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The study of the feeding habits variability (spatial and temporal scales) allows us to evaluate the trophic interactions between species, thus, the short and long-term effects of the removal of different species by the presence of different phenomena. In this study, we carried out stable isotope (δ13C and δ15N) and stomach content analyses to infer the trophic linkages between two snapper species (Lutjanus synagris and Lutjanus griseus) captured in the littoral of Campeche, Mexico. In total, 781 specimens were collected (528 L. synagris and 253 L. griseus) and based on relative importance index [%PSIRI] both snapper species consumed based on the prey-specific index of relative importance (PSIRI), Penaeidae family (PSIRI = 23.41%) was the most important species in the diet of Lutjanus synagris, while Callinectes sapidus (PSIRI = 21.45%) was the primary prey of Lutjanus griseus. The isotopic analyses indicated that both snapper species feed in the coastal-marine (δ15N: 10.6 to 12.1‰ and δ13C: -15.7 to -12.7‰); however, according to PERMANOVA, low diet similarity was found between snapper species (R = 0.07, P < 0.01), also, significant differences was detected in the δ15N and δ13C values between L. synagris, and L. griseus. Therefore, despite both snapper species presents similar trophic positions (L. synagris: 4.2 ± 0.2; L. griseus: 3.9 ± 0.1) and feeding behavior (according to SIBER = opportunistic predators), a low trophic overlap was observed, probably associated with the differential use of habitat in the coastal zone; where L. synagris is ecologically fed in areas of seagrass, while L. griseus is probably intermittent between pasture and mangrove areas, therefore, the role of each species is crucial in the dynamics of coastal-marine ecosystems as predators and potential structuring of the populations of their prey.

Migratory marine megafauna generally move vast distances between productive foraging grounds and environmentally stable breeding grounds, but characterizing how they use these habitats to maintain homeostasis and reproduce is difficult. We used isotope analysis of blue whale skin strata (n = 621) and potential prey (n = 300) to examine their migratory and foraging strategies in the eastern Pacific Ocean. Our results suggest that most whales in the northeast Pacific use a mixed income and capital breeding strategy, and use the California Current Ecosystem as their primary summer-fall foraging ground. A subset of individuals exhibited migratory plasticity and spend most of the year in the Gulf of California or Costa Rica Dome, two regions believed to be their primary winter-spring breeding grounds. Isotope data also revealed that whales in the southern Eastern Tropical Pacific generally do not forage in the northeast Pacific, which suggests a north-south population structure with a boundary near the equator.

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.

Rationale Distinct techniques employed to preserve different types of tissues may affect stable isotope analyses conducted on samples, and this is critical when field work takes place in remote areas. To investigate this, the stable isotope ratios (δ13 C and δ15 N values) obtained using two methods commonly used to preserve humpback whale (and other cetaceans) skin samples were compared. Methods A total of 54 pairs of skin samples of humpback whales from the southern Baja California Peninsula, Mexico, were preserved in ethanol (90%) and by freezing, between 2007 and 2009. The δ13 C and δ15 N values were determined using a PDZ Europa ANCA-GSL elemental analyzer interfaced to a PDZ Europe 20-20 isotope ratio mass spectrometer. Parametric and nonparametric tests were used to compare the isotopic results. Results A significant (t = 4.93; p = 0.000003) variation of −0.92‰ was found between the mean δ13 C values in ethanol (from −19.38‰ to −16.07‰; mean = −17.86‰) and freezing (from −20.67‰ to −16.44‰; mean = −18.78‰) techniques. No significant (U = 1314, p = 0.38) differences were observed in the δ15 N values. The δ13 C values were compared between preservation methods for each of the three years under analysis. Significant differences were observed in 2007 (t = 3.45; p = 0.0012) and 2008 (t = 3.13; p = 0.0030), but not for 2009 (t = 1.66; p = 0.12). Conclusions Based on the results of this study, the use of ethanol to preserve humpback whale skin samples collected for stable isotope analysis is not recommended, particularly regarding the analysis of δ13 C values. This study serves as a point of reference for future research on humpback whales or other whales involving skin samples preserved by freezing or in ethanol.

Intra-population resource partitioning is a foraging strategy that could minimize intra-specific competition. This behavior may be ecologically relevant for species in recovery like the Guadalupe fur seal Arctocephalus philippii townsendi (GFS), which was considered extinct 70–80 years ago. The present study provides, via scat and stable isotope (δ15N and δ13C) analyses, trophic knowledge around GFSs from Guadalupe Island just prior to and the 2013 breeding season, with emphasis on inter-individual variability. A total of 107 scat samples were analyzed, and 98 neonate fur samples (proxies for adult female foraging) were isotopically assessed. The overall trophic spectrum included 12 items, with a slight increase in diversity among main prey during the second half of the breeding season. The isotopic analysis revealed three distinct groups, reflecting apparent variations in trophic position and coastal/oceanic habitat use. As in previous studies, a mostly teutophagous diet was clear; however, our work is the first to identify inter-individual prey and habitat partitioning. Based on our results and those of other studies, GFSs exhibited an opportunistic foraging strategy across the breeding season. Both analyses were complementary in terms of diversification and useful for the understanding GFS foraging strategies, which are relevant to evaluating population recovery as factors such as prey availability is suggested to be critical to this species recovery.

Habitat degradation can affect trophic ecology by differentially affecting specialist and generalist species, and the number and type of interspecific relationships. However, the effects of habitat degradation on the trophic ecology of coral reefs have received limited attention. We compared the trophic structure and food chain length between two shallow Caribbean coral reefs similar in size and close to each other: one dominated by live coral and the other by macroalgae (i.e., degraded). We subjected samples of basal carbon sources (particulate organic matter and algae) and the same 48 species of consumers (invertebrates and fishes) from both reefs to stable isotope analyses, and determined the trophic position of consumers and relative importance of various carbon sources for herbivores, omnivores, and carnivores. We found that both reefs had similar food chain length and trophic structure, but different trophic pathways. On the coral-dominated reef, turf algae and epiphytes were the most important carbon source for all consumer categories, whereas on the degraded reef, particulate organic matter was a major carbon source for carnivores. Our results suggest that the trophic structure of the communities associated with these reefs is robust enough to adjust to conditions of degradation.

RATIONALE The jumbo squid Dosidicus gigas is a fishery resource of considerable economic and ecological importance in the Mexican Pacific. Studies on its habitat preferences are needed to understand recent fluctuations in the abundance and availability of the species. Stable isotope analysis allows us to infer ecological aspects such as spatial distribution and trophic preferences. METHODS We used an isotope ratio mass spectrometer, automated for carbonate analysis, and coupled to an elemental analyzer, to determine the isotopic composition of statoliths (δ18 O and δ13 C values) and beaks (δ13 C and δ15 N values) from 219 individuals caught over two fishing seasons (2007 and 2009) off the coast of Santa Rosalia, in the central Gulf of California. We used these isotopic ratios to assess variation in spatial and trophic preferences by sex, size, and fishing season. RESULTS In the 2009 group, we observed significant differences in statolith δ13 C values and beak δ13 C and δ15 N values between males and females. Between size groups, we observed significant differences in statolith δ18 O and δ13 C values in 2007 and in beak δ13 C and δ15 N values during both seasons. Both seasons were characterized by high overlap in δ18 O and δ13 C values between sexes and in 2009 between size groups. We observed low trophic overlap between sexes in 2009 and between size groups during both seasons. CONCLUSIONS The isotopic ratios from statoliths and beaks indicate that D. gigas has changed its spatial and trophic preferences, a shift that is probably related to changes in the species' diet. This intraspecific variation in preferences could be related to characteristics such as size, which may influence squid distribution preferences.

Wastewater pollution in seagrass has been documented for decades. In areas where baseline data are lacking, such as the Mexican Caribbean, the δ15N of seagrass can provide information on status and trends. The aims of this study were to determine the spatial and temporal variation in δ15N values of T. testudinum from 2009 to 2017, to explore the nature and causes of isotopic variability, which must be fully understood, and to examine how isotopic variability is linked to wastewater on the coast. Samples of T. testudinum were collected during 2011–2017 in Cancún and from 2009 to 2017 in Mahahual, and analysed on a mass spectrometer. The δ15N values in Cancún (9.0±1.3 ‰) were significantly (P

Stable isotope analysis in mysticete skin and baleen plates has been repeatedly used to assess diet and movement patterns. Accurate interpretation of isotope data depends on understanding isotopic incorporation rates for metabolically active tissues and growth rates for metabolically inert tissues. The aim of this research was to estimate isotopic incorporation rates in blue whale skin and baleen growth rates by using natural gradients in baseline isotope values between oceanic regions. Nitrogen (δ15N) and carbon (δ13C) isotope values of blue whale skin and potential prey were analyzed from three foraging zones (Gulf of California, California Current System, and Costa Rica Dome) in the northeast Pacific from 1996–2015. We also measured δ15N and δ13C values along the lengths of baleen plates collected from six blue whales stranded in the 1980s and 2000s. Skin was separated into three strata: basale, externum, and sloughed skin. A mean (±SD) skin isotopic incorporation rate of 163±91 days was estimated by fitting a generalized additive model of the seasonal trend in δ15N values of skin strata collected in the Gulf of California and the California Current System. A mean (±SD) baleen growth rate of 15.5±2.2 cm y-1 was estimated by using seasonal oscillations in δ15N values from three whales. These oscillations also showed that individual whales have a high fidelity to distinct foraging zones in the northeast Pacific across years. The absence of oscillations in δ15N values of baleen sub-samples from three male whales suggests these individuals remained within a specific zone for several years prior to death. δ13C values of both whale tissues (skin and baleen) and potential prey were not distinct among foraging zones. Our results highlight the importance of considering tissue isotopic incorporation and growth rates when studying migratory mysticetes and provide new insights into the individual movement strategies of blue whales.