The dynamics of Rhizophora mangle litter production and decomposition were studied in a tropical coastal lagoon on the Gulf of Mexico in Veracruz, Mexico over a year (October 2002-October 2003. This region is characterized by three seasons: northerly winds (called 'nortes'), dry, and rainy. Annual litter production (1116 g m )2 ) followed a seasonal pattern with leaf litter as the main fraction (70%) with two peaks in the dry and one in the rainy season. Leaf decomposition was evaluated with two types of litter bag in each season: fine mesh (1Â1 mm) and coarse mesh (3Â7 mm). Decomposition data were adjusted to a single negative exponential model. The results indicated faster decomposition rates in the coarse litter bag and significant differences among seasons. However these differences occurred after the 60th day of decomposition, indicating that leaching and microbial action were responsible for more than 50% of mass loss. After this period, the effects of aquatic invertebrates were evident but depended on climatic conditions. In the rainy season, the gastropod Neritina reclivata was associated with increasing leaf decomposition rate. In the 'nortes' season, the effect of aquatic invertebrates was smaller, and there were no differences in the decay constants calculated for the two litter bag types. High litter production represents an important input of organic matter which, through decomposition, may represent an important source of C, N, and P in this aquatic system.

This study analyzes the relationship between physical and chemical factors and the algal communities in tropical streams in micro-watersheds where [70% of their area has different land uses, specifically, cloud mountain forest, coffee plantations, and livestock pastures. Physical, chemical, and biological variables were measured monthly in each stream over a 1-year period. The concentrations of nitrates ? nitrites, total suspended solids (TSS), and silica in the streams were found to differ during the dry and rainy seasons. Coffee-plantation streams showed the highest levels of suspended solids, nitrates ? nitrites, and sulfates. Based on chlorophyll a concentration, the forest and coffee-plantation streams are oligo-mesotrophic, while pasture streams are meso-eutrophic. Forest streams displayed the lowest levels of richness and algal diversity, followed by coffee-plantation streams, whereas pasture streams were the most diverse. Chlorophyll a concentration and species richness depended on land use and season. Forest coverage was positively correlated with acidophilous and oligo-eutraphentic diatom species. Coffee coverage displayed a significant positive correlation with motile species and a significant negative correlation with pollution-sensitive diatom taxa. The results show that diatom assemblages responded to micro-watershed conditions and can be used to monitor the effects of land use on streams in tropical regions.

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Ciclo anual del fitoplancton con énfasis en las especies potencialmente nocivas en bancos ostrícolas de la laguna de Términos, sureste del Golfo Resumen.-Para definir la composición de la comunidad fitoplanctónica con énfasis en las especies nocivas en los bancos ostrícolas de la laguna de Términos, SE del Golfo de México, 6 sitios de muestreo fueron monitoreados mensualmente desde agosto 2012 a septiembre 2013. Se midió la temperatura del agua, salinidad, potencial de hidró geno, saturación de oxígeno, nutrientes inorgánicos y la abundancia de fitoplancton. La temperatura y la salinidad se caracterizaron por diferencias estacionales marcadas. Los valores de pH y saturación de oxígeno sugirieron un predominio de la actividad fotosintética. La comunidad fitoplanctónica se caracter izó por el predominio de nanoflagelados y dia tomeas. La abundancia de fitoplancton y su variación estacional presentaron los valores mínimos (10 3 células L -1 ) durante la época de secas (febrero-mayo) y valores al tos (10 6 célul as L -1 ) dur ante la temporada de lluvias (junio-septiembre). Otra característica importante de la comunidad fitoplanctónica fue la presencia de especies de dinoflagel ados nocivos: Akashiwo sanguinea, Karenia cf. mikimotoi, Pyrodinium bahamense var. bahamense, Prorocentrum mexicanum y P. minimum. Las cianobacterias Anabaena y Cylindrospermopsis cuspis alcanzaron abundancias de 1.9x10 6 y 1.3x10 6 células L -1 , respecti vamente. Los g éneros Alexandrium y Pseudo-ni tzschia estuvi eron presentes, pero los taxones no fueron identificados a nivel de especie. En conclusión, la comunidad fitoplanctónica se somete a cambios en la composición de especies y en la estructura de la comunidad durante cada temporada climática, en respuesta a la variación ambiental, que permite el desarrollo de la comunidad fitoplanctónica de acuerdo a las condiciones imperantes. Palabras clave: Cambios estacionales, cianobacterias, diatomeas, dinoflagelados, lagunas costerasAbstract.-To define the composition of the phytoplankton community, with an emphasis on harmful species, 6 stations were monitored monthly in the oyster beds of Términos Lagoon, SE Gulf of Mexico, from August 2012 to September 2013. Water temperature, salinity, hydrogen potential, oxygen saturation, inorganic nutrients and abundance of phytoplankton were determined. Temperature and salinity were characterized by marked seasonal differences. The pH values and the oxygen saturation suggest a predominance of photosynthetic activity. The phytoplankton community was characterized by the dominance of nanoflagellates and diatoms. , respectively. The genera Alexandrium and Pseudo-nitzschia were present, but the taxa were not identified to the species level. In conclusion, the phytoplankton community undergoes changes in both species composition and structure of the community during each climatic season, in response to environmental variation, which allows the development of the phytoplankton community according to the conditions. Key words: Seasonal changes, cyanobacteria,...

In order to evaluate the risk for marine ecosystem and human health, the diversity and morphology of diatoms of the genus Pseudo-nitzschia were studied. Weekly sampling was performed at seven geo-referenced sites in the National Park Sistema Arrecifal Veracruzano, SW Gulf of Mexico, during the annual cycle from May 2005 to May 2006. Samples were taken in the 30-cm surface layer of the water column with a phytoplankton net of 20-µm mesh size. With the use of light, transmission and scanning electron microscopy, seven Pseudo-nitzschia species were identified: non-toxic P. cf. subcurvata (examined only by light microscopy) and P. brasiliana, and potentially toxic, causative agents of amnesic shellfish poisoning (ASP) due to domoic acid: P. calliantha, P. cuspidata, P. delicatissima, P. pseudodelicatissima and P. pungens. It is concluded that there is a potential risk of ASP in the study area. P. brasiliana and P. calliantha are new records for the SW Gulf of Mexico. Comparisons with studies conducted in the northern Gulf of Mexico indicate that the diversity of Pseudo-nitzschia in the Gulf of Mexico may be greater than currently documented and that some species (e.g., P. multiseries) may have biogeographic limitations (e.g., temperatures below 27 o C).Key words: amnesic shellfish poisoning, diatoms, Gulf of Mexico, morphology, new records, Pseudo-nitzschia, taxonomy, Veracruz. 98: 51-72 (2012) 52 RESUMEN Con el fin de evaluar el riesgo para el ecosistema marino y la salud humana, se estudió la diversidad y la morfología de las diatomeas del género Pseudo-nitzschia del Parque Nacional Sistema Arrecifal Veracruzano, en el suroeste del Golfo de México. Se realizaron muestreos semanalmente en siete sitios georeferenciados durante un ciclo anual de mayo de 2005 a mayo de 2006. Las muestras se tomaron de la capa superficial de 30 cm de la columna de agua con una red fitoplanctónica de 20 µm de tamaño de malla. Con ayuda de los microscopios fotónico, electrónico de transmisión y electrónico de barrido se identificaron siete especies de Pseudo-nitzschia: las no tóxicas P. cf. subcurvata (estudiada solamente en el microscopio fotónico) y P. brasiliana, y las potencialmente venenosas, causantes de la intoxicación amnésica por consumo de mariscos (ASP) debido al ácido domoico: P. calliantha, P. cuspidata, P. delicatissima, P. pseudodelicatissima y P. pungens. Se concluye que existe riesgo potencial de ASP en el área de estudio. P. brasiliana y P. calliantha son nuevos registros para el suroeste del Golfo de México. Las comparaciones con los estudios en el norte del mismo cuerpo marino indican que la diversidad de Pseudonitzschia en el Golfo de México puede ser más alta que la documentada en el presente, y que algunas especies (e.g., P. multiseries) pueden tener limitaciones ecológicas y biogeográficas (e.g., temperaturas menores de 27 o C). Acta Botanica MexicanaPalabras clave: diatomeas, Golfo de México, intoxicación amnésica por consumo de mariscos, morfología, nuevos registros, Pseudo-nitzschia, taxonomía, Verac...

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Epiphytic dinoflagellates were studied in 250 samples from 10 sites in Chelem (a semi-enclosed mangrove lagoon) and Dzilam de Bravo (an exposed coastal locality), on the northern coast of the Yucatan Peninsula, during five surveys in [2008][2009]. Temperature, salinity, turbidity, pH, dissolved oxygen, nitrates, nitrites, phosphates, silicates, urea, extractable water column chlorophyll-a, precipitation, and wind speed and direction were measured. The Chelem lagoon system showed minor variability in physical-chemical characteristics compared to the exposed site at Dzilam de Bravo. Dinoflagellates were associated with all the host macrophytes examined including four seagrass species and 33 macroalgal species representing 24 genera. A total of 20 dinoflagellate taxa from 12 genera were recovered from these substrates. The genus Prorocentrum contained the largest number of individual species. The variation in mean epiphytic dinoflagellate abundance over both localities ranged from ~200 to 3500 cells g -1 substrate wet weight. Cell abundances at individual sites, in contrast, ranged from ~100 to >25 000 cells g -1 substrate wet weight. This variation is typical of the patchy distribution of these species in time and space.