The incredible diversity of coral reef ecosystems is being threatened by factors associated with global climate change and local pollution. Today diseases have increased and are killing more corals. Seeing this increase in frequency and severity of diseases affecting coral reefs around the globe, we have made learning more about coral immune systems a priority.
At the University of Texas at Arlington we are addressing one area of knowledge that has been lacking – making sense of disease patterns and figuring out why some species are disease susceptible and some resistant. Our research, recently published in the journal PLOS ONE, focused on 14 species of Caribbean corals and found that, suprisingly, the older species are doing better.
To reach this conclusion, we worked with Ernesto Weil at the University of Puerto Rico at Mayagüez. The Caribbean, including Puerto Rico, has been hit particularly hard by disease outbreaks. Up to eight different diseases affect species there, with many outbreaks causing significant mortality on the reef.
We amassed 140 samples of healthy Caribbean coral spanning 14 species from reefs closely monitored by Weil. We then developed a phylogenic tree, a kind of map that traces the evolutionary history of corals, which allowed us to group them according to the time they diverged as a species. Some of the oldest corals in the study, such as Porites astreoides or “mustard hill coral”, have been around for more than 200m years, while others diverged to become a new species as recently as 7m years ago.
Ocean health and diversity are inexorably linked to the coral reefs around the world, not to mention the fate of industries such as fishing and tourism. The threats of pollution, overfishing and climate change have weakened species and made them more susceptible to conditions such as white plague and yellow band disease.
When a disease outbreak hits a reef, it can kill up to 50% of a specific species. This loss of species can change the structure of reef along with the fish and animals that use it. This can reduce the characteristic colour and beauty we associate with reefs. To keep coral reefs “teeming with life”, corals need to be healthy and there needs to be a diversity of species.
Species that have been around for longer and experienced and survived stressful events are more resilient. The goal of our work was to test this hypothesis with respect to disease and immunity.
We assembled information about the diseases affecting each species and then looked at base-level immunity in the lab. We analysed each data set to determine whether a “phylogenic signal” existed. A phylogenetic signal is when organisms in closely related species have characteristics that are more similar to each other than they are to more distant species.
Extracting proteins from the coral samples allowed us to conduct immune assays testing six immune traits that we thought showed a good overall picture of a species’ disease susceptibility. Two factors in particular – the inhibition of bacterial growth and melanin concentration – were higher in older corals and likely play a role in disease resistance. For example, coral species that diverged over 200m years ago can kill up to 41% of bacterial growth, versus just 14.6% in newer coral species. Corals with higher concentrations of melanin in their tissues may be better prepared to kill a pathogen before it can establish and cause an infection.
The disease patterns seem to bear out the lab findings – with the “modern” lineages we examined suffering as many as eight different diseases and “older” lineages suffering as few as one. While these results are confined, for now, to Caribbean species of coral, we are excited about the potential new avenues for research these results may take us both in other locations around the Caribbean and around the globe.
This work provides both an explanation and the basis for a look into the future. Coral reefs continue to undergo stress, and some species will handle this better than others. Our research provides clues that the older species may be more likely to survive current conditions and helps understand why that is.
Unlike mainstream media, we’re not capitulating to Trump.
As a dizzying number of corporate news organizations – either through need or greed – rush to implement new ways to further monetize their content, and others acquiesce to Trump’s wishes, now is a time for movement media-makers to double down on community-first models.
At Truthout, we are reaffirming our commitments on this front: We won’t run ads or have a paywall because we believe that everyone should have access to information, and that access should exist without barriers and free of distractions from craven corporate interests. We recognize the implications for democracy when information-seekers click a link only to find the article trapped behind a paywall or buried on a page with dozens of invasive ads. The laws of capitalism dictate an unending increase in monetization, and much of the media simply follows those laws. Truthout and many of our peers are dedicating ourselves to following other paths – a commitment which feels vital in a moment when corporations are evermore overtly embedded in government.
Over 80 percent of Truthout‘s funding comes from small individual donations from our community of readers, and the remaining 20 percent comes from a handful of social justice-oriented foundations. Over a third of our total budget is supported by recurring monthly donors, many of whom give because they want to help us keep Truthout barrier-free for everyone.
You can help by giving today. Whether you can make a small monthly donation or a larger gift, Truthout only works with your support.