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

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-06, Vol.112 (24), p.7513-7518
• Main Authors: Pettay, D. Tye, Drew C. Wham, Robin T. Smith, Roberto Iglesias-Prieto, Todd C. LaJeunesse
• Format: Article
• Language: English
• Subjects: Animals; Anthozoa - parasitology; Bacteria; Biological Sciences; calcification; Caribbean Region; Climate Change; Coral Reefs; corals; Dinoflagellida - genetics; Dinoflagellida - isolation & purification; Dinoflagellida - physiology; Ecosystem; ecosystems; endosymbionts; environmental degradation; Genetic diversity; Genetic Variation; global warming; Humans; Indian Ocean; Introduced Species; invasive species; long term effects; Nonnative species; Pacific Ocean; reef corals; Symbiodinium; Symbiosis; Zooxanthella
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1502283112

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. Significance This research documents the spread of an opportunistic coral endosymbiont, Symbiodinium trenchii , from the Indo-Pacific into the Greater Caribbean, a region afflicted by human-related impacts including climate warming and environmental degradation. As a symbiont, it increases the resilience of photosynthetic corals to environmental perturbation but may diminish the animal’s capacity to calcify and build reefs. This work exposes a critical need to better understand the consequences of microbial introductions (even mutualistic species) on ecosystem stability and function and raises questions about the long-term impact of new, but maladapted, symbioses on the productivity of reef coral communities in the Atlantic Ocean.