Mangroves live in the salty, water-logged soil of tidal areas and have evolved in special ways to suit this environment. Some block salt with their roots, while others excrete salt through their leaves. Mangroves on Tidy Island include all four kinds of mangroves common to this region: red, black, white, and buttonwood.

Mangroves, even of the same kind, vary greatly in size; from small shrubs to large trees, depending on their local environment. Those on the south shore of the island are affected by wave action, while those on the north shore are sheltered by the mainland. In the mangrove swamp that constitutes most of the island, they are greatly affected by the tides. The easiest way to tell one mangrove from another is by looking carefully at their leaves. The differences are shown in photos here.

Mangroves on Tidy Island: Reds

Red mangroves are easy to identify because of branching roots that are mostly out of the water. These help the red mangrove resist wave action and are permeable to water and oxygen, while blocking salt. Reds seek out areas that are usually underwater or very wet. As a result, they are found on the outer edge of mangroves at the shoreline and in swampy areas inland.

Red mangroves on the north shore of the island live in calmer water where sand does not build up. Barnacles colonize their roots, seen here at low tide.

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Red mangroves on the north shore of the island live in calmer water where sand does not build up. Barnacles colonize their roots, seen here at low tide.

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The mangrove swamp that makes up the largest part of the island supports red mangroves only in very wet areas and along the criss-crossing mosquito ditches.

Mangroves on Tidy Island: Blacks

Among the mangroves of Tidy Island, blacks are most plentiful, populating the entire mangrove swamp area. They are more tolerant of salt than reds but less tolerant of deep water. Their bark is not very rough and dark brown, nearly black. A spoil pile from a mosquito ditch is in the background.

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The open conditions along the south shore allow black mangroves that predate the development of the island to grow very large. A preservation area maintained by the Tidy Island Condominium Association contains several old specimens like this, along with reds, whites, and buttonwoods.

In contrast to reds, black mangroves have roots that are entirely underground except for snorkel-like “pneumatophores” that bring in oxygen. The pneumatophores need to extend above the water surface at least some of the time, which limits the depth of water where black mangroves can live. The roots can extend for 30-40 feet.

Unlike red mangroves, the roots of blacks do not block salt. Instead, they get rid of it by excretion through glands on the leaves. In the mangrove swamp area, where the concentration of salt in the surface water can get very high, crystals of salt form on the leaf surfaces.

Mangroves on Tidy Island: Whites and Buttonwoods

While reds and blacks are easy to tell apart by their roots, blacks and whites have similar root structures. The best way to tell them apart is by the difference in leaf color. In this photo there is a white in the foreground and a black immediately behind. Further back (extreme left) there are more whites, stunted because of high salinity.

In contrast to the whites in the preceding photo, these are growing in a more favorable environment and are large enough to form a cover over the boardwalk. Their bark is rougher than that of the blacks and lighter in color.

Buttonwoods grow in open areas where salt concentration is fairly low, living at the edges of the mangroves rather than within them.

Mangrove Reproduction

Mangroves reproduce in an unusual way, well-suited to their environment; they give birth to live plants called propagules. After dropping from the parent, propagules must remain in the water for a period of about 5 (white), 14 (black), or 40 (red) days. It will develop into a new mangrove if it is lucky enough to lodge on a bed of sediment.

Shoreline development, especially construction of bulkheads and finger canals, destroyed most of the mangroves that once surrounded Sarasota Bay. Tidy Island and the adjacent mainland to the east to Long Bar Point account for most of the mangroves that remain. But mangroves will quickly repopulate a shoreline restored to a more natural state receptive to propagules.