Reproduction
  Abalones, top shells, and turban shells have separate sexes.   All species spawn freely into the seawater and  fertilisation occurs there. 
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  Spawning, fertilisation, & larval development
  Considered in this section are topics relating to spawning, fertilisation, & larval development, while the topic of  SETTLEMENT, METAMORPHOSIS, & RECRUITMENT can be found in its own section. The accounts below are divided into 2 sections: Haliotis, and Calliostoma & Chlorostoma.
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Haliotis

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Research study 1
 
photograph of an abalone showing exhalent water flow

Abalones spawn in late winter-late summer, depending upon species. Gametes pass from the gonads via the kidneys into the mantle cavity.  From there they exit the animal in the exhalent water flow via the 3 most posterior openings of the shell.

 

 

Northern abalone Haliotis kamtschatkana showing
seawater exiting from exhalent holes in the shell 0.6X

 

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Research study 2

 

graph showing seasonal gonadal indices in abalone Haliotis cracherodiiMaximum gonadal growth of Haliotis cracheroidii in the Monterey Bay area of California occurs during summer, graph showing relationship of gonad index and seawater temperature in Haliotis cracherodiiand spawning is in late summer (graph on Left). Note in the graph on the Right that spawning in H. cracheroidii takes place while seawater temperature is still rising. Polysaccharide stores in the foot drop progressively through the spring and summer, suggesting that these are the primary energy materials used in gonadal production.  On the basis of these data, the authors suggest that food availability is not a factor in directly regulating gonad growth.  However, this is true only in the strictest sense, for without food being available and eaten to build up foot stores of carbohydrates at an earlier time, gonadal growth could not take place. In a following investigation the senior author reports that the polysaccharide in the foot tissue is likely to be glycogen. Lipid levels in the foot and digestive gland do not show any consistence change relative to the reproductive cycle. Webber & Giese 1969 Mar Biol 4: 152; see also Boolootian et al. 1962 Biol Bull 122: 183; Webber 1970 Physiol Zool 43: 213.

NOTE  gonad growth in the Left graph is expressed as an photograph of digestive gland/gonad organs in abalone Haliotis cracherodii an index: mass of gonad relative to mass of soft tissues including gonad (index x 100 = %).  Mature gonads of both male and females H. cracheroidii constitute between 15-20% of soft body mass

NOTE  gonad index in the graph on the Right is calculated as the proportion of cross-sectional area of the digestive gland/gonad complex represented by gonad (see photo on Right)

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Research study 3
 

drawing of an early trochophore of abalone Haliotis rufescensAlthough embryonic development of red abalones Haliotis rufescens is well known drawing of a free-swimming veliger larva of abalone Haliotis rufescensnow owing to extensive research relating to aquaculture, an early study done at Pacific Grove, California is worth mentioning. Here, a trochophore stage is reached at about 9h after fertilisation, and this hatches to an early veliger after about 24h (at 17-19oC). The author is unable to rear the larvae through to metamorphosis, although nowadays this is done routinely in abalone-culture facilities. Carlisle 1962 Nautilus 76: 44.

NOTE larval dimensions are not provided

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Research study 4
 
photograph of egg of abalone Haliotis kamtschatkana photograph of trochophore of abalone Haliotis kamtschatkana photograph of veliger larva of abalone Haliotis kamtschatkana photograph of 40-d juvenile of abalone Haliotis kamtschatkana

Laboratory studies on early development in Haliotis kamtschatkana in Victoria, British Columbia show that the egg is about 150um in diameter and development to the first larval stage, the trochophore, takes about a day (at 12-13oC).  The prototroch on the photograph of 1-mm juvenile of abalone Haliotis kamtschatkanatrochophore bears cilia, which enable the larva to rotate vigorously within its capsule, thus facilitating hatching. Hatching occurs 30h after fertilisation to a swimming trochophore, and within a few hours this becomes a veliger larva.  The veliger is non-feeding, and settles within a few days, perhaps in response to dwindling energy reserves in its body.  Metamorphosis to a juvenile takes about a day, and a few days after that the juvenile is crawling about and rasping food with its radula. No gas-exchange pores are evident in the 40d-juvenile (above Right) but, by 1mm in size, the juvenile possesses several such pores, and growth lines are evident on the shell. Page 1997 Biol Bull 193: 30; photos modified from Bevelander 1988 Abalone Gross and Fine Structure The Boxwood Press, Pacif Grove, 80 pp.

NOTE  lit. “wheel carry” G. referring to the circular ring of cilia used for propulsion by the larva.  The trochophore swims vigorously within the egg membrane and this activity is thought to help in the hatching process.  After hatching, the trochophore larval stage is free-living for only a few hours before it develops into the settling phase, the veliger

NOTE  lit. “sail” L.

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Research study 5
 

graph comparing fecundity of female abalone Haliotis kamtschatkana in wave-sheltered and wave-exposed sitesIn wave-exposed areas of Barkley Sound, British Columbia northern abalone Haliotis kamtschatkana are generally smaller in size than ones from more wave-sheltered areas.  Examination of histological sections of gonads from each type by scientists from DFO, Pacific Biological Station, Nanaimo show that the stunted individuals mature at a smaller size than ones from sheltered areas.  Spawning in both regions occurs April-July (see graph on Left). Note that both populations exhibit only desultory spawning in May of the second year of study.  Although females of comparable size have similar fecundities in the 2 areas, the ones living in sheltered regions, by virtue of larger size, are considerably more fecund than ones from the “surf” areas (see graph on Right).  The graph compares fecundity of females at both wave-sheltered and wave-exposed sites in Barkley Sound, along with a sample of much larger females from Haida Gwai.  Campbell et al. 2003 J Shellf Res 22: 811.graph comparing fecundity of abalone Haliotis kamtschatkana at 3 locations in British Columbia

NOTE  at the time of publication this species continues to be listed by the Committee on the Status of Endangered Wildlife in Canada as a “threatened” species.  Commercial harvesting has been closed since 1992

NOTE  gonad index is estimated from the ratio of cross-sectional areas of gonad and digestive gland/gonad complex X 100

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Research study 6
 

drawing showing location of gonad in an abalone Haliotisgraph showing relationship between size and fecundity in female abalone Haliotis rufescensResearchers at Bodega Marine Laboratory determine that red abalone Haliotis rufescens in northern California mature sexually at about 60-130mm shell length, with males maturing at a smaller size than females.  Fecundity of females increases exponentially with increasing shell length and peaks at 2,850,000 eggs at a size of 215mm (see graph).  Although senescence begins at this size, egg production in these older females is still equal to or greater than that of mid-sized females.  In fact, egg production by females at the legal size limit for collection of 215mm amounts to about 68% of the total egg production.  The authors note that any management strategy that protects these large females, such as restricting collection of larger-sized females or establishment of marine protected areas, will help maximize egg production in the population.  Rogers-Bennett et al. 2004 J Shellf Res 23: 553. 

NOTE eggs are sampled from the gonad on the outer side of the conical organ as shown in this diagram

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diagram showing sperm responses to eggs of red abalone and brine shrimpResearchers at Scripps Institution of Oceanography, La Jolla, California have identified a sperm-attractant chemical in red abalones Haliotis rufescens.  Such a chemical was thought previously to be present not only by inference from results of studies on other aquatic species (not abalone), but also from observations that sperm in close proximity to live eggs swim significantly faster and orient towards the egg surfaces (see illustration on Right).  The attractant chemical turns out to be the L-isomer of amino acid tryptophan.  The sperm are responsive to tryptophan at extremely low concentrations (10-8mol . liter-1, but not at concentrations higher than this.  The tryptophan released from an egg actually forms a plume that increases a sperm’s target by as much as 5-fold.  Although the ubiquitous nature of tryptophan in all living cells suggests that it may be a nonspecific signal from egg to sperm, other observations on abalone fail to support this.  Thus, the authors note that sperm from red and green (H. fulgens) abalone are only attracted to soluble factors released from conspecific eggs.   The results represent an invaluable contribution to the field of abalone reproduction.  Riffell et al. 2002 J Exp Biol 205: 1439.

NOTE  tests show the D-isomer of tryptophan to be inactive

 

Orientation and swimming speed of abalone sperm to an
abalone egg (top) and a brine-shrimp egg (CONTROL,
bottom). Individual sperm are videotaped for 30sec,
thus providing an estimate of swimming speed. Note
that sperm swim significantly in the direction of a
conspecific abalone egg (2o), but non-significantly in the
direction of an heterospecific brine-shrimp egg (60o)

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Research study 7
 

graph comparing fertilisation success in red abalone Haliotis rufescens in relation to shear forces and sperm concentrationA later study conducted by the same research group at the University of California, Los Angeles examines fine-scale aspects of egg and sperm behaviour in red abalone Haliotis rufescens. Most comparable previous studies have been done with gametes in still water.  Of interest here is how variation in fluid-shear forces during small-scale turbulence in the egg boundary layers affect fertilisation success.  In perfectly still water the sperm orientate via an egg-produced chemical attractant, swim to the eggs, and fertilise them.  A sperm’s locating ability is enhanced through a mechanism of helical klinotaxis; that is, it follows an attractant gradient by rotating through it.  At any level of turbulence, the sperm must encounter the eggs, themselves rotating, while being transported within a laminar-shear flow (see photograph).  Not unexpectedly, encounter rates and fertilisation success are greatest at the lowest shear tested (0.1sec-1) and fall off as shear increases beyond 1.0sec-1 (see graph).  At low rates of shear, swimming behaviour overpowers fluid motion; at high rates, the reverse is true.  The authors’ results show that sperm exhibit maximal fertilisation success under experimental conditions most closely simulating the hydrodynamic features present in natural adult habitats. The authors comment that red abalone aggregate at sites where water motion is substantially reduced, and spawning is generally during calmest conditions. The paper is filled with interesting methodologies and results, and provides a unique look at how turbulent flow and shear forces affect egg-sperm interactions in abalone.  Riffell & Zimmer 2007 J Exp Biol 210: 3644. Photograph of spawning abalone courtesy Larry Friesen.photo composite of sperm of an abalone slipping past an egg, having been affected by shear force

abalone Haliotis rufescens spawning spermNOTE  flow measurements within kelp forests Macrocystis pyrifera inhabited by red abalone specify the range of fluid-dynamic conditions for testing in laboratory flow tanks

Male Haliotis rufescens spawning.
Muscular contractions of the foot
create the gamete jets, or plumes

Photo sequence showing a sperm slipping past
a rotating egg in a shear force of 2sec-1

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Research study
 

One anticipated effect of climate change on the oceans is increasing acidification through greater carbon-dioxide dissolution and thus lower pH values.  Potential effects of lower pH on survival of larvae of red abalone Haliotis rufescens, an important commercial species, is investigated by researchers at the University of California, Santa Barbara.  To assess pH effects the researchers measure tolerances of larvae in culture to heat shock (1h exposure to 8 experimental temperatures ranging from 15oC to 35oC), and expression of 2 genes involved in shell formation, over 4 stages in larval development: pre-torsion, post-torsion, late veliger, and pre-metamorphosis.  Results for heat tolerance are variable and not in a predicted order and, surprisingly, results for gene expression for shell formation indicate no effect.  One comment on the validity of the study, not considered by the authors, is that the treatments are all acute exposures, and this of course is not what abalone that have been acclimated to slowly rising pH values over the years from present time to the year 2100 will have been accustomed to. If pHs are not buffered in abalone, then larvae will develop from eggs in ovaries that have been bathed in hemolymph at the pH of current ocean levels, and there would be no acute shock for them as experienced in the present experiments. Of course, this comment, if applicable, would have had greater relevance had there been significant results.  Zippay & Hofmann 2010 J Shellf Res 29 (2): 429.

NOTE  what pH levels to use?  The authors simulate ocean pH at present and anticipated future levels of atmospheric CO2-concentration by bubbling CO2-enriched air through seawater at 380ppm (present day), 570ppm (a future intermediate level), and 990ppm (predicted level for the year 2100).  Both future levels are based on a “business as usual” scenario; that is, with no major change in international policies relating to discharge of greenhouse gases into the atomosphere.  The pH values resulting from these 3 treatments are 8.1 representing CONTROL or present-day ocean pH, 8.0 for intermediate, and 7.9 for “worst-case-scenario” in the year 2100

NOTE  based on past studies on a number of other taxa on effects of elevated CO2 levels, the authors predict a significant negative effect on calcification

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Calliostoma & Chlorostoma

 

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Research study 1

 

Observations at the Friday Harbor Laboratories, Washington show that the top shell Calliostoma ligatum has separate sexes and spawns in broadcast fashion. The light green-coloured eggs are released in mucus-coated strings, 10-90 eggs in each string. Each egg is covered with a gelatinous coat and chorion. In laboratory culture at 7-9oC development to metamorphosis takes about 2wk. Holyoak 1968 Veliger 30: 369.

NOTE  the author notes that the 3-4d swimming/crawling stage may be shortened in the presence of a favourable substratum. In the experiments described here the larvae metamorphose onto a clean glass surface

NOTE in another study on spawning in C. ligatum in San Luis Obispo County, California the author notes the release of about 3000 eggs in strings, each containing 10 or more eggs, in July in the laboratory from a single specimen.  The eggs are green and 20-30µm in diameter.  Hunt 1980 Veliger 22: 292.

photograph of top shell Calliostoma ligatum

drawing of unfertilised egg of top shell Calliostoma ligatum

drawing of trochophore of top shell Calliostoma ligatum

A trochophore larval stage is passed through within the egg capsule. Scale bar = 200um

drawing of early veliger of top shell Calliostoma ligatu

Within a few days the trochophore transforms into an early veliger larva (500um in length)

drawing of prehatch veliger larva of top shell Calliostoma ligatu

After 6d a mature veliger hatches out, swims about for 3-4d, and settles to the sea bottom (925um in length). The veliger is non-feeding.

drawing of early juvenile of top shell Calliostoma ligatuMetamorphosis takes place after another 3-4d.  Newly metamorphosed juveniles are about 0.9mm in length. The author notes that this developmental pattern is primitive in comparison with other world species of Calliostoma in which eggs are attached to the substratum and develop directly to a crawling juvenile. Scale bar = 200um
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Research study 2
 

photograph of a black turban-snail Chlorostoma funebralis emerging from its shellLaboratory studies in Oregon show that the black turban shell Chlorostoma funebralis spawns green-coloured, free-floating eggs that develop to veliger larvae by 40h (14oC).  The velum is small and is used for locomotion, but not for feeding.  Metamorphosis occurs by 7d and growth of the adult shell is evident by 15d.  The juveniles feed on benthic detritus and diatoms.  After 6mo the juvenile has a shell length of 2.1mm.  Moran 1997 Mar Biol 128: 107.

NOTE Chlorostoma funebralis can apparently be sexed by the colour of the crawling surface of their foot.  Females are darker and males are lighter.  A collection of 161 snails at Cape Arago, Oregon, for example, is separable on the basis of colour differences into 74 females and 53 males, with the remaining 34 being of intermediate colour.  Frank 1969 The Veliger 11: 440

 

This is what you look at to determine sex, but you need to have
several specimens of known sex as a reference. Sexes may be
unequivocably determined by presence of a penis on the right side
of the male. The head of this specimen is upside-down at the Right

photograph of black turban snail Chlorostoma funebralis drawings of development in black turban snail Chlorostoma funebralis from egg to 15-d juvenile
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Research study 3
 

graph showing growth of post-settlement Chlorostoma funebralisResults of a later developmental study on Chlorostoma funebralis are presented by researchers in Baja California.  Despite warmer culture temperatures of 19oC, developmental times are actually comparable to those recorded in the previous Research Study 7, as follows.  A trochophore is reached by 9-10h, competent veliger by 7-8d, settlement at 8d, and a feeding juvenile by 14d (see drawings below).  Food for the juveniles in culture is rehydrated kelp Macrocystis pyrifera that was previously dried. Growth rate of post-settlement juveniles is shown in the graph on the Right. Guzmán del Próo et al. 2006 The Veliger 48: 116.

NOTE the authors have fitted a linear regression line to their data, seen faintly in black on the graph; however, the expected relationship, a curvilinear one, is shown by the superimposed green line

 
developmental stages for Chlorostoma funebralis
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