Changes in Fish Diets and Food Web Mercury Bioaccumulation Induced by an Invasive Planktivorous Fish

Abstract

Abstract. The invasion, boom, collapse, and reestablishment of a population of the planktivorous threadfin shad in Clear Lake, California, USA, were documented over a 20-year period, as were the effects of changing shad populations on diet and mercury (Hg) bioaccumulation in nearshore fishes. Threadfin shad competitively displaced other planktivorous fish in the lake, such as inland silversides, young-of-year (YOY) largemouth bass, and YOY bluegill, by reducing zooplankton abundance. As a result, all three species shifted from a diet that was dominated by zooplankton to one that was almost entirely zoobenthos. Stable carbon isotopes corroborated this pattern with each species becoming enriched in d 13 C, which is elevated in benthic vs. pelagic organisms. Concomitant with these changes, Hg concentrations increased by ;50% in all three species. In contrast, obligate benthivores such as prickly sculpin showed no relationship between diet or d 13 C and the presence of threadfin shad, suggesting that effects of the shad were not strongly linked to the benthic fish community. There were also no changes in Hg concentrations of prickly sculpin. The temporary extirpation of threadfin shad from the lake resulted in zooplankton densities, foraging patterns, isotope ratios, and Hg concentrations in pelagic fishes returning to pre-shad values. These results indicate that even transient perturbations of the structure of freshwater food webs can result in significant alterations in the bioaccumulation of Hg and that food webs in lakes can be highly resilient.

Mercury Residues and Productivity in Osprey and Grebes From a Mine‐dominated Ecosystem

“…1); however, there were no discernible annual or long-term monotonic trends in Hg concentrations in the Oaks Arm, where Hg problems would most likely occur. Eagles-Smith et al (2008b) showed, however, that some short-term changes in fish Hg concentrations were related to the presence/absence of invasive fish species such as the threadfin shad, suggesting that this species can potentially change trophic relationships to the point of altering the Hg '' period (1992-1995). The short-dashed line represents a 1:1 ratio, the solid line is a fitted linear regression (P , 0.01, r 2 ¼ 0.90), and the long-dashed lines indicate 95% CI.…”

“…The proximate cause of elevated Hg residues in biota in Clear Lake, California, USA, has been mostly point source erosion or acid mine drainage input from the Sulphur Bank Mercury Mine Superfund Site (Suchanek et al 1998(Suchanek et al , 2000a(Suchanek et al , b, 2008b; Fig. 1).…”

How do aquatic communities respond to contaminants? It depends on the ecological context

“…Similarly, invasion of zebra mussels in the Great Lakes likely maintained elevated concentrations of PCBs in spottail shiner, even though PCB inputs were declining [32]. Finally, in a lake invaded by a planktivorous fish, native forage fish shifted their diet to benthic carbon, resulting in a 50% increase in their Hg concentrations [33]. In summary, although the effects of invasive species on contaminant concentrations in other consumers are variable, these situations provide excellent opportunities to test context-dependent responses.…”

Mine‐derived Mercury: Effects on Lower Trophic Species in Clear Lake, California

“…Additional control was attempted using lakewide applications of methyl parathion from 1962 to 1975. Furthermore, deliberate and/or accidental introductions of several alien planktivorous species, (1) inland silversides (Menidia beryllina) in 1967, (2) threadfin shad (Dorosoma petenense) in 1985, and (3) the predaceous plankter Leptodora kindtii in 1985, may have altered their populations significantly (see Eagles-Smith et al 2008). Nonetheless, this long-term data set provides an excellent opportunity to evaluate whether there is a relationship between chironomid and chaoborid populations vs. Hg in Clear Lake.…”