The methods developed made Eucheuma the world’s most
widely farmed seaweed. However, it was released from
open-cage experiments into Hawaiian coastal waters
where it smothers and kills coral, creating devastation.
It spread and smothered at least half the reefs in Kaneohe
Bay (Conklin and Smith, 2005).
An effective tool to combat invasive algae in Hawaii is
the Super Sucker, an underwater vacuum cleaner that
scoops up about 800 lbs of the invasive algae each hour.
It sucks the algae off the reef and places it on a barge above
water so that noninvasive marine life can be sorted out and
returned to the water. The alien algae are packed into sacks
and delivered to taro farmers for use as fertilizer. Noted
coral reef biologist Thomas Goreau thinks that this will
give only temporary results unless the excess nutrients that
promote the algal growth are removed. In a letter to
Science Magazine, he wrote, “No amount of sucking them
off will work when they grow right back because they are
overfertilized. It is the suckers paying for this
well-intentioned, but ultimately futile, effort who will be
hosed unless the underlying causes of eutrophication are
removed” (Goreau, 2008).
A long-term solution may depend on increasing the
populations of sea urchins that eat the invasive algae
(Conklin and Smith, 2005). The sea urchin population
around Hawaii has declined because of excessive
harvesting for their gonads, prized by sushi eaters.
Researchers are learning how to propagate them so that
they can place baby urchins on newly vacuumed reefs to
graze on little bits of algae.
Common periwinkle snail: Littorina littorea
The common periwinkle was introduced from Europe to
the East Coast of the United States but the dates are uncertain. Using molecular genetics, Blakeslee et al. (2008)
estimated it was about 500 years ago. It feeds primarily
on algae on rocks at the shoreline. The snail is so abundant
that most people think of it as a normal part of the coastal
habitat. It is found on rocky shores in the northeast, where
it has become so abundant that its voracious grazing has
destroyed much of the intertidal algal vegetation. It can
also live in intertidal marshes and subtidal areas. It has
caused a gradual transformation of the New England coast
from rocks with abundant seaweed cover to the bare rocks
that most people today think of as natural (Bertness,
1984). The state of New Hampshire actually passed
a law protecting this edible species from out-of-state
poaching. In salt marshes, the snails are eaten by diamondback terrapins and by blue crabs.
Asian clams: Potamocorbula amurensis
In the late 1980s, the Asian clam became established in
San Francisco Bay, replacing the native clam, Macoma
balthica, as the dominant benthic macroinvertebrate
(Nichols et al., 1990). It is a filter feeder, and its rapid
spread has reduced phytoplankton in the bay, which
means less food for zooplankton, which means less food
for fish. The invader is eaten by diving ducks and lives
closer to the surface of the mud than Macoma, increasing
its availability to the ducks. This clam has altered nutrient
cycling and caused major ecosystem changes.
A related clam on the East Coast is Corbicula fluminea,
which arrived in the late 1970s and is abundant in the
Potomac River. When it was first discovered, scientists
were worried that it would cause major problems like the
zebra mussel in the Great Lakes (attaching to surfaces,
blocking intake pipes for water supply systems, etc.), but
it does not attach to hard surfaces since it lacks byssus
threads. This clam instead settled on sandy bottom
sediments, and after it arrived there were increases in submerged aquatic vegetation and fish (Phelps, 1984). It also
serves as food for birds and muskrats, and after its arrival
the water quality and clarity actually improved, possibly
due in part to its filter feeding. The improvement in water
quality may also have been due to improved sewage treatment and a ban on phosphorus in laundry detergents, but at
the very least, this outcome means that not all invasions
are ecological disasters.
Green crab: Carcinus maenas
Called “green crab” in the United States and “shore
crab” in Europe, this species is native to the Atlantic
coasts of Europe and Northern Africa, found on protected
rocky shores, pebbly beaches, mudflats, and tidal
marshes. It thrives in a wide range of salinity and temperature and has invaded numerous coastal areas, including
South Africa, Australia, and both coasts of North
America. Although it is called a green crab, large individuals (about 3 in across) may be brownish red. Its larvae
can survive in the plankton for over 2 months, dispersing
many miles up and down the coast. After the larvae
develop in the sea, they are swept into coastal
waters and estuaries by tides and currents where they
molt and settle out as juveniles in the intertidal zone.
If conditions are suitable, they will survive and reproduce, establishing new populations and extending its
range (Figure 3).
There have been two major invasions of America, first
in the mid-1800s when they reached the Atlantic coast,
probably in crevices of fouled ship hulls. They found
suitable habitat in coastal bays from New Jersey to Cape
Cod. In the early 1900s, they spread north to Nova Scotia,
and their arrival in Maine in the 1950s coincided with
dramatic declines in the soft clam fishery. The second
major invasion was detected in 1989 in San Francisco
Bay where they probably arrived as larvae in ballast
water of commercial ships (Grosholz and Ruiz 1996). It
is also possible that they were hanging onto the fouling
on ships or could have been in with the sea grass and kelp
used for packing and shipping lobsters and bait worms to
the West Coast.
It is an effective forager, able to open bivalves more
quickly than most other crabs, which makes it a strong
competitor for the food sources of native crabs, fishes,
and birds and a threat to shellfisheries. It feeds on many
organisms, including clams, oysters, mussels, marine
INVASIVE SPECIES
367
widely farmed seaweed. However, it was released from
open-cage experiments into Hawaiian coastal waters
where it smothers and kills coral, creating devastation.
It spread and smothered at least half the reefs in Kaneohe
Bay (Conklin and Smith, 2005).
An effective tool to combat invasive algae in Hawaii is
the Super Sucker, an underwater vacuum cleaner that
scoops up about 800 lbs of the invasive algae each hour.
It sucks the algae off the reef and places it on a barge above
water so that noninvasive marine life can be sorted out and
returned to the water. The alien algae are packed into sacks
and delivered to taro farmers for use as fertilizer. Noted
coral reef biologist Thomas Goreau thinks that this will
give only temporary results unless the excess nutrients that
promote the algal growth are removed. In a letter to
Science Magazine, he wrote, “No amount of sucking them
off will work when they grow right back because they are
overfertilized. It is the suckers paying for this
well-intentioned, but ultimately futile, effort who will be
hosed unless the underlying causes of eutrophication are
removed” (Goreau, 2008).
A long-term solution may depend on increasing the
populations of sea urchins that eat the invasive algae
(Conklin and Smith, 2005). The sea urchin population
around Hawaii has declined because of excessive
harvesting for their gonads, prized by sushi eaters.
Researchers are learning how to propagate them so that
they can place baby urchins on newly vacuumed reefs to
graze on little bits of algae.
Common periwinkle snail: Littorina littorea
The common periwinkle was introduced from Europe to
the East Coast of the United States but the dates are uncertain. Using molecular genetics, Blakeslee et al. (2008)
estimated it was about 500 years ago. It feeds primarily
on algae on rocks at the shoreline. The snail is so abundant
that most people think of it as a normal part of the coastal
habitat. It is found on rocky shores in the northeast, where
it has become so abundant that its voracious grazing has
destroyed much of the intertidal algal vegetation. It can
also live in intertidal marshes and subtidal areas. It has
caused a gradual transformation of the New England coast
from rocks with abundant seaweed cover to the bare rocks
that most people today think of as natural (Bertness,
1984). The state of New Hampshire actually passed
a law protecting this edible species from out-of-state
poaching. In salt marshes, the snails are eaten by diamondback terrapins and by blue crabs.
Asian clams: Potamocorbula amurensis
In the late 1980s, the Asian clam became established in
San Francisco Bay, replacing the native clam, Macoma
balthica, as the dominant benthic macroinvertebrate
(Nichols et al., 1990). It is a filter feeder, and its rapid
spread has reduced phytoplankton in the bay, which
means less food for zooplankton, which means less food
for fish. The invader is eaten by diving ducks and lives
closer to the surface of the mud than Macoma, increasing
its availability to the ducks. This clam has altered nutrient
cycling and caused major ecosystem changes.
A related clam on the East Coast is Corbicula fluminea,
which arrived in the late 1970s and is abundant in the
Potomac River. When it was first discovered, scientists
were worried that it would cause major problems like the
zebra mussel in the Great Lakes (attaching to surfaces,
blocking intake pipes for water supply systems, etc.), but
it does not attach to hard surfaces since it lacks byssus
threads. This clam instead settled on sandy bottom
sediments, and after it arrived there were increases in submerged aquatic vegetation and fish (Phelps, 1984). It also
serves as food for birds and muskrats, and after its arrival
the water quality and clarity actually improved, possibly
due in part to its filter feeding. The improvement in water
quality may also have been due to improved sewage treatment and a ban on phosphorus in laundry detergents, but at
the very least, this outcome means that not all invasions
are ecological disasters.
Green crab: Carcinus maenas
Called “green crab” in the United States and “shore
crab” in Europe, this species is native to the Atlantic
coasts of Europe and Northern Africa, found on protected
rocky shores, pebbly beaches, mudflats, and tidal
marshes. It thrives in a wide range of salinity and temperature and has invaded numerous coastal areas, including
South Africa, Australia, and both coasts of North
America. Although it is called a green crab, large individuals (about 3 in across) may be brownish red. Its larvae
can survive in the plankton for over 2 months, dispersing
many miles up and down the coast. After the larvae
develop in the sea, they are swept into coastal
waters and estuaries by tides and currents where they
molt and settle out as juveniles in the intertidal zone.
If conditions are suitable, they will survive and reproduce, establishing new populations and extending its
range (Figure 3).
There have been two major invasions of America, first
in the mid-1800s when they reached the Atlantic coast,
probably in crevices of fouled ship hulls. They found
suitable habitat in coastal bays from New Jersey to Cape
Cod. In the early 1900s, they spread north to Nova Scotia,
and their arrival in Maine in the 1950s coincided with
dramatic declines in the soft clam fishery. The second
major invasion was detected in 1989 in San Francisco
Bay where they probably arrived as larvae in ballast
water of commercial ships (Grosholz and Ruiz 1996). It
is also possible that they were hanging onto the fouling
on ships or could have been in with the sea grass and kelp
used for packing and shipping lobsters and bait worms to
the West Coast.
It is an effective forager, able to open bivalves more
quickly than most other crabs, which makes it a strong
competitor for the food sources of native crabs, fishes,
and birds and a threat to shellfisheries. It feeds on many
organisms, including clams, oysters, mussels, marine
INVASIVE SPECIES
367