The stunning underwater world that’s at risk as the Iran war drags on

A view of the vibrant coral reef at one of Musandam Peninsula's popular diving sites in Khasab, Oman, in August 2025. (Mahmut Serdar Alakus/Anadolu Agency/Getty Images via CNN Newsource)

Not far from the vessels stuck in the Persian Gulf lies an ecological wonder. The highly contested Strait of Hormuz is home to dolphins and the most diverse coral population in the region, an underwater world that scientists say could be in jeopardy as conflict swirls around it.

Currently, about 2,000 vessels trapped in the Gulf are carrying a total of around 21 billion litres of oil. There have been at least 16 attacks on ships in the Persian Gulf and near the Strait of Hormuz since the war broke out.

Nina Noelle, a spokesperson from Greenpeace, an independent global campaigning network that focuses on environmental issues, told CNN that through continuous monitoring, the group’s researchers “regularly detect oil slicks in the region,” including one linked to the Iranian vessel Shahid Bagheri that was struck by a U.S. warplane in early March.

According to the organization, the vessel is still leaking oil “near the Khuran Strait and poses a potential risk to nearby protected wetlands.” The Khuran Strait is a narrower passageway that runs north of the Strait of Hormuz.

The Strait of Hormuz’s geographical position makes it a crucial site not just politically but ecologically as well — it sits at a transition zone between the deep, cool Gulf of Oman and the shallow, warm Persian Gulf. Currents sweeping in from the Gulf of Oman carry nutrients and larvae that fuel plankton blooms and coral reefs, while deeper upwellings draw in reef fish and migratory whale sharks that pass through seasonally.

In more peaceful times, scuba diving and dolphin-watching in Musandam Governorate, a part of Oman that borders the strait, was a magnet for tourism. The strait provides nesting grounds for sea turtles, and the coast of Oman is home to the critically endangered and nonmigratory Arabian humpback whales, with dugongs and sea snakes in the surrounding waters.

As the conflict drags on, scientists are increasingly concerned about the impact of oil spills on animals in the region.

“Many of the compounds found in crude oil will target heart function and respiration,” said Martin Grosell, professor and chair of the department of marine biology and ecology at the University of Miami’s Rosenstiel School of Marine, Atmospheric and Earth Sciences. “Prolonged oil exposure will lead to an overexertion of the stress response, and that suppresses immune function, rendering animals more susceptible to infections and other types of environmental insults.”

Crude oil also disrupts animals’ nervous systems, Grosell added, impairing their senses and ability to navigate, process input, and properly orient themselves in their environment. This affects how they respond to predators and find prey, meaning harm to individual animals can cascade through the entire ecosystem.

What animals live in the strait?

The Strait of Hormuz, a narrow passage between Iran to the north and Oman and the United Arab Emirates to the south, sits at the mouth of the Persian Gulf. Aaron Bartholomew, a professor of biology at the American University of Sharjah in the U.A.E., who has conducted field research throughout the region, describes the strait as the ecological crown of the Gulf.

“The Strait of Hormuz is known for having the most diverse and some of the highest coral cover in all of the Gulf,” Bartholomew said. The richest concentrations sit on the Iranian side of the strait, as well as along parts of the southern Gulf coast. The coral reefs in the area have been heavily impacted by bleaching events linked to rising ocean temperatures, but they have endured while corals elsewhere have not.

Bartholomew explained that Gulf conditions push marine life to its physiological limits. “We have very, very hot temperatures during the summer and surprisingly cold temperatures in the winter,” he said. “We also have elevated salinity because of all the evaporation from the Gulf,” he added, referring to high concentrations of dissolved salts in the water that typically cause ecological harm.

In most of the world’s oceans, such extremes would be lethal to coral. Here, the conditions have produced “arguably the toughest corals in the world,” Bartholomew said. He said that the corals in the region are important for researchers who are actively studying them as a model for how they might survive the hotter, more volatile oceans that the human-fueled climate crisis will bring.

“Corals are the most biodiverse ecosystem in the oceans, and they support a wide variety of fish and invertebrate species,” Bartholomew added. “They’re certainly important for fisheries. They’re important for tourism as well.”

Beyond the reefs, the waters around the strait support a dense and varied community of animals. Indo-Pacific humpback dolphins and Indo-Pacific bottlenose dolphins live along the Musandam Peninsula in northern Oman. Bartholomew said he’s concerned about such mammals that have to rise to the surface to breathe.

Offshore islands, such as Sir Bani Yas Island, scattered between Iran and the U.A.E., serve as nesting sites for green and hawksbill sea turtles. “It’s well documented that oil spills in the U.A.E. waters lead to turtle mortality, so they basically die in the oil spill itself and then wash up on shore,” Bartholomew said.

Sea snakes also occupy the shallow coastal waters of the U.A.E.. Whale sharks pass through seasonally as they follow mackerel tuna that spawn in the oil-rich offshore waters of Qatar. Because fishing is prohibited near the rigs, these waters have become an accidental marine-protected area. “The whale sharks follow them in and eat the eggs of the spawning mackerel tuna,” Bartholomew explained.

There are also mangroves “up and down the southern coast, particularly in Abu Dhabi emirate, but also in the northern emirates as well, such as Ras Al Khaimah and also Umm Al Quwain,” Bartholomew said. Gray mangroves, or Avicennia marina, are abundant in the area and are typically resilient to oil spills, “as long as what is known as their pneumatophores are not covered,” Bartholomew said. Pneumatophores are exposed root structures that stick up and act like snorkels, reaching above the surface to transport oxygen to the mangrove tree’s underground roots. Because of this, mangroves “can generally survive oil spills, but if their pneumatophores are covered up, then they’ll be impacted and potentially die.”

Farther from the strait, in the shallow seagrass meadows west of Abu Dhabi and south of Qatar, lives the world’s second-largest population of dugongs, a mammal closely related to manatees. “We have some of the largest continuous seagrass beds in the world there,” Bartholomew said. Though the dugongs are currently buffered from the conflict in the strait, Bartholomew noted that a spill reaching their coastal waters would pose a serious threat.

What does oil do to animals?

The University of Miami’s Grosell has spent 15 years studying the impacts of oil on marine life following the 2010 Deepwater Horizon disaster in the Gulf of Mexico.

“You’ve heard the saying that oil and water don’t mix, but that is not true,” Grosell said.

Wave action on the water’s surface can break oil into smaller droplets that sink into the ocean depths. “Crude oil, or even refined oil, is a very complex mixture of thousands of chemicals.” Some toxic chemicals are also released from the oil and enter the water column, the ocean habitat that extends from the surface to the seafloor.

When chemicals from oil dissolve into the water column, water-breathing animals such as fish absorb them through their gills and corals absorb them directly through their tissues. Oil that is on the surface is harmful to animals that come up to the surface to breathe, such as dolphins, sea turtles and sea snakes.

For both air breathers and water breathers, many chemicals in crude oil target the heart and respiratory function, the immune system, the sensory system and the central nervous system.

“Some of these compounds found in crude oil will affect sensory systems: the ability to smell things, the ability to see things and the ability to detect vibrations in the environment,” Grosell said. Corals face similar effects as “they catch prey from the water through fine tentacles and would be exposed to the chemicals that are found in the water column during oil contamination.”

“There are also reports of effects on the central nervous system,” affecting the ability of animals to process input from their sensory systems. Research on oil spills in the Gulf of Mexico has also shown that exposure to oil can reduce fish reproduction, Grosell added.

Altogether, these factors can affect how animals make decisions and how long they live. The chemical effects of crude oil on animals can be less immediately lethal to them than being directly smothered by oil in a spill, “but in a complex environment where you’re constantly balancing obtaining resources and avoiding being preyed upon, those effects on decision-making, or on sensory systems, or even subtle effects on your heart could lead to shorter lifespans for a lot of these animals.”

Because of the intricacies of predator-prey relationships, impacts on individual organisms will ripple across the ecosystem, Grosell said. He believes that as more vessels remain in the strait, more oil spills are likely to occur, compounding the detrimental environmental impact.

By Asuka Koda, CNN