Direct and indirect effects of burrowing crab Chasmagnathus granulatus activities on erosion of southwest Atlantic Sarcocornia‐dominated marshes

Abstract

Using field measurements and field experiments, we investigated the effect of a dominant Southwest Atlantic intertidal burrowing crab, Chasmagnathus granulatus, on the inland growth of tidal creeks and creek genesis in salt marshes. By burrowing intensively on marsh sediments, this crab changed sediment physical parameters, such as penetrability, water content, and shear strength, which are related to sediment resistance to erosion. There were positive relationships between crab density and activities occurring in the creek heads and creek growth rates. Field experiments show that the presence and activity of C. granulatus and the presence of their burrows enhance the growth rates of tidal creeks, promoting marsh erosion. When crabs were present, these creeks grew faster than did creeks in which crabs were excluded. Furthermore, the interaction (disturbance and herbivory) between crabs and the dominant halophyte marsh plant, Sarcocornia perennis, generate circular depressions that accumulate standing water (salt pans), which in turn facilitates the creation of new creeks in the marsh surface, which evolve, to a greater extent, into fully functional tidal creeks because of colonization by crabs, which in turn further enhances creek growth rates. These direct and indirect effects of crabs on marsh erosion provide strong evidence of the importance of bioturbation and biological processes to the erosion and geomorphology of marshes.

The influence of habitat, season and tidal regime in the activity of the intertidal crab Neohelice (=Chasmagnathus) granulata

“…Crabs are present in the upper-and mid-intertidal zones. Burrows from the mudXat range between 60 and 90 cm in length and those from the upper salt marsh are deeper, reaching 150 cm (Escapa et al 2007); those in the S. alterniXora belt have not been described yet. The sampled area corresponded to the S. alterniXora marsh and the mudXat.…”

“…Consequently, there were 8 sets of data per habitat and season, obtained every 6 h approximately. Additional qualitative observations were made of burrow length and water retention during a tidal cycle in San Antonio and in the lower salt marsh of Bahía Blanca in order to draw a comparison with the other sites where the information is already available (see Iribarne et al 1997;Escapa et al 2007). …”

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

“…Mar 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.…”

Crab Bioturbation and Herbivory May Account for Variability in Carbon Sequestration and Stocks in South West Atlantic Salt Marshes

“…These mounds are easily eroded in areas subjected to high speed currents, especially at the head of tidal creeks, basins, and banks where a net loss of sediment occurs . At a landscape scale, this process increases the inland growth rate of tidal creeks (Escapa et al, 2007). Furthermore, the experimental exclusion of crabs at the head of creeks and basins demonstrate a direct link between crab bioturbation and erosion by decreasing the inland growth rate of tidal creeks (Escapa et al, 2007).…”

“…At a landscape scale, this process increases the inland growth rate of tidal creeks (Escapa et al, 2007). Furthermore, the experimental exclusion of crabs at the head of creeks and basins demonstrate a direct link between crab bioturbation and erosion by decreasing the inland growth rate of tidal creeks (Escapa et al, 2007). In areas less affected by currents, such as mudflat plains and inside the salt marsh matrix, the sedimentary balance is positive showing a net increase in sediment deposited into burrows of 380 and 1200 g sediment per m 2 per day in salt marshes and mudflat plains respectively ).…”