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Key words: California,
invasions, kelp,
nonindigenous, Undaria,
wakame
Abstract
The Asian kelp Undaria
pinnatifida was
discovered in southern
California in the spring
of 2000, and by the
summer
of 2001 had been
collected at several
California sites from
Los Angeles to Long
Beach Harbors and
Catalina Island
as far north as Monterey
Harbor. From its native
range in the
northwestern Pacific,
Undaria has now been
introduced
to the northeastern and
southwestern Atlantic
and the southwestern and
northeastern Pacific,
through a combination
of intentional transport
for cultivation,
accidental transport
with oysters, as fouling
on vessel hulls, and
possibly
other means. In the
northeastern Pacific,
water temperatures are
suitable for its
establishment from at
least Baja
California to British
Columbia, where it is
likely to grow well in
sheltered and partially
sheltered waters.
The discovery of several
populations of the large
Asian kelp Undaria
pinnatifida (Harvey)
Suringar
(in the brown algal
order Laminariales) in
southern
California marks the
latest stage in the
anthropogenic
global spread of this
species, which began in
the
1970s. Undaria is native
to Japan, northern China
and
Korea, where it is
cultivated and sold
commercially for
food. It has become
established in the
Mediterranean
Sea, Atlantic Europe,
New Zealand, Tasmania
and
Argentina.
The first California
specimens of Undaria
were discovered
in Los Angeles Harbor in
March 2000. By
August 2001, several
additional harbor
populations
had been found on
floating piers or in
shallow water
as far as Monterey Bay,
500 km to the north, and
at
depths of up to 25m in a
bay on Catalina Island,
about
35 km offshore of Los
Angeles (Figure 1, Table
1).
In Japan, U. pinnatifida
exhibits considerable
morphological
variability correlated
with latitude, and the
form
in southern California
matches that which is
found in
southern Japan (Okamura
1915, p. 267) (Figure
2).
The maximum length of
Undaria fronds in nature
is usually about 1.5 m,
but fronds as long as 3m
have been recorded in
cultivation (Perez et
al. 1984).
These fronds, comprising
a holdfast, stipe (stem)
and
blade, are diploid
sporophytes. Haploid
spores are
formed following meiotic
division of the initial
diploid
nucleus in unilocular
sporangia that are
grouped in
fertile areas called
sori. Kelps are grouped
into families
primarily on the basis
of the position of sori.
In
the Laminariaceae, they
are produced on the
blade,
while in the Alariaceae
they are restricted to
special
structures called
sporophylls. In Alaria
and Pterygophora
on the California coast,
the sporophylls are
flattened outgrowths
arising from the stipe
proximal
to the blade. In U.
pinnatifida, by
contrast, the
sporophylls
are ruffled wings along
both sides of the
flattened
lower portion of the
stipe. The generic name
is derived from unda,
the Latin word for wave,
referring to the
ruffled wing.
After the laterally
biflagellate, haploid
spores are
released, they typically
swim for up to 5–6 h
before
settling on a firm
substrate, where they
develop directly
into microscopic,
filamentous male and
female gametophytes
(Kanda 1936; Hay and
Luckens 1987).
Biflagellate
male gametes are
released and fertilize
the
eggs retained in the
female gametophytes,
which then
develop in situ into
embryonic sporophytes.
Growth
boundaries reported in
various studies range
from 3 to
20 ◦Cfor sporophytes and
10 to 24 ◦Cfor
gametophytes
(Sanderson 1990;
Wallentinus 1999; Sinner
et al.
2000), though Undaria
sporophytes have been
reported
in habitats with a
temperature range of
0–27 ◦C (Hay
1990; Castric-Fey et al.
1999). Undaria occurs
mainly
in salinities above 27
psu, but occasionally
down to
around 20 psu
(Wallentinus 1999).
Undaria’s first
appearance outside of
the northwestern
Pacific was in the Etang
de Thau, a lagoon on the
Mediterranean coast of
France, in 1971, having
apparently
been imported
accidentally with
Pacific oysters
(Crassostrea gigas),
which are cultivated in
the lagoon.
Undaria subsequently
spread along the south
coast of
France, to two sites in
Italy, and to several
Atlantic coast
sites from northwestern
Spain to The Netherlands
and
southern England,
through a combination of
intentional
transport for
cultivation and
accidental transport
with
oysters or as fouling on
vessel hulls, and
possibly by
other means. Itwas
discovered in NewZealand
in 1987,
where it has spread to
numerous sites on North,
South
and Stewart islands, in
Tasmania in 1988, in
Golfo
Nuevo in Argentina in
1992, and in Port
Phillip Bay
in southeastern
Australia in 1996
(details provided in
Table 2).
From the descriptions of
Undaria’s various
introductions
together with our own
observations in southern
California, some
patterns in its
distributional ecology
and reproduction can be
discerned. First,
sporophytes
grow on any available
firm substrate,
including rocks,
wood, concrete, metal,
plastic, glass, rubber
and on
or over various
organisms (including
coralline algae,
seagrass blades,
chaetopterid and
serpulid worm tubes,
bivalves, barnacles and
ascidians), and are
often found
just below the waterline
attached to breakwaters,
seawalls,
buoys, ropes, floating
piers or the hulls of
vessels
(Hay and Luckens 1987;
Sanderson 1990; Hay
1990;
Piriz and Casas 1994;
Lewis 1999; Sinner et
al. 2000;
K.A. Miller pers. comm.
2001). Second, they
prefer
sites that are at least
somewhat protected,
though they
can grow in open coast
sites (Hay and Villouta
1993;
Floc’h et al. 1996; Hay
and Luckens 1987).
Third,
their growth is not
prevented by organic
pollution. At
several sites, colonized
areas are close to urban
sewage
emissions (Curiel et al.
1994; Castric-Fey et al.
1999;
Talman et al. 1999;
Cecere et al. 2000).
Fourth, in
some areas of
introduction,
seasonality is similar
to
that observed in Japan,
that is, sporophytes
begin rapid
growth in winter, mature
in late spring, and
disintegrate
and disappear in summer
when water temperatures
reach 20–25 ◦C (Hay and
Villouta 1993). In other
sites, including the
Brittany Coast of France
and in
New Zealand, there are
two or more generations
per
year, with sporophytes
present and spore
release occurring
throughout all or nearly
all of the year (Hay and
Villouta 1993;
Castric-Fey et al.
1999).
Water temperatures along
the Pacific Coast of the
United States are
favorable for the
establishment of
U. pinnatifida from at
least Baja California to
British
Columbia. Sheltered and
partially sheltered
regions
including the Southern
California Bight,
Monterey
Bay, the more oceanic
parts of San Francisco
Bay,
Tomales and Humboldt
Bays, and Puget Sound
would
seem to offer excellent
growing conditions. Much
of
the intervening coast
may be too exposed,
although
there are reports of
populations on exposed
shores in
Japan, NewZealand and
Tasmania (Hay 1990; Hay
and
Villouta 1993).
Once established, the
eradication or control
of populations
of Undaria is probably
impossible. A single
frond releases an
astronomical number of
zoospores,
which appear to settle
randomly. Probably all
fertilized
eggs develop into
embryonic sporophytes.
If
the latter manage to
survive grazers, their
very rapid
growth ensures continued
survival unless the
spores
settle intertidally,
causing the frond to be
damaged by
sunlight when it is
exposed by low tides.
Eradication
efforts based on manual
removal have been
unsuccessful,
and the eradication of
an established
population
through the use of
biocides would appear to
be impossible
except perhaps in an
enclosed basin (Burridge
and Gorski 1998; Curiel
et al. 1998; Sinner et
al.
2000).
Undaria has likely been
encountered by anyone
who
has been served a cup of
miso soup in a Japanese
restaurant.
Thin green pieces of
wakame (the Japanese
name
for Undaria) are
traditionally floated on
the soup, to
which they impart flavor
and texture. For
centuries,
Japanese have harvested
wakame from nature,
preserved
it in various ways, and
used it as food. Recipes
that include wakame may
be found in various
specialty
cookbooks (e.g. Madlener
1977; Arasaki and
Arasaki
1983). Wakame is found
in abundance on partly
protected
rocky coasts all along
the Sea of Japan and
from
southern Hokkaido to
southern Honshu on
Japan’s east
coast, where it grows in
the lowest intertidal
zone and
subtidally to a depth of
about 15m (Saito 1975).
To
prevent the exhaustion
of the natural resource
and to
improve productivity,
various methods of
cultivation
have been developed in
Japan since 1952. In
general,
the thalli are induced
to grow on suspended
ropes or
nets in the field or in
tanks. The cultivation
of wakame
was successfully
exported to China in
areas with relatively
sparse natural
populations in the
1930s, and to
Taiwan in 1981
(Wallentinus 1999; Zhang
et al. 1984).
In 1998, the production
of wakame from natural
populations
in Japan amounted to
2839 tons valued at $8.3
million, while
production from
cultivation amounted
to 70,670 tons valued at
$132.5 million (H. Ohba,
pers. comm.).
Establishment of large
populations of
Undaria in California
would almost certainly
lead to
harvesting by Asian
immigrants, either for
personal or
commercial use.
In the northeastern
Pacific, Undaria joins
at least
four other established
Japanese seaweeds. The
wellpublicized
brown alga Sargassum
muticum (Yendo)
Fensholt (Critchley et
al. 1990) and green alga
Codium
fragile subsp.
tomentosoides (van Goor)
P.C. Silva
(Trowbridge 1998), and
the relatively
unheralded red
alga Lomentaria
hakodatensis Yendo
(Cabioc’h and
Magne 1987), are widely
distributed along the
coast.
The red alga Gelidium
vagum Okamura has been
found in Tomales Bay,
California, where it was
probably
introduced from Japan by
way of oyster farms
in British Columbia and
Washington (Renfrew et
al.
1989; Hughey et al.
1996).
Acknowledgements
The third author’s
contributionwas
supported by grants
from the State Water
Resources Control Board,
the
California Department of
Fish and Game and the
National Fish and
Wildlife Foundation.
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