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Gracilaria salicornia is one of the most successful
invasive algae on reef flats. It appears competitively linked with the
native G. coronipfolia and G. parvispora, but its mat form
allows for a more robust growth rate, and it is hardier than the natives.
Gracilaria salicornia in Hawaiian Islands
Gracilaria salicornia on reef flat at
Thalli consist of solid, brittle, cylindrical to compressed
branches, 2 - 5 mm in diameter. Axes 3 - 18 cm long and 1.5 mm broad, with
branches usually irregularly arranged. Both axes and branches are regularly
or irregularly constricted or continuous, with both conditions occurring on
the same plant or neighboring plants. Plants often prostrate and
overlapping, with lateral branches running along substrate, spreading in
mats to 30 cm or broader, with rocks and pebbles between branches, or erect
with an inconspicuous discoid holdfast and occasional secondary attachments.
Gracilaria spp. are extremely variable in Hawaiian
waters. Although normally cylindrical, the branches are frequently found
flattened, and sometimes plants are compressed throughout.
Cortex 1-2 layered, cells 4-6 by 10-12
mm, basal hair cells common; medullary
cells relatively small (to other Gracilaria sp.) Tertrasporangia
scattered over surface, 16-20 by 40-45 mm.
Spermatangia in pits. Cystocarps globose, constricted at base, 1.4 - 1.8 mm
diameter, with few to many tubular nutritive cells; pericarp cells in
relatively straight anticlinal rows of oval to rounded cells.
Gracilaria salicornia is found in tidepools and on reef
flats, intertidal to subtidal 4 meters deep, attached to limestone and
basalt substrates. Intertidal plants are often without constrictions,
subtidal plants with constrictions.
Hawai‘i: O‘ahu, Hawai‘i Island.
Mechanism of Introduction: First
found in 1971 in Hilo Bay, Hawai‘i. Introduced to Kane‘ohe Bay and Waikiki
in the 1970’s.
Worldwide: Wide spread throughout
the warm Indian and Pacific Oceans.
Gracilaria salicornia is very successful in calm,
protected waters. It has spread over 5 kilometers from its point of
introduction on O‘ahu since it was introduced in 1978. This alien algae is
usually sterile in Hawaiian waters, but has been found to propagate sexually
as well as asexually. Its widespread dispersal is accomplished primarily
through fragmentation. Molecular fingerprinting shows a high degree of
genetic similarity within a community, supporting the idea that dispersal
occurs by cloning through the fragmentation process. This species is thought
to compete with the native reef algae, such as
G. coronopifolia, for
substrate on the reef flat. Compared to other Gracilaria species,
G. salicornia appears more flexible to light adjustments and seems to
have a higher growth rate. High abundance appears to be associated with
moderate water motion. This species successfully competes with other
macroalgae by forming large, intricate mats that cover the substrate and
inhibit settlement of other algae.
When other more desirable cultured Gracilaria species
or the wild G. coronopifolia are not available for consumption, G.
salicornia is used as a substitute. Its "crunchiness" is gaining favor,
and this species has been sold under the name "robusta" in O‘ahu.
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.
Larned, S.T., 1998. Nitrogen- versus phosphorus-limited
growth and sources of nutrients for coral reef macroalgae. Marine
Biology, 132: 409-421.
Magruder, W.H., and J.W. Hunt, 1979. Seaweeds of Hawai‘i.
Oriental Publ. Co., Honolulu, Hawai‘i.
Nishimura, N.J. 2001. Assessment of Genetic Variability
in the Invasive Red Alga, Gracilaria salicornia (C. Agardh) Dawson. Using
Multi-locus DNA Fingerprinting. Masters Thesis, University of Hawai‘i at
Manoa, Honolulu, Hawai‘i.
Rodgers, S.K, and E.F. Cox, 1999. Rate of spread of
introduced rhodophytes Kappaphycus alvarezii, Kappaphycus striatum, and
Gracilaria salicornia and their current distributions in Kane‘ohe Bay,
O’ahu, Hawai’i. Pacific Science 53: 232-241.
Ecological Success of Alien/Invasive Algae in Hawai‘i:
Marine Invasives in Hawai‘i: