Hurricanes are disasters on land. Are they just as destructive to marine life under the sea?

This year's hurricane season has been weird for several reasons, from the historic Hurricane Hilary that hit California to the historic Hurricane Otis that hit Acapulco, Mexico this week. There have been a lot of "historic" storms lately thanks to how climate change is altering weather patterns across the planet.

The National Oceanic and Atmospheric Administration (NOAA) forecasts this hurricane season, spanning June 1 to Nov. 30, will be more intense than normal, with up to 21 storms severe enough to warrant a name throughout the season. 

Hurricanes form when warm ocean temperatures cause hot air to rise. These temperature changes cause a lot of ocean mixing, dredging up cooler water from the bottom of the ocean as deep as 300 feet and creating waves as tall as 60 feet. As the atmosphere becomes warmer due to trapped greenhouse gases from burning fossil fuels, it has a greater capacity for holding water vapor, which means hurricanes are bringing more rainfall, while also being slower-moving, wider-ranging and more volatile. This means their strength can increase more rapidly, said Sally Warner, Ph.D., an associate professor of climate science at Brandeis University.

These storms, which are called hurricanes if they form in the Atlantic and tropical storms if they form in the Pacific, which can be some of the most damaging and expensive. But for every hurricane that we prepare for on land, many fizzle out in the ocean without ever becoming a cause for concern. Regardless of whether a storm reaches the level of a hurricane or stays confined to the ocean in what's sometimes called a "fish storm," there are some creatures that are impacted either way: ocean-dwellers.

"The wave action from hurricanes can extend pretty deep within the water column," Warner told Salon in a video interview. "In the open ocean environment, if a species has the ability to go deeper, they'll go deeper or swim out of the way — sharks, dolphins, large fish, things like that."

In one study that tracked a group of blacktip sharks during Hurricane Gabrielle in 2001, young sharks migrated to deeper waters along with changes in barometric pressure associated with the approaching hurricane, returning to their nursery within two weeks after the storm.

But fast swimmers don't always evacuate in time. After Hurricane Ida in 2021, a dolphin got stuck in a drainage pond for two years before being rescued. When Hurricane Rita struck Louisiana in 2005, seven dolphins were stranded as far as 11 kilometers inland, according to a report from the National Marine Fisheries Service. Earlier this month, Hurricane Idalia similarly stranded a group of manatees inland in Florida, a repeat of what happened after Hurricane Hermine trapped sea cows on flooded golf course ponds in 2016. 

Most of the ponds these animals were found in weren't adequately salty for these sea creatures to survive long-term, and some were found with skin lesions caused by swimming in polluted waters. But runoff from flooding caused by hurricanes can also pollute the ocean with debris and dramatically reduce the salinity of coastal environments. Runoff polluted with waste or fertilizers — like the millions of gallons of hog feces that drained into North Carolina's coastal waters after Hurricane Florence in 2018 — disturbs the chemical composition of the ocean and can cause algae blooms that lower the oxygen supply in deep water, Warner said.

"Maybe some species are able to move out of the way but then they come back to where they want it to live and their habitat has been destroyed," Warner said. "That also can have a detrimental impact."

Low oxygen levels were thought to be what killed 280 million fish in Louisiana after Hurricane Ida in 2021. While many fish species are able to evacuate like larger sea animals, the aftermath of hurricanes can be associated with the loss of millions of dollars — and sea creatures — in fishing communities. In one study analyzing the marine environment off the coast of Florida after two hurricanes struck in 2004, researchers found the salinity in coastal areas dropped so much that freshwater fish temporarily took over the ecosystem, although it returned to what it was pre-hurricane within about three months.

The extreme ocean mixing that occurs with a hurricane can also produce giant underwater waves that break deep within the ocean, said Noel Gutiérrez Brizuela, a Ph.D. candidate in physical oceanography at the University of California, San Diego. The ocean responds to these strong forces by reverberating waves that pump various ocean layers up and down, he added. While these waves aren't moving particularly fast, slower-moving or stationary creatures like turtles or shellfish can be tossed around like the spin cycle of a washing machine in this turmoil.

"If you were a fish or a whale or whatever under a hurricane, you would be thrown around and up and down by these waves, which act over scales of hundreds up to 1,000 kilometers," Brizuela told Salon in a phone interview. "A cycle of these waves will take about 30 to 40 hours."

All of this mixing can also churn up huge amounts of sand that cover structures like corals that are important to sea life. A 2017 study in Florida and Puerto Rico found that 12% of reefs in the region were destabilized or broken off when struck by Hurricanes Irma and Maria. Many coral species are already under threat of extinction due to coral bleaching caused by rising temperatures, and these are especially vulnerable to stronger storms breaking them apart, said Shay Viehman, Ph.D., a research ecologist at NOAA who studies coral reefs.

"Coral reefs are commonly called the 'rainforest of the sea' because they have so many organisms that live in them and there's so much diversity," Viehman told Salon in a phone interview. "If the reef itself is destroyed through hurricanes or any other mechanism, that means the home for fish and urchins and crabs and so many different species that live down in the reef is gone."

Although hurricanes are called disasters on land and have been responsible for thousands of deaths, they can actually provide some benefits to sea creatures. 

For example, cooler water dredged up from deep in the ocean can cool off coral that is in danger of being bleached from warm ocean temperatures. It can also deliver much-needed oxygen to places like the "Dead Zone" in the Gulf of Mexico, where algae blooms effectively suffocate bottom-dwellers like crabs and sea stars, Warner said. Certain species like phytoplankton might also benefit from all of this mixing because they feed on nutrients dredged up from the ocean floor.

At the end of the day, these storms are natural phenomena that have been occurring in the ocean long before humans were around to feel their impacts on land. After all, many of the negative impacts on sea creatures, like flooding polluting coastal waterways or animals being trapped inland, are caused by human activity — just like our greenhouse gas emissions have heated the atmosphere to make the conditions in which these storms are more powerful.

"Hurricanes have existed for millions of years and marine life has evolved with it," ​​Brizuela said. "We haven't necessarily adopted or adapted our lifestyle to make sure that it's resilient to these events."