Effects of temperature and competition on foraging in indigenous rock (Cancer irroratus) and recently introduced green (Carcinus maenas) crabs from Newfoundland and Labrador, Canada

Matheson, Kyle Alexander (2012) Effects of temperature and competition on foraging in indigenous rock (Cancer irroratus) and recently introduced green (Carcinus maenas) crabs from Newfoundland and Labrador, Canada. Masters thesis, Memorial University of Newfoundland.

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Abstract

This thesis determined experimentally how temperature (cold [4°C] versus warm [ 12°C] water) affects predation success in indigenous rock (Cancer irroratus ) and recently introduced green ( Carcinus maenas ) crabs from Newfoundland and Labrador under non-competitive and competitive conditions. Prey (the blue mussel, Mytilus edulis ) capture and size selection as well as associated foraging behaviors were measured in both crab species. Additional factors (crab size, prey size, chela loss, and chemical cues from conspecifics and heterospecifics) were included to gain further insights about how this green crab introduction may alter the structure of shallow benthic ecosystems in this region. Analysis of predation data under non-competitive conditions indicated that 1) mussel capture in rock and green crabs was higher in large than small individuals, 2) chela loss decreased mussel capture uniquely in rock crabs while causing only subtle changes in mussel size selection in both species, and 3) chemical cues from other crabs did not affect mussel capture in rock crabs, yet altered mussel size selection and the frequency of foraging behaviors in small rock crabs only. Increasing temperature from 4 to 12°C exacerbated these patterns by significantly increasing mussel capture in both species. Analysis of predation data under competitive conditions indicated that 1) green crabs primarily grasped the mussel before rock crabs regardless of temperature and body size and chela loss in rock crabs, 2) the number of contests between rock and green crabs was unaffected by temperature and body size and chela loss in rock crabs though the frequency of strong physical interactions was higher in contests with large than small rock crabs, and 3) large rock crabs initiated contests with green crabs more frequently than smaller conspecifics in warm water only while winning more contests than small rock crabs regardless of temperature. Therefore, the introduction of green crab to Newfoundland and Labrador (currently the northern distribution limit of the species) may negatively impact foraging in rock crabs, whether the latter are equal or larger in size than the largest green crabs. The observed marked preference by small green crabs for small mussels suggests that green crabs may alter mussel populations in this region, which could affect interactions with other species that rely on mussels as a food source.

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