Greater functional diversity and redundancy of coral endolithic microbiomes align with lower coral bleaching susceptibility

The skeleton of reef-building coral harbors diverse microbial communities that could compensate for metabolic deficiencies caused by the loss of algal endosymbionts, i.e., coral bleaching. However, it is unknown to what extent endolith taxonomic diversity and functional potential might contribute to thermal resilience. Here we exposed Goniastrea edwardsi and Porites lutea, two common reef‐building corals from the central Red Sea to a 17-day long heat stress. Using hyperspectral imaging, marker gene/metagenomic sequencing, and NanoSIMS, we characterized their endolithic microbiomes together with ¹⁵N and ¹³C assimilation of two skeletal compartments: the endolithic band directly below the coral tissue and the deep skeleton. The bleaching-resistant G. edwardsi was associated with endolithic microbiomes of greater functional diversity and redundancy that exhibited lower N and C assimilation than endoliths in the bleaching-sensitive P. lutea. We propose that the lower endolithic primary productivity in G. edwardsi can be attributed to the dominance of chemolithotrophs. Lower primary production within the skeleton may prevent unbalanced nutrient fluxes to coral tissues under heat stress, thereby preserving nutrient-limiting conditions characteristic of a stable coral-algal symbiosis. Our findings link coral endolithic microbiome structure and function to bleaching susceptibility, providing new avenues for understanding and eventually mitigating reef loss.Subject terms: Microbial ecology, Microbial ecology     

The Drosophila TRPL ion channel shares a Rab-dependent translocation pathway with rhodopsin

The Drosophila visual transduction cascade is embedded in the rhabdomeres of photoreceptor cells and culminates in the opening of the two ion channels, TRP and TRPL. TRPL translocates from the rhabdomeres to the cell body upon illumination and vice versa when flies are kept in the dark. Here, we studied the mechanisms underlying the light-dependent internalization of TRPL. Co-localization of TRPL and rhodopsin in endocytic particles revealed that TRPL is internalized by a vesicular transport pathway that is also utilized, at least partially, for rhodopsin endocytosis. TRPL internalization is attenuated under light conditions that result in a high rate of rhodopsin internalization and is highest in orange light that result in very little rhodopsin internalization. In line with a canonical vesicular transport pathway, we found that rab proteins, Rab5 and RabX4, are required for the internalization of TRPL into the cell body. Our results provide insight into stimulus-dependent internalization of a prominent member of the TRP superfamily.     

Evidence for coral range expansion accompanied by reduced diversity of Symbiodinium genotypes

Coral Reefs - Zooxanthellate corals are threatened by climate change but may be able to escape increasing temperatures by colonizing higher latitudes. To determine the effect of host range...     

Human-induced salinity changes impact marine organisms and ecosystems

Climate change is fundamentally altering marine and coastal ecosystems on a global scale. While the effects of ocean warming and acidification on ecology and ecosystem functions and services are being comprehensively researched, less attention is directed toward understanding the impacts of human-driven ocean salinity changes. The global water cycle operates through water fluxes expressed as precipitation, evaporation, and freshwater runoff from land. Changes to these in turn modulate ocean salinity and shape the marine and coastal environment by affecting ocean currents, stratification, oxygen saturation, and sea level rise. Besides the direct impact on ocean physical processes, salinity changes impact ocean biological functions with the ecophysiological consequences are being poorly understood. This is surprising as salinity changes may impact diversity, ecosystem and habitat structure loss, and community shifts including trophic cascades. Climate model future projections (of end of the century salinity changes) indicate magnitudes that lead to modification of open ocean plankton community structure and habitat suitability of coral reef communities. Such salinity changes are also capable of affecting the diversity and metabolic capacity of coastal microorganisms and impairing the photosynthetic capacity of (coastal and open ocean) phytoplankton, macroalgae, and seagrass, with downstream ramifications on global biogeochemical cycling. The scarcity of comprehensive salinity data in dynamic coastal regions warrants additional attention. Such datasets are crucial to quantify salinity-based ecosystem function relationships and project such changes that ultimately link into carbon sequestration and freshwater as well as food availability to human populations around the globe. It is critical to integrate vigorous high-quality salinity data with interacting key environmental parameters (e.g., temperature, nutrients, oxygen) for a comprehensive understanding of anthropogenically induced marine changes and its impact on human health and the global economy.     

Adapting with Microbial Help: Microbiome Flexibility Facilitates Rapid Responses to Environmental Change

Animals and plants are metaorganisms and associate with microbes that affect their physiology, stress tolerance, and fitness. Here the hypothesis that alteration of the microbiome may constitute a fast-response mechanism to environmental change is examined. This is supported by recent reciprocal transplant experiments with reef corals, which have shown that their microbiome adapts to thermally variable habitats and changes over time when transplanted into different environments. Further, inoculation of corals with beneficial bacteria increases their stress tolerance. But corals differ in their ability to flexibly associate with different bacteria. How scales of microbiome flexibility may reflect different metaorganism adaptation mechanisms is discussed and future directions for research are pinpointed. It is posited that microbiome flexibility is a broad phenomenon that contributes to the ability of organisms to respond to environmental change. Importantly, adapting with microbial help may provide an alternate route to organismal adaptation that facilitates rapid responses.     

Spatio-Temporal Analyses of Symbiodinium Physiology of the Coral Pocillopora verrucosa along Large-Scale Nutrient and Temperature Gradients in the Red Sea

Algal symbionts (zooxanthellae, genus Symbiodinium) of scleractinian corals respond strongly to temperature, nutrient and light changes. These factors vary greatly along the north-south gradient in the Red Sea and include conditions, which are outside of those typically considered optimal for coral growth. Nevertheless, coral communities thrive throughout the Red Sea, suggesting that zooxanthellae have successfully acclimatized or adapted to the harsh conditions they experience particularly in the south (high temperatures and high nutrient supply). As such, the Red Sea is a region, which may help to better understand how zooxanthellae and their coral hosts successfully acclimatize or adapt to environmental change (e.g. increased temperatures and localized eutrophication). To gain further insight into the physiology of coral symbionts in the Red Sea, we examined the abundance of dominant Symbiodinium types associated with the coral Pocillopora verrucosa, and measured Symbiodinium physiological characteristics (i.e. photosynthetic processes, cell density, pigmentation, and protein composition) along the latitudinal gradient of the Red Sea in summer and winter. Despite the strong environmental gradients from north to south, our results demonstrate that Symbiodinium microadriaticum (type A1) was the predominant species in P. verrucosa along the latitudinal gradient. Furthermore, measured physiological characteristics were found to vary more with prevailing seasonal environmental conditions than with region-specific differences, although the measured environmental parameters displayed much higher spatial than temporal variability. We conclude that our findings might present the result of long-term acclimatization or adaptation of S. microadriaticum to regionally specific conditions within the Red Sea. Of additional note, high nutrients in the South correlated with high zooxanthellae density indicating a compensation for a temperature-driven loss of photosynthetic performance, which may prove promising for the resilience of these corals under increase of temperature increase and eutrophication.