animals on cultured food for longer than is typical for seed
produced later in the season. The conditioned brood stock
is spawned, fertilized eggs collected, and the larvae are
raised in tanks supplied with food, usually in the form of
cultured microalgae. These larvae are held until they reach
a size when they are ready to settle or set. Larval life span
is determined by temperature, but for most species, the larval period is 10–20 days. Under optimal culture conditions, cultured species set at the lower end of the time
spectrum. There are always exceptions to any generality
dealing with bivalve culture. Instead of tanks and cultured
algae, at least one commercial operation relies on lined
open ponds and natural phytoplankton production for larval and nursery culture.
At setting, epifaunal and infaunal species may be
treated differently. Epifauna such as oysters may be transferred to settling tanks and set as single animals or
attached as clusters to shell or alternate materials. Scallops
may be set on mesh or, as with infauna, allowed to attach
by their byssus and then washed from the setting tank and
placed in the appropriate containers. For many species,
there is an intermediate nursery where late-stage larvae
or immediate post-set are placed in a mesh-bottomed container and water, with cultured algae, is recirculated in the
top and out of the bottom mesh (a downweller). Once the
animals reach an appropriate size (typically about
0.75–1 mm), they are placed either on raceways or into
upwellers (a mesh bottom cylinder where water flows up
through the mesh, across the animals, and out through
a pipe near the top). Scallops may be left in mesh bags
and hung in a tank that is supplied with unicellular algae.
Once seed reach several mm in size, it is no longer economically feasible to culture algae for food, and the hatchery/nursery reverts to pumping water and food from the
environment. Depending on location and species, these systems can be placed on land, or as floats in the water, but all
are characterized by the use of some form of pumping
mechanism to force water and food through the container
of animals. If protected areas are available near a power
source, floating systems can be utilized and pumping cost
can be greatly reduced. If land-based systems are used,
pumping costs are increased, but system security is
improved. Epifauna may be kept in upwellers while infauna
may be placed in raceways where sediments accumulate,
helping to protect the seed from fouling. Fouling and overset control can also be achieved by coarsely filtering the
water to remove potential fouling organisms, treating the
tank and animals on a weekly basis with fresh water, air
drying, or other methods. The treatment methods work well
with species that tightly close (oysters), but cannot be utilized for species that cannot completely close their shells
(scallops). As the animals grow, there is a constant need
to increase both the space for the animals and the pumping
capacity. These requirements mean that there is a trade-off
between the maintenance and feeding requirements in the
nursery and the potential losses incurred by planting small
animals in nature.
To this point, the spatial area required for producing
large numbers of animals is relatively modest. Most animals spawned in the spring will be placed in areas for
grow-out in the fall. In some instances involving seed that
did not reach planting size or when larger sized animals
are needed, a nursery system that uses the passive movement of water through a cage (floating or on the bottom)
or a nursery plot where animals are maintained at high
density is utilized. The nursery plots are typically placed
in easily accessed, sheltered locations. Nursery structures
and grow-out structures (see below) are typically similar,
but animals are usually at higher density and protection
devices use finer mesh in the nursery.
Grow-out
Once animals reach a size where they can be planted for
growth to market size, there are many methods depending
on the needs of the organism, the environmental conditions, regulatory framework, and the value of the final
product. Extensive methods (low density over a large area
with minimal bed preparation and no predator protection),
intensive methods (high-density bottom plantings with
some form of predator protection), or “water column”
methods (seed placed on long lines, hung from strings,
placed in cages/trays or other containment vessels, or
attached to stakes placed in the intertidal) are all utilized.
Epifaunal organisms may be placed in the inter- or
subtidal directly on bottom beds that usually receive some
preparation before planting. This may be rudimentary
cleaning during the harvest of the prior crop or elaborate
after harvest fallowing, followed by cleaning and
resurfacing. In sites with large tidal amplitude, low earthen
berms constructed on the tidal flats may be seeded or used
to “finish” adults. These berms, topped by the incoming
tide, retain water when the tide recedes, allow a longer
feeding period, and ameliorate temperature fluctuations.
More intensive methods for epifauna utilize structures in
the intertidal areas to contain the animals. These can be
poles or stakes driven into the bottom and wrapped with
mesh containing seed (bouchot culture for mussels) racks
on which oysters are placed in bags arrayed horizontally
(rack (or trestle) and bag culture) or seed may be set on
stakes and that are placed horizontally (stick culture) in an
intertidal area. Alternatively, cables can be stretched over
the flats and baskets or cages attached to the lines
(intertidal long-line culture). Cages offer both containment
and some predator protection but must be maintained to
prevent fouling from occluding the mesh. Structures in this
zone must withstand storm and ice conditions, and an alternate site, in deeper water, a protected location, or a cool
moist environment on shore, may be needed to provide protection. Fouling may be controlled by proper siting, turning
the bags to expose the surface to the sun, power washing,
other mechanical methods, or antifouling coatings. Rarely,
chemical fouling control, such as dipping the containers
and the animals in a brine solution, is utilized.
86
BIVALVE AQUACULTURE
produced later in the season. The conditioned brood stock
is spawned, fertilized eggs collected, and the larvae are
raised in tanks supplied with food, usually in the form of
cultured microalgae. These larvae are held until they reach
a size when they are ready to settle or set. Larval life span
is determined by temperature, but for most species, the larval period is 10–20 days. Under optimal culture conditions, cultured species set at the lower end of the time
spectrum. There are always exceptions to any generality
dealing with bivalve culture. Instead of tanks and cultured
algae, at least one commercial operation relies on lined
open ponds and natural phytoplankton production for larval and nursery culture.
At setting, epifaunal and infaunal species may be
treated differently. Epifauna such as oysters may be transferred to settling tanks and set as single animals or
attached as clusters to shell or alternate materials. Scallops
may be set on mesh or, as with infauna, allowed to attach
by their byssus and then washed from the setting tank and
placed in the appropriate containers. For many species,
there is an intermediate nursery where late-stage larvae
or immediate post-set are placed in a mesh-bottomed container and water, with cultured algae, is recirculated in the
top and out of the bottom mesh (a downweller). Once the
animals reach an appropriate size (typically about
0.75–1 mm), they are placed either on raceways or into
upwellers (a mesh bottom cylinder where water flows up
through the mesh, across the animals, and out through
a pipe near the top). Scallops may be left in mesh bags
and hung in a tank that is supplied with unicellular algae.
Once seed reach several mm in size, it is no longer economically feasible to culture algae for food, and the hatchery/nursery reverts to pumping water and food from the
environment. Depending on location and species, these systems can be placed on land, or as floats in the water, but all
are characterized by the use of some form of pumping
mechanism to force water and food through the container
of animals. If protected areas are available near a power
source, floating systems can be utilized and pumping cost
can be greatly reduced. If land-based systems are used,
pumping costs are increased, but system security is
improved. Epifauna may be kept in upwellers while infauna
may be placed in raceways where sediments accumulate,
helping to protect the seed from fouling. Fouling and overset control can also be achieved by coarsely filtering the
water to remove potential fouling organisms, treating the
tank and animals on a weekly basis with fresh water, air
drying, or other methods. The treatment methods work well
with species that tightly close (oysters), but cannot be utilized for species that cannot completely close their shells
(scallops). As the animals grow, there is a constant need
to increase both the space for the animals and the pumping
capacity. These requirements mean that there is a trade-off
between the maintenance and feeding requirements in the
nursery and the potential losses incurred by planting small
animals in nature.
To this point, the spatial area required for producing
large numbers of animals is relatively modest. Most animals spawned in the spring will be placed in areas for
grow-out in the fall. In some instances involving seed that
did not reach planting size or when larger sized animals
are needed, a nursery system that uses the passive movement of water through a cage (floating or on the bottom)
or a nursery plot where animals are maintained at high
density is utilized. The nursery plots are typically placed
in easily accessed, sheltered locations. Nursery structures
and grow-out structures (see below) are typically similar,
but animals are usually at higher density and protection
devices use finer mesh in the nursery.
Grow-out
Once animals reach a size where they can be planted for
growth to market size, there are many methods depending
on the needs of the organism, the environmental conditions, regulatory framework, and the value of the final
product. Extensive methods (low density over a large area
with minimal bed preparation and no predator protection),
intensive methods (high-density bottom plantings with
some form of predator protection), or “water column”
methods (seed placed on long lines, hung from strings,
placed in cages/trays or other containment vessels, or
attached to stakes placed in the intertidal) are all utilized.
Epifaunal organisms may be placed in the inter- or
subtidal directly on bottom beds that usually receive some
preparation before planting. This may be rudimentary
cleaning during the harvest of the prior crop or elaborate
after harvest fallowing, followed by cleaning and
resurfacing. In sites with large tidal amplitude, low earthen
berms constructed on the tidal flats may be seeded or used
to “finish” adults. These berms, topped by the incoming
tide, retain water when the tide recedes, allow a longer
feeding period, and ameliorate temperature fluctuations.
More intensive methods for epifauna utilize structures in
the intertidal areas to contain the animals. These can be
poles or stakes driven into the bottom and wrapped with
mesh containing seed (bouchot culture for mussels) racks
on which oysters are placed in bags arrayed horizontally
(rack (or trestle) and bag culture) or seed may be set on
stakes and that are placed horizontally (stick culture) in an
intertidal area. Alternatively, cables can be stretched over
the flats and baskets or cages attached to the lines
(intertidal long-line culture). Cages offer both containment
and some predator protection but must be maintained to
prevent fouling from occluding the mesh. Structures in this
zone must withstand storm and ice conditions, and an alternate site, in deeper water, a protected location, or a cool
moist environment on shore, may be needed to provide protection. Fouling may be controlled by proper siting, turning
the bags to expose the surface to the sun, power washing,
other mechanical methods, or antifouling coatings. Rarely,
chemical fouling control, such as dipping the containers
and the animals in a brine solution, is utilized.
86
BIVALVE AQUACULTURE