Study reveals that corals which store fat are more able to survive bleaching events.
When the water in which they live gets too warm, corals become unhealthy and turn white – known as bleaching. What is actually happening is that the algae that lives in the coral, and makes food for them, are lost.
Healthy corals get their day-to-day energy from sugar that the algae make through photosynthesis. They also eat zooplankton which they use for growth, healing and reproduction. During bleaching, their nutritional state is thrown completely out of balance.
“When coral is bleached, it no longer gets enough food energy and so it starts slowing down in growth and loses its fat and other energy reserves – just like humans do during times of hardship,” said lead researcher in the study, Verena Schoepf.
Corals eventually start consuming their own bodies, as human bodies do when severely malnourished. And while all the corals in the study were able to eat zooplankton, the ones who had more fat fared better than the rest.
Those with less fat hadn’t healed even a year later.
Climate change is one of the main threats to coral reefs today, and mass bleaching events due to periods of warmer water have increased in frequency over the past decades. More worringly still, severe bleaching is expected to occur annually around the world later this century, putting more than 90% of reefs at risk. In the Caribbean, this is projected to occur as early as 2040.
In the study Porites divaricata and Orbicella faveolata were able to recover in a year from bleaching, whilst Porites astreoides still had reduced energy stores. As energy reserves promote bleaching resistance, failure to recover from annual bleaching within one year is likely result in the future demise of heat-sensitive coral species.
Annual coral bleaching and the long-term recovery capacity of coral. Verena Schoepf, Andréa G. Grottoli, Stephen J. Levas, Matthew D. Aschaffenburg, Justin H. Baumann, Yohei Matsui, Mark E. Warner. Published 18 November 2015.DOI: 10.1098/rspb.2015.1887