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Elysia crispata (Sacoglossa, Gastropoda) is a tropical sea slug known for its ability to incorporate functional chloroplasts from a variety of green macroalgae, a phenomenon termed kleptoplasty. This sea slug, amenable to laboratory cultivation, produces mucus, a viscous secretion that serves diverse purposes including protection, locomotion, and reproduction. In this study, we profiled the antimicrobial, antioxidant, and anti-inflammatory activities of the mucus of this sea slug. Results revealed inhibitory activity against several bacterial strains, more pronounced for Gram–negative bacteria. Particularly interesting was the strong inhibitory effect against Pseudomonas aeruginosa, a bacterial species classified by the WHO as a high-priority pathogen and associated with high-risk infections due to its frequent multidrug-resistant profile. Similar inhibitory effects were observed for the mucus native protein extracts, indicating that proteins present in the mucus contributed significantly to the antimicrobial activity. The mucus also showed both antioxidant and anti-inflammatory activities. The latter activities were associated with the low molecular weight (<10 kDa) fraction of the mucus rather than the native protein extracts. This study opens the way to further research on the biotechnological applications of the mucus secreted by this unique marine organism, particularly as an antimicrobial agent. [ABSTRACT FROM AUTHOR]

Simple Summary: Climate change has made bleaching events increasingly common in coral reefs. As such, scientists are rushing to better understand what will be the outcomes of bleaching on these tropical ecosystems. However, scientific focus is mostly being given to the direct impacts promoted by these events (e.g., mass mortality of corals, coral reef decay, community transitions), with indirect ones remaining largely overlooked (e.g., impacts on trophic interactions of highly specialized animals). Organisms directly affected by bleaching display a poorer nutritional value, but the effects this may have on their predators remain largely overlooked. To address this gap in scientific research, we advocate the use of the model predator–prey pair featuring the nudibranch sea slug Berghia stephanieae and its prey, the photosymbiotic glass anemone Exaiptasia diaphana. As the two species are already used as models in other research fields, one can build upon existing knowledge to determine if and how this highly specialized sea slug, that only preys upon glass anemones, is affected in terms of survival and reproductive fitness when only bleached prey are available. Moreover, this model pair will also allow investigating if such trophic effects cascade over consecutive generations, shaping populations and ultimately ruling species survival. Bleaching events associated with climate change are increasing worldwide, being a major threat to tropical coral reefs. Nonetheless, the indirect impacts promoted by the bleaching of organisms hosting photosynthetic endosymbionts, such as those impacting trophic interactions, have received considerably less attention by the scientific community. Bleaching significantly affects the nutritional quality of bleached organisms. The consequences promoted by such shifts remain largely overlooked, namely on specialized predators that have evolved to prey upon organisms hosting photosynthetic endosymbionts and benefit nutritionally, either directly or indirectly, from the available pool of photosynthates. In the present study, we advocate the use of the model predator–prey pair featuring the stenophagous nudibranch sea slug Berghia stephanieae that preys upon the photosymbiotic glass anemone Exaiptasia diaphana to study the impacts of bleaching on trophic interactions. These model organisms are already used in other research fields, and one may benefit from knowledge available on their physiology, omics, and culture protocols under controlled laboratory conditions. Moreover, B. stephanieae can thrive on either photosymbiotic or aposymbiotic (bleached) glass anemones, which can be easily maintained over long periods in the laboratory (unlike photosymbiotic corals). As such, one can investigate if and how nutritional shifts induced by bleaching impact highly specialized predators (stenophagous species), as well as if and how such effects cascade over consecutive generations. Overall, by using this model predator–prey pair one can start to truly unravel the trophic effects of bleaching events impacting coral reef communities, as well as their prevalence over time. [ABSTRACT FROM AUTHOR]