Food Web and Invertebrate Ecology Studies in Pacific Coast Estuaries

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Invertebrate communities provide food for several economically and ecologically important fish and waterbird species in coastal estuaries.  Scientists at the WERC San Francisco Bay Estuary Field Station specialize in studying foraging ecology of waterbirds and fishes, general food web dynamics across estuaries, and the effects of habitat restoration and other factors on waterbird prey availability.

label for USGS WERC Invertebrate Ecology lab

Both physical and biological factors can influence the type and amount of invertebrates that support fish and waterbird species in coastal estuarine habitats.  Dr. Susan De La Cruz and her team of researchers at the WERC San Francisco Bay Estuary (SFBE) Field Station study the foraging ecology of migratory birds and the factors that influence invertebrate food availability for waterbirds and fish.  The SFBE Invertebrate Ecology Laboratory (IEL) was established to help study macroinvertebrate communities across a mosaic of habitat types within the San Francisco Bay-Delta, Pacific Northwest and other coastal ecosystems.  The IEL assesses benthic community ecology, foraging ecology of waterbirds and fishes, and food web dynamics to enhance our current understanding and management of estuarine habitats.  

 

WERC researchers collecting samples in the field

USGS WERC researchers collecting samples in the field. (Credit Sierra Blakely. Public domain.)

Laboratory Capabilities  

The IEL is equipped to collect invertebrate samples from a range of freshwater, marine, and terrestrial environments such as tidal marshes, tidal mud flats, shallow subtidal, and managed ponds or agricultural fields. Using specialized sampling gear, the IEL team measures environmental variables like water depth and quality (temperature, dissolved oxygen, pH, and salinity),  sediment grain size (percentage of sand, silt, and clay), and sediment chemistry (e.g., nitrate, sulfur, and organic matter) to help characterize and relate the physical environment to macroinvertebrate densities.

The IEL staff includes several experienced taxonomists skilled in identifying a broad range of invertebrates, from terrestrial insects to organisms living in coastal sediments. The team also specializes in multi-variate community analyses, bioenergetics modeling and stable isotope analysis for food webs studies.

Photos of lab technicians

USGS lab technicians identifying invertebrate species in samples. (Credit: David Nelson/USGS. Public domain.)

What Drives Mudflat Food Availability for Migratory Birds?

Shorebirds and waterfowl rely on diverse communities of intertidal invertebrates as food to fuel their long-distance migrations.  Invertebrates found in intertidal mudflats may be especially sensitive to environmental changes such as sedimentation and sea-level rise.  To help determine how changes to intertidal habitat may influence food for migratory birds, it is important to first understand which mudflat features influence the types and amounts of invertebrate prey available.  

IEL scientists are currently modeling relationships between intertidal macroinvertebrates and their environment. With widespread environmental changes expected in critical estuaries for waterbirds along the Pacific Flyway, such as California’s San Francisco Bay-Delta, identifying the most important drivers of food availability will help WERC researchers project how well estuaries will be able to fuel migration in the future. Using these data, resource agencies can develop strategies to maintain populations of invertebrates and the waterbirds that rely on them.

 

Scientists sampling benthic invertebrates

Researchers sample the sediments of shallow-water areas for invertebrates. (Credit Hannah Mittelstaedt/USGS. Public domain.)

Assessing Invertebrate Prey Availability in Essential Fish Habitat

Estuaries provide essential foraging habitat for sensitive and economically important fish species, many of which feed on macroinvertebrates living in surface sediments. Regular maintenance dredging is common in shallow waters to keep harbors and marinas navigable; however, its impact on the types and amount of benthic macroinvertebrates available for foraging fish is not well understood. IEL scientists are comparing macroinvertebrate species abundance and biomass between dredged shallow areas and adjacent undredged areas in California’s San Francisco Bay-Delta to measure differences in food availability and quality for economically important fish species. Results of this study will provide information on how the timing and frequency of shallow dredging influences essential fish habitat.

 

Benefits of Living Shorelines for Invertebrate and Waterbird Communities

San Francisco Bay-Delta is a highly urbanized estuary that has lost many historical eelgrass beds and oyster reefs that once provided habitat for invertebrates, fish and waterbirds. In collaboration with state and university partners, the SFBE has been evaluating “living shoreline” restoration efforts, which strive to create self-sustaining eelgrass beds and oyster reefs with the dual goal of providing habitat for native species and shoreline protection against sea-level rise and storm surges.  SFBE scientists are measuring the response of waterbirds and their macroinvertebrate prey to these experimental restoration treatments within the San Francisco Bay. Their results are providing important feedback on how to design future living shorelines to maximize habitat benefits for migratory birds.