Changes in the Ultrastructures of the Coral Pocillopora damicornis after Exposure to High Temperature, Ultraviolet and Far-Red Radiation

Cnidarian models for toxicology

Coral reefs and tropical habitats are threatened worldwide by global warming and pollution stress. The purpose of these studies was to evaluate potential strategies for using jellyfish for toxicological assessments and as potential toxicological models for corals and other Cnidarians. Laboratory studies were conducted with jellyfish and three species of corals that were exposed to copper; and studies with corals exposed to pyrene and elevated temperatures were conducted. Observational (pulsation rate in jellyfish and bleaching in corals) as well as cellular biomarker responses (glutathione (GSH), lysosomal destabilization, and tissue Cu in jellyfish; GSH in corals) were assessed. Jellyfish pulsation rate, lysosomal destabilization, and tissue Cu levels were significantly correlated. Likewise, GSH levels were significantly correlated with tissue Cu, lysosomal destabilization and pulsation rates. Jellyfish tended to be more sensitive than corals to Cu exposures. Studies were conducted with adults and larvae of brain corals and other species from Curaçao to determine the baseline glutathione levels. Glutathione levels of these Cnidarians were much lower than those of more traditional bioindicators such as mussels or oysters. Glutathione levels of adult jellyfish were lower than adult coral levels. The GSH levels of early life history stages of corals (especially larvae) were lower than adult levels, potentially indicating that these stages could be more sensitive than adults. The GSH levels of the younger coral stages were similar to the GSH levels of jellyfish adults. Species-specific differences in the sensitivity of corals to the different pollutants were observed. This work was facilitated by partnerships with Discovery Place Science (a public science exploration center), CARMABI (Caribbean Research and Management of Biodiversity), and SECORE International which are actively engaged in the culture of Cnidarians and marine educational programs.

The interactive impacts of a constant reef stressor, ultraviolet radiation, with environmental stressors on coral physiology

Reef-building corals create one of the most biodiverse and economically important ecosystems on the planet. Unfortunately, global coral reef ecosystems experience threats from numerous natural stressors, which are amplified by human activities. One such threat is ultraviolet radiation (UVR) from the sun; a genotoxic stressor that is a double-edged sword for corals as they rely on sunlight for energy. More intense UVR has been shown to have greater direct impacts on animal physiology, and these may be exacerbated by co-occurring stressors. The aim of this systematic literature review was to examine if the same applies to corals; that is, if the co-exposure of a constant stressor (UVR) with other stressors has a greater impact on coral physiology than if these stressors occurred separately. We reviewed the biochemical and cellular processes impacted by UVR and the defenses corals have against UVR. The main stressors investigated with UVR were temperature, nitrate, nutrient, oil, water motion, and photosynthetically active radiation (PAR). UVR generally worsened the physiological impacts of other stressors (e.g., by decreasing zooxanthellae and chlorophyll densities). There were species-specific differences in their tolerance to UVR (differences in zooxanthellae populations, sunscreen production and depth) and environmental stress (e.g., resilience to some oils), and that ambient levels of UVR were often beneficial (i.e., nullifying impacts of nitrates). We highlight areas of future investigation including examining and assessing other interacting stressors and their impacts (e.g., ocean acidification, ocean deoxygenation, toxins and pollutants), investigating impacts of multiple stressors with UVR on the coral microbiome, and elucidating the effects of multi-stressors with UVR across early-life history stages (especially larvae). UVR is a pervasive stressor to corals and can interact with other environmental conditions to compromise the resilience of corals. This environmental driver needs to be more comprehensively examined alongside climate change stressors (e.g., temperature increases, ocean acidification and hypoxia) to better understand future climate scenarios on reefs.