Ecological Significance of Chara
Chara (muskgrass) occupies a unique ecological position in freshwater lake systems. It is simultaneously a valuable ecological component of clear, nutrient-poor lakes — where it serves as a keystone organism for water quality, sediment stability, and biodiversity — and a nuisance organism in eutrophic ponds and enriched water bodies where its growth is excessive and its odor is objectionable. Understanding the ecological context of any chara population is essential before any management decision is made. The same genus may be a protected indicator of ecological health in one lake and a management target in another.
Chara as a Water Quality Indicator
Chara is widely recognized as one of the most reliable biological indicators of oligotrophic (low-nutrient, high-clarity) freshwater conditions. The presence of dense, healthy charophyte beds in a lake is strong evidence that: water clarity is good (Secchi depth typically >2 meters), total phosphorus is low (typically <15–25 μg/L), the lake has not been severely impacted by agricultural or urban nutrient inputs, and the water body is in relatively good ecological condition. Conversely, the disappearance of chara beds from a historically chara-dominated lake — often replaced by vascular plant species that tolerate higher nutrients, or by filamentous algae — is a classic early warning signal of eutrophication.
Ecological monitoring programs in Europe (particularly in the Netherlands, where charophyte restoration is a major ecological management goal) and the United States have used charophyte bed presence, coverage, and species composition as indicators of lake ecological status. The European Water Framework Directive explicitly includes aquatic macrophyte and charophyte assessment as criteria for ecological status classification of lakes.
Sediment Stabilization
Chara beds play a critical sediment stabilization function in lakes, particularly in shallow, wind-exposed lakes where resuspension of sediment by wave action is a significant water quality concern. Dense chara beds reduce current velocity near the sediment surface, dampen wave energy, and bind sediment particles with their rhizoid networks. This physical stabilization reduces turbidity, maintains water clarity, and prevents phosphorus-laden bottom sediment from being resuspended into the water column during wind events. In some shallow lake restoration projects, establishment of charophyte beds has been deliberately used as a strategy to reduce sediment resuspension and internal phosphorus loading — with documented improvements in water clarity and phosphorus concentration following charophyte colonization.
Waterfowl and Wildlife Support
Chara is a significant food source for many waterfowl species, particularly diving ducks and swans. The oögonia (egg-like female reproductive structures) are consumed by canvasbacks, redheads, ring-necked ducks, and other diving ducks. Swans (particularly tundra swans and mute swans) feed heavily on chara in some lake systems, and tundra swans staging on migration use charophyte-dominated lakes preferentially. The nutritional value of chara oögonia — high in protein and fat — supports waterfowl in pre-migration staging. Loss of charophyte beds from eutrophication has been linked to declines in diving duck populations in some regions of the upper Midwest and Great Lakes area, where historical charophyte beds have been lost to phosphorus enrichment.
Allelopathy and Algae Suppression
Chara is one of the few submerged organisms documented to produce allelopathic (growth-inhibiting) compounds that suppress phytoplankton and filamentous algae. Laboratory and field studies have shown that water containing chara can significantly inhibit algal growth compared to water without chara, and that removal of chara beds from lakes is sometimes associated with increases in phytoplankton and algal blooms. The mechanism involves the release of phenolic compounds and other allelochemicals from chara tissue into the surrounding water. This allelopathic function means that chara beds — when healthy — actively contribute to the low-turbidity, low-algae conditions associated with oligotrophic lakes. It is one reason why restoration of charophyte beds is considered a viable strategy in some shallow lake restoration programs.
Conditions That Lead to Nuisance Growth
While chara's ecological value is highest in clear, nutrient-poor lakes, some Chara species tolerate elevated nutrients and can reach nuisance densities in enriched, shallow water bodies. In these situations, dense chara mats create problems similar to other nuisance plants: obstruction of swimming and boating, oxygen dynamics effects at night when respiration consumes oxygen, and — most problematically from a user perspective — the strong garlic odor that decomposes chara produces when biomass dies. In small ornamental ponds and shallow, nutrient-enriched basins, nuisance chara management may be warranted. See chara control methods for management guidance.
References
- van den Berg, M.S. (1999). Charophyte colonization in shallow lakes. Freshwater Biology 42:487–499.
- Simons, J. & Nat, E. (1996). Past and present distribution of stoneworts in the Netherlands. Acta Botanica Neerlandica 45(3):307–320.
- Wium-Andersen, S., et al. (1982). Allelopathic effects on phytoplankton by substances isolated from aquatic macrophytes. Oikos 39(2):187–190.