Disclaimer:

The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

---

Common name: tropical seagrass

Synonyms and Other Names: Barkania stipulacea, Thalassia stipulacea, Zostera stipulacea

Red Sea seagrass

Identification: From (den Hartog 1970, Ruiz and Ballantine 2004, Willette and Ambrose 2009, and Kuo 2020):

Habit: submerged, marine perennial with underground rhizomes.

Roots: singular at each node along the rhizome

Stems: up to 2 mm in diameter, internodes up to 2 cm, and two scales per node, each up to 16 mm long by 6 mm wide

Leaves: glabrous (hairless), branched in pairs at nodes with petioles (leaf stalks), linear to oblong in shape, up to 60 mm long by 9 mm wide with serrated margins. Cross veins along a very pronounced midvein extend to the intramarginal nerve

Flowers: unisexual with separated sexualities on plants (dioecious). Only male flowers are currently known in the Caribbean Sea (Winters et al. 2020)

Fruits/seeds: capsules with up to 30 seeds

Look-alikes: Halophila baillonis, H. decipiens, H. engelmannii, and H. ovalis (non-native) are four Halophila species that share the Caribbean Sea, with H. ovalis being the other non-native seagrass. Halophila baillonis and H. engelmannii have four or more leaves arranged in whorls at the end of the stem (leaf petioles are very short), H. decipiens has trichomes (hair) on the leaves and cross veins that are less dense than leaves on H. stipulacea, and H. ovalis, at least the clonal introduction in the intracoastal waters of Florida, has narrower and shorter leaves than H. stipulacea, with entire (non-serrated) leaf margins (Wunderlin and Hansen 2011).

Native Range: Red Sea, Persian Gulf, and the Indian Ocean (den Hartog 1970)

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Growth occurs at a rate of up to 6.7 cm per day at depths up to 32 m between 21-28°C (Winters et al. 2020). Stem densities reached 600/m² in five years since establishment in four bays of St. John Island, U.S. Virgin Islands (Willette et al. 2020). Growth occurs in summer months in the Northern Hemisphere, with flowering in July, and plants with both male and female flowers preferring shallow depths (Beca-Carretero et al. 2020). A common garden experiment indicated that H. stipulacea plants from the Caribbean (St. Eustatius) had higher growth rates in shoot and leaf formation and rhizome elongation that did H. stipulacea plants from its native range in the Red Sea (Winters et al. 2023).

Halophila stipulacea responds to cold temperatures by reducing leaf area and increasing below-ground biomass (Nguyen et al. 2020a). Halophila stipulacea has a unique mechanism for adapting to solar irradiance by chloroplast clumping during peak sunlight, which makes more translucent leaves than in mornings and nights (Drew 1979).

Only male plants have been reported in the Caribbean Sea (Winters et al. 2020). Reproduction is assumed entirely clonal in the western Atlantic region through rhizome growth and fragmentation.

Beds of H. stipulacea were observed to remain to intact after multiple hurricanes near Culebra, Puerto Rico, while native seagrass beds containing Thalassia testudinum decreased post-storm and were replaced with H. stipulacea by up to 45% cover in one location where absent prior to storms (Hernández-Delgado et al. 2020, Sánchez-González et al. 2025). Grazing by sea turtles may be the mechanism for competitive advantage over native sea grasses. Christianen et al. (2019) found a preference for native seagrass, Thalassia testudinum, over H. stipulacea, which allows for rapid spread of H. stipulacea into disturbed beds. 

Means of Introduction: Fragments of H. stipulacea are created from removal of fish traps in the Caribbean, with more abundant and larger fragments associated with longer fishing periods (Willette and Ambrose 2012). Fragments are also created from vessels, which is likely the vector for introduction into the Caribbean Sea (Ruiz and Ballantine 2004). Stem fragments as small as 2 cm remained viable for up to four days (Willette et al. 2020). Secondary spread could also be occurring through regional storms and currents.

Status: Established in the U.S. Virgin Islands, Puerto Rico, and the southeast coast of Florida.

Impact of Introduction:

Summary of species impacts derived from literature review. Click on an icon to find out more...

Ecological

Fitness: Native seagrass (Thalassia testudinum) abundance was decreased through competition with Halophila stipulacea over a four year period in Lac Bay (Smulders et al. 2017). Studies in the Mediterranean Sea found similar impacts from H. stipulacea on native seagrasses (Sghaier et al. 2014, Winters et al. 2025).

Food web: Carnivorous nocturnal fishes (Lutjanus synagris and Haemulon flavolineatum) were more abundant in H. stipulacea beds than in native seagrass beds in waters near St. Thomas, USVI (Olinger et al. 2017). Again, similar food web impacts were found in the Mediterranean Sea on omnivorous vertebrates (Di Genio et al. 2021, Palmer et al. 2021).

Habitat alteration: Amphipods and crustaceans on H. stipulacea transplants were more abundant than on native Syringodium filiforme in Prince Rupert Bay, and H. stipulacea beds supported larger fish (Willette and Ambrose 2012). Habitat alteration impacts were likewise shown in the Mediterranean Sea (Di Martino et al. 2006, Conte et al. 2021). Halophila stipulacea was shown to rapidly spread into disturbed native seagrass beds in Bonaire after selective grazing on native seagrass, Thalassia testudinum, by sea turtles, Chelonia mydas (Christianen et al. 2019).

Nutrients: Organic Carbon stocks were stored at higher rates in H. stipulacea beds than native Cymodocea nodosa and Posidonia oceanica beds in the Mediterranean (Apostolaki et al. 2019, Wesselmann et al. 2021). However, this pattern was not attributed to H. stipulacea in the Caribbean (Vaughn et al. 2024).

Remarks: Biomedical applications of Halophila stipulacea have been researched (Kandemir-Cavas et al. 2019, Bel Mabrouk et al. 2020, Sansone et al. 2021, Chebaro et al. 2024).

References: (click for full references)

Apostolaki, E.T., S. Vizzini, V. Santinelli, H. Kaberi, C. Andolina, and E. Papathanassiou. 2019. Exotic Halophila stipulacea is an introduced carbon sink for the Eastern Mediterranean Sea. Scientific Reports 9:9643. https://doi.org/10.1038/s41598-019-45046-w.

Beca-Carretero, P., A. Rotini, A. Mejia, L. Migliore, S. Vizzini, and G. Winters. 2020. Halophila stipulacea descriptors in the native area (Red Sea): A baseline for future comparisons with native and non-native populations. Marine Environmental Research 153:104828. https://doi.org/10.1016/j.marenvres.2019.104828.

Bel Mabrouk, S., M. Reis, M.L. Sousa, T. Ribeiro, J.R. Almeida, S. Pereira, J. Antunes, F. Rosa, V. Vasconcelos, L. Achour, A. Kacem, and R. Urbatzka. 2020. The Marine Seagrass Halophila stipulacea as a Source of Bioactive Metabolites against Obesity and Biofouling. Marine Drugs 18(2):88. https://doi.org/10.3390/md18020088.

Bonanno, G., and S.A. Raccuia. 2018. Seagrass Halophila stipulacea: Capacity of accumulation and biomonitoring of trace elements. Science of the Total Environment 633:257-263. https://doi.org/10.1016/j.scitotenv.2018.03.196.

Campbell, J.E., A. Allen, D.C. Sattelberger, M.D. White, and J.W. Fourqurean. 2025. First record of the seagrass Halophila stipulacea (Forsskal) Ascherson in the waters of the continental United States (Key Biscayne, Florida). Aquatic Botany 196:103820. https://doi.org/10.1016/j.aquabot.2024.103820.

Cassell, J.S., E. Cruz-Rivera, S. Wyllie-Echeverria, and P. Jobsis. 2024. Variation in nutritional quality of an invasive seagrass does not explain its low palatability to two key herbivores in a Caribbean Bay. Aquatic Botany 190:103711. https://doi.org/10.1016/j.aquabot.2023.103711.

Chebaro, Z., J.E. Mesmar, A. Badran, A. Al-Sawalmih, M. Maresca, and E. Baydoun. 2024. Halophila stipulacea: A Comprehensive Review of Its Phytochemical Composition and Pharmacological Activities. Biomolecules 14(8):991. https://doi.org/10.3390/biom14080991.

Christianen, M.J.A., F.O.H. Smulders, M.S. Engel, M.I. Nava, S. Willis, A.O. Debrot, P.J. Palsbøll, J.A. Vonk, and L.E. Becking. 2019. Megaherbivores may impact expansion of invasive seagrass in the Caribbean. Journal of Ecology 107(1):45-57. https://doi.org/10.1111/1365-2745.13021.

Conte, C., A. Rotini, G. Winters, M.I. Vasquez, G. Piazza, D. Kletou, and L. Milgliore. 2021. Elective affinities or random choice within the seagrass holobiont? The case of the native Posidonia oceanica (L.) Delile and the exotic Halophila stipulacea (Forssk.) Asch. from the same site (Limassol, Cyprus). Aquatic Botany 174:103420. https://doi.org/10.1016/j.aquabot.2021.103420.

den Hartog, C., 1970. The sea-grasses of the world. North-Holland, Amsterdam.

Di Martino, V., M.C. Blundo, and G. Tita. 2006. The Mediterranean introduced seagrass Halophila stipulacea in eastern Sicily (Italy): temporal variations of the associated algal assemblage. Vie et Milieu/Life & Environment 56(3):223-230. https://hal.sorbonne-universite.fr/hal-03228754/document.

Di Martino, V., B. Stancanelli, and A. Molinari. 2007. Fish community associated with Halophila stipulacea meadow in the Mediterranean Sea. Cybium 31(4):451-458. https://doi.org/10.26028/cybium/2007-314-006.

Drew, E.A. 1979. Physiological aspects of primary production in seagrasses. Aquatic Botany 7:139-150. https://doi.org/10.1016/0304-3770(79)90018-4.

García-Escudero, C.A., C.S. Tsigenopoulos, V. Gerakaris, A. Tsakogiannis, and E.T. Apostolaki. 2022. ITS DNA Barcoding Reveals That Halophila stipulacea Still Remains the Only Non-Indigenous Seagrass of the Mediterranean Sea. Diversity 14(2):76.

Hernández-Delgado, E.A., C. Toledo-Hernández, C.P. Ruíz-Díaz, N. Gómez-Andújar, J.L. Medina-Muñiz, M.F. Canals-Silander, and S.E. Suleimán-Ramos. 2020. Hurricane Impacts and the Resilience of the Invasive Sea Vine, Halophila stipulacea: a Case Study from Puerto Rico. Estuaries and Coasts 43:1263-1283. https://doi.org/10.1007/s12237-019-00673-4.

Kandemir-Cavas, C., H. Pérez-Sanchez, N. Mert-Ozupek, and L. Cavas. 2019. In Silico Analysis of Bioactive Peptides in Invasive Sea Grass Halophila stipulacea. Cells 8(6):557. https://doi.org/10.3390/cells8060557.

Katsanevakis, S., I. Wallentinus, A. Zenetos, E. Leppäkoski, M.E. Çinar, B. Oztürk, M. Grabowski, D. Golani, and A.C. Cardoso. 2014. Impacts of invasive alien marine species on ecosystem services and biodiversity: a pan-European review. Aquatic Invasions 9(4):391-423. https://doi.org/10.3391/ai.2014.9.4.01.

Kolatkova, V., F.O.H. Smulders, E.A. Ward, and M. Vohnik. 2022. Range expansion of Marinomyxa marina, a phytomyxid parasite of the invasive seagrass Halophila stipulacea, to the Caribbean. Aquatic Botany 182:103554. https://doi.org/10.1016/j.aquabot.2022.103554.

Kuo, J. 2020. Taxonomy of the Genus Halophila Thouars (Hydocharitaceae): A Review. Plants 9(12):1732. https://doi.org/10.3390/plants9121732

Mejia, A.Y., A. Rotini, F. Lacasella, R. Bookman, M.C. Thaller, R. Shem-Tov, G. Winters, and L. Migliore. 2016. Assessing the ecological status of seagrasses using morphology, biochemical descriptors and microbial community analyses. A study in Halophila stipulacea (Forsk.) Aschers meadows in the northern Red Sea. Ecological Indicators 60:1150-1163. https://doi.org/10.1016/j.ecolind.2015.09.014.

Nguyen, H.M., I. Savva, P. Kleitou, D. Kletou, F.P. Lima, Y. Sapir, and G. Winters. 2020a. Seasonal dynamics of native and invasive Halophila stipulacea populations—A case study from the northern Gulf of Aqaba and the eastern Mediterranean Sea. Aquatic Botany 162:103205. https://doi.org/10.1016/j.aquabot.2020.103205.

Nguyen, H.M., N.S. Yadav, S. Barak, F.P. Lima, Y. Sapir, and G. Winters. 2020b. Responses of Invasive and Native Populations of the Seagrass Halophila stipulacea to Simulated Climate Change. Frontiers in Marine Science 6:812. https://doi.org/10.3389/fmars.2019.00812.

Olinger L.K., S.L. Heidmann, A.N. Durdall, C. Howe, T. Ramseyer, S.G. Thomas, D.N. Lasseigne, E.J. Brown, J.S. Cassell, M.M. Donihe, M.D. Duffing Romero, M.A. Duke, D. Green, P. Hillbrand, K.R. Wilson Grimes, R.S. Nemeth, T.B. Smith, and M. Brandt. 2017. Altered juvenile fish communities associated with invasive Halophila stipulacea seagrass habitats in the U.S. Virgin Islands. PLoS ONE 12(11):e0188386. https://doi.org/10.1371/journal.pone.0188386.

Palmer, J.L., D. Beton, B.A. Çiçek, S. Davey, E.M. Duncan, W.J. Fuller, B.J. Godley, J.C. Haywood, M.F. Hüseyinoglu, L.C.M. Omeyer, M.J. Schneider, R.T.E. Snape, and A.C. Broderick. 2021. Dietary analysis of two sympatric marine turtle species in the eastern Mediterranean. Marine Biology 168:94. https://doi.org/10.1007/s00227-021-03895-y.

Papenbrock, J. 2012. Highlights in Seagrasses’ Phylogeny, Physiology, and Metabolism: What Makes Them Special? International Scholary Research Notes 2012:103892. https://doi.org/10.5402/2012/103892.

Por, F.D. 1971. One Hundred Years of Suez Canal—A Century of Lessepsian Migration: Retrospect and Viewpoints. Systematic Biology 20(2):138-159. https://doi.org/10.2307/2412054.

Rindi, F., F. Maltagliati, F. Rossi, S. Acunto, and F. Cinelli. 1999. Algal flora associated with a Halophila stipulacea (Forsskål) Ascherson (Hydrocharitaceae, Helobiae) stand in the western Mediterranean. Oceanologica Acta 22(4):421-429. https://doi.org/10.1016/S0399-1784(00)88725-3.

Ruiz, H., and D.L. Ballantine. 2004. Occurrence of the seagrass Halophila stipulacea in the tropical West Atlantic. Bulletin of Marine Science 75(1):131-135. https://www.ingentaconnect.com/contentone/umrsmas/bullmar/2004/00000075/00000001/art00011.

Sánchez-González, J.L., C.P. Ruiz-Díaz, C. Toledo-Hernández, and A.M. Sabat. 2025. Effects of a Category One Hurricane on Caribbean Native and Invasive Seagrasses. Caribbean Journal of Science 55(1):65-80. https://doi.org/10.18475/cjos.v55i1.a8.

Sansone, C., C. Galasso, M.L. Martire, T.V. Fernández, L. Musco, A. Dell’Anno, A. Bruno, D.M. Noonan, A. Albini, C. Brunet. 2021. In Vitro Evaluation of Antioxidant Potential of the Invasive Seagrass Halophila stipulacea. Marine Drugs 19(1):37. https://doi.org/10.3390/md19010037.

Scheibling, R.E., D.G. Patriquin, and K. Filbee-Dexter. 2018. Distribution and abundance of the invasive seagrass Halophila stipulacea and associated benthic macrofauna in Carriacou, Grenadines, Eastern Caribbean. Aquatic Botany 144:1-8. https://doi.org/10.1016/j.aquabot.2017.10.003.

Sghaier, Y.R., R. Zakhama-Sraieb, and F. Charfi-Cheikhrouha. 2014. Effects of the invasive seagrass Halophila stipulacea on the native seagrass Cymodocea nodosa. Pages 167-171 in 5th Mediterranean Symposium on Marine Vegetation. Portorož, Slovenia, 27-28 October 2014.

Smulders, F.O.H., J.A. Vonk, M.S. Engel, and M.J.A. Christianen. 2017. Expansion and fragment settlement of the non-native seagrass Halophila stipulacea in a Caribbean bay. Marine Biology Research 13(9):967-974. https://doi.org/10.1080/17451000.2017.1333620.

Tsirintanis, K., E. Azzurro, F. Crocetta, M. Dimiza, C. Froglia, V. Gerovasileiou, J. Langeneck, G. Mancinelli, A. Rosso, N. Stern, M. Triantaphyllou, K. Tsiamis, X. Turon, M. Verlaque, A. Zenetos, and S. Katsanevakis. 2022. Bioinvasion impacts on biodiversity, ecosystem services, and human health in the Mediterranean Sea. Aquatic Invasions 17(3):308-352. https://doi.org/10.3391/ai.2022.17.3.01.

Vaughn, K.M., A. Durdall, D.A. Willette, M. Brandt, S. Costa, and K.W. Grimes. 2024. Sediment carbon storage in subtidal beds of the invasive seagrass Halophila stipulacea along an extreme water depth gradient, St. Thomas, U.S. Virgin Islands. Aquatic Botany 194:103778. https://doi.org/10.1016/j.aquabot.2024.103778.

Wesselmann, M., N.R. Geraldi, C.M. Duarte, J. Garcia-Orellana, R. Díaz-Rúa, A. Arias-Ortiz, I.E. Hendriks, E.T. Apostolaki, and N. Marbà. 2021. Seagrass (Halophila stipulacea) invasion enhances carbon sequestration in the Mediterranean Sea. Global Change Biology 27(11):2592-2607. https://doi.org/10.1111/gcb.15589.

Willette, D.A., and R.F. Ambrose. 2009. The distribution and expansion of the invasive seagrass Halophila stipulacea in Dominica, West Indies, with a preliminary report from St. Lucia. Aquatic Botany 91(3):137-142. https://doi.org/10.1016/j.aquabot.2009.04.001.

Willette, D.A., and R.F. Ambrose. 2012. Effects of the invasive seagrass Halophila stipulacea on the native seagrass, Syringodium filiforme, and associated fish and epibiota communities in the Eastern Caribbean. Aquatic Botany 103:74-82. https://doi.org/10.1016/j.aquabot.2012.06.007.

Willette, D.A., J. Chalifour, A.O.D. Debrot, M.S. Engel, J. Miller, H.A. Oxenford, F.T. Short, S.C.C. Steiner, F. Védie. 2014. Continued expansion of the trans-Atlantic invasive marine angiosperm Halophila stipulacea in the Eastern Caribbean. Aquatic Botany 112:98-102. https://doi.org/10.1016/j.aquabot.2013.10.001.

Willette, D.A., K.L. Chiquillo, C. Cross, P. Fong, T. Kelley, C.A. Toline, R. Zweng, and R. Muthukrishnan. 2020. Growth and recovery after small-scale disturbance of a rapidly-expanding invasive seagrass in St. John, U.S. Virgin Islands. Journal of Experimental Marine Biology and Ecology 523:151265. https://doi.org/10.1016/j.jembe.2019.151265.

Winters, G., S. Beer, D.A. Willette, I.G. Viana, K.L. Chiquillo, P. Beca-Carretero, B. Villamayor, T. Azcárate-García, R. Shem-Tov, B. Mwabvu, L. Migliore, A. Rotini, M.A. Oscar, J. Belmaker, I. Gamliel, A. Alexandre, A.H. Engelen, G. Procaccini, and G. Rilov. 2020. The Tropical Seagrass Halophila stipulacea: Reviewing What We Know From Its Native and Invasive Habitats, Alongside Identifying Knowledge Gaps. Frontiers in Marine Science 7:300. https://doi.org/10.3389/fmars.2020.00300.

Winters, G., C. Conte, P. Beca-Carretero, H.M. Nguyen, L. Migliore, M. Mulas, G. Rilov, T. Guy-Haim, M.J. González, I. Medina, D. Golomb, N. Baharier, M. Kaminer, and K. Kitson-Walters. 2023. Superior growth traits of invaded (Caribbean) versus native (Red sea) populations of the seagrass Halophila stipulacea. Biological Invasions 25:2325-2342. https://doi.org/10.1007/s10530-023-03045-z.

Winters, G., H.M. Nguyen, and M. Kaminer. 2025. Expansion of Halophila stipulacea in parallel with declines of native seagrasses in the eastern Mediterranean Sea. Aquatic Botany 196:103829. https://doi.org/10.1016/j.aquabot.2024.103829.

Wunderlin, R.P. and B.F. Hansen. 2011. Guide to the Vascular Plants of Florida. 3rd edition. University Press of Florida, Gainesville, FL.

Author: Pfingsten, I.A.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.