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Summary¶

Shifting Species

The oceans are predicted to warm by at least 1.8° F (1°C) in the coming century, shifting the distributions of different organisms up and down the coasts.
Heat-tolerant species like shrimp may expand their ranges northward, while heat-intolerant species like soft clams and winter flounder may lose southern habitat.
For example, the southern distribution boundaries of marine species in New England moved north when water temperatures rose in Massachusetts Bay in the mid 20th Century.
Scientists believe it is possible that commercially important soft clams could be eliminated from Chesapeake Bay if water temperatures remain near 90°F (32°C) in summer.
On the other hand, shrimp could begin to support commercial fisheries as far north as the Chesapeake Bay.
As water temperatures change, so do the creatures that inhabit marine environments, and species will have new predators, prey, parasites, diseases, and competitors to contend with.
For example, the oyster parasite Perkinsus marinus (called Dermo) has spread northward into northeastern states when winter water temperatures have risen.
How most species will adjust to these changes is unpredictable, and some that are not able to adapt may go extinct locally or globally. Others may prove to be more resilient than we know.

New Threats

Climate change brings threats to ecosystems beyond warmer water.
As the sea rises, salt marshes and mangrove swamps backed by seawalls or human development may face dramatic losses if the habitat can't migrate inland.
These ecosystems will face submersion, waterlogged soils, and salt stress.
When these ecosystems are damaged or destroyed, they can no longer mitigate damage from storms, making human communities on land are more vulnerable to coastal hazards.
Climate change is also likely to change rainfall patterns.
More runoff will mean increased saline and thermal stratification of the water at coasts and bays with more nutrients from runoff.
This causes eutrophication, the overfertilization of water by human-generated phosphates and nitrates, which leads to algal blooms that deplete dissolved oxygen.
On the other hand, less runoff would increase coastal salinity and concentrate the effects of pollution in bays, lakes, and rivers.
In 2000, a 25-month drought badly damaged the ecosystem in 100,000 acres of salt marsh along Louisiana's coast.
Permanent runoff decreases in the lagoons of Texas, Mobile Bay, Apalachicola Bay, and Tampa Bay could greatly reduce fish populations.

New Dynamics

Climate change will also likely alter wind and ocean circulation patterns.
A warmer ocean surface will increase temperature stratification, inhibiting the upwelling of nutrients and oxygen available to phytoplankton, the food source for fish.
For example, a 2.7°F (1.5°C) sea surface warming off the coast of California between 1951 and 1993 resulted in a 70% decline in zooplankton.
Changing winds can also increase or decrease upwelling as they blow on surface waters. * This cuts both ways; where upwelling might increase because of climate change-related wind shifts, ecosystem productivity could increase.
Still, scientists calculate a 5% decrease in global productivity if atmospheric CO2 doubles.

Vulnerable Ecosystems

Wetlands, estuaries and coral reefs are the most vulnerable marine ecosystems to climate change.
Ocean acidification has a lot to do with this, since decreasing pH makes it harder for corals to build and maintain their skeletons.
Scientists have calculated that under doubled CO2 conditions, coral reefs will experience on average a 20 to 30% decrease in calcification.
But there is a second reason climate change is bad news for coral: higher temperatures prompt corals to expel their photosynthetic partner algae, a traumatic event known as bleaching.
These algae make food from light, enabling corals to grow in nutrient-poor waters. Without them, corals usually die.
The world's worst recorded bleaching event occurred in 1998 and destroyed about 16% of the world's coral reefs. Sea surface temperatures were more than 0.3°F (0.2°C) warmer than average that year, a huge jump compared to prior years.
As a result of rising temperatures, most coral reefs are predicted to experience near-annual bleaching events exceeding the extent of the 1998 event by 2040, and those in the Caribbean and Southeast Asia may reach that point by 2020.

Impacts on Fisheries

Rising sea levels and increased erosion or algal blooms can both reduce available light and/or smother unbleached corals, making it harder for them to survive.
Because healthy reefs support healthy fisheries, commercial and recreational fishing may likewise suffer.
What's more, fisheries can suffer when land-based climate changes. For example, if the timing of the spring melt changes, that can harm river-spawning salmon.