This study describes the reef fish assemblages of Isabel Island and their relation with the benthos heterogeneity. A total of 39 visual transects from 19 different localities were performed in the zones North, South, East, and West around the island during December 2002, October 2004, and April 2005. The species composition and their abundance were registered in each transect. Video-transects were also performed to estimate the cover of benthic morpho-functional groups. A total of 9,956 specimens of fishes belonging to 118 species, 85 genera, and 51 families were registered. The 58.3% of the species have biogeographic affinity to the Panamic province. Six endemic species of the Mexican Pacific were registered, including two species endemic to the Gulf of California. According to the biological value index seven species were dominant in the island: Thalassoma lucasanum, Prionurus punctatus, Stegastes flavilatus, Halichoeres dispilus, Acanthurus xanthopterus, Abudefduf troschelii, and Johnrandallia nigrirostris. The indexes of diversity and evenness were not significantly different between the four zones of the island. However, there was a relation between the zones with higher biodiversity (South and East) and some components of the benthic habitat. The principal component analysis found that the cover of corals and rocks are highly related with the dominant species of the island, while the zones with highest proportion of sand, sponges, and gorgonians have less influence on fish diversity.

Additive partitioning was applied to variation in reef fish spatial diversity at Isla Isabel National Park, Nayarit state, Mexico, and to identify the environmental and spatial variables that best explains it. Analyses included expected and observed species curves, rare species analysis, additive partitioning of alpha-and beta-diversity, and canonical redundancy analysis. A total of 10,517 individuals were recorded from 75 species and 33 reef fish families, representing 85% of expected richness. Species richness beta-diversity was dependent on the site scale, while the alpha-diversity of the Shannon diversity was most significant at the transect scale. Canonical partitioning showed species richness and Shannon diversity was explained by spatially-structured environmental components. Variation in species composition and abundance was explained by a purely environmental component. Therefore, elements of habitat structure (especially corals), topographic complexity, and refuge availability determine fish species diversity. Our results suggest that greater emphasis is required to conserve sites that promote b-diversity, increasing fish spatial diversity. In Isla Isabel, these sites would be mostly those located at eastern and southern of protected sides, where coral reef patches are well represented. The

Cuarenta especies de equinodermos fueron recolectadas en las zonas intermareal y submareal somero de 14 sitios de bahía Chamela. Destacan 7 nuevos registros para la costa de Jalisco. Los análisis de escalonamiento multidimensional no métrico y el índice de similitud de Jaccard permitieron identificar grupos y entidades aisladas de acuerdo a la contribución y frecuencia de las especies de 4 clases de equinodermos en los sitios de la bahía y en otras localidades del Pacífico tropical mexicano (PTM). La mayor similitud se presentó con las localidades del golfo de California. Los índices de distinción taxonómica promedio (Δ + ) y su variación (Λ + ) fueron utilizados para analizar la diversidad de equinodermos en los niveles de especie, género, familia, orden y clase para cada sitio de la bahía y para distintas localidades del PTM de acuerdo al número de jerarquías taxonómicas de alto orden y la variabilidad en su diversidad taxonómica. La riqueza de especies de Chamela representa el 20% de la diversidad total de equinodermos de las zonas intermareal y submareal somero del PTM, lo que indica su importancia en la contribución a la diversidad taxonómica de la región.

A number of specimens of the Californian lancelet, Branchiostoma californiense Andrews, 1893 were found in Isla Melendres, Sinaloa and Bahía Chamela, Jalisco, in the Mexican Pacific. The specimens were collected with a biological dredge on sandy bottoms. Some morphometric and meristic characters of the collected specimens are described and discussed herein. This is the first record of the species for the Bahía Chamela in the central Mexican Pacific and second for the Sinaloa state in the Gulf of California, confirming their distribution along the Eastern Pacific from the coast of California coast, USA to Panama. However, an extensive area of the southern Mexican Pacific (∼1,500 km from Colima to Chiapas) have scarce records of this species, this possibly due to the lack of sampling effort on this group in the area.

The popularity of ecotourism in the marine protected areas of Mexico has increased over the last 10 years; in particular there is a large development of a SCUBA diving industry in the Mexican Pacific including Isabel Island. Given the risks associated with human activity in the marine environments around this island, we propose two ecotourism management strategies: (1) the creation and use of underwater trails, and (2) the estimation of the specific tourism carrying capacity (TCC) for each trail. Six underwater trails were selected in sites that presented elements of biological, geological, and scenic interest, using information obtained during field observations. The methodology used to estimate the TCC was based upon the physical and biological conditions of each site, the infrastructure and equipment available, and the characteristics of the service providers and the administrators of the park. Correction factors of the TCC included elements of the quality of the visit and the threat and vulnerability of the marine environment of each trail (e.g., divers' expertise, size and distance between groups of divers, accessibility, wind, coral coverage). The TCC values ranged between 1,252 and 1,642 dives/year/trail, with a total of 8,597 dives/year for all six trails. Although these numbers are higher than the actual number of recreational visitors to the island (~1,000 dives per year), there is a need for adequate preventive management if the diving sites are to maintain their esthetic appeal and biological characteristics. Such management might be initially directed toward using only the sites and the TCC proposed here.