RESUMO
The spatial patterns of taxonomic diversity of annelid polychaete species from the continental shelf in the Southern Gulf of Mexico were examined in this study. We used taxonomic distinctness and its spatial variations to explore the diversity patterns and how they change between Southern Gulf of Mexico regions. In addition, using taxonomic distinctness as a dissimilarity measure and Ward's Clustering, we characterized three distinct faunal assemblages. We also investigated patterns of richness, taxonomic distinctness, and distance decay of similarity between sampling stations as a ß-diversity measure. Finally, we examined the spatial relationships between polychaete assemblages and environmental variables to test the relative importance of spatial and environmental components in annelid polychaete community structure from the Southern Gulf of Mexico. We used a combination of eigenvector-based multivariate analyses (dbMEMs) and distance-based redundancy analysis (dbRDA) to quantify the relative importance of these explanatory variables on the spatial variations of taxonomic distinctness. The significance level of spatial and environmental components to the distribution of polychaete species showed that the combined effect of spatial processes and sediment characteristics explained a higher percentage of the variance than those parameters could alone.
Assuntos
Biodiversidade , Poliquetos , Animais , Golfo do México , Poliquetos/classificação , Ecossistema , Sedimentos GeológicosRESUMO
Due to their location in tropical latitudes, mangrove forests are susceptible to the impact of hurricanes and can be vastly damaged by their high-speed winds. Given the logistic difficulties regarding field surveys in mangroves, remote sensing approaches have been considered a reliable alternative. We quantified trends in damage and early signs of canopy recovery in a fringe Rhizophora mangle area of Marismas Nacionales, Mexico, following the landfall of Hurricane Willa in October 2018. We monitored (2016-2021) broad canopy defoliation using 21 vegetation indices (VI) from the Google Earth Engine tool (GEE). We also mapped a detailed canopy fragmentation and developed digital surface models (DSM) during five study periods (2018-2021) with a consumer-grade unmanned aerial vehicle (UAV) over an area of 100 ha. Based on optical data from the GEE time series, results indicated an abrupt decline in the overall mangrove canopy. The VARI index was the most reliable VI for the mangrove canopy classification from a standard RGB sensor. The impact of the hurricane caused an overall canopy defoliation of 79%. The series of UAV orthomosaics indicate a gradual recovery in the mangrove canopy, while the linear model predicts at least 8.5 years to reach pre-impact mangrove cover conditions. However, the sequence of DSM estimates that the vertical canopy configuration will require a longer time to achieve its original structure.
Assuntos
Tempestades Ciclônicas , Rhizophoraceae , México , Tecnologia de Sensoriamento Remoto/métodos , Áreas AlagadasRESUMO
Within the last few decades, tropical coastal systems such as beaches, dunes, and mangrove forests have experienced high annual rates of loss worldwide due to natural and anthropogenic impacts. Historical remote sensing data have been used to map and monitor these fragile systems, as well as to track specific events through time. The purpose of this study was to examine coastal trends along Marismas Nacionales in Mexico, which is the largest wetland complex of the western coast of the Pacific Ocean. The opening of the Cuautla Canal in 1976 and the construction of several hydroelectric power dams have severely impacted this wetland system. Shoreline variability was estimated based on representative remote sensing images over half a century (1970 to 2019). Results indicate that, after 49 years, 805 ha of beach deposits have been lost in the Cuautla Canal and at the beach ridge region that should otherwise be an accretional coastal zone. Conversely, the southern section of the study site shows 406 ha of constant accretion during the same period due to the presence of the unobstructed San Pedro River. Our study highlights the adverse effects of engineering projects, such as inlets and hydroelectric dams throughout tropical coastal systems that have strongly depended on freshwater input from upstream rivers.