[Seasonal variations of community structures phytoplankton in groundwater discharge areas along the Northern Yucatán Peninsula coast]. / Variaciones estacionales de la estructura comunitaria del fitoplancton en zonas de descarga de agua subterránea en la costa norte de la Península de Yucatán.

The highly touristic Yucatán Peninsula is principally constituted with coastal marine environments. Like other coastal areas, this has been affected by the increase of waste water discharge, hydrological modifications and land use changes in the area. The phytoplankton community structure is one of the main components of coastal ecosystems and the most affected in hydrological processes. In order to follow the seasonal variations, the phytoplankton was characterized to follow the hydrological variability in two sites (Dzilam and Progreso) of the Northern Yucatán Peninsula. For this, cruises were carried out monthly during one year, from April 2004 to March 2005, with two samplings per season (dry, rainy and "nortes"). Hydrological variability was associated with seasonality and directly linked to groundwater discharges in the Dzilam area, and waste water discharges in the Progreso area. The highest nutrient concentrations occurred mainly during the rainy season. The phytoplankton community changes observed throughout the year suggested that the hydrological and chemical variability associated with seasonality and anthropogenic impacts have a strong influence. The substitution of diatoms by dinoflagellates as the dominant group in Progreso was the result of seasonal variability itself, but also could have been caused by eutrophic processes; while in Dzilam, the major presence of diatoms could have been favored by groundwater discharges. The results of this study can be used to understand the linkages between stressors from the anthropogenic activities and coastal water quality and changes.

Variaciones estacionales de la estructura comunitaria del fitoplancton en zonas de descarga de agua subterránea en la costa norte de la Península de Yucatán / Seasonal variations of community structures phytoplankton in groundwater discharge areas along the Northern Yucatán Peninsula coast

Seasonal variations of community structures phytoplankton in groundwater discharge areas along the Northern Yucatán Peninsula coast. The highly touristic Yucatán Peninsula is principally constituted with coastal marine environments. Like other coastal areas, this has been affected by the increase of waste water discharge, hydrological modifications and land use changes in the area. The phytoplankton community structure is one of the main components of coastal ecosystems and the most affected in hydrological processes. In order to follow the seasonal variations, the phytoplankton was characterized to follow the hydrological variability in two sites (Dzilam and Progreso) of the Northern Yucatán Peninsula. For this, cruises were carried out monthly during one year, from April 2004 to March 2005, with two samplings per season (dry, rainy and “nortes”).Hydrological variability was associated with seasonality and directly linked to groundwater discharges in the Dzilam area, and waste water discharges in the Progreso area. The highest nutrient concentrations occurred mainly during the rainy season. The phytoplankton community changes observed throughout the year suggested that the hydrological and chemical variability associated with seasonality and anthropogenic impacts have a strong influence. The substitution of diatoms by dinoflagellates as the dominant group in Progreso was the result of seasonal variability itself, but also could have been caused by eutrophic processes; while in Dzilam, the major presence of diatoms could have been favored by groundwater discharges. The results of this study can be used to understand the linkages between stressors from the anthropogenic activities and coastal water quality and changes.

La zona costera es el principal ambiente marino en la Península de Yucatán (SE, México). Sin embargo, se ha visto afectada con el incremento de las descargas de aguas residuales, modificaciones hidrológicas y cambios de uso del suelo. El fitoplancton es una de las comunidades más afectadas por la variabilidad hidrológica. Se caracterizó la estructura de la comunidad de fitoplancton en función de la variabilidad hidrológica en dos sitios (Dzilam y Progreso) a lo largo de la costa Norte de Yucatán. Se realizaron muestreos mensuales durante un año, de abril 2004 a marzo 2005, mediante dos muestreos por época (secas, lluvias y nortes). La variabilidad hidrológica se asocia al patrón climático y está ligado a los aportes de agua subterránea en Dzilam y a las aguas de desecho en Progreso. Estacionalmente, las mayores concentraciones de nutrientes se produjeron principalmente en época de lluvias. Los cambios observados en el fitoplancton a lo largo del año sugieren que la variabilidad hidrológica y química asociada a la estacionalidad y a los impactos antropogénicos tienen una fuerte influencia. La sustitución de diatomeas por dinoflagelados como grupo dominante en Progreso es el resultado de la variabilidad estacional en sí, pero también podría verse favorecido por procesos eutróficos. En Dzilam la mayor presencia de diatomeas es favorecida por las descargas de agua subterránea. Estos resultados pueden utilizarse para comprender los vínculos entre los factores de estrés de las actividades antropogénicas y la calidad del agua.

[Hurricane impact on Thalassia testudinum (Hydrocharitaceae) beds in the Mexican Caribbean]. / Impacto por huracanes en las praderas de Thalassia testudinum (Hydrocharitaceae) en el Caribe Mexicano.

Hurricanes have increased in strength and frequency as a result of global climate change. This research was conducted to study the spatio-temporal distribution and changes of Thalassia testudinum, the dominant species in Bahia de la Ascension (Quintana Roo, Mexico), when affected by heavy weather conditions. To complete this objective, a 2001 Landsat ETM+ image and the information from 525 sampling stations on morpho-functional and coverage of T. testudinum were used, and the seeds generated for the classification of eight benthic habitats. To quantify the changes caused by two hurricanes, we used two images, one of 1988 (Gilberto) and another of 1995 (Roxanne); other three data sets (2003, 2005 and 2007) were also used to describe the study area without major weather effects. Six categorial maps were obtained and subjected to analysis by 8 Landscape Ecology indexes, that describe the spatial characteristics, structure, function, change of the elements (matrix-patch-corridor), effects on ecosystems, connectivity, edges, shape and patch habitat fragmentation. Models indicate that T. testudinum may be classified as a continuum (matrix), since the fragments were not observed intermittently, but as a progression from minimum to maximum areas in reference to their coverage (ecological corridors). The fragments do not have a regular shape, indicating that the impacts are recent and may be due to direct effects (high-intensity hurricanes) or indirect (sediment). Fragments of type "bare soils" have a discontinuous distribution, and are considered to be the sites that have remained stable over a long timescale. While more dense coverage areas ("beds", "medium prairie" and "prairie") have low fragmentation and high connection of fragments. Features have an irregular perimeter and radial growth of formal; suggesting that the impact of meteors has no effect on the resilience of T. testudinum in this ecosystem, indicating good environmental quality to grow in this bay.

Impacto por huracanes en las praderas de Thalassia testudinum (Hydrocharitaceae) en el Caribe Mexicano

Hurricane impact on Thalassia testudinum (Hydrocharitaceae) beds in the Mexican Caribbean. Hurricanes have increased in strength and frequency as a result of global climate change. This research was conducted to study the spatio-temporal distribution and changes of Thalassia testudinum, the dominant species in Bahia de la Ascension (Quintana Roo, Mexico), when affected by heavy weather conditions. To complete this objective, a 2001 Landsat ETM+ image and the information from 525 sampling stations on morpho-functional and coverage of T. testudinum were used, and the seeds generated for the classification of eight benthic habitats. To quantify the changes caused by two hurricanes, we used two images, one of 1988 (Gilberto) and another of 1995 (Roxanne); other three data sets (2003, 2005 and 2007) were also used to describe the study area without major weather effects. Six categorial maps were obtained and subjected to analysis by 8 Landscape Ecology indexes, that describe the spatial characteristics, structure, function, change of the elements (matrix-patch-corridor), effects on ecosystems, connectivity, edges, shape and patch habitat fragmentation. Models indicate that T. testudinum may be classified as a continuum (matrix), since the fragments were not observed intermittently, but as a progression from minimum to maximum areas in reference to their coverage (ecological corridors). The fragments do not have a regular shape, indicating that the impacts are recent and may be due to direct effects (high-intensity hurricanes) or indirect (sediment). Fragments of type "bare soils" have a discontinuous distribution, and are considered to be the sites that have remained stable over a long timescale. While more dense coverage areas ("beds", "medium prairie" and "prairie") have low fragmentation and high connection of fragments. Features have an irregular perimeter and radial growth of formal; suggesting that the impact of meteors has no effect on the resilience of T. testudinum in this ecosystem, indicating good environmental quality to grow in this bay. Rev. Biol. Trop. 59 (1): 385-401. Epub 2011 March 01.

Thalassia testudinum es la macrófita dominante en Bahía de la Ascensión (Quintana Roo, México), se estudió para conocer su distribución espacio- temporal y determinar si fue afectada por el paso de huracanes que se han visto incrementados en fuerza y frecuencia por el cambio climático. Partiendo de una imagen Landsat ETM+de 2001 y usando información de grandes grupos morfofuncionales y de cobertura de T. testudinum adquiridas en 525 estaciones de muestreo, se obtienen las semillas para la clasificación supervisada de los hábitats bénticos (8 clases). Con el fin de cuantificar los cambios ocasionados por dos huracanes, se usaron dos imágenes, una de 1988 (Gilberto) y 1995 (Roxanne) y tres más (2003, 2005 y 2007) para monitoreo sin efectos meteorológicos mayores; a estos 6 mapas categóricos se les aplicó un análisis de Ecología del Paisaje usando 8 índices que describen las características espaciales, de estructura, función, cambio de los elementos (matriz-mancha-corredor), efectos sobre el ecosistema, conectividad, bordes, forma del parche y fragmentación del hábitat. Los modelos indican que T. testudinum puede clasificarse como un continuo (matriz), pues los fragmentos no se observan de forma intermitente, sino como una progresión de zonas mínimas a máximas en referencia a su cobertura (corredores ecológicos). No poseen una forma regular, indicando que los impactos son recientes y pueden ser debidos a efectos directos (huracanes de alta intensidad) e indirectos (aporte de sedimentos). Los fragmentos de tipo "suelos desnudos" presentan una distribución discontinua, considerándose sitios que han permanecido estables en una larga escala de tiempo; las zonas con coberturas más densas ("camas", "praderas medias" y "praderas") presentan baja fragmentación y alta conexión de sus fragmentos. Las características de poseer un perímetro irregular y crecimiento de formal radial, sugieren que el impacto de los meteoros no tiene efecto en la capacidad de resiliencia de T. testudinum en este ecosistema, indicando el buen estado de la calidad ambiental de la bahía para su crecimiento.