Influence of pelagic sargassum influxes on the δ15N in Thalassia testudinum of the Mexican Caribbean coastal ecosystem.

The conservation of Mexican Caribbean Ecosystems (MCE) involves ensuring their capacity to provide resources and ecosystem services to society. Monitoring programs are necessary to establish their management and ensure their sustainability. Thalassia testudinum is the community used to determine anthropogenic influence, in which wastewater is the primary anthropogenic nitrogen source. The extensive amount of pelagic sargassum that enters the area and its decomposition may be additional nitrogen sources in MCE. In the present study, the δ15N in T. testudinum was examined from 2009 to 2019 to infer the nitrogen contribution from pelagic sargassum to MCE. T. testudinum δ15N values showed significant depletion from June/October 2014 to 2019 concerning previous periods. Pelagic sargassum was an alternative nitrogen source, and its leaching reduced T. testudinum δ15N values in MCE.

Changes in the enrichment of dissolved inorganic nutrients in the coastal waters of the Mexican Caribbean, influenced by submarine groundwater discharges 2016-2019.

The resident and tourist population in the Mexican Caribbean has grown exponentially, increasing the availability of dissolved inorganic nutrients in coastal waters through submarine groundwater discharge (SGD). Recently, a new massive drift of Sargassum spp. has occurred that can provide new organic matter and enrich coastal water with nutrients. In different sites in the Mexican Caribbean, the chemical composition of the water was analyzed, and the δ15N of Thalassia testudinum was determined between 2016 and 2019. Evidence of SGD was observed in Akumal Bay due to high silicate concentrations and its negative correlation with salinity. Seasonal and interannual variation in NH4+ concentration was observed at these sites. In October 2018, SGD contributed ∼70 times more nitrogen and ∼194 times more phosphorus than the decomposition of the pelagic macroalgae Sargassum spp. The δ15N data showed that Akumal Bay received nitrogen of anthropogenic origin and that nitrogen fixation processes or probably assimilation of nitrogen of the leachates of pelagic Sargassum spp were dominant at Mahahual and Xahuayxol.