Data from: Microbial invasion of the Caribbean by an Indo-Pacific coral zooxanthella

Human-induced environmental changes have ushered in the rapid decline of
coral reef ecosystems, particularly by disrupting the symbioses between
reef-building corals and their photosymbionts. However, escalating
stressful conditions enable some symbionts to thrive as opportunists. We
present evidence that a stress-tolerant “zooxanthella” from the
Indo-Pacific Ocean, Symbiodinium trenchii, has rapidly spread to coral
communities across the Greater Caribbean. In marked contrast to
populations from the Indo-Pacific, Atlantic populations of S. trenchii
contained exceptionally low genetic diversity, including several
widespread and genetically similar clones. Colonies with this symbiont
tolerate temperatures 1–2 °C higher than other host–symbiont combinations;
however, calcification by hosts harboring S. trenchii is reduced by nearly
half, compared with those harboring natives, and suggests that these new
symbioses are maladapted. Unforeseen opportunism and geographical
expansion by invasive mutualistic microbes could profoundly influence the
response of reef coral symbioses to major environmental perturbations but
may ultimately compromise ecosystem stability and function.