The composition, distribution, and abundance of the jellyfish community of a shelf area of the Mexican tropical Pacific were surveyed during August 1988. Zooplankton samples were collected along transects on the outer and inner sectors of the continental shelf to determine the structure of the jellyfish community and its variation in this area during the rainy season. A total of 23 species were recorded, with Aglaura hemistoma, Solmundella bitentaculata, Liriope tetraphylla, Pelagia noctiluca, and Rhopalonema velatum being the most abundant. The total abundance of medusae and of the most abundant species was statistically independent of depth and distance to the coast. Hence, the total jellyfish abundance of the most abundant species, and Shannon's Diversity index had a uniform distribution in both the inner and the outer shelf; furthermore, neritic-oceanic forms and oceanic species occurred indistinctly over the entire continental shelf. On the outer shelf A. hemistoma and S. bitentaculata were most abundant; the former species, together with L. tetraphylla, weakly characterized the inner shelf jellyfish community. The narrowness of the shelf, the wide distribution of the most abundant forms, and the possible effect of local advective processes from the oceanic zone masked a definite gradient across the shelf. Three species have not been recorded previously in the Mexican Pacific: Amphinema dinema (Péron and Lesueur, 1810), Sarsia coccometra Bigelow, 1909, and Clytia mccradyi (Brooks, 1888). The finding of A. dinema is the first in the Eastern Pacific.

Se estudió la composición, distribución y abundancia de la comunidad de medusas de la plataforma continental en el Pacífico mexicano durante agosto 1988. Las muestras de zooplancton provienen de transectos en las zonas externa e interna de la plataforma para determinar la estructura de la comunidad de medusas y su variación durante la época de lluvias. Se identificaron 23 especies; las más abundantes fueron Aglaura hemistoma, Solmundella bitentaculata, Liriope tetraphylla, Pelagia noctiluca y Rhopalonema velatum. La abundancia total de las medusas y la de las especies más abundantes fue estadísticamente independiente de la profundidad y de la distancia a la costa. Por tanto, la abundancia total de las medusas, la de las especies más abundantes y la diversidad de Shannon tuvieron una distribución uniforme en ambas zonas, interna y externa de la plataforma. Adicionalmente, las formas nerítico-oceánicas y las plenamente oceánicas se presentaron de manera indistinta a través de la plataforma. En la parte externa de la plataforma A. hemistoma y S. bitentaculata fueron las especies más abundantes; por su parte, la primera de éstas, junto con L. tetraphylla, caracterizaron aunque débilmente, la comunidad de medusas de la parte interna de la plataforma. La estrechez de la plataforma, la amplia distribución de las especies más abundantes y los posibles efectos locales de procesos advectivos desde la zona oceánica ocultaron un gradiente definido a través de la plataforma. Se encontraron 3 especies que no habían sido registradas previamente en el Pacífico mexicano: Amphinema dinema (Péron and Lesueur, 1810), Sarsia coccometra Bigelow, 1909, y Clytia mccradyi (Brooks, 1888). La presencia de A. dinema representa el primer registro de esta especie en el Pacífico oriental.

Aurelia aurita is a scyphozoan, abundant in the Mexican Caribbean during summer. Although usually innocuous, there is evidence of it causing harm to humans. This work investigates the biological activities of crude and fractionated extracts of A. aurita. Live specimens were collected between July and September 1999 from the Mexican Caribbean. The tentacular margin was dissected immediately and frozen at -50ºC. A nematocyst suspension was prepared, discharged, and the supernatants lyophilized. Hemolytic assay was performed with lyophilized crude extract on bovine, sheep, and human red blood cells. Erythrocyte sensitivity to the toxin was ranked in descending order: human, sheep, and bovine. Toxic activity on Artemia nauplii was evaluated using the same crude extract for different exposure periods (3, 5, and 10 hours); only 48 and 72 hour old Artemia nauplii showed 50% mortality. Partial toxin purification was completed by sequential liquid chromatography using three gels (Sephadex G-200, DEAE Sephadex A-50, and Sephadex G-100). Intramuscular neuroactivity was detected in the crab Ocypode quadrata for two partially purified fractions. These fractions were found to have molecular weight components of 66 and 45 kDa, respectively.