Blue-green algae, scientifically known as cyanobacteria, are photosynthetic bacteria found in diverse aquatic environments, including lakes, rivers, and oceans. Though often called algae, these microscopic organisms are bacteria that perform photosynthesis. While cyanobacteria are a natural part of aquatic ecosystems, certain conditions can lead to their rapid proliferation, resulting in algal blooms. These blooms typically occur in warm, calm, and nutrient-rich waters, reducing water quality and posing environmental and health concerns.
Tiny Organisms at the Base of the Food Web
Microscopic organisms, particularly zooplankton, are primary consumers of blue-green algae within aquatic food webs, grazing on phytoplankton including cyanobacteria. Examples include rotifers, cladocerans (like Daphnia), and copepods. These tiny grazers primarily consume cyanobacteria through filter-feeding, drawing water through specialized structures.
While many zooplankton species can consume cyanobacteria, their preference varies; however, certain rotifers and ciliates actively feed on blooms. Some copepods possess gut bacteria that enable them to break down cyanobacterial toxins, allowing them to utilize them as food. Protozoa, such as ciliates and heterotrophic dinoflagellates, also graze on cyanobacteria, particularly during initial bloom development.
Fish and Other Aquatic Animals
Larger aquatic animals, including certain fish species, also consume blue-green algae, directly or indirectly. Filter-feeding fish, such as gizzard shad and silver carp, directly ingest cyanobacteria from the water column. Silver carp, for example, have dense, sponge-like gill rakers capable of straining microscopic particles as small as 4 microns, allowing them to efficiently consume phytoplankton, including cyanobacteria.
Other fish species indirectly consume cyanobacteria by preying on zooplankton that have grazed on them, transferring energy up the food web. Some aquatic invertebrates also consume blue-green algae. Certain filter-feeding bivalves remove cyanobacteria, and some insect larvae graze on them.
Ecological Balance and Bloom Control
The combined feeding activities of these diverse organisms maintain ecological balance within aquatic ecosystems. A healthy ecosystem typically has a robust community of grazers that regulate cyanobacteria populations. These natural consumers act as a biological control, preventing large, problematic algal blooms.
Biodiversity among these grazers enhances an ecosystem’s resilience against excessive cyanobacterial growth. Thriving, diverse grazer populations exert significant pressure on cyanobacteria, keeping their numbers in check. However, high nutrient levels or potent cyanotoxins can disrupt grazer populations, allowing blooms to intensify. This intricate web of consumption highlights how natural processes contribute to the health and stability of aquatic environments.