As a coastal archaeologist and expert in prehistoric and historic settlement sites in the Chesapeake Bay region, Darrin Lowery of the Smithsonian’s National Museum of Natural History and University of Delaware, is carefully watching the effects of coastal erosion and rising sea levels on coastal archaeological sites. As sea levels creep slowly upward, scores of these sites are slipping under water and becoming more difficult, if not impossible, to excavate and study.

Image right: Darrin Lowery examines soils and peat marsh for evidence of ancient landscapes and sea level rise on the Mockhorn Island in Virginia. (Photo by Mike Hardesty, Washington College)

Of equal concern, says Lowery, are the chemical processes that accompany rising seas, which can modify and deteriorate the stone tools that early Americans used to hunt and prepare food and clothing hundreds of years ago. Lowery is co-author of a recent paper in the Journal of Archaeological Science on the geochemical impacts to prehistoric artifacts in coastal zones. He recently answered a few questions about his work.

Q. How do the chemical processes of sea level rise affect primitive stone tools?

A. Slowly rising sea levels result in the regular input of sediment and organic matter into low-lying areas, essentially creating areas covered in tidal marsh. Sulfidization in a tidal marsh is a process that reduces iron to its ferrous state and produces pyrite, turning stone artifacts black. A prehistoric projectile point made of jasper that has been exposed to sulfidization looks like it is made of a different type of stone called chert. This is a challenge to archaeologists because it is generally assumed that broad lithic categories can be distinguished between stone tools that are made of either chert or jasper. Over time this process can change the look of a stone artifact both inside and out.

Image left: Jasper (A) and chert (B) projectile points found at eroding shoreline sites in the Middle Atlantic. (Images courtesy Darrin Lowery)

A second process common in salt marshes is sulfuricization, which creates sulfuric acid. Highly corrosive, this acid attacks the silicate structure of a stone tool, first staining the rock with a reddish brown color and eventually causing the artifact to decompose. Having these artifacts disappear from the historic record is also of great concern to archaeologists. For a museum curator, safely storing iron-rich stone tools or artifacts that have been exposed to acid sulfate is problematic.

Q. Is sea level rise the only culprit in these changes?

A. No. The widespread practice of dredging sediment from the bottom of estuaries or along the coast and using it to build up shorelines and create living coastlines and areas for housing developments can create a situation that results in a sulfuric-acid producing machine. Marine sediments that have been oxygen-starved for several millenia are dredged up, brought to the surface and exposed to oxygen. Aerobic bacteria working on the sulfates in the sediments create sulfuric acid, as well as a series of iron oxides. If the acid is dissolving silica in iron-rich prehistoric stone tools from archaeological sites on the coast, as I have witnessed, I can only imagine how it is impacting marine life in the area adjacent to the dredge spoils.

Image right: This freshly broken projectile point made of jasper reveals the gradual precipitation of pyrite into its core, a process that has dramatically changing its color.

Q. Can you determine how much sea levels have risen since prehistoric times in North America 1,000 years ago?

A. Humans don’t like to get their feet wet so we know that prehistoric coastal sites now underwater or buried in a tidal marsh were once terrestrial, and that people were once eating, sleeping and living on these spots. Because we know that some prehistoric settlement sites in the Chesapeake Bay area are situated beneath a meter of tidal marsh peat, we can use certain “known-age” iron-rich artifacts from these submerged coastal sites to assess rates of sea level rise, as well as the rates of acid sulfate chemical change. From this we can also gauge the accuracy of the reported sea level rise rates over the past few centuries.

Surveying a large number of drowned prehistoric sites gives us the opportunity to understand those rates and the reported magnitudes.

Q. Are your projects in the Chesapeake region only focused on prehistoric settlement sites?

A. With one of my research projects, I am trying to assess the reported historic rates of sea level rise using, in part, farm fields next to tidal marshes that were first plowed long ago. We have numerous detailed historic maps showing the topographically low tidal marsh areas around the Chesapeake Bay. These maps, which encompass the last 165 years, show many tilled upland hummocks surrounded by tidal marsh. Agriculturally mixed soils are a distinctive archaeological feature formed when the thin organic soil has been turned and thickened by the plow. Back in the 17th, 18th, and 19th centuries, farmers in these low tidal marsh areas around the Chesapeake Bay didn’t have much land and they cleared every upland area right up to the edge of the marsh for cultivation. The 1840s and 1850s coastal survey maps clearly show the tilled field boundaries and historic structures on these upland hummocks.

Image left:  The chemical processes that accompany rising seas is evident on the two halves of this jasper biface projectile point. The top of this artifact was found along the eroded forested upland (B). The bottom part (C) was altered by geochemical processes in the eroded upland area surrounded by tidal marsh (D) where it was found.

I’m geo-referencing these historic maps and overlaying them with recent satellite images to form a single comparative map. By doing this I can see the historic distribution of plowed fields and farms in these low coastal areas and compare them with today. Fieldwork in these areas has allowed me to relocate the historic plowed or tilled field boundaries. Many of the shorelines have been eroded by the effects of wind and waves. However, the historic plowed fields have not been inundated or covered by tidal marsh peat over the past 150 years.

What I’ve observed is that sea levels in the Chesapeake Bay may have come up a little bit in the last 150 years but I don’t believe they have risen as much as one foot, as some groups are reporting. In all my years of shoreline surveys I have never seen a 17th, 18th, or 19th century domestic site beneath a covering of tidal marsh peat. I think people are mistaking shoreline erosion and land loss, caused by wind and water chewing away at unconsolidated terrestrial sediments, with sea level rise.

For example, currently at Kent Narrows in the Chesapeake, a series of hummocks above sea level appear as upland landscapes with the same dimensions on the earlier 1840s coastal maps. Also on the Chesapeake’s Hoopers Island are a series of hummocks that were being tilled in the 1840s, the plowed landscape features are still there adjacent to the marsh and above sea level. I have observed the same conditions on Messongo Creek on Virginia’s eastern shore.

If sea levels had risen as much as one foot over the past century, the aerial extent of these isolated upland landforms should have shrunk in size and the historic plow zones associated with the hummocks should have been covered or partially covered by expanding tidal marsh.

It is important to remember that sediment erosion along shorelines does not equate to sea level rise and sediment accretion along shorelines does not equate to a sea level fall. As an example, Sharp’s Island at the mouth of the Choptank River consisted of more than 700 acres of land in 1847, but by the mid-1950’s the island had completely eroded away. Meanwhile, in 1849, Fisherman’s Island at the mouth of the Chesapeake Bay on Virginia’s eastern shore did not exist. Fisherman’s Island today consists of more than 1,800 acres of land and the island also has an extensive forested upland.

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Image left: SERC scientist João Canning Clode observes a green porcelain crab in his laboratory at the Smithsonian Environmental Research Center.

But what happens to these fair-weather travelers during a severe cold snap, such as the one that occurred in January 2010 across much of the southeastern and eastern United States? To investigate, Smithsonian Environmental Research Center scientist João Canning Clode and colleagues at the Environmental Research Center in Edgewater, Md., tested the cold-water tolerances of invasive green porcelain crabs (Petrolisthes armatus) in their laboratory. Crabs were collected in Georgia and brought to the lab where they were subjected to one of three temperature treatments. The first was a control treatment of constant moderate winter temperature. The second was treatment in which the temperature was dropped to mimic the cold snap of January 2010, and the third treatment consisted of the extreme cold temperatures of a severe winter.

Canning-Clode and his colleagues found that most of the crabs in the control treatment survived (83%), but many of the crabs in the second cold treatment (61%) and all of the crabs in the third extreme cold treatment (100%) died. Crabs that survived cold treatment number two were sluggish, possibly making them more susceptible to predation and impacting their ability to feed, the scientists determined.

The scientists determined that prolonged exposure to cold temperatures also may compromise the green porcelain crab’s ability to overcome cumulative cold events, such as the two other record cold snaps that occurred in February and March of 2010.

Image right: A green porcelain crab (Photo by Juan Antonio Baeza)

The loss of more than 60% of their population during each cold period might explain the recent dramatic decline of the green porcelain crab in Georgia in 2010, suggesting that extreme cold spells may limit or prevent the northward spread of this invasive species.

Several climate models used to predict how species will react to climate change in the next 100 years have projected a continued decline of global biodiversity and increased spread of introduced species. Many of these models focus on temperature increases, but few have evaluated the impact of severe weather like cold snaps, Canning-Clode and his colleagues write in a paper on their study recently published at PLoS ONE.

For Canning Clode “the core message of this paper is that yes, climate change is happening, but cold is also part of this change. We believe these periodic cold events will limit the range expansion of Petrolisthes armatus as well as other Caribbean creep species” –Monaca Noble, SERC

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Image right: The coral reef crustacean Sadayoshia edwardsii (Photo by Gustav Paulay)

At depths of between 8 and 12 meters (26 to 39 feet), scientists collected dead coral heads from five different locations. At two sites where removing coral is prohibited, the scientists collected man-made sampling devices that had been left in the water for one year. Combined, the coral heads and devices had a surface area of just 6.3 square meters (20.6 square feet), yet 525 different species of crustaceans were found living on them.

Image left: Laetitia Plaisance searches for crustaceans on a dead coral head. (Photo by Christine Hoekenga)

“So much diversity in such a small, limited sample area shows that the diversity of crustaceans in the world’s coral reefs—and by implication the diversity of reefs overall—is seriously under-detected and underestimated,” says Nancy Knowlton, the Sant Chair for Ocean Science at the Smithsonian’s National Museum of Natural History, co-author of the survey that was just published in the journal PLoS ONE.

“We found almost as many crabs in 6.3-square meters of coral as can be found in all of the seas of Europe,” explains Knowlton. “Compared to the results of much longer and labor-intensive surveys we found a surprisingly large percentage of species with a fraction of the effort.” This shows, says Knowlton, that the statistical uncertainty of estimates of the numbers of animals living in the world’s coral reefs “is huge.”

Image right: Nancy Knowlton dismantles a dead coral head in search of crustaceans living inside.

The study is the first biodiversity survey of coral reefs from three tropical oceans to use DNA barcoding. Lead author Laetitia Plaisance of the Smithsonian’s National Museum of Natural History and the Scripps Institution of Oceanography, explains: “Given the urgency of the state of the world’s coral reefs we used DNA barcoding because it is very fast and very cheap,” she says. “We just need to take a bit of tissue from a specimen and sequence it.”

Image left: The coral-reef crustacean Thor ambionensis (Photo by Gustav Paulay)

“DNA barcoding provides a standardized, cost effective method of coming to grips with the staggering diversity of the world’s oceans,” Knowlton explains. “It has enormous potential for use in broad global surveys, allowing us to find out what is living in the ocean now, and to keep track of it in the future.”

Crustaceans collected for the survey were only those the scientists could see, and ranged in size between 5 millimeters and 5 centimeters (0.2 to 1.9 inches) long. All animals from which DNA was sequenced were preserved so they could be examined by taxonomists at a later date.

Image right: A coral-reef crustacean known as Raoulserenea ornata (Photo by Gustav Paulay)

“We collected dead corals because live corals defend themselves from being inhabited by other invertebrates,” Plaisance says. “Live corals have only symbionts—crabs and shrimp—living with them and these animals also defend their coral.”
Once a coral dies its structure becomes covered with algae, sponges, crustaceans, worms, mollusks and other creatures.

Image left: The coral-reef crustacean Pilumnus tahitensis (Photo by Gustva Paulay)

Given the complexity and extent of the world’s coral reefs, the survey covered only a very limited depth and habitat range, Plaisance explains, “and yet we have so many more species than we ever expected.”

Present estimates of reef species diversity are between 600,000 to more than 9 million species worldwide. “We cannot give a new estimate today but we may be able to in a few years,” Plaisance says.

Using man-made sampling structures at some 50 sampling sites around the world, Plaisance is now working with the Smithsonian and the National Oceanographic and Atmospheric Administration on another survey that will include all of the many organisms that live on coral reefs.

“The Diversity of Coral Reefs: What Are We Missing?” was co-authored by Laettia Plaisance, Nancy Knowlton, M. Julian Caley of the Australian Institute of Marine Science; and Russell E. Brainard of the National Oceanic and Atmospheric Administrating.

Sampling locations for this study were: Indian Ocean—Ningaloo, western Australia. Western Pacific Ocean—Lizard and Heron Islands, Great Barrier Reef, Australia. The central Pacific—French Frigate Shoals, northwestern Hawaiian Islands; Moorea, French Polynesia; and the northern Line Islands. The Caribbean—Bocas del Toro, Panama.

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The dodo’s large size and inability to fly were adaptations that allowed this bird to survive some of the most hostile conditions and climactic events imaginable. Only in the 1600s did a force more deadly than extreme drought and volcanic eruptions lead to its extinction: humans.

Image right: Painting of a dodo head by Cornelis Saftleven. Done in 1638,  this painting may be one of the last illustrations made of a live dodo. (Image from Boijmans Museum, Rotterdam)

In a recent paper in the journal “The Holocene” a team of scientists detail the extreme conditions that caused the death of some 500,000 animals on Mauritius during the mid-Holocene at around 4000 years ago. The evidence is a thick bed of fossil bones on Mauritius that spans an area of about 5 acres—the site of a former freshwater lake bed. The fossil layer is dominated by the remains of thousands of dodos and giant tortoises, as well as many small reptiles and flying birds.

Image left: Dodo bone in a matrix of mud, seed and other fossils excavated in a dry lake bed on the Island of Mauritius. (Image copyright Kenneth Rijsdijk/Dodo Research Programme)

Using radiocarbon dating of the bones, oxygen isotope analysis of geologic features on Mauritius and nearby islands, and the study of the island’s water table, the scientists determined the animals died during an extreme drought that lasted several decades. “Dodos, tortoises, lizards and other animals gathered here because the lake was one of the few sites on the island with fresh water,” says Hanneke Meijer, an ornithologist at the Smithsonian’s National Museum of Natural History and one of the paper’s co-authors.

“It is evident that a lot of animals suffered and died during this period, and their populations were greatly reduced,” Meijer continues, “but no species, including the dodo, went extinct during this extreme drought.” Fossil evidence reveals that “all animals were still living and the island’s ecosystem was intact at the time humans arrived in the 1600s.”

Image right: The excavation site on the island of Mauritius where the remains of some 500,000 animals were found, victims of an extreme drought some 4,000 years ago. (Image copyright Mikel Rijsdijk/Dodo Research Programme)

The dodo was resilient, and perfectly adapted to the island’s habitat, Meijer explains. “The island had no predators or carnivores and the dodo had no need to flee, so it lost its ability to fly. It received a reputation as stupid because it did not flee from humans” and human-introduced predators after they arrived at the dodo’s home in the 1600s.

Today, Meijer says, the forest cover on Mauritius has been reduced by 98 percent with only a few patches of original forest remaining. Considerable resources have been directed to preserving the island’s few remaining endemic species, such as the Mauritian kestrel. (The island’s giant tortoises went extinct in the 1800s when Dutch trade ships filled their holds with these long-lived animals to use as fresh meat on long voyages to and from Indonesia. “Mauritius was a popular stop because it provided fresh water and lots of food,” Meijer says)

Image left: Researchers at the Mauritius Island excavation site sieving excavated mud for small bones, teeth and plant remains. (Image copyright Mikel Rijsdijk/Dodo Research Programme)

Should another extended drought occur similar to the mid-Holocene event, it is very likely the remaining endemic species on Mauritius would not survive as the environment is so degraded. “Even many of the native plant species in the few remaining forest patches would probably perish,” Meijer says.

“With modern climate change scientists are very interested in how island animals adapt, as their ability to move to less disturbed areas is limited,” Meijer explains. “It has always been thought that animals on islands are particularly sensitive to climate change.” In the case of the dodo and other species on Mauritias, this new study reveals an island population highly resilient to climate change.

The article “Mid-Holocene (4200 kyr BP) mass mortalities in Mauritius (Mascarenes): Insular vertebrates resilient to climatic extremes but vulnerable to human impact,” appeared recently in the scientific journal “The Holocene.” (Rijsdijk, K.F., Zinke, J., de Louw, P.G.B., Hume,J.P., van der Plicht, J., Hooghiemstra, H., Meijer, H.J.M., Vonhof, H.B., Porch, N., Florens, F.B.V., Baider, C., van Geel, B., Brinkkemper, J., Vernimmen, T. & Janoo, A., 2011. Mid-Holocene (4200 kyr BP) mass mortalities in Mauritius (Mascarenes): Insular vertebrates resilient to climatic extremes but vulnerable to human impact. The Holocene, doi:10.1177/0959683611405236)

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Images left and below: The variation in biodiversity from place to place, called beta diversity, are actually very similar as you move from the tropics to the poles when you account for the number of species present in the first place. (Photos by Christian Ziegler)

“The same ecological processes seem to be working worldwide. The difference is that tropical organisms have been accumulating for vast periods of time,” said Nathan J.B. Kraft, post-doctoral fellow at the University of British Colombia, who led the research team.

“This study shows how collecting data using the same methods at sites around the world, similar to what we do at the Center for Tropical Forest Science–Smithsonian Institution Global Earth Observatories Network, offers new insights into the processes that shape ecological communities,” said Comita, formerly a post-doctoral fellow at the National Center for Ecological Analysis and Synthesis, now an assistant professor at The Ohio State University. “We found that measurements of variation in biodiversity from place to place, called beta diversity, are actually very similar as you move from the tropics to the poles when you account for the number of species present in the first place.”

Forests in Canada and Europe may have much more in common with tropical rainforests than previously believed. “We see that biodiversity patterns can be explained not by current ecological processes, unfolding over one or two generations, but by much longer-term historical and geological events,” said Kraft, who will join the faculty at the University of Maryland next year.

“Fossils tell a similar story,” said STRI scientist, Aaron O’Dea, co-author, with Willem Renema and others, of a 2008 article in Science showing that marine biodiversity hotspots could be traced back to ancient areas of tectonic activity. “Geological history reveals that glaciations and mass extinctions have lasting effects on the structure of biological communities. It bears witness to the devastation that occurs when accumulated biodiversity is lost: a threat we are facing today.”

The team, which also included researchers from institutions in the U.S., Canada and New Zealand, was supported by the U.S. National Center for Ecological Analysis and Synthesis and the U.S. National Science Foundation.–Beth King, Smithsonian Tropical Research Institute

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Image left: A honeybee pollinates and apple blossom.

“Invertebrate conservation is hard to justify when many people see each insect as a potential pest or each spider as a potential health threat,” write the paper’s authors, who include entomologists Terry Erwin and Pedro Cardoso of the Smithsonian’s National Museum of Natural History. In general the public is unaware of the critical role invertebrates play in the health of the ecosystem or the conservation threats that these creatures now face.

In addition, policymakers are often poorly informed about the details of invertebrate conservation, the scientists say. “Many assume that in protecting a single large animal, that animal will serve as an ‘umbrella species’ protecting all the other species—including invertebrates—in its habitat. “This view is however largely unsupported and untested,” the scientists say.

Image right: The tree-nesting tropical ant Cephalotes atratus (Stephen Yanoviak)

Remarkably, most of the world’s invertebrates remain unknown and have never been studied or described by scientists. The vast majority of species now going extinct due to human activities—about 3,000 a year—belong mainly to understudied groups of invertebrates, ‘the little things that run the world,’ the scientists write.  “Because most invertebrates are undescribed, their geographic distribution is unknown as is their abundance, ways of life and sensitivities to pollution and habitat change.” Basic science for the study of invertebrates is scarce and underfunded.

Image left:  Bonaire box jelly fish, St. Vincent Island, Caribbean (Photo by Ned DeLoach)

To remedy the problem the scientists offer a number of suggestions, including:  More invertebrates should be placed on red lists of endangered species and in environmental impact statements; a stronger link must be made in the public imagination between invertebrate conservation and human well-being; sampling and analytical methods for biodiversity assessment and monitoring should be improved; and long-term ecological studies should be initiated to monitor ecosystem change.

“Invertebrate conservation is only possible with the preservation of ecosystems and their structure, function and processes,” the scientist’s conclude. “Only by preserving all species and guaranteeing interactions and ecosystem services may we reach the goal of overall biodiversity conservation.”

Photo right: A living colony of cupuladriid bryzoans, tiny coral-like marine organisms. (Photo by Aaron O’Dea)

“The seven impediments in invertebrate conservation and how to overcome them,” appeared in the journal Biological Conservation, and is authored by Pedro Cardoso, Terry Erwin, Paulo Borges of the Azorean Biodiversity Group, Portugal, and Tim New of La Trobe University, Australia.

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The research was led by scientists from the Centre for Ecology and Hydrology and the University of Cambridge, UK. The results were published online today in the scientific journal “Nature Climate Change.”

Image right: Leaf litter around the buttress roots of a tropical tree at the study site in Panama.

The researchers used results from a six-year experiment in a rainforest at the Smithsonian Tropical Research Institute in Panama, to study how increases in litterfall–dead plant material such as leaves, bark and twigs which fall to the ground–might affect carbon storage in the soil. Their results show that extra litterfall triggers an effect called ‘priming’ where fresh carbon from plant litter provides much-needed energy to micro-organisms, which then stimulates the decomposition of carbon stored in the soil

Lead author Emma Sayer from the Smithsonian Tropical Research Institute and the Centre for Ecology and Hydrology said, “Most estimates of the carbon sequestration capacity of tropical forests are based on measurements of tree growth. Our study demonstrates that interactions between plants and soil can have a massive impact on carbon cycling. Models of climate change must take these feedbacks into account to predict future atmospheric carbon dioxide levels.”

Image left: Undergrowth showing leaf litter at the Smithsonian Tropical Research Institute study site. (Photos by Emma Sayer)

The study concludes that a large proportion of the carbon sequestered by greater tree growth in tropical forests could be lost from the soil. The researchers estimate that a 30% increase in litterfall could release about 0.6 tonnes of carbon per hectare from lowland tropical forest soils each year. This amount of carbon is greater than estimates of the climate-induced increase in forest biomass carbon in Amazonia over recent decades. Given the vast land surface area covered by tropical forests and the large amount of carbon stored in the soil, this could affect the global carbon balance

Tropical forests play an essential role in regulating the global carbon balance. Human activities have caused carbon dioxide levels to rise but it was thought that trees would respond to this by increasing their growth and taking up larger amounts of carbon. However, enhanced tree growth leads to more dead plant matter, especially leaf litter, returning to the forest floor and it is unclear what effect this has on the carbon cycle.

“Soils are thought to be a long-term store for carbon but we have shown that these stores could be diminished if elevated carbon dioxide levels and nitrogen deposition boost plant growth,” Sayer adds.

Co-author Edmund Tanner, from the University of Cambridge, said, “This priming effect essentially means that older, relatively stable soil carbon is being replaced by fresh carbon from dead plant matter, which is easily decomposed. We still don’t know what consequences this will have for carbon cycling in the long term.” –Source: Center for Ecology and Hydrology

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The idea that the colder temperatures of high-latitude regions act as a natural barrier to invasive species is a misconception.

Image right: The European green crab, Carcinus maenas. (Photo by Hans Hillewaert)

“Environmental conditions along the coastline of Alaska and many other high-latitude areas would not prevent successful invasion of non-native marine species with distributions now restricted to lower latitudes,” the scientists write in a recent paper published in the conservation biogeography journal “Diversity and Distributions.”

The team, which includes Anson Hines, director of the Smithsonian Environmental Research Center; Gregory Ruiz, head of the Center’s Marine Invasions Research Lab, and Portland State University ecologist Catherine de Rivera, base their predictions on a series of niche models they created for four taxonomically diverse marine species: the European green crab (Carcinus maenas), rough periwinkle (Littorina saxatilis), bay barnacle (Amphibalanus improvisus) and the sea squirt (Styela clava).

Image left: Sea squirt, Styela clava. (Photo courtesy Fisheries and Oceans Canada)

Using a wide range of scientific data detailing where each species is presently established around the globe—both in their natural and introduced ranges—the scientists created computer models projecting where else on Earth they might logically thrive. Much of the Pacific coast of Alaska came up as a strong match for each of the species. The geographic range of all four animals received a strong nudge northward in the models when higher temperatures predicted from climate change (a rise of between 1.5 and 7 degrees Celsius) were factored in.

The scientists point out that their study focuses on only four invasive species out of more than two hundred that have become established in the region adjacent to Alaska, from California to British Columbia. If more invasive species do move north into Alaska it will likely come through an increase in the frequency and intensity of introductions, the scientists write—namely on commercial ships and recreational vessels, through aquaculture, and through the live trade of animals as food, pets and bait.

Invasive species ride in the ballast water of oil tankers and some cargo ships. Cruise ships and cargo barges can carry invasive species attached to their hulls.

Image right: The shell of the rough periwinkle, Littorina saxatilis. (Photo Amy Benson, USGS)

Alaska has been spared so far from an influx of invasive species, the scientists say, because the magnitude of shipping and other human-mediated transfer mechanisms has been historically low. In recent years however, vessel traffic has increased considerably along the Alaskan coast. For example, more than 7,000 ships arrived to Alaskan waters in 2004 alone, discharging over 4 million metric tons of ballast water. Shipping and other human activities are projected to increase in this region, especially if climate change brings warmer temperatures.

The probability of invasions in Alaska is likely to increase with global warming even without the help of ballast water introductions, the scientists conclude. “On a global scale, the suitability of Alaskan waters is not unique, as other high-latitude areas also offer environmental match for these species,” the scientists write.

“The ranges of all four species have slowly been moving northward up the coast and they may spread further up the coast by ocean currents,” Catherine de Rivera says.

The article “Potential for high-latitude marine invasions along western North America,” authored by Catherine de Rivera, SERC ecologist Brian Steves, SERC ecologist Paul Fofonoff, Anson Hines and Greg Ruiz, appeared in the journal Diversity and Distributions.

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