AB 13:51-64 (2011)  -  DOI: https://doi.org/10.3354/ab00342

ABSTRACT: Placopecten magellanicus start their lives as free-living veligers, then become byssally attached juveniles, mobile young adults and finally generally sedentary large adults. Although biomechanical considerations help explain this size dependence of swimming activity, the patterns of muscle use and the physiological capacities of the adductor muscle could change with size. Measurements of in vivo force production (in 2004) and muscle metabolic capacities (in 2008) were used to assess how P. magellanicus (Îles-de-la-Madeleine, 47°23’N, 61°52’W) of 30 to 98 mm in shell height (SH) use the adductor muscle during escape responses. Principal components analysis of escape response behaviours revealed that parameters associated with endurance and phasic contraction frequency were associated on the first 2 axes, whereas measures of force production were linked on the third axis. Individual scores from the first and third principal components showed a significant size dependence, with values first increasing and then decreasing with SH. Scallop size influenced escape response endurance, clap numbers and force production in a similar fashion. These metrics of muscle use generally peaked at SH ~70 mm. Physiological attributes, including muscle enzymatic activities and phosphoarginine content, peaked at SH ~60 mm. Although the gonadosomatic index increased with size, it did not explain the scaling of escape response behaviours or muscle metabolic capacities. Ecological considerations, particularly predation risk, may explain this allometric pattern.

KEY WORDS: Size · Muscle metabolic capacities · Scallop · Placopecten magellanicus