Sea anemones are sessile marine invertebrates, often mistaken for plants due to their flower-like appearance. These animals belong to the phylum Cnidaria, making them relatives of jellyfish and corals. They typically attach themselves to hard surfaces like rocks, wharves, or coral reefs, though some species can burrow into soft sediment or even float freely. Their bodies are cylindrical, topped with an oral disc featuring a central mouth surrounded by tentacles.
Primary Food Sources
Sea anemones are carnivores that primarily consume other animals. Their diet depends on their size and prey availability in their habitat. Smaller anemones often feed on microscopic organisms like plankton, while larger species capture substantial prey. Common food items include small fish, crustaceans such as shrimp and crabs, and other small invertebrates. Some larger anemones consume bigger creatures like jellyfish or starfish.
How Sea Anemones Capture Food
Sea anemones employ their tentacles for food capture. These tentacles are equipped with specialized stinging cells called cnidocytes, which contain nematocysts. When triggered by physical contact or chemical cues, the nematocyst rapidly ejects a harpoon-like structure. This harpoon injects venom into the prey, paralyzing or killing it. The venom includes neurotoxins that immobilize the prey.
Once subdued, tentacles maneuver the captured meal towards the central mouth. After ingestion, food enters a sac-like gastrovascular cavity where digestion occurs. Indigestible parts are expelled through the mouth, as anemones possess a single opening for both food intake and waste elimination.
Beyond Captured Prey: Other Ways Anemones Feed
Beyond actively capturing prey, some sea anemones obtain nutrients through symbiotic relationships, notably with photosynthetic algae called zooxanthellae. These microscopic algae live within the anemone’s tissues and produce sugars, oxygen, and other organic compounds through photosynthesis. The anemone receives these nutrients, supplementing its diet, especially in shallow, sunlit waters. In return, the anemone provides the algae with carbon dioxide, inorganic nutrients, and a protected environment.
Deep-sea anemones, living without sunlight, have developed other feeding strategies. Some derive sustenance from chemosynthesis, where certain bacteria convert chemical compounds into organic matter. For example, Ostiactis pearseae, a deep-sea anemone near hydrothermal vents, hosts intracellular bacteria that use hydrogen sulfide to produce organic carbon. Additionally, some anemones absorb dissolved organic matter directly from seawater. They may also consume detritus, often called “marine snow,” which consists of dead organic material, fecal matter, and other particles that drift from the upper ocean layers.