Ecosystem engineers drive creek formation in salt marshes

Area of Science:

• Ecology
• Marine Biology
• Environmental Science

Background:

• Ecosystem engineers significantly influence organisms and processes across various spatial scales.
• The specific engineering effects of similar species can vary unpredictably.
• Salt marshes are critical ecosystems facing challenges like sea level rise.

Purpose of the Study:

• To investigate the role of four burrowing crab species (Sesarma reticulatum, Eurytium limosum, Panopeus herbstii, Uca pugnax) in shaping tidal creek networks in salt marshes.
• To understand how these crabs, particularly Sesarma reticulatum, impact Spartina alterniflora and creek erosion.
• To differentiate the engineering effects of Sesarma reticulatum from other sympatric crab species.

Main Methods:

• Field observations of crab burrows in relation to creek heads and Spartina alterniflora stem loss.
• Mesocosm experiments to assess soil excavation and plant biomass reduction by different crab species.
• Measurements of water percolation rates and biomass decomposition at creek heads versus marsh platforms.
• Vegetation removal experiments to simulate herbivory effects on creek head growth.

Main Results:

• Sesarma reticulatum was strongly associated with creek heads and significantly reduced Spartina alterniflora biomass in mesocosms.
• Other crab species excavated less soil and did not impact Spartina alterniflora.
• Creek heads with vegetation removed showed increased growth rates.
• Percolation rates and decomposition were significantly higher at creek heads compared to the marsh platform.

Conclusions:

• Sesarma reticulatum enhances creek growth through sediment excavation and herbivory, increasing water flow and erosion at creek heads.
• This species may also promote creek expansion via increased surface/subsurface erosion and organic matter decomposition.
• While Sesarma reticulatum negatively impacts plants and increases erosion at small scales, it facilitates marsh drainage and promotes overall marsh health at larger scales by expanding tidal creek networks.