Endosymbiotic dinoflagellates (Family Symbiodiniaceae) are directly responsible for coral survival during climate change, as the breakdown of the coral-dinoflagellate symbiosis leads to coral bleaching and often mortality. Despite methodological progress, assessing the physiology of Symbiodiniaceae in hospite remains a complex task. Bio-optics, biochemistry, or -omics techniques are expensive, often inaccessible to investigators, or lack the resolution required to understand single-cell physiological states within endosymbiotic dinoflagellate assemblages. To help address this issue, we developed a protocol that generates a physiological profile of Symbiodiniaceae cells while simultaneously determining cell densities using an entry-level benchtop flow cytometer. Two excitation/emission profiles in the red spectrum target light-harvesting complex-associated pigments, while green and yellow autofluorescence provides insight into antioxidant-associated pigments. Excitation/emission profiles are generated for each individual cell, simultaneously profiling thousands of Symbiodiniaceae cells, thus increasing statistical power to discriminate between groups even when effect sizes are small. As flow cytometry is adopted as a robust and efficient method for endosymbiont cell counting, integration and expansion of our protocol into existing workflows allows quantification of endosymbiont photophysiology and stress-signatures with minimal additional effort.

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As climate change progresses rapidly, biodiversity declines, and ecosystems shift, it is becoming increasingly difficult to document dynamic populations, track fluctuations, and predict responses to climate change. Concurrently, publicly available databases and tools are improving scientific accessibility, increasing collaboration, and generating more data than ever before. One of the most successful projects is iNaturalist, an AI-driven social network doubling as a public database designed to allow citizen scientists to report personal biodiversity reports with accuracy. iNaturalist is especially useful for the research of rare, dangerous, and charismatic organisms, but requires better integration into the marine system. Despite their abundance and ecological relevance, there are few long-term, high-sample datasets for jellyfish, which makes management difficult. To provide some high-sample datasets and demonstrate the utility of publicly collected data, we synthesized two global datasets for ten genera of jellyfishes in the order Rhizostomeae containing 8412 curated datapoints from both iNaturalist (n = 7807) and the published literature (n = 605). We then used these reports in conjunction with publicly available environmental data to predict global niche partitioning and distributions. Initial niche models inferred that only two of ten genera have distinct niche spaces; however, the application of machine learning-based random forest models suggests genus-specific variation in the relevance of abiotic environmental variables used to predict jellyfish occurrence. Our approach to incorporating reports from the literature with iNaturalist data helped evaluate the quality of the models and, more importantly, the quality of the underlying data. We find that free, accessible online data is valuable, yet subject to biases through limited taxonomic, geographic, and environmental resolution. To improve data resolution, and in turn its informative power, we recommend increasing global participation through collaboration with experts, public figures, and hobbyists in underrepresented regions capable of implementing regionally coordinated projects.

The collapse of the coral-dinoflagellate relationship under stress, as, for example, induced by increasing sea surface temperatures due to climate change, leads to coral bleaching and coral mortality. While symbiont shuffling or community shifting has been put forth as a rapid adaptive mechanism in corals, reported instances of these phenomena typically focus on environmental extremes rather than natural seasonal increases in sea surface temperatures that may lead to thermal stress, requiring regulation and acclimation of endosymbiotic Symbiodiniaceae. Understanding the dynamic nature of Symbiodiniaceae endosymbiont community responses to seasonal environmental fluctuations is necessary to help predict the limits of acclimation and adaptation potential. We used a combination of flow cytometry, 3D scanning, and ITS2 DNA metabarcoding to quantify Acropora pulchra Symbiodiniaceae community assemblage composition and function in situ in Guam (Micronesia). Samples were collected during the onset of seasonal warming and the time of year during which corals experience the highest sea water temperatures. Flow cytometry allowed us to expediently generate physiological profiles for thousands of individual endosymbiont cells using their autofluorescent signatures. Under variable environmental conditions, Symbiodiniaceae assemblages displayed site and season-specific photophysiological acclimation signatures while community composition and cell densities in host tissues remained homogeneous across sites. Variable photoacclimation patterns during the early season was followed by an island-wide convergence of photophysiological acclimation signatures during the season that sees the highest water temperatures in Guam. Our results show that photoacclimation rather than symbiont community assemblage reorganization allows for acclimation of Acropora pulchra to seasonal extremes in water temperatures.