Nutrition & growth
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Shell & growth


photograph of inside of abalone shell Haliotis rufescensThis varied section includes aspects of shell & growth of abalones, and related turban snails and top-shells. Topics of FEEDING & NUTRITION and FOOD PREFERENCES of these taxa are considered in their own sections.



For convenience abalones are dealt with in the first section below, followed by related trochid snails (note that the numbering of the Research Studies is not in sequence in these two sections because they were split only later).


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  Family Haliotidae: abalones
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Research study 1
drawing showing layers in the shell of a gastropod photograph of nacreous shell of abalone Haliotis rufescens drawing showing how sunlight is diffracted into its component wavelengths as it passes into and out of the nacreous shell of an abalone

The shell of an abalone, as in all gastropods, is secreted by the edge of the mantle, and consists of 3 parts: an inner nacreous layer, which is iridescent, a middle prismatic (chalky) layer, and a thin outer periostracum layer made of protein.  The first two layers consist of crystals of calcium carbonate, and differ in the hardness, size, and orientation of the crystals. 

NOTE  lit. “mother of pearl” Fr.

NOTE lit. “around shell” G.

Nacre is made up of thin, flat crystals in overlapping layers.  It provides a uniformly smooth surface against which the soft body tissues rub.  The prismatic or chalky layer, in comparison, is comprised of much larger and softer crystals of calcium carbonate. The iridescence of nacre ("mother-of-pearl") is created by light penetrating to different depths into the layers of crystals, being diffracted into its many component wavelengths, and re-emitted. 
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Research study 2

The iridescence of abalone nacre is simply a physical characteristic of the shell; it plays no functional role in the animal’s life.  However, like pearls in photograph of shell of abalone Haliotis rufescens with plastic implant for artificial pearl manufacturepearl oysters, an abalone will form beautiful blister pearls in response to parasitic organisms, such as worms, clams, and sponges, which burrow into its shell from the outside.  Shell repairs of this sort must negatively affect growth because of the extra allocation of energy required. Trial studies at the Bamfield Marine Sciences Centre, British photograph of inside of abalone shell showing blister pearl of nacre in process of formationColumbia employing plastic and other inserts in the shells of red abalone Haliotis rufescens from California show that it is indeed possible to create raised blister pearls for use in jewellry making. Shells courtesy Peter Fankboner, SFU, Burnaby.

External surface of shell of H. rufescens
with plastic implant for pearl production. Note
also the erosion caused by burrowing organisms 0.4X

Internal surface of same shell showing
blister pearl in process of formation 0.4X


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Research study 3


An example of negative effects of shell-inhabiting parasites on growth of abalone is presented in a study at an abalone farm in Cayucos, California.  Here, a sabellid polychaete Terebrasabella heterouncinata infests the leading edge of shells of Haliotis rufescens and seriously affects subsequent drawing of abalone Haliotis rufescens shell with infestation of sabellid worms Terebrasabella heterouncinatagrowth. Apparently, the shells become much more porous and brittle than in uninfected individuals, and new growth of the shell is directed downwards, forming a lip.  The respiratory pores of the abalone may also become clogged.  The effect is more severe in older, slower-growing abalone than in younger, faster-growing ones.  A young abalone can quickly encapsulate a bunch of worms and extend its shell beyond them.  Fortunately, the sabellid produces a crawling larva, not a free-swimming one, and infested abalone in a hatchery can be quarantined.  The authors note that this is the first report of a sabellid inhabiting the shells of abalone.  Oakes & Fields 1996 Aquaculture 140: 139.

NOTE more information on this worm is available elsewhere: LEARN ABOUT TUBEWORMS: HABITATS & ECOLOGY


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Research study 4


photograph of abalone shell Haliotis sp. showing dietary-induced colour bandingThe colours of abalone shells come from bilin-type pigments incorporated from algal foods into the proteinaceous outer covering, or periostracum.  Studies on diet and shell colour in several abalone species in Santa Barbara, California confirm that shell colours are red on diets of red algae, and pale green/green-white/blue-black/blue-green/white-turquoise on diets of kelps Macrocystis spp. and Nereocystis luetkeana. Moreover, for one population of red abalone Haliotis rufescens, colour banding-patterns correlate well with seasonal change of diet from red algae to brown kelp N. luetkeana.  Thus, during spring-autumn (Jun-Sep) when kelps are seasonally plentiful, growth produces a wide band of white-coloured shell.  During winter (Nov-Apr), when kelps undergo seasonal die-off, the shells exhibit a narrower red band from diets of red algae.  The specimen shown here has a large initial red band because of a 4yr absence of brown algae N. luetkeana from its Morro Bay, California habitat.  The author suggests that such annual banding patterns may provide useful information for fisheries managers on age and growth rates in red abalone.  Olsen 1968 Veliger 11: 135; Olsen 1968 Biol Bull 134: 139.

NOTE  more information on shell structure in abalones, and use of the shell in physical defense and possibly camouflaging can be found elsewhere in this learn-about section: PREDATORS & DEFENSES: PHYSICAL DEFENSES

NOTE  mainly H. rufescens, H. sorenseni, H. corrugata, and H. cracherodii, but other species are included in the study

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Research study 5

map of Barkley Sound, British Columbia showing sites for translocation studies of abalone Haliotis kamtschatkana shell-colour researchPinto or northern abalone Haliotis kamtschatkana of a few weeks in age cultured at the Bamfield Marine Sciences Centre, British Columbia show colour change in the shell coincidental with switch in diet from diatoms to macroalgae.  Other field experiments show that individuals of 5-10cm shell length can be translocated from less productive wave-exposed sites in Barkley Sound, British Columbia to more productive protected sites to speed up growth.  The new sites are located in and just below beds of kelp Macrocystis integrifolia.  After 9mo at the new sites the abalones are 8% larger in size, compared with only 4% at the original site.  The authors of the study conclude that while it is possible to translocate H. kamtschatkana to enhance their growth, the feasibility of such an enterprise would depend on recovery percentages. Emmett & Jamieson 1988 Fish Bull 87: 95.

NOTE  in the study these range from 39-72%

photograph of juvenile abalone Haliotis kamtschatkana being grown n culture facility at the Bamfield Marine Sciences Centre, British Columbia
Juvenile H. kamtschatkana being grown in a culture facility at Bamfield, British Columbia. Note the different colour-bandings presumably reflecting different food-stuffs being consumed 1X
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Research study 6

graph showing comparative growth of several species of abalone

A comparison of growth of juveniles of 3 species of abalones in La Jolla, California shows clear differences in temperature optima corresponding to the average depths at which each species lives.  Thus, the green abalone Haliotis fulgens, the most shallow-dwelling species (0-5m depth), grows best at 24-27oC.  The next deepest of the three, the pink abalone H. corrugata (1-20m), grows best around 21oC, and the deepest species, the red abalone H. rufescens (10-25m), grows best around 15-18oC. Leighton 1974 Fish Bull 72: 1137.

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Research study 11

photograph of snail Calliostoma ligatum courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washingtonphotograph of snail Margarites pupillus courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, WashingtonAt some point in growth the shell of most gastropods begins to coil. What initiates coiling in abalone and other primitive gastropods?  One idea is that the larval shell remains flexible and uncalcified until after torsion, and that muscle contraction during torsion deforms the shell and initiates the process of coiling.  A study on time of calcification in several species of vetigastropods, including Haliotis kamtschatkana, Margarites pupillus, and Calliostoma ligatum, shows that the shell of the first species is quite rigid and brittle prior to torsion, while shells of the last 2 species are more flexible despite being calcified. From these results the authors conclude that while initiation of shell coiling by contraction of larval retractor muscles is unlikely in Haliotis owing to the brittleness of the shell, it cannot be ruled out for the 2 trochid species. Collin & Voltzow 1998 J Morph 235: 77. Photograph of abalone courtesy Kevin Lee, Fullerton, California diverKevin; other photographs courtesy Linda Schroeder, Pacific Northwest Shell Club, Seattle, Washington PNWSC.

photograph of juvenile abalone Haliotis sp. courtesy Kevin Lee, Fullerton, California NOTE the authors also included 2 limpet species in their study, with results similar to those for abalone






Juvenile abalone Haliotis sp.
in Santa Catalina Island,
California showing early
stages of coiling 3X

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Research study 12

map showing location for study of growth of red abalone Haliotis rufescensgraph showing growth of red abalone Haliotis rufescens in California
A study on growth of red abalone Haliotis rufescens in Santa Rosa Island, California (see map) by researchers at the California Department of Fish and Game show that maximum shell length of 175-200mm is reached within 8-10yr  (see graph).  The authors note that elsewhere in California the species may reach 300mm shell length.  Haaker et al. 1998 J Shellf Res 17: 747.

  data from 2,145 tagged individuals are collected over a 5yr period from 1978-82

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Research study 12.1

graph showing shell size versus age for a population of abalone Haliotis kamtschatkana in southeastern AlaskaResearchers at the Alaska Department of Fish & Game report on shell microstructure, and deposition of growth rings and seasonal check-marks in northern abalone Haliotis kamtschatkana collected at 7 sites in southeast Alaska. Shell growth is mainly in summer, with a distinctive larger ring appearing in the shell at that time, and a growth check being laid down at the growing edge of the shell in mid-winter (see photograph upper Right). Ring structures can be best seen when the shell spire is ground down, polished, and treated. However, despite ample description and a set of micrographs of sections of shells (one of these can be seen on the lower Right), it is difficult for a reader to visualise what a ring exactly is. Growth checks are easy, as they are visually obvious lines marking an interruption in shell growth. Given that an abalone shell is structured as follows: an outside layer of periostracum (proteinaceous, protective), a middle prismatic layer of calcium carbonate crystals, and an inner nacreous layer of hard, flat aragonitic crystals laid down in layers or laminae, then how can a ring have nacre both above and below the prismatic layer (or sometimes a double prismatic layer) as seen in the photograph? Perhaps a diagram would have made things clearer. Some rings consist only of a brown organic material and, as these appear to be deposited adventitiously, should be ignored when doing ring counts for aging purposes. The authors confirm the annularity of the rings by examining a sample of shells from individuals of known ages. The authors provide a graph showing shell length versus age (upper Left). Shepherd et al. 2000 J Shellf Res 19 (1): 219.

NOTE the researchers find that while these check lines do indicate annual interruptions in shell growth, they are sometimes obscured, so age estimates using them may not be as accurate as counting rings in the shell

Back-lit shell of 6yr-old abalone Haliotis kamtschatkana
Back-lighted shell of a 5yr-old H. kamtschatkana showing several check lines. In this species the 1yr line is usually lost at about 3yr of age. In this specimen, there are actually two lines at the 3yr location 1X
cross-sectional view of a growth ring in the shell spire of a northern abalone Haliotis kamtschatkana
Cross-sectional view of a growth ring in the shell spire of Haliotis kamtschatkana. The authors describe many types of rings. This one has a double layer of large prismatic crystals sandwiched between 2 layers of laminated flat crystals of nacre 2800X
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Research study 13

graph comparing sizes of abalones worldwidesize comparison of largest temperate abalone species Haliotis rufescens from northeast Pacific and largest tropical abalone H. mariae from the Arabian PeninsulaThere are some 56 extant species and 42 extinct species of abalone in the world.  In a thoughtful paper that can’t be treated in its entirety here, a group of scientists from the University of California and Mount Desert Island Biological Laboratory, Maine analyse the phylogeography of body-size evolution in living and extinct Haliotis species.  Their results indicate that distribution of living  abalones is nearly cosmopolitan, being absent only from the western North Atlantic coast and from the Pacific coast of South America.  However, the cosmopolitan species tend to be tropical and small in size, while the large species are found exclusively in cold-water ecosystems dominated by macroalgae such as kelps (see illustrations).  Shell-length data obtained from the fossil record suggest that large body size arose quite suddenly at the end of the Miocene, some 5.3mya.  At the onset of the last glacial age coastal ecosystems became dominated by large, fleshy algae.  Estes et al. 2005 Paleobiology 31 (4): 591.

NOTE  some of the largest species, such as H. rufescens (to 31cm shell length) are found on the west coast of North America in habitats dominated by kelps Macrocystis pyrifera, M. integrifolia, and others, generally considered to be nutritionally superior foods for abalones and related snails

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Research study 14

graph plotting shell length over age for red abalone Haliotis rufescens at Point Cabrillo over 6yr periodTo determine growth rates of red abalone1 Haliotis rufescens at 5 sites around Point Cabrillo in northern California researchers tag2 and recover nearly 4,362 individuals over a 6yr period (a considerable number are recaptured, some up to 3 times). From these data the authors assemble growth statistics3 for each site over a minimum of 3 separate years, and one (at Point Cabrillo North, shown here) over 6yr. Geibel et al. 2010 J Shellf Res 29 (2): 441.

NOTE1 at a maximum of 31cm shell length, this is the largest abalone species in the world. Although closed to commercial fishing along with other species south of San Francisco, red abalone may be fished recreationally on the northern coast of California

NOTE2 the authors remark that “growth structures useful for aging red abalone are unknown” which, based on what is known from Research Study 12.1 above, is clearly incorrect

NOTE3 the von Bertalanffy method is used to fit growth curves for each year for those sites where sufficient tagging/recovery data are available

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  Family Trochidae & F. Turbinidae
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Research study 7

photograph of black turban snail Chlorostoma funebralis showing recent growth linesBlack turban shells Chlorostoma funebralis feed on algae in the mid- to low-intertidal graph showing difference in age of black turban snails Chlorostoma funebralis at a standard shell diameter in central Oregon and northern Washingtonzone.  Counts of annual growth lines, which are quite easy to see on shells that are not damaged, indicate a lifespan of 30yr or more.  Growth rates vary considerably among west-coast populations. For example, 2cm-diameter individuals are estimated to be 6yr old in central Oregon (Sunset Bay)and 15yr old in northern Washington (Mukkaw Bay). In British Columbia Tegula apparently grows even more slowly, lives longer, and attains larger body size.  These differences are unlikely to be related to latitudinal temperature differences; rather, more to differences in food types, food availability, and intertidal position.  Oregon observations from Darby 1964 Veliger 6(Suppl): 6, Frank 1965 Growth 29: 395, and Frank 1975 Mar Biol 31: 181; Washington data from Paine 1969 Ecology 50: 950. Photo of Chlorostoma funebralis courtesy Gary McDonald, Long Marine Laboratory, Santa Cruz.

NOTE  two of these studies related shell diameter to annual growth lines on the shell (Darby 1964, Paine 1969), while the third interpreted growth increments from “marked-and-recaptured” individuals using growth models (Frank 1965)

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Research study 7.1

table of regeration rates after experimental damage to shells of black-turban snails Chlorostoma funebralisA 2wk springtime study of shell growth in black-turban snails Chlorostoma funebralis at Hopkins Marine Station, California reveals that normal growth of the operculum edge averages about 8um per day. Wound repair is done at about the same rate (see table, selected results only). At this rate it would take a snail about a year to add just 3mm length to its shell, so even over a life span of 30y that would represent only 9cm increase in length. A shell of 3cm diameter would be roughly 18-20cm in uncoiled length or twice the 9cm length just noted. The author does not mention the nutritional condition of the test subjects and it is possible that they were unfed during their time in the laboratory. Regeneration of shell is done by the mantle folds and new shell includes the black-pigmented prismatic layer. Peppard 1964 The Veliger 6 (suppl.): 59.

NOTE the researcher uses a graded size range of 28 individuals from 13-28mm diameter, the largest being about 30y in age. Although growth would be expected to be relatively less in older animals, this is not apparent in the data (not shown here)

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Research study 8

Often the shell spires of Chlorostoma funebralis are heavily eroded (see photo in Research Study 7 above).  A fungus Pharcidia balani is implicated in the shell erosion and to offset this the snail secretes a secondary layer from within.  The normal shell is comprised of the usual 2 photographs of prismatic and nacreous crystalline structure in shells of black turban snails Chlorostoma funebralismolluscan layers: an outer prismatic layer consisting of elongated crystals of calcium carbonate (photo on far Left) representing about 10-20% of the shell thickness, and an inner nacreous layer consisting of plate-like crystals representing the remainder (the photo on far Right shows the transition between the two layers).  Studies at the Bodega Marine Laboratory, California indicate that the repair material repeats the composition of the original shell, so at a repair zone there may be 4 layers: outer prismatic/outer nacre and inner prismatic/inner nacre.  Apparently, however, the repair material has a different physical structure than the original crystalline form, namely, a cross-lamellar form.  The author does not discuss why the original shell material is not deposited in this harder form, but perhaps it is more energy costly to do so.  Geller 1982 Veliger 25: 155.

NOTE another form of calcium-carbonate crystal that is harder in structure. Scale bars =10um

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Research study 9

The frequency of shell repair in an intertidal gastropod like Chlorostoma funebralis can be an indicator of fitness.  Thus, a “survivor” snail will exhibit many repair marks, while a less fit snail may be, shall we say, dead.  Collections of C. funebralis and Nucella ostrina from various types of habitats in Bodega Bay, California reveal that the frequency of shell repair varies, not surprisingly, between habitats.  In surge channels, for example, 39% of 450 specimens of Chlorostoma collected show repair marks, while in mussel beds only 4% show repair marks.  Comparative data for 434 specimens of Nucella are: 15% with marks in surge channels, 9% in mussel beds, and 5% in tidepools.  The author speculates that the more intense wave action in surge channels and the fact that the channels represent a handy conduit for predatory crabs and fishes make this type of habitat a generally more risky one for snails.  Geller 1983 Veliger 26: 113.

NOTE a neogastropod, or whelk, included here for convenience

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Research study 10

Use of scanning electron-microscopic techniques to follow shell repair in Chlorostoma funebralis reveals a sequence of metabolic change in tissues of mantle, foot, and digestive gland, followed by deposition of aragonite crystals.  The sequence of repair of experimentally inflicted damage to the shell is followed in the photographic depictions below.  Reed-Miller 1983 Biol Bull 165: 265; Reed-Miller 1983 Biol Bull 165: 723.

NOTE  scanning e-microscopic views of the crystalline layers of shells of Chlorostoma funebralis and several other species can be found at Reed-Miller 1981 p. 243 In, Scanning electectron microscopy IV (Johari, ed.) IIT Research Institute, Chicago

scanning e-microscope image of a shell of Chlorostoma funebralis with a small window cut in it to monitor its regeneration
The shell is damaged by cutting a small window. 14-48h later there is an increase in rough endoplasmic reticulum, Golgi complexes, and mitochondria in manle, foot, and digestive-gland tissues
scanning e-microscope image of a shell of Chlorostoma funebralis in early stages of regeneration
One week later these changes are accompanied by initial shell repair, involving deposition of small spindle-shaped crystals that, while constrained within an organic matrix, are otherwise randomly distributed
scanning e-microscope image of a shell of Chlorostoma funebralis in early stages of regeneration By 3-6d the tissues show widened intracellular spaces and other types of spherules.  At the cut site the spindles have coalesced to form a sheet of mineralised tissue that covers the shell window
By 3-6d after the cut, the tissues show widened intracellular spaces and deposition of different types of spherules.  At the cut site the spindles have coalesced to form a sheet of mineralised tissue that covers the shell window.
After 2mo, dumbbell-shaped crystal aggregates are visible on the shell surface. By 4mo regeneration is complete. The experiments are run at 15oC
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