Evaluating mercury biomagnification in fish from a tropical marine environment using stable isotopes (δ¹³C AND δ¹⁵N)

Abstract

Concentrations of total mercury (T-Hg) and methylmercury (MeHg) were measured in zooplankton and 13 fish species from a coastal food web of the Gulf of Oman, an arm of the Arabian Sea between Oman and Iran. Stable isotope ratios (delta13C and delta15N) also were determined to track mercury biomagnification. The average concentration of T-Hg in zooplankton was 21 +/- 8.0 ng g(-1) with MeHg accounting 10% of T-Hg. Total mercury levels in fish species ranged from 3.0 ng g(-1) (Sardinella longiceps) to 760 ng g(-1) (Rhizoprionodon acutus) with relatively lower fraction of MeHg (72%) than that found in other studies. The average trophic difference (Deltadelta13C) between zooplankton and planktivorous fish (Selar crumenopthalmus, Rastrelliger kanagurta, and S. longiceps) was higher (3.4 per thousandth) than expected, suggesting that zooplankton may not be the main diet or direct carbon source for these fish species. However, further sampling would be required to compensate for temporal changes in zooplankton and the influence of their lipid content. Trophic position inferred by delta15N and and slopes of the regression equations (log10[T-Hg] = 0.13[delta15N] - 3.57 and log10[MeHg] = 0.14[delta15N] - 3.90) as estimates of biomagnification indicate that biomagnification of T-Hg and MeHg was lower in this tropical ocean compared to what has been observed in arctic and temperate ecosystems and tropical African lakes. The calculated daily intake of methylmercury in the diet of local people through fish consumption was well below the established World Health Organization (WHO) tolerable daily intake threshold for most of the fish species except Euthynnus affinis, Epinephelus epistictus, R. acutus, and Thunnus tonggol, illustrating safe consumption of the commonly consumed fish species.

Biomagnification Profiles of Trace Elements through the Food Web of an Integrated Shrimp Mangrove Farm in Ba Ria Vung Tau, South Vietnam

“…The log Hg concentration-δ 15 N regression slope of 0.048 found in this study was comparable to the slope of 0.07 reported for Hg in a tropical coastal food web in the Gulf of Oman (Al-Reasi et al, 2007). However, this slope was remarkably smaller than that observed for the Mekong River food web (0.114) (Ikemoto et al, 2008), Arctic marine food webs (0.197-0.32) (Jarman et al, 1996;Atwell et al, 1998;Campbell et al, 2005) and for biota in Lake Murray, Papua New Guinea (0.28) (Bowles et al, 2001).…”

Regional variation in mercury and stable isotopes of red snapper (Lutjanus campechanus) in the northern gulf of Mexico, USA

“…Despite the importance of marine fish in human diets and high levels of Hg observed by monitoring agencies [2], much of the research that has been conducted on aquatic Hg cycling has occurred in freshwater ecosystems [3]. Studies of Hg bioaccumulation in marine ecosystems often examine fish collected from limited geographic areas [4][5][6][7]. How Hg concentrations in fish vary within ocean basins has not been well studied.…”

Mercury Biomagnification Through a Coral Reef Ecosystem

“…Additionally, differences in community productivity and structure are thought to influence the degree of biomagnification. Primary and secondary production, species diversity, food chain length and complexity (i.e., number of trophic links per species) are all believed to be influential factors affecting biomagnification efficiency (Cabana et al 1994;Stemberger and Chen 1998;Al-Reasi et al 2007). For example, Cabana et al (1994) found fish in lakes with longer food chains have higher Hg concentrations than fish from lakes with short food chains.…”

“…They suggested that structurally complex food webs, comprising many lateral links, may attenuate the degree of biomagnfication due to pathways that do not lead to top predators (Stemberger and Chen 1998). Other studies have subsequently argued that lower biomagnification in certain ecosystems may be attributed to more complex food webs (Al-Reasi et al 2007;Lavoie et al 2013).…”