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Physical habitat property mediates biotic resistance to non-indigenous species invasion.
Byers, James1,2, 1 2
ABSTRACT- A non-indigenous clam, Nuttallia obscurata, has invaded coastal soft-sediment habitats of the northeastern Pacific. I surveyed 35 sites within northern Washington, USA and found Nuttallia almost exclusively in sandy substrates and higher in the intertidal than most native clams. Its distinctive distribution suggested that tidal height and sediment composition may be important physical factors controlling predation refuges available to Nuttallia. I tethered Nuttallia for 24 hours in the high intertidal where it is typically found and in the low intertidal where it was never found. Clams restrained to the surface suffered high mortality from crab predation at both tidal heights; control clams with unrestricted movement exhibited high mortality only in the low intertidal. I repeated the experiment after manipulating the sediment substrate within each intertidal height. At both tidal heights clams placed on mud substrate, naturally common in the low intertidal, suffered high mortality rates. Nuttallia on loosely packed sand substrate, naturally found in the upper intertidal, however, survived better because they buried deeper than in the tightly packed mud. Caged control clams at both tidal heights suffered no mortality. Apparently native predators are mitigating community level impacts of an invader by excluding Nuttallia or relegating it to a zone not often inhabited by native species, thereby reducing potential competitive interactions. These findings illustrate that physical characteristics can mediate biotic resistance to an invader, thus controlling invasion success and community-level impacts.
KEY WORDS: physical-biological coupling, predator-free space, Cancer productus, clams