PHYCOLOGICAL SOCIETY OF AMERICA
- The genus Antithamnion is found everywhere in the world!
Most representatives of the genus are found in the Pacific Ocean,
and it is believed that the genus originated in the Pacific.
 According to the literature, Antithamnion
can be found in almost all water temperatures: off the coast of Alaska,
British Columbia, along Washington, Oregon, California, Hawaii,
the Caribbean, Japan, Korea, Australia, New Zealand, South Africa,
Bangladesh, the Arabian Sea, Namibia, the Azores, the Canary Islands,
Spain, the Mediterranean, the Black Sea, the Adriatic Sea, Ireland,
and the North Sea. Most of the species have a regionally restricted
distribution, but at least 4 have been found to have large distributions
reaching into both hemispheres!  This
global distribution of Antithamnion indicates that the
genus can tolerate a wide range of temperatures and salinities,
although particular species may be more regionally adapted to a
smaller range of temperatures and salinities, and majority of species
prefer cold temperate waters.
A. defectum has been reported mostly along the Pacific coast
of North America from Alaska to Mexico, but also along the Pacific
coast of the Russia, China, Sakhalin Is., Japan, Korea, Brittany in
the Atlantic and the Red Sea. 
The genus Antithamnion
is commonly found
along the Pacific North American coast from Alaska to Mexico,
and there are 12 species from Oregon north to Alaska. 
is characteristically found off
the Pacific coast from Alaska to Baja California. 
is found in waters from Baja to
Monterey, California, indicating that it prefers warmer water.
There was one record of it from Alaska, but this record was never
 A. kylinii
in 1989 to have a range between British Columbia and Mexico. 
Antithamnion defectum is common in the waters of Monterey
Bay, as is A. dendroidem., A. kylinii as well as
some other species such as A. glanduliferum, and A.
have also been found in the Bay in the past. The records
from the Gilbert M. Smith Herbarium at
Hopkins Marine Station indicate that A. defectum will grow epiphytically
on a wide variety of other algae from large Macrocystis to
Calliarthron, epizoically on Cryptochiton stelleri (a
large chiton found in Monterey Bay) ,
epilithically on rocks, and also commonly on the pilings and other
man-made structures at the Monterey Wharf. The wide variety of substrates
on which Antithamnion will grow may give it a generalist
advantage, rarely being in danger of having no place to settle and
grow, unlike obligate epiphytes which have one particular host. In
addition, being an epiphyte could potentially allow Antithamnion to
travel in currents, as the large algae to which Antithamnion is
attached can drift long distances. This, in turn, could increase
its dispersal range.
Effects of Global Warming on Distribution
According to the Partnership
for Interdisciplinary Studies of Coastal Oceans (PISCO) data-base,
Antithamnion dendroidem's northern
limit to distribution is currently Monterey Bay, California. With
the current rise in sea surface temperature due to global warming,
there is a possibility of a northward-shift in distribution of this
species. Future monitoring of this species' distribution could be
very interesting. In addition, a look into the past at historical
distribution could also provide evidence for global warming. A much
more exhaustive survey would need to be done through herbariums along
the central California coast; however, in my searches in the last
couple months, I have found mostly A. dendroidem
as opposed to other species of Antithamnion. Interestingly,
most specimens of Antithamnion in the Gilbert M. Smith Herbarium,
collected primarily by Isabella Abbott in the 1950s-60s, are A.
defectum. The herbarium contains only three specimens
Could Antithamnion species distributions already
have shifted over the last fifty years?
amazing study was done in 1969 by James Markham at Friday Harbor on
the patterns of epiphytic growth on Nereocystis luetkeana, the
large bull kelp which is also common on the wave-swept coastline
of Carmel, CA. This study found that young Nereocystis plants
appeared in April, and epiphytes began to colonize them by June,
but were not abundant until August. The first to colonize the plants
was a diatom, Navicula grevillei, which completely
disappeared once Enteromorpha linza appeared in
July. Antithamnion appeared in August, and by October it
was the dominant alga on the stipes. On the upper portions of the
stipe (above 100 cm depth) which often laid horizontal on the water
surface, Enteromorpha dominated
the upper, light-exposed side, while Antithamnion and Ectocarpus
shared the underside of the stipe. Below 100 cm, Antithamnion outcompeted
most epiphytes, and extended down to deeper parts
of the longest stipes. I think this may reflect a sensitivity
to high light intensity, or the fact that it is out-competed by Enteromorpha above
100 cm where light is high. Its dominance below 100 may be due to its
high growth rate and its ability to grow under lower light levels due,
at least in part, to accessory pigments. There is more
Antithamnion's growth under various light conditions on the
Possibly the most fascinating part of this study was the distribution
of various life-stages of Antithamnion on the Nereocystis
stipes. Small, slow growing, vegetative Antithamnion grew
on the upper and lower limits of the distribution. Inside of the vegetative
Antithamnion at the top and bottom were the female gametophytes,
and in the middle of the stipe were the tetrasporophytes. Male plants
were so small and uncommon that they did not dominate anywhere on
the stipe. This same pattern existed on shorter stipes in shallower
water and on longer stipes in deeper water. This pattern was hypothesized
not to be governed primarily by light, but by some other factor present
at the bottom as well. More ecological studies of these patterns are
A further experiment with artificial plastic kelps showed the same
pattern of distribution suggesting Nereocystis was important
only as the substratum. The lack of Antithamnion
on the lowest part of the stipe was hypothesized to be due to snail
grazing, as Antithamnion is abundant on rocks on the benthos.
 It is an interesting pattern to see Antithamnion
reproductive on the middle portion of the stipe surrounded
on either side by vegetative Antithamnion.
Where I found Antithamnion:
I found Antithamnion defectum on horizontal rock surfaces
at 30 feet (9 meters) while diving on the Western side of the Breakwater
in Monterey Bay, as well as on the Monterey Bay aquarium water-intake
pipe at 45 feet (13.7 meters). At Breakwater, Antithamnion was sharing
the rock with crustose coralline algae, Pugetia fragilissima,
juvenile Mazzaella flaccida (previously Iridaea flaccida),
Fauchea laciniata, and Polysiphonia sp. On the aquarium
intake pipe Antithamnion was growing among many other tiny red algae
such as Polysiphonia, Callithamnion, Pterothamnion, and Microcladia.
The water temperature at both sites was 55 degrees Fahrenheit (12.8
degrees Celsius), which is the warmer end of the range of temperatures
for central California.
I found A. dendroidem growing on a buoy line
on the edge of the Hopkins Marine Life Refuge, on the aquarium sea-water
intake pipe, on a floating boat launch dock at the Monterey harbor,
on a Macrocystis pyrifera pneumatocyst (float) which had
drifted onto Carmel Beach, on the stipe of Nereocystis leutkeana
which had washed ashore on South Asilomar beach, and even growing
in the outdoor laboratory bins at the marine station!
To see more pictures, including underwater shots of Antithamnion,
please go to the Photo Gallery page.
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Is Antithamnion intertidal?
Based on where I found Antithamnion and where
it was found in the past, I hypothesize that it is unlikely to be
found in the intertidal. This may be due to its delicate and fragile
structure which could easily be damaged if rubbed against rocks by
crashing waves. The fact that it is found on rocks deeper in the water
where wave action is minimized and within the protected area of the
wharf further supports this hypothesis. In addition, the thin single
celled structure of Antithamnion
would probably desiccate more quickly than a thicker algae, which is
why I never found it in a place where it could fall below the tidal
line. However, the fact that Antithamnion is found on Nereocystis
stipes which are usually in areas with high wave action indicates that
it probably can withstand significant water motion. Its ability to
flatten down against the stipe probably reduces most of the drag.
Is Antithamnion an invasive species?
I believe that Antithamnion could be classified as having
a fast growth rate and perhaps even an opportunistic life-style. Adult
Antithamnion are present in the Hopkins tanks within two months
of running sea water through the tank. Furthermore, the Japanese A.
pectinatum is now officially an invasive species in the Venice
harbor in Italy, and it has competed well for space with indigenous
species.  Antithamnion's
ability to live on almost any substratum, survive year-round, grow
quickly, and live all over the world makes it a great competitor.
Benefits to the Kelp Forest Community?
Although Antithamnion may be a great competitor and even
invasive in some parts of the world, it also may provide a benefit
to the community in which it lives. A recent study found that gametophytes
of the kelps
Nereocystis luetkeana and Alaria esculenta became
epiphytic on several algae, including Antithamnion
defectum.  In this way, A.
defectum harbors a microscopic life-stage of these kelps,
indirectly contributing to the recruitment of the large sporophytes
characteristic of kelp forest communities.
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© 2005 Charlotte Stevenson