Coastal ecosystem engineers and their impact on sediment dynamics: Eelgrass–bivalve interactions under wave exposure

Abstract

Habitat forming ecosystem engineers play critical roles in structuring coastal seascapes. Many ecosystem engineers, such as seagrasses and epifaunal bivalves, are known to have positive effects on sediment stability and increase coastal protection and ecosystem resilience. Others, such as bioturbating infaunal bivalves, may instead destabilize sediment. However, despite the common co-occurrence of seagrasses and bivalves in coastal seascapes, little is known of their combined effects on sediment dynamics. Here, we used wave flumes to compare sediment dynamics in monospecific and multispecific treatments of eelgrass, Zostera marina, and associated bivalves (infaunal Limecola balthica, infaunal Cerastoderma edule, epifaunal Magellana gigas) under a range of wave exposures. Eelgrass reduced bedload erosion rates by 25-50%, with digital elevation models indicating that eelgrass affected the sediment micro-bathymetry by decreasing surface roughness and ripple sizes. Effects of bivalves on sediment mobilization were species-specific; L. balthica reduced erosion by 25%, C. edule increased erosion by 40%, while M. gigas had little effect. Importantly, eelgrass modified the impacts of bivalves: the destabilizing effects of C. edule vanished in the presence of eelgrass, while we found positive additive effects of eelgrass and L. balthica on sediment stabilization and potential for mutual anchoring. Such interspecific interactions are likely relevant for habitat patch emergence and resilience to extreme wave conditions. In light of future climate scenarios where increasing storm frequency and wave exposure threaten coastal ecosystems, our results add a mechanistic understanding of sediment dynamics and interactions between ecosystem engineers, with relevance for management and conservation.

Eelgrass (Zostera spp.) associated phytomyxids are host‐specific congeneric parasites and predominant eukaryotes in the eelgrass rhizosphere on a global scale

“…They are considered important ecosystem engineers and provide a variety of essential ecosystem services such as habitat and feeding ground for numerous animal assemblages (including commercially important fish and invertebrates), prevention of coastal erosion by reducing the hydrodynamic energy of waves, and stabilization of the seafloor sediment. (Bos et al, 2007;Kennedy et al, 2018;Meysick et al, 2022;Surugiu et al, 2021). With nine currently recognized species and a geographical range encompassing areas from the tropics to the subpolar regions, eelgrasses represent the most widely distributed and the second most diverse group of seagrasses altogether (Moore & Short, 2007).…”

Eelgrass (Zosteraspp.) associated phytomyxids are host-specific congeneric parasites and predominant eukaryotes in the eelgrass rhizosphere on a global scale

“…They are considered important ecosystem engineers, providing a variety of essential ecosystem services such as habitat and feeding ground for numerous animal assemblages (including commercially important fish and invertebrates), prevention of coastal erosion by reducing the hydrodynamic energy of waves, and stabilization of the seafloor sediment. (Bos et al 2007, Kennedy et al 2018, Surugiu et al 2021, Meysick et al 2022). With nine currently recognized species and a geographical range encompassing areas from the tropics to the subpolar regions, eelgrasses represent the most widely distributed and the second most diverse group of seagrasses altogether (Moore and Short 2007).…”