Behavioral Control of Swash-Riding in the Clam Donax variabilis

Abstract

Clams of the species Donax variabilis migrate shoreward during rising tides and seaward during falling tides. These clams spend most of the time in the sand, emerging several times per tidal cycle to ride waves. Migration is not merely a passive result of waves eroding clams out of the sand; rather clams actively jump out of the sand and ride specific waves. Such active migration is experimentally demonstrated during a falling tide by comparing the motion of dead and live clams; live clams emerge from the sand and move seaward even when dead ones do not. As low tide approaches, live clams become progressively less active. They cease migrating for 2 hours around low tide and resume jumping to migrate shoreward after the tide has turned. During the rising tide, far from being passive, the clams jump out to ride only the largest 20% of waves. Specifically, they choose swash that have the largest excursion, i.e., those swash that move furthest on the beach.

Competitive interactions in macroinfaunal animals of exposed sandy beaches

“…The macroinfaunal animals of exposed sandy beaches are mobile and often exhibit regular tidal migration and swash riding behaviors (Trueman 1971;McLachlan et al 1979;Ansell 1983;Ellers 1995aEllers , 1995bBrown 2001;Jaramillo et al 2001). Those behaviors enable invertebrates to spend more time in the active intertidal swash, a zone which provides better feeding opportunities for suspension feeders and scavengers, while serving as a refuge from vertebrate predators, both avian from above and piscine from below.…”

Helpful habitant or pernicious passenger: interactions between an infaunal bivalve, an epifaunal hydroid and three potential predators

“…It is possible that a clam with the hydroid, due to its increased stability during passive transport, can ride swash of greater speeds. However, because Donax uses sound cues to emerge from the sand and ride only the largest waves (Ellers 1995b(Ellers , 1995c, it is unlikely that Donax with the hydroid will regularly experience greater swash speeds than Donax without the hydroid. At the same swash speeds, clams with hydroid colonies traveled at significantly slower speeds before orienting and traveled significantly shorter distances per each swash ride than clams with no hydroid (Fig.…”

Tide, time and space: Scales of variation and influences on structuring and sampling beach clams

“…Like other beach clams (Leber, 1982;Donn et al, 1986;Ellers, 1995), D. deltoides can move up and down the beach with the tide to maintain their position in the swash zone; throughout sampling clams were often observed 'riding waves' up and down each beach with the incoming and outgoing tides, respectively. These clams may not move all the way to the upper swash limit at high tide, but remain at a lower height on the beach (e.g.…”

“…residual variance) was mostly greatest in all density analyses. The behaviour of clams and their ability to move rapidly over short distances and periods of time by utilizing waves and currents (Leber, 1982;Ellers, 1995) could explain some of the patchiness among replicate samples. Notably, many clams were at times caught in some replicate samples within a patch, but few or no individuals were caught in the other adjacent samples (b20 m apart).…”