Enteromorpha flexuosa (Wulfen) J. Agardh
Family: Ulvaceae
Common names: Hollow Green Weed
Synonyms: Enteromorpha flexuosa subsp. flexuosa lexuosa ssp. flexuosa
Enteromorpha flexuosa image
Enteromorpha flexuosa  

Species Description: Enteromorpha flexuosa is a filamentous light green alga with worldwide distribution in shallow brackish or marine habitats (Mairh, Pandey and Tewari 1986, Littler and Littler 1989). The term 'enteromorpha' literally means 'intestine shaped' and is used to describe the hollow, tube-like filaments of this species.

E. flexuosa grows to 20 cm but generally tends to be smaller. It typically grows in clusters on mangrove roots, rocks, wood or as an epiphyte on other plants. It is found at depths ranging from the high intertidal zone to approximately 5 m. below the surface. Species of this weedy genus are often the first to colonize open substrata (Beach et al. 1995).

The ecological success of E. flexuosa and other pioneering species is in part attributed to the readily available pool of motile unicells that are able to rapidly colonize new areas. The chance for successful settlement of these cells is greatly enhanced because gametes and zoospores of this species remain viable for 10 or more days due to their ability to photosynthesize, often achieving photosynthetic rates approaching those of the adult thalli (Beach et al. 1989).

Regional Occurrence: E. flexuosa is an excellent pioneer species and is highly cosmopolitan in shallow marine or brackish habitats.

IRL Distribution: E. flexuosa is found lagoon-wide. It is common in inlet areas and around spoil islands and grows in tufts on substrata such as mangrove roots, wood, rocks, etc., primarily at low tide level. It is often epiphytic on other algae and seagrasses. E. flexuosa is highly abundant during the summer months in Florida.

Age, Size, Lifespan: Mairh, Pandey and Tewari (1986) observed maximum growth and increase in the biomass of E. flexuosa when it was growing at or near the surface of the water. Significantly lower biomass was observed when E. flexuosa was grown at a depth of 40 cm. If left undisturbed and ungrazed by fish and invertebrates, E. flexuosa can grow to approximately 20 cm.

Abundance: Highly abundant, especially throughout the summer months in Florida.

Reproduction: Optimum reproduction temperature is under 30°C (Mairh, Pandey and Tewari 1986) in waters with a pH of approximately 8.2.

E. flexuosa is highly fecund (Beach et al. 1989), with propagule release via both mitotic spores and meiotic gametes occurring on a daily basis in the lower latitudes. Release of reproductive cells (spores and gametes) into the intertidal zone is driven by tidal and lunar rhythms (Smith 1947, Christie and Evans 1962, Beach et al. 1995). Spores and gametes of this species are photosynthetically competent upon release into the water column, with unicells remaining motile for up to 11 days. Both gametes and zoospores have higher cellular respiration rates when compared to parental tissues, presumably due to their motility. Additionally, the photosynthetic rate for gametes and zoospores of E. flexuosa and several other pioneering species is substantially higher than photosynthetic rates observed in the reproductive cells of later successional genera such as the kelps (Phaeophyta). Thus, motility coupled with photosynthetic ability increase the ecological success in settlement and recruitment of this species.

Temperature: Growth of this species in outdoor ponds in India (Mairh, Pandey and Tewari 1986) showed that E. flexuosa was able to sustain growth in water temperatures as high as 30°C. Favorable growth was maintained at temperatures ranging from 15.5 - 30°C.

At 33°C, bleaching of a few branches begins to occur, and above this temperature, adverse effects on growth increase as more and more branches become bleached.

Salinity: euryhaline

Trophic Mode: autotrophic

Competitors: E. flexuosa is an excellent pioneer species, able to colonize newly available substrata year-round (Emerson and Zedler 1978). Yet, it is not a good competitor with other successional species. Emerson and Zedler (1978), in an experimental study of recolonization of intertidal algae following disturbance, showed that E. flexuosa tends to be present in low density (as measured in % cover) throughout the year in undisturbed zones. Following disturbance to an area, the density of this species increases dramatically within 2-3 weeks. However, as other algae become established, the percent cover for this species declines. This observation suggests that E. flexuosa may be unable to maintain dominance in the presence of later successional species such as Ulva rigida, Lithrothrix aspergillum, and other perennial algae (Emerson and Zedler 1978).

Habitat: E. flexuosa is found to depths of 5 meters in shallow brackish areas, or marine habitats in close proximity to freshwater seeps (Littler and Litter 1989). It is also likely to be found in areas influenced by municipal or industrial discharge. Rosas and Ruiz (1989) showed that Enteromorpha species, as well as some Ulva species, develop abundantly in zones directly affected by pollution, even as the abundance of other genera decreases. In areas affected by pollutive discharge, E. flexuosa becomes a highly successful fouling organism.

Associated Species: E. flexuosa is often found in association with pioneering species such as Ulva sp. and other fouling organisms. These are often the first plants to colonize freshly disturbed areas, or open substrata.

Economic Importance: E. flexuosa has some commercial importance due to its antibacterial activity against Mycobacterium tuberculosis (Mairh, Pandey and Tewari 1986). This algal species has also been investigated for its potential value as a bioindicator of trace metal pollution in coastal waters (Sivalingam 1978).

Aguilar-Rosas L, Pacheco-Ruíz I. 1986. Variaciones estacionales de las algas verdes (Chlorophyta) de la costa Noroccidental de la Península de Baja California. Ciencias Marinas 12: 73-78.

Beach KS, Smith CM, Michael T, Shin HW. 1995. Photosynthesis in reproductive unicells of Ulva fasciata and Enteromorpha flexuosa: implications for ecological success. Mar Ecol Prog Ser 125: 229-237.

Christie AO, Evans LV. 1962. Periodicity in the liberation of gametes and zoospores of Enteromorpha intestinalis Link. Nature 193: 193-194.

Emerson SE, Zedler JB. 1978. Recolonization of intertidal algae: an experimental study. Mar Biol 44: 315-324.

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

Mairh OP, Pandey RS, Tewari A. 1986. Culture of Enteromorpha flexuosa (Wulf) Jag (Chlorophyceae) in outdoor pool. Indian J Mar Sci 15: 212-218. Washington,

Sivalingam PM. 1978. Biodeposited trace metals and mineral content studies of some tropical marine algae. Bot Mar 21: 327-330.

Smith GM. 1947. On reproduction of some Pacific coast species of Ulva. Am J Bot 34: 80-87.

Enteromorpha flexuosa image
Enteromorpha flexuosa  
Enteromorpha flexuosa image
Enteromorpha flexuosa