Predators & defenses
 

Veliger larvae of abalones and other gastropods are eaten by planktonic carnivores and a host of filter-feeding benthic invertebrates (also some fishes). This section deals with a few topics relating to PREDATORS of abalones and relatives.

DEFENSES, including a possible defensive function of torsion, are considered in a section entitled LARVAL DEFENSES.  Adult abalones and related snails, such as top and turban shells, have various lines of PHYSICAL, CHEMICAL, and BEHAVIOURAL defenses against predators.

A juvenile abalone Haliotis kamtschatkana
runs from a small sunflower star Pycnopodia
helianthoides
at the Right of the picture

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  Predators
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Research study 1
  Abalones are preyed upon at every stage of life.  As juveniles, they are eaten by sea otters, sea stars, crabs, hermit crabs, and probably sea urchins, and by fishes such as cabezon and kelp greenling.  As adults, abalones are eaten by sea otters, sunflower stars, crabs, octopuses, and sometimes rays.  In Pacific Grove, California, inhabited by sea otters for more than 40yr, almost all abalone (mostly Haliotis rufescens) shelter in rock crevices where they compete for food and space with similarly hiding purple sea-urchins.  Lowry & Pearse 1973 Mar Biol 23: 213; Hines & Pearse 1982 Ecology 63: 1547.
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Research study 2
 

sea otter eats an abalone, courtesy SierraSolOn a dive to catch an abalone an otter may first try to dislodge it with its paws.  If this fails the otter may use a rock to try to break or dislodge the prey from its attachment.  Tool use in this way has long been suspected from SCUBA observations showing shells with pieces broken from them, and from anecdotal reports of sea otters with softball-sized rocks at the surface. Otters are also reported to use stones to break clams.  One in situ SCUBA observation at Pacific Grove, California describes an otter using a 1-kilo stone (later weighed by the authors) to pound at an abalone for 15sec at 3 hits per second, followed by a break for air and then another 30-sec bout of pounding.  Although over 100 hits failed to break the shell, the abalone was weakened enough for the otter to pull it free and eat it at the surface.  This may be the first formal documentation of tool use in sea otters.  Houk & Geibel 1974 Cal Fish Game 60: 207. Photograph courtesy SIERRASOL and an unknown photographer.


Sea otter eats an abalone

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Research study 3
 

Recognition of predators in gastropods is through chemical perception by a special organ, the osphradium, at the front of the mantle cavity and, in abalones, also by the many pallial tentacles around the periphery of the body.  The paired cephalic tentacles appear to be used mainly for food recognition and the eyes have no image-resolving ability.  The eyes of snails do, however, provide light-dark perception, and enable responses to shadows passing overhead and to location of under-rock hiding places.  Abalone drawings modified from Crofts 1929 HALIOTIS  Publ XXIX Liverpool Mar Biol Comm Memoirs, Univ Press Liverpool.

NOTE  lit. “head” G.

NOTE  abalone eyes are of the pigment-cup type, with a crytalline lens (yellow in the drawing), pigmented cells, and retinal cells

 

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Research study 4

 

Additional chemosensory organs identified in Chlorostoma funebralis and in other vetigastropods are bursicles located at the bases of the drawing of bursicles on the ctenidia of Chlorostoma funebralis as a representative vetigastropodctenidial filaments.  The bursicles are swellings (actually pockets) and are positioned directly in the path of respiratory currents flowing between the ctenidial filaments.  The bursicles are well endowed with nerves originating from a longitudinal nerve running along the lower part of the ctenidium, that itself arises from the branchial ganglion. An osphradial nerve also arises from the branchial ganglion. Normally, Chlorostoma responds to the touch or scent of sea stars Pisaster by running away; however, following the severence of different regions of the osphradial and ctenidial nerves, the escape response to scent is lost, but not the response to touch, showing that the test specimens are otherwise healthy and confirming that the bursicles are involved in defense.  Szal 1971 Nature 229: 490. 

NOTE  vetigastropods in which the bursicles have been identified include abalones, keyhole limpets, Calliostoma spp., other Chlorostoma spp., and Pomaulax spp.

NOTE  lit. (“purse” L.) referring to their pocket-like shape 

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