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.

Defining Patterns in Ocean Quahog (Arctica islandica) Sexual Dimorphism along the Mid-Atlantic Bight

“…Fertilization efficiency is a serious constraint for free-spawning species (Levitan 2006, Luttikhuizen et al 2011. Recently, Tettelbach et al (2017) found evidence for horizontal movement, dubbed "hard clam walking," in Mercenaria mercenaria, in which both hard clam sexes were equally as likely to "walk" toward a member of the opposite sex. This behavior has not been documented in Arctica islandica, but it has in other clams, such as Spisula solidissima (Tettelbach et al 2017).…”

“…Recently, Tettelbach et al (2017) found evidence for horizontal movement, dubbed "hard clam walking," in Mercenaria mercenaria, in which both hard clam sexes were equally as likely to "walk" toward a member of the opposite sex. This behavior has not been documented in Arctica islandica, but it has in other clams, such as Spisula solidissima (Tettelbach et al 2017). Observations of A. islandica movement have been limited to burrowing behavior (Taylor 1976, Strahl et al 2011, and the degree to which horizontal movement is common within the order Venerida is unknown.…”

Rapid two-anchor crawling from a milliscale prismatic-push–pull (3P) robot

“…Crawling locomotion is broadly defined as movement across a surface in which forward progression is enabled by body movements rather than limb movements [1]. A diverse array of animals demonstrate crawling locomotion including insect larvae [10], worms [11], clams [12,13], and snakes [14]. Similarly, many bioinspired crawling robots have been built and studied across a wide array of mechanical designs including soft-bodied, origami, and rigid crawling robots [15][16][17][18][19].…”

Assessment of the Relationship of Stock and Recruitment in the Atlantic Surfclam Spisula solidissima in the Northwestern Atlantic Ocean

“…Many examples are available of fisheries being overfished to the point where recruitment declines and the stock collapses (Cushing 1971, Hilborn & Walters 1992, Myers et al 1996, shellfish are no exception (Jackson et al 2001, Tettelbach et al 2013. For sessile and sedentary species, the potential of Allee effects cannot be discounted (Shepherd et al 1998, Kraeuter et al 2005, Tettelbach et al 2013, although behavioral adaptations may mitigate the probability (Buroker 1983, Ambrogio & Pechenik 2009, Tettelbach et al 2017). An example is the hard clam Mercenaria mercenaria, where unsustainable fishing mortality led to recruitment overfishing in both North Carolina and New York (Peterson 2002, Kraeuter et al 2005.…”