Reef fish have pooped on coral since time immemorial. While it’s a normal part of the coral reef ecosystem, a recent study out of UC Santa Barbara suggests that changing environmental conditions could be throwing this dynamic off kilter. The findings, which appear in Frontiers in Microbiology, document how climate change can alter ecological relationships.

While conducting research in the lagoon on Mo’orea, French Polynesia, authors Leïla Ezzat and Deron Burkepile noticed the fish droppings on the coral. The scientists could easily have overlooked what is a routine occurrence on the reef, but they were curious what effect this might have when combined with rising ocean temperatures.

“If corals are healthy and they’re not stressed out, then that poop is not a bad thing,” said Burkepile, a professor in the Department of Ecology, Evolution, and Marine Biology. It’s potentially even beneficial, providing important nutrients to the reef denizens.

“But when corals are stressed out, like during a marine heatwave,” he continued, “this natural, relatively benign interaction becomes something pretty malignant.”