The January/February 2016 issue of Brown University’s Alumni Magazine includes a feature of Cashes Ledge and Dr. Jon Witman, who is a professor of biology at the university and a Cashes Ledge expert. Having dived at Cashes Ledge for more than 30 years, Witman has seen the underwater mountain range evolve from a bountiful ecological environment to a still-productive but threatened habitat. Below is an excerpt from the article by Louise Sloan. Read the full version here.
It’s not exactly a trip to the Statue of Liberty or Muir Woods. To get to Cashes Ledge, part of a proposed national monument in the Atlantic Ocean’s Gulf of Maine, you have to get in a boat and head to a spot about eighty miles east of Cape Ann, Massachusetts. After the four-hour trip, you drop an anchor near Ammen Rock, the tallest pinnacle in Cashes Ledge, a twenty-five-mile-long underwater mountain chain. Ammen Rock rises from the sea floor 720 feet below to within thirty feet of the water’s surface. Once there, divers set up a buoy marking the spot, the only clue to Cashes’s underwater marvels. Then they jump into forty-degree water that’s moving at a speed of two to three knots—about as fast as a class II rapids—and “swim like hell for the buoy,” says Professor of Biology Jon D. Witman, who has been conducting research at Cashes Ledge for more than thirty years.
As you pull yourself hand-over-hand down the buoy rope, Witman says, you slowly make out what looks like the ocean floor. But, as you get closer, you realize it’s moving. What you’re looking at is the canopy of an undersea jungle, a forest of kelp exponentially thicker than any you’ll find elsewhere in the coastal Gulf of Maine. Because of the distance between Cashes Ledge and the coast, where the water is clouded by runoff and other pollutants, sunlight penetrates deeply into the clear, cold water. As a result, the kelp grows as far down as 100 feet, and it grown unusually tall—up to fifteen feet.
. . .
Ten years ago, when the Conservation Law Foundation (CLF) asked Witman, who teaches Brown undergrads the basics of ecology, to recommend an ocean area to protect, Cashes was the obvious answer. Witman describes it as a “Disneyland of biodiversity” containing every kind of ocean bottom habitat, all in a concentrated space. Combined with the food pump provided by the waves, this dense habitat contains a rare proliferation of sea creatures representing an unusual variety of species. The complexity helps create more ecosystem stability and probably greater resilience to withstand such threats as climate change. With this range of creatures filtering water, removing carbon, producing oxygen, and providing all the other “ecosystem services” that the fish we eat depend on, Witman says, Cashes is a key to the health and productivity of the entire Gulf of Maine, including areas where commercial fishermen harvest cod.
The deep-water canyons, seamounts, and underwater mountain ranges in the coastal waters of New England are gaining recognition for their importance to the health of fish populations like the struggling Atlantic cod. But these unique geological formations are also critical for the marine mammals that call the North Atlantic home.
Hail the Whales
The Atlantic coast is a veritable highway for migrating whales, which travel from breeding grounds in the south to feeding grounds in the north each year. But with many species facing reduced habitat, diminished populations, and increased boat traffic, this annual journey has become more and more difficult. These growing threats make areas of food abundance and shelter, such as Cashes Ledge and the New England Canyons and Seamounts, ever more critical to the success of migrating whales’ journeys.
Cashes Ledge and the canyons and seamounts are unique in the Atlantic because their topography creates ideal conditions for plankton, zooplankton, and copepods – the main food for migrating minke, right, and humpback whales – to thrive. They also serve as spawning ground for larger food sources – including many squish, fish, and crustaceans. Altogether, this rich abundance of species adds up to a bountiful buffet for whales and other marine mammals.
Sperm whales have often been spotted in the waters of seamounts, taking advantage of the reliable food, and Cashes Ledge serves as an oasis for hungry whales on their journey north.
The healthy kelp domino effect
These areas are not only crucial to whales; other marine mammals depend on them as well. Cashes Ledge boasts the largest coldwater kelp forest on the Atlantic seaboard, a habitat that creates ideal spawning grounds for cod, herring, and hake. The abundance of fish in turn feeds seals and porpoises, as well as whales.
Scientists have noted a positive correlation between the size of an undersea kelp forest and populations of marine mammals, suggesting that more, healthy kelp means more marine mammals. That makes protecting areas with large kelp forests such as Cashes Ledge even more important.
Even marine mammals that don’t visit Cashes Ledge itself still benefit from the protection of the area’s kelp forest, thanks to the “spillover effect:” Fish spawned in the shelter of the rocky crevasses and havens of the kelp forests disperse beyond Cashes Ledge and feed sea animals throughout the Gulf of Maine.
Across the globe, underwater mountain and canyon habitats have proved to be important areas where marine mammals congregate to feed – and the canyons, seamounts, and ledges off the coast of New England are no different. Unfortunately, these important ecosystems are delicate and facing threats from harmful fishing gear and climate change.
With so much at stake, it is vital to protect these places – not only for their inherent ecological value, but also so that they may sustain the mammals that depend on them.
Our dive team is back! Over the next two weeks the team will return to the Gulf of Maine and Cashes Ledge to explore more of New England’s beautiful ocean and marine life!
This year from June 1 to June 14, onboard the R/V Tioga, the team will travel the 100 miles off the coast to Cashes Ledge, an underwater mountain range in the center of the Gulf of Maine that rises to within 40 feet of the surface. The steep slopes and ridges of Cashes Ledge create internal waves that mix nutrient- and oxygen-rich water. This mixing supports incredible productivity and biodiversity like no other place in the Gulf of Maine and gives rise to the deepest and largest cold water kelp forest along the Atlantic seaboard. The unique ecological conditions draw in a rich diversity of marine species ranging from bottom-dwelling sea stars, sea anemones, and purple sponges to fish like cod, wolfish, and bluefin tuna to endangered North Atlantic right whales and humpback whales.
Our dive last year captured breathtaking photographs and video of Cashes Ledge, the Isles of Shoals, and the inshore Gulf of Maine. This year, we will be able to go deeper than before – too far for the team to go themselves. Using an ROV, the team will explore down the flanks of the ledge all the way to the muddy basin below. Weather depending, we will also try to ascend the peak of Fippennies Ledge, just west of Cashes. Cashes Ledge harbors an assemblage of marine habitats and we want to see them all!
In addition to capturing stunning video and photo images of Cashes Ledge and other areas in the Gulf of Maine, including habitat and wildlife, the dive will serve to advance Dr. Jon Witman’s research on kelp, cod, and Cashes Ledge. Dr. Jon Witman is a marine ecologist who led the first ecological study of overfishing in the Gulf of Maine and has spent decades studying invertebrate and fish communities on Cashes Ledge and other marine habitats in the region.
Much like last year, this year’s exact dive locations will depend on a lot factors like weather and visibility. We are off to a rainy start, but those clouds should clear soon, and we hope to head out on the water. Stay tuned over the next two weeks for more updates, and be sure to follow New England Ocean Odyssey and Conservation Law Foundation on Facebook and Twitter so you can explore with us and help build awareness and support for New England’s ocean. We look forward to revealing more of the amazing wonders beneath New England’s waves!
The Omnibus Habitat Amendment comment period ends tomorrow, January 8th at 5pm. This amendment proposed by the New England Fisheries Management Council threatens to open currently closed areas in the Gulf of Maine, in particular the Cashes Ledge Closed Area.
Cashes Ledge is not only a beautiful underwater mountain range and the location of the largest kelp forest on the Atlantic seaboard, but an essential fish habitat for a plethora of marine species, such as New England’s iconic cod. You can learn more and watch an incredible underwater video of Cashes Ledge here.
70% of Cashes Ledge is in danger of being reopened to damaging fishing practices such as bottom trawling. Such action would destroy vital habitat and ruin this biodiversity hotspot.
Sign on to our letter now asking NOAA and the Council to maintain all current protections for Cashes Ledge. Don’t wait because time is running out!
Many NEOO readers may have come across a description of the relationship between sea otters, sea urchins, and kelp in a biology textbook. A quick recap: sea otters prey on sea urchins, which live in kelp beds and which, in turn, prey on the kelp itself. Sea otter predation, then, protects kelp from predation and allows kelp forests to flourish. Fewer of us are likely to have heard of the Atlantic wolffish, but this snaggle-toothed New England native plays the same role here that the sea otter does in the Pacific: keeping the urchin population down and the kelp population up. Of course, this is good news for kelp, but is it good news for us as well?
The answer is a resounding yes. Kelp provides essential habitat for countless marine species, including commercially important fish. Furthermore, scientific evidence suggests that kelp forests, like their terrestrial equivalents, play an important role in carbon sequestration.
Plants take in and store CO2 as part of the process of photosynthesis. Some of the carbon stored in plants is soon released when the plant decomposes, but some is sequestered in carbon sinks. Forests, swamps, and especially the ocean are all important carbon sinks. Kelp, boasting both a high uptake of atmospheric CO2 and an ocean floor habitat, is a particularly important player in carbon sequestration, and this role is becoming even more important in the face of rising atmospheric carbon dioxide levels and anthropogenic climate change.
New England is home to abundant and diverse kelp forests, notably at Cashes Ledge, where forests of towering laminarian and perforated shotgun kelp grow thickly on the undersea mountain slopes, sheltering abundant fauna including whales, seals, sharks, and commercially important fish such as the Atlantic cod. Detritus from this kelp forest tumbles off the ledge into the neighboring basin, where these nutrients are recycled back into the ecosystem and fuel incredible productivity. Kelp forests like the one at Cashes Ledge may be a critical component of our oceans’ ability to mitigate and adapt to climate change and ocean acidification caused by rising atmospheric carbon dioxide.
The loss of an apex predator such as the Atlantic wolffish, and a subsequent increase in herbivores (urchins, in this case), leading to a decrease in carbon sequestering plants such as kelp is a well-known effect called a trophic cascade. We can speed such trophic cascades along, in this case either by reducing Atlantic wolfish populations through bycatch and habitat destruction, or by skipping this step altogether and decimating kelp forests through destructive fishing practices such as bottom trawling. Unfortunately, we’ve done just that—Atlantic wolffish are severely depleted, and the kelp forest at Cashes Ledge is threatened by a New England Fishery Management Council proposal that would reopen 75 percent of the area surrounding the kelp forest to commercial fishing (this area has been protected since 2002).
The news that apex predators such as the Atlantic wolfish can help preserve healthy populations of kelp, and that kelp in particular is a highly efficient carbon sequestering plant, tells us two things. First, while the Atlantic wolffish alone may not have much impact on overall climate change mitigation, protecting important predators like the wolffish will build resilience for our ecosystems in more ways than we can count. Second, we New Englanders should support habitat protection and responsible fishing practices that allow our kelp forests to continue flourishing. In doing so, we will promote carbon sequestration and provide habitat for countless fish—including the Atlantic wolffish, that friend of the kelp. After all, in the end, all ecosystems are cyclical.
Brian Skerry was struck by the vivid colors of these cunner when he visited Cashes Ledge recently. He said they were “quite stunning, like the garibaldi in California.” Ranging from the Gulf of St. Lawrence to Chesapeake Bay, cunner are common inshore fish in the Gulf of Maine, but Cashes Ledge provides ample offshore habitat and some of this fish’s favorite foods: including shrimp, lobsters, mussels, and sea urchins.
Diminutive in stature, cunner don’t get very big – up to a foot or so, and weighing less than 3 pounds – but what they lack in dimension they make up for in dazzle.
Above – Brian Skerry and Luis Lamare get ready to photograph Cashes Ledge on their recent dive. Photograph by Christian Conroy.
What’s so special about Cashes Ledge? In this second of a planned series of dives on this New England biodiversity hotspot, Brian Skerry was joined by marine ecologist, Jon Witman, an expert on Cashes Ledge. Jon has been studying Cashes Ledge for 35 years, and has been watching how the diversity and abundance of sea life has been changing there, and how it has responded to its current limited-protection status. We talked to him and found out more about why Cashes Ledge is so important to the Gulf of Maine, and what we can do to keep it thriving.
Why have you spent so much time on Cashes Ledge?
Cashes Ledge is a fascinating and wild offshore place that helps us understand how marine ecosystems tick. It is also a unique storehouse of Atlantic marine biodiversity. Cashes Ledge provides an opportunity to understand why biodiversity matters in an ecological sense. Unfortunately, we are losing marine biodiversity in the world’s oceans faster than we can study it.
Currently, I’m trying to figure out how the whole benthic ecosystem out on Cashes Ledge – from the fish, to the kelp forests and the diverse invertebrates communities have changed over the past decades. I’m particularly interested in how resilient the system is to human disturbance and to climate-related changes in the oceanography.
When we studied Cashes Ledge intensively in the 1980’s, it was like a time machine providing a fleeting glimpse of what New England marine coastal communities might have been like hundreds of years ago, when lots of large predatory fish – especially cod, were commonplace close to shore. We videotaped over 100 cod an hour going by an area of bottom about the size of a large picnic table on Cashes Ledge, compared to no cod seen at the same depth at coastal sites in the Gulf of Maine.
I actually saw a whale cod as long as a diver and schools of Atlantic bluefin tuna while diving on Cashes Ledge then. There have been substantial reductions of predatory fish since then, which is something I’m studying, but Cashes Ledge is still a vitally rich ecosystem compared to coastal ones that have been more heavily impacted by humans.
What other kinds of interesting animals have you seen on Cashes Ledge?
There are layers of marine life on Cashes Ledge, including minke, right, humpback and pilot whales, blue sharks, basking sharks, atlantic white sided dolphins, big schools of bluefin tuna chasing herring, whale cod, red cod, pollock, wolffish, torpedo rays, squid, strange feather stars called crinoids, and unusual sponges and sea squirts typical of sub arctic areas of Scandinavia.
Can you talk about the internal waves and why they are important?
The top of the ridge on Cashes Ledge is an incredibly dynamic place – layers of plankton in warmer overlying waters are driven right down to the bottom as much as 20 times a day by these phenomena known as internal waves. This is a big deal because the downwelling plankton layers are pulses of concentrated food that sustain bottom dwelling organisms and, in effect, fuel the food web.
We stumbled across this phenomenon in the course of our scuba dives to the top of the ridge at 30 m. One dive team would go down and report that the water on the bottom was cold and beautifully clear but the next team an hour later found pea soup visibility in greenish warm water. This, of course, turned out to be the plankton layer pushed down onto the bottom like a yo-yo by internal waves.
The temperature increase was so large that we could feel the warm water through our drysuits. At that time, the prevailing view of the subtidal zone was that it was a stable place with nearly constant environmental conditions, compared to the rocky intertidal zone. But out on Cashes we were documenting as much as 5 degree centigrade temperature increases in 10 minutes right on the rocky sea floor at 30 m depth.
Internal waves are like a sine wave travelling along the boundary between the warm surface waters and the colder layer below. They can be huge – spanning 50 m vertically in some parts of the world and 30 m high on Cashes. I’ve seen these downwelling green water waves approaching the ridge on Cashes Ledge while scuba diving and sitting off the ridge in the Johnson Sea Link submersible – it’s one of the most spectacular things I’ve seen underwater.
What makes Cashes Ledge so unique?
There are at least three things make Cashes Ledge so unique. First of all, it is the largest continuous kelp forest in offshore waters on the entire east coast of the US. The kelp grow unusually deep there, beyond 30 m depth. The forest and the ledge itself provide many valuable goods and services to keep the offshore Gulf of Maine ecosystem healthy, vibrant, and productive. For example, it’s a nursery habitat for commercially valuable groundfish. It’s also an energy rich food source for marine life living in habitats both on the ledge and far away from it – in the form of detritus as the kelp breaks down.
Secondly, the Cashes Ledge ecosystem contains a wide range of different bottom types – it isn’t just all rocky ledge. Just like on a mountain slope in the Green or White Mountains in New England, there are cobble and boulder fields on the lower sides of rocky slopes on Cashes Ledge. Deeper down, the sea floor is covered in sand and gravel that grades into soft bottom areas of silt and mud in the basins. So what you have in the Cashes Ledge underwater landscape is a representative collection of most of the major types of bottom habitats found in the Gulf of Maine, but in an incredibly compact area, as ecosystems go.
Each of those different habitat types has its own community of species that do especially well in that particular habitat. For example, there are pink northern shrimp, clams, and tube worms living in the muddy basins at the edge of a boulder field, then communities of soccer ball-sized yellow sponges, bright red sea anemones, and little upright calcified candelabras called bryozoans that look like miniature coral reefs, attached to the boulder tops. Different habitats enhance biodiversity overall. If you sum up all the different species living in each of these different types of habitats from kelp forests to the muddy basins, you have some of the highest biodiversity levels in the Gulf of Maine right on Cashes Ledge.
Finally, as an abrupt topographic high in relatively clear, shallow, sunlit waters, Cashes Ledge is an especially productive offshore ecosystem in the Gulf of Maine. I mentioned the role of the kelp detritus exporting food to adjacent ecosystems, but the dynamic oceanography of the ledge itself also contributes to the productivity of the bottom community in the way that internal waves push concentrated layers of plankton to the top of the ridge.
I think both mechanisms help make Cashes Ledge such a productive area for many species – including groundfish and marine mammals. We’ve seen minke whales feeding in the slicks of internal waves on Cashes Ledge, presumably due to high concentrations of food there.
What kind of protection does Cashes Ledge need and why?
As special as it is, Cashes Ledge is a very vulnerable marine ecosystem. Right now Cashes Ledge has a small amount of protection from certain types of fishing activity as an Essential Fish Habitat and as a Habitat Area of Special Concern. This is laudable and a real achievement by fisheries managers in New England. However, this protection is only temporary and it could be eliminated at any moment. It could be opened to fishing practices that further deplete stocks of groundfish, damage biodiverse communities, and decrease the sustainability of the kelp forests.
Because it is such a unique, valuable, and diverse New England marine ecosystem, the rocky ridge, adjacent bottom habitats, and the overlying water column on Cashes Ledge need permanent protection from human impacts. It has been shown many times that marine protected areas help exploited stocks recover and can ensure the sustainability of biodiversity and other goods and services that keep our oceans healthy. We also know that really small protected areas don’t do these jobs very well, so it pays in the long run to preserve larger areas containing different types of habitats.
Globally, we aren’t doing a very good job of protecting the oceans as less than 2% of the worlds oceans are fully protected, despite all the scientific findings showing that marine ecosystems are under ever increasing levels of stress from all sorts of human impacts.
The almighty cod – the most legendary fish in our New England waters. Atlantic cod is greyish-green, and a renowned dweller of the Gulf of Maine. It is a staple of our traditional cuisine and a historic driver of our economy. You‘ve seen an Atlantic cod, right? But have you ever seen a red Atlantic cod?
How the red cod got its color is a mysterious tale, and one that even dedicated Gulf of Maine fish researchers don’t fully understand yet. Red cod live throughout the North Atlantic, in discrete populations. The red cod you see in these photos, pictured along with the traditionally colored “olive cod,” live on Cashes Ledge, about 80 miles off the coast of Gloucester, Massachusetts. They are the same species of fish, but they don’t fraternize much. The red cod and olive cod seem to be on different reproductive schedules. They also eat different things and have different ranges. Olive cod like to wander around the North Atlantic, but red cod tend to hang out in one place – “shallow, kelpy habitats,” according to Graham Sherwood, Research Scientist at the Gulf of Maine Research Institute in Portland, Maine. Shallow and kelpy is just where Brian Skerry found these red cod – in fact, in about 40 feet of water. Well, it was shallow for cod, anyway.
Why are they red? The food red cod eat, things like crabs, lobsters, and worms, are high in carotenoids – naturally-occurring chemicals which give the fish the ability to turn red. Not all cod that eat these things turn red, though – deeper dwelling olive cod remain traditionally cod-colored even on a high-carotenoid diet. Sherwood speculates that there might be an adaptive advantage to the red coloring for shallow-living cod. Perhaps the shallow water cod need better U/V protection. Or, more likely, it makes it easier to hide in all that red kelp.
There haven’t been any studies yet to indicate whether or not red cod are genetically distinct from olive cod. It’s possible that a red cod and an olive cod could come from the same parents, but be different in appearance and behavior due to having hatched in different habitats. One deeper and darker, one shallower and kelpier. Possible, but unlikely, says Sherwood. He thinks that, while they are the same species of fish, they may be genetically different enough to look and behave distinctly from each other. Maybe different populations of cod began spawning at different times, to take advantage of optimal environmental conditions, and over time they differentiated into the red and olive types. But, nobody knows for sure yet.
The color and habitat preference aren’t the only differences between the cod. Red cod are less streamlined than olive cod – no need to be shaped like a sports car if you’re just going to hang out in the garage. They also have shorter snouts than olive cod. Although, says Sherwood, if it weren’t for the color difference you would have a hard time telling them apart. Maybe because these fish tend to be homebodies, hanging out in remote places like Cashes Ledge, or in shallow inshore waters that are not targeted by fisheries, we’re less likely to run into them. Brian, a 35 year veteran of diving in the Gulf of Maine, says they are unlike anything he has ever seen.
The red cod are just one example of the amazing biological diversity that is found at Cashes Ledge. We can’t wait to show you more as our Ocean Odyssey continues!