Jellyfish are marine invertebrates, recognized by their bell-shaped bodies and trailing tentacles. They inhabit oceans globally, from surface to deep sea. Lacking a backbone, they are classified as cnidarians, a group that also includes corals and sea anemones.
How Jellyfish Capture Food
Jellyfish capture prey using specialized mechanisms. Their tentacles are armed with microscopic stinging cells, called cnidocytes, which contain harpoon-like nematocysts. When triggered, these nematocysts rapidly fire, injecting venom to immobilize or kill prey.
Jellyfish also use bell contractions to facilitate feeding. The rhythmic pulsations help them move through the water, bringing food items within reach of their tentacles. Once prey is subdued, oral arms, thicker than the tentacles, waft food towards the central mouth on the underside of their bell.
Jellyfish swallow prey whole, as they cannot chew. The mouth leads to a digestive cavity where food is broken down and nutrients absorbed. Undigested waste is expelled through the same opening, as jellyfish have a single orifice for both ingestion and egestion.
What Jellyfish Consume
Jellyfish are carnivorous predators with a diverse diet varying by species, size, and habitat. Their diet primarily consists of plankton, including zooplankton (e.g., small crustaceans) and phytoplankton.
Larger jellyfish consume a broader range of prey, including small fish, fish eggs, and larval stages of various marine animals. These predators use potent venom to subdue active food sources. Some species, like the lion’s mane jellyfish, also engage in cannibalism, preying on smaller jellyfish.
Food availability influences jellyfish growth and reproduction. When abundant, they rapidly increase in size and numbers, forming dense aggregations known as blooms. Certain species, like the moon jellyfish, are suspension feeders, collecting food particles that drift through the water rather than actively hunting.
Who Preys on Jellyfish
Despite stinging defenses, jellyfish are a food source for various marine animals. Sea turtles, especially leatherbacks, are notable predators, with jellyfish forming nearly their entire diet. These turtles have specialized throats lined with papillae, protecting them from stings and aiding efficient swallowing.
Various fish species also consume jellyfish, including the ocean sunfish (Mola mola). Other fish predators include chum salmon, sablefish, rockfish, herring, anchovies, grey triggerfish, whale sharks, and spadefish.
Marine birds, such as fulmars, penguins, and albatrosses, also eat jellyfish. Other marine organisms like crabs, whales (e.g., humpbacks), sea anemones, and nudibranchs also prey on jellyfish. Larger jellyfish species also prey on smaller ones.
Jellyfish’s Place in the Marine Food Web
Jellyfish hold a dynamic position in marine food webs, serving as both consumers and a food source. As voracious predators, they compete with fish for plankton and consume fish eggs and larvae. This competition and direct predation can negatively impact fish populations, especially during rapid increases in jellyfish populations, known as blooms.
The consumption of plankton by jellyfish can limit the energy transfer to higher trophic levels, as jellyfish biomass is not readily consumed by as many predators as fish. Studies indicate that jellyfish can shunt food energy toward bacteria.
Jellyfish also contribute to nutrient cycling by transporting elements like nitrogen and phosphorus as they drift through water layers. They can provide shelter and feeding opportunities for small fish and other organisms seeking refuge among their tentacles. This benefits juvenile fish by offering protection from larger predators and access to food scraps.