Watermeal (Wolffia spp.) represents the smallest flowering plant globally, appearing as minute, light green, free-floating specks that often resemble cornmeal. This aquatic plant typically thrives in still or slow-moving freshwater environments, such as ponds, lakes, and ditches, where it forms colonies on the water’s surface. It is a rootless plant, barely visible to the unaided eye, yet it can spread across calm water bodies.
Direct Consumers of Watermeal
Various aquatic animals consume watermeal. Fish species, particularly those introduced for vegetation management, include watermeal in their diets. Tilapia (Oreochromis niloticus) are effective biological controls, voraciously consuming watermeal, duckweed, and filamentous algae. However, these warm-water fish cannot survive temperatures below 55 degrees Fahrenheit, limiting their use to warmer climates or seasonal stocking.
Grass Carp (Ctenopharyngodon idella) also consume watermeal. While they eat watermeal and duckweed, grass carp often prefer other submerged aquatic plants, making them less effective for primary watermeal control in mixed plant environments. Koi, smaller relatives of grass carp, also consume watermeal and duckweed. Their size allows for efficient consumption, especially if stocked preventatively in spring.
Waterfowl feed on watermeal from the water’s surface. These birds can also inadvertently transport watermeal to new bodies of water, as the tiny plants cling to their feathers. Native panfish like bluegill and sunfish may inhabit watermeal-containing waters, but their consumption is generally incidental, and they are not primary control agents. Aquatic invertebrates, such as insect larvae or snails, might consume watermeal, but their impact is typically less significant than fish or waterfowl.
Ecological Role of Watermeal Consumption
Watermeal consumption plays an important role in aquatic ecosystems, contributing to their balance and health. As a primary producer, watermeal converts sunlight into energy through photosynthesis. When animals consume watermeal, this energy is transferred up the aquatic food web, supporting various trophic levels.
Watermeal consumers help regulate its populations. Unchecked growth can form dense mats covering the water surface, blocking sunlight to submerged plants and potentially depleting oxygen, which harms other aquatic life, including fish. Consumption by fish and waterfowl helps prevent such overgrowth, maintaining dissolved oxygen levels and light availability. A balanced presence of watermeal and its consumers contributes to a diverse and healthy aquatic environment, ensuring proper ecosystem functioning.
Factors Influencing Watermeal Consumption
Several environmental and biological factors influence watermeal consumption. Water quality and nutrient levels are significant. High nutrient levels, particularly nitrogen and phosphorus from agricultural runoff or animal waste, can accelerate watermeal’s growth. This rapid growth can outpace animal consumption efforts, making effective control more challenging. Poor water quality can also stress consumer populations, reducing their feeding efficiency.
Predators of watermeal consumers can also impact consumption rates. For instance, a large population of predatory fish like bass may reduce the numbers of fish like tilapia that consume watermeal, allowing watermeal populations to increase. Habitat suitability is another important factor; water temperature, depth, and absence of extreme pollution are crucial for consumer survival and effectiveness. If other preferred food sources are readily available, watermeal consumers may choose alternatives, reducing watermeal consumption. Grass carp, for example, often consume other aquatic plants before turning their attention to watermeal.