Mercury Stable Isotopes Reveal Influence of Foraging Depth on Mercury Concentrations and Growth in Pacific Bluefin Tuna

Pelagic ecosystems are changing due to environmental and anthropogenic forces, with uncertain consequences for the ocean's top predators. Epipelagic and mesopelagic prey resources differ in quality and quantity, but their relative contribution to predator diets has been difficult to track. We m...

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Bibliographic Details
Published in:Environmental Science & Technology
Main Authors: Madigan, Daniel J., Li, Miling, Yin, Runsheng, Baumann, Hannes, Snodgrass, Owyn E., Dewar, Heidi, Krabbenhoft, David P., Baumann, Zofia, Fisher, Nicholas S., Balcom, Prentiss, Sunderland, Elsie M.
Format: Report
Language:English
Published: AMER CHEMICAL SOC 2018
Subjects:
Engineering
Environmental Sciences & Ecology
Environmental
Environmental Sciences
THUNNUS-ORIENTALIS
TROPHIC TRANSFER
NORTH-ATLANTIC
ARCHIVAL TAGS
FOOD WEBS
PELAGIC FISHES
OCEAN
METHYLMERCURY
ECOSYSTEM
FRACTIONATION
Pacific
North Atlantic
Online Access:http://ir.gig.ac.cn/handle/344008/38501
https://doi.org/10.1021/acs.est.7b06429
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Summary:Pelagic ecosystems are changing due to environmental and anthropogenic forces, with uncertain consequences for the ocean's top predators. Epipelagic and mesopelagic prey resources differ in quality and quantity, but their relative contribution to predator diets has been difficult to track. We measured mercury (Hg) stable isotopes in young (<2 years old) Pacific bluefin tuna (PBFT) and their prey species to explore the influence of foraging depth on growth and methylmercury (MeHg) exposure. PBFT total Hg (THg) in muscle ranged from 0.61 to 1.93 mu g g(-1) dw (1.31 mu g g(-1) dw +/- 0.37 SD; 99% +/- 6% MeHg) and prey ranged from 0.01 to 1.76 mu g g(-1) dw (0.13 mu g g(-1) dw +/- 0.19 SD; 85% +/- 18% MeHg). A systematic decrease in prey delta Hg-202 and Delta Hg-199 with increasing depth of occurrence and discrete isotopic signatures of epipelagic prey (delta Hg-202: 0.74 to 1.49 parts per thousand; Delta Hg-199: 1.76-2.96 parts per thousand) and mesopelagic prey (delta Hg-202: 0.09 to 0.90 parts per thousand; Delta Hg-199: 0.62-1.95 parts per thousand) allowed the use of Hg isotopes to track PBFT foraging depth. An isotopic mixing model was used to estimate the dietary proportion of mesopelagic prey in PBFT, which ranged from 17% to 55%. Increased mesopelagic foraging was significantly correlated with slower growth and higher MeHg concentrations in PBFT. The slower observed growth rates suggest that prey availability and quality could reduce the production of PBFT biomass.

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