title for learn-about section on whelks & relatives in A SNAIL'S ODYSSEY
  Predators & defenses
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  Escape by swimming, crawling, hiding, or biting
  This section on predators & defenses is divided into topics of escape by swimming, crawling, hiding, or biting considered here, and
DURING EARLY DEVELOPMENT
ESCAPE BY BURIAL
SHELL COLOURS & CAMOUFLAGE
SHELL SCULPTURING
SHELL SIZE & THICKNESS, and
NOXIOUS SECRETIONS, considered in other sections.
 
Research study 1
 

photograph of olive shell Callianax biplicata crawling over the sand surfaceAs unusual as it seems, the olive shell Callianax biplicata is able to swim away from contact with potential predators.  Usually on contact with a sea star such as Pisaster brevispinus, Callianax is more likely to turn sharply and crawl away, or to burrow into the sand.  Sometimes, however, it rears up, withdraws its propodium, and extends composite drawing showing swimming postures in olive shell Callianaxthe metapodia sideways and forwards.  This flips the snail onto its back in a half somersault. The metapodium is now extended horizontally on both sides as a flat membrane and is flapped.  The motion lifts the snail from the substratum and carries it a short distance in upside-down swimming.  Edwards 1969 Veliger 11: 326.

NOTE shown here is swimming of the related Callianax zanoeta from the Gulf of California.  Drawings from Farmer 1970 Veliger 13: 73.

 


Olive shell Callianax biplicata creates a shallow
trench as it crawls along the sand surface 0.5X

 
Research study 2
 

photograph of snail Alia carinata Linda SchroederResearchers at Bodega Marine Laboratory, California describe  interesting escape behaviours in the columbellid snail Alia carinata in response to predatory sea stars Leptasterias hexactis.  The snails are customarily found on low intertidal rocks and algae or on the blades of surfgrass Phyllospadix scouleri, where they sometimes encounter Leptasterias. In laboratory experiments where Alia meets a sea star while crawling on a blade of surfgrass, perception of the sea-star’s scent leads to the snail flaring the tip of its siphon and pointing it towards the sea star.  Contact with a tube foot of the predator causes Alia to rear up on the hind portion of its foot, twist quickly through an arc of 180o, then run quickly away with its siphon flared and pointed towards the sea star.  In laboratory trials, 20 out of 20 individuals react in some positive way to contact with Leptasterias, while the same number of  individuals show no response to contact with a control metal probe or a non-predatory sea star Patiria miniata.  Field results are similar.  Contact with Leptasterias on a blade of surfgrass sometimes causes the snail to fall off, in which case it may later return by crawling up its still-attached mucous thread.  In about half the laboratory trials the snail will strike back at encroaching tube feet of the predator with its long proboscis, biting them and causing them to withdraw.  Fishlyn & Phillips 1980 Biol Bull 158 (1): 34. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington.

 
Research study 3
 

photograph of collumbellid snail Amphissa columbiana Linda SchroederResearch in Oregon on the defensive behaviour of snails Amphissa columbiana to predatory sea stars Pisaster ochraceus and Leptasterias hexactis show a stepwise increase in response from first contact with a predator’s arm to probing by the tube feet.  In the first instance, the snail twists its shell through an arc of 120o and crawls away at a velocity twice its normal rate (2.8 to 5.8 mm . sec-1).  In the second instance, the snail twists as before, but now it uses its proboscis to detach the adhering tube feet.  Usually, only a touch is required, but the author is unclear whether the radula is employed.  Kent 1981 The Veliger 23 (3): 275.  Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington.

NOTE  later research shows that the radula is, indeed, used for these up-close encounters (see Research Study 6 below)

 
Research study 4
 

photographs of ochre star Pisaster ochraceus and whelk Nucella ostrina


Observations of whelks Nucella ostrina at the Bodega Bay Laboratory, California reveal that they respond to scent or touch of sea stars Pisaster ochraceus with defined escape behaviours.  These include rocking of the shell, turning, and 180o reversal of direction of movement.  Miller 1986 Veliger 28: 394.

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photograph of a hatchling whelk Nucella ostrina, taken from a video courtesy of Louis Gosselin, Thompson Rivers University, British Columbia

CLICK HERE to see a video of a crawling hatchling Nucella ostrina about 1d after leaving the egg capsule. At this stage in life the snail must be vulnerable to a host of motile predators and its chief defense is probably hiding. Except for the tiniest and/or slowest predators, crawling would not be an effective defense. Note the thin shell of the hatchling. Its crawling speed is only about 1cm per minute 20X.

NOTE video replays automatically

 
Research study 5
 

Experiments on whelks at the Bamfield Marine Sciences Centre, British Columbia show that Nucella lamellosa can discriminate between the effluents of predatory and non-predatory crabs.  Thus, while Nucella crawls away from seawater that has passed over known predatory crabs Cancer photograph of whelks Nucella lamellosa with snail Lirabuccinum dirumproductus, they are indifferent to seawater pasing over non-predatory kelp crabs Pugettia producta and lithode crabs Lopholithodes mandtii  Interestingly, Nucella actually appears to be attracted to the scent of small shore crabs Hemigrapsus nudus, a species known to feed on small-sized snails and thus to be a potential predator of juvenile Nucella.  The results suggest that Nucella can assess from a distance the relative risks posed by different species of crabs and respond accordingly.  As for the apparent attraction to H. nudus, the authors suggest that it may aid the snails in finding protective under-rock refuges, habitats also occupied by the crabs. It is an interesting suggestion, but one that probably will need further researching. Marko & Palmer 1991 Biol Bull 181: 363.

NOTE  the test device is a plastic platform, perforated to allow water to drain through, that receives seawater from holding containers on either side.  A snail placed on the platform thus simultaneously contacts seawater from 2 sources, either crab vs. no-crab, or other combinations.  A snail crawling off the platform to one side or the other is scored as making a choice

 

Three whelks Nucella lamellosa, probably feeding
on barnacles Balanus glandula. The snail at
the lower left is Lirabuccinum dirum 1.4X

 
Research study 6
 

Research at Friday Harbor Laboratories and Shannon Point Marine Laboratory, Washington reveals that while the small intertidal/subtidal snail Amphissa columbiana readily falls prey to crabs such as Cancer spp. and Telmessus cheiragonus, it is rarely  eaten by sea stars.  In fact, in laboratory tests using 10 sea-star species found commonly in Amphissa’s habitat, only 3 snails are eaten out of 200 offered in a 7d period.  For 3 of the sea-star species used, it may have been that snails are not regular dietary items, but for 4 other species, all known to prey on snails of one kind or another (Evasterias troschelii, Leptasterias hexactis, Pisaster ochraceus, and Pycnopodia helianthoides), the answer appears to lie in an unusual defensive behaviour of the snails.  On attack by Leptasterias, for example, the snail inserts its proboscis deep into the ambulacral groove of one of the arms of the attacking sea star and slices into the vital radial nerve with its radula (see drawings below).  The radula extends from the end of the proboscis and has saw-like cusps that can quickly slice into tissue,  In the ambulacral groove of the sea-star’s arm this nerve lies close to the surface and is protected only by a thin epidermis.  The injury generally repels the attacker and the afflicted arm is often rendered useless for several days.  For the larger sea-star predators with longer more aggressive tube feet, such as Pycnopodia and Pisaster, the proboscis and radula are used only to nip at attacking tube feet. The authors never observe the snails to use their probosces defensively when under attack by crabs.  Braithwaite et al. 2010 J Shellf Res 29 (1): 217.

NOTE  these are Pteraster tesselatus, Solaster dawsoni, and S. stimpsoni

NOTE  the initial response of Amphissa to attachment of tube feet by an attacking sea star is to twist its shell rapidly from side-to-side, a behaviour described in an earlier Research Study

 
drawing of snail Amphissa columbiana in the act of slicing the radial nerve of attacking sea star Leptasterias hexactis drawing of proboscis tip with radula of snail Amphissa columbiana E-micrograph of radula of Amphissa columbiana showing double row of bicuspid teeth drawing of ambulacral groove of sea star showing sliced radial nerve
Snail Amphissa columbiana attempting to slice the radial nerve of attacking sea star Proboscis tip with extended radula of snail Amphissa columbiana E-micrograph of radula of Amphissa columbiana showing double row of cusps Drawing of ambulacral groove of sea star showing sliced radial nerve
 
Research study 7
 

graph showing avoidance responses by whelks Nucella ostrina to different risk cuesgraph showing hiding times in shell for whelks Nucella ostrina subjected to different risk cuesWhelks Nucella ostrina basically have only 2 options for avoidance defense from predators: to withdraw passively into their shells or to crawl actively away.  Are these strategies used randomly, or does one type of threat elicit one response and another type, the other?  What happens if both types of threats are perceived simultaneously? Are the responses “either/or”, or does one, say, passive withdrawal, grade into active escape crawling, or vice versa, or is the response a synergistic one? These interesting questions are addressed by researchers at Friday Harbor Laboratories, Washington using upstream stimuli of experimentally crushed conspecific snails and a pair of predatory crabs Cancer productus.  Snails are tested one at a time.  Results show that cues from injured prey snails mainly induce active avoidance crawling away from the cue source, while those from crabs induce passive avoidance withdrawal into the shell (see graph on Left), and also increase the time spent hiding in the shell (see graph on Right).  Snails exposed to both types of cues at one exhibit an intermediate response:  snails remain longer in their shells than when exposed only to injured prey, and initiate crawling-away behaviour sooner than when exposed to crabs alone (see graph on Right).  Thus, the 2 risk cues are not perceived separately and acted on independently; rather, the response is additive.  Mach & Bourdeau 2011 J Exp Mar Biol Ecol 409: 166.

 
Research study 8
 

histograms showing hiding and feeding responses of invasive oyster drills Urosalpinx and Ocinebrina to the presence of crabs Cancer productusAlthough it seems likely that invasive whelk species would instinctively recognise danger from snail-eating native crab species, up until now this has apparently not been tested.  Researchers at Shannon Point Marine Center, Anacortes, Washington redress this omission in a nicely designed series of experiments where invasive whelks Urosalpinx cinerea and Ocinebrina inornata are exposed to emanations from crabs Cancer productus feeding on conspecific prey from upstream locations and from crabs alone.  On detection of the chemical cues, both species of whelks hide more (see upper set of graphs) and reduce their own feeding activities on juvenile oysters (see lower set of graphs).  Closer examination of the interaction using Urosalpinx cinerea shows that this species more strongly reacts to cues from injured conspecifics, but still recognises and reacts to the upstream presence of the crab alone (results not shown here).   Defensive responses of both invasive whelk species are the same whether an individual is alone or among a group of conspecifics.  Grason & Miner 2012 Oecologia 169: 105.

NOTE  both species were introduced along with shipments of culture oysters Urosalpinx cinerea from the east coast and Ocinebra inornata from Japan.  Photographs of each species can be found at LEARN ABOUT CRABS: FOODS & FEEDING

NOTE  these could be from the crab itself, known as kairomones, or alarm chemicals released from damaged conspecific snails being eaten.  A kairomone is a chemical released by one species, usually a predator, that benefits an individual of another species, usually the prey species, without benefiting or harming the first species

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