USGS Launches Multidisciplinary Investigation of Northeast Pacific Sea Otter Populations and Nearshore Ecosystems

By Jim Bodkin, Christian Zimmerman, Dave Douglas, Keith Miles, Lizabeth Bowen, Tim Tinker, William Perry, Lyman Thorsteinson, Mike Murray (Monterey Bay Aquarium), Seth Newsome (University of Wyoming), and Linda Nichol (Fisheries and Oceans Canada) March 2010

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Above: Sea otter in Simpson Bay, Prince William Sound, Alaska, 2002. The sea otter is a keystone species that plays a critical role in maintaining the structure and health of its ecosystem. Photograph © R. Davis, Texas A&M University. [larger version]

At the interface between oceans and continents, coastal ecosystems are shaped not only by processes unique to the nearshore environment but also by influences from the neighboring sea and land. Influences from the open ocean include currents that deliver nutrients (such as nitrogen and phosphorus) and food resources (such as phytoplankton—"primary producers" that convert inorganic material and sunlight into biomass—and zooplankton, which transfer that biomass to animals higher in the food web). Ocean influences also include factors that challenge the present-day equilibrium, such as ocean acidification, sea-level rise, and ocean warming. Coastal ecosystems receive freshwater, sediments, and additional nutrients from the land, which can impose challenges that include pollutants and pathogens associated with burgeoning human populations.

Our understanding of the physical processes that cause climate change, sea-level rise, and ocean acidification is advancing, thanks to accumulating data and refined computer models; but the implications for biological systems are only beginning to be explored. To improve our understanding of the factors affecting nearshore biological communities, the new USGS project is focusing on sea otter populations in the Northeast Pacific. Sea otters occur in geographically separate populations that span more than 30° of latitude and vary in status from gradually increasing to declining. In the sea otters' food web, the primary producers are kelps (large seaweeds belonging to the class of brown algae); and food energy is transferred through benthic (bottom-dwelling) invertebrates, such as clams, crabs, mussels, and urchins, to high-level consumers, such as fishes, birds, and mammals. The sea otter is an apex predator (at the top of its food web) and a keystone species. Just as an arch will collapse if the keystone at its top is removed, an ecosystem will change drastically if a keystone species is removed. Sea otters serve as a focal point for understanding the variables that influence their ecosystem—sea otters integrate the combined effects of watersheds, oceans, and the nearshore environment into their diet, behavior, condition, and health, which is ultimately reflected in their abundance and population trends over time.

Above: Geographic bounds and conceptual components of USGS Pacific nearshore-ecosystem study, including six geographically distinct sea otter populations (from west to east, Katmai, Prince William Sound, Southeast Alaska, British Columbia, Washington, and California). The study design integrates several decades of USGS research on sea otter populations and the results of recolonizations and reintroductions, which have resulted in separate populations across a gradient of human perturbations to watersheds. [larger version]

Above: Simplified nearshore marine food web, in which kelps and sea grasses provide primary production and benthic invertebrates transfer energy to apex consumers. Dark arrows indicate transfer of energy upward, and light arrows indicate consumption and predation. Curved arrows indicate inputs from terrestrial and oceanic sources into the nearshore. [larger version]

The USGS-led study will contrast six geographically distinct sea otter populations, including two populations listed as "threatened" under the Endangered Species Act, to identify factors contributing to variations in the animals' density and abundance. The study design incorporates ecosystem productivity (both oceanic and nearshore), watershed inputs, and sea otter diet and nutrition as primary factors potentially regulating population abundance and growth rates. Ecosystem productivity will be estimated by measuring growth rates of nearshore fishes and by analyzing remotely sensed data—including such data as ocean temperature and chlorophyll concentrations provided by satellite imagery (for example, from the Landsat and MODIS [Moderate Resolution Imaging Spectroradiometer] programs), and air temperature and wind velocity provided by oceanographic stations. Human modifications of the watershed and terrestrial inputs into the nearshore will be estimated by analyzing remotely sensed data, including satellite imagery, as well as data collected by hydrographic stations (which measure such variables as rainfall, streamflow, and the concentration of certain chemicals in stream water). Sea otter diet and nutrition will be estimated through direct observation of foraging animals and analysis of stable isotopes obtained from whiskers.

Left: Phytoplankton bloom (water that looks turquoise) near the coast of Vancouver Island, British Columbia, Canada. Image collected by MODIS (Moderate Resolution Imaging Spectroradiometer) on the Aqua satellite, June 25, 2006, processed by Jeff Schmaltz, NASA Visible Earth. [larger version]

Concurrently, the researchers will use noninvasive, gene-expression technology to evaluate the health and condition of sea otters relative to the nearshore ecosystem. When a gene is "expressed" in response to stressful stimuli, it produces genetic material (messenger RNA, or mRNA) that instructs cells to produce proteins that combat the ill effects of the stimuli. Specific pollutants and pathogens are known to activate certain genes, and by identifying and quantifying the mRNA products, researchers can use gene expression in concert with clinical evaluation to best diagnose an organism's state of health relative to exposure to contaminants or diseases. As part of this new project, blood samples collected from sea otters in each population will be analyzed for evidence of genes expressed by organic pollutants, metals, parasites, bacterial infection, viral infection, injury, and thermal stress (difficulty in maintaining body temperature due to, for example, contamination of fur by spilled oil).

Above left: Veterinarian Mike Murray (Monterey Bay Aquarium; left) and Jim Bodkin record a sedated sea otter's vital signs and prepare to take a blood sample for gene-expression analysis, which will reveal information about the animal's exposure to pollutants and disease. The animal will be released after it has been examined and tagged and the sedative has been reversed. Photograph taken August 2009, aboard the research vessel Norseman off the Kenai Peninsula, Alaska. [larger version] Above right: Liz Bowen conducts gene-expression analysis on sea otter blood samples at the University of California, Davis, September 2009. [larger version]

The combined data sets on nearshore and ocean productivity, watershed inputs, sea otter diet and nutrition, and sea otter gene expression will support the analysis of a complex array of interacting variables likely responsible for the present status of each of the six sea otter populations and, by inference, the health and condition of their nearshore ecosystems.

The data acquired by this study will inform and support future modeling efforts to forecast nearshore ecosystem responses to anticipated environmental change, such as increasing air and sea temperatures, sea-level rise, ocean acidification, contaminants, and disease.

Above left: Sea otter mother and pup in Simpson Bay, Prince William Sound, Alaska, 2002. The new USGS research will be used to understand and quantify the influence of ecosystem productivity, food limitation, and human sources of pollution and infectious disease on sea otter populations. Photograph © R. Davis, Texas A&M University. [larger version] Above right: George Esslinger (USGS; left) and Heather Coletti (National Park Service) use spotting scopes in 2006 to observe sea otters in Glacier Bay, Alaska, and determine what they are eating. [larger version]

Key partners in this study include the U.S. Fish and Wildlife Service, the National Park Service, the Minerals Management Service, the Exxon Valdez Oil Spill Trustee Council, the North Pacific Research Board, Fisheries and Oceans Canada, the University of Wyoming, the Washington Department of Fish and Wildlife, the California Department of Fish and Game, and the Monterey Bay Aquarium.

2009 Spring Survey Shows Drop in California Sea Otter Numbers September 2009

Sea-Otter Study Reveals Striking Variability in Diets and Feeding Strategies May 2008

Coastal Ecosystem Responses to Influences from Land and Sea USGS

Sea Otter Studies at WERC USGS

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March 2010

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New Study of Pacific Sea Otter Populations and Nearshore Ecosystems

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