Thursday, July 15, 2010

Bellwether Indicators of Cape Cod’s Salt Marshes

Joseph Ingoldsby

As you sit on the beaches of Cape Cod this summer, look closer at the subtle changes to the coastal landscape that herald shifting landscapes and species in a rapidly changing world. For example, the advance of the southern Sesarma reticulatum crab around the tip of Provincetown to Wellfleet and beyond raises a number of questions about observable changes due to climate change. Ocean temperature increases with increased tidal inundation and incremental sea level rise along the coast are precipitating a migration of species and a loss of biodiversity. The advance and colonization of the Sesarma crab to Cape Cod represents a broken trophic cascade, where native predators are missing from the equation. The raccoon population on Cape Cod has crashed with outbreaks of distemper. The night herons lost their historic rookeries to development of coastal properties along the shore. The diamondback terrapin ended up in the soup pots of sailing ships. The predacious blue crab was slow to follow the expansion of the nocturnal Sesarma crab, which over-winters deep beneath the peat and root mass of the tall Spartina alterniflora. The Low Marsh Zone serves as a protective defense between land and sea.

The High Marsh Zone has not been spared from the incremental changes of ocean warming and expansion. Spartina patens- salt marsh grass has been documented to die back along the tidal creeks, where tidal inundation is more frequent and prolonged. The weakened plants are more susceptible to disease and there is debate on the opportunistic infection of pathogens and galls, affecting the Spartina patens plants in certain regions along the Atlantic coast.

Scientists express concern about documented changes along the coastal Atlantic. In the journal Nature, scientists from the United States, Britain, Germany and Japan said they have found "robust" evidence that sea levels have risen over the past 16 years as the upper layers of the world's oceans have warmed and caused water expansion. They looked to the ocean for signals of climate change because the oceans absorb up to 90 percent of the heat that reaches Earth from the sun. The oceans have warmed by at least three-tenths of a degree Fahrenheit since 1993, and where sea levels were rising by only 1 millimeter a year 100 years ago, the rate is now 3 millimeters a year, said John Lyman, an oceanographer with the National Oceanographic and Atmospheric Administration. The effects may seem small, but they are highly significant, he said.

Recent projections on the velocity of climate change by scientists at the Carnegie Institution, Stanford University, the California Academy of Sciences and the University of California, Berkeley calculated the temperature velocity for different parts of the world based on current and projected future climate models. The findings pinpoint those ecosystems of critical environmental concern where biodiversity is most threatened by the speed of climate change. The study found that global warming would impact flatter areas as mangrove swamps, flooded grasslands, coastal marshes and savannas with a velocity of 1 km a year.

This will lead to a relocation of plant and animal species to shifting landscapes or extinctions within the century. Scientists have told the UN that our actions have pushed extinctions to 1,000 times the historic natural background rate. Biodiversity losses accelerate as ecosystems approach tipping points. The five main pressures driving biodiversity loss are habitat change, over-exploitation, pollution, invasive alien species and climate change.

In the United States alone, 30% of the nation’s plant and animal species are at risk of disappearing, and over 500 species are missing or may already be extinct. We have lost over half of our nation’s original wetlands, 98% of our tall-grass prairies, 99% of America’s original savannas, and virtually all virgin forests east of the Rockies. Today, there is recognition that change is progressing with such speed that shifts and loss of plants and species can be documented within our lifetime.

© Joseph Emmanuel Ingoldsby, 2010

My related publications include Vanishing Landscapes: The Atlantic Salt Marsh, Leonardo Journal 42-2-2009, MIT Press; Requiem for a Drowning Landscape, Orion Magazine, 2009; and Vanishing Landscapes and Endangered Species, The Science Exhibition- Curation and Design, Museums etc Press, U.K. 2010

Joseph Ingoldsby can be reached at

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