Research study 0

graph showing seasonal changes in % indices of gonad, digestive gland, and adductor muscles in female rock scallops Crassadoma giganteaA researcher at Western Washington University, Bellingham provides details on the annual reproductive cycle of female rock scallops Crassadoma gigantea.  Gametogenesis commences in January and basically continues through the year.  A partial spawning occurs in June, but at no time is the gonad ever completely free of developing eggs.  Based upon mass loss in the adductor photograph of a rock scallop Crassadoma gigantea on the half shellmuscle coincidental with gametogenesis, the author proposes that it may be at least one storage site for nutrients required for gamete formation.  Resorption of old oocytes may represent an additional nutrient source.  More interestingly, and something not mentioned in later publications, is the presence of oocytes in some male gonads.  Based upon this observation and the greater number of larger females than males in the population, the author thinks that this species may undergo a protandrous type of reproductive cycle, that is, male at the juvenile stage transforming later in life to female.  Lauren 1982 Can J Zool 60: 2333.

The main items of interest in this scallop-on-the-half-shell are the adductor
muscle, ctenidia, mantle edge, and sponge-riddled shell edge (the sponges are0.5X

Research study 1

Scallops are broadcast spawners and sexes are (generally) separate.  Spawning occurs in summer in both species of Chlamys, but can readily be induced in the laboratory by several means, including slow temperature increase.  Eggs of spiny scallops Chlamys hastata are 70┬Ám in diameter and in laboratory culture at 12oC gastrulate 20h after fertilisation, reach the trochophore stage 30h after fertilisation, and the D-stage veliger 50h after fertilisation.  Veligers are free-swimming for 40d and feed on phytoplankton.  Metamorphosis takes place over a 24-48h period.  After this the juvenile or spat crawls about hinge-first for a day or two and then begins to form the adult shells.  At this time the larger left valve has strong radial striations while the smaller right valve is smoother.  Hodgson & Burke 1988 Biol Bull 174: 303.

NOTE in this study, for example, from 12 to 18oC over 2h

NOTE  at 40d the 2 valves surround the entire larva and can open and clos.  The early bivalve shell is known as a prodissoconch I and the later one as a prodissoconch II

Research study 2

Rock scallops Crassadoma gigantea spend their early life as a free-swimming scallop. During this time they attach with byssus threads and swim about like Chlamys spp. After 3-5yr they cement to a rock surface and grow to customary large size over another few decades. The shells become quite thick, partly owing to settlement and growth of boring organisms, such as worms and sponges, that riddle and weaken the exposed uppermost valve and cause compensatory secretion of shell by the inner mantle tissue. A large specimen may be 30-40yr of age, or perhaps even older. Photo courtesy Linda Schroeder, Pacific NorthWest Shell Club, Seattle, Washington PNWSC.

Juvenile purple-hinge rock scallop Crassadoma gigantea


Crassadoma gigantea with growths of blue sponge, coralline and other algae, and boring sponge Cliona celata (yellow dots are its exhalent chimneys) 0.6X

Upper shell valve of Crassadoma showing the honeycomb structure owing to boring by Cliona celata. Note the more pristine appearance of the newer, outer edge of shell 0.5X

Lower shell valve of Crassadoma showing distinctive purple hinge. The attachment area of the large adductor muscle is evident 0.5X
Research study 3

photograph of section of ripe gonad of a female rock scallop Crassadoma giganatea showing matureeggsA researcher at Humboldt State University Marine Laboratory, California provides information on the reproductive cycle of rock-scallops Crassadoma gigantea.  Data obtained from gonad sectioning at 3-6wk intervals of both sexes over a 1yr period show that individuals are ripe and that spawning could be induced throughout most of the year.  Malachowski 1988 J Shellf Res 7 (3): 341.



Cross-sectional view of ripe gonad of a female rock
scallop Crassadoma gigantea showing eggs 100X

Research study 4

The energy required for development in rock scallops Crassadoma gigantea is derived mainly from lipid provided as yolk by the brood parent.  Specific values obtained in a study in at the Pacific Biological Station, British Columbia reveal that the energy required for transformation from a pre-metamorphic larva to a 25d-old juvenile stems from catabolism of 60% lipid, 2% carbohydrate, and 38% protein.  During metamorphosis it may take up to a week for the larval feeding organ, the velum, to be replaced by the juvenile/adult feeding organ, the ctenidium, and endogenous stores of energy must be sufficient to tide the young scallop over this critical period.  The juvenile begins feeding soon after metamorphosis, but apparently this is insufficient to meet the energy demands for soft-tissue growth and shell deposition, as well as for maintenance.  Juvenile survival, therefore, crucially depends upon there being sufficient energy available both before and after metamorphosis.  Whyte et al. 1992 J Exp Mar Biol Ecol 163: 13; see also Whyte et al. 1990 Mar Biol 106: 239.  

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