Crab: snail size-structured interactions and salt marsh predation gradients

Abstract

We studied size-structured predator-prey interactions between blue crabs (Callinectes sapidus) and marsh periwinkles (Littoraria irrorata) with a combination of field studies, laboratory experiments and individual-based modeling. Size distributions of Littoraria differed among years at the same sites in a salt marsh and could largely be explained by dominance of strong cohorts in the population. At a given site, abundance increased with elevation above tidal datum. Size-selective predation by blue crabs does not appear to be an important regulator of snail size distributions but may have a major effect on local abundance. Laboratory studies indicated that predator-prey interactions between Callinectes and Littoraria are strongly size-dependent. Crabs were generally effective at feeding on periwinkles at size ratios greater than approximately 6 (crab width: snail length). At lower size ratios crabs were far less effective at manipulating the snails, which often survived but with damaged shells. An individual-based model which incorporated information about incidence of snail shell scarring (resulting from non-lethal interactions) and snail density, predicted reduced predation rates and smaller average crab size with distance from the low tide refugium for crabs.

Trophic heterogeneity in salt marshes of the northern Gulf of Mexico

“…Tall-form Spartina generally borders open water and is characterized by low grass densities, whereas dense swards of short-form Spartina are found in the poorly drained soils of the high marsh (this study, Weigert & Pomeroy 1981, West & Williams 1986, Silliman & Bertness 2002. Increased grass densities, coupled with the topographical controls discussed above, can impose a filter on both the size and number of predators capable of reaching the inland regions of the marsh (West & Williams 1986, Schindler et al 1994, Lewis & Eby 2002.…”

Flexible prey handling, preference and a novel capture technique in invasive, sub-adult Chinese mitten crabs

“…6 Handling time of T. fluviatilis prey against A carapace width and B average chela height for E. sinensis operculum which required more time. In comparison, whilst handling snails, other crab species primarily crush the shell rather than pull the flesh from the aperture which shortens handling time (Zipser & Vermeji, 1978;Bertness & Cunningham, 1981;Schindler et al, 1994;Shigemiya, 2003;Rochette et al, 2007). This behaviour of crushing a molluscan shell may not be possible in sub-adult E. sinensis as they do not possess a distinct crushing chela, and also, in the present study, the crabs were relatively small individuals (10-40 mm carapace width).…”

“…Carcinus maenas and Callinectes sapidus Rathbun, 1896 can use a similar technique to that described for E. sinensis given R. peregra when handling other species of snails. Both these species use their chelae to pull the flesh directly from the species of snail given through the aperture or use their chelae to chip around the aperture to gain better access (Schindler et al, 1994;Rochette et al, 2007). Eriocheir.…”

Habitat size, flora, and fauna: Interactions in a tidal saltwater marsh

“…Littoraria can exert significant top-down control on Spartina production through grazing (Silliman and Zieman, 2001;Silliman and Bertness, 2002). Littoraria populations can be food-and habitat-limited (Stiven and Kuenzler, 1979), although predation, primarily by the blue crab, Callinectes sapidus, can also be important in structuring them (Hamilton, 1976;Schindler et al, 1994). Spartina provides a refuge from blue crab predation;…”

“…Littoraria on the edges of the marshes may be vulnerable to pelagic and epibenthic predators, especially blue crabs, foraging at the edges of marshes (Hamilton, 1976;Schindler et al, 1994). Blue crab abundance is highest at the edge of marshes and declines by about 70% within the first 5-6 m (Minello and Rozas, 2002), and both predation on Littoraria and blue crab abundance are higher at marsh edges than in the interior (Lewis and Eby, 2002).…”