Plastics are dominating the earth to an extreme point. It’s become common to find a discovery about how plastics are affecting our ecosystems. Now, researchers recently discovered that plastics are entering the food web through tiny larval fish.
The ocean has ribbons of smooth, calm water that form naturally on the ocean’s surface called ocean slicks. Larval fish congregate in ocean slicks to find shelter and feast on prey. Unfortunately, they don’t only feast on prey, but on prey-sized plastics too. In a study, the researchers found the fish nurseries to have more plastic than fish with a ratio of 7-to-1. The study was published in the journal Proceedings of the National Academy of Sciences (PNAS).
Anela Choy, a biological oceanographer, who wasn’t involved in the study, said: “This is perhaps the most vulnerable life stage of pelagic fish.”
Choy believes this new study raises important questions about the effects of plastic consumption at such a fragile life stage.
The Study
Dr. Jonathan Whitney, an NOAA marine ecologist, and his colleagues, initially set out to study larval fish, but plastics interfered and outnumbered their prime subject. When the fish eggs hatch, tiny fish the size of a pencil tip spend their first days to weeks at the ocean surface feeding and growing before returning to their natural habitat. Since there was little to no knowledge about where the baby fish go, what they consume, and how they find their home years later, the researchers wanted to find out.
Since previous research suggested that ocean slicks concentrate plankton and other nutrients, the researchers thought they might serve as ideal nurseries for baby fish. The team decided to investigate ocean slicks off the west coast of Hawaii, where there is abundant marine life with a variety of ecosystems coverage.
From 2016 to 2018, the researchers towed a customized net inside and outside ocean slicks 100 times to sample larval fish diversity. When they inspected their hauls, they realized their study wasn’t going to be just about fish.
Inspecting Their Catch
The team manually picked through the catch. They found over 11,000 larval fish, including coral reef fish; blennies and goatfish, open water fish; Mahi Mahi and swordfish, and anglerfish from deep waters. “It shows how briefly interconnected these vastly different ecosystems are,” said co-author Dr. Gareth Williams, a marine biologist at Bangor University, UK.
The nets caught eight times as many fish in Ocean slicks than in adjacent waters, which confirmed the slicks’ role as a fish nursery. However, even though the water looked crystal clear inside, these slicks had 10,000 pieces of plastic, outnumbering the fish 7-1.
The researchers dissected hundreds of larval fish and found that 8% had consumed microplastics the size of prey. “The vast majority of larval fish die before reaching adulthood, so the poor diet comes at a time when the fish are already exceedingly vulnerable,” explained Williams.
Plastic ingested by adult fish is linked to liver toxicity, tumors, malnutrition, behavioral problems, and death. However, these effects could be much worse in baby larval fish that haven’t fully developed their liver, which can filter toxins. At the moment, there is little knowledge about the consequences of larval fish consuming plastics.
Furthermore, the study may not be accurate because the researchers used a net that may have missed smaller pieces of plastic, so, the problem could be even worse.
Conclusion
Larval fish play a huge role in the ocean food web, if they eat plastic, the predators that eat them could potentially get harmed from the plastic themselves. Seabirds snatch them off the surface when they’re hungry while large fish, including tuna, eat them from below. Humans also eat the fish when they’re fully grown, such as Mahi Mahi, and their predators.
Whitney said:
Finding plastics in these little guys was honestly kind of an emotional hit. Climate change is a huge punch to ocean fish. Overfishing another punch. And now, at their most vulnerable stages, there’s yet another human-induced impact.
A variety of human-induced impacts such as habitat loss, climate change, poaching, and over-fishing are threatening biodiversity and marine life. Unfortunately, we can now add plastic ingestion by larval fish to that list too. Larval fish aren’t the only sea creatures found eating plastic. Recently in Florida, a baby turtle was found with 104 pieces of plastic in its digestive tract.
