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Coral reefs in the Caribbean and Gulf of Mexico are increasingly suffering from anthropogenic nutrient inputs principally from fertilizers as identified by their δ15N signatures. To determine if primary producers are passively affected by anthropogenic nitrogen enrichment in a coral reef community, carbon: nitrogen ratios (C:N mol mol−1) were measured. The C:N ratio was used as a proxy for nitrogen enrichment in primary producers when the ratio decreases, and for lipid plus carbohydrate in terms of C, and protein in terms of N in primary producers and consumers. Lipid classes and the triacylglycerol to sterol (TAG:ST) ratio were used to evaluate energy storage as an indication of nutritional quality in the six most abundant primary producers, and of nutritional condition in ten ubiquitous consumers in a coral reef in the Gulf of Mexico under river influence. A low C:N ratio revealed nitrogen enrichment in primary producers. Among the lipids, high TAG proportions were detected in phytoplankton and zooxanthellae suggesting that they have a higher nutritional quality in terms of energy, followed by sea grass, mangrove, and macroalgae. During the rainy season TAG:ST increased in primary consumers such as echinoderms, and top predators such as the perciform fish Bodianus rufus, Ocyurus chrysurus and Caranx hippos, suggesting an increase in energy storage. In contrast, TAG:ST decreased in the principal habitat providing coral Montastrea cavernosa, along with a decrease in the phospholipid proportion suggesting a poor nutritional condition. There were three species with no change in their TAG:ST ratio: the sponge Aplysina sp., the masked goby Coryphopterus personatus and the surgeon fish Achanturus chirurgus. The lower value of TAG, TAG:ST ratio and phospholipid proportion in the coral M. cavernosa suggests that the reported abundance of zooplankton does not satisfy the energy demand of M. cavernosa during the rainy season.

Trophic interactions in food webs must be considered in order to assess the trophic role of different species in the ecological network structure as well as the relationship between resource use and interactions between different organisms. Such studies provide important information for ecosystem-based fisheries management. Thus, our goal was to analyze the trophic overlap between blue shark ( Prionace glauca ) and shortfin mako ( Isurus oxyrinchus ) off the west coast of Baja California Sur, Mexico, in order to infer their diet preferences and spatial distribution. We sampled the dorsal white muscle of 39 P. glauca and 35 I. oxyrinchus in December 2009 and March 2011. No significant differences between sexes or maturity stage were identified for P. glauca from either sampling location, indicating similar foraging preferences. For I. oxyrinchus , there was a significant difference in the δ 13 C values for males and females, suggesting different foraging preferences or movement patterns. The trophic positions and the SIBER analysis assigned to both tertiary predators in this study indicate that P. glauca is a specialist, while I. oxyrinchus is a generalist. Significant differences were also identified in the δ 15 N and δ 13 C values for P. glauca and I. oxyrinchus , indicating low overlap between these two shark species. These patterns suggest that these two sharks have different trophic preferences and migratory histories; thus, each species plays a unique trophic role off the west coast of Baja California Sur, Mexico.

Environmental changes have been associated with natural climatic variability or human activity. Water resources management is, perhaps, the most drastic change observed in the coastal environment. However, external forcings such as the El Nino event have important implications in the global and regional hydrological balance. These environmental changes have an impact on the density and biomass of the ichthyofauna in the Terminos Lagoon (TL) for the past 30 years, presumably, associated with variations in the temperature and surface salinity of the sea. Therefore, in the present study, δ18O was quantified in otoliths of two important species due to their dominance: Stellifer lanceolatus and Eucinostomus gula, and to understand the environmental changes reflected in both species. The δ18O was analyzed in otoliths of these two species captured in 1998/1997, 2006/2007 and 2016/2017 and were compared with in situ temperature and salinity data. Sea surface temperature and salinity increased by 2 °C and 9, respectively, between 1997 and 2017. Stellifer lanceolatus δ18O values was in isotopic equilibrium with seawater calcite; while, E. gula is not in isotopic equilibrium. The δ18O of S. lanceolatus and E. gula varied significantly with the increase in salinity (R2 = 0.8987 and R2 = −0.2964) and not with the sea surface temperature. S. lanceolatus is an excellent bioindicator of changes in sea surface salinity in this region of the Gulf of Mexico.

The Terminos Lagoon is located in the south-eastern Gulf of Mexico and is ecologically and economically important due to its biological diversity of valuable fish and wildlife resources. It is adjacent to the Campeche Bank in the southern Gulf of Mexico, which is well known for its intensive production of fuel and gas. Therefore, the aims of this study are to characterize zones that are influenced by biogenic and/or lithogenic processes, based on the geochemistry of specific chemical elements. For this study, elements such as Al, As, Ca, Cu, Fe, Li, Mn, Mo, Ni, Pb, V, and Zn were determined in surface sediments. The V:Ni ratio does not indicate the presence of fuel in the sediment. The enrichments of Ni and Ca were quantified, and their distributions were found to be indicative of lithogenic influence in the western area of the lagoon at Boca del Carmen and predominantly biogenic influence at the eastern area of the lagoon in Puerto Real.

Nutrient inputs associated with population growth threaten the integrity of coastal ecosystems. To assess the rapid increase in tourism, we compared the δ15N from Thalassia testudinum collected at sites with different levels of tourism development to detect the N inputs of wastewater discharge (WD) along the coast of Quintana Roo. The contributions of nitrogen enriched in 15N are directly related to the increase of WD inputs in areas of tourism development (Nichupte Lagoon in Cancun) and decreased toward Bahia Akumal and Tulum. The δ15N from T. testudinum was significantly lower at Mahahual and Puerto Morelos. In areas of the lowest development and with tourist activity restricted, such as the Yum Balam Reserve and Sian Ka'an Biosphere Reserve, the δ15N values were relatively enriched compared to Mahahual and Puerto Morelos. Therefore, Puerto Morelos and Mahahual may be used for baseline isotopic monitoring where tourist activities are growing and can lead to environmental pressure on the reef lagoon ecosystem. The anthropogenic N input has the potential to impact, both environmentally and economically, the seagrass meadows and the coral reefs along the coast of Quintana Roo and the Caribbean.