Mercury in deepwater chondrichthyans off southeastern Australia
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Trophic structure and biomagnification of mercury in an assemblage of deepwater chondrichthyans collected off southeastern Australia
H. Pethybridge, E. C. V. Butler, D. Cossa, R. Daley, A. Boudou
ABSTRACT:
Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were used to evaluate trophic structure and mercury biomagnification in an assemblage of 16 deepwater chondrichthyans (primarily, two squaliformes: Centroselachus crepidater and Etmopterus baxteri) collected from continental waters off southeastern Australia, through 2004 to 2006. In all species, mean trophic position (quantified by δ15N) ranged from 3.5 to 4.7 (indicative of tertiary consumers). Minor variation in δ13C enrichment was observed between species (–18.7 to –17.1‰) with the exception of Squalus acanthias (–19.3 ± 0.1‰). Total mercury (THg) levels ranged from 0.3 to 4.5 mg kg-1 (wet mass, wm) with the highest concentrations correlated with increasing individual size and TP. Using published (TP and THg) data on low–mid trophic prey groups collected from the study area, THg biomagnification factors between selected predator–prey associations and trophic magnification factors (TMF) within various assemblage and community groupings were calculated. As an assemblage, deepwater elasmobranchs demonstrated moderate rates of THg biomagnification, as indicated by the regression slope (0.20 δ15N = 0.68 TP; TMF = 4.8) while higher rates were reported in the extended continental shelf/slope community (0.32 δ15N = 1.13 TP; TMF = 13.4). Among-system differences in TMF were found between low–mid vs. mid–high order food chains and between shelf/upper-slope vs. mid-slope vs. benthic food webs signifying that bioaccumulation pathways are closely related to physical-chemical (bathome affinity) and community (presumably species composition and food chain length) structure.
Marine Ecology Progress Series – Prepress Abstract, doi: 10.3354/meps09593.