Cannonball Jellyfish (Stomolophus meleagris)
Stephanie F. Loria
With the diversity of life in the ocean still largely unknown, this month we honor a marine organism, the cannonball jellyfish (Stomolophus meleagris). Cannonball jellies, like other jellyfish belong to the phylum Cnidaria, one of the oldest animal lineages originating approximately 740 million years ago (Park et al. 2012). During their life cycle, most cnidarians exhibit two different morphological forms: the motile medusa stage (aka the typical jellyfish form) and the sessile polyp stage (like sea anemones). For jellyfish, the medusa is the sexually reproducing form and most jellyfish species are dioecious meaning that each medusa is either male or female and not hermaphroditic. Male medusae release sperm into the water which fertilize eggs externally or internally in female medusae. Fertilized eggs hatch to form larvae that can then travel long distances to find a substrate to attach to and metamorphosize into the polyp form. Polyps later transform into medusae and the life cycle repeats.
To feed, cnidarians use nematocysts (stinging cells which look like they have tiny barbs) on their tentacles to paralyze prey and then digest the prey using enzymes in a gastrovascular cavity. As jellyfish have no anus, all food must enter and leave through the same opening. Cannonball jellyfish, although found across the world's oceans are most common on the southeastern coast of North America (Wikipedia). If you find yourself walking along the beaches in South Carolina, a state where these jellyfish are quite common, you might see some washed-up cannonball jellies with tiny crabs on them as depicted in the image below. These juvenile spiders crabs (Libinia dubia) are not eating the dead jellyfish but are rather cast away in a catastrophic jellyfish shipwreck. The juvenile spider crabs have a symbiotic relationship with the cannonball jellyfish, sharing its food and using it for protection (Afford & Patel).
The future of cannonball jellyfish populations is uncertain as this North American species has become a delicacy in Asia and business has been booming (Narula 2014). Carolinan fishing companies are harvesting these jellyfish via trawling and shipping them to the other side of the world to be sold in fish markets (Narula 2014). The profits from harvesting jellyfish are enormous, with some fisherman making 10000 USD per day (Narula 2014). However, the ecological impacts of harvesting cannonball jellyfish may soon be realized as environmental groups warn that excessive trawling and pollution from jellyfish processing plants may outweigh the monetary benefits to local communities (Narula 2014).
Afford, H. & T. Patel. Stomolophus meleagris, cannonball jellyfish. Animal Diversity Web. University of Michigan, Museum of Zoology.
Narula, S. K. 2014. 'Jellyballs' are serious business. The Atlantic.
Park, E., D. S. Hwang, J. S. Lee, J. I. Song, T. K. Seo & Y. J. Won. 2012. Estimation of divergence times in cnidarian evolution based on mitochondrial protein-coding genes and the fossil record. Molecular phylogenetics and evolution. 62: 329-345.
Cannonball Jellyfish. Wikipedia.