608
W. Judson Kenworthy et al.
and global scales (Duarte, 2002). The fluid medium
surrounding the seagrass biome is seldom bounded
by discrete barriers. Organisms and water constituents move between systems, therefore, management actions in one system can have a direct effect on another system, and in many instances these
can occur at very large scales (Roberts, 1997; Jameson et al., 2002; Johnson et al., 2003). Attributes
associated with conservation biology can be used
to organize research programs addressing different
scales. Broad scale research programs linking upstream watershed activities with investigations in the
estuary, the reef tract, and the coastal shelf are needed
to effectively conserve and protect seagrasses. This
is an opportunity for landscape ecologists, physical oceanographers, and remote sensing specialists to collaborate with biologists, ecologists, geographers, and social scientists to synthesize information and construct holistic models for seagrass
conservation.
4. Invasive Species
Biological invasions threaten the structural integrity
and function of natural systems of plants and animals
(Carlton and Geller, 1993; Walker and Kendrick,
1998). There are only a few examples of the interactions between non-native and indigenous species
involving seagrass ecosystems; however, with the
globalization of trade and the predictions for climate
change, there are likely to be more issues associated
with species invasions in the future. The only known
large-scale displacement of seagrasses by an invasive species has been documented in the Mediterranean, where an introduced green alga, Caulerpa
taxifolia, has had a negative impact on the seagrasses
P. oceanica and C. nodosa (Meinez et al., 1995; Ceccherilli and Cinelli, 1997; Dumay et al., 2002). Additionally, the extension of a new Caulerpa species
(C. racemosa) in the same region induced similar
effects (Dumay et al., 2002; Piazzi and Ceccherilli, 2002). The discovery of C. taxifolia in southern California (Williams and Grosholz, 2002) suggests that future interactions involving other seagrass
species and nonnative introductions by macroalgae
may occur. While the scientific community is still debating the ecological implications of the Caulerpa
species invasions, introduction of macroalgae into
nonnative coastal plant communities may become
more common and problematic than previously believed (den Hartog, 1997). Sargassum muticum can
threaten the patch stability of Z. marina if meadows
are beginning to fragment (den Hartog, 1997), but no
wide spread outbreaks of S. muticum have yet been
reported.
In the Great Bay Estuary of New Hampshire in
the United States, the European green crab (Carcinus maenas) affects the survival of transplanted Z.
marina by shredding the leaves and destroying apical meristems (Davis et al., 1998). Bioturbation is
not uncommon in seagrass meadows and sometimes serves as an important mechanism for recycling nutrients, as a disturbance vector, or may act
as a key natural stressor (Orth, 1975; Suchanek,
1983); however, the presence of the non-native green
crabs threatens the restoration potential of Z. marina
meadows in the northeastern United States. Without
some form of caging to protect the seagrasses or
some modification of the shredding behavior, green
crabs effectively destroyed recently transplanted eelgrass.
The introduction of non-native seagrasses has
been documented in at least two instances. Zostera
japonica was first reported in the Pacific northwest
region of the United States in 1952. It was theorized that vegetative fragments or seeds of this seagrass were carried either by ballast water or in oyster
(Crassostrea gigas) crates when these oysters were
imported from Japan early in the 20th Century (Harrison and Bigley, 1982). The exact point of entry
is a matter of speculation, but the distribution of Z.
japonica is now widespread in the region with substantial populations at several sites around southern
British Columbia in Canada, Washington State, and
Oregon (Wyllie-Echeverria and Ackerman, 2003).
The State of Washington protects Z japonica as a
priority habitat (Pawlak, 1994) while the State of
California, after finding a population in Humboldt
Bay (40.47 N; 124.09 W) in the summer of 2002,
executed a plan of eradication without conducting a
risk analysis of secondary impacts (personal communication, Susan McBride California Sea Grant
Program, Eureka, CA). Where it occurs, Z. japonica has changed the physical nature of the habitat
and the density and richness of the indigenous fauna
(Posey, 1988). Baldwin and Lovvorn (1994) describe
the importance of these plants for herbivorous dabbling ducks (e.g. Anas americana, A. acuta) and
brant geese (Branta bernicla), so whether this invasion warrants eradication is still subject to debate;
calling into question any program of removal that
W. Judson Kenworthy et al.
and global scales (Duarte, 2002). The fluid medium
surrounding the seagrass biome is seldom bounded
by discrete barriers. Organisms and water constituents move between systems, therefore, management actions in one system can have a direct effect on another system, and in many instances these
can occur at very large scales (Roberts, 1997; Jameson et al., 2002; Johnson et al., 2003). Attributes
associated with conservation biology can be used
to organize research programs addressing different
scales. Broad scale research programs linking upstream watershed activities with investigations in the
estuary, the reef tract, and the coastal shelf are needed
to effectively conserve and protect seagrasses. This
is an opportunity for landscape ecologists, physical oceanographers, and remote sensing specialists to collaborate with biologists, ecologists, geographers, and social scientists to synthesize information and construct holistic models for seagrass
conservation.
4. Invasive Species
Biological invasions threaten the structural integrity
and function of natural systems of plants and animals
(Carlton and Geller, 1993; Walker and Kendrick,
1998). There are only a few examples of the interactions between non-native and indigenous species
involving seagrass ecosystems; however, with the
globalization of trade and the predictions for climate
change, there are likely to be more issues associated
with species invasions in the future. The only known
large-scale displacement of seagrasses by an invasive species has been documented in the Mediterranean, where an introduced green alga, Caulerpa
taxifolia, has had a negative impact on the seagrasses
P. oceanica and C. nodosa (Meinez et al., 1995; Ceccherilli and Cinelli, 1997; Dumay et al., 2002). Additionally, the extension of a new Caulerpa species
(C. racemosa) in the same region induced similar
effects (Dumay et al., 2002; Piazzi and Ceccherilli, 2002). The discovery of C. taxifolia in southern California (Williams and Grosholz, 2002) suggests that future interactions involving other seagrass
species and nonnative introductions by macroalgae
may occur. While the scientific community is still debating the ecological implications of the Caulerpa
species invasions, introduction of macroalgae into
nonnative coastal plant communities may become
more common and problematic than previously believed (den Hartog, 1997). Sargassum muticum can
threaten the patch stability of Z. marina if meadows
are beginning to fragment (den Hartog, 1997), but no
wide spread outbreaks of S. muticum have yet been
reported.
In the Great Bay Estuary of New Hampshire in
the United States, the European green crab (Carcinus maenas) affects the survival of transplanted Z.
marina by shredding the leaves and destroying apical meristems (Davis et al., 1998). Bioturbation is
not uncommon in seagrass meadows and sometimes serves as an important mechanism for recycling nutrients, as a disturbance vector, or may act
as a key natural stressor (Orth, 1975; Suchanek,
1983); however, the presence of the non-native green
crabs threatens the restoration potential of Z. marina
meadows in the northeastern United States. Without
some form of caging to protect the seagrasses or
some modification of the shredding behavior, green
crabs effectively destroyed recently transplanted eelgrass.
The introduction of non-native seagrasses has
been documented in at least two instances. Zostera
japonica was first reported in the Pacific northwest
region of the United States in 1952. It was theorized that vegetative fragments or seeds of this seagrass were carried either by ballast water or in oyster
(Crassostrea gigas) crates when these oysters were
imported from Japan early in the 20th Century (Harrison and Bigley, 1982). The exact point of entry
is a matter of speculation, but the distribution of Z.
japonica is now widespread in the region with substantial populations at several sites around southern
British Columbia in Canada, Washington State, and
Oregon (Wyllie-Echeverria and Ackerman, 2003).
The State of Washington protects Z japonica as a
priority habitat (Pawlak, 1994) while the State of
California, after finding a population in Humboldt
Bay (40.47 N; 124.09 W) in the summer of 2002,
executed a plan of eradication without conducting a
risk analysis of secondary impacts (personal communication, Susan McBride California Sea Grant
Program, Eureka, CA). Where it occurs, Z. japonica has changed the physical nature of the habitat
and the density and richness of the indigenous fauna
(Posey, 1988). Baldwin and Lovvorn (1994) describe
the importance of these plants for herbivorous dabbling ducks (e.g. Anas americana, A. acuta) and
brant geese (Branta bernicla), so whether this invasion warrants eradication is still subject to debate;
calling into question any program of removal that