PROVIDENCE, R.I. [Brown University] — For nearly half a century, Brown University marine biologist Jon Witman has been diving Cashes Ledge, an underwater mountain range in the center of the Gulf of Maine that is home to one of the largest kelp forests on the East Coast.
Witman has made more than 20 trips to the area, located 80 miles offshore, as part of a long-term monitoring effort to observe how climate change is affecting the kelp forest community of Cashes Ledge, and every time, the team discovers something new. An expedition earlier this summer offered a few encouraging surprises amid the widely observed decline of marine ecosystems.
Cashes Ledge presents a unique opportunity to observe the effects of a warming ocean on not only different species of kelp but also on the innumerable fish, sea urchins, crustaceans, mollusks, invertebrates and other creatures that live in and subsist on the plants that flourishes along the 30-mile ridge.
“The reason we’re so focused on Cashes Ledge is that it’s exceptional — it has the most offshore biodiversity in the Gulf of Maine,” said Witman, who recently retired from teaching at Brown and became a professor emeritus of ecology, evolution and organismal biology. “It’s like a living museum of Gulf of Maine marine life.”
On the expedition in late June, Witman was joined by longtime collaborator Elizabeth Kintzing from the University of New Hampshire; Jennifer Adler, an underwater photographer who studied marine biology as an undergraduate at Brown; and Robert Lamb, who earned a Ph.D. in biology from Brown in 2019 and is now a research assistant professor at the University of Florida.
Because of storms and seven-foot waves, the team was only able to dive for one day, which was barely enough time to measure kelp plants, collect specimens and census fish populations, Witman said. Near the surface of the water, the team saw 20-foot basking sharks, giant ocean sunfish and fulmars, tube-nosed seabirds that are more typical of northern seas like the Canadian Arctic. Deeper under the water, they dove among goosefish, pollock and dogfish sharks.
To the team’s surprise, the kelp forest looked better than it did two years ago: while the number of plants appeared to have slightly decreased, the mass and volume seemed to have increased, which Witman said is an indication of sustained productivity. (Lab analyses will quantify the team’s observations.) Lamb found that fish, especially cunner and pollock, were abundant in the kelp forest.