Hidden world just below the surface

Composite image showing a small portion of the diversity of larval and juvenile fishes and invertebrates found living in surface slick nurseries
Composite image showing a small portion of the diversity of larval and juvenile fishes and invertebrates found living in surface slick nurseries | Image: Jonathan Whitney

Ocean surface slicks are nurseries and highways for many species of fish

A team of scientists in Hawai’i have discovered that a diverse array of marine animals find refuge in ‘surface slicks’. These ocean features create a superhighway of nursery habitat for more than 100 species of commercially and ecologically important fish larvae.

Surface slicks
Surface slicks | Image: Angela Stippkugel

Surface slicks are meandering lines of smooth surface water formed by the convergence of ocean currents, tides, and variations in the seafloor. Although scientists have long-believed that slicks are important for fish, the tiny marine life that slicks contain has remained elusive.

To unravel the slicks’ secrets, the research team conducted more than 130 plankton net tows inside the surface slicks and surrounding waters. They then combined those in-water surveys with a new technique to remotely sense slick footprints using satellites.

Larval fish and squid collected in surface slicks in West Hawai‘i
Larval fish and squid collected in surface slicks in West Hawai‘i | Image: Jonathan Whitney.

The study* showed that larval fish densities in surface slicks were, on average, over 7 times higher than the surrounding waters. Surface slicks function as a nursery habitat for marine larvae of at least 112 species of commercially and ecologically important fishes. Other species found included coral reef fish, deep-sea species such as lanternfish plus snails, crabs, and shrimp.

We were shocked to find larvae of so many species, and even entire families of fishes that were only found in surface slicks, this suggests they are dependent on these essential habitats

Dr. Jonathan Whitney – lead author and marine ecologist at NOAA, former postdoctoral fellow at the Joint Institute for Marine and Atmospheric Research (JIMAR) in UH Mānoa’s School of Ocean and Earth Science and Technology (SOEST)

While slicks may seem like havens for all tiny marine animals, there’s a hidden hazard lurking in these ocean oases: plastic debris. Within the study area, 95% of the plastic debris collected into slicks, compared with 75% of the floating organic debris. Larvae may get some shelter from plastic debris, but it comes at the cost of chemical exposure and incidental ingestion.

Microplastics found in plankton sample during a 5-min tow at the surface in West Hawai‘i
Microplastics found in plankton sample during a 5-min tow at the surface in West Hawai‘i
Image: Karla Balagso.

“Until we stop plastics from entering the ocean,” Whitney said, “the accumulation of hazardous plastic debris in these nursery habitats remains a serious threat to the biodiversity hosted here.”

*Research by NOAA’s Pacific Islands Fisheries Science Center, the University of Hawai’i (UH) at Mānoa, Arizona State University and elsewhere. Their findings were published in the journal Scientific Reports.

SOURCE 1, SOURCE 2, SOURCE 3

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