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Vertical distribution, sex ratio, size structure and mate encounters of Firoloida desmarestia in the southern Gulf of Mexico were analyzed during 4 seasons (in February, May, August and November). A total of 395 individuals were collected with an opening−closing net at 5 levels of the 105 m upper water column. Results indicated that the species reproduces throughout the year, with a reproductive peak in May and a low reproductive period from August to February. Length measurements indicated that females (as long as 30 mm) are larger than males (18 mm). Estimations of a 'spatial overlap' index showed a high overlap degree between sexes, suggesting that patterns in their vertical distribution are not a reproductive barrier. Sex ratio (F:M) at birth seemed to be 1:1, but during most of the year the adult sex ratio was dominated by females. We propose that larger dimensions and faster swimming speeds of females provide competitive advantages over males in searching for food and avoiding predators. Simulations of mate encounters indicated that values during the low reproductive season were low under turbulent and nonturbulent conditions (< 4.9 males d −1 female −1), but enough to fertilize a high percentage of females. During the high reproductive season, encounters were as high as 17.2 males d −1 female −1 because the high density of adult population and the influence of wind-induced turbulence. We suggest that some biological features of females (seminal receptacle and exocrine gland) compensate for the low encounter rates. A conceptual model for the population dynamics of F. desmarestia is proposed.

A reef system in the southwestern Gulf of Mexico is affected by anthropogenic activities, sourced by urban, fluvial, and sewage waters. Dissolved metals have higher concentrations during the rainy season. V and Pb, were derived from an industrial source and transported to the study area by rain water. On the other hand, Jamapa River is the main source for Cu and Ni, which carries dissolved elements from adjacent volcanic rocks. Principal Component Analysis shows a common source for dissolved nitrogen, phosphates, TOC, and suspended matters probably derived from a sewage treatment plant, which is situated near to the study area.

Cambios morfológicos y sedimentológicos en playas del sur del Golfo de México y del Caribe noroeste 21 ResumenEl presente trabajo tiene como objetivo comparar variaciones morfológicas y sedimentológicas entre las playas del Sur del Golfo de México y de la Riviera Maya (Caribe noroeste) realizando dos muestreos regionales de sedimentos del frente de playa, perfiles topográficos de las playas y analizando el posible efecto del ascenso del nivel del mar por el calentamiento global. La diferencia entre muestreos varía entre 26 años y 32 años. Se estudian perfiles de playa, variaciones de línea de costa, parámetros texturales y composición de arenas superficiales del frente de playa. En este estudio se considera el estado de marea, precipitaciones y eventos meteorológicos. Se encontraron en localidades geográficas cercanas, 23 estaciones en los muestreos antiguos y recientes. Los perfiles de playa presentan variaciones, siendo más largos en ocasiones para los muestreos recientes que para los antiguos. La concavidad de los perfiles de playa sugiere que hay más perfiles recientes característicos de erosión. Las líneas de playa analizadas mediante imágenes LANDSAT de diversos años, sugieren la influencia de procesos antrópicos y meteorológicos; estos últimos podrían indicar una conexión entre deposición y erosión de playas en localidades no muy alejadas. Tanto la comparación de parámetros texturales como composicionales demostraron su utilidad en el análisis comparativo de arenas de playa antiguas y recientes. Resultó más común encontrar clasificaciones más pobres en sedimentos recientes que en sedimentos antiguos, lo que puede sugerir una interferencia mayor de factores antrópicos en sedimentos recientes, o una mayor variación de los parámetros oceanográficos. A través del análisis de componentes principales se observa que el mayor peso estadístico para terrígenos está dado por minerales pesados y para sedimentos carbonatados por pellets, esta relación refleja condiciones favorables para la erosión y posible empobrecimiento de organismos litorales y de aves.Palabras clave: Golfo de México, Riviera Maya, frente de playa, textura, composición de arenas, línea de costa. Abstract This study aims to compare morphological and sedimentological variations between the beaches of the Southern Gulf of

Functional diversity measures help to understand the underlying mechanisms explaining the relationship between organisms and environment. This work examined the mesozooplankton community of an estuary under the hypothesis that the upper (&lt; 25 psu) and lower (&gt; 25 psu) zones are functionally different in terms of feeding strategies, trophic groups, camouflage, buoyancy, and defense against predators, due to the salinity gradient. We used the ‘community-weighted mean trait values’ (CWM) and a fuzzy correspondence analysis (FCA) in combination with three functional indices (FRic: functional richness, FEve: functional evenness, FDiv: functional divergence) to test our hypothesis. Zooplankton samples were taken in the tropical Sontecomapan estuary, southern Gulf of Mexico, in June 2018 and October 2019. A total of 21 zooplankton groups were recognized, all of them present in the lower estuary. Results showed significant differences (p&lt; 0.05) in the FRic and FDiv values between the two zones, as well in the CWM metric. Results of the FCA showed that the lower estuary was characterized by herbivorous filter feeders that use watery bodies, flattened body forms, mucus houses, or ‘wings’ for buoyancy; highly transparent bodies (associated with gelatinous body structure) for camouflage and predators’ avoidance and, shells or carapaces as antipredator tactics. The upper estuary was characterized by omnivorous cruising predators that use their appendages or swim bladders for buoyancy, with ‘medium’ and ‘low’ levels of transparency, associated with chitinous and skin-protected body structures, which provide alternative ways for camouflage and spines or fast swimming behavior to protect from predators. These findings evidenced that the upper and lower zones of an estuary exhibit differences in the function of the zooplankton community and shed new light on the comprehension of estuaries’ ecological function.