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.

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.