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This study simulated the connectivity patterns among 7 coral reef systems in the southern Gulf of Mexico. Two subgroups of reefs were considered: one near the mainland over the narrow western shelf, and the other over the wide Campeche Bank (CB). A particle-tracking module was coupled to a realistic simulation with the Hybrid Coordinate Ocean Model in order to study the transport and dispersion of particles in near surface waters. The simulation consisted of the launch of 100 passive particles (virtual larvae) from each reef, every 24 h over a 5 year period; it considered species lasting up to 35 d in the plankton and assumed no seasonality in reproduction. On the western shelf, connection was northwards from March to August, and southwards from September to February; over the CB edge, the connection was northwestwards throughout the year. Over the western shelf, reefs showed a strong degree of interconnectivity and high particle retention. Higher self-recruitment was most likely due to the passage of synoptic-scale atmospheric systems and their associated changes in wind and current direction. In contrast, CB reefs exhibited lower connectivity and less larval retention. Over the western edge of the Bank, connectivity was almost unidirectional because of the influence of the cyclonic gyre in the Campeche Bay, which causes particles to disperse over a wide area with low probabilities of selfrecruitment. The main connection pathway was the confluence zone between neritic and oceanic waters over the outer shelf of the Bank. Connection between the 2 groups of reefs was weak.

ABSTRACT. To extend our knowledge about spatial and temporal variations in the structure of estuarine fish communities, diel samplings (collections every 2 h) were carried out every two months over a one-year period in two different habitats (vegetated and nonvegetated). We collected a total of 34,766 individuals, corresponding to 72 species, most of them with marine and tropical affinities. Species richness was significantly higher in the vegetated habitat, whereas abundance (number of fish) was higher in the nonvegetated habitat. The diel pattern of abundance showed peaks at dusk and dawn, whereas richness was higher at night. Seasonally, fish abundance and species richness showed peaks during January, March, and July-September, and these peaks were related to the entry of temperate species, production processes in the system, and rainfall pattern. Fish assemblages showed significant differences among habitats, day/night, and months. In the vegetated habitat, Lagodon rhomboides, Menidia beryllina, and Orthopristis chrysoptera were the predominant species. Microphagus species such as Brevoortia gunteri, Brevoortia patronus, and Mugil curema were predominant during the warm, dry season (March-May) and they were more abundant during the day. In contrast, predatory species such as Citharichthys spilopterus and Opsanus beta were more abundant during the rainy season and their capture was higher at night. The two most numerically abundant species, Anchoa mitchilli and Membras martinica, showed a twilight pattern, with abundance peaks at dusk and dawn, respectively. Hence, in Pueblo Viejo Lagoon (Mexico), the spatiotemporal changes in species composition are in part related to predator avoidance and feeding strategies, through a coupling of life histories with the diel and seasonal variation in the availability of resources, the presence of submerged vegetation playing an important role in this dynamic.Key words: Ruppia maritima, mean trophic level, predator avoidance, diversity, fish assemblages. RESUMEN. Con el objetivo de contribuir al conocimiento de las variaciones espaciotemporales en la estructura de las comunidades de peces estuarinos, cada dos meses se realizaron muestreos nictímeros (colectas cada dos horas) en dos ambientes diferentes (con vegetación y sin vegetación) durante un año. En total se capturaron 34,766 individuos, correspondientes a 72 especies, de origen principalmente marino y tropical. La riqueza de especies fue significativamente mayor en el hábitat con vegetación sumergida, mientras que la abundancia lo fue en el hábitat sin vegetación. El patrón nictímero de la abundancia mostró pulsos al anochecer y al amanecer, mientras que la riqueza fue mayor durante la noche. Estacionalmente, la abundancia y la riqueza presentaron pulsos en enero, marzo y julio-septiembre, los cuales se relacionan con el ingreso de especies templadas, procesos de producción dentro del sistema y el régimen de lluvias. El conjunto de especies mostró diferencias significativas entre hábitat, día/noche y meses. En el hábit...

Spatial, seasonal and diel distribution patterns were analysed over a 2-year period for Diapterus auratus and Eucinostomus melanopterus in Pueblo Viejo lagoon, a tropical coastal lagoon in Veracruz, Mexico. A total of 216 samples were collected with 329 individuals of D. auratus and 170 of E. melanopterus. Diapterus auratus individuals were captured throughout a wider range of environmental conditions, and consequently its spatial niche breadth was significantly greater (P < 0.001) than that of E. melanopterus. In general, more individuals were captured at localities with submerged vegetation (Ruppia maritima), with 70% for D. auratus and 87.2% for E. melanopterus, although only the latter species showed significant spatial differences. A spatial segregation influenced by distance from the lagoon inlet and salinity was observed between the species. It is considered that this segregation may allow resource partitioning and minimize interspecific competition. A relatively low niche overlap (4.9%) was observed for the two species. Seasonal capture peaks of D. auratus were related to rainfall and the productivity pattern in the lagoon system. Seasonal fluctuations in monthly mean number of D. auratus were correlated with preceding variations in local rainfall (r ¼ 0.86, P < 0.02). Moreover, seasonal capture peaks of D. auratus coincided with ecosystem primary production peaks. Although E. melanopterus exhibited no significant seasonal differences, its maximum numbers also coincided with an ecosystem primary production peak and recruitment patterns. In 24-h cycle analysis, both species were captured mainly around mid-day, with minor peaks at dawn and/or at dusk. Generally, few individuals were collected during hours of darkness. It was proposed that diel abundance variation of gerreids might be related to both light penetration in the water column and feeding activity. Food availability within Pueblo Viejo lagoon appears to be an important factor influencing fish abundance.

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Siphonophores are exclusively marine cnidaria and their predatory role in plankton foodwebs is well recognised. In this study, we analyse the structure and the spatial extent of siphonophore assemblages in relation to changes in freshwater outflows and food availability in the southern Gulf of Mexico during a high (October) and a low (April) outflow periods. A total of 149 samples were collected using a 505 lm multiple closing net at 1-6 levels (0-100 m) of the water column, depending on the bathymetry. Data on siphonophore species biovolumes (ml 100 m -3 ) were treated by means of the Bray-Curtis Dissimilarity Index, and two distinctive assemblages were identified: the 'inner' and the 'outer' assemblages, located over the inner and outer shelves. Temperature, salinity, zooplankton biomass, and siphonophore species were included in a Principal Component Analysis (PCA) to identify the factors associated with each assemblage. Geographical distribution of the assemblages practically remained the same during both seasons and its cross-shelf variability was stronger than the vertical one. Seasonally, diversity values were higher in October, when the highest river discharges occur. Spatially, the lowest diversity and mean siphonophore biovolumes values were registered in the 'inner assemblage', where the highest and lowest salinity values were recorded. We suggest that even when extreme salinity values (>36.5 or <34) might depress siphonophore populations in the coastal area, enough food availability in the concerned areas might mitigate the negative effect of salinity, since a positive and significant (p < 0.05) relationship was found between siphonophores biovolume and zooplankton biomass. Bassia bassensis, Diphyes dispar and Enneanogum hyalinum, present in both assemblages during both seasons, were able to survive in a wide range of salinity values, following perhaps, their prey. All the 23 species here registered were found in the 'outer assemblage'; however, Abylopsis eschscholtzi, Chelophyes appendiculata and Diphyes bojani were more associated with the 'outer' group according to the PCA results. Enneagonum hyalinum was the only species frequently encountered and abundant in the 'inner assemblage' during both seasons and, supporting previous observations, this species might be considered as an indicator of nearshore waters.

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