Research study 2

Maximum gonadal growth of Haliotis cracheroidii in the Monterey Bay area of California occurs during summer, and 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 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)

Although embryonic development of red abalones Haliotis rufescens is well known now 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 17-19^oC). 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

In 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.

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

Researchers 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

An interesting study conducted by researchers 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.

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

Photo sequence showing a sperm
slipping past a rotating egg at 2sec^-1

Research study 1

Results of a later developmental study on Chlorostoma funebralis are presented by researchers in Baja California.  Despite warmer culture temperatures of 19^oC, 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