larval fish and squid collected in surface slicks off the western coast of the Big Island of Hawai‘i
Ocean slicks run parallel to the shore just west of the Big Island of Hawaii. Credit: Joey Lecky

Despite their name, ocean slicks have nothing to do with oil. These patches of smooth water, roughly a few meters wide and up to several kilometers long, form when water currents collide.

Now, scientists working in waters off the western coast of the Big Island of Hawaii have shown that slicks host a rich diversity of young fish, squid, shrimp, crabs, and snails. This discovery sheds light on a long-standing mystery in marine ecology: Where do juvenile marine species predominantly congregate, and how might this placid environment influence their survival and dispersal?

“Ocean slicks are not well studied.”

“Ocean slicks are not well studied,” said Jesús Pineda, an oceanographer at the Woods Hole Oceanographic Institution in Massachusetts who was not involved in the research. “This study highlights the importance of [ocean slicks] in the ecology of marine organisms.”

Smooth Water Around the World

Ocean slicks are common and can be easily spotted from the air. They look like ribbons of smooth surface water, said Jonathan Whitney, a biologist at the Joint Institute for Marine and Atmospheric Research in Honolulu and leader of the new research.

Caused by interacting currents, ocean slicks are transient and often last just an hour or so. They’ve been seen around the world, mostly close to coastlines, but they’re particularly common near Hawaii.

Surprisingly, not a lot of research has focused on ocean slicks in the 50th state, said Whitney. “They’ve always been there, but they’ve been ignored.”

Diversity of larval fish and squid collected in surface slicks off the western coast of the Big Island of Hawaii. From left to right, the first row shows a jackfish and damselfish; the second row shows a squid paralarva, filefish, and chubb, and the third row shows a triggerfish larva, triggerfish juvenile, and queenfish juvenile. Credit: Jonathan Whitney

Taking a Dive in Hawaii

Now Whitney and his team have taken a literal dive into ocean slicks off the Big Island. In 2016 and 2017, Whitney and a team of biologists, oceanographers, wave specialists, and mapping experts studied water chemistry, currents, and marine life in the ocean slicks using boat- and drone-based measurements.

The researchers found that young fish were, in general, about 7 times more abundant in slicks than in the adjacent water, Whitney reported last week at the 2018 Ocean Sciences Meeting in Portland, Ore. The researchers found that at least a dozen families of fish, squid, shrimp, crabs, and snails exist predominantly in ocean slicks.

“It’s incredible to have baby tuna next to little gobi reef fish next to deep-sea angler fish.”

Ocean slicks “are concentrating all of these amazing animals,” said Whitney. That makes them a unique habitat in which young marine creatures from very different environments interact, a marine nursery of sorts. “It’s incredible to have baby tuna next to little gobi reef fish next to deep-sea angler fish,” said Whitney.

This new finding may lead to welcome insights about larvae from a wide range of different ocean habitats, he added. “We have very poor understanding of what larval fish do between when they’re spawned and when they come back to their adult habitat. That’s been a black box in marine ecology.”

Opening the Black Box

Whitney and his team are currently using satellite imagery and local time-lapse photography—from a camera mounted on a private home in Hawaii overlooking the water—to better understand when and where slicks form.

By combining this information with biological and environmental research, the scientists hope to get a handle on how ocean slicks affect the survival and dispersal of young marine life, Whitney said. After that, “our next big step is to…quantify the importance of this habitat to the overall ecosystem,” he said.

—Katherine Kornei (email:; @katherinekornei), Freelance Science Journalist 


Kornei, K. (2018), Calm waters off Hawaii harbor a “nursery” of sea life, Eos, 99, Published on 22 February 2018.

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