By Jonny Lupsha, News Writer

An ocean cleanup device has recovered plastic from the sea, The Guardian reported. This event marks the first time such a tool has done so. It provides an example of the human impact on the oceans.

According to The Guardian article, the floating mechanism—which is called a boom—was created by Dutch scientists to catch plastic. Currently, an island of garbage “three times the size of France” wades in the Pacific Ocean. The 2,000-foot-long device is pulled behind a boat and skims along the ocean’s surface, netting debris before being reeled in by the ship’s crew. Among the trash it picked up from the “Great Pacific Garbage Patch” was a milk crate and a car tire. The boom and the need for it captured a microcosm of the devastating impact humans are having on the sea.

The End of Coral

Higher water temperatures can cause what’s called “heat pollution” in the ocean, causing coral bleaching. So how does it qualify as “pollution?”

“It has a toxic effect directly on many of the different organisms in the sea,” said Dr. Harold J. Tobin, Professor of Geoscience at the University of Wisconsin-Madison. “What happens to corals is that when the sea surface temperatures exceed normal, summer high temperatures by about one degree or so, the corals respond by expelling symbiotic algae that live within the coral polyps—the zooxanthellae.”

This is coral reef bleaching. Without the zooxanthellae, corals die, no longer building reefs. Sometimes heat pollution happens naturally, but often it’s man-made. Another coral killer is ocean acidification, which is caused by high amounts of carbon dioxide—CO₂—settling into the ocean, changing the pH balance of sea water. Small changes have big effects.

“Just a small change in that alkalinity down towards the direction of more acid interferes with the corals’ ability to make their shells,” Dr. Tobin said. “They make their coral skeleton—the reef itself—from calcium carbonate, also known as limestone, and if there’s more carbonic acid in the water it dissolves the limestone or more directly interferes with their ability to secrete the limestone and make the hard reef structure.”

Marine biologists consider a total extinction of reef-building coral to be a very real possibility.

Solid Waste in the Ocean

Solid waste is a much more visible, tangible problem in the world’s oceans, and can be measured by three characteristics. The first, Dr. Tobin said, is the concentration of the pollutant; if it’s in trace amounts and a low toxicity level to things around it, it’s not as large a concern as it is in larger amounts.

The toxicity level itself is the second characteristic. “The actual degree to which that particular pollutant is damaging—the amount of it ingested by an organism required to cause damage—is a major factor,” he said.

Third is the persistence, or the length of time the pollutant stays in the environment. “Many pollutants are broken down by organic processes or by ultraviolet sunlight relatively quickly so they make it into the water, but then they break down,” Dr. Tobin said. “They have low persistence; they have short persistence time. That makes them less of a problem than the ones that have very long persistence in the ocean.”

Runoff from land and activities like sewage dumping introduce the most problematic pollutants to the ocean. Dr. Tobin gave examples including mercury, lead, certain organic compounds used for industrial purposes, and pesticides.

The Great Pacific Garbage Patch is the most ominous proof of man-made pollution in the ocean, but it’s far from the only one. Mounting evidence like coral death and studies of the marine food web—which often provide fish with stomachs full of plastic—also show the outcomes of human impact on aquatic life.

Dr. Harold J. Tobin contributed to this article. Dr. Tobin is Professor of Geoscience at the University of Wisconsin-Madison. He earned his B.S. in Geology and Geophysics from Yale University and his Ph.D. in Earth Sciences from the University of California, Santa Cruz.