Invaders Under the Ice
Written by: Lindsay Yoder, Aquatics Program Coordinator
Curly leaf pond weed and its turion. Photo credit: haydenlakewid.com
As winter temperatures move in and lakes across the Lower Hudson Valley begin to freeze, it seems only natural to assume that life beneath the ice stalls. Frogs and turtles go into hibernation, insect activity slows down, and many aquatic plants die off from colder temperatures. Despite this, when the spring sun melts the ice and the lakes begin to warm, some of the first aquatic plants we see are New York’s most aggressive aquatic invasive species (AIS): curly-leaf pondweed (Potamogeton crispus) and Eurasian watermilfoil (Myriophyllum spicatum). So why is this? For the answer, we look to a physiological or behavioral process known as overwintering.
Overwintering can be simply summarized as the process through which an organism “waits out” or passes through tough winter conditions. For some organisms, this may mean entering a phase of diapause (or extended state of low metabolic activity), overwintering in larval or egg portions of a life cycle when the individual is more weather-tolerant or migrating to warmer climates during the harsher conditions of winter. Most invasive aquatic plants will slow vegetative growth when light or water supply is low, but these plants also exhibit other incredible adaptations and physiological and anatomical features to gain a competitive edge. Rhizomes are underground stems that persist through the winter and sprout new leaves once photosynthesis starts up again in the spring. Tubers are small, potato-like carbohydrate storage capsules that aid in growth in the spring. But turions, the primary overwintering method for curly-leaf pondweed, are one of the most successful methods for long-term growth. Turions are modified buds of the plant that form along the stem and at the ends of branches. Curly-leaf pondweed plants can produce hundreds of these buds every season, which drop off in mid-July and begin growing in their winter form, which requires less energy and persist under up to 2 feet of ice!
Eurasian watermilfoil also overwinters successfully in our area, but not through buds, tubers, or rhizomes, but through sheer tenacity! Robust adult plants are capable of surviving throughout winter and can also start new colonies through a process of fragmentation, when smaller pieces of a mature plant will fragment off in the fall and take root throughout the winter. This means that once the sun hits the water in the spring, they have a clear advantage over other plants whose growth has only just begun.
Many native aquatic plants do not overwinter, so these mechanisms give invaders a competitive edge that allows them to form the dense, thick infestations we’ve come to associate with widespread species like Eurasian watermilfoil and curly-leaf pondweed. Other invasives that are less common like hydrilla (Hydrilla verticillata) also have this ability, which makes prevention, early detection, and rapid response critical to maintaining the health of natives in our waterways.
Eurasian water milfoil. Photo credit: bugwood.org
