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  • José H. Leal

Southwest Florida Shells

There are millions of mollusks living offshore along Southwest Florida’s shallow, 80-mile-wide continental shelf (the part of the continent under water). When cold winter winds from the north or northwest blow in the Gulf of Mexico, the water moves in directions that drive many mollusks (or empty shells) onto the shore. The effect is enhanced along barrier islands such as Sanibel, Captiva, Cayo Costa, and south to Fort Myers Beach, Keewaydin, Marco, Kice, and the Ten Thousand Islands. In the summer, with changes in weather patterns and weakening of northern winds, there is less accumulation of shells along the shoreline. Except during hurricanes and tropical storms, the beaches of the Gulf of Mexico barrier islands are rarely pounded by big waves, while on the few beaches on the bay side of the islands are narrower, usually devoid of waves, and with mud or fine sand mixed with mud.

Cluster of Clouded Periwinkles, Littoraria nebulosa, on dead black mangrove, at Kice Island.

Environmental conditions, such as water temperature, salinity, dissolved oxygen, and chemicals released by human activities (fertilizers, etc.), vary from time to time, affecting the molluscan populations. These variations may occur seasonally, or from one year to the next. This may cause some species of shells to be more plentiful one year, only to be replaced by others in the following year, and so on.

Shell of the Ponderous Ark, Noetia ponderosa, from Sanibel Island.

One of the tasks of the National Shell Museum is to provide a better understanding of the biodiversity of mollusks in Southwest Florida. To that effect, the Museum has been publishing and bringing up-to-date its online guide to Southwest Florida Shells since the late 1990s. (The guide will be upgraded to a new, more user-friendly edition, using a new online platform, within the next couple of months.) And the renovated set of exhibits on the second floor (in progress) will include a new version of our traditional Southwest Florida Shells exhibit. Don’t miss these upgrades when their times come!


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