Floating Dock Life

Click on any critter in the scene for more information.

The waterways of southwest Florida contain a large number of concrete floating docks. Once it has become “seasoned” from initial colonization by bacteria, the concrete provides a hard substrate that is suitable habitat for a diverse group of marine and estuarine organisms.

Many of the same animal and plant groups that grow on coral reefs will take up residence on concrete. The circled area within the picture shows an assemblage of barnacles, oysters, colonial tunicates, boring sponges, and green algae. Also undoubtedly present, but barely visible are bryozoans, soft corals, and mussels. All of these animals are filter feeders, either trapping plankton on nets of sticky tissue, their gills, or by waving net-like arms in the water. The sheepshead in the foreground is an opportunistic feeder on the shellfish. A variety of forage fishes and predators can usually be seen around and beneath such docks, both seeking shelter and lurking in wait for careless prey.

Even in the most turbid waterways, these floating docks usually support good plant growth, because sunlight penetrates at least a few inches into the water. Stormwater runoff is one of the controlling factors for things that colonize floating docks on Naples Bay and in its tributary waterways. The volume of runoff is so high that we can often see a well-defined layer of fresh water on the surface of the Bay. Fresh water is lighter than salt water and will float on it with little mixing unless it is agitated. The rainfall that descends on much of the interior of Collier County ends up in the Golden Gate Canal system, and eventually dumps into the Gordon River. The end result is a layer of fresh water that can be from several inches to several feet in thickness. Prolonged exposure to fresh water can kill barnacles, sponges, and other encrusting organisms. Once the salinity is restored, recolonization is rapid, and builds on the empty houses of the deceased.

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