As Oceans Warm, the World’s Kelp Forests Begin to Disappear

Kelp forests — luxuriant coastal ecosystems that are home to a wide variety of marine biodiversity — are being wiped out from Tasmania to California, replaced by sea urchin barrens that are nearly devoid of life.

A steady increase in ocean temperatures — nearly 3 degrees Fahrenheit in recent decades — was all it took to doom the once-luxuriant giant kelp forests of eastern Australia and Tasmania:  Thick canopies that once covered much of the region’s coastal sea surface have wilted in intolerably warm and nutrient-poor water.  Then, a warm-water sea urchin species moved in.  Voracious grazers, the invaders have mowed down much of the remaining vegetation and, over vast areas, have formed what scientists call urchin barrens, bleak marine environments largely devoid of life.

Today, more than 95 percent of eastern Tasmania’s kelp forests — luxuriant marine environments that provide food and shelter for species at all levels of the food web — are gone.  With the water still warming rapidly and the long-spine urchin spreading southward in the favorable conditions, researchers see little hope of saving the vanishing ecosystem.  

“Our giant kelp forests are now a tiny fraction of their former glory,” says Craig Johnson, a researcher at the University of Tasmania’s Institute for Marine and Antarctic Studies.  “This ecosystem used to be a major iconic feature of eastern Tasmania, and it no longer is.”

The Tasmanian saga is just one of many examples of how climate change and other environmental shifts are driving worldwide losses of giant kelp, a brown algae whose strands can grow to 100 feet.  In western Australia, increases in ocean temperatures, accentuated by an extreme spike in 2011, have killed vast beds of an important native kelp, Ecklonia radiata.  In southern Norway, ocean temperatures have exceeded the threshold for sugar kelp — Saccharina latissima — which has died en masse since the late 1990s and largely been replaced by thick mats of turf algae, which stifles kelp recovery.  In western Europe, the warming Atlantic Ocean poses a serious threat to coastal beds of Laminaria digitata kelp, and researchers have predicted “extirpation of the species as early as the first half of the 21st century” in parts of France, Denmark, and southern England. 

And in northern California, a series of events that began several years ago has destroyed the once-magnificent bull kelp forests along hundreds of miles of coastline.  A brief shutdown of upwelling cycles left the giant algae groves languishing in warm surface water, causing a massive die-off.  Meanwhile, a disease rapidly wiped out the region’s urchin-eating sea stars, causing a devastating cascade of effects:  Overpopulated urchins have grazed away much of the remaining vegetation, creating a subsurface wasteland littered with shells of starved abalone.  Scientists see no recovery in sight.   

A 2016 study noted a global average decrease in kelp abundance, with warming waters directly driving some losses.  But the researchers said that a characteristic of kelp forest declines is their extreme regional variability.  Some areas are even experiencing a growth in kelp forests, including the west coast of Vancouver Island, where an increasing population of urchin-hunting sea otters has reduced the impacts of the spiny grazers, allowing kelp to flourish.  Ultimately researchers say, warming ocean waters are expected to take a toll on the world’s kelp forests.  The 2016 paper, coauthored by 37 scientists, concluded that “kelp forests are increasingly threatened by a variety of human impacts, including climate change, overfishing, and direct harvest.”

Read more at As Oceans Warm, the World’s Kelp Forests Begin to Disappear