Document: LIN-3-80-5

Native species response to invasion: Effects of green crabs on soft-shell clam behavior and morphology.

WHITLOW, W.L.* ^1,2

University of Michigan Ann Arbor MI 48109 USA ¹
Wells National Estuarine Research Reserve Wells ME USA ²

Abstract:
Invasive predators may decimate native populations because the natives evolved in a community without similar predators and lack specific adaptations for effective predator avoidance. To prevent the loss of native species, we must determine whether natives have the potential to respond effectively to invasive predators. We can then manage invaded areas by promoting conditions that favor effective native responses. In Maine, predation by invasive green crabs, Carcinus maenas, is a factor in the decline of native soft-shell clams, Mya arenaria. If clams behaviorally respond to the invasive crab by digging deeper, this may reduce vulnerability. However, siphon length limits clam depth in the sediment because a stretched siphon has a smaller diameter, decreasing food and oxygen intake rates. Hence, clams face a trade-off between decreased predation and decreased feeding rates at greater depths in the sediment. If clams can morphologically respond to predator cues by allocating energy to siphon growth, this would overcome the reduction in feeding rates deeper in the sediment. We tested the hypothesis that clams change both behavior and morphology in response to invasive crab foraging to balance the trade-off between predator avoidance and feeding rate. Laboratory and field experiments tested how clams responded to either chemical cues from crabs or crab foraging activity. In the laboratory, we exposed juvenile clams to crab odor or normal seawater. In the field, we built crab exclosure, enclosure, and control plots containing either juvenile or adult clams. We measured depth in the sediment, shell length, width, thickness, weight, tissue weight, and siphon length for all clams. In the laboratory, juvenile clams exposed to crab odor buried deeper, but showed no difference in siphon growth or shell growth. In the field, clams in crab enclosure and control plots were deeper, but showed no difference in siphon growth or shell growth. Overall, results indicate native clams can respond to invasive crabs by digging deeper in the sediment to avoid predation. However, lack of increases in siphon growth indicates decreased feeding rates may also be responsible for clam population declines.

Keywords: invasive species, predator avoidance, trade-offs, morphological plasticity, behavior, Carcinus maenas, Mya arenaria

This abstract is being presented at: 9:30 AM in session:
Oral Session #7: Aquatic Ecology: Shellfish to Snails.