The molluscan fauna of Bonaire

I absolutely adore natural history. A lot of people don't know what the term means, but I define it as the study of how organisms live - what do they eat, what eats them, where do they live, how long do they live, how do they reproduce, etc. It is the foundation on which all ecology stands. You would be shocked how poorly-studied natural history is for many species on Earth. We (that's the collective 'we' - all humanity) have mapped the functions of every single gene in fruit fly embryos, but we have no clue how most species on the planet feed themselves. It boggles the mind.

Snail shells on the limestone in Bonaire

So we're going to take a quick break from pretty coral reef photos from my vacation in Bonaire and talk about snails. 

On a hike in Washington Slagbaai National Park, I noticed some shells on the ground. They were bleached white and nestled in little holes in the limestone foot path. I assumed they were dead, perhaps the last calcareous remnants of some snails that got thrown from the ocean in a strong wind and perished on the rock. This assumption was strongly challenged when I picked one up and noticed it had an intact operculum - you know, the little hard door that a snail uses to seal up its shell. The operculum could only mean one thing: there was a live snail inside! Part of my brain still believed they were marine snails that had wandered away from their water source, but we kept finding shells. Not just one species, either - at least two. They had to be land snails.

When we finished reached the tiny museum back at the entrance to the park, I noticed a display on the land snails of Bonaire. There it was: Cerion uva bonairensis. The shell looked exactly like the ones I had seen on our hike. A little reading online indicates that the species is very common, especially in limestone habitats, and that its shell varies considerably based on environmental conditions. In fact, the species Cerion uva is divided into three subspecies, one of which occurs on each of the islands of Aruba, Bonaire, and Curaçao. I even found a good paper on the population genetics of Cerion uva that suggests the snails may have been carried between the ABC islands by humans in recent centuries.

So here's my question: how do snails survive in the desert? Every snail I have ever met lives and dies by its water supply. I had a hard time conceptualizing a snail that doesn't desiccate or suffocate in the Caribbean sun. Well, it looks like Cerion uva is different from most of the snails I have ever met: it has lungs and breathes air! As to how they keep from drying out in the sun, I have one hint, which is a source that mentions estivation in Cerion. It seems these hardy terrestrial snails go into a type of hibernation when conditions are unsuitable for normal life. I'm not sure of the details, but I would have no trouble believing the snails I picked up with their carefully-sealed opercula were estivating. There's not a ton of information on the natural history of Cerion, but what bits I could find were utterly fascinating. 

Periwinkels on a rock in the surf zone in Bonaire

On another day, I emerged from a dive site on Bonaire's western coast and found a number of colorful snails on a rock at the shore. The snails were being splashed with waves, so I concluded they must be marine snails. A little hunting online showed I was right: my wave-worn buddies were Cenchritis muricataus, a type of periwinkle. This species is in the same family as many of the periwinkles I'm familiar with at temperate latitudes. They feed by scraping small algae from rocks in the surf zone, and they reproduce by releasing feeding larvae into the water column. The snails felt eminently familiar. 

I'm sure some of my friends and family - even scientific colleagues - would laugh at my compulsive need to identify every species I come across, even on vacation. In response, I suggest they pick up a snail.