Climbing as an avoidance behaviour in the salt marsh periwinkle, Littorina irrorata (Say)

In salt marshes from New York to Texas, Littorina irrorata (Say) occurs on stalks of tall grass, moves onto the substratum to feed during low tide and climbs above the water during high tide. To determine if climbing leads to reduced mortality from predation or other causes, snails were tethered to grass stalks either near, or well above, the substratum, in caged, open and roofed treatments at Wakulla Beach in northwestern Florida. Rates of injury and mortality were significantly greater in snails restricted near the substratum in open and roofed sites. Rates of mortality varied seasonally, with greatest rates from late spring to early autumn. Injuries and deaths declined to nearly zero from mid-November to April, the period during which two important predators, the blue crab Callinectes sapidus Rathbun and the crown conch Melongena corona Gmelin, move offshore or bury in the inter- or subtidal mud. Mortality from attacks by conchs and crabs was greatest in late spring, and least in winter. Mortality of snails in cages (i.e. mortality from causes other than predation by conchs and crabs) was greatest in summer, less in spring and autumn, and least in winter. Regardless of season, more snails were attacked by conchs than by crabs. By remaining above water during high tide Littorina irrorata suffered significantly less predation by conchs and crabs and may have also been subject to less mortality from other inter- or subtidal carnivores or osmotic stress. It is therefore concluded that the circatidal climbing behaviour of marsh periwinkles reduces the risk of injury and mortality from predation in addition to that from other sources.