Sea anemones are captivating marine invertebrates, often mistaken for plants due to their vibrant, flower-like appearance. These animals are sessile, meaning they remain attached to a surface, and possess a cylindrical body topped by an oral disc surrounded by tentacles. While appearing passive, sea anemones are in fact predators with a distinct feeding strategy.
External Prey
Sea anemones are carnivorous animals that consume a diverse range of organisms. Their diet includes small fish, crustaceans such as shrimp and crabs, and zooplankton. Larger species can capture prey like jellyfish or starfish. They are opportunistic feeders, eating anything of suitable size within reach.
The specific diet of a sea anemone varies by species and habitat. Some consume land insects like ants and spiders that fall into the water, demonstrating adaptable habits. This adaptability allows them to thrive in various marine ecosystems, from intertidal zones to the deep sea.
Capturing Meals
Sea anemones capture food using tentacles equipped with specialized stinging cells called cnidocytes. Each cnidocyte contains a tiny, harpoon-like nematocyst. Stimulated by prey, these nematocysts rapidly fire, injecting paralyzing venom. This neurotoxin immobilizes or kills prey, facilitating consumption.
Once subdued, tentacles move the meal to the central mouth on the oral disc. The mouth leads to a sac-like gastrovascular cavity, serving as both stomach and circulatory system. Powerful digestive enzymes break down food, often disintegrating small animals within 15 minutes. Indigestible parts, like bones or shells, are expelled through the same mouth opening.
Internal Food Production
Many sea anemones supplement external prey capture with internal food production. This involves a mutualistic symbiotic relationship with single-celled photosynthetic algae, primarily zooxanthellae (genus Symbiodinium), residing within the anemone’s tissues, particularly in their tentacles and oral disc. These algae photosynthesize, converting sunlight into sugars and organic compounds. The anemone utilizes these products, such as glucose, glycerol, and amino acids, as a substantial energy and nutrient source.
In return for these vital nutrients, the anemone provides the algae with a protected environment, sunlight access, and compounds like carbon dioxide and nitrogenous waste needed for photosynthesis. This partnership is especially important for anemones in sunlit, nutrient-poor waters, providing a significant portion of their energy. While active predation occurs, this internal food production offers a consistent and often substantial nutritional supplement, highlighting the diverse ways sea anemones obtain sustenance.