Cannibalism, refugia and the molting blue crab

Abstract

In this study, we examined how habitat and tidal stage influence predation upon molting blue crabs Callinectes sapidus. On 3 separate occasions we monitored the survival of tethered soft crabs in each of 2 different-sized marsh creeks and 2 seagrass sites, during both low and high tides. On one of these occasions, we also tethered hard crabs. Survival was much lower for soft crabs than for hard crabs, indicating that crabs may be particularly vulnerable when they molt. In both seagrass and marsh creeks, there was a tidal influence upon soft crab survival, with greater survival during low tides. There was no generalized difference in survival of soft crabs between habitats, i.e. marsh creek versus grassbed. Survival was high in the small marsh creek, but lower ~n the large marsh creek. In both creeks survival remained relatively constant throughout the summer. In contrast, survival did not differ between the 2 seagrass sites and was comparable to that in the small marsh creek early in the summer, but decreased to levels comparable to the large marsh creek by summers end. In the marsh creek, micro-habitat also influenced survival, with greater survival along the creek edge micro-habitats than in the creek centers. Cannibalism was the only identifiable source of mortality among tethered crabs. These results demonstrate that where and when a crab molts may greatly influence its chances for survival.

Effects of ghost fishing on the population of red king crab (Paralithodes camtschaticus) in Womens Bay, Kodiak Island, Alaska

“…Size range (mm carapace length) Proportion for crustaceans (Leffl er, 1972), or shortly after molting, when they are particularly vulnerable to predation (Shirley et al, 1990;Ryer et al, 1997;Marshall et al, 2005). However, for the intermolt period of red king crab, our estimate is likely an accurate picture of mortality.…”

Population density, survival and movement of blue crabs in estuarine salt marsh nurseries

“…PC was smaller, composed of many pools and rivulets, and had a greater percentage of edge microhabitat relative to HS; 33% of the total marsh area in PC was classified as edge habitat (< 3 m from unvegetated mud), while only 7% of the total marsh area in HS was edge habitat. Survival of blue crabs is higher along marsh edge microhabitats than the central channel of tidal creeks, and higher in small tidal creeks compared to large ones (Ryer et al 1997). Other habitat features were qualitatively similar and probably did not contribute to differences in crab density.…”

“…Mortality rates may also vary as a function of body size since larger individuals attain a relative refuge from predation with size . Smaller individuals also molt more frequently than larger crabs, and are particularly vulnerable to increased predation immediately following molting while in a soft-shell state (Ryer et al 1997 ; Wolcott & Hines 1990), and are more likely to emigrate from study populations than smaller crabs. While we used CW as a covariate to assess size-specific differences in survival, a decrease in mortality with size may be balanced by an increase in emigration with size.…”

Salt marshes as nurseries for nekton: testing hypotheses on density, growth and survival through meta-analysis

“…Five of the studies were field tethering experiments using either young blue crabs (4 studies) or brown shrimp as the prey. Survival in subtidal marsh creeks was compared with open water and seagrass in Chesapeake Bay and New Jersey (Shirley et al 1990, Wilson et al 1990a, Ryer et al 1997). Survival within marsh edge vegetation was compared with open water and seagrass in Mobile Bay and Mississippi Sound, AL ) and Christmas Bay, TX (Minello 1993).…”