The “poster child” for global warming is the polar bear. But many other animals are already feeling the effects of global climate change on the oceans. Find out about the changing climate's impact on the earth’s population of sea turtles, right whales, penguins, seals, lobsters, and cod.
Image taken during a NOAA expedition
What is the effect of reduced sea ice on polar bears?
The Arctic’s top predator, the polar bear, is affected both by the reduction in sea ice and by reduced stocks of its primary food, the ringed seal. Polar bears use sea ice as a platform for hunting their prey and for resting. They catch adult seals when they come up through the holes in the sea ice and search out the snow-covered ice caves of seal pups.
But sea ice is decreasing throughout their Arctic range due to climate change. Ice reduction decreases the abundance of seals, and increases the amount of energy and time needed for hunting, leaving less energy for reproduction. Rising temperatures mean that large areas of the ocean that were once frozen throughout the year now become open water. Polar bears often have to swim long distances between areas of stable ice.
As sea ice becomes thinner and multi-year ice disappears, a greater proportion of females make their dens on land, expending more energy to get there. Decreases in the physical condition of females and in reproduction have already been documented.
Image from a USGS expedition
Polar bears are often described as completely dependent on ice for their survival. The Arctic Climate Impact Assessment Report in 2005 stated that polar bears are unlikely to survive the complete loss of summer sea-ice cover. A 2007 report from the U.S. Geological Service estimated that as a result of sea-ice decline, today’s population of about 22,000 polar bears would decrease by two-thirds by the year 2050, even with moderate projections for future climate change.
In 2008, the U.S. Fish and Wildlife Service listed the polar bear as a threatened species under the Endangered Species Act, the nation's primary tool for conserving imperiled plants and animals. A threatened species is defined as “likely to become endangered in the foreseeable future.”
How are sea turtles affected by climate change?
Taken by New England Aquarium
Educator Jessica Lavash in
Padre Island, Texas.
Rising temperatures, rising sea levels and other trends are having an effect on the world’s sea turtles. Six sea turtles are already on the endangered species list — green turtles, hawksbills, loggerheads, Kemp’s ridleys, Olive ridleys and leatherbacks.
All female turtles come ashore at nesting beaches, dig nests in the sand, lay their eggs and then return to the sea. Erosion of nesting beaches caused by rising sea level and more intense storms adds the potential for further dangers to nesting beaches where people, dogs, rats and raccoons already prey on the eggs of marine turtles.
Climate change directly affects the reproduction of sea turtles in three ways. First, sea level rise will affect significant nesting beach areas on low-level sand beaches such as Bonaire, the Maldives and the Great Barrier Reef. Second, rising temperatures increase the chance that sand temperature will exceed the upper limit for egg incubation, which is 34 degrees C. Third, rising temperatures bias the sex ratio toward females because temperature during incubation determines the sex of the egg. Loggerhead turtle nests in Florida are already producing 90 percent females owing to high temperatures, and if warming raises temperatures by an additional 1 degree C or more, no males will be produced there.
Adult feeding patterns are also affected by climate change. Sea grass beds are in decline, water temperature is higher on intertidal sea grass flats, and coral reefs, typically feeding grounds for green turtles, are affected by bleaching.
was rescued, rehabilitated and
released with help from the
New England Aquarium in 2005.
Sea turtles have existed for more than 100 million years and have survived ice ages, sea level fluctuations of more than 100 meters and major changes to the continents and the seas. As a result, they may be able to respond to unfavorable nesting temperatures or inundation of beaches as they have in the past, by seeking out new nesting sites or modifying the seasonality of nesting. It may however take decades or centuries for sea turtles to re-establish and stabilize their habitats, and steadily encroaching human development of coastal areas makes the availability of new habitat for them very limited.
How are right whales affected by climate change?
A member of the New England Aquarium's
observing a right whale.
North Atlantic right whales, which can grow to more than 55 feet long and weigh 70 tons, range from Nova Scotia to the southeastern United States and migrate the length of the East Coast. Today there are fewer than 500 right whales left in the world. These animals have been protected since 1935 and listed as endangered since the early 1970s.
It has long been recognized that humans have brought the right whale to the brink of extinction through whaling and commercial fishing activities. But there may be another human activity that could have an even greater impact on the remaining whales — human-induced global warming. The key is a tiny crustacean, Calanus finmarchicus, a key food source for right whales, as well as for cod, haddock, herring and mackerel. Without dense patches of this zooplankton, female whales can’t bulk up to prepare for calving, carry a pregnancy to term or produce enough milk. When the concentration of zooplankton is too low, right whales do not feed; such highly concentrated patches often occur where currents converge or at the boundary of water of different densities. Changes of seawater temperature, winds and water currents can affect patch formation of zooplankton. Aquarium researchers have noted that shifts in zooplankton populations could affect North Atlantic Right Whale ranges.
Between 1997 and 1999, zooplankton numbers plummeted. Over 50 years of observation, scientists have learned that zooplankton are abundant when the North Atlantic Oscillation (NAO) Index — which charts variations in atmospheric pressure centers over the North Atlantic — is predominantly positive. When it becomes negative, the numbers decline. Right whales illustrate the dramatic “downstream” significance of NAO conditions. In the winter of 1996, the NAO index exhibited its largest drop of the century. This atmospheric phenomenon has a dramatic effect on the great ocean conveyor belt, the mixing of the warm salty waters that move north with the Gulf Stream and the cold less-salty water moving south from the Labrador Sea. Resulting changes in the water in the Northwest Atlantic determine zooplankton ecology.
Photo taken by the Aquarium's
Right Whale Research Team during the
annual Photo ID expedition to Lubec, Maine.
Video of this event is on their blog.
The big drop occurred in 1998; it took two years before the 1996 drop in the NAO Index had its effects on the zooplankton population downstream in the Gulf of Maine, where it dropped tenfold. By 1999 the zooplankton numbers were climbing back up again. However, because of the right whales’ long reproductive cycle, the consequences of this climatic event were not over yet for the whales. In 1999, only one right whale calf was born, the lowest on record (there were 21 born in 1996). But in 2001, two years after the abundance of the zooplankton increased, 30 right whale calves were born, the most recorded since 1982.
Where does all this fit into global warming? Some scientists suggest that increased climate variability or a prolonged period of negative NAO index, which are both expected under a global warming scenario, would undermine the already tenuous recovery of the North Atlantic right whale.
The New England Aquarium is an active supporter of right whale research and an integral part of the North Atlantic Right Whale Consortium, founded in 1986. The consortium, which includes U.S. and Canadian institutions, includes individuals and organizations active in right whale research, conservation and management. Together, they are working to ensure the long-term conservation and recovery of right whales in the North Atlantic. Hear more on this issue in this NPR presentation of Dr. Robert Kenney, adjunct professor of oceanography at the University of Rhode Island, discussing the impact of warmer oceans and changing food supply on the critically endangered North Atlantic right whale.
A wild southern rockhopper penguin
photographed off the coast of Chile
by New England Aquarium penguin
biologist Caitlin Hume. More photos and
videos are on her blog.
How have penguins been affected by global climate change and a decrease in sea ice?
Beginning in the mid-1960s and stabilizing in the mid-1980s, there were small temperature increases, ranging from .97 to .3 degrees C per decade. These temperature increases correlate, with a two- to nine-year lag, with a severe decline in rockhopper penguins, emperor penguins and Adelie penguins, as well as albatrosses and seals. All of these species are primarily squid eaters, eating krill and fish to a lesser extent. The reason for the decrease is not known, but declines in sea ice and a consequent decline in krill are likely.
There was also a dramatic decline in penguins in Antarctica, probably caused by disappearing sea ice over the past century. Adelie and emperor penguins, which are dependent on sea ice, have declined from 300 breeding pairs to 9 in the Western Antarctic peninsula, with a decline of 50 percent in Terre Adelie. Adelie penguins have declined by 70 percent on Anvers Island along the Antarctic Peninsula but are thriving at more southerly Ross Island. Conversely, open-ocean feeding penguins, the chinstrap and the gentoo, have taken advantage of the ice’s retreat, invading southward along the Antarctic Peninsula.
Many penguins have survived severe climate change during the last 3 million years, showing the resilience of the species. Adelie penguins and chinstrap penguins, for example, have founded or deserted colonies on different parts of the Antarctic coast at various times during the past 5,000 years in response to changes in the amount of sea ice and the amount of ice-free land. More penguins nested at Terra Nova Bay on the southern Victoria Land coast between 3,900 and 4,900 years ago than today, because the weather was warmer and the bay less ice-bound. Thus these species may not go extinct, as other locations for feeding and breeding could become available. Nevertheless, the temperature-related change they face certainly confers risk. The issue now may be about the rapid pace of the climate changes, possibly coming faster than the birds can adapt.
A harp seal sighted in Boston's inner harbor.
More photos and description on the Marine Mammal blog.
How have seals been affected by climate change?
Various Arctic wildlife populations have been forced to adapt to changes in their habitats. According to scientists, the retreat of sea ice has reduced the platform that seals traditionally use to rest between searches for fish and mussels. The warming climate is changing the ocean’s ecology to such a degree that the survival of seals and their young has increasingly become a concern for marine biologists. The loss of sea ice in Antarctica has caused a decrease in the amount of algae, plankton and krill, the foundation of the ocean’s food chain.
In recent years, scientists have directed their attention to the impacts of climate change in the Bering Sea’s ecosystem, which appears to be showing early climate change effects including the reduction of food for bottom-dwelling creatures. A recent study shows that global warming will greatly affect the Bering Sea’s phytoplankton. Any changes affecting this ecosystem are of crucial importance, as the Bering Sea produces half of the fish caught in the United States, and almost a third worldwide, every year. The Bering Sea has typically had a large presence of phytoplankton. Phytoplankton are eaten by zooplankton, which are in turn eaten by large fishes. The changes observed in the Bering Sea’s ecosystem affect the marine mammals, including seals, that are part of its food chain.
One of the lobsters in the New England Aquarium's
What is the impact of warmer waters on lobsters?
The American lobster has long been a symbol of New England, particularly of the state of Maine. Lobster habitats range from Long Island and northern New Jersey to the mouth of the Bay of Fundy in Canada.
Lobsters are cold-blooded, their body temperatures determined by the water in which they live. Higher temperatures cause cold-blooded animals to use more energy for respiration, leaving less energy for feeding, growth, energy storage, immune response and reproduction. Much of a lobster's life is related to the temperature on the ocean floor — what it eats, how successfully it breeds, where it migrates.
As ocean temperatures fluctuate, so do the lobsters' habits. Lobsters can respond to temperature changes by changing their habitat. For example, lobsters are likely to move toward higher latitudes or to areas cooled by tidal mixing. In New England, for example, such populations will move north toward the Bay of Fundy.
Warming temperatures increase the lobster’s respiration rate and oxygen needs while reducing the amount of dissolved oxygen available. Research has found that as water temperatures rise above 69 degrees F, lobsters' respiration rate increases to a point where their demand for oxygen exceeds the supply, causing physiological stress.
Scientists have also seen evidence linking rising seawater temperatures to the spread of lobster shell disease in Massachusetts’ waters. Caused by a bacterial infection in the carapace, lobster shell disease has become dramatically more common in recent years. A new type of shell disease was observed in New England in the late 1990s, when temperatures were higher than in previous years, and has been steadily moving northward toward Maine and Canada. The incidence of shell disease is strongly related to the number of days during which water temperatures exceed 20 degrees C (68 degrees F).
The mechanism by which higher temperatures increase shell disease is not yet known, although it may increase the rate of growth of a bacteria suspected to cause the disease. It also affects the lobsters’ rate of growth so that they attain sexual maturity more quickly. In contrast to males, which molt every year, mature females do not molt during the year they carry eggs, and only molt every two years. This long period provides more time for bacteria to infect females’ shells, and higher sea temperature accelerates the rate at which they attain this vulnerable state.
The Aquarium actively collaborates with fishermen and scientists to develop a greater understanding of lobster shell disease and to develop possible solutions. In the Aquarium’s lobster lab, lobsters are hatched, raised and bred in a small research hatchery onsite. The Aquarium has the only year-round production facility for American lobsters in the United States. Hear more about American lobster shell disease in this NPR presentation from Senior New England Aquarium scientist Michael Tlusty.
A white lobster grown as
part of the Aquarium's
One surprising recent development has been an increase in numbers of lobsters in the Gulf of Maine. This may also be due to ocean warming, as It may be that the newly warmer waters spur a longer growing season, encourage more rapid growth, cause lobsters to hatch earlier and provide better conditions for larval lobsters. Another reason for the larger numbers may be that warmer temperatures and over-fishing have depleted the stocks of cod, a species that preys on lobsters.
A farmed Atlantic cod photographed
as part of the University of New Hampshire's
How will climate change affect local fish such as cod?
Commercial fish and shellfish, including cod and lobster, have thresholds of water temperature that limit the conditions under which they can reproduce and grow. Temperature influences the location and timing of spawning, which affects the growth and survival of young cod. It is believed that a temperature of 54 degrees F is the maximum for cod survival and that temperatures above 47 degrees lead to a decline of growth and survival of cod.
Traditionally, the conditions on Georges Bank, an enormous shoal off the Massachusetts coast, have been ideally suited to the growth and reproduction of cod. There, the intersection of the warm Gulf Stream with the cold, nutrient-rich Labrador current provides optimum conditions for phytoplankton, the zooplankton that eat them and the cod larvae that eat them.
Atlantic cod has been a staple of the New England fishing industry since English sea captains named Cape Cod for their plentiful catch. Despite decreased yields due primarily to over-fishing in recent years, Massachusetts is still the top cod-producing state, with fish coming from Georges Bank and the Gulf of Maine. The Aquarium is working to help maintain the species stock by being engaged in research to improve cod survivability after being released. Generally, phases of low production have corresponded with periods of high water temperatures and other factors.
The effects of rising temperatures on cod, for example, may be significant. Currently, temperatures in our waters are at the top of cod’s favored range. If, under the IPCC high emissions scenario, the maximum temperature for cod is reached, this species could disappear from the waters south of Cape Cod. Off Georges Bank, cod could be vulnerable to loss of habitat. And the Gulf of Maine, north from Georges Bank, is likely to continue to support adult cod throughout the century, but not juvenile cod.