Invasive cordgrass modifies wetland trophic function

Area of Science:

• Ecology
• Marine Biology
• Invasive Species Research

Background:

• Vascular plants, particularly invasive cordgrass (Spartina spp.), significantly alter coastal wetland ecosystems globally.
• Understanding the trophic consequences of these invasions is crucial for predicting ecosystem-level changes and impacts on biodiversity.

Purpose of the Study:

• To investigate the trophic consequences of a Spartina hybrid invasion in San Francisco Bay.
• To document differences in benthic community biomass and trophic structure between invaded and uninvaded sediments.
• To test the hypothesis that species consuming Spartina detritus are more tolerant to invasion than those consuming algae.

Main Methods:

• Documented differences in benthic community biomass and trophic structure in invaded versus uninvaded sediments.
• Utilized natural abundance stable isotope analyses and mixing models to initially assess infaunal diets.
• Conducted 15N-labeled Spartina detritus isotopic enrichment experiments on and below the sediment surface in invaded and unvegetated areas.

Main Results:

• The invaded ecosystem exhibited a trophic shift from an algae-based to a detritus-based food web.
• Capitellid and nereid polychaetes, and oligochaetes, which persist in invaded areas, assimilated 15N from labeled Spartina detritus.
• Amphipods, bivalves, and other less tolerant taxa consumed primarily surficial algae, as indicated by 13C enrichment experiments.

Conclusions:

• The findings support a 'trophic shift' model for ecosystem responses to wetland plant invasion.
• Spartina invasion alters food web structure by promoting detritivores over algae consumers.
• This shift may reduce trophic support for higher-level consumers like fish and migratory birds.