Invasive aquatic plants can cause real harm in lakes and ponds. They can spread between water bodies via many different pathways – they’ve been known to hitch rides on boat trailers, for instance, and can also spread via floods, wind, or even gardening.
Aquatic vegetation can also stow away on more mobile organisms – either when plant fragments cling to fur or feathers (a form of locomotion that crayfish may also take advantage of), or when animals or birds eat their seeds.
As a team of researchers recently reported in the journal Freshwater Biology, aquatic plant seeds eaten by waterfowl fare differently depending on what type of plant they come from. The scientists fed mallard ducks and greylag geese seeds from four different aquatic plants, two of which are invasive in Europe (where the scientists are based).
The researchers found that the seeds of one of the invasive species were particularly successful in making the trip through the gut of the birds intact – they recovered more than a third of the Ludwigia grandiflora (or water primrose) seeds from the birds’ waste, but less than a tenth of each of the other types of seeds they fed to the birds.
The scientists also attempted to grow the seeds they retrieved – after all, if seeds can’t develop once they’ve gone through digestion, it doesn’t matter if birds spread them around. They found that “[f]or mallards, 9.14% of the tested seeds germinated successfully, compared to 24.18% for the greylag geese.” Some of those seeds were retained in the birds’ guts for 72 or even 96 hours before they were excreted, though the seeds of one plant species, the other invasive, Spartina densiflora (or cordgrass), only sprouted if they spent eight hours or less inside the birds.
Ducks and geese can travel much farther than plants can on their own over three or four days. “Ducks and geese evidently have the potential for long-distance transport of alien and native plant seeds,” the authors write, “with maximal dispersal distances of well over 1,000 km,” or 620 miles, about 20 miles farther than the drive from Chicago to Chattanooga, Tenn. That’s a long way for an aquatic plant to hitch a ride.