Differential accumulation of cadmium and changes in glutathione levels as a function of symbiotic state in the sea anemone Anthopleura elegantissima

Abstract

Coastal ecosystems are increasingly impacted by anthropogenic activities and contaminant inputs, including heavy metals. This paper investigates the responses to laboratory cadmium exposures in the North American Pacific coast temperate sea anemone Anthopleura elegantissima. Anemones were exposed to cadmium chloride (control, 20 and 100 μg l −1 Cd) for 14 days (sampled at days 0, 2, 7 and 14) and analyzed for Cd content using inductively coupled plasma mass spectroscopy (ICP-MS). Higher levels of Cd were demonstrated in symbiotic anemones compared to symbiont-free (aposymbiotic) anemones (e.g. 100 μg l −1 Cd exposure at day 14; 12.4±2.4 and 4.5±1.9 ng Cd mg −1 dry weight, respectively; t-test; p<0.001). These higher levels in symbiotic anemones were not due to increasing uptake of Cd by the algal symbionts (levels in algal-containing pellet fractions were constant over dose and time; t-test; p>0.05) but rather to increased accumulation by both partners. No changes in algal cell density were observed in symbiotic anemone tentacle clips at any dose or time point (ANOVA; p>0.05). Changes in glutathione (GSH) levels have been proposed as a useful biomarker in other marine invertebrates in response to heavy metal stress, but GSH studies have not been reported for this species. We demonstrate the presence of GSH in A. elegantissima and its depletion (58.2% of control values) following 1-week exposure to buthionine sulfoximine (BSO), a nontoxic chemical known to deplete GSH. Levels of GSH were higher in symbiotic compared to aposymbiotic anemones (control averages, 563±81 and 485±58 nmol GSH mg −1 wet weight, respectively; t-test; p<0.001). Following Cd exposure, significant reductions ( t-test; p<0.05) in GSH levels were observed only in the aposymbiotic anemones (exposure to 100 μg l −1 Cd resulted in a 27% reduction from control levels at day 14). Our results demonstrate that the accumulation of Cd depends upon symbiotic state and provides the first identification of a GSH response in anemones and indeed in any cnidarian in response to heavy metals.