Drift Away

Photo credit: Saco River Estuary Project Team

Photo credit: Saco River Estuary Project Team

Imagine you’re walking along the banks of a river in Maine, listening to the twittering of birds and marveling at the beautiful view across the meadows of marsh grass to the sparkling water.  Something catches your eye.  It’s bright!  As you walk closer to investigate, it starts to take on a familiar shape, but… it can’t be…a lemon?  If you had been walking along on the Saco River Estuary in Maine last summer or fall, this could very well have happened.  A group of researchers from the University of New England released hundreds of lemons, oranges, and summer squashes, labeled with a number and a website, into the Saco River and then waited for their fruit to be found, and the calls to come in.

Why would anyone release hundreds of perfectly good fruits into a river? 

It might seem like a crazy thing to do, but of course there’s more to the story.  These researchers were conducting what is known as a drifter study.  In a drifter study, a floating object or drifter (usually not a fruit) is released into a moving body of water, such as a river or the ocean, and allowed to passively move as the currents or winds might dictate.  After a period of time, these drifters, are collected and the location at which they are found is documented.  Using this relatively simple strategy, researchers can learn about where water, and anything passively floating in that water, is moving. 

Tracks of drifters released by researchers in the Gulf of Maine from 1988 to 2014. (The black is the land - can you see Cape Cod?) Credit: James Manning, NOAA http://www.neracoos.org/drifters

Tracks of drifters released by researchers in the Gulf of Maine from 1988 to 2014. (The black is the land - can you see Cape Cod?) Credit: James Manning, NOAA http://www.neracoos.org/drifters

Drifter studies are far from uncommon, and far from a new technique.  As technology has advanced, so too have the drifters, including becoming equipped with real-time GPS to track their movement from release until recapture.  In the Gulf of Maine alone, oceanographers and marine biologists have released hundreds of drifters since the mid-1980s to study how ocean currents move.  Researchers have used this information to track oil spills, predict spread patterns of harmful algal blooms (such as red tides or green tides), estimate the dispersal of power plant or sewage plant effluent, test mathematical models of ocean currents, and understand the movement patterns of larval fish and lobsters.

So, what were the University of New England researchers trying to do with their fruit?

They were using the fruit to model the passive movement patterns of plant material floating in the estuary.  They are interested in one plant in particular, the common reed Phragmites australis subspecies australis.  Phragmites was introduced to the United States from Europe in the early 1800s and subsequently spread across the entire country.  In fact, today it is found in every one of the 48 contiguous states (Ironically, as the Phragmites population had exploded in the US, its populations in Europe are shrinking and it is the focus of conservation efforts).  Phragmites has continued to spread and outcompete native plant species in wetlands.  As Phragmites spreads, it not only displaces native species, but it also alters the structure and ecology of the wetland.  Many organisms, such as juvenile fish, depend on wetlands for survival.  The alteration of these habitats by Phragmites can have detrimental effects on these organisms.

Photo credit: Ruth Maclean, Gulf of Maine Research Institute, vitalsignsme.org

Photo credit: Ruth Maclean, Gulf of Maine Research Institute, vitalsignsme.org

The impacts of Phragmites extends beyond these impacts on other plants and fish.  Because it grows in dense and tall patches, it can alter the hydrology of wetlands, and when it dies pose a fire risk.  Given the dramatic effects of this plant, many people are concerned about controlling its growth and spread. 

How does Phragmites spread?  Like many other plants, the seeds are transported by wind or water.  However, Phragmites has a second strategy for spreading: by growth of underground stems or rhizomes.  These rhizomes are what allows Phragmites to develop such dense patches.  Along shorelines, where sediment erosion is occurring, these rhizomes can also become exposed, break free, and if they make landfall and rebury, produce a new plant (and a new stand).

Exposed rhizomes of Phragmites australis.  When exposed like this they are at risk of breaking away. Photo credit: Smithsonian Environmental Research Center

Exposed rhizomes of Phragmites australis.  When exposed like this they are at risk of breaking away. Photo credit: Smithsonian Environmental Research Center

Fruit was released from sites of large Phragmites stands.  Where the fruit made landfall provides information about where rhizome pieces of Phragmites might also make landfall and establish a new stand.  With this information, managers and researchers can focus control and monitoring efforts on high risk areas.

So, why fruit? It’s biodegradable!  A project aimed at restoration and preservation would have a hard time justifying releasing plastics into the very resource it’s meant to protect.

The next time you're walking along a river, estuary, or coast and you see a fruit, pick it up because you may have just found some important scientific data!  Projects like this one depend on citizens to report their discoveries.


References and Resources:

For more on drifter studies: Drifter research projects in the Gulf of Maine (and archive of data)

For more on the invasive reed Phragmites australis:

Phragmites biology and management in the Great Lakes

Phragmites and other invasive plants

For more on the Saco River Estuary:

University of New England Drifter study

Follow what's going on with the University of New England Saco River Estuary Project

Learn more about the Saco River Estuary Restoration Efforts