Pet Jellyfish Facts: Upside Down Jellyfish (Cassiopeia Xamachana)
Upside-down jellyfish (Cassiopeia xamachana) are another member of the order Rhizostomae. The specific name, xamachana, means Jamaican, although its natural habitat is not exclusive to Jamaican waters. Populations exist throughout the Gulf of Mexico and the Caribbean, as well as along the Florida coast. They are also present in the middle of the world in the Pacific Ocean. Although not native to these waters, inverted jellyfish were introduced to the Hawaiian Islands during World War II, most likely from jellyfish polyps that attached themselves to the bellies of warships returning from the Philippines.
This species is prevalent in warm, shallow tropical waters, such as mangroves. They are often called mangrove jellyfish because they are frequently found in large aggregations in these swampy regions. Unlike many species of jellyfish, inverted jellyfish are entirely marine. None have been found in brackish or fresh waters.
These jellyfish spend their lives completely differently than most other jellyfish. Jellyfish typically spend much of their time floating freely on ocean currents. Upside down jellyfish swim freely until they reach about 2 cm. Then their bell inverts and they sink to the bottom of the ocean floor. From there, they will spend most of their adult life upside down on the muddy substrate with their tentacles pointing upwards to capture the ever-present zooplankton from the water columns.
Like blue jellies, upside down jellies have a symbiotic relationship with zooxanthellae. This is the same symbiosis that occurs with many species of jellyfish and corals. In addition to providing essential nutrients, these golden algae also produce oxygen to help support respiratory metabolic functions that jellyfish need to survive in low-oxygen environments. This is of particular importance for upside down jellyfish because they spend most of their lives nestled in a muddy substrate and must rely on their food to reach them. Due to their specialized feeding habits, upside-down jellies are usually found in nutrient-rich waters with high concentrations of decaying matter to support the zooplankton team within these swampy, saltwater environments.
Inverted jellyfish have flat, saucer-shaped bells. Their umbrellas are typically greenish gray or blue. They have a central depression or exumbrella on their hood. The ex-umbrella acts as a suction device to help them stay anchored to the ocean floor. Instead of a single mouth, they have 4 elaborately branched oral arms. These arms have a frilly, lace-like appearance, similar to many leafy green vegetables. They are often known as cabbage head jellyfish because of these appendages. This species is believed to be a filter feeder and also relies on some form of absorption of dissolved nutrients directly from the water to supplement its nutritional needs.
Upside down jellyfish do not directly inject their prey like most jellyfish do. Their nematocysts (stinging cells) are controlled by the cnidocil. This is the equivalent of a mechanically or chemically activated grenade launcher. The stinging cells released from the cnidocil produce a cnidoblast that will stun or paralyze nearby prey. The jellyfish then begin to ingest their prey with their main mouth openings. Once the prey is reduced to food fragments, these nutrient particles pass into secondary mouths for further digestion.
Jellyfish cnidoblasts also function as a self-defense mechanism. If abruptly disturbed, large groups of these jellyfish will launch upwards from the ocean floor and release their nematocysts. This massive release of venom into the water is usually enough to ward off potential predators. The toxic compound is generally inconsequential to humans. It can cause an itchy or tingling sensation on the skin or a rash in people more sensitive to the poison.
Upside down jellyfish can reach up to 14 inches in diameter in the wild. In captivity, a maximum growth potential of 8 inches is more realistic. Depending on their size in captivity, upside down jellyfish may be fed zooplankton or small invertebrates and fish. To allow your symbiotic algae to photosynthesize properly, a conductive lighting system to a marine reef tank is highly recommended. These jellyfish have a higher temperature tolerance than most scyphozoan jellyfish. Jellyfish or adult jellyfish can be found throughout the year. However, the optimum temperature for these adult jellyfish is between 75-78 F. This simulates the height of the adult season. Upside-down jellies typically strobilate during the summer or early fall. While most scyphozoans strobilize during the winter months.