At two different ecological zones (Canal de San Lorenzo and transitional), located at Bahía de La Paz, we analysed changes in the cetacean community (Shannon and Simpson indexes) in relation to annual and seasonal changes in sea surface temperature, water transparency and inferred and reported food availability. Six odontocete and six mysticete species were recorded during the study period. Due to their high relative abundance and persistent presente, the long beak common (Delphinus capen&) and bottlenose (Tursiops truncatus) dolphins, as well as Bryde's whales (Balaenoptera edeni) were, respectively, the most important odontocete and mysticete community members. The evidente indicates that sea surface temperature and water transparency, besides food availability, show predictable seasonal and annual changes related to the influente of tropical water masses and to large scale oceanographic phenomena, such as El Nifio Southem Oscillation and La NiAa. Nevertheless, cetacean diversity did not show consequent changes. The cetacean community was more diverse and stable at the transition between seasonal and annuai oceanographic conditions. Cetacean diversity changed significantly at smaller time and space scales, detined by the interaction of particular annual, seasonal and local conditions. This and changes in species richness, mediated by the temporal residence of migrating species of temperate waters or more sporadic tropical visitors, indicate the existence of fast and important changes in species abundance and substitution rates, associated with the behavioural ecology of the species and fluctuations in the ecosystem's metabolism.

Chione cortezi es una especie de bivalvo poco conocida que ha sido reportada con una distribución que incluye el Golfo de California hasta la Bahía Magdalena en la costa oeste de Baja California. Debido a que no se tienen observaciones recientes de la especie fuera del extremo norte del Golfo de California, se realizaron dos expediciones de búsqueda de ejemplares de esta especie en mayo y julio de 1996. Se revisaron, además, los registros del Centro Interdisciplinario de Ciencias Marinas en La Paz, Baja California Sur, México. Los resultados de este estudio indican que esta especie está restringida a la Reserva de la Biosfera del Alto Golfo de California y el delta del Río Colorado. Se analizan alternativas que explican la discrepancia entre la distribución reportada y la encontrada. Se llega a la conclusión de que los reportes de distribución geográfica fueron basados en una confusión de especies entre Chione fluctifraga y C. cortezi.

The measure of the environmental impact of a sand dam in the Estero de Punta Banda is presented. The dam is part of the installations of an oil well jackets factory that was never finished. The purpose of the study is to evaluate the change in the benthic community in the dam area. The methodology proposed by Green (1979) in the suboptimal design was followed. Magnitude of change was searched by community ordination, with principal components technique and index of biological value. ANOVA test and the community ordination show a clear distinction between the dam area and the comparison areas. Descriptive indexes show that the dam biota is intermediate, between the control areas with influence of marsh and human activities. An ecological impact is assumed, consisting in the change of the sediment, with effects in food availability and risk of bird predation. The impact indicates that the system is frail to human encroachment.

Villarreal Chávez, G. Impacto de la depredación por Melongena melongena (L.) sobre las poblaciones del ostión Cmssostren virginica (Gmelin) en la Laguna de Tampamachoco, Veracruz. Impact of predation by Melongena melongena (L.) on the populations of the oyster Cmssostrea virginica (Gmelin) in Laguna de Tampamachoco, Veracruz. Ciencias Marinas, 15(Z): 556.5, 1989. RESUMENCon el objetivo de determinar el grado de impacto de la depredación del caracol Melongena melongena sobre el ostión Cmwostma vitginica se realizó una investigación en la Laguna de Tampamachoco, cerca de la ciudad de Tuxpan, Veracruz.Los resultados indican que la densidad del caracol en la zona de estudio es de 0.0007 individuos/m2, mientras que si sólo consideramos los cuadrantes en la zona de distribución preferencial es de 0.00437 individuos/m2.El caracol habita en todos los sustratos muestreados, pero se encuentra preferentementeen la zona y tipo de sustrato que prefiere el ostión, y su dieta incluye en proporción apreciable a la ostra (28%). La importancia de la depredación por caracoles, como causa de muerte no es de consideración debido a que la densidad de población de Melongena melongena es muy baja.Se concluye que Melongena melongena no representa una merma excesiva en el potencial pesquero del ostión y que por lo tanto es injustificada la campaña de exterminio existente, por otra parte el uso del caracol como recurso es de rentabilidad muy dudosa por la rareza en que se encuentra éste. ABSTRACTIn order to determine the degree of impact of predation by the snail Melongena melongena on the oyster Crassosttra virginica, a study was carried out at Laguna de Tampamachoco, near the City of Tuxpan, Veracruz, Mexico.

The crustacean assemblages of Bahfa de Todos Santos are studied in order to t'ind their characteristics and the important environmental factors associated. The results show the g. resence of three areas: the first with rocky bottom and sea grasses; the second with bare me mm to fine sand, and the third with the bottom polluted by human activities. The first and second have one crustacean assemblage each and the third has none. The animal-sediment relationships in these environments are discused as well as the crustacean fauna's origin from areas covered by detritic leaves found in the east part of the bay. This paper work deals with the distribution of the communities of malacostracean crustacean (decapods, isopods and CIENCIAS MARINAS (Mex.