Upside-Down Jellyfish

For the first time since purchasing our Longboat Key condo, I have observed upside-down jellyfish along the seawall of Sarasota Bay.  Long residents of Bermuda, the Caribbean and the Florida Keys, these unusual jellies began appearing in the Bay over the past decade, perhaps due to warming sea temperatures though nutrient availability (related to human activity) may play a role.

Unlike most jellyfish, that feed and breed in the open ocean waters, upside-down jellyfish, also known as mangrove jellyfish, attach themselves to the bottom in shallow waters.  Their flattened bell has a central depression that serves as a suction cup to prevent detachment when waves or currents rake the shallows.  Four branched arms, festooned with short, thick tentacles reach up into the water, filtering plankton on which the jellyfish feeds.  Upside-down jellies also have a symbiotic relationship with photosynthetic algae that color their tentacles and provide an additional source of food (carbohydrates) for their host; it is this relationship that explains the behavior of these jellyfish, ensuring adequate sun exposure for the algae.

The upside-down jellies tend to congregate at human-distrubed sites but there is some concern that their blooms may adversely impact coral reefs, seagrass communities and other benthic ecosystems.  They, in turn, are fed on by a variety of marine creatures, including sunfish and leatherback sea turtles.