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Species Name: Gracilaria tikvahiae
Common Name: Graceful Red Weed
Synonymy: None

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Plantae Rhodophyta Rhodophyceae Gigartinales Gracilariaceae Gracilaria

    Species Description

    Gracilaria tikvahiae is a highly opportunistic species common in estuaries and bays, especially where nutrient loading leads to either seasonal or year-round eutrophication (Peckol and Rivers 1995a, 1995b). Its morphology is highly variable, with colors ranging from dark green to shades of red and brown; with outer branches that can be either somewhat flattened or cylindrical in shape (Littler and Littler 1989). It can be found in protected, quiescent bays, as well as in high energy coastline habitats. This species grows free or attached to rocks or other substrata, and can reach a height of 30 cm (Littler and Littler 1989). G. tikvahiae grows to depths of approximately 10 m, but is most common at depths less than 1m.


    Regional Occurrence

    Gracilaria tikvahiae occurs from cold temperate regions along the eastern Atlantic coast from Nova Scotia to warm subtropical regions around the east and west coasts of Florida and into the Caribbean.

    IRL Distribution

    Found lagoon-wide in the Indian River Lagoon


    Age, Size, Lifespan

    Gracilaria tikvahiae can grow vegetatively over an indefinite period of time and has been shown to have a high growth rate under non-limiting light and nutrient conditions (Hanisak 1981, LaPointe, Dawes and Tenore 1984, LaPointe and Duke 1984, Peckol and Rivers 1995a, 1995b). The productivity of this species can be as high as any terrestrial crop on earth. Consequently, it has become the focus of several studies into its commercial value, primarily as a producer of hydrocolloids such as agar and carrageenan (Silverthorne and Sorenson 1971, Dawes 1987, Hanisak 1987).


    Gracilaria tikvahiae is abundant throughout its range. It can be especially dominant in areas of high eutrophication.




    Can be propagated vegetatively over long periods of time.



    Optimum growth of G. tikvahiae occurs between 24°C - 30°C (Hanisak in Hwang, Williams and Brinkhuis 1987). It can survive, but does not grow at temperatures below 12°C (LaPointe and Ryther 1981).

    Temperature, more than light intensity, is the critical factor which affects the seasonal variation in the amounts of proteins, carbohydrates, and the R-Phycoerythrin:Chlorophyll a ratio (the ratio of red photopigments to the primary green photopigment) in Gracilaria tikvahiae. As long as nutrients are not limiting, protein and carbohydrate levels tend to show an inverse relationship to both temperature and light, decreasing as temperature and light increase.


    euryhaline. Gracilaria tikvahiae is highly plastic in its responses to changing salinity and temperature (Dawes 1994).

    Other Physical Tolerances

    As an opportunistic species, Gracilaria tikvahiae is better able to tolerate eutrophic conditions than some other algae. Under eutrophic conditions, it accumulates as dense unattached mats which may reach more than 0.5 m in thickness and account for greater than 90% of the standing algal biomass (Peckol and Rivers 1995). Aggregation of this kind often creates a highly reducing environment rich in ammonia and low in oxygen. Gracilaria tikvahiae tolerates hypoxia relatively well, and tends to reduce its level of cellular respiration in order to offset poor environmental conditions. (Peckol and Rivers 1995).

    Under laboratory conditions, net photosynthesis and growth of Gracilaria tikvahiae decreases when pH of the culture medium increases above 8.0


    Trophic Mode

    Gracilaria tikvahiae is an autotrophic species, capable of storing relatively large amounts of dissolved nitrite (NO2-), nitrate (NO3-), and amino acids as a nitrogen pool. This capacity suggests that growth in this species can be somewhat uncoupled from nutrient uptake. a concept which has several beneficial applications to the aquaculture industry, particularly if optimal growth can continue after all available nitrogen has been removed from the water (Hwang, Williams and Brinkhuis 1987).

    Light intensity and temperature mediate the uptake of nitrate and ammonium in macroalgae. LaPointe , Dawes and Tenore (1984) showed that light intensity is also the major factor which influences seasonal variation in the levels of Chlorophyll a, R-Phycoerythrin and % Nitrogen in Gracilaria tikvahiae tissues, with reduced light intensity causing increased levels of photopigments. Photosynthesis and growth rates for this species are maximized when light intensity is high and temperature is in the optimum range of 24 - 30°C. However, studies have suggested (LaPointe and Duke 1984) that in order to maximize growth, macroalgae have the ability to increase their photosynthetic capacity by optimizing pigment levels based on lighting conditions. In Gracilaria tikvahiae, acclimation to reduced light intensity results in an increase in both pigment levels and photosynthetic ability. Acclimation to light saturation results in decreased pigment levels and increased photosynthetic capacity.


    In a field experiment performed in a eutrophic embayment in Massachusetts (Peckol and Rivers 1995), G. tikvahiae had a growth rate up to 4 times faster in mixed-species plots under saturating light conditions than did Cladophora vagabunda, a primary competitor. However, under limiting lighting conditions, C. vagabunda showed a higher growth rate. These results suggest that distributional patterns of these species are influenced greatly by interspecific competition, with G. tikvahiae being a better competitor under optimum lighting conditions, and C. vagabunda being a better competitor under low-light conditions. Distribution patterns in the bay appear to confirm this finding: Gracilaria tikvahiae was restricted to shallower areas of the bay; and C. vagabunda was found in nearly monospecific stands at deeper levels.

    Gracilaria tikvahiae may have another competitive advantage as well. It has rapid growth and nitrogen uptake rates, with high nitrogen storage capacity in its tissues. Rivers and Peckol (1995) found that while C. vagabunda was capable of utilizing only dissolved CO2, Gracilaria tikvahiae was able to use several different forms of dissolved inorganic carbon (DIC), a nutrient not normally considered limiting to algae. Thus, the amount of DIC present could aid in indirectly controlling some important aspects of photosynthesis.


    Common in both high energy and low energy zones. It is often found in highly eutrophic areas where it forms thick, unattached mats that can comprise over 95% of the standing biomass (Peckol and Rivers 1995).


    Special Status


    Economic Importance

    Large-scale cultivation of Gracilaria tikvahiae for production of agar and other hydrocolloids is becoming more feasible with the advancement of land-based aquaculture systems (Huguenin 1976, Bird et al. 1981, Habig and Ryther 1983, DeBusk and Ryther 1984). Gracilaria tikvahiae is also under consideration as a potential energy-producing plant. When fermented, this plant is among one of the highest methane producers. Additionally, because it is highly opportunistic, G. tikvahiae has been shown useful as a tertiary treatment alternative for aquaculture and sewage effluent (Ryther 1979).


    Bird KT, Hanisak MD, Ryther J. 1981. Chemical quality and production of agars extracted from Gracilaria tikvahiae grown in different nitrogen enrichment conditions. Botan Mar 24: 441-444.

    Dawes CJ. 1987. The biology of commercially important tropical marine algae. In: Bird KT, Benson P (eds), Seaweed cultivation for renewable resources. Elsevier, Amsterdam: 155 - 190.

    Dawes CJ. 1994. Physiological differentiation of the red seaweed Gracilaria tikvahiae from a mangel estuary, exposed coast, and culture. Bull Mar Sci 54: 361-366.

    DeBusk TA, Ryther JH. 1984. Effects of seawater exchange, pH and carbon supply on the growth of Gracilaria tikvahiae (Rhodophyceae) in large-scale cultures. Botan Mar 27: 357-362.

    Habig C, Ryther JH. 1983. Methane production from the anaerobic digestion of some marine macrophytes. Resour Conserv 8: 271-279.

    Hanisak MD. 1981. Recycling the residues from anaerobic digesters as a nutrient source for seaweed growth. Botan Mar 24: 57-62.

    Hanisak MD. 1987. Cultivation of Gracilaria and other macroalgae in Florida for energy production. Developments in Aquaculture and Fisheries Science (Netherlands). pp. 191 - 218.

    Huguenin JE. 1976. An examination of problems and potentials for future large-scale intensive seaweed culture systems. Aquaculture 9: 313-342.

    Hwang SP, Williams SL, Brinkhuis BH. 1987. Changes in internal dissolved nitrogen pools as related to nitrate uptake and assimilation in Gracilaria tikvahiae McLachlan (Rhodophyta). Botan Mar 30: 11-20.

    Lapointe BE, Duke CS. 1984. Biochemical strategies for growth of Gracilaria tikvahiae (Rhodophyta) in relation to light intensity and nitrogen availability. J Phycol 20: 488-495.

    Lapointe BE, Tenore KR, Dawes CJ. 1984. Interactions between light and temperature on the physiological ecology of Gracilaria tikvahiae (Gigartinales: Rhodophyta). Mar Biol 80: 161-170.

    Lapointe BE, Ryther JH. 1978. Some aspects of the growth and yield of Gracilaria tikvahiae in culture. Aquaculture 15: 185 - 193.

    Littler DS, Littler MM, Bucher KE, Norris JN. 1989. Marine Plants of the Caribbean, a Field Guide from Florida to Brazil. Washington, DC: Smithsonian Institution Press.

    Peckol P, Rivers JS. 1995. Competitive interactions between the opportunistic macroalgae Cladophora vagabunda (Chlorophyta) and Gracilaria tikvahiae (Rhodophyta) under eutrophic conditions. J Phycol 31: 229-232.

    Peckol P, Rivers JS. 1995. Physiological responses of the opportunistic macroalgae Cladophora vagabunda (L.) van den Hoek and Gracilaria tikvahiae (McLachlan) to environmental disturbances associated with eutrophication. J Exper Mar Biol Ecol 190: 1-16.

    Rivers JS, Peckol P. 1995. Interactive effects of nitrogen and dissolved inorganic carbon on photosynthesis, growth, and ammonium uptake of the macroalgae Cladophora vagabunda and Gracilaria tikvahiae. Mar Biol 121: 747-753.

    Ryther JH. 1979. Treated sewage effluent as a nutrient source for marine polyculture. Seminar Proc Eng Assesment. US EPA. EPA 430/9-80-006.

    Silverthorne W, Sorensen PE. 1971. Marine algae as an economic resource. Mar Tech Soc Ann Conf 7: 523 - 33.

Report by: K. Hill, Smithsonian Marine Station
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Page last updated: July 25, 2001

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