Hermit crabs living in highly acidified seawater (pH 6.8) were less likely to leave a suboptimal shell in favor of an optimal shell. Those that did change shells took longer to do so. Crabs in acidified water also moved less and had lower flicking rates of their antennae (a ‘sniffing’ behavior in decapods). Reduction in seawater pH apparently disrupted the resource assessment and decision-making processes of these crabs. (Laboratory study)