Only five species of marine insects are able to survive in the open ocean. Capable of walking along the surface of the ocean, these “sea skaters” (Halobates) boast several adaptations that allow them to thrive thousands of miles away from land. They are wingless—no need for such limbs in an open ocean environment that’s free of barriers—unlike their winged cousins on land that are required to navigate trees, mountains, and other objects.
“Halobates cope with storms at sea by surrounding themselves in an air bubble,” said Lanna Cheng, who has studied sea skaters at Scripps Institution of Oceanography at UC San Diego for more than 40 years. “They also have very efficient UV-absorbing chemicals in their cuticles to protect them against radiation damage and they have the ability to store lipids to tie them over periods of starvation.”
Cheng is coauthor of a paper released this week indicating that the sea skater’s environment is changing due to human-produced trash. Sea skaters must lay their eggs on floating objects such as feathers, wood, or pumice. According to Cheng and colleagues, plastic has added itself to that list in spectacular fashion. In the new study led by Scripps graduate student Miriam Goldstein, the researchers estimated that there has been a 100-fold increase in human-produced plastic garbage in the ocean.
In 2009 Goldstein led an ambitious group of graduate students in the Scripps Environmental Accumulation of Plastic Expedition (SEAPLEX) to the North Pacific Ocean Subtropical Gyre aboard the Scripps research vessel New Horizon. During the voyage to the “Great Pacific Garbage Patch” the researchers documented an alarming amount of human-generated trash, mostly broken down bits of plastic the size of fingernails floating across thousands of miles of open ocean.
The new study, published in the May 9 online issue of the journal Biology Letters, reveals that Halobates sericeus has exploited the influx of plastic fragments as new surfaces for their eggs, leading to a rise in the insect’s egg densities in the North Pacific Subtropical Gyre. Such an increase, documented for the first time in a marine invertebrate (animal without a backbone) in the open ocean, may have consequences for animals across the marine food web, such as crabs that prey on sea skaters and their eggs.
“This paper shows a dramatic increase in plastic over a relatively short time period and the effect it’s having on a common North Pacific Gyre invertebrate,” said Goldstein. “We’re seeing changes in this marine insect that can be directly attributed to the plastic.”
Cheng, who joined Scripps in 1970, has studied open ocean and coastal Halobates species on expeditions to Hawaii, the Galapagos, Fiji, Tonga, Thailand, Malaysia, and many other locations. Off Mexico, one of her colleagues once collected a discarded milk jug with some 30,000 Halobates eggs, likely laid by hundreds of females.
“Although it is worrisome to see the increasing abundance of plastic trash, they may provide much-needed hard surfaces for Halobates egg laying,” said Cheng. “What effect these may have in the ocean food chain remains to be seen.”
The new study follows a report published last year by Scripps researchers in the journal Marine Ecology Progress Series showing that nine percent of the fish collected during SEAPLEX contained plastic waste in their stomachs. That study estimated that fish in the intermediate ocean depths of the North Pacific Ocean ingest plastic at a rate of roughly 12,000 to 24,000 tons per year.
The Goldstein et al. study compared changes in small plastic abundance between 1972-1987 and 1999-2010 by using historical samples from the Scripps Pelagic Invertebrate Collection and data from SEAPLEX, a NOAA Ship Okeanos Explorer cruise in 2010, information from the Algalita Marine Research Foundation as well as various published papers.
“Plastic only became widespread in late ’40s and early ’50s, but now everyone uses it and over a 40-year range we’ve seen a dramatic increase in ocean plastic,” said Goldstein. “Historically we have not been very good at stopping plastic from getting into the ocean so hopefully in the future we can do better.”
In addition to Goldstein and Cheng, Marci Rosenberg, a student at UCLA, contributed to the report.
-- Mario C. Aguilera