Stable isotope analyses revealed the influence of foraging habitat on mercury accumulation in tropical coastal marine fish

Abstract

Bioaccumulation of toxic metal elements including mercury (Hg) can be highly variable in marine fish species. Metal concentration is influenced by various species-specific physiological and ecological traits, including individual diet composition and foraging habitat. The impact of trophic ecology and habitat preference on Hg accumulation was analyzed through total Hg concentration and stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) analyses in the muscle of 132 fish belonging to 23 different species from the Senegalese coast (West Africa), where the marine ecosystem is submitted to nutrients inputs from various sources such as upwelling or rivers. Species-specific ecological traits were first investigated and results showed that vertical (i.e. water column distribution) and horizontal habitat (i.e. distance from the coast) led to differential Hg accumulation among species. Coastal and demersal fish were more contaminated than offshore and pelagic species. Individual characteristics therefore revealed an increase of Hg concentration in muscle that paralleled trophic level for some locations. Considering all individuals, the main carbon source was significantly correlated with Hg concentration, again revealing a higher accumulation for fish foraging in nearshore and benthic habitats. The large intraspecific variability observed in stable isotope signatures highlights the need to conduct ecotoxicological studies at the individual level to ensure a thorough understanding of mechanisms driving metal accumulation in marine fish. For individuals from a same species and site, Hg variation was mainly explained by fish length, in accordance with the bioaccumulation of Hg over time. Finally, Hg concentrations in fish muscle are discussed regarding their human health impact. No individual exceeded the current maximum acceptable limit for seafood consumption set by both the European Union and the Food and Agriculture Organization of the United Nations. However, overconsumption of Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. some coastal demersal species analyzed here could be of concern regarding human exposure to mercury.

Mercury isotopes as tracers of ecology and metabolism in two sympatric shark species

“…Top predators using coastal ecosystems are known to feed on different food webs (Bird et al, 2018), inducing exposure to different sources and concentrations of contaminants (Le Croizier et al, 2016, 2019b. To characterize dietary resources, nitrogen and carbon stable isotopes (δ 15 N and δ 13 C) are traditionally used in ecotoxicological studies (Le Bourg et al, 2019;Le Croizier et al, 2020), reflecting respectively the trophic position (Pethybridge et al, 2018) and foraging habitat (Bird et al, 2018) of consumers.…”

The trophic ecology of marine catfishes in south-eastern Brazil

“…In the present study, the slope of the linear regression between THg and δ 15 N (0.34), used as measurement of biomagnification across food webs (Kidd et al, 1995), was higher than those observed by Al-Reasi et al (2007) in Gulf of Oman (0.07), Muto et al (2014) in the Santos continental shelf (0.13), and Di Beneditto et al (2012) (0.25) and Kehrig et al (2013) (0.21) in the same region as our study. Although biomagnification studies in tropical marine ecosystems are limited, this range (0.07-0.34), already observed by Lavoie et al (2013) in tropical marine food webs, reflects the different composition and vertical position in the water column (higher Hg bioavailability in the bottom sediment for benthic/demersal organisms) of the tropical food webs and/or differences in the growth rate of organisms (Muto et al, 2014;Le Croizier et al, 2019). It is already known that the biomagnification of Hg can vary greatly between marine ecosystems (Cossa et al, 2012), or even between environments of the same ecosystem (Cresson et al, 2015).…”

“…The accumulation might occur in ariids in the adjacent marine waters of the PSR estuary in accordance with the findings of other authors that suggest that larger and/or older fish have higher THg concentrations due to longer exposure and the difficulty of eliminating mercury, as THg has a very slow excretion rate due to the metal's high affinity for thiol groups that constitute the protein fraction of the muscles (Nakao et al ., 2007). Second, the elevated assimilation of species closely related to the bottom sediment, that provides higher Hg bioavailability than the water column (Muto et al ., 2014; Le Croizier et al ., 2019), by G. genidens ( Callinectes sp. – highest THg in prey and P. porosissimus – highest THg in prey fishes) and A. luniscutis (Sciaenidae fish) resulted in the higher THg than in B. bagre .…”

“…Although biomagnification studies in tropical marine ecosystems are limited, this range (0.07–0.34), already observed by Lavoie et al . (2013) in tropical marine food webs, reflects the different composition and vertical position in the water column (higher Hg bioavailability in the bottom sediment for benthic/demersal organisms) of the tropical food webs and/or differences in the growth rate of organisms (Muto et al ., 2014; Le Croizier et al ., 2019). It is already known that the biomagnification of Hg can vary greatly between marine ecosystems (Cossa et al ., 2012), or even between environments of the same ecosystem (Cresson et al ., 2015).…”

“…This tool has been used in ecological studies as a good indicator of the trophic level of organisms (Fry & Chumchal, 2012), but it can also be used to identify spatiotemporal patterns of fish bioaccumulation (Buckman et al ., 2017; Liu et al ., 2017) and biomagnification processes (Cresson et al ., 2015; Chouvelon et al ., 2018). Tropical estuaries are known as source of anthropogenic Hg for fish feeding in coastal areas (Le Croizier et al ., 2019). In estuarine and coastal environments, it is estimated that 90% of the river-derived Hg is buried in sediments on ocean margins (Chester, 1990), highlighting the contribution of estuaries to the transport of Hg to coastal marine waters and, consequently, to the associated food webs.…”