title for learn-about section on whelks & relatives in A SNAIL'S ODYSSEY
  Foods, feeding, & growth
 

Whelks living in intertidal or shallow subtidal regions feed on various hard-shelled prey, mostly mussels and barnacles.  Olive shells in sand habitats have more diverse feeding modes and diets.

Topics in this secion include diets, considered here, and
RADULAR DRILLING,
CALIFORNIA CONE SHELLS: CUSPS USED AS HARPOONS,
USE OF SHELL SPINES IN FEEDING,
FACTORS IN DIET SELECTION,
GROWTH & MATURATION
, and
HATCHLINGS AS PREDATORS considered in other sections. 

  black dot
  Diets
  Topics in this secion include diets, considered here, and RADULAR DRILLING & CUSPS, CALIFORNIA CONE SHELLS: CUSPS USED AS HARPOONSUSE OF SHELL SPINES IN FEEDING, FACTORS IN DIET SELECTION, GROWTH, and HATCHLINGS AS PREDATORS considered in other sections.
  black dot
Research study 1
 

photograph of whelk Nucella ostrina sitting on a prey barnacle Semibalanus cariosusCategorisation of prey species eaten by 287 whelks Nucella ostrina in Mukkaw Bay, Washington shows their principal prey (95%) to be 3 species of acorn barnacles (Balanus glandula, Chthamalus dalli, and Semibalanus cariosus).  The remaining 5% of the whelks in the sample are eating mussels Mytilus spp. Paine 1966 The Am Nat 100: 65.

 

 

 

 

A whelk Nucella ostrina positions itself
on a barnacle Semibalanus cariosus,
perhaps in preparation for drilling 2X

 

  black dot
Research study 2
 

A study at the University of Washington on diets of Hawaian and west-coast cone shells reveals that the approximately 8 species of Conus  in Hawai’i have comparatively specialised diets, while a single species Conus californicus in California has a highly diverse diet, in fact, the most diverse known for any of the world’s 500-or so Conus species.  The explanation is that competition for food resources in Hawai'i and other tropical areas has led to diet specialisation, while the lack of co-occuring cone shells as potential competitors for C. californicus has led to diet generalisation.  Of a total of 56 food items identified for C. californicus, snails comprise 25 (8 spp.),  bivalves 15 (9 spp.), polychaetes 13 (9 spp.), amphipods 1, fishes 1, and cephalopods 1.  Kohn 1966 Ecology 47 (6): 1041.

  black dot
Research study 3
 

photograph of an olive shell Callianax biplicata burrowing in sandIn shallow sands, the subterranean movements of olive shells Callianax (Olivella) biplicata are readily visible from above from its burrowing tracks.  The species apparently has versatile feeding modes, from deposit-feeding, to suspension-feeding, to eating algae and animal prey.  Edwards 1969 Am Zool 9: 399.

 

 

 

 

Olive shell Callianax biplicata burrowing on a
sand beach near Tofino, British Columbia 1X

  black dot
Research study 4
 

photograph of mud snails Ilyanassa obsoleta eating a dead crabThe eastern mud snail Ilyanassa obsoleta was introduced to the west coast in shipments of oysters Crassostrea virginica in San Francisco, California in 1907, in Willapa Bay, Washington in 1945, in Boundary Bay, British Columbia in 1952, and possibly in other locations.  The snails feed on detritus, diatoms, algae, dead plant and animal flesh and, based on often high population densities, are highly successful.  They apparently out-compete other mud snails for food, eat their eggs, and even exclude various detrital-eating spionid worms by taking their food.  Their life span is about 5yr. Ilyanassa is unusual in having a crystalline style, a feature usually associated with bivalves.  The authors suggest that it may be an adaptation for processing plant starches in the diet.  Curtis & Hurd 1981 Veliger 24: 91.

NOTE  this species is a vector for several trematode flatworms, at least one type of which causes swimmer’s itch in marine habitats

Mud snails Ilyanassa obsoleta feeding
on a dead crab Cancer magister 0.3X

  black dot
Research study 5
 

drawing of a leafy horn-mouth snail attacking a clam in a burrow in the rockField diets of leafy-hornmouth shells Ceratostoma foliatum vary geographically.  For example, in the San Juan Islands, Washington, their diet is mainly barnacles and pholadid bivalves such as Penitella, while in areas of Oregon they eat mainly bivalves, with littleneck clams Protothaca staminea representing 49% of the diet, the California date mussel Adula californiensis 49%, and Hiatella arctica the remaining 2%.

Most littleneck clams (82%) are drilled at the juncture of the shell edges where the shells are thinnest, and only 18% in the main part of the shell valves.  The drawing shows a Ceratostoma attacking a Protothaca within an old pholid burrow in a rock.  The snail has inserted its foot into the burrow. The 2 lobes of the foot form a guide down which the proboscis is extended for drilling.  Spight et al. 1974 Mar Biol 24: 229; drawing modified from Kent 1981 The Nautilus 95: 38.

NOTE the author has drawn the foot and tentacles symmetrically on either side of the labial spine...could the function of the spine be to maintain the symmetry of the tentacles in relation to the foot?

  black dot
Research study 6
 

photograph of whelk Nucella ostrina feeding on barnacles Balanus glandula and Chthamalus dalli in a crackA study of prey species eaten by Nucella emarginata in Pacific Grove, California over a 4mo period during Jan-May shows an apparent preference for barnacles Balanus glandula out of a total of 7 prey species.  Twenty-four other potential prey invertebrate species, not listed, are present in the habitat but not eaten.  The snails feed only when immersed by the tide, but remain in feeding position during air exposure.  West 1986 Ecology 67: 798.

NOTE  the 7 species include 4 species of barnacles, 2 of limpets, and one of mussels. Further details on diet selection in these whelks can be found in: FOODS, FEEDING, & GROWTH: FACTORS IN DIET SELECTION

 

A whelk Nucella ostrina feeds on barnacles
Balanus glandula
and Chthamalus dalli 2.5X

  black dot
Research study 7
 

schematic showing food preferences of whelks Acanthinucella punctulata in Pacific Grove, Californiaphotograph of whelk Acanthinucella punctulata courtesy Gary McDonald, Santa Cruz, CaliforniaIn Pacific Grove, California whelks Acanthinucella punctulata eat mostly barnacles Chthamalus spp., but many other prey items are also consumed.  With the exception of limpets, the pattern of prey selection is generally in accordance with the relative abundances of prey (see schematic).  Limpets tend to be avoided, perhaps because they can readily escape.  When the whelk’s tentacles contact a suitable prey item, it climbs onto the prey and begins to drill, generally into the thickest part of the shell.  Once a borehole is created it inserts its proboscis and begins to feed, detaching meat in “relatively large chunks” and passing them into the esophagus.  Sleder 1981 Veliger 24: 172. Photograph courtesy Gary McDonald, Santa Cruz, California and CALPHOTOS.

  black dot
  RETURN TO TOP