If you’ve walked along the Hudson shoreline,
you’ve probably seen thorny, black water-chestnut
seedpods, thick stands of common reed along railroad
tracks, mute swans gliding across the water, carp
splashing in the shallows, chunky shells of Atlantic
rangia on beaches, and the thin, sharp shells of zebra
mussels littering shorelines from Newburgh north.
All of these are alien species, brought here by
humans, either deliberately or accidentally, that did not
live in the Hudson when Henry first sailed up the river.
All, no doubt, have strong effects on other plant and
animal species. Documenting the dramatic effects of
one invasive species – the zebra mussel invasion on the
Hudson – has been the focus of our research group at
the Institute of Ecosystem Studies (IES).
Zebra mussels are small (less than 4 cm long),
black-and-white striped bivalves that attach tenaciously
to solid objects – stones, bricks, shells, wood, plants,
and boat hulls – below the water line in fresh or
slightly brackish water. The adults are filter-feeders,
eating phytoplankton, small zooplankton, large bacteria,
and organic detritus.
During the summer, the adults release huge
numbers of eggs and sperm (one female may make a
million eggs each year) into the water, which develop
into free-swimming larvae. If the larvae get enough to
eat and aren’t eaten by a predator, they settle down
onto a solid object
and grow into
mature in just one
year, and may live
for four to six years.
Zebra mussels are
but spread into
when canals were
waterways in the
early 19th century.
In about 1985, they
hitched a ride to
Detroit in the ballast
water of an ocean-
going ship. Since
then, they’ve spread
to rivers and lakes
from Quebec and Minnesota to New Orleans. They
appeared in the Hudson in 1991, and are common
everywhere in the estuary between Troy and the
Since September 1992, the Hudson’s zebra mussel
population has been huge (50 billion to 600 billion