For those who are unfamiliar, corals are marine invertebrates that typically live in colonies, and typically have a symbiotic relationship with algae. The “main” organism is a polyp – a jellyfish-like creature that builds the calcium carbonate structures that we recognize as “coral”. For the species that have symbiotic algae incorporated into the polyp’s body, the algae are the source of the coral’s bright colors, and when temperatures get too high, the polyp expels the algae, causing “bleaching”. If the temperature lowers and the polyps get new algae, they can recover. If they can’t do that, then they eventually die. This, plus the corrosion from ocean acidification, are the most widely known effects of global warming on coral.

The algae are important, because they both consume waste generated by the polyp, and they produce nutrients for it via photosynthesis. Unfortunately, it seems that expulsion due to a stressed polyp isn’t the only threat. There’s now reason to believe that marine heat waves can come with viral epidemics for the algae specifically:

Lead author Lauren Howe-Kerr said coral and marine disease researchers are paying closer attention to coral viruses in the wake of studies in October 2021 and February 2022 that found evidence suggesting viral infections of symbiotic dinoflagellates might be responsible for stony coral tissue loss disease (SCTLD). One of the deadliest coral diseases ever recorded, SCTLD has been decimating reefs in Florida and the Caribbean since it was first identified in 2014.

“While this study is not focused on SCLTD, it builds our understanding of coral viruses, and particularly RNA viruses that infect coral endosymbionts,” said Howe-Kerr, a Rice postdoctoral researcher who co-authored the study with more than a dozen colleagues from Rice, Northeastern University, the University of Oregon, the University of the Virgin Islands, Rutgers University, Oregon State University, George Mason University, New Zealand’s National Institute of Water and Atmospheric Research and the Mote Marine Laboratory’s Coral Reef Research and Restoration Center in Summerland Key, Florida.

“Our work provides the first empirical evidence that exposure to high temperatures on the reef triggers dinoRNAV infections within coral colonies, and we showed those infections are intensified in unhealthy coral colonies,” Howe-Kerr said.

The study was carried out at the Moorea Coral Reef Long-term Ecological Research station on the Pacific Ocean island of Moorea in French Polynesia. Moorea, which is about 20 miles from Tahiti, is ringed by coral reefs. Samples from 54 coral colonies around the island were collected twice a year between August 2018 and October 2020. The warmest water temperatures during that span were in March 2019. Reefs across the island suffered heat-related stress during this period, including widespread bleaching.

The study sites were located in a variety of reef zones that were subject to different kinds of environmental stress. For example, ocean-facing forereefs are deeper, with cooler and more consistent water temperatures, while near-shore fringing reefs in lagoons are subjected to the highest temperatures and greatest temperature variability.

This makes perfect sense to me. It’s well known that most organisms, when placed under various kinds of stress, are more vulnerable to disease. This is true of humans, and as far as I know, it’s true of all of our distant relatives covering this planet. It’s part of why the ongoing climate crisis is so scary – the changing conditions are putting everything under some level of increased stress. That doesn’t, by itself, guarantee doom, but it increases the odds of something going wrong when there aren’t resources to handle it. For every little bit the temperature rises, we all get just a little less wiggle room. For humans, the biggest disease risk that’s discussed is exposure to new zoonotic diseases like COVID-19, the myriad of ways in which life is getting worse for most of us for societal reasons are already putting us in some danger, and the rise in heatwaves and other such disasters is only going to make that worse.

I like talking about global solidarity, but in many ways that needs to extend well beyond our own species. We need to consume other organisms to survive, but in order for that to happen, we need those organisms to, you know, exist. If you need a direct benefit, coral reefs support fish that many people depend on for food, but healthy ecosystemns do far more for us than just the direct filling of our bellies. When I talk about finding ways to integrate with ecosystems, rather than existing in opposition to them, it’s not just because I have a utopian vision of literally green cities, it’s because I don’t think we’ve got much chance at a real future without doing that. The upside is that, while there’s a long way to go, most of the steps we need to take will make life better in the short term, too. I doubt there’s much we can do to help coral, in the short term, but life is persistent, and if we can change our ways in time, I have little doubt that nature will recover.