Ecological impacts and evolutionary
consequences of the European green crab invasion
Edwin Grosholz, Ph.D.
University of California, Davis
Wednesday, October 13, 1999
3:00 p.m.—Pacific Forum
Invasive species
rank among the most serious threats to the health of coastal ecosystems. We have used
long-term data and experiments in both field and laboratory to quantify the ecological
consequences of the invasive European green crab on more than 20 species of invertebrates
and 13 species of shorebirds in Bodega Harbor, CA. Within three years of the invasion, our
results show that green crab predation has resulted in a 90-95% reduction of several
native invertebrates, including clams and shore crabs. These prey populations have
remained at very low abundances for five years since the introduction of the green crab.
Also, significant indirect effects of green crab predation have also occurred during the
same period, including large increases in non-prey species such as polychaetes and
tube-building crustaceans. However, changes in invertebrate prey populations have not yet
resulted in changes in shorebird populations wintering in the Bodega Harbor system. We
have also begun to quantify the evolutionary consequences of the green crab invasion by
comparison of North American with a parallel invasion in Australia. We show that crabs in
invading populations are significantly larger in comparison with the native European
range. Recent molecular genetic comparisons of native and introduced populations show
substantial reduction in genetic diversity suggesting the possibility that the apparent
"ecological release" may have genetic basis. We are now developing methods to
test this idea.
Invasive species
rank among the most serious threats to the health of coastal ecosystems. We have used
long-term data and experiments in both field and laboratory to quantify the ecological
consequences of the invasive European green crab on more than 20 species of invertebrates
and 13 species of shorebirds in Bodega Harbor, CA. Within three years of the invasion, our
results show that green crab predation has resulted in a 90-95% reduction of several
native invertebrates, including clams and shore crabs. These prey populations have
remained at very low abundances for five years since the introduction of the green crab.
Also, significant indirect effects of green crab predation have also occurred during the
same period, including large increases in non-prey species such as polychaetes and
tube-building crustaceans. However, changes in invertebrate prey populations have not yet
resulted in changes in shorebird populations wintering in the Bodega Harbor system. We
have also begun to quantify the evolutionary consequences of the green crab invasion by
comparison of North American with a parallel invasion in Australia. We show that crabs in
invading populations are significantly larger in comparison with the native European
range. Recent molecular genetic comparisons of native and introduced populations show
substantial reduction in genetic diversity suggesting the possibility that the apparent
"ecological release" may have genetic basis. We are now developing methods to
test this idea.