PARENT SESSION
Oral Session # 63: Marine Ecology II: Communities, Barnacles, and Clams.
Presiding: RA Feagin
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.

Claming Up: Mercenaria Reduce Apparancy to Whelk Predators Via Waterborne Chemical Cues.

Smee, Delbert^*,1, Weissburg, Marc¹, ¹ School of Biology Georgia Institute of Technology, Atlanta, GA, USA

ABSTRACT- Immobile organisms minimize predation risk by reducing their apparency from, or defending themselves against, consumers. Hard clams, Mercenaria mercenaria, are heavily preyed upon by both crabs and gastropods, and Mercenaria predators locate their prey by following waterborne odor plumes released by clams while they feed. Previous experiments have shown that clams grow more slowly in habitats where predation levels are high, suggesting that hard clams may reduce their apparency to predators by ceasing to feed. Clam feeding (pumping) behavior was measured in the presence and absence of blue crab Callinectes sapidus and knobbed whelk Busycon carica predators in multiple flow regimes. Our results indicate that clam pumping behavior was significantly reduced in the presence of both blue crabs and knobbed whelks. Pumping was suppressed to the same degree when clams were exposed to predator exudates compared to exposure to the predators themselves, which indicates that clams are detecting their predators via a waterborne chemical cue. The effects of blue crab presence on clam pumping were reduced in turbulent flows when the crabs were placed 1 m away, but clam responses to whelks remained similar in all flow conditions. Clam perceptual distance of crabs was reduced by turbulence, and clam feeding was suppressed less by crab exudates than whelk exudates. The stronger suppression of feeding by whelks may be indicative of the greater threat this predator poses to clams. Whelks are able to follow odor plumes in turbulent flow conditions whereas blue crabs are not. Therefore, a blue crab 1 m away poses less threat to a clam in a turbulent flow. Since crabs move much faster than whelks, brief interruptions in pumping would be sufficient to disguise clams from crabs.

Key words: Knobbed Whelk, Mercenaria, Blue Crab, Chemical Cue