This week we will begin discussing one of the most prevalent and problematic aquatic invasive plant species in the State of North Carolina: Hydrilla verticillata. Many of you have undoubtedly run into this plant on Kerr Lake, Lake Gaston, Roanoke Rapids Lake or a number of other lakes throughout the State. For starters, let’s talk about how exactly Hydrilla got here and what makes it such a problem for our local water bodies.
Hydrilla was first discovered in the U.S. in the late 1950s and early 1960s in the state of Florida. By the early 1970s it had taken over every major water body in all drainage basins in the state. Today, Hydrilla continues to spread in Florida and currently covers over 100,000 acres of water in 43% of Florida’s public lakes. Hydrilla can now be found in all Southeastern States as far north as New York, and in many western states including California.
There are two “biotypes” of hydrilla in North America. Populations from Florida to South Carolina are typically “dioecious” female. Dioecious means that the plant has distinct male and female organisms. Most populations north of Lake Marion in South Carolina, including those found in Kerr Lake and Lake Gaston are monoecious, meaning they have both male and female reproductive structures on a single plant. We will talk more about monecious and dioecious hydrilla when we discuss management of these plants later on.
Hydrilla is troublesome in a water body for a number of reasons. For one, once hydrilla invades an aquatic ecosystem, it drives out all native aquatic plants that are beneficial to the aquatic ecosystem. Hydrilla’s competitive edge comes from a number of unique life strategies. Hydrilla can grow in less than 1% of sunlight, allowing it to grow up underneath other plants and to survive at greater depths (up to 20+ feet in Kerr and Gaston). It can grow in nearly any temperature and can even grow in water of near 50% the salt content of sea water. There are very few bodies of water in the world in which Hydrilla can’t establish.
Hydrilla also has excellent survival and dispersal strategies. Hydrilla spreads via fragmentation meaning that the plant breaks apart (either by natural breaking or disturbance from boat propellers) and produces entirely new plants. Hydrilla stems even as small as one inch can establish in new parts of a lake and become an entirely new plant. If that’s not bad enough, Hydrilla also produces special survival structures called tubers and turions. The turions break off the stems in the fall and can drift for long distances before sinking to start a new plant. The tubers grow on the plants roots and detach in the fall producing new plants. A single tuber can lead to the production of several hundred others in the course of one season! Recent research at North Carolina State University has shown that tubers can survive for up to seven years in the sediment before sprouting. The long survival time of the tubers creates the major challenge in getting rid of the plant.
Once sprouted, Hydrilla’s speed of growth is fast and furious. Hydrilla plants can double their biomass every two weeks during optimal growing conditions. Once Hydrilla reaches the surface, it will expand horizontally covering the entire water surface while rapidly producing new stem growth through branching. It also doesn’t help that when Hydrilla was introduced into the U.S., it came without any of it’s natural enemies like herbivorous fish and insects. The voracious nature of Hydrilla and tangled mats that it forms has a number of environmental, economic and cultural impacts. Next week we will discuss some of these impacts and what is at stake for the general public.
If you have questions please contact your Aquatic Extension Associate, Brett M. Hartis, at (919)-515-5648 or email at bmhartis@ncsu.edu.
