Mercury Sources and Trophic Ecology for Hawaiian Bottomfish

Abstract

In Hawaii, some of the most important commercial and recreational fishes comprise an assemblage of lutjanids and carangids called bottomfish. Despite their importance, we know little about their trophic ecology or where the mercury (Hg) that ultimately resides in their tissue originates. Here we investigated these topics, by analyzing muscle samples for mercury content, nitrogen, carbon, and amino acid specific nitrogen isotope ratios in six species distributed across different depths from the Northwestern Hawaiian Islands (NWHI) and the Main Hawaiian Islands (MHI). Fishes had different sources of nitrogen and carbon, with isotopic values suggesting benthic food sources for shallow nearshore species. High trophic position lutjanids that foraged in deeper water, benthic environments generally had higher Hg levels. Model results also suggested that benthic Hg methylation was an important source of Hg for shallow benthic feeders, while deepwater sources of mercury may be important for those with a diet that derives, at least in part, from the pelagic environment. Further, despite the lack of freshwater sources of Hg in the NWHI, statistical models explaining the variation in tissue Hg in the MHI and NWHI were nearly identical, suggesting freshwater Hg inputs were not a major source of Hg in fish tissue.

Spatial trends in a biomagnifying contaminant: Application of amino acid compound–specific stable nitrogen isotope analysis to the interpretation of bird mercury levels

“…Because trophic amino acids, such as glutamic acid, are likely present in greater abundance than other amino acid types (e.g., source amino acids such as phenylalanine), they may have played an important role in regulating bulk δ 15 N values in eggs. Whether this is the case in all types of biological samples merits further study, but in recent work involving fish, trophic position estimates stemming from the use of bulk and source δ 15 N values were generally consistent with δ 15 N GluPhe values (Sackett et al ).…”

Intra‐trophic isotopic discrimination of 15N/14N for amino acids in autotrophs: Implications for nitrogen dynamics in ecological studies

“…Kitazato, & Ohkouchi, 2007;Choy, Popp, Hannides, & Drazen, 2015;Dharampal & Findlay, 2017;Gaebler, Vitti, & Vukmirovich, 1966;McCarthy, Benner, Lee, & Fogel, 2007;McClelland & Montoya, 2002;Naito et al, 2016;Popp et al, 2007;Sackett, Drazen, Choy, Popp, & Pitz, 2015;Sherwood, Iehmann, Schuber, Scott, & McCarthy, 2011;Steffan, Chikaraishi, Currie, et al, 2015). Chikaraishi et al (2009) measured this "inter"-trophic isotopic discrimination between consumers and their diets and established the following equation (1) to estimate the trophic position (TP Tr/Src ) of organisms in food webs:…”

“…Amino acid metabolism within consumers causes predictable enrichment in their 15 N compared to their diets. By quantifying the magnitude of this isotopic discrimination among unique amino acids through compound‐specific isotope analysis (CSIA), ecologists have achieved unprecedented insights into complex food webs (e.g., Batista, Ravelo, Crusius, Casso, & McCarthy, ; Chikaraishi, Kashiyama, Ogawa, Kitazato, & Ohkouchi, ; Choy, Popp, Hannides, & Drazen, ; Dharampal & Findlay, ; Gaebler, Vitti, & Vukmirovich, ; McCarthy, Benner, Lee, & Fogel, ; McClelland & Montoya, ; Naito et al., ; Popp et al., ; Sackett, Drazen, Choy, Popp, & Pitz, ; Sherwood, Iehmann, Schuber, Scott, & McCarthy, ; Steffan, Chikaraishi, Currie, et al., ). Chikaraishi et al.…”

Mercury in Cobia from Estuarine and Offshore Waters of the Southeastern United States: Fisheries Implications

“…; Sackett et al. ). Foraging ecology, food web dynamics, factors related to the onset of maturity, and age‐related factors all contribute to the extent of mercury bioaccumulation in Cobias.…”

“…Stable isotope data and fatty acid signatures also suggest that Cobias are more closely linked to benthic food sources than is typical for other large, pelagic fishes (Cai et al 2007). Available mercury in benthic prey may be different from that in pelagic prey; it also could vary with mercury dynamics in specific habitats or regions (Newman et al 2011;Driscoll et al 2012;Sackett et al 2015). Foraging ecology, food web dynamics, factors related to the onset of maturity, and age-related factors all contribute to the extent of mercury bioaccumulation in Cobias.…”