Weekly “What is it?”: Red mangrove

Mangrove prop roots can grow towards the soil from branches hanging 6 feet or more above the water! Photo credit: Carrie Stevenson, UF IFAS Extension

With long protrusions hanging from its branches and leggy, above-water prop roots, the fascinating adaptations of the red mangrove (Rhizophora mangle) tree give the distinct feeling it is a little more “alive” than everything around it. Its propagules (seed pods) and prop roots are unique outgrowths that help secure these crucial plants into wet, shifting soil. In subtropical ecosystems, mangroves dominate the salt marsh landscape. They are shrubby trees that can expand across the shoreline and when left alone, can reach heights of 50’ tall.

Propagules (seed pods) of the red mangrove are torpedo-shaped, and can drop directly from a parent tree and be replanted in the sediment below. Photo credit: Carrie Stevenson, UF IFAS Extension

On a recent trip to the Sarasota area, I was fascinated to realize for the first time that the torpedo shape of a black mangrove propagule works in a very specific way. Walking along a boardwalk, I noticed dozens of the long bean-like pods at my feet. I pushed several over into the tangle of mangroves, and then just for fun I dropped a few over the boardwalk into the muck. I was delighted to realize that when dropped straight down, the weighted, pointy end of the propagule landed perfectly upright in the mud, as if I’d planted it. This is the same way they fall from parent trees, and it sets up the seed to easily begin sprouting in place. If they don’t land vertically in the mud but into open water, the propagules float and can stay viable for up to a year!

The prop roots of red mangrove trees crisscross between plants to support them all in the mucky coastal soil. Photo credit: Carrie Stevenson, UF IFAS Extension

In addition to dropping little vertical torpedoes into the soil, red mangroves also spread and stabilize by sprouting prop roots from their horizontal branches. These long protrusions grow towards the water and underwater substrate, eventually lodging into the soil and supporting the overall root structure of the plant. This complex root system helps control shoreline erosion and forms a surface for oysters and sponges to attach and grow. The crisscrossing root zones above and underwater form an ideal habitat and refuge for countless species of fish and crabs. These include three crabs specific to mangroves, a mangrove tree snake and cuckoo, and important sportfish like snook, snapper, and grouper.

In south Florida, mangrove forests dominate the natural shorelines of salt marsh habitats. Photo credit: Carrie Stevenson, UF IFAS Extension

The typical growing range for red mangroves in Florida has historically been from Cedar Key to the Florida Keys along the Gulf, then up to Daytona Beach along the Atlantic. Several studies, however, have recently found established populations growing further north, particularly around the Apalachicola area. Several years ago, we even had a half dozen red mangroves survive more than a year in Big Lagoon State Park here in the Perdido area. This is a phenomenon observed worldwide, as climate change has resulted in fewer hard freezes and allowed these subtropical/tropical plants to migrate into the temperate zone.


Posted: August 25, 2021

Category: Natural Resources
Tags: Weekly What Is It

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