subtitle for learnabout section of A SNAIL'S ODYSSEY
  Life on the high shore
 

Waves & currents

  This section on life on the high shore is divided into topics of waves & currents, considered here, and DESICCATION, THERMAL TOLERANCE, SALINITY TOLERANCE, and VISION & OTHER SENSORY INPUTS, considered elsewhere.
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Research study 0
 
drawing showing crawling response of Littorina kennae in a current

Research at Hopkins Marine Station, Pacific Grove, California shows that Littorina keenae in currents has a positive rheotaxis and so, like most snails, tends to crawl into a current (see illustration on Left).  Interestingly, although the initial movement is counter-clockwise, the final resting orientation appears to maximise water flow through the mantle cavity (see illustration near Right).  The author thinks that the turning response of a crawling snail may owe to hydrodynamic forces on its asymmetrical shell that tend to push it to the left in a current (see illustration far Right).  Neale 1965 The Veliger 8 (1): 7.

NOTE formerly Littorina planaxis

drawing showing final resting orientation of Littorina keenae in a current drawing showing hydrodynamic force on an empty Littorina keenae shell in current
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Research study 1
 

graph showing effect of wave force on size of littorinid snails Littorina sitkana and L. plenaA finding in a study comparing morphological differences in shells of two easily confused species, Littorina scutulata and L. plena, is that shell sizes are smaller in both species with increasing wave forces in the habitat. Rugh 1997 Veliger 40: 350.

NOTE for original study see IDENTIFICATION OF LITTORINES

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Research study 2
 

The Littorina species scutulata and plena are morphologically similar, and much attention has been paid to means of separating them visually.  In a study of collections of snails from map showing collection sites for study of tenacity and size in relation to wave exposure in 2 species of littorinid snails Littorina scutulata and L. plenasites in Puget Sound and the Washington open coast, a researcher investigates ecological differences between the 2 species. The sites differ markedly in degree of wave exposure, but the author is unable to find drawing showing experimental device for measuring tenacity in littorine snailscorrelative differences in tenacity in either of the 2 species.  Comparison of foot area against shell height (= length) reveals no significant difference between the species, nor does a comparison of tenacity with foot area.  Hohenlohe 2003 Veliger 46: 162.

NOTE  to measure tenacity, a spring balance is used in conjunction with a means to increase force (see schematic on Right). There are many refinements that can be applied to this basic method, such as what type of lifting force to apply (shear or vertical), what type of substratum to use, number of replicates on the same animal, lab or field, and so on.   However, as long as methods are standardised within a study, then the data should permit comparisons within that study, but not necessarily between studies.  For example, an earlier report on tenacity in L. scutulata of 12-15mm shell length lists stationary tenacity as 1100g . cm-2 and moving tenacity as 500g . cm-2, quite different from the approximately 200g . cm-2 values reported in this study for stationary tenacity in equivalent-sized littorines. For earlier report see Miller 1974 J Exp Mar Biol Ecol 14: 99

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Research study 3
 

photograph of collecting site for winkles Littorina keenae for dislodgement/return studygraph showing percentage returns of littorines Littorina keenae that have been experimentally dislodged into the wavesThe cartoon-winkle L. scutulata that is the central player in ODYSSEY was tossed off its perch in the upper intertidal region and successfully made it back home, but not without numerous, some quite harrowing, adventures. But what is it like in real life for a winkle that is dislodged by waves or other causes? Does dislodgement lead to a successful return, perhaps a distant displacement, or a likely death? The answers to these questions are provided by researchers at Hopkins Marine Station, California who attach numbered tags to 3 separate groups of 50 high-shore winkles Littorina keenae (arrow in photo denotes one of 3 collection/dislodgement sites) and toss the snails into the water at high tide during periods of different wave heights, and record numbers returning over a 1mo period. The good news for winkles is that return-rate statistics are surprisingly high, at 54-90% (see graph; controls are individuals that are collected, tagged, and returned to the same place on the shore). The authors additionally note a strong preference for snails to return to the approximate tidal heights from which they were collected, but not actually “homing” to their original sites. Wave heights during dislodgement have no significant effect on percentage of snails returning. Several of the “non-returnees” are later found as dead but undamaged shells, occupied by hermit crabs, having possibly fallen prey to “digesting” type predators such as sea anemones and seastars. Miller et al. 2007 J Mar Biol Ass UK 87: 735. Photograph courtesy the authors.

NOTE the dislodgement experiments also test for wave-turbulence effects. Individuals selected are adults of >7mm shell length

NOTE the authors note that some of the test snails may have found their way back to the top of the shore, but outside of the delineated census area; hence, survival may well have been more than reported here

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