The Shellfish Farm News
November 2004
Deepwater oyster
farms increase biodiversity
At a
technical conference held at the end of September in Campbell
River for farmers, scientists and regulators, it was reported
that deepwater oyster farms increase species biodiversity.
Researchers from Malaspina University-College presented
the results of on-going studies that have shown that remarkably
diverse invertebrate (animal) communities are associated
with BC's suspended shellfish culture systems.
Up to 60 different types of species were found on the raft
culture systems, which are thereby functioning as artificial
living reefs. These species settled as larvae on the rafts
and included sea cucumbers, sea urchins, marine worms, and
small shrimp. In addition to this many species of fish utilize
deepwater oyster farms as a refuge from predators and as
feeding stations, grazing on the organisms that have settled
there. According to the researchers, the oyster rafts function
similarly to mangroves in tropical ecosystems, because of
the settlement surfaces, visual barriers to predators, and
nursery areas for juvenile fish that the rafts provide.
The number of species that settle on rafts
will vary from site to site, as well as seasonally and according
to farm activities. Larval settlement of organisms on the
oyster crop and culture trays starts almost as soon as the
oyster seed is first placed in the water. Settlement of some
species such as barnacles can overwhelm the crop, smothering
it and excluding many of the other organisms as well. Oyster
farmers avoid exposing new seed to the period of heaviest
barnacle sets, which typically occur in the early spring,
but this is sometimes unavoidable and requires cleaning of
oyster trays. Mussels can also settle on oysters so heavily
that it smothers them, however unlike barnacles, mussels are
not as easy to remove because of the tough threads with which
they attach to the oyster trays. Fortunately, diving ducks
love to harvest mussels from the outside of oyster trays.
Farmers depend on the seasonal migration of scoter ducks which
arrive in the early fall and clean the summers' accumulation
of mussels off the rafts.
Dave
Mitchell is a Registered Professional Biologist and General
Manager of Fanny Bay Oysters Ltd.
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