Accelerated erosion of saltmarshes infested by the non-native burrowing crustacean Sphaeroma quoianum

Abstract

Lateral erosion of saltmarshes is affected by many abiotic and biotic factors. While abiotic factors are typically regarded as primary drivers of erosion, biotic influences such as burrowing or bioturbating taxa can also extensively modify the physical structure of this marine habitat. Many estuaries on the Pacific coast of North America have been invaded by populations of the burrowing non-native isopod Sphaeroma quoianum, which are thought to exacerbate the erosion of saltmarshes. We conducted a mensurative experiment to examine the relationship between populations of S. quoianum and lateral erosion rate of saltmarshes in Coos Bay, Oregon, USA. After 1 yr, we measured higher lateral erosion rates, more undercutting, and higher numbers of calved and slumped marsh sections in marsh sites infested by S. quoianum than in uninfested sites. This effect was also consistent at smaller spatial scales: we found lateral erosion was 300% higher in burrowed areas than in adjacent (within approx. 1 m) unburrowed areas within infested sites. Our results suggest that the prodigious burrowing by dense populations of S. quoianum can accelerate erosion rates in saltmarshes and are substantial geomorphic agents of change in estuaries on the Pacific coast of North America. KEY WORDS: Erosion · Ecosystem engineering · Biogeomorphology · Bioturbation · Biological invasions · Saltmarshes · Sphaeroma quoianum Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 419: [129][130][131][132][133][134][135][136] 2010 consumers, or biostabilizers (Belanger & Bedard 1994, Butler 1995, Widdows et al. 2000, Paramor & Hughes 2004, Jefferies et al. 2006, Escapa et al. 2007.Burrowers/bioturbators and consumers both can greatly increase the rate of erosion of marshes. Fauna directly reduce the stability of the sediment and accelerate erosion through trampling, burrowing, bioturbation, or other forms of physical disturbance (Dionne 1985, Talley et al. 2001, Escapa et al. 2007). Burrowing by the crab Chasmagnathus granulatus decreases sediment shear strength and increases the erosion rate of saltmarshes in Argentina (Escapa et al. 2007). Dionne (1985) observed extensive marsh erosion from trampling and foraging by geese in Quebec. Furthermore, bioturbation by increasing densities of Manila clams resulted in an exponential increase of sediment erosion in flume experiments (Sgro et al. 2005). Herbivores indirectly accelerate erosion by reducing the abundances of sediment biostabilizers. For example, herbivory and bioturbation by the polychaeate Nereis diversicolor reduces the abundance of marsh plants leading to increased erosion in marshes (Paramor & Hughes 2004). The presence of the diatom-grazing amphipod Corophium volutator significantly decreases sediment shear strength (Gerdol & Hughes 1994) and increases erosion rates (Widdows et al. 2009) in marsh sediment.On the Pacific coast of North America, over 93% of salt marshes have been lost as a result of human activities (Bromberg Gedan & Silli...

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