Too much heat, slower currents and too little oxygen: more fish die in Biscayne Bay

FIU Institute of Environment researchers are investigating the cause of a fish kill that occurred on Biscayne Bay over Labor Day weekend.

Signs of trouble began bubbling up on Sept. 1 when the institute’s buoys began registering low oxygen levels, higher temperatures and slower currents leading to potential stagnation, Research Professor Henry Briceño said.

“That’s not good news,” he said. “Usually when that does combine, we have some very bad conditions for fish to survive.”

Dead fish were reported across different areas of Biscayne Bay although the effects of the drop in oxygen do not initially appear to be as deadly as the fish kill that occurred in 2020, where tens of thousands of fish and other marine life were estimated to have been killed.

Institute of Environment researchers were among the first to respond then to study the massive algal bloom that appeared after the 2020 fish kill.

Again, Briceño suspects pollution entering the bay from land is a likely contributor to the fish kill. Once these nutrients enter the bay, they tend to trigger algal blooms that consume available oxygen. The problem becomes worse at night when already diminished seagrasses have no sunlight to help make new oxygen for fish and other marine life to breathe.

Researchers headed into the water Sept. 8 to collect more samples and perform more measurements that could further shed light on conditions in the bay.

In part because of the research performed at FIU’s Institute of Environment, the university is ranked No. 11 in the world for positive impact on life below water by The Times Higher Education Impact Rankings.