Florida just had the hottest recorded ocean temperature. Here’s what that means for the environment

A bluestriped grunt
A bluestriped grunt explores a coral reef in Key West, Fla. (Joseph Prezioso/AFP via Getty Images)

This year’s summer of record-breaking heat set another milestone Monday when a buoy in Manatee Bay just off the coast southwestern Florida registered an ocean temperature of 101.1 degrees Fahrenheit. This follows the same buoy reading of 100.2°F on Sunday. The previous world record for warmest ocean temperature was 99.7°F in Kuwait Bay, according to a 2020 study

The latest readings continue a monthlong trend of bath-like temperatures in Florida waters that could have devastating effects on plant and animal life.

“This is shocking, it’s unprecedented,” Stefanie Sekich, of the Surfrider Foundation, an ocean-protection advocacy group, told Yahoo News. “It’s actually quite frightening.”

Why the ocean temperatures are so hot

July has seen the record for the hottest average global temperature broken repeatedly, as climate change has contributed to numerous dramatic heat waves. The oceans, which have absorbed 90% of the increased heat from climate change, have also been seeing a stunningly hot summer: Global ocean surface temperatures last month were the highest in 174 years of data.

“These ocean temperatures over the globe have been increasing for the past month,” Sekich said. “In the North Atlantic, parts of Europe have seen the ocean temperature increase of 7 degrees [Fahrenheit] more than it usually is at this time of year.”

Due to a stagnant heat dome in Florida, Sekich said, “hot air is just sitting over the ocean.”

Since the summer is far from over, Sekich predicted ocean temperatures in the Northern Hemisphere will continue to rise in the weeks ahead.

Coral bleaching

A researcher puts a fragment of coral on a reef rock to help restore coral reefs
A researcher puts a fragment of coral on a reef rock to help restore coral reefs, near Key West, Fla. (Chandan Khanna/AFP via Getty Images)

Scientists say that increased ocean temperatures can cause a number of interlocking problems. Warmer water can cause coral bleaching, in which corals release algae living inside them, causing the coral to turn white and, sometimes, die off.

Although Florida has recently experienced spotty bleaching in August, as heat accumulates all summer, severe bleaching events have already begun this July. On July 20, the Coral Restoration Foundation reported that Sombrero Reef, a popular snorkeling and scuba diving site near the Florida Keys that is home to endangered star corals, recently experienced a coral bleaching event with a 100% mortality rate.

“On July 20th, CRF teams visited Sombrero Reef, a restoration site we’ve been working at for over a decade. What we found was unimaginable — 100% coral mortality,” Phanor Montoya-Maya, restoration program manager at Coral Restoration Foundation, said in a statement. "We have also lost almost all the corals in the Looe Key Nursery in the Lower Keys.”

Sea grasses

“Sea grasses are another vital ecosystem, they’re an essential fish habitat, they’re the primary food source for manatees, which have been plummeting in recent years,” Chris Robbins, associate director of science at Oceans Conservancy, an environmental advocacy group, told Yahoo News. “Sea grasses are very vulnerable to warmer waters.” Because warmer air and water temperatures lead to more evaporation, salinity spikes and sea grasses cannot survive in the saltier water.

“The last time we saw a massive seagrass die-off resulting from high water temperatures, high salinities, low oxygen was during the El Nino event in 2015, and of course we’re now in an El Nino event in 2023,” said Robbins.

Sea grasses are already suffering from the algal blooms in Florida waters in recent years, because algal blooms block the sunlight, which is a problem because sea grasses need sunlight to perform photosynthesis.

Algal blooms such as the notorious red tides that can cause harm to humans and lead to swarms of dead fish washing ashore are caused by human activities such as fertilizer use and sewage entering the water, which increase the levels of nutrients such as nitrogen that feed algae, and they grow more rapidly in warmer water.

Fish and shellfish

Dead fish killed by a toxic algae bloom
Dead fish killed by a toxic algae bloom, in Sarasota, Fla. (Jesus Olarte/AFP via Getty Images)

Warmer water holds less oxygen, and algal blooms exacerbate that because the algae breathe in oxygen. Fish and shellfish can suffocate and die as a result.

“We could potentially see fish die-offs in places where we have low oxygen,” Robbins said.

In a sort of doom loop, that in turn could worsen algal blooms as the decaying fish corpses release nutrients that feed the algae.

What can be done

A red tide warning at Lido Key Beach in Sarasota, Fla.
A red tide warning at Lido Key Beach in Sarasota, Fla. (Jesus Olarte/AFP via Getty Images)

“Obviously, we need to get off fossil fuels,” Sekich said. “If we keep putting greenhouse gasses into the atmosphere we’re going to keep seeing these effects of climate change.”

In the short term, to reduce the severity and duration of red tides, Robbins urged the state and federal governments to implement policies and infrastructure investments to reduce nutrient pollution by decreasing the use of fertilizer and upgrading wastewater systems.

“If and when these things happen, we’ll potentially need to reduce other stressors on these systems,” Robbins said. For example, the allowable quota of fish that can be caught by commercial fishing operations may have to be lowered.

Sekich noted that there are billions of dollars in the Inflation Reduction Act and the bipartisan infrastructure law for coastal resilience; states can apply for these funds and, if granted, use for projects like mangrove restoration, which help absorb heat and protect coastlines against sea level rise.