title: Hard clam walking: Active horizontal locomotion of adult Mercenaria mercenaria at the sediment surface and behavioral suppression after extensive sampling.
abstract: Locomotion of infaunal bivalve mollusks primarily consists of vertical movements related to burrowing; horizontal movements have only been reported for a few species. Here, we characterize hard clam walking: active horizontal locomotion of adults (up to 118 mm shell length, SL) of the commercially important species, Mercenaria mercenaria, at the sediment surface-a behavior only briefly noted in the literature. We opportunistically observed walking over a 10-yr period, at 9 different sites in the Peconic Bays, New York, USA, and tested several hypotheses for the underlying cause of this behavior through quantitative field sampling and reproductive analyses. Hard clam walking was exhibited by males and females at equal frequency, predominantly during June/July and October, when clams were in peak spawning condition. Extensive walking behavior appears to be cued by a minimum population density; we suggest it may be mediated by unidentified pheromone(s), infaunal pressure waves and/or other unidentified factors. There was no directionality exhibited by walking clams, but individuals in an area of extensive walking were highly aggregated and walking clams were significantly more likely to move toward a member of the opposite sex. Thus, we conclude that hard clam walking serves to aggregate mature individuals prior to spawning, thereby facilitating greater fertilization success. In the process of investigating this behavior, however, we apparently oversampled one population and reduced clam densities below the estimated minimum threshold density and, in so doing, suppressed extensive walking for a period of >3 years running. This not only reinforces the importance of detailed field investigations of species biology and ecology, even for those that are considered to be well studied, but also highlights the need for greater awareness of the potential for research activities to affect focal species behavior.
authors.affiliation: Department of Biology, LIU-Post, Brookville, New York, United States of America.
authors.forename: Stephen T
authors.identifier: http://orcid.org/0000-0003-3715-1235
authors.initials: ST
authors.lastname: Tettelbach
authors.affiliation: Southeast Fisheries Science Center, NOAA, Miami, Florida, United States of America.
authors.forename: James R
authors.initials: JR
authors.lastname: Europe
authors.affiliation: College of Natural Resources, University of California Berkeley, Berkeley, California, United States of America.
authors.forename: Christian R H
authors.initials: CR
authors.lastname: Tettelbach
authors.affiliation: Marine Program, Cornell Cooperative Extension of Suffolk County, Southold, New York, United States of America.
authors.forename: Jason
authors.initials: J
authors.lastname: Havelin
authors.affiliation: School of Marine & Atmospheric Sciences, Stony Brook University, Southampton, New York, United States of America.
authors.forename: Brooke S
authors.initials: BS
authors.lastname: Rodgers
authors.affiliation: Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, United States of America.
authors.forename: Bradley T
authors.initials: BT
authors.lastname: Furman
authors.affiliation: Department of Biology, Cornell University, Ithaca, New York, United States of America.
authors.forename: Marissa
authors.initials: M
authors.lastname: Velasquez
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D005260:Female; D005306:Fertilization / Q000502:physiology*; D008124:Locomotion / Q000502:physiology*; D008297:Male; D049891:Mercenaria / Q000502:physiology*; D018401:Sample Size; D012724:Sex Attractants; D016138:Walking / Q000502:physiology*
chemical_list: D012724:Sex Attractants