(full paper is archived in the Miller Library)
Title: Mytilus interactions:
interspecific aggregation of three mussel
species
Student Author(s): Friedman, Rachel
Faculty Advisor(s): Somero, George
Pages: 25
Location: Final Papers Biology 175H
Date: June 2007
Abstract: Invasive species have become an
important concern for marine ecosystem function
and conservation. Many studies have shown the
negative effects of an exotic species on native
species through increased competition or other
behavioral changes. My study examined three
mussels of the genus Mytilus found along
the central coast of California, each with a
unique life history and ecological
characteristics. M. californianus,
the ribbed mussel, is a native species that forms
dense beds in rocky intertidal habitats; the
native blue mussel, M. trossulux, and the
invasive blue mussel, M.
galloprovincialis, are found in bays and
estuaries. Mytilus
galloprovincialis, which entered
California waters some time in the middle of the
20th century, has replaced the native blue mussel
from Southern California up to the latitude of
Monterey Bay,
where both blue mussels co-occur. I sought to
determine how the three congeners differed (i) in
aggregation behavior, which can influence growth
and reproductive output; and (ii) vulnerability
to predatory whelks of the genus Nucella.
Aggregation behavior was compared in the absence
and presence of whelks. Clumping behavior was
analyzed to identify species preferences in
neighboring mussels. All aggregatons in
whelk-free seawater, except for M.
galloprovincilis when grouped with M.
californianus, showed significant preference
for mixed species assemblages. Under
predation-pressure conditions, none of the
mussels in combination with M. trossulus
demonstrated a significant preference for a
specific neighbor in the aggregation. The
presence of whelks also yielded slightly larger
aggregation sizes. To extend the predation
portion of this experiment, two species of
predatory whelk, Nucella emarginata and
Nucella ostrina, were given the choice
between the native and invasive blue mussels.
Nucella ostrina demonstrated a preference
for the native mussel but N. emarginata
did not, suggesting that native predators could
potentially feed upon and thereby contribute to
the regulation of the invasive populations.
However, the invasive has not yet been deterred
by native predators. Overall, results of this
study provide preliminary data for further work
on mussel aggregation and predation and the
dynamics of invasive and native poplations on the
western coast of the United States.