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Gracilaria tikvahiae was introduced for commercial
relieve the overharvesting of the native G. parvispora. Containment
to mariculture sites have been fairly successful, but its opportunistic
nature makes it a potentially
successful invasive species.
Herbarium sheets of Gracilaria tikvahiae
showing morphological variations.
Thallus 12-15 cm tall, comprised of finely branched clumps,
irregularly branched, 1mm wide. Axes compressed or flattened,with short
laterals bering more slender than axes with spinous branchlets. Branching
mostly dichotomous, but can be highly irregular, with dichotomous below,
alternate above and dichotomous at apices. Apices tapered and pointed, often
unevenly forked with one side longer than the other. In the wild, the
plant can range from dark green to shades of red and brown.
The morphology of this alga is highly variable. Plants grown
commercially are often completely dichotomously branched with axes and
branches of nearly the same diameter throughout. Cultured plants are often
very dark green to nearly black.
Medullary cells irregular, 70-270
mm diam. Cortex is 2-3 cells thick;
surface cells round to angular, 5-13 mm
diam., densely pigmented. Tetrasporangia oval to spherical, 10-35
mm diam., 17-45
mm long, cruciately divided, scattered
in surface layers. Spermatangia in sori, scattered. Cystocarps
hemispherical, to 1mm diam., numerous; carposporangia spherical to oval,
15-40 mm diam.
Gracilaria tikvahiae is found intertidal, less that 1
meter, attached to limestone and basalt substrates. In the Caribbean and
Florida where it is very common, G. tikvahiae is found in protected
and high-energy intertidal habitats in estuaries and bays to 10 meters deep.
This plant may grow unattached or attached to rocks or coral rubble.
Hawai‘i: Near Oceanic Institute,
Mechanism of Introduction:
species was brought to the Hawaiian Islands from Florida in 1987 for
Worldwide: Nova Scotia, Western
Atlantic, Canada to Florida.
Gracilaria tikvahiae has a widespread distribution
throughout the world, and is often associated with eutrophic conditions. As
demonstrated by its temperate and tropical locations, it is able to tolerate
large environmental variations in levels of nitrogen, irradiance and
temperature. This red alga has also been found to have a high nutrient
uptake efficiency, making it a successful invasive in many types of marine
environments. Because of its hardiness and greater adaptability than the
Hawaiian endemic species, G. tikvahiae has the potential to be an invasive species on Hawaiian
Gracilaria tikvahiae was brought to the Hawaiian islands
in 1987 to relieve the dwindling availability of
G. coronopifolia and
G. parvispora, the two most popular edible species of the genus. This
species has a high growth rate under non-limiting irradiance and nutrient
conditions. It also has the ability to store large amounts of dissolved
nitrate and nitrite, enabling it to continue growth in conditions of
fluctuating nitrogen availability. Productivity of G. tikvahiae can
be as high as any terrestrial crop on earth and is being studied for its
viability as an agar weed.
Established populations of Gracilaria tikvahiae have
not been found in the wild in Hawai‘i, although occasional escapes have been
reported. This species has not reproduced sexually in mariculture but does
quickly reproduce vegetatively, and has demonstrated successful invasive
characteristics elsewhere. It’s success on intertidal areas with moderate
water motion makes it a potential competitor of the two already stressed
endemic species, G. coronopifolia and G. parvispora. With the
growing concern of eutrophic conditions developing along Hawaiian coastlines
due to coastline development and G. tikvahiae’s opportunistic nature,
this species needs to be carefully handled for mariculture and wild
populations should be reported and monitored.
Abbott, I.A., 1999. Marine Red Algae of the Hawaiian
Islands. Bishop Museum Press, Honolulu, Hawai‘i.
Doty, M.S. 1986. Experiments with Gracilaria in
Hawai‘i, 1983-1985. Hawai‘i Botanical Science Paper, no. 46, University of
Hawai‘i, Honolulu, Hawai‘i.
Littler, D.S. and Mark M., 2000. Caribbean Reef Plants.
OffShore Graphics, Washington, D.C.
Peckol, P., B. Demeo-Anderson, J. Rivers, I. Valiela, M.
Maldonnado, and J. Yates, 1994. Growth, nutrient uptake capacities and
tissue constituents of the macroalgae Cladophora vagabunda and
Gracilaria tikvahiae related to site-specific nitrogen loading rates.
Marine Biology 121:
Schneider, D.W, and R.B. Searles, 1991. Seaweeds of the
Southeastern United States. Duke University Press, London, England.
Marine Invasives in Hawai‘i:
The Indian River Lagoon Species Inventory: