Estructura de las comunidades de corales y octocorales de Isla de Aves, Venezuela, Caribe Nororiental / Structure of the coral and octocoral communities of Isla de Aves, Venezuela, Northeast Caribbean

The Isla de Aves Wildlife Refuge is the northernmost portion of the Venezuelan territory generating 135 000km² of Exclusive Economic Zone. Studies on coral communities are scarce and old (1970s), due to its location 650km northeast of La Guaira Port and because it has military facilities. To upgrade baseline information we estimated size structure, percent live cover, species composition and abundance of corals and octocorals. We evaluated 16 sites around the island using the AGRRA Protocol (band-transects 10 m²) between 1.5 and 21m depth (n=67 transects), and visual surveys conducted in other five sites. We recorded 2 327 colonies belonging to four hydroid species and 36 species of stony corals in 11 families. The values for diversity, dominance and evenness of the coral community ranged between 0.78 and 2.12 (SW), 0.15 and 0.61 and 0.57 y 0.92 respectively. Most coral species had relative abundance values under 3%, except Porites astreoides (25.57%), Pseudodiploria strigosa (18.22%) and Siderastrea siderea (14.44%). They were represented mostly by smaller colonies, between 3 and 30cm in maximum diameter and between 0 and 5cm high. A total of 13 octocoral species belonging to three families were identified. Pseudopterogorgia americana was the most abundant species. The mean percent of live coral (including hydrocorals) was 22.30% (SE=1.73) (15.45% for dead coral, SE=3.28). Dead coral had the highest percentage of dissimilarity between sites (9.21%) (ANOSIM) and 16.57% contribution (SIMPER analysis). Octocoral live cover ranged from 0 to 21.35% with a mean of 6.38% (SE=0.99). Research on benthic communities of Isla de Aves should continue, especially in the deeper areas, to assess ecological conditions.

El Refugio de Fauna Silvestre Isla de Aves (RFSIA) representa la porción más septentrional del territorio Venezolano, generando 135 000km² de Zona Económica Exclusiva. Los estudios sobre sus comunidades coralinas son escasos y en su mayoría datan de la década de los setenta, por su ubicación a 650km al nor-este del Puerto de la Guaira y por su condición de zona militar. Para actualizar y obtener una línea base cuantitativa sobre la estructura de las comunidades coralinas de la isla, se estimó la cobertura lineal, estructura de tallas, composición y abundancia de corales y octocorales. Evaluamos 16 sitios alrededor de la isla empleando el Protocolo AGGRA (banda-transectas de 10m²) entre 1.5 y 21m de profundidad (n= 67 transectas) y se realizaron censos visuales en 5 sitios más. Observamos un total de 2 327 colonias pertenecientes a cuatro especies de hidrozoos y 36 especies de corales pétreos pertenecientes a 11 familias. Los valores de diversidad, dominancia y equitatividad de la comunidad de corales oscilaron entre 0.78 y 2.12 (S-W); 0.15 y 0.61 y 0.57 y 0.92 respectivamente. La mayor parte de los corales presentaron valores de abundancia relativa menores al 3%, a excepción de Porites astreoides (25.57%), Pseudodiploria strigosa (18.22%) y Siderastrea siderea (14.44%). La estructura de tallas de estas especies estuvo representada en su mayoría por las categorías de tallas más pequeñas, entre los 3 y 30cm de diámetro máximo y entre 0 y 5cm de altura. Se identificaron un total de 13 especies de octocorales pertenecientes a 3 familias, siendo Pseudopterogorgia americana la especie dominante en abundancia. La cobertura promedio de coral vivo (incluyendo hidrocorales) fue de 22.30% (SE=1.73) (coral muerto 15.45%,SE=3.28). El coral muerto es la que presentó el mayor porcentaje de disimilaridad entre sitios (9.21%) (ANOSIM); con un porcentaje de contribución de 16.57% (Análisis SIMPER). La cobertura viva lineal de octocorales varió entre 0 y 21.35% (SE=3.65) con un promedio de 6.38% (SE=0.99). Las investigaciones sobre las comunidades bentónicas de Isla de Aves deben continuar, especialmente en las zonas más profundas, para evaluar las ocndiciones ecológicas.

Fauna bentónica asociada a una pradera de Thalassia testudinum (Hydrocharitaceae) en el Parque Nacional Morrocoy, Venezuela / Benthic fauna associated to a Thalassia testudinum (Hydrocharitaceae) bed in the Parque Nacional Morrocoy, Venezuela

The benthic fauna and diel variation in a shallow seagrass bed (Thalassia testudinum) were studied in Playa Mero, Venezuela. Samples of organisms and sediments were taken using PVC cylinders, 5cm in diameter, along a transect perpendicular to the coast. Seagrass cover, shoot density and biomass were estimated. The seagrass cover was homogeneous along the transect. The intermediate zone had the highest number of shoots and of above-ground and rhizome biomass. Composition and abundance of benthic organisms were related with seagrass and sediment characteristics. Sediment organic matter content and organism abundance were highest near the shore Molluscs, polychaetes, oligochaetes and nematodes were the most abundant groups. Species richness was higher in daytime (40 versus 28 at night). Gastropods were the most abundant organisms both at day and night while polychaetes and crustaceans increased during the day, and holoturids were more numerous at night.

Estructura de la comunidad de peces arrecifales de Playa Mero, Parque Nacional Morrocoy, Venezuela / Reef fishes community structure from Playa Mero, Parque Nacional Morrocoy, Venezuela

The coral reef fish community was studied in Playa Mero, Morrocoy National Park, after the mass mortality of January, 1996 with a systematic sampling design. Transects and quadrates were used for corals, and a visual census for fishes. The coral community is highly disturbed with extensive areas of dead coral covered by algae, and low coverage and richness of coral species, gorgonians, sponges and briozooans. These factors have generated a relatively homogeneous environment with respect to the fish community, which was dominated by Scaridae and Pomacentridae that represented 75% of fish. Dominant fishes were mainly herbivorous (75.4% of all fish) apparently because of the disturbance that caused the settling of algae.

Estructura de una comunidad arrecifal en Falcón, Venezuela, antes y después de una mortalidad masiva / Reef community structure at Falcón, Venezuela, before and after a massive mortality

Morrocoy National Park used to be considered the most important continental coral reef of Venezuela. However, in January of 1996, there was a massive mortality of the benthic organisms for unknown reasons. The coral reef community was monitored since 1995, the year before the event, and yearly after that, until June 1999, by sampling linear transects and quadrats. A total of 26 hard corals were recorded in the study site (Playa Mero) in 1995 (36.56% cover), which already had some deterioration because 90.86% of the living coral cover was represented basically by four species, M. annularis with 51.36%, Colpophyllia natans with 18.22%, Agaricia agaricites with 11.58% and Porites porites with 9.70%. Three months after the event, living coral cover was only 4.84% and algae, particularly Dyctiota spp. covered most of the surface (81.89%). Benthic organisms suffered massive mortality over the whole depth gradient and in most park reefs. Even after three years the reef community shows highly perturbed conditions, with 85% of the total cover represented by the categories: dead coral, dead coral overgrowth by algae and sand. From the initial coral richness of the area (26 species) only nine species were observed although in very low cover (<1%), except for M. annularis and M. franksi, which presented lightly higher percentages.