This milfoil is the only non-native milfoil species in Wisconsin - seven native species are found here. It is easiest to identify when it is blooming or has fruits on it. Eurasian water-milfoil has slender stems encircled by feathery leaves in groups. The stems branch and commonly grow to lengths up to 10 feet. Eurasian water milfoil produces small, 4-parted flowers on a spike that sticks out of the water two to four inches. The flowers are either four-petaled or without petals. The fruit is a hard, capsule with four seeds. The plant stem is often reddish-brown. Look for 12-21 pairs of leaflets per leaf to help distinguish Eurasian water-milfoil from Northern water-milfoil, the most similar native milfoil. The native plant typically has 7-11 pairs of leaflets. Don't mistake the common plant called coontail for the milfoil, it does not have individual leaflets.
Effects of invasion:
This invader grows quickly in spring and forms a dense leaf canopy in the water that shades out native aquatic plants. Because it can spread rapidly by fragmentation, it can block out sunlight needed for native plants to grow. This can lead to areas where all the plants are just Eurasian water-milfoil, which is not a diverse habitat. This disrupts predator-prey relationships by keeping out larger fish, and takes away nutrient-rich native plants that waterfowl need. Eurasian water-milfoil may also lead to poor water quality and algae blooms in infested lakes.
Polymorpha (part of this alien's scientific name), means "many forms." Zebra mussels come in many colors. Most are white or cream-colored with jagged brown or black stripes. However, some individual mussels have been found that are all-white, all-black, or have stripes going the other direction. Zebra mussels are members of the phylum Mollusca (mol-US-ka), or mollusks. Mollusca comes from the Latin word, mollis, meaning soft. Slugs, snails, octopuses, clams, and oysters are all mollusks. Mussels are bivalve mollusks. Bivalves have two shells that are held together by a strong ligament.
How They Multiply: Male zebras release a cloud of sperm into the water. Female zebras release a cloud of eggs. A female zebra mussel can produce 30,000 to 1,000,000 eggs in one year!
Impact When zebra mussels feed on plankton, they remove incredible amounts of food from the water. They can filter about 1 quart of water each day. They leave the water clear, sometimes too clear. The zebras grow on top of the native mussels and smother them. With plankton removed from the water, more sunshine reaches the bottom. Plants living here grow rapidly. They also use zebra mussel droppings as fertilizer. Bottom-feeding fish feast on the waste produced by the zebra mussels. Their numbers increase. Zooplankton and small fish which feed on plankton have less to eat. Their numbers decrease. Larger fish which feed on the small fish decrease in number. The zebra mussels take food, space, and oxygen, causing the death of native mussels.