Contrasting patterns of habitat-specific recruitment success in sympatric species of thalassinidean shrimp: Effects of epibenthic bivalve shell with implications for population control in areas with commercial oyster culture

Burrowing ghost shrimp (Neotrypaea californiensis) and mud shrimp (Upogebia puggetensis), which construct extensive subterranean burrow systems in estuarine intertidal and shallow subtidal sediments, have had a considerable impact on two of Washington State's coastal aquatic resource programs. First, burrowing shrimp have been the focus of an intense environmental conflict over the use of carbaryl, an organocarbamate pesticide applied to intertidal mudflats to eradicate shrimp on commercial oyster beds. A comprehensive review of this complex and unresolved issue is presented, with particular focus on the ecology and recruitment dynamics unique to each species of burrowing shrimp. Second, burrowing shrimp have threatened the success of an intertidal shell habitat program designed to enhance recruitment of juvenile Dungeness crabs. Within a few months of deployment, only 30% of shell remained on the sediment surface (epibenthic shell). Most of it sank into the mud (subsurface shell), largely due to the incessant burrowing activities of the underlying ghost shrimp population. Recruitment of newly settled 0+ ghost shrimp, however, was significantly reduced in epibenthic shell habitat compared to both subsurface shell and bare mud. Results of experiments suggest that postlarval substrate selection for mud over shell and restricted mobility in epibenthic shell were responsible, at least in part, for habitat-specific distribution patterns, while Dungenesscrabs residing in epibenthic shell could have further modified population demographics through predation on 0+ ghost shrimp. The presence of epibenthic shell did not, however, deter recruitment of mud shrimp; rather, it facilitated the establishment of a mud shrimp population where none existed prior to habitat construction. Epibenthic shell may have increased sediment compaction and reduced particle resuspension in the ghost shrimp bed, enabling mud shrimp to occupy a habitat that otherwise would have been too unstable. Densities of 0+ and older mud shrimp were higher in epibenthic shell than in either subsurface shell or bare mud where ghost shrimp were still prevalent. Postlarval substrate selection for shell over mud and post-settlement immigration by juvenile and adult mud shrimp into the shell plot contributed to patterns of distribution, while predation by Dungeness crabs had no observable effect on recruitment success.