Posts Tagged ocean temperatures

Nov 20 2017

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.

By Alastair Bland

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exceeded the threshold for sugar kelp — Saccharina latissima — which has died en masse since the late 1990s and largely been replaced by thick mats of turf algae, which stifles kelp recovery.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.

Routine summertime spikes in water temperature in eastern Tasmania have pushed kelp forests over the edge.

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.”

In eastern Tasmania, sea surface temperatures have increased at four times the average global rate, according to Johnson, who along with colleague Scott Ling has closely studied the region’s kelp forest losses. This dramatic environmental change began in the mid-20th century and accelerated in the early 1990s. Giant kelp — Macrocystis pyrifera — does best in an annual water temperature range of roughly 50 to 60 degrees Fahrenheit, according to Johnson. He says routine summertime spikes into the mid-60s pushed the kelp over the edge. First in Australia, and subsequently in Tasmania, the kelp forests vanished. The Australian government now lists giant kelp forests as an endangered ecological community.

The progression of the destruction of a kelp forest in Tasmania by urchins, from left to right. The Australian island state has lost more than 95 percent its kelp forests in recent decades. Courtesy of Scott Ling

As waters warmed, something else also happened. The long-spine sea urchin, which generally cannot tolerate temperatures lower than 53 degrees Fahrenheit, traveled southward as migrant larvae and established new territory in Tasmanian waters. Lobsters — which prey on urchins — had been heavily fished here for decades, and consequently few predators existed to control the invading urchins, whose numbers boomed.

Since the 1980s, long-spine urchins — Centrostephanus rodgersii — have essentially taken over the seafloor in southeastern Australia and northeastern Tasmania, forming vast urchin barrens. An urchin barren is a remarkable phenomenon of marine ecology in which the animals’ population grows to extraordinary densities, annihilating seafloor vegetation while forming a sort of system barrier against ecological change. Once established, urchin barrens tend to persist almost indefinitely.

“For all intents and purposes, once you flip to the urchin barren state, you have virtually no chance of recovery,” Johnson says.

In some places, like the southwestern coast of Hokkaido, in Japan, and the Aleutian Islands, urchin barrens have replaced kelp forests and have remained for decades.

This bodes poorly for eastern Tasmania, where expansive areas in the north have already been converted into barrens. Urchins have not yet overrun southeastern Tasmania. “But we’re seeing the problem moving south, and we’re getting more and more urchins,” says Johnson, who expects roughly half the Tasmanian coastline will transition into urchin barrens. “That’s what we have in New South Wales.”

Warm ocean temperatures, a sea star disease outbreak, and a boom in urchin populations decimated several major kelp beds in northern California between 2008 and 2014. California Department of Fish and Wildlife

A similar scenario is unfolding in northern California, where local divers and fishermen have watched the area’s bull kelp forests collapse into an ecological wasteland. As in Tasmania, the change has resulted from a one-two punch of altered ocean conditions combined with an urchin boom.

The problems began in 2013, when a mysterious syndrome wiped out many of the sea star species of the North American west coast. Sea stars — especially Pycnopodia helianthoides, the sunflower sea star — eat urchins. With the predators abruptly absent in the region, the population of purple sea urchins — Strongylocentrotus purpuratus — began growing rapidly.

By coincidence, a simultaneous onset of unusual wind and current patterns slowed the upwelling of cold, nutrient-rich bottom water, which typically makes the waters of the west coast of North America so productive. Kelp forests, already under attack by armies of urchins, disappeared.

The upwelling cycles have since resumed. “But the system just can’t recover, even with a shift back in water temperature,” says Kyle Cavanaugh, an assistant professor of geography at the University of California, Los Angeles who has studied global kelp ecosystems. “The urchins are just everywhere.”

Divers surveying the seafloor have seen purple urchin numbers jump by as much as 100-fold, according to Cynthia Catton, a biologist with the California Department of Fish and Wildlife who has been surveying the environment since 2002. Urchins  — dozens per square meter in places — continue to gnaw away the remnant scraps of the vanishing kelp forests, 95 percent of which have been converted to barrens, Catton says.

Urchins — dozens per square meter in places — continue to gnaw away the remnant scraps of the vanishing kelp forests.

Other animals also depend on kelp, and the region’s red abalone are now starving in droves. The population has collapsed, and the recreational harvest could be banned in the coming year, Catton says. Juvenile fish use kelp as nursery habitat, and certain species of rockfish may see declines in the absence of protective vegetation. Predatory fish, like lingcod, may move elsewhere to hunt. Populations of the commercially valuable red urchin, Mesocentrotus franciscanus, are also being impacted as their gonads — finger-sized golden wedges listed on sushi menus as uni — shrivel away, making the urchins no longer worth harvesting.

An urchin barren is considered to be an “alternative stable state” to the kelp forest ecosystem and is almost invincibly resistant to change. Johnson says that while it takes relatively high urchin densities to graze a kelp forest down to a barren, the animals must be almost eradicated entirely to allow a shift back to a kelp forest. In other words, he says, “The number of urchins needed to create a barren is much greater than the number of urchins needed to maintain it.”

Part of the reason urchin barrens are difficult to reverse is the hardiness of the urchins themselves. Foremost, they are almost immune to starvation, and once they’ve exhausted all vegetation will outlive virtually every other competing organism in the ecosystem. In the urchin barrens of Hokkaido, which formed roughly 80 years ago for reasons that remain unclear, individual urchins have lived in the collapsed environment for five decades, according to a 2014 analysis.

What’s worse, the hungrier urchins get, the more destructive they become. Research has shown that the calcite deposits that form urchins’ jaws and teeth enlarge when the animals are stressed by hunger — a rapid adaptation that allows them to utilize otherwise inedible material.

A bull kelp forest as seen from the surface of Ocean Cove in northern California in 2012 and 2016. Kevin Joe and Cynthia Catton, California Department of Fish and Wildlife

“They’re now eating through barnacles, they’re eating the calcified coralline algae that coats the rocks, they’re eating through abalone shells,” Catton says of the purple urchins in northern California. “The magnitude of their impact increases as their food supply diminishes.”

They become aggressive, too. Whereas urchins in healthy kelp ecosystems tend to dwell in crevices for much of their lives and wait for drifting kelp to come their way, in a barren state they exit their hiding places and actively hunt for food. “They form these fronts, and they graze along the bottom and eat everything,” says Mark Carr, a marine biologist at the University of California, Santa Cruz.

In the kelp forests of Alaska’s Aleutian Islands chain, urchin barrens began forming in the 1980s, causing local declines in various fishes, bald eagles, and harbor seals. The transition began when the population of sea otters started to decline, possibly because of increased predation by killer whales. Green urchin numbers skyrocketed, and the animals destroyed the kelp forests along hundreds of miles of the archipelago. “The densities are getting ridiculous,” says Matthew Edwards, a San Diego State University biologist who has studied the region. “In some places we have hundreds of urchins per square meter.”

In Tasmania, Johnson and Ling are leading an effort to protect areas that haven’t yet been overwhelmed by the long-spine urchin. The best chance they see is to boost localized populations of predatory rock lobsters. Fishery officials are on board with the plan, Johnson says, and have tightly restricted lobster harvest in order to help increase their numbers. Johnson and Ling have also been directing the translocation of large lobsters into test site barrens.

“It’s like seeing a forest you once knew turn into a desert,” says one scientist.

But the measures have been only moderately successful. Ling is currently re-surveying dozens of study sites first assessed in 2001, and he says urchin density has more than doubled in some locations. On relatively small barrens surrounded by healthy reef ecosystems, the scientists have seen progress as translocated lobsters knock down urchin numbers sufficiently to allow some vegetation to grow back.

“But on those extensive barrens, you can pour in as many large lobsters as you like, and they will eat hundreds of thousands of urchins, but they cannot reduce the urchins enough for any kelp to reappear,” he says. “Even if you turned all those urchin barrens into marine protected areas tomorrow, you could wait 200 years and you still wouldn’t get a kelp forest back.”

In central California, kelp forests are still thriving, a fact Carr credits to one animal.

“We have sea otters down here, and they’re voracious predators of urchins,” he says.

Carr, both a research diver and a recreational abalone diver, says he has watched the decline of northern California’s kelp forests with great sorrow.

“It’s like seeing a forest you once knew turn into a desert,” he says. “Not only do you lose all the trees, but all the smaller plants around them die, until there’s nothing left.”


Originally published: http://e360.yale.edu/

Dec 17 2015

November Takes a Bite Out of ‘the Blob’

Warm expanse that heated up West Coast waters is beaten, but not yet broken

The so-called “blob” of infamous warm ocean waters that has gripped the West Coast and shaken up its marine ecosystems in the past two years is battered, but not dead yet, NOAA scientists report.

Strong winds blowing south from Alaska toward California dominated the West Coast through much of November, bringing cold air and some new upwelling of deep, cold water that weakened the warm patches that had long made up the blob, said Nathan Mantua, leader of the Landscape Ecology Team at NOAA Fisheries’ Southwest Fisheries Science Center in Santa Cruz, California. Patches of ocean that had been as much as 2 to 3 degrees C warmer than average in October have now dropped sharply to around 0.5 to 1.5 degrees C above average. Some areas along the Northern California Coast have even dropped to slightly below average temperatures for this time of year, he said.

SST anomalies, Nov 2015 and Dec 2015

Sea surface temperature maps from early November and early December illustrate decline of the large patches of warm water off the West Coast that have become known as “the blob.” The maps chart the difference between current and average sea surface temperatures, with darker red illustrating temperatures farther above average.

The blob has become one of the best-known temporary features of the world’s oceans, a big red expanse on temperature maps that has earned headlines in the New York Times and other outlets around the world. It has also become one of the hottest topics in climatology and oceanography, with scientists looking for possible links to climate change and the California drought; shifting distributions of marine species; and the unprecedented harmful algal bloom that has encompassed the West Coast, shutting down crabbing and clamming for months.

The one main exception to the blob’s decline is a narrow band of still-warm water along the coast from Southern California to San Francisco that remains about 3 degrees C above normal for this time of year. But the band may also be an early signal of the arrival of El Niño-related ocean currents, which are expected to cause more warming along the Pacific Coast in the next few months, Mantua said.

SST anomalies off U.S. West Coast

A close-up of sea surface temperatures off the West Coast, with red illustrating areas warmer than average and blue representing areas below average.

Research scientist Nick Bond of the NOAA Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington originally coined the term, “the blob,” to describe the warm expanse. He said climate models agree the strip of warm water will remain along the West Coast, perhaps helping the blob hang on. He figures that the conditions might continue “well into 2016, and be of great enough magnitude to matter to marine ecosystems. How much is the big question.”

“Unusually warm temperatures still dominate the Pacific between Hawaii and the West Coast, but the amount of warmth is lower now than it has been for most of the past two years,” Mantua said. “As we get into the winter months, the expected El Niño influence on North Pacific weather and ocean currents includes more dramatic changes in West Coast ocean temperatures that will likely include coastal warming and offshore cooling.”

Previous articles

A Remarkable Warming of Central California’s Coastal Ocean (Jul 30, 2014)

Unusual North Pacific Warmth Jostles Marine Food Chain (Sep 8, 2014)

Oncoming El Niño Likely to Continue Species Shakeup in Pacific (Oct 1, 2015)

Contact: SWFSC Fisheries Ecology Division, Landscape Ecology Team

Current conditions: What’s happening now?

Below are the most recent sea surface temperature anomaly maps for the U.S. West Coast and the Northeast Pacific. These images are generated live from a data server, so they make take a few seconds to display.

Sea surface temperature anomalies, U.S. West Coast

Sea surface temperature anomalies, Northeast Pacific


Read the original story: https://swfsc.noaa.gov/

Jun 11 2015

Ocean investigators set their sights on Pacific Ocean ‘blob’

 

A huge swath of unusually warm water that has drawn tropical fish and turtles to the normally cool West Coast over the past year has grown to the biggest and longest-lasting ocean temperature anomaly on record, researchers now say, profoundly affecting climate and marine life from Baja California to Alaska.

Researchers remain uncertain what caused the mass of warm seawater they simply call “the blob,” or what it’ll mean long term for the West Coast climate. But they agree it’s imperative to better understand its impact, as it may be linked to everything from California’s drought to record numbers of marine mammals washing up on Northern California shores.

The blob — that’s the technical term — first appeared in late 2013 as a smudge of warm water near Alaska. It then expanded southeast and merged with warm waters farther south, growing into an anomaly that extended from the Aleutian Islands to Baja California and stretched hundreds of miles west toward Hawaii.

“Just the enormous magnitude of this anomaly is what’s incredible,” said Art Miller, an oceanographer at the Scripps Institute of Oceanography in La Jolla. He was among nearly 100 scientists from Canada, the U.S. and Mexico who gathered recently at Scripps for the first time to share research about the warm-water mass.

The warmest ocean temperatures in the blob now are around 5 degrees Fahrenheit above average.A huge swath of unusually warm water that has drawn tropical fish and turtles to the normally cool West Coast over the past year has grown to the biggest and longest-lasting ocean temperature anomaly on record, researchers now say, profoundly affecting climate and marine life from Baja California to Alaska.

Researchers remain uncertain what caused the mass of warm seawater they simply call “the blob,” or what it’ll mean long term for the West Coast climate. But they agree it’s imperative to better understand its impact, as it may be linked to everything from California’s drought to record numbers of marine mammals washing up on Northern California shores.

The blob — that’s the technical term — first appeared in late 2013 as a smudge of warm water near Alaska. It then expanded southeast and merged with warm waters farther south, growing into an anomaly that extended from the Aleutian Islands to Baja California and stretched hundreds of miles west toward Hawaii.

“Just the enormous magnitude of this anomaly is what’s incredible,” said Art Miller, an oceanographer at the Scripps Institute of Oceanography in La Jolla. He was among nearly 100 scientists from Canada, the U.S. and Mexico who gathered recently at Scripps for the first time to share research about the warm-water mass.

The warmest ocean temperatures in the blob now are around 5 degrees Fahrenheit above average.

“They’re just so far off the mean that they’re shocking,” Miller said.

The blob continues to evolve. In the last month, seasonal upwelling of cooler water in Northern California has split it into two separate masses once again. And 2015 is shaping up to be an El Niño year, marked by unseasonably warm waters off the coast of South America. What researchers don’t know is if El Niño will exacerbate or neutralize the blob.

20150610_075433_SJM-OCEANBLOB-0611-90

Researchers agree that unusually slack winds are to blame for the warming ocean off the West Coast, though they don’t know what drove the drop in wind. Stronger winds typically cause deep, cooler water to rise to the surface.

“If you don’t blow the wind as much, you don’t stir the ocean as much,” Miller said. The same mechanism, he said, also may be preventing rainfall from reaching California.

In August, a temperature sensor in Monterey Bay picked up its highest temperature reading ever recorded, said Francisco Chavez, a physical oceanographer at the Monterey Bay Aquarium Research Institute. On land, 2014 was the hottest year on record in California and temperatures remained higher than average until spring of this year.

Less ocean stirring also reduces upwelling of nutrient-rich deep water to the surface, which researchers think is directly related to die-offs in some marine mammals and declines in sardine fisheries. The dearth of nutrients cascades up the food chain through the ecosystem, resulting in less phytoplankton and hungrier sea lions and seals.

A California sea lion pup recovers at The Marine Mammal Center. Researchers say the phenomenon of the so-called 'ocean blob' of unusually warm Pacific Ocean water is causing a decrease in the food available to the pups' mothers, and increasingly, they are abandoning their offspring because they can't feed them. Credit Pat Wilson © The Marine Mammal Center

A California sea lion pup recovers at The Marine Mammal Center. Researchers say the phenomenon of the so-called ‘ocean blob’ of unusually warm Pacific Ocean water is causing a decrease in the food available to the pups’ mothers, and increasingly, they are abandoning their offspring because they can’t feed them. Credit Pat Wilson © The Marine Mammal Center

Sea lion pup Percevero (center) is one of more than 200 patients at The Marine Mammal Center in Sausalito, California. Researchers say the phenomenon of the so-called 'ocean blob' of unusually warm Pacific Ocean water is causing a decrease in the food available to the pups' mothers, and increasingly, they are abandoning their offspring because they can't feed them. Credit © The Marine Mammal Center

Sea lion pup Percevero (center) is one of more than 200 patients at The Marine Mammal Center in Sausalito, California. Researchers say the phenomenon of the so-called ‘ocean blob’ of unusually warm Pacific Ocean water is causing a decrease in the food available to the pups’ mothers, and increasingly, they are abandoning their offspring because they can’t feed them. Credit © The Marine Mammal Center

Volunteers from The Marine Mammal Center release California sea lions at Chimney Rock in Point Reyes National Seashore in 2014. Researchers say the phenomenon of the so-called 'ocean blob' of unusually warm Pacific Ocean water is causing a decrease in the food available to the pups' mothers, and increasingly, they are abandoning their offspring because they can't feed them.Credit Conner Jay © The Marine Mammal Center

Volunteers from The Marine Mammal Center release California sea lions at Chimney Rock in Point Reyes National Seashore in 2014. Researchers say the phenomenon of the so-called ‘ocean blob’ of unusually warm Pacific Ocean water is causing a decrease in the food available to the pups’ mothers, and increasingly, they are abandoning their offspring because they can’t feed them.Credit Conner Jay © The Marine Mammal Center

In 2014, the Marine Mammal Center in Sausalito saw more stranded California sea lions and northern elephant seals than average, according to center marine scientist Tenaya Norris, and record numbers of dying Guadalupe fur seals have washed up so far in 2015. Norris said that only about 60 percent of the mammals they rescue recover enough to be returned to the wild.

This year, sea lion pups in particular are stranding much earlier than usual, a sign that their mothers are abandoning them — an alarming indication that there’s just not enough food in the water.

“It’s a failure on the mothers’ part to adequately provision the pups,” Norris said. “They’ve been successfully foraging for years, so they should be able to find food if it’s out there.”

Paradoxically, Chavez said, 2014 in Monterey Bay was a “bonanza” for many species of birds, dolphins and whales. He hypothesized that nutrient upwelling didn’t disappear; it just shifted into cooler water closer to the coast, condensing an ecosystem that typically stretches tens of miles to only a few miles offshore. It’s unclear, however, whether the warm-water blob has played a role in the unusual number of dead whales — a dozen so far this year — that have washed ashore along Northern California beaches.

With still so many unknowns, the researchers in La Jolla agreed to meet again this coming fall. Until then, they all have homework: run climate models and dig deeper into data for patterns in weather, ocean chemistry and marine life.

“I don’t think that we found the smoking gun at the meeting,” Chavez said.


Read the original story: mercurynews.com

Feb 23 2015

Sardines move north due to ocean warming

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Original post: Phys.org

Sardines, anchovies and mackerels play a crucial role in marine ecosystems, as well as having a high commercial value. However, the warming of waters makes them vanish from their usual seas and migrate north, as confirmed by a pioneering study analysing 57,000 fish censuses from 40 years. The researchers warn that coastal towns dependent on these fishery resources must adapt their economies.

The continued increase in water temperature has altered the structure and functioning of across the world. The effect has been greater in the North Atlantic, with increases of up to 1.3 ºC in the average temperature over the last 30 years.

This variation directly affects the frequency and biogeography of a group of pelagic fish, which includes the sardine (Sardina pilchardus), anchovy (Engraulis encrasicolus), horse mackerel (Trachurus trachurus) and mackerel (Scomber scombrus), among others, which feed off phytoplankton and zooplankton and that are the staple diet of large predators such as cetaceans, large fish and marine birds. These fish also represent a significant source of income for the majority of coastal countries in the world.

Until now, scientists had not managed to prove whether the changes observed in the physiology of the pelagic fish were the direct result of the or if they were due to changes in plankton communities, their main food source, which have also been affected by global warming and have changed their distribution and abundance.

The new study, published in Global Change Biology and that has developed statistical models for the North Sea area, confirms the great importance of sea temperatures. “Time series of zooplankton and data have been included to determine the factor causing these patterns”, Ignasi Montero-Serra, lead author of the study and researcher in the department of Ecology at the University of Barcelona, explains to SINC.

Bioindicators of the health of the sea

To demonstrate the consequences of the warming of the seas, the research team analysed 57,000 fish censuses from commercial fishing performed independently along the European continental shelf between 1965 and 2012, extracted from data provided by the International Council for the Exploration of the Sea (ICES).

The study, the first to be carried out on such a large time scale and area, allows for the dynamics of this species to be understood in relation to the rapid warming of the oceans that has been happening since the eighties.

The results reveal that sardines and other fish (with fast life cycles, planktonic larval stage and low habitat dependence) are highly vulnerable to changes in ocean temperature, and therefore represent “an exceptional bioindicator to measure the direction and speed of climate change expected in the near future”, points out Montero-Serra.

Subtropicalization of North Sea species

Due to the accelerated increase in of the continental seas, sardines and anchovies (with a typically subtropical distribution) have increased their presence in the North Sea “even venturing into the Baltic Sea”, confirms Montero-Serra, who adds that the species with a more northern distribution (like the herring and the sprat) have decreased their presence.

The analysis is therefore a clear sign that species in the North Sea and Baltic Sea are “becoming subtropical […] where sardines, anchovies, mackerel and horse mackerel, more related to higher temperatures, have increased their presence”, says the researcher.

This is due to the pelagic fish being highly dependent on environmental temperatures at different stages of their life cycle: from reproductive migrations and egg-laying, to development and survival of larvae.

According to researchers, the changes in such an important ecological group “will have an effect on the structure and functioning of the whole ecosystem”. The expert warns that coastal towns that are highly dependent on these fishery resources “must adapt to the new ecological contexts and the possible consequences of these changes”, although they still do not know the scale of the socio-economic and ecological repercussions.