black jelly
Giant black jellyfish


Among the most popular exhibits at the Birch Aquarium are our jellies. The beauty and wonder of these animals is evident in the way they gracefully pulsate through the water. Jellies have a gelatinous consistency with no hard skeletal body parts, and their tissues are more than 95% water. They are delicate and easily damaged, so we designed special tanks with no sharp edges that might otherwise tear their soft bodies. The rounded tanks promote a circular water flow that prevents the animals from settling on the bottom or in corners. Specially designed plumbing also ensures a controlled water flow that helps protect the jellies from injury. Unique lighting lends a dramatic effect to our jelly exhibits. In Tank 8, containing moon jellies, an extra window admits light from the side along with conventional lighting from above. In both this tank and Tank 9, which contains sea nettles, narrow-beam spotlights illuminate the animals rather than the tanks, which are painted matte black. The overall effect is similar to that which would be seen in the open ocean.

Jelly Life

In the wild, jellies feed mainly on zooplankton, including other jellies, and small fishes encountered while drifting. At the aquarium, it is not practical to provide wild-caught zooplankton on a daily basis. Instead, our jellies are fed newly hatched brine shrimp larvae enriched with a nutritious supplement, along with frozen krill and other animals. Food is provided twice daily to keep our specimens healthy and strong. To maintain our exhibits we need to have jellies on hand year round. Uncertain availability and the desire to reduce collecting in the wild have led us to culture jellies on-site. The moon jellies now displayed have all been raised at the aquarium. We have also raised sea nettles and are currently working on propagating the purple-striped jelly and lion's mane jelly. Culturing jellies is very tedious work due to their complex life cycles. Moon jellies, for example, exist as separate sexes that release eggs and sperm. The fertilized eggs develop into larvae that eventually attach to the bottom and grow into polyps that resemble tiny sea anemones. As the polyps develop, they bud off minute, free-swimming juvenile jellies. We collect these barely visible juveniles, place them in a separate tank, and feed them high concentrations of enriched brine shrimp larvae until they have grown to a size suitable for display.

Giant Black Jellyfish

Named Chrysaora achlyos by scientists in 1997, the giant black jelly last appeared in large numbers along the San Diego shoreline in 1989. Then and now, its appearance (and disappearance) was sudden and mysterious. This species is easily recognized by its maroon to purplish-black bell,with tan flecks around the perimeter, and frilly, pink, trailing arms. Twenty-four thin tentacles hang from the margin of the bell. Individuals can reach a whopping 3 feet or more across and 25 feet in length!  Though little is known about this species, scientists hypothesize that it may be similar in habit to its close cousin, the purple-striped jelly (Chrysaora colorata), a few of which have been observed pulsing alongside Chrysaora. Like Chrysaora colorata, the giant black jelly probably dwells in calm waters offshore, but is occasionally transported inshore by changes in ocean circulation. With their limited swimming strength and delicate construction, these jellies are no match for pounding surf. Battered by waves, they break apart, the pieces eventually washing up on the beach. Feeling the sting Tentacles and parts of the body of the giant black jelly are armed with stingers, which aid in food capture and defense. Fragments of the animal, even on the beach, retain the ability to sting for quite a while. Every summer many swimmers feel the sting at area beaches. As one victim reported, "it's no picnic."

--Debbie Zmarzly Science Specialist