Upside-down-jellyfish

Description

Cassiopea andromeda is a jellyfish that belongs to the class Scyphozoa and the order Rhizostomeae. This jellyfish is found in low velocity, warm waters in coastal regions around the world such as: mangrove swamps, mudflats, canals, and turtle grass flats in Florida (Welsh et al., 2009). It is known as the “upside-down jellyfish” because it lies on the ocean floor with its aboral surface against the sand and the oral surface upright, exposed to the water. In this orientation, the upside-down jellyfish doesn’t look like a typical jellyfish and instead looks a lot like a flower on the seafloor. These jellyfish lie upside-down because it exposes their zooxanthellae to the sun and allows them to perform photosynthesis (Santhanakrishnan et al., 2012). Often times, these intriguing animals appear a green or gray/blue color because of the densely packed zooxanthellae embedded in the mesoglea of the body. Interestingly enough, Cassiopea andromeda has a special blue mesogloeal protein that shields the jelly against damaging solar radiation (Jantzen et al., 2010). Predators of this species include: sea turtles, tuna, sunfish, butterfish, and spiny dogfish.

Anatomy

The average length of the upside-down jellyfish is about 12 inches and the body of the jellyfish is known as the bell because it is a saucer-shaped umbrella. It is relatively flat with a well-defined central depression that gives the jellyfish the ability to stick to the bottom of the ocean floor. The other portion of the jellyfish is known as the oral surface and it bears eight frilly arms. Along with this, the oral surface consists of the feeding apparatus that includes the manubrium (Santhanakrishnan et al., 2012). The manubrium is a short central column that emerges from the center of the oral surface of the bell. Upside-down jellyfish do not have central mouths and instead have hundreds of tiny mouth openings that reside on the frills of the oral arms. In addition to the mouths, there are numerous club-shaped vesicular appendages that open into brachial canals. The number, shape, and size of the appendages varies with sex and age. Also, many of these appendages provide surface area for the deployment of zooxanthellae in the sunlight. It has even been considered that these appendages may help the jellyfish camouflage in grass beds as well.

Invasive Species

Cassiopea andromeda is widely distributed in the tropics but is also acknowledged globally as an invasive species. Its native range was in the Indo-Pacific, and more specifically the Red Sea. However, in 1886, Cassiopea andromeda was recorded in the Suez Canal, Aegean coast of Turkey, and the central Mediterranean Sea. In addition to this, there was a sudden appearance of Cassiopea andromeda in two shallow, widely separated coastal lakes known as Wallis Lake and Lake Illawarra. These were the first recordings of Cassiopeia living in eastern Australia (Keable, 2016). In the United States, Cassiopea andromeda resides in the Florida Keys, Caribbean, and Hawaii. One hypothesis of how this species came to America was that they were carried in the ballast of European ships when they crossed oceans in search of the new world.

Feeding Method

In addition to consuming nutrients produced by the zooxanthellae, the upside-down jellyfish also captures prey with their oral arms. These animals invert on the ocean floor and pulse their bells to move water over the surface of their arms. When water is driven over their oral arms, they are able to capture zooplankton prey by stunning them using nematocysts located in their oral arms. After the prey has been captured, digestion begins on the oral surface and then moves to a secondary mouth where it can be ingested.

Reproduction

The life cycle of Cassiopea andromeda is similar to other scyphozoans because it has a sessile polyp stage and a dominant mobile medusa stage. The scyphistoma will reproduce asexually by budding and each bud will settle and lead to the production of another immobile polyp. In time, the scyphistoma will produce the adult medusa through a process called strobilation (Neumann, 1979). Strobilation usually takes place during the winter and fall seasons. Eventually the strobilation process will result in the development of an immature ephyra which will continue to grow into a fully mature adult medusa. The medusa are gonochoristic and reproduce sexually when the female eggs are fertilized by sperm released from males. Females internally brood the young until the eggs hatch and become free-swimming planula. Finally, the small larvae settle on a substrate and complete the life cycle by developing into asexually reproducing polyp.

Defense

Cassiopea have nematocysts that function as a self-defense mechanism. If these jellies are disturbed, they will launch themselves upward from the sea floor and release their nematocysts. The massive venom release in the water is usually enough to ward off any potential predators. However, this toxic compound is generally insignificant to humans.

Interesting Facts

As noted above, upside-down jellyfish are fascinating creatures and there are many little details about them that make them unique. First off, these jellyfish are made up of: 95% water, 3% salt, and 2% protein. Another interesting fact about these jellies is that they have a higher temperature tolerance than most Scyphozoans. However, the optimum temperature for these adult jellies is between 75-78 degrees Fahrenheit. Furthermore, humans don't have to be too worried about getting stung by one of these jellies because they aren't very poisonous or deadly and don't sting often. Finally, one of my favorite facts about this jellyfish is that there are a few species of crabs that carry these jellyfish on their back for protection by using the jellyfish's oral arms as shields.

Citations

Hofmann, D. K., and M. Gottlieb. "Bud Formation in the Scyphozoan Cassiopea Andromeda: Epithelial Dynamics and Fate Map." Hydrobiologia 216-217.1 (1991): 53-59. Web.

Jantzen, C., C. Wild, M. Rasheed, M. El-Zibdah, and C. Richter. "Enhanced Pore-water Nutrient Fluxes by the Upside-down Jellyfish Cassiopea Sp. in a Red Sea Coral Reef." Marine Ecology Progress Series 411 (2010): 117-25. Web.

Keable, Stephen J., and Shane T. Ahyong. "First Records of the Invasive "upside-down Jellyfish", Cassiopea (Cnidaria: Scyphozoa: Rhizostomeae: Cassiopeidae), from Coastal Lakes of New South Wales, Australia." Records of the Australian Museum 68.1 (2016): 23-30. Web.

Neumann, R. "Bacterial Induction of Settlement and Metamorphosis in the Planula Larvae of Cassiopea Andromeda (Cnidaria: Scyphozoa, Rhizostomeae)." Marine Ecology Progress Series 1 (1979): 21-28. Web.

Sacca, Michael Post and Patrizia. "Cassiopea Andromeda." Animal Diversity Web. N.p., n.d. Web. 01 Dec. 2016.

Santhanakrishnan, A., M. Dollinger, C. L. Hamlet, S. P. Colin, and L. A. Miller. "Flow Structure and Transport Characteristics of Feeding and Exchange Currents Generated by Upside-down Cassiopea Jellyfish." Journal of Experimental Biology 215.14 (2012): 2369-381. Web.

Welsh, David T., Ryan J. K. Dunn, and Tarik Meziane. "Oxygen and Nutrient Dynamics of the Upside down Jellyfish (Cassiopea Sp.) and Its Influence on Benthic Nutrient Exchanges and Primary Production." Hydrobiologia 635.1 (2009): 351-62. Web.