Feeding & growth
  Like other bivalves, scallops feed on phytoplankton that they sieve from the water on their gills. Particles move along the gill edges in ciliated grooves and are sorted by the paired labial palps on either side of the mouth. Edible material moves along ciliated tracts into the mouth while inorganic and other inedible matter is gathered by the palps into mucousy blobs and these, along with feces, are periodically ejected from the mantle cavity by rapid clapping of the shell valves.
Research study 1

An early study on rock scallops Crassadoma gigantea in the Monterey area of California includes information on the free-living early stages, including feeding.  As well as providing planktonic particles to the ctenidia as food, water flow through the mantle cavity serves in jet-propulsed swimming and as an exit route for gametes, and for kidney, pseudofecal, and fecal discharges.  Yonge 1951 Univ Calif Publ Zool 55: 409.

drawing showing water flow through the mantle cavity of a juvenile rock scallop Crassadoma gigantea photograph into the mantle cavity of a juvenile rock scallop Crassadoma gigantea showing ctenidia drawing of body parts of an adult rock scallop Crassadoma gigantea
Rock scallops are free-living until a size of 2-4cm when they attach to the substratum surface on their right valve. Water is pumped into the mantle cavity by cilia on the ctenidia. It exits on either side of the dorsal hinge This view into the mantle cavity of an adult shows the mantle edge with multiple eyes and several leaves of the ctenidia. Mantle tentacles are relatively small in the adult, but large in the free-living juvenile (see previous drawing) The main internal organs of an adult include the ctenidia, mantle bearing short tentacles and multiple eyes, large shell adductor muscle, and gonad. A small, almost vestigial, foot is present in in both juvenile and adult
Research study 2
  diagram showing mooring arrangement of cages for growth study of rock scallops Crassadoma giganteaA field study on growth of rock scallops Crassadoma gigantea by a researcher from San Diego State University, California focuses on the effect of depth on growth of juveniles.  The juveniles are placed in cages and moored at 6 depths ranging from 8-120m (see diagram) and examined after 3mo (starting from August).   Water temperatures range from about 17oC at the shallow depth to about 11oC at the deepest depth.  Not unexpectedly, based upon more phytoplankton food and warmer temperatures at the shallower depths, juveniles maintained at the 8-30m stations grow almost 80% more than ones at the 60-90m stations.  The author remarks that growth is less than expected at the 8m depth probably owing to considerable fouling of the shells with barnacles, bryozoans, hydroids, and tunicates (food competition?).  Fouling is minimal at depths of 30-120m.  Leighton 1979 Mar Biol 51: 229.

NOTE  starting sizes range from 1-3cm diameter

NOTE  a second set was to have been examined after 1yr, but for whatever reason seems not to have been done



Research study 3

photograph showing a rock scallop excessively fouled with hydroids, anemones, and algaeA study on growth of purple-hinge rock scallops Crassadoma gigantea at Mission Bay near San Diego, California shows that test specimens grow best in deeper depths.  At a depth of 1m, for example, excessive fouling growth apparently interferes with growth.  Monical 1980 Proc Nat Shellfish Assoc 70: 14.

NOTE  test scallops are suspended in cages at 1, 4, and 6m below MLLW







Rock scallop Crassadoma gigantea excessively
fouled with hydroids, anemones, and algae 0.7X

Research study 4

photograph of shell hinge of rock scallop Crassadoma giganteagraph showing age and shell size of rock scallops Crassadoma gigantea from Vancouver Island, British ColumbiaResearchers from Memorial University, Newfoundland and Pacific Biological Station, British Columbia provide data on age and size of rock scallops Crassadoma gigantea collected at sites on Vancouver Island, British Columbia (see graph).  MacDonald & Bourne 1989 J Shellf Res 8 (1): 179.

NOTE  the aim of the study is to assess the mariculture potential of rock scallops; data not included here

NOTE  aging is done by counting annual growth lines on the calcareous portion of the hinge ligament

Hinge of rock scallop Crassadoma gigantea 4X

Research study 5

graph comparing age and size in scallops Chlamys hastata and C. rubidagraph showing size and age in a scallop Crassadoma giganteaStudies on age, growth, and energy partitioning in 3 shallow-water species of scallops in British Columbia show that the swimming species Chlamys hastata and C. rubida grow at a similar rate for the first 3yr, then mean shell height and soma mass become greater in the former species than in the latter (see graph on Left).  As well, reproductive output in the 2 species differs.  By 6yr of age, C. hastata has increased not only significantly more in size that C. rubida, but its reproductive output has been more than 2.5 times greater.  Both species continue to grow until they die.  In comparison, the sessile species Crassadoma gigantea  is free-living for several years, then cements itself to a rock for the remainder of its approximately 20yr lifespan.  From about age 14yr most of its production is gametes, with little somatic growth being evident (see graph on Right). MacDonald et al. 1991 Can J Fish Aquat Sci 48: 215.

NOTE  ages in Chlamys spp. are assessed from annual growth lines in the shell and hinge ligament, but only the last can be used for C. gigantea
photograph of sessile scallop Crassadoma gigantea

Divers should think
twice about removing
rock scallops C.
to eat.  A
specimen of 17cm shell height may be 20yr old

Two specimens of Chlamys sp. poised to swim. It is almost impossible to
distinguish the west-coast species C. hastata and C. rubida in the field,

especially when they are coverered with sponge or other growth 0.75X

Research study 6

graph showing age and growth of scallops Patinopecten caurinusAn investigation in Alaska by scientists from the National Marine Fisheries Service, NOAA shows that growth and size of Pacific sea scallops Patinopecten caurinus increases from sites in the southeast to sites in the northwest (see map and graph).  Age is determined by counting annual (winter) growth rings on the exposed upper valve.  photograph of Pacific plate scallop Patinopecten caurinusIgnell & Haynes 2000 Fish Bull 98: 849.

NOTE  data are from scallops collected in 1968 and thus provide a valuable “early-fishery” baseline.  The current fishery commenced in 1967


Pacific plate
scallop Patinopecten

Research study 7

A 6yr study of weathervane scallops Patinopecten caurinus in Kamishak Bay, Alaska by fisheries personnel of Alaska Department of Fish and Game reveals that individuals at 30-90m depth grow to a shell height of about 19cm at 23yr of age.  Gustafson & Goldman 2012  Alaska Dept Fish Game Fish Data Ser No. 12-62, Anchorage pp 1-66.

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