title for whelk section of A SNAIL'S ODYSSEY
   
title for learn-about section on whelks & relatives in A SNAIL'S ODYSSEY
  Habitat & community ecology
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  Shell morphology & habitat
  Topics in this diverse section include shell morphology & habitat, considered here, and SHORE-LEVEL SIZE GRADIENTS, AGENTS OF COMMUNITY STRUCTURE , and DEMOGRAPHY & HABITAT COMPLEXITY considered in other sections.
 

photograph of thick- and thin-shelled morphs of whelks Nucella lamellosaSome species of west-coast whelks, most notably Nucella lamellosa and N. ostrina, have a remarkable diversity of shell-shape and colour. For example, Nucella lamellosa in Barkley Sound, British Columbia have 2 contrasting shell morphometries.  One is a thinner-shelled morph usually bearing frilly sculpturing; the other, a thicker-shelled morph, usually smoothly textured.  There is some thought that the thicker morph is selected for in areas of greater density of whelk-eating crabs, but habitat may also play a role. In addition, colours and colour patterns of Nucella lamellosa and, to a lesser extent, N. ostrina, are quite striking as these photographs show. Photograph of orange N. lamellosa courtesy Chris Gunn, North Island Explorer.photograph of colour morphs of whelk Nucella lamellosa from southern British Columbia

NOTE the role of shell sculpturing in defense of whelks is considered elsewhere: PREDATORS & DEFENSES:SHELL SCULPTURINGphotograph of whelk Nucella lamellosa courtesy Chris Gunn, North Island Explorer




Different colour morphs of
whelks Nucella lamellosa
found along 20 linear meters
of rocky shoreline near White
Rock, British Columbia 0.5X

 

 

 

This colorful whelk Nucella lamellosa has put on
a growth spurt, but does the dramatic change in
colour owe to diet, genetics, or something else? 2X

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  West-coast whelks with notable shell ornamentation:
 

photograph of whelk Ceratostoma foliatum
Leafy hornmouth Ceratostoma foliatum 1.5X. See PREDATORS & DEFENSES:SHELL SCULPTURING

photograph of dead shell of whelk Pteropurpura trilata, provenance unknown
One of several related species of Pteropurpura (trilata?) from California 0.6X. Source of photo unknown
photograph of whelk Ocinebrina interfossa courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle
Ocinebrina interfossa 3X. Photograph courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle PNWSC
 
Research study 1
 

map of San Juan Islands, Washingto showing 12 locations from which different morphs of whelks Nucella lamellosa can be foundShell morphologies and colours1 of local populations of Nucella lamellosa are often distinctive enough that they can be identified as coming from specific areas.  In fact, one author2 distinguishes 53 different “morphs” of N. lamellosa in locations from California to the Aleutian Islands, Alaska.  Twelve morphs alone are described from the San Juan Islands, map showing locations where morphs of whelks Nucella lamellosa are collectedWashington.  If you wish to see life-size photographs of morphs from different locations in the San Juan Islands, Washington, click on a numbered button on the map on the Left. 

Morphs from other localities ranging from Knight Island, Alaska to San Francisco Bay, California can be accessed by clicking on the numbered buttons on the map on the Right.

Are all these morphs expressions of different genotypes, or simply phenotypic responses to different environments?  The author addresses this question and proposes that the source of the variability in N. lamellosa is primarily genetic, maintained by geographic and even “microgeographic” isolation.  Only size and, associated with this to some extent, degree of sculpturing3 , are thought by the author to be phenotypic expression of environmental differences, mainly in amount of food available and immersion time.  Clearly, if some researcher has the patience and inclination for a long-term study doing extensive inter-population crosses and translocational growth studies, it would be a very interesting study, indeed. Kincaid 1957 Local Races and Clines in the Marine Gastropod Thais lamellosa Gmelin  A population study  The Calliostoma Company, Seattle 75 pp.

NOTE1   predominant colours in Nucella lamellosa, either solid or in bands, are purple, white, chocolate brown, yellow, and orange

NOTE2   the book is written by Trevor Kincaid who, at its publication date in 1957, was an Emeritus Professor in the Department of Zoology at the University of Washington, Seattle.  By its uniquely personal features, it is likely to have had a limited printing; hence, may not be available in many university libraries.  Partly for this reason, over one-third of the 53 morphs of Nucella lamellosa described by Kincaid are reproduced here in the ODYSSEY.  The morphs featured are selected for their widespread geographic location, specific habitats occupied, and overall diversity of shape and colour.  However, all 12 morphs from San Juan Island are included to show the extent of variability in a relatively small geographic region

NOTE3 in his book the author uses the term "imbrication" to express the degree of sculpturing. The word means ornamentation of overlapping tiles or scales, or a pattern resembling this. It is a good one and probably should be adopted by all authors describing this particular form of ornamentation or shell sculpturing in Nucella spp. It would replace the currently used terms "frills" and "fluting" presently commonly used for N. lamellosa, including in the ODYSSEY

 
Research study 2
 

drawings of "fat" and "slender" phenotypes of whelks Nucella lamellosa from areas in Puget Sound, WashingtonIs there any experimental evidence to answer the question as to whether the morphs of Nucella lamellosa are expressions of different genotypes, or simply phenotypic responses to different environments?  One observation, although limited in scope, shows that offspring from “fat” parents from an area in Puget Sound, Washington near Seattle and offspring from “slender” parents from an area in San Juan Island, Washington, raised for 10mo under uniform laboratory conditions with barnacles provided ad libitum as food, all grow into a common “slender” form.  The author concludes that the parents’ shapes must be a phenotypic response to some environmental property other than food supply. No mention is made of the differential degree of shell sculpturing present. Clearly, further study of the subject is needed.  Spight 1973 J Exp Mar Biol Ecol 13: 215.

NOTE both sites are characterised as "calm-water"; no information is given on substratum types present

 
Research study 3
 

map of Barkley Sound showing locations where study of whelk morphology in relation to degree of wave exposure was donegraph showing the relationship between shell mass and shell capacity in 3 species of whelks Nucella in Barkley Sound, British ColumbiaAn investigation of shell shape in 3 species of whelks Nucella ostrina, N. lamellosa, and N. canaliculata in Barkley Sound, British Columbia reveals a wide variety of shell shape and shell mass that is species-specific and habitat related.

Of the 3 species, Nucella ostrina has the lowest shell mass per unit of shell capacity (see graph on Right). It lives high in the intertidal zone in areas ranging from full wave exposure to considerable shelter. An examination of 477 N. ostrina from 9 sites in Barkley Sound show that shell form photograph of whelks Nucella lamellosa from different areas of wave exposure and amount of sediments in Barkley Sound, British Columbiachanges from short and broad on open-coast wave-exposed areas (Pachena Point), to tall and narrow on sheltered promontories and on boulder beaches (Grappler Point; see graph and photographs lower Right). At least in N. ostrina, then, wave exposure does appear to have an effect on shell shape.photographs of shell morphs of whelks Nucella ostrina from locations in Barkley Sound, British Columbia with differing degrees of wave exposure

Nucella lamellosa is heavily armoured and inhabits low shore levels from moderate to extreme shelter. Armouring in this species may relate more to predation risk from crabs than from exposure to waves.  Morphologies of N. lamellosa range from a thicker-shelled form in sedimented sheltered areas, to a more fluted form in rocky sheltered areas characterised by clean water (see graph and photographs on Left).

photograph of whelk Nucella canaliculata from a wave-exposed area of Barkley Sound, British ColumbiaNucella canaliculata has a slightly more armoured shell and inhabits wave-exposed conditions but at lower shore levels (see graph and photograph on Left). Kitching 1976 J Exp Mar Biol Ecol 23: 109.

 
Research study 4
 

schematic showing the relationship between shell shape and shell length in Nucella lamellosa in relation to degree of wave exposureschematic showing the relationship between shell shape and shell length in Nucella ostrina in relation to degree of wave exposureA similar study to the foregoing one (Research Study 3 above), but comparing shell shapes of the 3 Nucella species in Barkley Sound, British Columbia with those at San Juan Island, Washington, arrives at a somewhat different conclusion about the effect of wave exposure on shell morphology. The author first compares shell shapes for each species for each geographical region, then presents a combined representation of the data clustered in 4 levels of wave exposure. Data for the first, geographical, comparison fail to show differences in shell shape for any species based on whether they are found in Barkley Sound or San Juan Island.

schematic showing the relationship between shell shape and shell length in Nucella ostrina in relation to degree of wave exposureAs for shell shape in relation to degree of wave exposure, there is no correspondence for N. lamellosa (see schematic upper Left), but for the other 2 species there is a tendency for longer individuals to be found in less wave-exposed areas. Note in the schematics on the Right the positions of the light greenish-blue patches representing individuals living in the least wave-exposed habitats. Overall, however, the author concludes that genetic influences are more important determinants of shell shape than environmental ones for these 2 species.  Crothers 1984 Biol J Linnean Soc 21: 259.

NOTE  the author defines shell shape in this paper as the ratio of length of shell to another ratio, length of shell divided by length of aperture (L/Ap).  This gives a simple and quick method of assessing variability in shell shape in Nucella, which fulfills the aim of the study, but it does not provide information on width or diameter or, more importantly, on shell mass. This other information may have been useful for comparisons with results of other studies  

 
Research study 5
 

photograph of snails Alia carinataA Californian researcher describes apparent habitat effects on shell form and colour in the columbellid snail Alia carinata. Individuals in eelgrass areas have distinctive shells that are short, broad, and stout, with unpatterned dark coloration.  Second-most distinctive are those occupying red-algal habitats that are tall and narrow in shape, with patterned colours.  Other types from rock and kelp habitats are similarly patterned in colour, but undistinctive in shape.  The author suggests that good dissemination by larvae and juveniles to different habitats and a measure of phenotypic plasticity lead to the different morphs.  Tupen 1999 The Veliger 42 (3): 249.  Photograph courtesy Udo Savalli, Arizona State University www.savalli.us

 

 

Colour variability in snails Alia carinata 3X

 

 
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