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Coastal Ecosystem Responses to Influences from Land and Sea

Introduction: Coastal ecosystems face unprecedented challenges at global and regional scales due to accelerated rates of environmental change that are occurring both offshore and onshore. The resulting stressors are a combination of cascading effects arising from increased atmospheric CO₂ emissions (global warming), elevated biological and chemical pollutants, and habitat modification associated with increasing human populations along coastlines. Expected effects of climate change include modifications to the hydrological processes responsible for transporting pollutants, nutrients, and sediments across watersheds that ultimately deposit in coastal ecosystems. Concurrently, sea level is rising, as are ocean temperatures and acidity. While our understanding of the physical processes that underlie climate change and ocean acidification are advancing, the implications for species and ecological systems are relatively unexplored.

Coastal ecosystems rely on functional interactions with both the terrestrial and ocean systems. In the northeastern Pacific, kelp forests and sea grasses form the base of a unique food web where primary production is transferred through benthic invertebrates such as clams and mussels to vertebrate consumers such as nearshore fishes, shorebirds, sea ducks, and sea otters (Fig. 1). Many of the invertebrates and fishes are long-lived and produce annual growth increments that integrate multiple sources of productivity over multi-annual time scales. These invertebrates can play an important role in regulating consumer abundance, but can also act as intermediate hosts for pathogens and may accumulate contaminants that are transferred to higher trophic levels, such as sea otters.

Figure 1. Simplified nearshore marine food web where kelps and seagrasses 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 at multiple levels from terrestrial and oceanic sources into the nearshore.

In the northeastern Pacific, sea otters are present in geographically distinct populations that span over 30 degrees of latitude and vary in status from increasing to declining, and include two populations listed as "Threatened" under the Endangered Species Act. Perhaps more importantly, rates of change in sea otter populations once increasing rapidly are exhibiting diminished rates, or potentially decline. Recognized constraints to sea otter populations include food limitation, predation, harvest, disease, and contaminants. Here, we propose to use coastal ecosystems, from highly urbanized California to relatively pristine Alaska, to better understand factors that currently influence these systems, and to provide the critical data and tools needed to establish how this coastal ecosystem, and by extension, how similar north temperate systems may respond to future environmental change. We will use the sea otter, an apex consumer and sentinel of ecosystem health, to identify the mechanisms, pathways and expressions of response to physical and biological ecosystem perturbations.

Research Objectives – Science Impact: We expect that this research will be used to understand and quantify the relative roles of ecosystem productivity, food limitation, and anthropogenic sources of pollution and infectious disease in regulating sea otter populations. Information on sea otter diet will provide current measures of the relative abundance and sizes of nearshore invertebrate species that may be useful in understanding how the nearshore ecosystem may respond to anticipated environmental change, including ocean acidification and ocean circulation. The study design encompasses an extensive (~ 6000 km) latitudinal gradient of: 1) atmospheric and ocean temperatures, 2) hydrological regimes, and 3) human influences, that will be essential for integrating physical and biological models of coastal ecosystem responses to current and expected environmental change and provides a foundation and framework to inform future stewardship and conservation of coastal ecosystems. Defining the current status of the system will support forecasting models related to expected effects of climate change and urbanization in both watersheds and in the oceans.

There are four primary objectives to this proposed work:

1) Estimate growth rates of long lived fishes through analysis of annual growth increments and use remotely sensed data (water temp and chlorophyll) as indices to the role of annual variability in primary productivity in defining the status of sea otter populations and the nearshore ecosystem,

2) Estimate human density and habitat modification (e.g., silviculture, agriculture, industrialization) within watersheds adjacent to sampled sea otter populations,

3) Estimate the dietary composition, caloric intake, and activity time budgets within and among geographically separate sea otter populations demonstrating different population histories and trajectories, to evaluate the role of prey populations in defining the status of sea otter populations, and potential cascading effects throughout the nearshore marine ecosystem, and

4) Incorporate gene expression within sea otter populations to assess the role of contaminants, infectious disease, parasites, and thermal stress as factors contributing to the condition of individual sea otters and the abundance and rates of change within and among isolated sea otter populations.

Methods Overview: We will evaluate the status of coastal ecosystems from southern CA to southwest Alaska (Fig. 2). We will sample isolated sea otter populations that span the range of recent environmental and ecological conditions, incorporating ecosystem productivity, watershed inputs, and sea otter diet and nutrition as factors regulating population abundance and growth rate. Ecosystem productivity will be estimated through growth rates of two species of nearshore fish, using otolith growth increments. Inputs from offshore and onshore (e.g. chlorophyll, sediments, freshwater) into the nearshore will be estimated through satellite imagery (e.g. Landsat, SeaWiFS & MODIS). Sea otter diet and nutrition will be determined through direct estimates of caloric intake rates. Concurrently, we will evaluate the health of the ecosystem as reflected in the expression of genes (as novel biomarkers) in each sea otter population specific to: 1) organic pollutants, 2) metals, 3) parasites, 4) bacterial infection, 5) viral infection, and 6) thermal stress. The combined data sets on: 1) nearshore productivity and inputs from land and sea, 2) sea otter diet and nutrition, and 3) gene expression will support a multivariate analysis of empirical factors likely responsible for directing the status and trend within and among geographically distinct sea otter populations. Analytical outcomes will be used to determine the present magnitude and scale of human influences from watersheds, which can then be used to forecast coastal ecosystem responses to anticipated environmental change such as increasing temperature, sea level rise, ocean acidification, contaminants, and disease.

Figure 2. Geographic bounds and conceptual components of proposed Pacific Nearshore study, including six geographically distinct sea otter populations (from west to east, Katmai, Prince William Sound, SE AK, British Columbia, Washington, and CA) watershed inputs (approximated), and oceanic influences.

Personnel: PI: J. L. Bodkin, jbodkin@usgs.gov, USGS Alaska Science Center, 4210 University Drive, Anchorage, AK 99508

Co-PIs: C. Zimmerman, D. Douglas, USGS, Alaska Science Center A. K. Miles, L.Bowen, & M.T. Tinker, W. Perry, USGS, Western Ecological Research Center; L. Thorsteinson, USGS, Western Fisheries Research Center

Collaborators: Minerals Management Service (MMS), National Park Service (NPS), U.S. Fish and Wildlife Service (FWS), Exxon Valdez Oil Spill Trustee Council, (EVOS), the North Pacific Research Board (NPRB) and the Monterey Bay Aquarium

Citation:

Bodkin, J. L. 2010. U.S. Geological Survey (USGS), Western Region: Coastal ecosystem responses to influences from land and sea, Coastal and Ocean Science: U.S. Geological Survey Fact Sheet 2010-3099, 2 p.

Other Resources:
Sea Otter Studies at WERC
Pacific Nearshore Project
National Park Service Inventory and Monitoring Program—Marine Nearshore
DOI on the Landscape Coastal Ecosystem Responses to Influences from Land and Sea Full Study Plan (2.09MB Word doc)

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