By: Rebecca Helm, Brown University EPSCoR Graduate Student in Casey Dunn’s lab

(Follow Helm on her blog and at Deep Sea News to read about all things jelly and the great ocean beyond)

Every year New England beaches are invaded with sticky, stringy jellies, drifting leisurely through summer weekends, leaving painful reminders in their wake.  But why is it they seemingly show up out of nowhere, and how are they able to return year after year?

Jellies live complex lives, like caterpillars and butterflies. The stinging jellies at the beach, like butterflies, are the last in a series of shapes a jelly has taken throughout its life. These adult jellies release eggs and sperm into the water, which fuse and develop into small pill-shaped planula larvae (left). These microscopic larvae swim through the ocean searching for a suitable spot to call home.

When a larva finds a worthy rock, shell or piece of wood to call its own, it attaches. Then it metamorphoses into creature that resembles a mini sea anemone – this stage is called a polyp (right). Unlike the planula larvae, the polyp has a mouth and stinging tentacles.  The polyp can eat, grow, and amazingly, bud off more polyps. Polyps are tough and survive through long, harsh winters.

When the temperature is warmer and food is abundant, the polyp absorbs its tentacles and splits into small pieces, resembling a stack of tires (video).  Each piece pops off as a baby jelly. Once all the young jellies have popped off, the polyp re-grows its tentacles and starts feeding again.  A single polyp can bud a carpet of new polyps and generate hundreds of jellies throughout a season!

With these types of numbers you can see how a quiet bay can easily turn into a jelly paradise in only a few short months. As the season changes the adult jellies begin to die, and for a short time the beach is safe for swimmers, until the cycle begins anew the following year.

See the original video and post at CreatureCast.org.