A recent study by the University of Hawai’i at Manoa has found that corals dominated by thermally sensitive algae demonstrate higher growth rates but only in cooler water. The research, led by Shayle Matsuda and Mariah Opalek, aims to understand how symbiotic algae and environmental factors influence coral growth and health, which is crucial for predicting the future of reefs and informing conservation efforts.
The study focused on rice corals hosting different types of symbiotic algae – those that can tolerate warmer water and those that are more susceptible to bleaching in warmer temperatures. Over a two-month period, the researchers measured the growth of corals with heat-tolerant and heat-sensitive algae. They also examined the impact of decreasing light levels on the growth patterns, as light is a major driver of symbiont distribution in Kāneʻohe Bay, Hawai’i.
During the warmer first month, the type of symbiont did not affect growth. However, in the cooler second month, corals with heat-sensitive algae grew up to 77% faster than those with heat-tolerant algae. This growth advantage was more pronounced in higher light treatments, which correspond to shallower depths on a reef.
The findings highlight the complexity of coral growth on reefs, with the type of symbiont a coral associates with potentially determining its competitive advantage. The study suggests that corals hosting thermally sensitive symbionts may only have a growth advantage during a few cooler months. As ocean temperatures continue to rise, the benefit of hosting thermally tolerant symbionts may outweigh any growth advantage associated with thermally sensitive species.
Understanding the tradeoff between growth and resilience is crucial for predicting the future of coral reefs. As global warming persists, coral stocks selected for specific traits or symbionts can help inform conservation interventions and contribute to the preservation of reefs. By protecting corals with the ability to withstand higher temperatures, researchers and conservationists can ensure the long-term survival of coral ecosystems.