Jellyfish, or sea jellies, are marine animals with bell-shaped bodies and trailing tentacles. Largely transparent and composed of about 95% water, they inhabit oceans worldwide, from surface waters to the deep sea. Despite their stinging cells, jellyfish are a food source for various marine animals, highlighting their role within the intricate marine food web.
Key Marine Predators
Among the most prominent consumers of jellyfish are sea turtles, particularly the Leatherback sea turtle. These large reptiles specialize in a diet of gelatinous prey, possessing unique adaptations like backward-pointing spines (papillae) lining their mouths and throats, which help them swallow slippery jellyfish whole and prevent escape. Their thick skin, particularly around their beaks, protects them from stinging cells. Leatherbacks are capable of consuming a significant portion of their body weight in jellyfish daily, with some reports suggesting up to 73%.
Large fish species also include jellyfish in their diets. The ocean sunfish, or Mola mola, feeds almost exclusively on jellyfish, consuming vast quantities to sustain its large size despite their low caloric content. Tuna and swordfish, fast-swimming pelagic predators, also eat jellyfish when available, gaining energy from this readily available prey. Some sharks, like whale sharks and tiger sharks, and certain seabirds such as fulmars, are opportunistic feeders that consume jellyfish.
Other Aquatic Eaters
Beyond larger, more well-known predators, a diverse array of other aquatic organisms also feed on jellyfish. Cannibalism is common among jellyfish, with some species preying on others. Adult comb jellies, a close relative, cannibalize their own larvae during periods of food scarcity, allowing adults to conserve energy and endure lean times.
Sea slugs, like nudibranchs, are also predators of jellyfish. Certain species, such as the blue dragon sea slug, consume jellyfish and can absorb and reuse their prey’s stinging cells (nematocysts) for their own defense. Crustaceans, such as arrow and hermit crabs, may also consume jellyfish, particularly those that are dying or readily available. Additionally, jellyfish larvae are vulnerable to predation by various zooplankton and small fish.
Jellyfish in the Ocean’s Food Web
Jellyfish occupy a significant position in the ocean’s food web, acting as both predators of plankton and fish larvae, and as prey for marine animals. Despite their gelatinous composition and stinging cells, they provide energy transfer to higher trophic levels within marine ecosystems. Predators help regulate jellyfish populations, which can sometimes experience rapid increases known as “blooms”.
The consumption of jellyfish by various species helps maintain balance within marine environments, preventing unchecked population growth that could disrupt the food web by consuming large amounts of zooplankton and fish eggs. Jellyfish also contribute to nutrient cycling as their bodies decompose, releasing nutrients back into the water. These interactions underscore that jellyfish are an important component of marine life, supporting various creatures.