Zooplankton biomass is recognized as an important indicator of secondary production, its spatial and temporal variation in neritic zones is particularly affected by discharges of the rivers, and the spatial-temporal effect of continental water discharges on the distribution of zooplankton biomass in the southern Gulf of Mexico was analyzed for 5 areas off the coasts of Veracruz, Tabasco and Campeche. The analyzed material was obtained from 534 samples collected during different climatic seasons from 1984 to 2001. The discharge volumes of 5 hydrological regions were obtained from the government's data base. The results obtained indicated that biomass variation throughout the seasons in the different areas was very similar to the pattern of discharges. The greater biomass values were recorded off Tabasco and the lower values off Veracruz, where the greater and lower continental water discharges were recorded respectively. Biomass variation depended on the discharges, not only in terms of an annual cycle, but was also directly related to the volumes discharged into the ocean. A Tree analysis made it possible to conclude that biomass is always low on the outer shelf and oceanic region of the southern Gulf of Mexico, independently of the season of the year or of a particular area. A greater biomass was recorded on the shallow shelf, with a magnitude that varied in relation to the area and season. The biomass off Campeche did not depend on the continental water discharges, but was generated on the Yucatán shelf.

La biomasa zooplanctónica es reconocida como un importante indicador de la producción secundaria; su variación espacio-temporal en zonas neríticas es afectada particularmente por las descargas de los ríos, por lo que se analiza el efecto espacio temporal de las descargas de aguas continentales en la distribución de la biomasa zooplanctónica en el sur del Golfo de México, en 5 áreas frente a las costas de Veracruz, Tabasco y Campeche. El material analizado proviene de 534 muestras recolectadas en diferentes estaciones climáticas entre 1984 y 2001. Los volúmenes de descargas de 5 regiones hidrológicas se obtuvieron de la base de datos gubernamentales. Los resultados muestran que las variaciones de la biomasa durante las estaciones del año en las diferentes áreas son muy similares al patrón de las descargas. Los mayores valores de biomasa ocurren enfrente de las costas de Tabasco y los menores frente a Veracruz, donde se tienen las mayores y menores descargas de aguas continentales respectivamente. La variación de la biomasa depende de las descargas, no sólo en términos de un ciclo anual, sino también directamente relacionada con el tamaño del volumen vertido al océano. El análisis de árbol permitió concluir que en el sur del Golfo de México sobre la parte externa de la plataforma y zona oceánica, la biomasa siempre es baja, independiente de la estación del año o del área de que se trate. La mayor biomasa ocurre sobre la plataforma en profundidades bajas, pero su magnitud varía dependiendo del área y de la época. La biomasa frente a Campeche no depende de las descargas de aguas continentales sino se genera sobre la plataforma de Yucatán.

Este estudo analisou o papel das forçantes barotrópica e baroclínicadas marés na agregação e dispersão do ictioplâncton no sul do Golfo do México. A amostragem do ictioplâncton e o cálculo dos parâmetros hidrográficos foram realizados durante Setembro de 1992 num ponto fixo de 180 m de profundidade, perto da quebra de plataforma (19º32'N - 92º38.5'W). Uma amostragem de tipo yoyo com CTD foi realizada durante 24 h e amostras biológicas foram tomadas a cada 2 h. Estas medidas foram combinadas com dados de densidade da água e velocidade obtidas de simulações do modelo do Sistema Regional de Modelo dos Oceanos (ROMS). Uma termoclina e duas haloclinas foram detectadas. O número de Froude aumentou com uma defasagem de 2 h com relação à maré barotrópica, sugerindo a existência de uma maré baroclínica. A agregação e a dispersão do ictioplancton mostraram variações verticais tanto em abundância quanto no número de taxa e larvas, com defasagem de 5 h em relação à máxima maré barotrópica e esteve em fase com a oscilação da termoclina. A oscilação vertical foi atribuída a um controle hidráulico forçado pela maré interna.

The role of vertical barotropic and baroclinic tidal forcing in the aggregation and dispersion of ichthyoplankton in the Southern Gulf of Mexico was analyzed in this study. Samplings of ichthyoplankton and the determination of hydrographic parameters were performed during September 1992 at a single point of 180 m depth, near the shelf break (19º32'N - 92º38.5'W). A 24 h CTD yo-yoing casting and biological samples were taken every 2 h and these measurements were combined with water velocity and density simulations from the Regional Ocean Model System (ROMS). One thermocline and two haloclines were depicted. The Froude number increased with a 2 h lag with respect to the maximal barotropic tide, suggesting the existence of a baroclinic tide. Aggregation and dispersion of the ichthyoplankton showed vertical oscillations in the abundance and the numbers of taxa and larvae with a 5 h lag with respect to the maximal barotropic tide and were in phase with the thermocline oscillation. The vertical oscillation was attributed to a hydraulic control forced by the internal tide.