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.

Evaluacion de las actividades del buceo recreativo sobre la estructura comunitaria de algunos arrecifes del Parque Nacional Archipielago de Los roques, Venezuela / Evaluation of the impact of recreational dive activity on the community structure of some coral reefs at Los Roques Archipelago National Park, Venezula

In order to evaluate if snorkeling had significant effects on coral community structure, three different coral reefs (Madrizqui, Pelona de Rabusqui and Crasqui) located at Archipelago Los Roques National Park, Venezuela, were surveyed. For each site, the coral community structure of two different areas, one subjected to intense snorkeling use (FB) and other not frequently used (PFB), were compared. Community structure was determined with 1 m2-quadrants and 20 m-long transects. These communities were described in terms of species richness, diversity (Shannon-Wiener) and evenness indexes, live and dead coral cover and cover of other organisms (sponges, octocorals and algae). Comparisons within sites were performed with a Kruskall-Wallis test. A total of 24 species of scleractinian corals were found. Live coral cover ranged from 29.9 +/- 26.43 (Crasqui) to 34.55 +/- 6.43 (Madrizqui), while dead coral cover ranged from 32.51 +/- 2.86 (Madrizqui) to 60.78 +/- 21.3 (Pelona de Rabusqui). The PFB areas showed higher live coral cover compared to FB areas; however, significant differences were only found in Crasqui and Pelona de Rabusqui (p < 0.05). Species richness, diversity and evenness were variable and no trends were observed between FB and PFB areas. The frequency of both damaged and diseased colonies were low (< 1), most damages observed were natural (parrotfish predation). Damages caused by divers such as fin impacts, were not found at the reefs studied. These results suggest that, currently, diving pressure is not as high to cause massive loses of live coral cover in these reefs. However, the lack of strict controls for these activities might produce long-term changes in the structure of these coral communities.

Estado actual de las enfermedades y otros signos de deterioro coralino en siete arrecifes del Parque Nacional Archipielago de Los Roques, Venezuela / Present state of diseases and other signs of reef deterioration at seven coral reefs at Los Roques Archipelago National Park, Venezuela

This work was aimed to determine the incidence of coral diseases in six different reef sites at the Parque Nacional Archipielago de Los Roques, Venezuela: Arrecife de herradura, Arrecife costanero, both at Dos Mosquises Sur Key, Boca de Cote, Carenero, Crasqui and Pelona de Rabusqui. Each reef was surveyed by using ten 10 m2-band transects (10 x 1 m), placed parallel to the long axis of the reef within a depth gradient ranging from 1 to 9 m depth. All healthy and injured corals, along each band transect, were counted and identified to species level. Additionally, all diseases and recent mortality that were still identifiable on each colony were also recorded. The occurrence of diseased colonies and other signs of reef decline between localities were compared by means of a Chi2 test. The absolute, relative and mean incidence was estimated for each disease and other signs of damage observed for all coral species surveyed at each site. The overall incidence of coral diseases was low for all the localities surveyed, only 6.04 of the 3 344 colonies observed, showed signs of diseases. The most important diseases recorded were the Yellow-Blotch Disease (YBD) and Dark Spots Disease (DSD) with 2.1 +/- 1.52 y 2.1 +/- 2.54, respectively. Significant differences were found in the incidence of coral diseases between reef sites (Chi2 p < 0.05). Finally, the occurrence of colonies injured by parrotfish bites and pomacentrids was higher compared with the incidence of coral diseases for all the reefs surveyed. In conclusion, currently the proportion of healthy colonies at Los Roques coral reefs is higher than the percentage of both diseased and injured colonies.

White plague disease outbreak in a coral reef at Los Roques National Park, Venezuela

Coral diseases have been reported as a major problem affecting Caribbean coral reefs. During August 2000, a coral mortality event of White Plague Disease-II (WPD-II) was observed at Madrizqui Reef in Los Roques National Park, Venezuela. This disease was identified as the major cause of coral mortality, affecting 24 of all colonies surveyed (n = 1 439). Other diseases such as Black Band Disease (BBD), Yellow Blotch Disease (YBD), Dark Spots Disease (DSD) and White Band Disease (WBD) were also recorded, but showed a lower incidence (0.14-0.97). Two depth intervals, D1 (5.5-6.5 m) and D2 (9-9.5 m) were surveyed with two sets of three band transects 50 x 2 m long, placed parallel to the long axis of the reef. All healthy and injured corals, along each band transect, were counted and identified to species level. Additionally, all diseases and recent mortality that were still identifiable on each colony also were recorded. The incidence of colonies affected by WPD-II ranged from 12.8 to 33 among transects, where thirteen species of scleractinian corals showed several degrees of mortality. The species most affected were Montastraea annularis (39.13), M. faveolata (26.67), M. franksi (9.86), Stephanocoenia intersepta (7.25), Colpophyllia natans (6.96), Diploria labyrinthiformis (2.99), Mycetophyllia aliciae (2.03), M. cavernosa (1.74), and D. strigosa (1.45). WPD-II was more common in the deeper strata (9-9.5 m), where 63 of the surveyed colonies were affected, although the disease was present along the entire reef. Presently, it is imperative to determine how fast the disease is spreading across the reef, how the disease spreads across the affected colonies and what the long-term effects on the reef will be.

Población de Lytechinus variegatus (Echinoidea: Toxopneustidae) y caracterÝsticas estructurales de las praderas de Thalassia testudinum en la Bahía de Mochima, Venezuela / Population of Lytechinus variegatus (Echinoidea: Toxopneustidae) and structural characteristics of seagrass of Thalassia testudinum in Mochima Bay, Venezuela)

To compare the general features of Thalassia testudinum seagrass at Mochima Bay with sea urchin (Lxtechinus variegatus) abundance and distribution, three T. testudinum seagrass beds were selected, from the mouth (strong wave exposure) to the inner bay (calm waters). Each site was surveyed by using 5 line transects (20 m long) parallel to the coast and 1 m2 quadrats. In situ measurements of T. testudinum cover, shoot and leaf density were taken. Estimation of dry biomass for each seagrass fraction (leaves, rhizomes and roots) and leaf length were obtained from 25 vegetation samples extracted per site using cores (15 cm diameter). A multivariate analysis of variance (Manova) and a less significative difference test (LSD) were performed to examine differences between sites and within sites at different depths. A stepwise multiple regression analysis was done, dependent variable was sea urchin density; independent variables: vegetation values at each site. The only seagrass species found in the three sites was T. testudinum, and cover was 56-100, leaf density 100-1000 leaf/m2, lengths 6-18.8 cm and shoot density 20-475 shoots/m2. The highest sea urchin densities were found at Isla Redonda and Ensenada Toporo (1-3.6 ind/m2), the lowest at Playa Colorada (0.6-0.8 ind/m2). Significant differences in seagrass features between sites were obtained (Manova p < 0.001), but not between depths (Manova p < 0.320). The regression coefficient between sea urchin density and seagrass parameters was statistically significant (r2 = 0.154, p < 0.007), however, total biomass was the only variable with a significant effect on sea urchin distribution (beta = 0.308, p < 0.032). The other variables did not explain satisfactorily L. variegatus abundance and distribution.