RESUMO
The Mexican Caribbean coral reef ecosystem has endured the effects of global and regional stressors and, recently, the massive arrivals of the free-living, floating brown algae Sargassum spp. This study aimed to evaluate spatiotemporal changes in the stony coral community structure in the southern Mexican Caribbean by a temporal comparison of live coral cover and colony density using a data set collected in 2008-2009 and a recent survey in 2021 within a Protected Natural Area. A multivariate analysis approach was used to reveal spatiotemporal changes in coral cover and colony densities. Coral cover ranged from 6.9 to 8.9% in 2008-2009 to 6.5% in 2021, the lowest values recorded for the area. Coral colony density ranged from 0.68 to 0.78 colonies m-1 in 2008-2009 to 0.68 colonies m-1 in 2021. The present results appear to represent subtle changes during the last decade.
Assuntos
Antozoários , Ecossistema , Animais , Recifes de Corais , Região do Caribe , MéxicoRESUMO
Understanding the mechanisms that allow the permanence of coral reefs and the constancy of their characteristics is necessary to alleviate the effects of chronic environmental changes. After a disturbance, healthy coral reefs display trajectories that allow regaining coral cover and the establishment of framework building corals. Through a comparative approach, in a patch reef partially affected by a ship grounding, we analyzed the successional trajectories in affected and unaffected sectors. Fleshy algae (which do not promote the recruitment of corals) dominated the reef surface irrespective of the impact of the ship grounding incident. Acropora species had near-zero contributions to community structure, whereas non-framework building corals like Porites sp. had a slightly higher recruitment. Cover of coral and calcareous crustose algae decreased over time, and neither the latter nor adult coral colonies had any effect on the occurrence probabilities of small corals. Sea urchin (Diadema antillarum) densities were generally low, and thus unlikely to contribute to reverting algal dominance. The successional trajectories of the community in the impacted and non-impacted sectors of the coral patch reef agree with the inhibition successional model, leading to the development of a degraded state dominated by fleshy algae. It is probable that the stability and resilience of this degraded state are high due to the ability of fleshy algae to monopolize space, along with low coral recovery potential.
Assuntos
Antozoários , Recifes de Corais , Animais , Ecossistema , Ouriços-do-MarRESUMO
Microbialites are highly diverse microbial communities that represent modern examples of the oldest life forms, stromatolites (dated >3.7 Ga). Bacalar Lagoon, in Mexico, harbors the largest freshwater microbialite occurrences of the world; yet diverse anthropogenic activities are changing the oligotrophic conditions of the lagoon. The objective of this work was to perform a spatial exploration of the microbialites of Bacalar Lagoon, analyze their prokaryote diversity, following a high throughput sequencing approach of the V4 region of the 16S rDNA, and correlate to the environmental parameters that influence the structure of these communities. The results indicate the presence of microbialites throughout the periphery of the lagoon. The microbiome of the microbialites is composed primarily of Proteobacteria (40-80%), Cyanobacteria (1-11%), Bacteroidetes (7-8%), Chloroflexi (8-14%), Firmicutes (1-23%), Planctomycetes (1-8%), and Verrucomicrobia (1-4%). Phylogenetic distance analyses suggests two distinct groups of microbialites associated with regions in the lagoon that have differences in their environmental parameters, including soluble reactive silicate (in the north), bicarbonates and available forms of nitrogen (ammonium, nitrates and nitrites) (in the south). These microbialite groups had differences in their microbiome composition associated to strong anthropogenic pressure on water quality (agriculture, landfill leachate, lack of water treatment infrastructure and intensive tourism), which were related to a loss of microbial diversity.
Assuntos
Bacteroidetes/classificação , Biodiversidade , Cianobactérias/classificação , Água Doce/microbiologia , Sedimentos Geológicos/microbiologia , Microbiota , Proteobactérias/classificação , Bacteroidetes/genética , Bacteroidetes/crescimento & desenvolvimento , Cianobactérias/genética , Cianobactérias/crescimento & desenvolvimento , Sedimentos Geológicos/análise , Sequenciamento de Nucleotídeos em Larga Escala , México , Nutrientes , Filogenia , Proteobactérias/genética , Proteobactérias/crescimento & desenvolvimento , RNA Ribossômico 16S/genéticaRESUMO
From mid-2014 until the end of 2015, the Mexican Caribbean coast experienced a massive influx of drifting Sargassum spp. that accumulated on the shores, resulting in build-up of decaying beach-cast material and near-shore murky brown waters (Sargassum-brown-tides, Sbt). The effects of Sbt on four near-shore waters included reduction in light, oxygen (hypoxia or anoxia) and pH. The monthly influx of nitrogen, and phosphorus by drifting Sargassum spp. was estimated at 6150 and 61kgkm-1 respectively, resulting in eutrophication. Near-shore seagrass meadows dominated by Thalassia testudinum were replaced by a community dominated by calcareous rhizophytic algae and drifting algae and/or epiphytes, resulting in 61.6-99.5% loss of below-ground biomass. Near-shore corals suffered total or partial mortality. Recovery of affected seagrass meadows may take years or even decades, or changes could be permanent if massive influxes of Sargassum spp. recur.