Water quality in the eastern karst region of the Yucatan Peninsula: nutrients and stable nitrogen isotopes in turtle grass, Thalassia testudinum

The Great Atlantic Sargassum Belt: Impacts on the Central and Western Caribbean-A review

Pelagic Sargassum spp. blooms pose a complex challenge to the Caribbean coast, affecting ecological, economic, and social dimensions. Since the formation of the Great Atlantic Sargassum Belt in 2011, these blooms have become an annual occurrence, lasting up to nine months each year. The Sargassum that washes ashore in the Western and Central Caribbean can reach tens of thousands of cubic meters per kilometer annually. These algae can carry pollutants, pathogens, and exotic species to coastal zones. As the algae decay, toxic gases and leachates are released, posing significant health risks to humans and other species. Ecologically, Sargassum landings contribute to beach erosion, nearshore waters eutrophication and transition from sandy to muddy sediments, and oxygen depletion, leading to losses in seagrass meadows flora and fauna. Mangrove ecosystems, inlets, and bays face disruptions in their biochemistry, hydrodynamics, and ecology, potentially shifting from carbon sinks to sources of greenhouse gases. Economically, the impact is severe, threatening the tourism and fishing industries crucial to the affected countries' economies. Socially, the blooms affect various aspects of well-being, including health, job quality, and connections to nature. Although progress has been made in understanding the impacts of Sargassum, much of the research has been concentrated in Mexico, primarily focusing on the ecological effects on coastal and beach environments. However, considerable knowledge gaps remain regarding the impacts of Sargassum on the ecosystems, economies, and social well-being of many other countries and territories in the region.

Genotoxic damage in green turtles (Chelonia mydas) exhibits regional and annual fluctuations

Tourism, urban development, and sargasso beaching caused environmental alterations in the Mexican Caribbean coasts. Little ecotoxicological information exists on the green turtle (Chelonia mydas) population inhabiting this region. Micronucleus (MN) and erythrocytic nuclear abnormalities (ENA) tests are non-destructive DNA damage biomarkers. We aimed to determine local (Punta Arenas, Akumal, Punta Herrero, and Xcalak) and annual (2015-2019) variability in MN/ENA frequency to understand genotoxic damage extent. Almost all the individuals sampled (n = 166) presented DNA damage (98.8%); the lack of correlations between MN/ENA and biological variables confirmed the usefulness of these tests as biomarkers. The southern foraging site had the highest number of MN/ENA; an increase over time was found in the most urbanized and the most protected sites, coinciding with previously reported regional variability of persistent organic compounds, heavy metals, and annual massive influx of sargasso. Considering the sentinel status of green turtles, the advantages of the blood tests, and the continuous accelerated urban development in the Caribbean, long-term monitoring of this species is advised.

Variability of the trophic state in a coastal reef system associated with submarine groundwater discharge in the Mexican Caribbean

Submarine groundwater discharges (SGD) have been associated with important sources of nutrients between the land and oceans that can generate eutrophication conditions. This study aims to analyze the behavior of nitrogen and phosphorus using the mixing curve method, to examine the variation of the trophic state using the Karydis Index, and to evaluate the δ15N in benthic organisms to trace the origin of nitrogen in neap tide (November) and spring tide (January) in the Manatí Cenote, and Nohoch-Teek reef lagoon in the Mexican Caribbean. Nitrogen and phosphate enrichment was in the Manatí Cenote during neap and spring tides. This enrichment was particularly noticeable in the reef lagoon during low tides in the areas influenced by SGD. In the Cenote, differences in the nitrate trophic state were observed, indicating an eu-mesotrophic condition during neap tide and a mesotrophic condition during spring tide. However, no significant differences were observed for ammonium (oligo-mesotrophic), nitrites, or phosphate compounds (oligotrophic). The trophic state reef lagoon exhibited a similar pattern but with different spatial variations. In both systems, phosphorus was a limiting nutrient, while δ15N suggested anthropogenic nitrogen uptake by several benthic organisms.

Seasonal nutrient loadings in four monsoonal micro/meso tidal tropical estuaries, west coast of India

Nutrient concentrations were studied seasonally along estuarine and fluvial regions of four micro/meso tidal rivers from Karnataka and Maharashtra, west coast of India. This study was performed to assess the pathway of nutrients across the salinity gradients and evaluate the impacts of weathering and human activity on nutrient concentrations. The rivers of Maharashtra had phosphate concentrations several orders of magnitude higher than the rivers of Karnataka. Nutrient vs salinity plots suggest nutrient addition for Maharashtra rivers and removal in Karnataka rivers. The nutrients in the Karnataka rivers were mostly affected by sewage outfall and anthropogenic activities (industries), while in the Maharashtra rivers, it was influenced by fertilizer application and wastewater discharge. The seasonal nutrient distribution suggests nutrient loadings occurred from the catchments during the wet (monsoon) season in all the rivers. Significant deviations from the Redfield ratio implied occurrences of algal blooms which could threaten those ecosystems.

Evidence of oxidative stress responses of green turtles (Chelonia mydas) to differential habitat conditions in the Mexican Caribbean

Important foraging and nesting habitats for Caribbean green sea turtles (Chelonia mydas) exist within the Mesoamerican Reef System in the Mexican Caribbean. During the last 25 years, urban development and touristic activities have drastically increased in Quintana Roo, Mexico. Moreover, in the last decade, massive pelagic sargasso blooms have also afflicted this region; however, information about the biochemical responses of Caribbean green turtles to these inputs is absent. This study aimed to assess if the oxidative stress indicators in the red blood cells of green turtles are valuable biomarkers of the extent of the anthropic impact in this region. Persistent organic pollutants (POPs) were also measured in the plasma of free-living green turtles during 2015-2018 to characterize these habitats further. As biochemical biomarkers, the production rate of superoxide radical (O2•-), carbonylated protein content, and lipid peroxidation (TBARS) levels, and the activities of superoxide dismutase, glutathione S-transferase (GST), catalase, glutathione peroxidase were measured in erythrocytes. A 15 % occurrence of fibropapillomatosis (FP) was revealed, with tumor size being positively correlated with CAT activity in the affected individuals. A multivariate analysis embracing all oxidative stress markers discriminated green turtles between years of capture (p < 0.001), with those sampled during 2015 presenting the highest production of O2•- (p = 0.001), activities of GST (p < 0.001), levels of TBARS (p < 0.001) and carbonylated proteins (p = 0.02). These local and temporal biochemical responses coincided with the first massive Sargassum spp. bloom reported in the region. The results of this study corroborate the utility of the oxidative stress indicators as biomarkers of environmental conditions (sargasso blooms and POPs) in the green turtle as sentinel species.

Ammonium depletion associated with the COVID-19 pandemic in the Mexican Caribbean

The Mexican Caribbean contributes significantly to Mexico's gross national product. The number of tourists declined from 16.7 million in 2019 to 8.8 million in 2020 due to the COVID-19 pandemic, with a rapid recovery of 13.5 million in 2021. Wastewater discharge is the primary contamination source associated with the tourism sector's demand for goods and services. Water quality could improve due to fewer tourists arriving during the COVID-19 sanitary emergency. This study aimed to quantify ammonium concentrations at eleven locations to evaluate water quality during the sanitary restriction due to the pandemic in the Mexican Caribbean. The ammonium concentrations were 85 % (Nov-2019), 89 % (Feb-2020), and 86 % (Feb-2021) higher than in Nov-2020, where six of the eleven sampled stations were below the detection limit (0.15 μM). Lower ammonium concentrations coincide with the sanitary restriction period and a decrease in affluent tourists.

The δ15N in Orbicella faveolata organic matter reveals anthropogenic impact by sewage inputs in a Mexican Caribbean coral reef lagoon

Coral-reef ecosystems provide essentials services to human societies, representing the most important source of income (e.g., tourism and artisanal fishing) for many coastal developing countries. In the Caribbean region, most touristic and coastal developments are in the vicinity of coral reefs where they may contribute to reef degradation. Here we evaluated the influence of sewage inputs in the coral reef lagoon of Puerto Morelos during a period of 40 years (1970-2012). Annual δ15N values were determined in the organic matter (OM) extracted from coral skeletons of Orbicella faveolata. Average protein content in the OM was 0.33 mg of protein g-1 CaCO3 (±0.10 SD) and a 0.03% of OM relative to the sample weight (n =100). The average of N g-1 CaCO3 was 0.002% (± 0.001 SD). The results showed an increase (p < 0.001) in δ15N over the time, positively correlated with population growth derived from touristic development. These findings emphasize the need to generate urban-planning remediation strategies that consider the impact on natural environments, reduce sewage pollution, and mitigate local stressors that threaten the status of coral-reef communities in the Caribbean region.

Assessing the influence of sewage outfalls on seagrass meadows using nitrogen isotopes

Untreated sewage discharged increases the nutrient loads and changes ecosystem functions. It increases the values of the nitrogen isotopic signature (δ15N) of primary producers such as seagrasses. Itaparica Island (Bahia, Brazil) has undergone extensive urbanization over 50 years. Most of the island has no sewage treatment, and a bridge's construction could increase its population ten times. We evaluated the effects of sewage inputs on the δ15N of seagrass (Halodule wrightii) across Itaparica Island in 14 areas of the island with different degrees of urbanization. Average values of δ15N ranged from -3.95 ‰ (±1.04 SD) to 2.73 ‰ (±1.61). The highest human occupation site also has the highest mean value of δ15N, and seagrass shoot density. The significant correlation (p < 0.05) between δ15N values and shoot density may indicate a possible anthropogenic pressure impacting meadow abundance. Despite a positive correlation, increased anthropogenic nutrient supply can support algae growth and harm seagrass ecosystems.

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.

Use of Microbiological and Chemical Data to Evaluate the Effects of Tourism on Water Quality in Karstic Cenotes in Yucatan, Mexico

Cenotes are spectacular karst formations in Yucatan, Mexico, often used for recreation. However, their impact on water quality has yet to be explored in detail. Therefore, during Easter, water samples were collected from four cenotes to identify variations in water quality associated with the presence of tourists. PCO of water quality, before (PH) and during Holy Week (HW) in 2019, explained 49.02% of the total variation. The indicators contributing to the first principal coordinate's variation were Sr, K, sulfate, and chloride (0.89). Whereas, alkalinity, temperature, conductivity, nitrate, and ORP contributed to the second PC. PERMANOVA indicated a significant interaction between "cenote" and "condition" factors, and post hoc paired comparisons indicated significant differences between PH and HW conditions. Significant correlations varied among the four cenotes as the result of hydrogeological differences. Whereas, numbers of visitors were correlated with at least one fecal-matter indicator, demonstrating anthropogenic influence on the cenotes' water quality.

Environmental degradation of the Mexican Caribbean reef lagoons

Insufficient attention to the large volumes of wastewater produced by expansive tourism and urban development in the north of the Mexican Caribbean has increased concerns on the ecological and economic sustainability of this important tourist destination, which is currently threatened by massive arrivals of pelagic Sargassum. Comparing environmental descriptions for sites exposed to contrasting anthropogenic pressure and before and during massive Sargassum tides, uncovered significant shifts in the environmental conditions in the last 20 years, from oligotrophic to mesotrophic-eutrophic conditions. The most significant changes were observed in the north, for habitats exposed to high anthropogenic pressure. Accordingly, the severe threat that massive Sargassum beaching currently represents for the survival of Caribbean coral reefs cannot be considered the only driver of reef eutrophication in the Mexican Caribbean, as the habitat degradation documented here has an important contribution from anthropogenic fertilization.

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.

Trophic structure of fish communities in mangrove systems subject to different levels of anthropogenic intervention, Tropical Eastern Pacific, Colombia

Mangroves are important ecosystems of tropical and subtropical shorelines. Anthropogenic activity decreases their habitat quality, affecting structural and functional trophic features. We hypothesized that higher levels of anthropogenic intervention generate diversity loss and modify the trophic structure of tropical mangrove fish communities. We compared the taxonomic and isotopic (δ¹³C/δ¹⁵N) composition, abundance, trophic position, and isotopic niche of fish communities from three mangrove systems with different anthropogenic intervention levels in the Colombian Pacific. Non-parametric statistical tests and a Bayesian approach were used to analyze data. A total of 1254 specimens belonging to 23 families, 25 genera, and 30 species were identified, presenting higher abundance (821) in moderate anthropogenic intervention level mangrove (Moderate-AIL), with high dominance of one species (Lile stolifera). The low anthropogenic intervention level mangrove (Low-AIL) was the second in abundance (291) but exhibited a greater number of species (23), while the high anthropogenic intervention level mangrove (High-AIL) presented the least abundance (142) and species number (17). The isotopic composition ​​reveals that Moderate and High-AIL mangroves presented enriched ¹³C and ¹⁵ N compared to Low-AIL (~ 2 to 4 ‰). Mean trophic position (TP) of communities was slightly higher in the more intervened systems (~ 1 to 2 orders of magnitude), as well as in specific species (Centropomus spp.). Isotopic niche width (TA and SEAc) was greater in High-AIL (41.1 and 9.2), more than doubled compared to Moderate-AIL (33.0 and 4.1). In High-AIL isotopic niche width increased, indicating lesser availability of prey and basal resources. The results obtained in this study support the proposed hypothesis and, suggest that anthropogenic intervention modifies diversity and food webs dynamics, affecting the transfer of matter and energy from macrotidal tropical mangroves to coastal ecosystems. However, it is recommended to be careful concluding differences based exclusively on the anthropogenic intervention level, since it is widely documented that mangrove settings also influence the analyzed trophic parameters.

A Review of Disturbances to the Ecosystems of the Mexican Caribbean, Their Causes and Consequences

In a relatively short timescale (less than 50 years), urbanization has caused many anthropogenic disturbances that have affected ecosystem health and, directly or indirectly, quality of life for the local human population. Global disturbances, such as climate change, can also have a substantial, overarching impact on ecosystems. In this scenario, natural disturbances, previously considered an integral part of ecosystem dynamics, can now cause irreversible change to the state of ecosystems, and at the same time, negatively impact social and economic systems. The objective of this study was to identify ecosystem disturbances at a site of interest to recommend strategies to improve coastal zone management. We chose the Mexican Caribbean as a case study, because its biological and cultural complexity render it an interesting location from a coastal management point of view. The PRISMA framework was used to conduct a systematic literature review to identify the ecosystem disturbances that affect this area, as well as the main causes and consequences of these disturbances. Additionally, we discuss how disturbances and their impacts, as screened through PRISMA, can be incorporated into a coastal zone management framework. Results need to consider the limitations associated with using this technique e.g., the degree of impact from a current disturbance may vary from that reported in an earlier publication. Despite its limitations, we believe that this methodology proves useful for identifying key ecosystem disturbances and their consequences, providing a useful tool for identifying appropriate actions to inform coastal zone management plans.

Caffeine and Paraxanthine as Tracers of Anthropogenic Wastewater in Coastal Lagoons in Yucatan, Mexico

Due to karstic bedrock geology and poor wastewater management practices, anthropogenic activities are impacting water quality in Yucatan's aquatic systems. Specifically, raw wastewater inputs to the aquifer subsequently flow to coastal lagoons through groundwater fluxes. This study establishes the presence of anthropogenic wastewater by measuring caffeine and its metabolite, paraxanthine, in four of Yucatan's major coastal lagoons: Celestun, Chelem, Dzilam de Bravo, and Ria Lagartos. Concentrations of caffeine ranged from non-detected (ND) to 2390 ng L^-1 and paraxanthine from ND to 212 ng L^-1, which correspond with pollution threats from anthropogenic wastewater inputs. The potential sources are: (1) direct in situ discharges from nearby urban settlements; and (2) contribution from submerged groundwater discharges. Overall, results indicate the potential of caffeine as an environmental tracer of anthropogenic wastewater contamination for the region.

Groundwater Quality in the Yucatan Peninsula: Insights from Stable Isotope and Metals Analysis

High surface water-groundwater connectivity characterizes watersheds underlain by karsts, increasing contaminant transport risks. However, karsts are highly complex, making research necessary to understand the transport of contaminants from the surface, through the aquifer, to discharge areas. In Yucatan, the lack of waste water treatment raises the risk of groundwater contamination. We monitored stable isotopes (δ¹⁸ O-NO₃ and δ¹⁵ N-NO₃ ), cadmium, and lead to document waste water contamination and transport during the rainy and dry seasons, using water samples collected along the Ring of Cenotes during each season. Specific conductance and pH showed no consistent seasonality, with conductance ranging from 0.5 to 55 mS/cm and pH ranging from 6.6 to 8.6 for most samples. Nitrate concentrations in the cenotes averaged 205 ± 260 μM and no seasonal pattern was observed. Cd and Pb concentrations were 0.1 to 37.9 μg/L and 0.2 to 243.2 μg/L, respectively. Nitrate stable isotope values were 2.6 to 27.2‰ for δ¹⁸ O and 1.2 to 20.7‰ for δ¹⁵ N. The statistical relationship between δ¹⁵ N and δ¹⁸ O, in dry season samples, indicated that denitrification was occurring. A scale measure for waste water recognition showed: (1) high variability among sites probably related with dry/rainy seasons and/or diverse anthropogenic activities; and (2) specific water quality variables that contribute to contamination at each site during each season. Importantly, our analyses indicate that in the area surrounding the Ring of Cenotes, waste water exhibits spatial and temporal patterns related to complex transport and dilution processes, as is the case in karsts in general.

Determining the origin and fate of nitrate in the Nanyang Basin, Central China, using environmental isotopes and the Bayesian mixing model

Identifying sources of nitrate contamination has been a long-term challenge in areas with different land uses. We investigated the biogeochemical processes and quantified the contribution of potential nitrate sources in the Nanyang Basin, the source area of the South to North Water Diversion Project in China. Hydrogeochemical characteristics, the dual-isotope method (δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^-), and the Bayesian mixing model (SIAR) were combined. The results for 160 samples indicated that mean nitrate concentrations of residential area (162.83 mg L^-1) and farmland (75.71 mg L^-1) were higher compared with those of surface water (16.15 mg L^-1) and forest (36.25 mg L^-1). Hydrochemical facies and molar ratios of major ions indicated that the natural environment was greatly impacted by anthropogenic activities. Nitrification, ammonium volatilization, and mixing effects were the dominant processes in nitrogen transformation. The contributions of different sources to nitrate contamination were 45.41%, 35.81%, 17.87%, and 0.91% for sewage and manure, soil organic nitrogen, synthetic fertilizer, and atmospheric deposition, respectively. Undeveloped infrastructure and sewage disposal in rural areas were the main causes of nitrate contamination. Our results provide a theoretical basis for the development of measures to guarantee long-term water supply of the South to North Water Diversion Project.

The Conservational State of Coastal Ecosystems on the Mexican Caribbean Coast: Environmental Guidelines for Their Management

The accelerated rate of environmental degradation of the Mexican Caribbean coast is alarming. In this work, spatial analysis procedures were applied to study relationships among wave and wind climates, water quality, and environmental degradation of the principal coastal ecosystems. We found an increasing North-South gradient in the preservation state of the coastal ecosystems, related to the degree of anthropization of the coastline. In the north, all analysed stressors exert high pressure on coral reefs, seagrass meadows, mangroves, and dunes, and cause chronic coastline erosion. The coastal ecosystems of the central and southern regions are more mature and healthier, and the most significant stressor is reduced water quality. The north has been most hit by high-intensity hurricanes, the frequency of which has increased in the Mexican Caribbean over recent decades. The status of conservation of the ecosystems, added to the long-term intensification of environmental pressures, particularly high-intensity hurricanes, will induce further deterioration if a coordinated management scheme is not adopted by decision-makers. To ensure effective coordinated management, plans should be made on a regional scale using shared guidelines. Spatial analysis procedures aid in prioritizing and adapting the shared guidelines depending on the identified major stressors and the preservation state of each region in the Mexican Caribbean.

The microbiome of modern microbialites in Bacalar Lagoon, Mexico

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.

Sargassum blooms in the Caribbean alter the trophic structure of the sea urchin Diadema antillarum

The arrival of large masses of drifting Sargassum since 2011 has caused changes in the natural dynamics of Caribbean coastal ecosystems. In the summer of 2015, unprecedented and massive mats of S. fluitans and S. natans have been observed throughout the Mexican Caribbean including exceptional accumulations ashore. This study uses stable isotopes to assess the impact of Sargassum blooms on the trophic dynamics of the Diadema antillarum sea urchin, a keystone herbivore on many Caribbean reefs. Bayesian models were used to estimate the variations in the relative proportions of carbon and nitrogen of assimilated algal resources. At three lagoon reef sites, the niche breadth of D. antillarum was analysed and compared under massive influx of drifting Sargassum spp. vs. no influx of Sargassum blooms. The effects of the leachates generated by the decomposition of Sargassum led to hypoxic conditions on these reefs and reduced the taxonomic diversity of macroalgal food sources available to D. antillarum. Our trophic data support the hypothesis that processes of assimilation of carbon and nitrogen were modified under Sargassum effect. Isotopic signatures of macroalgae associated with the reef sites exhibited significantly lower values of δ¹⁵N altering the natural herbivory of D. antillarum. The Stable Isotopes Analysis in R (SIAR) indicated that, under the influence of Sargassum blooms, certain algal resources (Dictyota, Halimeda and Udotea) were more assimilated due to a reduction in available algal resources. Despite being an abundant available resource, pelagic Sargassum was a negligible contributor to sea urchin diet. The Stable Isotope Bayesian Ellipses in R (SIBER) analysis displayed differences between sites, and suggests a reduction in trophic niche breadth, particularly in a protected reef lagoon. Our findings reveal that Sargassum blooms caused changes in trophic characteristics of D. antillarum with a negative impact by hypoxic conditions. These dynamics, coupled with the increase in organic matter in an oligotrophic system could lead to reduce coral reef ecosystem function.