Learn About Abalones & Relatives: Predators & defenses

Behavioral Defenses

Topics relating to predators & defenses include behavioral defenses, considered here, and LARVAL, PHYSICAL, and CHEMICAL defenses, considered in other sections.
photographs showing the twisting response of an abalone Haliotis kamtschatakan in response to an encroaching sunflower star Pycnopodia helianthoides Behavioral responses to an attacking sea-star predator in abalones and relatives include shell-twisting, tentacle movement, fast crawling, and sometimes releasing attachment of the foot and dropping to the sea bottom.

Research study 1

Adult abalones mostly sit openly on rocks, whereas juveniles often hide under rocks.  In Pacific Grove, California, sea otter predation is so intense that surviving abalones Haliotis rufescens are mostly found in crevices.  Do the abalones learn to hide in crevices, or has selection favoured a crevice-dwelling variant?  Neither seems likely.  We do know, however, that sea urchins Strongylocentrotus spp. co-inhabit these crevices and compete with the abalones for space and food.  Lowry & Pearse 1973 Mar Biol 23: 213.

Research study 2

drawing of an abalone showing external featuresOn contact with tube feet or scent of sea star predator, such as Pycnopodia helianthoides or Pisaster ochraceus, many west-coast species of abalone initiate escape and protective behaviour.  This includes moving of the epipodial tentacles, stiffening and swelling of the epipodium, rapid twisting of the shell back and forth, and rapid crawling.  Accompanying this may be release of a viscid white mucousy secretion.  This escape locomotion differs from ordinary locomotion in that the shell is elevated and the foot is lifted from the substratum in its central portion. Drawing (above) and information from Mongomery 1967 Veliger 9: 359; drawing rRight) from Crofts 1929 HALIOTIS Publ XXIX Liverpool Mar Biol Comm Memoirs, Univ Press Liverpool, 174 pp.
drawing of an abalone in fast locomotory speed
Note the raised central portion of the foot of this fast-crawling abalone
Haliotis kamtschatkana escaping from a sunflower star Pycnopodia helianthoides. The predator has been placed by a SCUBA-diver near to a quiescent abalone. Note that the abalone easily outdistances the fast-crawling sea star. Video courtesy James Mortimer, Bamfield.

Research study 3

of abalone Haliotis kamtschatkana to various sea starsEscape speeds of abalone Haliotis kamtschatkana in response to sea-star predators varies with the type of sea star.  The speeds shown here are ones recorded in laboratory tests.  James & Nolen 1978 Am Zool 18: 675.

NOTE neither Leptasterias nor Pisaster is a natural predator of abalones.

Research study 4

Although adult abalones and sea urchins in California compete for the same algal foods, juvenile abalones may be found sheltering for protection under the spine canopies of adult sea urchins, along with juvenile red and purple sea urchins and many other small invertebrates, including sea stars, ophiuroids, snails, crabs, worms, and amphipods. Laboratory tests in California show that survival of juvenile abalone in the presence of predatory crabs is almost 70% better when red sea-urchins are present than when they are absent.  Rogers-Bennett & Pearse 2001 Conserv Biol 15: 642-647.

Research study 5

photograph of black turban snails Chlorostoma funebralis in a surf-channel crevice

Larvae of black turban snails Chlorostoma funebralis settle in the higher regions of the intertidal zone and live there for several years before migrating downwards to lower areas.   Here, they contact sea-star predators, most notably ochre stars Pisaster ochraceus.   Defensive response by Chlorostoma to touch or close presence of predatory sea stars is sideways twisting followed by quick escape crawling, or releasing their hold on rocks and dropping to the sea bottom.  Feder 1963 Ecology 44: 505; Paine 1969 Ecology 50: 950.

Research study 6

Escape responses of Chlorostoma funebralis, involving shell-twisting and sometimes direct table of % strong responses of black turban snails Chlorostoma funebralis to several west-coast sea starscrawling up, onto, and over a potential predator, are graded depending upon whether or not the test species is a known predator.  Physical contact with several sea-star and whelk species in Pacific Grove, California elicits strong escape responses.

The only test species eliciting no, or only weak, responses in Chlorostoma are the bat star Asterina miniata and leather star Dermasterias imbricata. The first is an omnivorous scavenger, lives on muddy-bottom habitats, and rarely, if ever, encounters C. funebralis. The second, however, Dermasterias, is predatory on a wide variety of invertebrates including sea urchins, sea stars, and spongest.  Its lack of effect on Tegula is therefore somewhat surprising and may warrent further investigation.  Yarnall 1964 Veliger 6 (Suppl): 56.

NOTE  tests involve touching a tube foot (sea star) or piece of sole of foot (whelk) to Chlorostoma, then grading the intensity of response.  The author uses 4 categories of response in the study (strong, medium, weak, and absent) but, for economy of space, only percentages of Chlorostoma individuals (N = 50 for each pairing) showing strong responses are reported here.   “Touch” controls with a clean steel probe give an average of 12% strong responses out of 450 trials (50 with each test species)

Research study 7

schematic showing extent of overlapping distributions of top shells (Chlorostoma and Promartinia) and their sea-star predators

Of the species of Chlorostoma (Tegula) inhabiting rocky-shore and kelp-forest regions along the west coast two, C. (Tegula) funebralis and C.(Tegula) brunnea, live in mid-low/shallow subtidal regions where they regularly contact predatory sea stars Pisaster spp. and Pycnopodia helianthoides.

Two other species, Promartynia (Tegula) pulligo and C. (Tegula) montereyi, live primarily on the bottom portions of Macrocystis spp. and other large subtidal kelps and have less contact with Pisaster spp.  On some central California shores, C. (Tegula) brunnea, if not on the sea bottom, may be found on the tops of large kelps where it also has no contact with Pisaster. Lowry et al. 1974 Biol Bull 147: 386; Riedman et al. 1981 Veliger 24: 97.

Research study 8

photograph of snail Chlorostoma brunneaChlorostoma brunnea, which has more overlap with Pisaster species than do the other snails, relies on avoidance and fast crawling to escape, often combined with shell-twisting and, on vertical surfaces, release of attachment.

photograph of snail Promartynia pulligoPromartynia pulligo, in contrast, flees from contact with Pisaster species but clamps down on contact with Pycnopodia. 

photograph of snail Chlorostoma montereyi

Chlorostoma montereyi flees from contact with Pisaster species but, if caught, retreats deeply into its shell which is relatively larger than the other species.  Most often the sea star rejects what it may perceive as an empty shell.  Unable to outrun Pycnopodia, C. montereyi on capture allows its soft tissues to be touched by the sea star, which often leads to rejection, perhaps because of distasteful chemicals.  Feder 1963 Ecology 44: 505; Watanabe 1983 J Exper Mar Biol Ecol 71: 257;  sea also Watanabe 1984 Ecology 65: 920.

Research study 9

photograph of sea star Pisaster giganteus courtesey NOAA Channel Islands National Marine SanctuaryWhen touched by foraging sea stars Pisaster giganteus (see photo on Left) the snails photograph of snail Calliostoma ligatumPromartynia (Tegula) pulligo (see photo in previous Research study) and Calliostoma ligatum (photo on Right) rotate their shells vigorously, then release their attachment and tumble away.  Studies in California show that C. ligatum uniquely coats its shell with slippery mucus from glands on the posterior part of its foot, possibly to aid in this twisting response.  It also uses its radula to “bite” (scrape?) at the sea star.  Are these strategies effective in reducing predation by sea stars?  To test this, 33 individuals of each species are first narcotised, then placed along with untreated control snails (in groups of 4: 2 of each treatment group) 5-10cm in front of the leading arms of foraging P. giganteus in the field.  Under these experimental circumstances, the answer to our question is 'yes'.  Narcotised individuals of both species are significantly more likely to be captured than control individuals (see histogram on Right).  Moreover, significantly fewer unnarcotised C. ligatum are eaten than P. pulligo, possibly owing to its more effective defense (i.e., slippery shell; the author comments that no “biting” is seen in the field study).  Harrold 1982 The Amer Nat 119: 132; photo of P. giganteus courtesey NOAA Channel Islands National Marine Sanctuary.

NOTE  5-10min in seawater containing MgCl2

histogram showing % capture by sea stars Pisaster giganteus of snails narcotised and non-narcotised

Research study 10

At least 4 trochid-snail species co-inhabit beach areas in Santa Catalina Island, California with several sea-star and whelk predators.  Three of these, Chlorostoma aureotincta, Norrisia norrisi, and Pomaulax undosa will run from contact with Pisaster giganteus and other sea-star and whelk predators, but the fourth, Chlorostoma eiseni, stays put.  The authors credit histograms of growth of Pisaster giganteus fed on different snail species this behaviour with a 65% thicker shell and less digestible tissues in C. eiseni as compared with its congenitor C. aureotincta

If juvenile Pisaster are fed shell-less tissues of the two Chlorostoma species, growth is similar, suggesting that the species do not differ in nutritional value (Left-hand histogram).  However, growth of juvenile sea stars on intact snails is significantly slower on a diet of C. eiseni than C. aureotincta, possibly owing to the longer time taken for sea stars to digest the tissues of the former (Right-hand histogram).  In laboratory comparisons of digestibility, tissues of aureotincta are digested 3-fold quicker than those of eiseni.  Moreover, the overall time for Pisaster to eat a single C. eiseni in the lab is 11h versus 4h for C. aureotinctaSchmitt 1981 J Exp Mar Biol Ecol 54: 251.

NOTE  growth data for another asteroid species, not shown here, is similar to those presented for Pisaster giganteus

NOTE  the digestibility tests use 50% H2SO4 over 30min at 40oC

Research study 11

In the lower intertidal zones of California and Oregon beaches Chlorostoma funebralis co-occurs with a potential predatory crab Cancer antennarius.  Laboratory studies at Bodega Marine Laboratory, California show that adult crabs (7-10cm carapace width) are capable of eating all sizesof funebralis offered, up to 3cm diameter.  When exposed to crab-scented seawater in containers in the lab, a significant proportion of the prey snails crawls upwards in apparent escape in comparison with control snails in clean seawater (76 vs. 22%, respectively).  In running photograph of crab Cancer antennariusseawater, the percentages crawling upward are also significantly different (60 vs. 26%), but smaller in magnitude, probably owing to dilution of the crab scent in the flowing water.  Interestingly, funebralis from sites where C. antennarius is absent do not show the behaviour.  Geller 1982 J Exp Mar Biol Ecol 65: 19.<

NOTE  the crabs are positioned in mesh containers upstream from the test snails

Crab Cancer antennarius 0.4X

Research study 12

photographs of snail Norrisia norrisi to show extent of barnacle foulingThe snail Norrisia norrisi in Santa Catalina, California likes to inhabit large kelps1. In its lofty kelp habitat it has about a 4% chance each day of being dislodged. If this happens and it crawls on the sea bottom, it suffers 10-fold greater mortality than it would in the kelp habitat.  One of its benthic predators is the octopus Octopus bimaculatus, which drills2 and eats it.  If the octopus fails to drill completely through the shell of Norrisia, which happens quite often, the drill holes attract settling larvae of the barnacle Megabalanus californicus3 and the shell may become heavily fouled with these barnacles.  About 30% of the snails have barnacles growing on them.  If heavily fouled the snails have difficulty crawling back to the relative safety of the kelps.  When they attain their perches, they are dislodged twice as frequently and remain longer on the sea bottom than unfouled snails.  On the sea bottom, especially with their load of barnacles, they run the risk of being captured and consumed by benthic predators, such as octopuses, lobsters, and whelks. The author's measurements on locomotory rates indicate that moderately to heavily fouled snails are at least 25% slower than unfouled ones.  Moreover, data from laboratory tests on susceptibility of Norrisia to sea-star predators show that fouled snails have an 8-fold greater risk of being eaten than unfouled ones.  It’s double jeopardy: if the octopuses fail to kill Norrisia outright, their drill-holes become fouled with barnacles and indirectly lead to greater risk of death from other sources.  Schmitt et al. 1983 J Exp Mar Biol Ecol 69: 267.

NOTE1  the kelps are Macrocystis pyrifera and Eisenia arborea.  Counts by the researchers show that 97% of N. norrisi inhabit these kelps, while the remainder live on the sea bottom

NOTE2 the authors report that of 269 live Norrisia examined, 29% have been drilled by an octopus, and many of these are also encrusted with barnacles.  Why the octopuses fail so often to kill a snail is not known

NOTE3 this barnacle is virtually the only epibiont found on Norrisia in the study area

Research study 13

graph showing upward-climbing response of black turban snails Chlorostoma funebralis dependent upon intensity of sea-star presence increases from belowThe upward crawling behaviour of Chlorostomafunebralis in the presence of potential predators can greatly influence the species’ lower limit of distribution.  In southern California the lower limits of C.funebralis are generally higher than in northern California, possibly because of the greater abundance of predators in the southern regions.  Predators in this area include ochre stars Pisaster ochraceus, several crabs Cancer spp., and octopuses Octopus bimaculoides and O. bimaculatus – the last two of which are lacking at northern sites.  Predator intensity at each site is scored by direct quadrat counts and observation of transient predators (e.g., octopuses and crabs), and by indirect counts using the presence of characteristically crushed and drilled shells as indicative of crab kills and octopus kills, respectively.  Note in the graph on the Left that as the “predator score” increases (i.e., greater predat-ory intensity) at the 13 sites studied, so the lower limit of distribution Chlorostoma rises.

Reciprocal translocations of snails from one location to another, in some cases to different heights on the shore, provide supportive data.  For example, snails from San Luis Obispo and San Mateo, released on the shore at San Luis Obispo, move quickly upwards, regardless of whether they are released low on the shore or high on the shore (see graph lower Left). Results for the reciprocal transplant, from both locations and released on the shore at San Mateo, are shown in the graph at the graphs showing heights of black turban snails Chlorostoma funebralis at different sites in Californialower Right. Note that snails from the high "predator-score" location (San Luis Obispo) consistently move higher on the graphs showing heights of black turban snails Chlorostoma funebralis at different sites in Californiashore after translocation, in accordance with the author's predictions.

Also noteworthy is the generally lower heights attained by the two sets of funebralis in the translocation to San Mateo (graph on Right). The “predator score” is lower at the San Mateo site than at the more southerly San Luis Obispo site (4 vs. 6, respectively).  This general pattern is repeated in many other translocations.  The author proposes, based on these field experiments and on laboratory observations that the snails may be responding to chemical exudations from the predators.

The explanation for snails translocated from the southern population (San Luis Obispo) always ending up higher on the shore than snails from the northern population (San Mateo) may owe to long-term differences in the intensity of predation photograph of Octopus bimaculoides courtesy of Roger Hanlon, Woods Hole, Massachusettsby octopuses, which are much rarer in the intertidal zone in northern California.  However, an alternative explanation also provided by the author might be that acclimation to cooler, moister conditions at the more northern site (San Mateo) could keep the northern snails lower on the shore when translocated to the southern site.  This may also explain why the southern snails (San Luis Obispo) move higher on the shore than the northern snails (San Mateo) when translocated to the more northerly site.  Finally, funebralis generally is larger in the northerly populations than in the southerly ones, and larger snails are usually found higher on the shore than smaller ones.  Fawcett 1984 Ecology 65: 1214; photo of Octopus bimaculoides courtesy of Roger Hanlon, Woods Hole, Massachusetts.

NOTE  there are 12 sites in California ranging from San Diego County in the south to Sonoma County in the north, and one site at Pt. Anderson in Washington

NOTE  in this example, the 2 sites are separated latitudinally by about 300km

Research study 14

Studies in San Juan Island, Washington show that 3 “Margarites” species, M. (Pupillaria?) pupillus, M. (Pupillaria) salmonea, and M. (Pupillaria) rhodia, and Calliostoma ligatum, respond only weakly to the scent of predatory sea stars Leptasterias hexactis and Pisaster ochraceus.  However, if the sea stars are touched to the soft parts of the snails, escape reaction is greatly intensified.  All species twist their shells vigorously, rear up (often losing contact with the substratum), and sometimes somersault.  Hoffman 1980 Pac Sci 34: 233.

Research study 15

Top shells Pomaulax gibberosa in British Columbia often harbour a commensal polynoid worm that sometimes shows itself outside of the snail’s mantle cavity.  Whether the worm comes out to bite at a potential predator, similar to the behaviour of a mutualistic worm in keyhole limpets Diodora aspera, is not known.

In this photo the snail has partially emerged from the seawater in an aquarium tank. The worm may have come out to investigate the sudden change in living conditions 0.7X

Research study 16

photograph of ochre star Pisaster ochraceus in a tidepool with prey black turban snails Tegula funebralisOne doesn’t think of snails as having different behaviours but, just as in “higher” animals, one member of a snail species will behave differently than another member. One snail, for example, may crawl relatively more quickly than another, or seek a mate and hunt for food or shelter at different times and in different ways than another. Likewise, predatory sea stars will exhibit their own behavioral variability in activity levels and patterns. How these variations might interact proximally to mediate predation rates, and ultimately to determine whether the variability is maintained or eliminated in a community is examined for snails Chlorostoma funebralis and one of its predators, the ochre star Pisaster ochraceus, by researchers at the University of California, Davis. The researchers assess behavioral characteristics of each of abouit 40 snails (representing a single test batch), enclose them in an outdoor “mesocosm” for 2wk with a single P. ochraceus, and record who gets eaten. Eighteen replicates are done. Results show that the best behavioral correlate for maximum survival of a snail, not surprisingly, is good predator avoidance combined with being large in size. As would be expected, these effects are mediated by predator behavioral “type”. Thus, greater predator-avoidance behaviour is favoured with active sea stars, while lesser predator-avoidance behaviour is favoured with inactive sea stars. The authors note that both trends will tend to favour maintainance of trait variations within the 2 populations. Pruitt et al. 2012 The Am Nat 179 (2): 217.

NOTE recently re-classified to its original name Tegula funebralis

NOTE the authors give a good example of such interactions. A “bold” snail will benefit from seeking out food in high-risk foraging areas, but at the risk of greater predation


A common behavioral defense-response of a black turban shell
Tegula funebralis to a sea-star predator Pisaster ochraceus
in a tidepool is to escape by crawling out of the water

Research study 17

In a follow-up study, members of University of California, Santa Barbara further investigate the role of behavioral variabilities ("personalities") in defensive responses of black turban snails Tegula funebralis1 to predatory sea stars, in this case, Pisaster giganteus. This issue in question is whether "bold" individuals are at greater of lesser risk of being eaten than "fearful" ones. Through a series of predator-prey confrontation experiments, the researchers find in fact that fearless (bold) snails survive less well than fearful snails. The confrontations involve snails in a seawater tray being washed with seawater emanating from a centrally located perforated container holding a single Pisaster. Twenty-five test snails at a time are placed in the tray, washed with predator-tainted seawater for 30min, and their responses measured by distances they crawl up the walls of the tray to escape the perceived predator. Five replicates enable the repeatability and degree of each snail's behaviour to be assigned. The tradeoff for a snail is protection at cost of increased desiccation risk. So, in the researchers' view, a higher-crawling snail is a "bolder" snail. In a follow-up experiment 25- or 50-individual batches of the same snails are housed with a single Pisaster for 14d in a mesh-lidded arena and their survival recorded. Results show significantly lesser survival for larger-sized snails, for snails that crawled highest out of the water in the earlier test (i.e., the ones most bold2), and for snails in lowest density. The last is easiest to explain for it takes a while for a sea star to consume an individual snail, so all others benefit, in other words, dilution of risk). Susceptibility of larger snails may relate to their ease of detection and handling, or perhaps to their greater yield of nutrients and energy. The remaining category, the bold snails that crawl highest in the first experiment and are here eaten more readily than ones less bold, is more difficult to explain. But why are the highest crawlers considered bolder? Surely, they must be the most fearful because they escape the furthest. Aren't the bolder ones those the ones that hang back closer to the predator? Do the authors believe that like other herbivores3 that take risks to find richer foraging areas, these snails are heading up into danger to find algal foods sans sea-star predators? This is not what the snails are doing, rather, they are simply escaping. If they climb high enough to risk desiccation, then it will likely be too dry to feed. Another common defense response of Tegula funebralis in tidepools to the scent or touch of sea-star predators is to release their hold on the substratum and fall to the bottom. In this case, a bolder personality would hang on longer, just as it would not climb so high out of the water in the researchers' experiments. The basic premise defining a "bolder-personality" snail is hard for the reader to understand, just as is the authors' interpretation of their results. Foster et al. 2017 Current Zool 63 (6): 633.

NOTE1 the older name Chlorostoma funebralis is actually used by the researchers, which was correct at the time of publication

NOTE2 use of such terms as "personality", "bold", and "fearful" borders on anthropomorphism, that is, the attribution of human traits or emotions to non-human entities, in this case, to a snail. You might wonder how else to describe the snail's behaviour, if not with the handy single-word descriptors just mentioned. For example, is "the tendency for a snail to minimise its exposure to a predator by hiding away or moving away as quickly as possible", better than the descriptive term "fearful"? If fearful says all this without being anthropomorphic, then perhaps "fearless" would be okay as well. But does a snail feel "fear" or behave "boldly"? In their defense, the authors would likely say, "Oh, we know all of this and so do the readers...". But do they? Oddly enough, anthropologists/behaviorists are often the worst offenders in their use of anthropomorphisms

NOTE3 examples of "bolder personalities" in the vertebrate world might include antelope that venture out of the safety of the herd into better foraging afield and risk attack from a lion, or zebras in Africa so desperately wanting to drink at a water hole that they risk their lives from crocodile attack as they approach the water's edge