Cephalopodcast

Last summer we started noticing upside-down jellyfish (Cassiopeia sp.) appearing in abundance in Sarasota Bay, Florida. These are typically saucer-sized animals that are content to pulse upside-down (hence the name) on the bay bottom, exposing their frilly, weed-like tentacles to the sun. They aren’t supposed to have much of a sting, but apparently some people do get an allergic reaction to touching them.

These creatures have a symbiotic relationship with the algae that packs their tentacles. It is similar to the relationship between reef-forming, stony corals and their algae partners. These partners are called zooxanthellae (zoe-zan-thelly), or as we like to tell the kids, they are the green jelly in the belly of the corals. Not strictly accurate, but catchier than saying the dinoflagellate symbionts in the endoderm of hermatypic cnidarians. The algae photosynthesizes, producing oxygen and sugars that the animals use. In return, the animals give the algae a protective matrix to grow in, carbon dioxide and other waste products that act like fertilizers.

Typically you find these jellies further south in Florida and it’s unsual to see them this far north. This story just recently got some mainstream press coverage and by coincidence the inkspot blog posted some beautiful pictures and video of upside-down jellies nearly the same day.

It’s interesting to note that this article by Karla C. Garcia states that the upside-down jellies tend to expel their zooxanthellae under stressful conditions, like extreme water temperatures and changes in salilnity. In coral reefs, this process is commonly referred to as bleaching. Presumably the conditions in Sarasota Bay have change now in favor of recruitment by Cassiopeia larvae and their algae. Sarasota Bay has also been affected by several seasons of serious red tide outbreaks. It is interesting to speculate if this may have influenced the natural predators of the planktonic larvae.

And here’s the obligatory disclaimer. These animals are not fish, of course, and some people object to calling them jellyfish. They are an ancient lineage of animals that predate any finny creatures with backbones. Instead, simply call them sea jellies and you should be okay.

• Herald Tribune: Strange jellyfish move into Sarasota Bay
• inkspot: jellicles
• A Symbiotic Lifestyle: C. xamachana and Zooxanthellae