Jellyfish are marine invertebrates known for their bell-shaped bodies and trailing tentacles. These ancient creatures inhabit diverse ocean environments globally. Despite lacking a brain, heart, or lungs, jellyfish are effective predators with unique feeding strategies essential to marine ecosystems. Their diet and hunting methods are finely tuned to their environment and life stage, allowing them to thrive in various oceanic habitats.
What Jellyfish Consume
Jellyfish primarily consume plankton, including plant-like phytoplankton and animal-like zooplankton (e.g., copepods, krill, fish larvae). These abundant microscopic organisms form a foundational food source.
Beyond plankton, jellyfish also feed on small crustaceans, fish eggs, and larvae. Larger species can expand their diet to include small fish and even other, smaller jellyfish (cannibalism). This opportunistic strategy means they consume available prey, adapting their diet to the marine environment and seasonal food availability. Coastal jellyfish, for example, might access a broader range of prey than those in the open ocean, which rely more on plankton.
How Jellyfish Feed and Digest
Jellyfish are passive hunters, using tentacles to capture prey as they drift. Tentacles are equipped with stinging cells called cnidocytes, containing nematocysts. Upon contact, these nematocysts rapidly fire, releasing a barbed, venom-filled thread that paralyzes the organism. This process occurs quickly, often within a fraction of a second.
Once immobilized, the jellyfish uses oral arms to guide food to its single body opening, which functions as both mouth and anus. Food enters the gastrovascular cavity, a central digestive chamber. Enzymes break down prey here through extracellular digestion. Lining cells absorb nutrients, and undigested waste is expelled through the same opening.
Diverse Diets and Ecological Roles
Jellyfish diet varies significantly by species, size, and life stage. Smaller jellyfish might consume phytoplankton and microzooplankton, while larger ones tackle more substantial prey like shrimp or fish. Some species also engage in symbiotic relationships with microscopic algae called zooxanthellae. These algae live within the jellyfish’s tissues, producing sugars through photosynthesis that the jellyfish can utilize as a supplementary food source.
Jellyfish play a dual role in marine food webs, acting as both predators and prey. As predators, they control plankton, fish eggs, and larvae populations, influencing ecosystem dynamics. Conversely, jellyfish serve as a food source for various marine animals, including sea turtles, ocean sunfish, whales, and seabirds. Despite high water content, they provide valuable fatty acids and are an accessible food source for these predators, especially when abundant.