Nature's Fish Nurseries full of Micro Plastics

 Photo: NOAA Fisheries/Jonathan Whitney.

Many of the world’s ocean fish spend the first days to weeks of their lives feeding and developing at the ocean surface. Larval fish are the next generation of adult fish that will supply protein and essential nutrients to people around the world. NOAA’s Pacific Islands Fisheries Science Center in Hawaii and an international team of scientists conducted one of the most ambitious studies to date. They wanted to learn where larval fish spend their time and what they eat there.

The team found that surface slicks contained far more larval fish than neighboring surface waters. Surface slicks are naturally occurring, ribbon-like, smooth water zones at the ocean surface. They form when internal ocean waves converge near coastlines. The surface slicks are unusually still and aggregate plankton, which is an important food resource for larval fish.

“We found that surface slicks contained larval fish from a wide range of ocean habitats, from shallow-water coral reefs to the open ocean and down into the deep sea—at no other point during their lives do these fish share an ocean habitat in this way,” said Dr. Jonathan Whitney, a marine ecologist for the Joint Institute for Marine and Atmospheric Research and co-lead of the study. “Slick nurseries also concentrate lots of planktonic prey, and thereby provide an oasis of food that is critical for larval fish development and survival.”

Unfortunately, the team also discovered that the same ocean processes that aggregated prey for larval fish also concentrated buoyant, passively floating micro plastics. “We were shocked to find that so many of our samples were dominated by plastics,” said Dr. Whitney.

The scientists found that plastics were 126 times more concentrated in surface slicks than in surface water just a couple hundred yards away. There were seven times more plastics than there were larval fish. The majority of the plastics found in the surface slicks were very small (less than 1 mm).

Photo courtesy of David Liittschwager.

Larval fish prefer their prey this size. After dissecting hundreds of larval fish, the researchers discovered that many fish species ingested plastic particles. “We found tiny plastic pieces in the stomachs of commercially targeted pelagic species, including swordfish and mahi-mahi, as well as in coral reef species like triggerfish,” said Dr. Whitney. Plastics were also found in flying fish, which apex predators such as tuna and seabirds eat.

Recent studies have found that adult fish ingest plastic. This is the first study to show that larval coral reef fish and pelagic species are also consuming plastic, as early as days after they are spawned.

“Larval fish are foundational for ecosystem function and represent the future of adult fish populations,” said Dr. Jamison Gove, a research oceanographer for NOAA and co-lead of the study. “The fact that larval fish are surrounded by and ingesting non-nutritious toxin-laden plastics, at their most vulnerable life-history stage, is cause for alarm.”

Researchers are unsure of how harmful plastic ingestion is to larval fish. In adult fish, plastics can cause gut blockage, malnutrition, and toxicant accumulation. Larval fish are highly sensitive to changes in their environment and food. Prey-size plastics could impact development and even reduce survivorship of larval fish that ingest them.

Biodiversity and fisheries production are currently threatened by a variety of human-induced stressors such as climate change, habitat loss, and overfishing. Our research suggests we can likely now add plastic ingestion by larval fish to that list of threats,” said Dr. Gove. However, other scientists believe ocean plastic is not as great a threat to oceans as climate change or overfishing. While it is currently unknown the magnitude of the threat to the oceans, the ubiquitous use of plastic in our modern world and inadequate management of plastic waste has led to increased contamination of freshwater, estuary and marine environments with micro-plastics. Maybe you want to rethink your use of plastic.

The full article can be read at this https://www.pnas.org/content/116/48/24143
Citing:
Gove JM, Whitney JL, McManus MA, Lecky J, Carvalho FC, Lynch JM, Li J, Neubauer P, Smith KA, Phipps JE, Kobayashi DR, Balagso KB, Contreras EA, Manuel ME, Merrifield MA, Polovina JJ, Asner GP, Maynard JA, Williams GJ. 2019. Prey-size plastics are invading larval fish nurseries. Published in Proceedings of the National Academy of Sciences.