Figure 1.
Differential Carcinus survivorship with and without burrows access and predation exposure.
Tethered Carcinus with access to burrows to avoid desiccation and in cages to avoid predation experienced the highest survivorship, while those exposed to both stressors experienced significant mortality. These results underscore the role of Sesarma burrows as refuges from desiccation, which transform inhospitable die-off banks into benign intertidal habitats capable of sustaining large, burrow-dwelling Carcinus populations.
Figure 2.
Abundance of intertidal Sesarma and Carcinus in creek banks at healthy and die-off sites.
Note the order of magnitude difference in crab densities between site types. Carcinus outnumbered Sesarma at both sites, but were only common at sites with high Sesarma densities and consequently many burrow complexes and expansive die-off (bottom). Carcinus and Sesarma were never found in the same burrow and no evidence of predation was ever observed, suggesting Sesarma may exhibit a strong avoidance response to the presence of Carcinus.
Figure 3.
Abundance of intertidal Carcinus per creek banks at healthy and die-off sites between 2011 and 2012.
Note not only the magnitude difference in Carcinus densities between site types but also the difference in abundance trends across years. At healthy sites, Carcinus remains low over both 2011 and 2012. At die-off sites, however, Carcinus increases from 2011 to 2012.
Figure 4.
Carcinus addition reduces Sesarma functional density and herbivory across a spatial gradient.
(A) Sesarma grazing was reduced by the presence of a single, tethered Carcinus at 0m, and (B) Sesarma density was reduced at 0 and 0.5m but there was no evidence of predation, which is commonly seen in healthy marshes. This suggests that a single, large Carcinus can reduce Sesarma functional density and herbivory without directly consuming Sesarma (* denotes significant difference at P < 0.05).
Figure 5.
Sesarma exhibit species- and size-specific induced avoidance responses reflective of differences in predation rates.
(A) Escape response trials demonstrated that Sesarma flee faster in response to large Carcinus, Carcinus visual and olfactory cues, and other similarly sized predatory decapod crustaceans. Non-predatory crustaceans, small Carcinus, and Sesarma only trials were similar in the amount of time taken to exit the arena. (B) Large Carcinus and Callinectes preyed on Sesarma in overnight feeding trials, but predation was low for small Carcinus, Cancer, Libinia, and Limulus (* denotes significant difference at P < 0.05).