Getting Ahead of the Spread: Meet Halophila stipulacea, Florida's New Invasive Seagrass

A new invasive seagrass is spreading in Florida waters, and scientists are asking people to help watch for it. Halophila stipulacea is a small tropical seagrass that was first found in Florida in 2024 in Biscayne Bay near Key Biscayne. Since then, it has continued to spread, and a recent sighting at a marina in Tequesta marked the first reported establishment of this species in the Indian River Lagoon.

While seagrasses are important parts of healthy coastal ecosystems, not all seagrasses belong here. H. stipulacea is considered an invasive species because it can spread quickly and compete with Florida’s native seagrasses.

**What Is Halophila stipulacea?**

Close-up underwater view of invasive Halophila stipulacea seagrass, showing dense growth of narrow, bright green leaves forming a thick mat. — *Halophila stipulacea*. Photo credit: FDEP Southeast District

Halophila stipulacea is a small seagrass native to the Red Sea, Persian Gulf, and Indian Ocean. It has narrow, oval-shaped leaves that grow in pairs along a creeping stem called a rhizome. The leaves are usually dark green and much smaller than many of Florida’s native seagrass species.

This species is especially successful because it can survive in many different conditions. It tolerates a wide range of salinities, temperatures, water depths, and light levels. It can reproduce through seeds, underground rhizomes, and broken plant fragments that drift to new locations and take root.

How Did It Get Here?

Scientists believe H. stipulacea spread beyond its native range through shipping and boating activities. After expanding into the Mediterranean Sea, it later spread throughout parts of the Caribbean. The first record in continental U.S. waters was documented in August 2024 at Crandon Marina in Biscayne Bay. Researchers found dense patches inside the marina and additional patches nearby outside the marina.

Because marinas receive boat traffic from many locations, they are often the first places where invasive marine species become established. Scientists now encourage monitoring around marinas, ports, and boat anchorages throughout Florida.

Why Is It a Concern?

Informational page from a Florida Fish and Wildlife Conservation Commission invasive plant advisory on Halophila stipulacea. The page describes physical characteristics of the invasive seagrass, including paired leaves, creeping rhizomes, and root structures. Images show the species growing on the seafloor in its native range and detailed diagrams of leaf, root, flower, fruit, and rhizome features used for identification. — FWC identification guide for *Halophila stipulacea* highlighting key features such as paired leaves, creeping rhizomes, roots, and overall growth form of this invasive seagrass species.

Like other invasive species, H. stipulacea can change the habitats where it becomes established.

This seagrass grows rapidly and can form thick mats that cover large areas of the seafloor. These dense mats may crowd out native seagrasses, including turtle grass (Thalassia testudinum), shoal grass (Halodule wrightii), and manatee grass (Syringodium filiforme).

Native seagrass beds provide important habitat for fish, crabs, shrimp, and other marine animals. Many species use these underwater meadows as nursery areas where young animals can grow and find shelter from predators. When invasive seagrasses replace native species, the quality of that habitat may change. Studies have shown that H. stipulacea may provide less suitable habitat for some juvenile marine life than native seagrass communities.

Scientists are also concerned because native seagrasses help stabilize sediments and improve water quality. Replacing native seagrass with invasive species could alter these important ecosystem functions.

A New Sighting in the Indian River Lagoon

Recently, Florida Department of Environmental Protection staff discovered H. stipulacea during a site inspection at a marina in Tequesta. This finding is important because it represents the first reported establishment of the species in the Indian River Lagoon.

The sighting also shows that the plant continues to move northward along Florida’s coast. Early detection is critical because invasive species are often easier to manage before they become widespread. Keeping track of new locations helps scientists understand how quickly the species is spreading and where management efforts may be needed.

What Should You Do If You Find It?

If you think you have found Halophila stipulacea, do not remove it, pull it up, or move it.

This plant can spread through fragments. Disturbing it may create floating pieces that drift away and start new populations elsewhere. Instead, take photos and report the sighting.

Informational poster from the Florida Fish and Wildlife Conservation Commission about the invasive seagrass Halophila stipulacea. The page explains that the species is native to the Red Sea, Persian Gulf, and Indian Ocean, was first reported in Florida in 2024, and can rapidly spread to form dense mats that displace native seagrasses. Photos show close-up leaves and a dense underwater patch. The poster also provides reporting information and prevention tips. — FWC invasive plant advisory summarizing the impacts, identification, prevention, and reporting guidance for *Halophila stipulacea*.

To report a sighting:

Email photos and the location to InvasivePlants@MyFWC.com
Call 850-617-9430

How Can Boaters and Anglers Help?

Everyone who uses Florida’s waterways can play a role in slowing the spread of invasive species.

Before moving between water bodies:

Clean boats, trailers, anchors, fishing gear, and motors.
Drain any water from equipment.
Allow equipment to dry completely when possible.
Avoid anchoring directly in seagrass beds.
Never dump aquarium plants or animals into natural waters.

Even small plant fragments can hitch a ride on equipment and start a new infestation somewhere else. Prevention is often the easiest and least expensive way to protect Florida’s waterways.

The Bottom Line

Florida’s native seagrasses support fisheries, protect shorelines, improve water quality, and provide habitat for countless marine species. The arrival of Halophila stipulacea presents a new challenge because this fast-growing invasive seagrass can spread quickly and compete with native underwater plants.

The recent discovery in the Indian River Lagoon highlights the importance of awareness and early reporting. By learning how to recognize this species and reporting any sightings, Florida residents, boaters, anglers, and waterfront users can help protect our coastal ecosystems.

Learn More

Halophila stipulacea: An invasive seagrass on the move – What’s Happening Around Florida

Aggressive seagrass species discovered in Biscayne Bay | FIU News – Florida International University

Campbell, J. E., Allen, A., Sattelberger, D. C., White, M. D., & Fourqurean, J. W. (2024). 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

Halophila stipulacea | FWC

tropical seagrass (Halophila stipulacea) – Species Profile

Winters, G., Beer, S., Willette, D. A., Viana, I. G., Chiquillo, K. L., Beca-Carretero, P., Villamayor, B., Azcárate-García, T., Shem-Tov, R., Mwabvu, B., Migliore, L., Rotini, A., Oscar, M. A., Belmaker, J., Gamliel, I., Alexandre, A., Engelen, A. H., Procaccini, G., & Rilov, G. (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. https://doi.org/10.3389/fmars.2020.00300

Acknowledgment: The foundation for this article was provided by research and draft materials prepared by UF/IFAS Extension intern Laila Cohen. Microsoft Copilot assisted with content development, organization, and editing. Scientific accuracy, revisions, and final approval of the article were completed by the author.