Surveying sea life at Bunche Beach
“Ding” Darling Wildlife Society-Friends of the Refuge intern Jake Kelly reported on a December shorebird survey at Bunche Beach in Fort Myers with J.N. “Ding” Darling National Wildlife Refuge biological science technician Avery Renshaw.
Nature and wildlife are, as expected, unpredictable, and the many different species of shorebirds we hoped to see pecking at the sand during low tide were scarce. However, that does not mean the survey was a bust.
We found plenty of interesting life stranded on shore after the tide receded. The farther we walked, comb jellies began to appear all over the beach. Comb jellies, also known as ctenophores, are much more than a clear blob in the sand. They are one of the five major lineages to arise early in animal evolution. A recent study published in Nature in 2023 provides evidence of comb jellies potentially being the oldest animals on earth, roaming the oceans close to 700 million years ago.
Comb jellies are not jellyfish, who belong to the group cnidarians. While jellyfish use their tentacles to catch and hold onto prey, comb jellies use eight rows of giant fused cilia, or combs, to propel themselves through the water. When picking up the stranded jellies, we could see the cilia running down the body, which would reflect faint shimmering green lines in the light.
There were also many sand dollars scattered around. Some had dried up, while others, still alive, had pushed sand through luneles, the oval-shaped holes on their rigid skeleton — called a test — to bury themselves a few inches beneath the surface. You can tell when a sand dollar is buried because there will be five holes in the surface sand, matching the luneles.
Some of the usual suspects on Bunche Beach — and my favorites — are baby horseshoe crabs. Since many are the size of a dollar coin, you can follow their winding trails in the sand to discover their location. Horseshoe crabs are some of the oldest living species on earth, surviving five mass extinctions in the past 475 million years and remaining relatively unchanged.
We came across a few molts, as well, which can be identified by a split along the front rim where the horseshoe crab slipped out. During molting, a whole new shell will grow under the old one before it no longer fits. Juvenile horseshoe crabs molt 16 — or 17, in the case of females — times before they reach sexual maturity. After that, their carapace is their forever home.
Exploring the tidal flats on Bunche Beach is a great way to become familiar with the local shorebird populations and the many other organisms that play an important role in the ecosystem.