Manganese uptake and partitioning between the tissue of the anemone host Exaiptasia pallida and Symbiodinium spp., including assessment of stress and recovery.

Manganese (Mn) is essential for global steel and Mn-iron (Fe) alloy production. The human health effects of elevated Mn concentrations have been well established, but studies on its impact on marine invertebrates are limited. This study is the first to investigate Mn uptake in the sea anemone Exaiptasia pallida after chronic exposure (0.5, 1, 10, and 100 mg/L) for 24-d. Following exposure, E. pallida were transferred to ambient seawater for 6-d to assess Mn depuration. Mn accumulation and partitioning in host tissue and symbionts (Symbiodinium spp.), tentacle retraction, and symbiont cell density were measured during exposure and depuration. Mn concentrations were substantially higher in symbionts than tissue in all treatments after 24-d. No significant difference was observed for symbiont cell density after Mn exposure. Tentacle retractions were significantly higher in all Mn exposed treatments than controls at all time points. Mn depuration was observed for both tissue and symbionts but was more rapid in symbionts. This study reveals that Symbiodinium spp. can play a role in Mn uptake and depuration in anemones, but Mn loading does not affect cell density. These results help understand metal uptake and depuration in complex relationships between Symbiodinium spp. and other host taxa like corals.