Fugitive species: a plant’s life on the run
Seabeach amaranth is a threatened species found along the Atlantic coast with unique survival mechanisms.
Seabeach amaranth (Amaranthus pumilus) is a native plant species found along Atlantic Coast barrier beaches, from South Carolina to Massachusetts. Decline in the northern part of its range caused by coastal development, sea level rise, increased recreation, and beach stabilization structures led to the plant being protected as threatened under the Endangered Species Act in 1993.
Dubbed a ‘fugitive plant’ due to its dispersal mechanisms, seabeach amaranth spreads its seeds at the whim of the winds and tides. Through its uniquely evolved life cycle, seabeach amaranth lives its life on the run.
Circle of life
As an annual plant, seabeach amaranth completes a full life cycle in the span of a few months. In April, the plant undergoes germination, growing from seed to sprig. In July, the clump of round, green leaves, reminiscent of spinach, grow low to the ground and start producing small, inconspicuous yellow flowers. In late July and August, it produces seeds.
And here is where it gets interesting.
The seeds can be dispersed while the plant is still alive, carried by wind or water in small, buoyant seed capsules to be planted by Mother Nature along the shoreline. Some seeds may also be carried by birds and dispersed over greater distances.
Other times, the seeds get buried along with the plant after it dies in the fall, covered by the movement of winter sands. These seeds have the chance to regrow in the same location as the parent plant. Biologists theorize that the seed capsules that don’t immediately germinate can survive long periods of time buried beneath the sand, creating natural seed banks that might someday grow if the conditions are right.
With these different dispersal mechanisms, the fugitive plant is increasing its chances for future success. It has the opportunity to perpetuate growth in its current location and colonize new beach habitat at the same time if conditions allow.
Room to Grow
Seabeach amaranth typically grows in low elevation overwash flats on barrier island beaches, where there is minimal competition from other plants. Overwash is habitat where waves have washed over dunes on the beach and deposited sand and sediment slightly further inland. Seabeach amaranth is most successful in a naturally functioning environment where seeds can be transported to new overwash habitat by erosion and littoral drift, movement of sand by the waves.
With a quickly changing climate and increasing sea levels, the magnitude and frequency of erosion will change, greatly impacting coastal wildlife and communities. Retaining natural levels of erosion, that species like seabeach amaranth requires, while also protecting the integrity of the coast presents a challenge. Installing manmade “hard” structures on the beach front, like sea walls or rip rap, may seem like a decent option to combat erosion, but these structures often disrupt normal coastal processes and diminish wildlife habitat.
An example of a more natural solution may be replanting beach grasses and vegetation along the shoreline, however these plants often outcompete species like seabeach amaranth and reduce the amount of available habitat for shorebirds.
How do we protect this plant and a functioning coastline when these solutions all seem to have flaws?
Early succession leads to success
Seabeach amaranth consistently populates new habitat each year. The plant thrives in early successional habitat, habitat that is not yet colonized by other vegetation. The plant can effectively trap sand with its roots and with its leaves, creating small, low elevation dunes in the places it grows.
As dunes develop and new plants, like beachgrass, start to grow or are planted in this habitat, seabeach amaranth is “on the run” again, sending out seeds and cropping up in other places along the shore. Protecting existing early successional habitat give the plants the area they need to colonize.
In cases where beach reconstruction and renourishment projects are occurring, the Service often recommends that environmental engineers create new early successional habitat. This type of design should promote the overwash and the natural formation of additional early successional habitat. This is done by creating dunes at lower elevations.
Creating this new habitat helps to mitigate for any harmful effects to wildlife from varying construction on the beach. This is beneficial for plants like seabeach amaranth and shorebirds. Seabeach amaranth is a good indicator of shorebird habitat because birds, like piping plovers, prefer to feed and breed in early successional habitat too!
Short term solutions
Beyond sea level rise, the primary threats to this plant are related to human activity. Off-road vehicle traffic, heavy recreational use, development, and other activities that cause habitat adjustments can all impact this plant.
Landowners can be instrumental in helping protect seabeach amaranth though! Some coastal landowners protect this sensitive plant by installing fencing and signage around plants during the growing season, providing a buffer from immediate danger.
As a fugitive species, seabeach amaranth will forever be on the run, but we want to make sure that it has healthy habitat available whenever it has opportunity to take root.
