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| NAS - Nonindigenous Aquatic Species |
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Common Name: green alga, grass kelp
Synonyms and Other Names: Ulva intestinalis, Gut weed
Taxonomy: available through 
Identification: Thalli of this species of green alga are yellow green to vibrant or dark green and tubular, hollow, wrinkled, convolute, intestine-like, and crumpled looking. Individual cells are often relatively round or ovoid but sometimes may be rectangular or polygon-shaped. They are generally arranged randomly but in some cases can form disorganized rosettes. Plants may be branched or unbranched. Samples from the Portage River, Ohio are branched. Branching may be inversely related to salinity. Near the Detroit River in the Great Lakes drainage there have been two forms recorded, namely E. intestinalis f. maxima and E. intestinalis f. cylindracea (Taft 1964; Kapraun 1970; Catling and McKay 1980; Hadi et al. 1989; Blomster et al. 1998). In Ohio, E. intestinalis colonies grow up to 20 cm long. Cells are around 10–25 by 16–18 microns (Taft 1964).
Size: colonies to 20 cm long
Native Range: E. intestinalis is a relatively cosmopolitan species known to form blooms in a diverse range of habitats around the world (Cummins et al. 2004). Authors discussing its introduction to the Great Lakes drainage typically mention that it is considered native to the Atlantic coast of North America (Mills et al. 1993).
Nonindigenous Occurrences: E. intestinalis was first recorded in 1926 by a salt plant at Wolf Creek near Silver Springs, New York, which is part of the Lake Ontario drainage (Muenscher 1927). It was then reported in 1951 from the Portage River drainage, which is part of the Lake Erie drainage, near Elmore, Ohio in an upwelling spring (Taft 1964). Finally, it was recorded in 1979 near the Ojibwa Salt Mine by the Detroit River, which flows out of Lake St. Clair and into Lake Erie (Catling and McKay 1980).
Ecology: E. intestinalis has an enhanced ability to form blooms in eutrophic conditions. It exhibits rapid nutrient uptake, growth, and osmoregulation, particularly in conditions of reduced salinity and light. Optimal salinity for growth may be around 15–24‰ but varies greatly depending on the population. Although growth is typically positively related to salinity, many populations can survive and grow in freshwater conditions. In fact, the negative effects of low salinity can be offset by increased nutrient concentrations. In reality, E. intestinalis populations around the world consist of various ecotypes that are somewhat genetically different from each other, each specifically adapted to grow best in a different salinity regime. Most ecotypes, however, exhibit very broad salinity tolerance (Edwards et al. 1988; Martins et al. 1999; Kamer and Fong 2000; Kamer and Fong 2001; Cohen and Fong 2004; McAvoy and Klug 2005).
E. intestinalis occurs in many different habitat types and takes many different forms. It has been recorded in fresh to saline waters from ditches, pools, rockpools, canals, moorlands, and bedrock. It can grow epiphytically, epilithically, as unattached floating monostromatic sheets, detached floating ropes, attached mats of monostromatic tubes, and as proliferous bottle brush forms (Moss and Marsland 1976; Reed and Russell 1978; Vadas and Beal 1987; Hadi et al. 1989; Simons 1994; Blomster et al. 1998; Baeck et al. 2000; Blomster et al. 2002; Romano et al. 2003; Bjoerk et al. 2004).
E. intestinalis can exhibit two stages, the sexual gamete-producing gametophyte and the asexual zoospore-producing sporophyte. Gametes are biflagellate and zoospores are typically quadriflagellate. Sporophytes usually occur over a wider temperature and salinity range than gametophytes. The latter are generally not well adapted to low salinity values and extended periods of desiccation. Sporophytes are often also capable of reproducing over longer time periods than gametophytes (Pringle 1986; Cordi et al. 2001). Swarmers can survive for around 5–8 days in motile form. They disperse well as they are positively phototactic and thus can remain high in the water column, allowing them to be carried far away from parent populations (Hoffman and Camus 1989).
In Ohio, E. intestinalis has been recorded from shady regions of the Portage River with almost no flow in shallow bedrock pools where upwelling through limestone faults occurs (Taft 1964). On the other hand, at the Ojibwa salt mine near the Detroit River, forms of this species have occurred on rocks subject to wave action in an effluent stream and lagoon (Catling and McKay 1980). Finally, as previously mentioned, the population originally found near a salt plant at Wolf Creek, New York (Muenscher 1927) has decreased and may no longer even be present, probably due to decreased salinity (Marcus et al. 1984).
Means of Introduction: E. intestinalis was accidentally released into the Great Lakes drainage (Mills et al. 1993).
Status: Established where recorded. However, populations are greatly reduced or possibly no longer present in the Wolf Creek drainage due to decreased salinity (Marcus et al. 1984).
Impact of Introduction: A) Realized: Unknown.
B) Potential: E. intestinalis is responsible for algal blooms with various impacts around the world, sometimes in places where it may be native. In Australia, blooms can be associated with massive declines in seagrasses (Cummins et al. 2004). E. intestinalis typically forms green tides in the Baltic Sea in eutrophic conditions (Alstroem-Rapaport and Leskinen 2002), where it may be associated with food web alterations. In such conditions, grazing pressure often cannot control massive blooms (Lotze et al. 2000; Lotze and Worm 2002). In the Gulf of Maine, blooms of novel floating rope forms have colonized the substrate, causing anoxia with the potential to exert negative impacts on bivalve species (Vadas and Beal 1987).
E. intestinalis is also associated directly or in part with negative impacts on diversity or specific taxa in different regions. In some Indian coastal areas, filamentous forms of E. intestinalis are associated with lower faunal community diversity than more bushy algae (Yogamoorthi 1998). In European coastal waters, epiphytic benthic diatoms prefer growing on monosiphonous forms of E. prolifera to colonizing broad and flattened forms of E. intestinalis (Holt 1980). Some marine forms of E. intestinalis are more difficult to handle and ingest for grazers such as Littorina littorea than species with more frond structure (Watson and Norton 1985). Groups of epibionts amongst which E. intestinalis figures can exert increased drag on snails living in high flow conditions, causing them to invest more energy in foot muscles and less in growth (Wahl 1996). Finally, in conditions of N scarcity on the coast of southern California, E. intestinalis can out-compete Ulva expansa in estuaries and lagoons (Fong et al. 1996).
Remarks: Common name: Gut weed
References
Alstroem-Rapaport, C. and E. Leskinen. 2002. Development of microsatellite markers in the green algae Enteromorpha intestinalis (Chlorophyta). Molecular Ecology Notes 2(4):581-583.
Baeck, S., A. Lehvo, and J. Blomster. 2000. Mass occurrence of unattached Enteromorpha intestinalis on the Finnish Baltic Sea coast. Annales Botanici Fennici 37(3):155-161.
Bjoerk, M., L. Axelsson, and S. Beer. 2004. Why is Ulva intestinalis the only macroalga inhabiting isolated rockpools along the Swedish Atlantic coast? Marine Ecology Progress Series 284:109-116.
Blomster, J., C. A. Maggs, and M. J. Stanhope. 1998. Molecular and morphological analysis of Enteromorpha intestinalis and E. compressa (Chlorophyta) in the British Isles. Journal of Phycology 34:319-340.
Blomster, J., S. Back, D. P. Fewer, M. Kiirikki, A. Lehvo, C. A. Maggs, and M. J. Stanhope. 2002. Novel morphology in Enteromorpha (Ulvophyceae) forming green tides. American Journal of Botany 89(11):1756-1763.
Catling, P. M. and W. G. McKay. 1980. Halophytic plants in southern Ontario. Canadian Field Naturalist 94(3):248-258.
Cohen, R. A. and P. Fong. 2004. Physiological responses of a bloom-forming green macroalga to short-term change in salinity, nutrients, and light help explain its ecological success. Estuaries 27(2):209-216.
Cordi, B., J. Peloquin, D. N. Price, and M. H. Depledge. 2001. The influence of UV-B radiation on the reproductive cells of the intertidal macroalga, Enteromorpha intestinalis. Aquatic Toxicology (Amsterdam) 56(1):1-11.
Cummins, S. P., D. E. Roberts, and K. D. Zimmerman. 2004. Effects of the green macroalga Enteromorpha intestinalis on macrobenthic and seagrass assemblages in a shallow coastal estuary. Marine Ecology Progress Series 266:77-87.
Edwards, D. M., R. H. Reed, and W. D. P. Stewart. 1988. Osmoacclimation in Enteromorpha intestinalis: long-term effects of osmotic stress on organic solute accumulation. Marine Biology 98:467-476.
Fong, P., K. E. Boyer, J. S. Desmond, and J. B. Zedler. 1996. Salinity stress, nitrogen competition, and facilitation: what controls seasonal succession of two opportunistic green macroalgae? Journal of Experimental Marine Biology and Ecology 206(1-2):203-221.
Hadi, R., A. M. Hadi, K. M. Bahram, and A. A. S. Hassan. 1989. The new recorded species of Enteromorpha in Baghdad area, Iraq. Bulletin of the Iraq Natural History Museum 8(2):163-172.
Hoffmann, A. J. and P. Camus. 1989. Sinking rates and viability of spores from benthic algae in central Chile. Hoffman, A. J. and P. Camus. Journal of Experimental Marine Biology and Ecology 126:281-291.
Holt, G. Benthic diatoms on green algae in Norway and Faeroe Islands, Scotland, UK. Blyttia 38(1):9-18.
Kamer, K. and P. Fong. 2000. A fluctuating salinity regime mitigates the negative effects of reduced salinity on the estuarine maroalga, Enteromorpha intestinalis (L.) link. Journal of Experimental Marine Biology and Ecology 254(1):53-69.
Kamer, K. and P. Fong. 2001. Nitrogen enrichment ameliorates the negative effects of reduced salinity on the green macroalga Enteromorpha intestinalis. Marine Ecology Progress Series 218:87-93.
Kamer, K., P. Fong, R. Kennison, and K. Schiff. 2004. Nutrient limitation of the macroalgae Enteromorpha intestinalis collected along a resource gradient in a highly eutrophic estuary. Estuaries 27(2):201-208.
Kapraun, D. F. 1970. Field and cultural studies of Ulva and Enteromorpha in the vicinity of Port Aransas, Texas. Contributions in Marine Science 15:205-285.
Lotze, H. K., B. Worm, and U. Sommer. 2000. Propagule banks, herbivory and nutrient supply control population development and dominance patterns in macroalgal blooms. Oikos 89:46-58.
Lotze, H. K. and B. Worm. 2002. Complex interactions of climatic and ecological controls on macroalgal recruitment. Limnology and Oceanography 47(6):1734-1741.
Marcus, B. A., H. S. Forest, and B. Shero. 1984. Establishment of freshwater biota in an inland stream following reduction of salt input. Canadian Field Naturalist 98(2):198-208.
Martins, I., J. M. Oliveira, M. R. Flindt, and J. C. Marques. 1999. The effect of salinity on the growth rate of the macroalgae Enteromorpha intestinalis (Chlorophyta) in the Mondego estuary (west Portugal). Acta Oecologica 20(4):259-265.
McAvoy, K. M. and J. L. Klug. 2005. Positive and negative effects of riverine input on the estuarine green algae Ulva intestinalis (syn. Enteromorpha intestinalis) (Linnaeus). Hydrobiologia 545:1-9.
Mills, E. L., J. H. Leach, J. T. Carlton, and C. L. Secor. 1993. Exotic species in the Great Lakes: a history of biotic crises and anthropogenic introductions. Journal of Great Lakes Research 19(1):1-54.
Moss, B. and A. Marsland. 1976. Regeneration of Enteromorpha intestinalis. British Phycological Journal 11(4):309-313.
Muenscher, W. C. 1927. Spartina patens and other saline plants in the Genesee Valley of western New York. Rhodora 29:138-139.
Pringle, J. D. 1986. Swarmer release and distribution of life-cycle phases of Enteromorpha intestinalis Chlorophyta in relation to environmental factors. Journal of Experimental Marine Biology and Ecology 100(1-3):97-112.
Reed, R. H. and G. Russell. 1978. Salinity fluctuations and their influence on bottle brush morphogenesis in Enteromorpha intestinalis. British Phycological Journal 13(2):149-153.
Romano, C., J. Widdows, M. D. Brinsley, and F. J. Staff. 2003. Impact of Enteromorpha intestinalis mats on near-bed currents and sediment dynamics: flume studies. Marine Ecology Progress Series 256:63-74.
Simons, J. 1994. Field ecology of freshwater macroalgae in pools and ditches, with special attention to eutrophication. Netherlands Journal of Aquatic Ecology 28(1):25-33.
Taft, C. E. 1964. The occurrence of Monostroma and Enteromorpha in Ohio. Ohio Journal of Science 64:272-274.
Vadas, R. L. and B. Beal. 1987. Green algal ropes: a novel estuarine phenomenon in the Gulf of Maine. Estuaries 10(2):171-176.
Wahl, M. 1996. Fouled snails in flow: potential of epibionts on Littorina littorea to increase drag and reduce snail growth rates. Marine Ecology Progress Series 138(1-3):157-168.
Watson, D. C. and T. A. Norton. 1985. The physical characteristics of seaweed thalli as deterrents to littorine grazers. Botanica Marina 28(9):383-387.
Yogamoorthi, A. 1998. Ecological studies on phytal fauna associated with intertidal seaweeds from south east coast of India. Journal of Ecobiology 10(4):245-250.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 7/16/2007 Citation for this information:
Rebekah M. Kipp. 2009. Enteromorpha intestinalis. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1714> Revision Date: 7/16/2007
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