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Surface water samples from the Yucatan shelf presented Cd concentrations similar to those reported internationally for non-polluted coastal and marine waters. V concentrations, on the other hand, fall within the range of anthropogenically polluted waters (25% of the sampling sites). In the study area, the probable sources of V could be: (1) carbonate sediments leaching V into the water column and co-transported with fine sediments resuspending as a result of the complex hydrodynamics in the area or, (2) accidental spills from cargo ships transporting oil between the Atlantic and the Gulf of Mexico. Significant spatial and temporal differences were found for both metals; therefore, a regional interval concentration is suggested for V from 1.28 to 1.84 μg L−1 and Cd from 0.003 to 0.09 μg L−1. These differences could primarily be the result of the observed hydrology and hydrodynamics created by the Yucatan current, submarine groundwater discharges and upwelling. [ABSTRACT FROM AUTHOR]

Megabenthic communities on continental margins benefit from structural complexity of the seafloor and sedimentary dynamics. These communities were tested in the outer margins of the Yucatan continental shelf (YCS) during August 2016 to evaluate the relationships between community attributes with environmental variables. The total capture was 1,366 103 ind km−2 and 2,078 kg ash free dry weight (AFDW) km−2, distributed among 319 species. Crustaceans and molluscs were co-dominant in abundance (576,629 ind km−2 ∼42.2% and 481,372 ind km−2 ∼35.2%), while crustaceans and sponges were the greatest contributors to community biomass (699.84 kg AFDW km−2 ∼33.6% and 47.8 kg AFDW km−2 ∼23.0%). Local diversity was higher than reported for other areas of the GoM, showing a pseudo-latitudinal gradient of richness related to the karstic bottom and autogenic species. Beta diversity showed no species loss in these communities. The BIOENV test pointed to longitude, temperature, sorting, vanadium, 2.6-dimethyl naphthalene, latitude, chlorophyll, average grain size, n-C16 and n-C23 as the most important variables. Hydrocarbons were recorded at lower concentrations than the threshold effects level (TEL) reference values; however, the significant correlation between richness and dibenzothiophene must be evaluated. Beta diversity exhibited a high turnover and functional diversity showed an absence of regional distribution. Differences in benthic megafauna among sites were because of gradients in latitude and concentrations of aliphatic compounds which can be attributed to the distance from the stations to the coastline or groundwater flow. Environmental monitoring programmes are recommended because of petrogenic compounds that influence the community structure. [ABSTRACT FROM AUTHOR]