Coral-seaweed interactions may impact reef resilience
A new study has revealed butterflyfish are particularly fussy about their food and shelter needs, avoiding corals that have come in contact with seaweed. Conducted by the University of Delaware, the study is the first to critically evaluate how coral-seaweed interactions will impact coral associated reef fishes, a key component of coral reef resilience.
In controlled experiments in Fiji, it was discovered that coral-feeding and coral-associated butterflyfishes overwhelmingly avoided corals that had contact with seaweeds. This was true regardless of whether the visual cue of the seaweed itself was present, leading researchers to conclude that coral-seaweed interactions produced chemical cues that remained even after the seaweed was removed.
“Butterflyfish are kind of like the canary in the coal mine,” said Danielle Dixson, an assistant professor in the School of Marine Science and Policy housed in the College of Earth, Ocean, and Environment. “When problems start to happen, they will be hit first because of their strong reliance on coral for food and shelter, so understanding their ecology is important before reefs become too degraded or just aren’t there,” she added.
Reefs in crisis
As a result of climate change, overfishing and pollution, previously healthy reefs have been converted to seaweed-dominated wastelands at an alarming rate. Since the 1980s, coral reef cover has decreased by 80-90 percent in the Caribbean and by 50 percent in the tropical Pacific.
This shift is compromising delicate coral reef ecosystems, reducing reef productivity and resilience and also local food and tourism opportunities and decreasing habitat for marine organisms. While micro-algae have a symbiotic relationship with coral, macro-algae such as seaweed compete with coral for space on the reef. Seaweed grows faster than coral, but plant-eating fish typically keep the ecosystem in check.
As more reefs degrade, scientists struggle to understand why. Theories suggest overfishing of predatory fish leaves fewer herbivores to eat the seaweed or rising temperatures and fertilizer runoff causes the seaweed to flourish, disrupting the ecosystem. “Realistically, both things are happening,” Dixson said. Whether the corals are chemically changing internally in a way that makes them less nutritious or they actually taste bad due to the energy expended to defend themselves against the seaweed is unknown.
Drastic transformations can already be observed in Fiji, where coral reefs can be found alongside a seaweed-choked wasteland. While seaweed overgrowth is a consequence of environmental changes, animal behaviors could also be a driving factor. “We need to start understanding these interactive effects, especially the behavioral choices that could be exacerbating issues that we’re not even thinking to give fish credit for,” Dixson said. Study results were published in the Nature Publication Scientific Reports.