast: Ensenada de Oricao, 0.28 ind/m2 (2002) and 1.05 ind/m2 (2003), and Chichiriviche de la Costa, 0.84 ind/m2 (2002) and 0.74 ind/m2 (2003). In Mochima, the mean density before the mortality for D. antillarum oscillated between 0.28 and 4 ind/m2, after the mortality event the mean density varied between 0.15 ind/m2 (2000) and 0.47 ind/m2 (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/m2) and Cayo Sur (0.95 ind/m2) respectively, whereas other sites showed densities below 0.1 ind/m2. The density registered at Playuela in 2003 is lower than that reported before the mortality event (0.58-3.64 ind/m2). 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/m2 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.