As the weather gets warmer by the day and we find ourselves walking on the beach or cruising through our winding creeks, you will probably come across an unusual but abundant jellyfish, the cannonball jellyfish! They may seem like scary-looking creatures, but they are actually harmless and serve as a harbinger of the arrival of another charismatic species in the region – the leatherback turtle.
A clumsy, seemingly defenseless ball of jelly, cannonball jellyfish (Stomolophus meleagris) storm our estuary in late spring every year in such numbers that it seems like an invasion. These drifters, carried by ocean currents, have come to breed; large adults are most abundant in the spring, migrating from offshore waters into Port Royal Sound to release their offspring into our salt marshes.
Smacks of cannonball jellyfish (that’s right – a group of jellyfish is called a ‘smack’!) drift with ocean currents and make daily vertical migrations from the dark depths to the surface to feed on plankton. The cannonballs aren’t alone in this seasonal migration; many of them have hitchhikers! On most cannonball jellyfish, you’ll also find a spider crab (Libinia dubia), a symbiotic species catching a free ride and food resources. A spider crab first links up with their cannonball jelly host as a planktonic larva, where they live the early stages of development inside the jelly. The juvenile spider crabs feast on the plankton-filled jelly that the cannonball has captured and created. They occasionally will feed on their cannonball host if their appetite becomes ferocious enough!
Cannonball jellyfish feed on zooplankton, especially bivalve larvae in their second stage of development (referred to as veligers). A substantial population of cannonball jellyfish is also considered a good indicator of water quality and the health of the bivalve population (i.e., oysters, mussels, clams). So, lots of cannonballs suggest lots of healthy, tasty oysters and clams for people! Harmful algal blooms, oil spills, and nonpoint pollution can cause major die-offs in planktonic organisms, which can result in a drop in food sources for these jellyfish.
Cannonball jellies are also a significant food resource for many charismatic species found in our waters, including the largest turtle on the planet — the leatherback sea turtle. A single leatherback turtle can consume nearly 70% of its body weight in jellyfish in a single day! That’s a whopping 2,000 pounds of jellyfish!
Unfortunately, plastic bags look a lot like jellyfish when floating underwater, making them one of the more susceptible species to the hazardous effects of plastic pollution in the marine environment. WWF estimates that more than half of the world’s sea turtles have ingested plastic waste in their lifetime, which leads to digestive blockages and often results in death.
Although some people have reported a minor sting from contact with cannonball jellies, they are relatively harmless and provide numerous benefits to life in the Port Royal Sound. When we see them arrive, we know the Loggerhead Turtles are not far behind!
HOW YOU CAN HELP
– Cheer when you see the cannonball jellyfish arrive in the Port Royal Sound! They are very cool and a sign of good ecological health!
– Keep plastic bags out of the water! We don’t want our turtles to confuse them with tasty cannonballs
– Support efforts around the region to strengthen plastic ordinances to reduce the amount of plastic in our environment