It has been a long time since I have been to South Beach — so I can’t comment on how things work there — but the beaches of Sanibel Island, Florida are most definitely in the category “clothing required.” I traveled to Sanibel just a few weeks ago seeking warmth, relaxation, and nature, and I found all of those in abundance. The weather was a perfect mix and it was a classy place with myriad pools and tropical drinks. The interesting natural habitats, however, were much more engaging than I had expected, and despite the laissez-faire approach to apparel on their sandy Atlantic-side equivalents, I found Sanibel a place for clothes.
Sanibel has several large nature preserves, including the Ding Darling National Wildlife Refuge. I had expected to see some interesting species such as red-eared sliders, roseate spoonbills, wood storks, and of course a lot of alligators. What I hadn’t anticipated was the incredible diversity of invertebrates, and was excited to find out that Sanibel’s beaches are rated as some of the best “shelling” beaches in the world.
Most of us have participated in “shelling” with out even knowing it, but on Sanibel this casual pass time — that occupies summer visitors from Cape Cod to the Keys — becomes serious business. At first, I walked up and down the beaches picking from the thousands of colorful and oddly shaped shells. It was not until I met my first real “sheller,” however, that I learned that the main event had already taken place for that day, and most of the interesting shells had been scooped up. It turns out, early in the morning a small caste of vacationer-naturalists take to the beaches just before sunup and search for shells with flashlights. I initially dismissed this as extreme, but later in the day found my self “happening” in to a hardware store for a new flashlight. The next morning, there I was before the sun rose, ankle deep in the surf searching for shells. I certainly found some nice specimens — the Florida fighting conch, banded tulips, and the apple murex — and it was amazing to see so many of the live mollusks in the shallows. Although this was in itself a rewarding experience, and I repeated it several times, I never found the shells that most intrigued me.
To me, the most interesting shells on Sanibel are carrier shells, and I learned about their abundance and diversity not on the beaches but at the Bailey-Matthews Shell Museum, which is a fabulous stop on the main road on Sanibel. It might sound like an obscure bio-nerd’s paradise, but it is actually engaging for even those who are mildly interested in nature, and children also have lots to do there. The scavenger hunt in the museum so engaged my four-year olds that they actually asked to go back the next day. One stop on the scavenger hunt was a great display of the carrier shells, which are gastropopds in the genus Xenophora (Xenophoridae). The mature individuals in this group do not look anything like smooth classic shape of their close relatives. The Xenophora look instead like an intertebrate trash heap, with many shells and dead coral fragments attached to their upward-facing surface.
And this is no mistake – these animals actively select shells and fragments from their environment and cement them to their own shell to make them appear as cluttered assemblages. Like most examples of potential camouflage, the underlying mechanism for this behavior, as well as its adaptive value, are largely unstudied. However, some (Feinstein and Cairns 1998) have speculated that this intriguing and apparent example of animal clothing is used for concealment. It will take a few more trips to Sanibel before I can do anything more than identify this example, and I am hoping simply to find a xenophorid on my next early morning commune with the Sanibel shellers.
Reference: Feinstein, N. and S. D. Cairns. 1998. Learning from the collector: A survey of azooxanthellate corals affixed by Xenophora (Gastropoda: Xenophoridae), with an analysis and discussion of attachment patters. Nautilus 112(3): 73-83.