Aquatic plants are an essential part of freshwater and marine ecosystems, providing food and shelter for fish, insects, and other aquatic life. But what actually eats these water-dwelling plants? As primary producers in aquatic food chains, a wide variety of organisms consume aquatic plants to obtain energy and nutrients.
If you’re short on time, here’s a quick answer: Fish, aquatic invertebrates like snails and crustaceans, waterfowl, and even some mammals eat aquatic plants as all or part of their diet.
In this comprehensive guide, we will explore the diverse organisms that eat freshwater and marine plants, from tiny invertebrates to large fish and birds. We’ll cover which species eat aquatic plants, which plant parts they consume, how they adapted to this diet, and the role aquatic herbivory plays in balancing ecosystems.
Invertebrates
Snails
Snails are prolific consumers of aquatic vegetation. Their rasping mouthparts allow them to scrape algae off surfaces and chew holes in the leaves of rooted plants (Cronin et al., 2015). Common snail species found grazing on aquatic plants include mystery snails, ramshorn snails, and trumpet snails.
While snails play an important ecological role, an overabundance can quickly decimate plant life in ponds and aquariums.
Crayfish and Crabs
Crayfish and crabs use their claws and mouthparts to shred and consume various aquatic plants. In fact, research shows that invasive crayfish can reduce aquatic plant biomass by 60-100% by combining grazing with uprooting behavior (Jackson et al., 2017).
This destruction of vegetation by crayfish leads to serious habitat loss for other species. Crabs similarly rip up plants to access roots and tubers for food.
Insect Larvae
The larvae of certain aquatic insects are voracious eaters of plants. Dragonfly nymphs grasp plants with hooked mouthparts, while the larvae of caddisflies, midges, and non-biting midges scrape plant tissue (Cattaneo and Mousseau, 1995).
Mayfly nymphs employ comb-like mouthparts to filter small algae and plant matter for ingestion. Though all lakes and ponds contain some insect larvae, excessive numbers can rapidly defoliate areas.
| Invertebrate | Consumption Methods |
| Snails | Scraping using radula, chewing holes |
| Crayfish | Shredding with claws and mouthparts |
| Dragonfly nymphs | Grasping with hooked mouthparts |
As shown, invertebrates employ an impressive variety of techniques to feed on aquatic vegetation. Maintaining balance between plant eaters and vegetation is crucial for the health of freshwater habitats.
Fish
Tilapia
Tilapia are omnivorous freshwater fish that feed on aquatic plants, algae, phytoplankton, zooplankton, insects, crustaceans and other small fish. They use their protruding jaw and pointed teeth to nibble and tear off pieces of aquatic vegetation.
Tilapia’s plant-based diet consists mainly of algae and aquatic macrophytes like hornwort, water lettuce, duckweed and water hyacinth. Their ability to consume large quantities of plants makes them excellent at controlling aquatic vegetation.
Carp and Goldfish
Carp and goldfish munch on submerged vegetation and algae covering the bottom of freshwater habitats. Their inferior mouths allow them to uproot plants and feed on stems, leaves and roots. Typical plants targeted by carp and goldfish include duckweed, pondweed, water lilies, water milfoil, water hyacinth and stonewort.
Carp also stir up bottom sediment to expose nutritious tubers, rhizomes and algae. Their voracious plant consumption helps regulate excess vegetation.
Catfish
Many catfish are omnivores that will eat aquatic plants along with other prey. Species like Corydoras feed on algae coating rocks, logs and other surfaces. Armored catfish scrape algae off surfaces with their suckermouths and eat aquatic mosses and vegetation.
Larger catfish like blue catfish may incidentally ingest plants while targeting small fish and invertebrates. Channel catfish consume duckweed, watermilfoil, pondweed and other plants during summer months when their growth is most rapid.
Others
Various other fish make meals out of aquatic flora as juveniles or adults. Young koi and common carp depend heavily on plants like duckweed for food. Grass carp are vegetarian fish introduced for aquatic plant control that consume up to three times their body weight daily in plants.Phytoplankton-eating fish like menhaden inadvertently ingest microscopic algae and diatoms.
Aquarium fish like silver dollars, rosy barbs and rainbow sharks will snack on aquatic plants in home tanks.
Birds
Ducks and Geese
Ducks and geese are commonly found foraging on aquatic plants in ponds, lakes, and wetlands. Their wide, flat bills are perfectly adapted for feeding on leaves, stems, roots, and seeds of aquatic vegetation.
Some species such as mallards, wood ducks, and Canada geese are dabbling ducks that tip-up to reach underwater plants, while others like canvasbacks are diving ducks that can submerge completely to feed on plants.
Ducks and geese eat a varied diet of aquatic plants. Some favorites include:
- Duckweed
- Water lilies
- Cattails
- Coontail
- Wild celery
- Widgeongrass
Large flocks of ducks and geese can decimate stands of aquatic vegetation. Their grazing helps keep wetland plant populations in check. However, overgrazing by waterfowl can also damage ecosystems if populations become too high.
Responsible hunting helps manage duck and goose numbers at sustainable levels.
Swans
Majestic swans also consume aquatic vegetation as a major part of their diet. The largest swans like trumpeter swans and mute swans use their long necks to reach plants growing deep underwater. Smaller tundra swans feed more like dabbling ducks, tipping headfirst to grab plants near the surface.
Favored foods include:
- Pondweeds
- Algae
- Watermilfoil
- Wild rice
- Grasses
With their strong bills, swans will even dig through muddy substrates to extract nutritious roots and tubers. This disturbance can uproot invasive species and release nutrients back into the water. Overall, swan grazing provides important ecosystem benefits for maintaining diverse, healthy aquatic habitats.
Coots and Moorhens
Coots and moorhens are rails frequently seen swimming and foraging in freshwater wetlands. They use their dexterous toes to grasp stems and leaves of aquatic plants, which make up 80-90% of their diet. Favored foods include:
- Duckweed
- Algae
- Arrowhead
- Water lilies
- Cattails
- Reeds
Coots and moorhens will graze on lush stands of vegetation at the water’s edge, leaving telltale cut edges on the plants. Their feeding provides some control on rampant growth of invasive wetland plants like purple loosestrife.
Overall, coots and moorhens fill an important niche as consumers of aquatic vegetation in freshwater habitats.
Mammals
Beavers
Beavers are semi-aquatic rodents that depend heavily on aquatic plants for their diet. They have strong, orange front teeth that are ideal for gnawing through and consuming aquatic vegetation (Aquatic plants comprise up to 90% of a beaver’s diet).
Some of the common aquatic plants favored by beavers include cattails, water lilies, pondweeds, and water milfoils.
Beavers construct dams to create ponds which enable them easier access to their preferred food. By accessing the below-water stems, rhizomes, and tubers of plants, they can feed on them throughout winter when most above-ground vegetation dies back.
Conservationists value beaver wetlands since their feeding significantly increases biodiversity and provides habitat for other species.
Manatees
Manatees are large, fully aquatic marine mammals that spend nearly all their time in shallow, slow-moving rivers, estuaries, saltwater bays, canals, and coastal areas. Their diet consists almost solely of aquatic vegetation such as seagrasses and freshwater vegetation (Manatees consume over 10% of their body weight in vegetation daily).
Some aquatic plants frequently eaten by manatees include turtle grass, shoal grass, manatee grass, cordgrass, pickerelweed, lawn grass, and water hyacinths. The gentle sea cows graze on plants by using their thick bristled snout to rummage through bottoms and dislodge vegetation.
By consuming such large quantities of plants, manatees play a key role in aquatic ecosystems.
Muskrats and Voles
Muskrats and voles are small, semi-aquatic rodents that live in wetlands across North America. They depend heavily on aquatic plants like cattails, reeds, pond lilies, bulrushes, pondweeds, and sedges to construct homes and sustain themselves (Upwards of 95% of a muskrat’s diet can originate from aquatic vegetation).
Muskrats feed on the rhizomes, stems, leaves, flowers and fruits of aquatic plants and often store plants within their homes to eat during winter. Voles graze on grasses and sedges growing in wet meadows.
The adaptations of muskrats and voles, like water-resistant fur, enable them to thrive in aquatic plant-rich habitats. Their burrows, trails, and feeding significantly impact wetland ecosystems.
| Mammal | Key Aquatic Plants Eaten | Daily Plant Consumption |
|---|---|---|
| Beavers | Cattails, water lilies, pondweeds, water milfoils | Up to 90% of diet |
| Manatees | Seagrasses, turtle grass, cordgrass, water hyacinth | Over 10% of body weight |
| Muskrats & Voles | Cattails, bulrushes, pondweeds, sedges | Up to 95% of diet |
To learn more about mammals that consume aquatic vegetation, check out sites like US Fish & Wildlife Service and National Wildlife Federation.
Ecological Importance
Aquatic plants play a vital role in maintaining the health and biodiversity of aquatic ecosystems. Here are some of the key ecological functions performed by aquatic plants:
Habitat Provision
Aquatic plants provide food, shelter and breeding grounds for many species of fish, amphibians, invertebrates and waterfowl. Their roots, stems and leaves create structural complexity that offers refuge and nesting sites.
For example, underwater meadows of seagrass support over 1,000 associated species of plants and animals.
Nutrient Cycling
Through the process of photosynthesis, aquatic plants produce oxygen that fish and other organisms need to breathe. Plants also absorb nutrients like nitrogen and phosphorus, preventing algal blooms. When plants die and decompose, nutrients are released back into the water.
Sediment Stabilization
The roots of aquatic plants help bind and stabilize bottom sediments. This prevents shoreline erosion and turbidity that can smother fish eggs and other benthic organisms. It also limits sediment runoff that can pollute nearby land areas.
Water Purification
Aquatic plants improve water quality by absorbing heavy metals, excess nutrients, and chemical pollutants from runoff. This ecosystem service helps filter contaminants and maintain clean, clear water conditions.
Flood Protection
Wetland plants help mitigate flooding by absorbing excess water during storms or high rainfall. They also stabilize shorelines and river banks, reducing erosion from waves, currents and rising water levels.
Carbon Sequestration
Like terrestrial plants, aquatic plants take up carbon dioxide from the water and atmosphere. This carbon is incorporated into their tissues and ultimately buried in sediments when the plants die. This long-term carbon storage helps regulate greenhouse gases and climate change.
Conclusion
As we have seen, aquatic plants have no shortage of hungry eaters from all branches of life. While many organisms occasionally eat aquatic vegetation, specialized herbivores help control excessive plant growth and recycle nutrients through the ecosystem.
Understanding what eats aquatic plants, and the adaptations that allow them to thrive on this diet, gives insight into how lake, river, and ocean food webs function. It also shows the vital role these primary producers play in sustaining higher consumers, making aquatic ecosystems complex, interconnected, and always fascinating.
