Warming Waters Drive Kelp Decline

Kelp has declined dramatically in the Gulf of Maine.

Gloucester Times: When diving in the Gulf of Maine a few years back, Jennifer Dijkstra expected to be swimming through a flowing kelp forest that had long served as a nursery and food for juvenile fish and lobster.

But Dijkstra, a University of New Hampshire marine biologist, saw only a patchy seafloor before her. The sugar kelp had declined dramatically and been replaced by invasive, shrub-like seaweed that looked like a giant shag rug.

“I remember going to some dive sites and honestly being shocked at how few kelp blades we saw,” she said.

The Gulf of Maine, stretching from Cape Cod to Nova Scotia, is the latest in a growing list of global hotspots losing their kelp, including hundreds of miles in the Mediterranean Sea, off southern Japan and Australia, and parts of the California coast.

Among the world’s most diverse marine ecosystems, kelp forests are found on all continental coastlines except for Antarctica and provide critical food and shelter to myriad fish and other creatures. Kelp also is critical to coastal economies, providing billions of dollars in tourism and fishing.

The likely culprit, according to several scientific studies, is warming oceans from climate change, coupled with the arrival of invasive species. In Maine, the invaders are other seaweeds. In Australia, the Mediterranean and Japan, tropical fish are feasting on the kelp.

Most kelp are replaced by small, tightly packed, bushy seaweeds that collect sediment and prevent kelp from growing back, said the University of Western Australia’s Thomas Wernberg.

“Collectively these changes are part of a recent and increasing global trend of flattening of the world’s kelp forests,” said Wernberg, co-author of a 2016 study in the Proceedings of the National Academy of Sciences, which found that 38 percent of kelp forest declined over the past 50 years in regions that had data.

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