Leaving the incubation chamber: Cellular and physiological challenges of the juvenile stage of the sea anemone Anthopleura hermaphroditica (Carlgren, 1899) to cope with fluctuating environmental stressors in the Quempillén estuary, southern Chile.

Environmental stress on early life stages has severe consequences for individual performance and population dynamics. The internal incubation process of the symbiotic intertidal anemone Anthopleura hermaphroditica ends when the juveniles leave the gastrovascular cavity of the adult, at which moment they are exposed to a highly stressful environment due to tidal changes and environmental radiation in the Quempillén estuary. To determine the cellular and physiological tolerance capabilities of juvenile anemones to changes in salinity and environmental radiation resulting from the abandonment of the gastrovascular cavity, an experiment with an orthogonal design was performed on individuals exposed to four levels of salinity (30.0, 22.5, 15.0 and 7.5 psu) and two of solar radiation (P/<400-700 nm; PAB/<280-700 nm). The cellular response was evaluated by estimation of peroxidative damage and total antioxidant capacity. In addition, the effects of salinity and radiation on the photosynthetic process (with and without inhibition of the photosynthetic process by the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)) and on the oxygen consumption rate were determined. Finally, the mean maximum effective concentration (EC₅₀) was determined for each of the experimental conditions. Overall, salinity, radiation and photosynthetic condition (and their interaction) influence the level of lipid peroxidation and total antioxidant capacity of juvenile A. hermaphroditica. Thus, levels of oxidative damage and antioxidant response increase with decreasing salinity and are exacerbated at salinities of 7.5 psu combined with UV-R radiation (PAB treatment). Photosynthesis by the zooxanthellae of the symbiont complex not only increases cell damage and antioxidant response, but also generates elevated oxygen levels higher than those utilized by the anemone through oxygen consumption rate. In this context, salinities ≤15 and ≤ 22.5 psu reduce oxygen production/consumption by the symbiont complex under P and PAB conditions, respectively. Consequently, juveniles photosynthesizing in the presence of PAB generate narrower physiological tolerance ranges to hyposaline conditions (EC₅₀ = 23 psu) than non-photosynthetic organisms exposed to P radiation treatment alone (EC₅₀ = 18 psu). Future studies are needed to determine the effect of radiation on the release of juvenile A. hermaphroditica from the gastrovascular cavity of adult anemones. Therefore, symbiotic photosynthetic activity mediates the interdependent effects of salinity and radiation on juveniles' cellular responses and physiological capabilities.