Assessment of aquatic food web and trophic niche as a measurement of recovery function in restored mangroves in the Southern Gulf of Mexico.

Mangroves are coastal wetlands with high biodiversity and productivity, with great interaction with coastal environments. In the face of worldwide mangrove loss, restoration projects attempt to recover ecosystem composition and functioning over time. Our objective was to examine and compare the food webs in mangrove areas with different restoration times and in a reference mangrove in Términos Lagoon, Mexico. We estimated the trophic structure, identified the carbon resources that maintain aquatic consumers through the analysis of stable isotopes, and compared the trophic niche of the restored mangroves with the reference mangrove. We analyzed environmental variables, trophic structure, and contributions of resources during three seasons: rainy, dry, and "nortes". Environmental changes and food structure changed in response to regional seasons. Bayesian mixing models indicated that food webs varied seasonally as a response to the primary productivity developed at Términos Lagoon. As expected, the assimilation of C3 plants in the reference mangrove was highest, as a primary ("nortes" season) and secondary resource (dry and rainy seasons). The restored mangroves depended mainly on allochthonous resources (seagrass, epiphytes, and phytoplankton). The assimilation of these resources highlighted the importance of connectivity and the input of sources of carbon from nearby coastal environments. Trophic niche analysis showed that the area with longer restoration time was more similar to the reference mangrove, which is evidence of the importance and efficacy of the restoration process, as well as the restoration of the ecosystem function over time.

Absence of hypoxia events in the adjacent coastal waters of Grijalva-Usumacinta river, Southern Gulf of Mexico.

Globally, oxygen concentration in many coastal areas is depleting. River nutrient discharges may produce hypoxia events. The Southern Gulf of Mexico receives the discharges of the Grijalva-Usumacinta River System, the second largest in the Gulf of Mexico. To evaluate the influence of river discharges on dissolved oxygen concentrations in the receiving coastal ecosystem, we studied the variation of physicochemical variables in the water column. During the dry season, the influence of the river waters to the coastal area is scarce, but during the rainy season the river plume reached ~9 km offshore. The lowest concentration of dissolved oxygen (3.6 mg L-1) was observed within the river plume. We concluded that, in the studied area, hypoxia events (oxygen concentrations ≤ 2 mg L-1) would occur during the rainy season, low winds and in deeper waters (>80 m depth).