Mangroves, Part II - Red Mangroves

I am incredibly lucky to live in an area dominated by mangroves. In fact, the watery mangrove landscape beloved by fishermen and naturalists alike has its own name around here, the "back country" or "back waters." This has been a good year for red mangroves. They are hanging heavy with "pencils," which any day now will drop off and float until they wash up onto a suitable growing surface.

Marco Island is considered the northernmost of the "10,000 Islands," the greatest concentration of mangroves left in the state. The development of Marco Island and my community, Isles of Capri, wreaked massive damage on the native flora and fauna, and mangroves in particular.  Fortunately there are a few places left in both areas where the mangroves  either escaped the devastation or have reestablished themselves. And both areas are now nestled within area protected by the Rookery Bay National Estuarine Sanctuary and Everglades National Park.

Undisturbed Mangroves Part of Rookery Bay Sanctuary

A warren of prop roots makes the red mangrove easy to distinguish. These roots stabilize the shallow-rooted trees, and  are vital in transporting oxygen. They possess numerous pores, lenticels, which admit oxygen and allow its transport to the feeding roots, and which close when inundated. In a dense growth of red mangroves it can be impossible to tell which roots belong to which trunk.

Prop Roots

The trees not only send down roots from the trunk, but also  long roots from large branches. The lenticels and the plant's low rate of transpiration make it possible for the plant to maintain high osmotic pressure in the roots, which allows them to take in water, but exclude the salt by a process of reverse osmosis.

Aerial Red Magrove Roots, Mixed Growth, HWY 952

Where hurricane action is rare, the trees can grow to 80 feet tall or more, with a girth of around 3 feet, but the frequency of storms in Florida keeps them much shorter and shrubbier. Some mangrove stands can show tall, straight trunks, while other trunks are contorted and can look even animate, tortured or ecstatic.

Red mangroves have shiny, slightly  yellow-green leaves arranged opposite each other on the branch. A special characteristic for the species is the long interpetiolar stipule. (Stipules in between the leaf stems, the petioles). At the very tip of the branch in this sketch the stipule has not fallen off yet.

Red Mangrove, Leaves, Stipules

The edges of the leaves are smooth. Undersides are paler than the top sides. They can get up to  a good 4 inches long, and an inch or more wide. Leaves are clustered at or near the ends of the branches, in order to harvest as much light as possible. There is not much understory in a red mangrove forest, but seedlings can get established where there are gaps in the foliage cover. They will stay in the seedling stage until enough light is created for them to grow larger.

Flowers are bell-shaped, with 4 waxy yellow sepals partly hiding 4 feathery white petals. The plant can self-pollinate. Pollen is wind-borne, but it is possible that some may be spread by insects.

Red Mangrove Flowers 

One of the criteria of inclusion in the "mangrove" group is viviparity - live birth.  The actual "seed" of mangroves germinates on the plant. The brownish-olive structures below are the fruits, with the propagules, the "pencils," beginning to develop.

When the propagules are mature they drop from the plants. Many land at the base of the plant, but others will float away, often in "rafts,"  with the next tide. Incredibly, the propagules can stay alive for a year. At first they float horizontally, but as they become waterlogged the heavier base begins to sink until the pencil is vertical. If it washes up onto a suitable site, it will send out roots and sprout leaves.

Red Mangrove Propagule

Propagule with New Roots Developing

It is impossible to overstate the importance of red mangroves, and mangroves in general, to the ecosystem. Their roots stabilize shell and mud deposits, provide anchoring places for microorganisms and mollusks, and serve as a nursury and shelter for small fish and other vertebrates. They, in turn supply food for wading birds and other predators. Roots, leaves and pencils are consumed by a variety of native animals and insects. The root region is rich in phytoplankton, the base of the marine food chain.

Mangroves absorb a huge amount of wind energy from hurricane winds and storm surges, often at their own cost. One needs only to see the path of mangrove devastation after a storm like Irma in 2017 to see the incredible force they absorb and deflect. Dense mangrove forests also provide places for birds to perch during the day and mangrove islands provide safe rookeries at night.

Mangroves are enormously effective at capturing and storing carbon. When mangrove habitats are destroyed, the environment gets a double whammy - first by the release of massive amounts of stored carbon, and second by the loss of a significant carbon-removing source.

In some regions red mangroves are used medicinally. They have proven antibacterial properties. Leaves and branches contain high levels of tannin, which is what makes the waters of estuaries and tidal rivers tea-colored. Around the world mangrove tannin is used for curing leather.

The very stuctures that allow the red mangroves to survive can also be their undoing. Lenticels can allow the entry of pathogens. If the lenticels are clogged by fine silt, oil or other clinging pollutants the plant will die. Large swaths of mangroves in Everglades National Park were killed by silt deposits by Hurricane Donna in 1960.

The plant also dies if water levels rise enough to cover the lenticels permanently. While mangroves are threatened in their native range by rising sea levels, they also are posing a threat to salt marsh habitats farther north. Previously these vital habitats were protected by the mangroves' intolerance of freezing weather, but warmer winters with fewer freezing epidsodes are allowing mangroves to invade. Red mangrove also is considered invasive in Hawaii, where it was introduced.

Red Mangrove Leaves and Stipules 

Sources: Frank C. Craighead, Sr. The Trees of South Florida. Vol I. University of Miami Press.
1971.

Ronald L. Myers and John J. Ewel, Eds. Ecosystems of Florida. University of Central Florida Press. 1990.

"Mangroves Against the Storm."

"Why Blue Carbon is REDD Hot."

Beverly J. Rathcke. "Mangroves: Ecology and Reproduction."

Mangroves

 Mangroves make up a group of plants that connect me deeply with my coastal SW Florida roots. Mangrove" is a collective term for a variety of unrelated species that share certain biological and structural traits which enable them to survive in highly saline and oxygen-poor soils. Three species in the U.S. are recognized as mangroves: the red mangrove, Rhizophora mangle, the black mangrove, Avicennia germinans, and the white mangrove, Laguncularia  racemosa.  Buttonwood, Conocarpus erectus, is considered a "mangrove associate" because it often grows on the land-most side of a mangrove forest. Red mangroves, with their conspicuous aerial and prop roots and often-contorted trunks, are probably the most familiar of the species. They also tend to grow the closest to the water's edge, but not always.

From the time I was 9 years old until I left for college I lived in a world bordered and somewhat defined by mangrove forests. Our house sat in a mixed palmetto-pine-scruboak habitat, but if was only about a mile by foot to the mangroves. By water they practically were next door, because it took only a few  minutes down our canal to get to the mangrove portion of the Estero River. Further upriver the mangroves gradually gave way to more terrestrial plants probably due to a rise in elevation. Boats of various sizes and types, including crude but effective homemade ones, were a huge part of our family life. We always headed downriver, toward Estero Bay, a half-world between water and land, rimmed by mangroves, dotted with mangrove islands, and rife with unmarked shoals and oyster beds.

Red Mangrove, Pen & Ink (in progress)

My father made aerial photographs of the mouth of the Estero River at low tide, and then marked the channel out into the bay with the most upright small black mangrove trunks he could find. I'm sure they've long been replaced by something more official. One woman who didn't know much about the way channels wind and bend commented once that the markers looked like they had been placed by a drunk. My father just chuckled and said that a little whisky helped when the work was cold and wet.

He got interested in canoes, and tried to make his own. They were clunky, tipsy craft made from plywood salvaged from some old signs he had. The first ones were impossible to balance, and we got lots of laughs from his capsizes in the canal, but he gradually worked out better proportions. They were still tippy, though, and he had to cajole me into going with him. Even wearing a life jacket, with him behind me, I felt my heart lurch with every paddle stroke. The boats were so short that the passenger had to wear a raincoat for protection against the steady "rain" of water thrown off from the double-bladed paddles.

Because my father wanted us back before motorboat began in earnest, we left before daylight, often in the dense predawn fog typical of the sw Florida coast. That made the experience even spookier for me. The mangroves seemed to form solid black walls above me, and the way forward was shrouded in mist.

It wasn't long before he bought 2 real canoes from Sears, Roebuck. They had wide, flat bottoms, and were difficult to capsize, and by then I had lost most of my fear of water, and had learned in Girl Scout camp how much fun capsizing canoes could be.

We scarcely were purists. My father had a genuine kayak paddle but didn't like the wrist motion. He made his own double-bladed paddles out of wood - crude things somewhere between 2x2's and 2x4's with notches for thumbs and a half-piece of soft pipe to cushion the inside of the fingers. Because he had knee trouble he sat up on the thwart, so we did too. We had 2 canoes, and sometimes my father and the three oldest of us children went out with him, exploring, racing, or just paddling. The one who drew passage with my strong, reliable father was in the catbird seat. Pairing with another sibling inevitably produced mutual accusations of slacking and ineptitude.

On lower-tide days our dog Trixie would follow us, and howl most piteously when the mangroves grew right into the water and blocked her progress. Taking her along was a dubious business, though, because she usually got seasick all over the boat. In those days there weren't many alligators around, so we didn't have to worry about her.

Mangrove Bay

When I was in high school my father and I "canoed" every morning before we had to leave for school, and went out most weekend mornings as well. Sometimes we talked; often we preferred to absorb the quiet as the skies lightened, and the dark walls formed by the mangroves flanking the river began to take form with leaves, branches and prop roots. At one point the river widened to a broad cove, and that was our turn-around place. We called it "Daybreak Cove," because our eastward turn revealed the brilliant pinks and golds of the rising sun flooding the sky and spilling over  the mangroves.

That was my first taste of a mangrove phenomenon that I truly love - the experience of coming out of a walled- in channel to emerge suddenly into pure space. It can be almost vertiginous - you feel you could just as well be floating high up in a volcanic crater instead of in a broad expanse at sea level. If it's windstill, the bay or cove's surface mirrors the sky, and the only sounds are of water quietly gurgling through the mangrove roots, or a bird's call. Even the distant drone of an airplane does not dispel the sensation of being in a primordial world, untouched by human influence.

Red Mangroves, Pencil Sketches 

Through college and the first years of grad school I returned home during breaks, and always found rejuvenation through canoe trips on the river and into the bay. Once my brother and I made it all the way to Estero Bay before the sun had risen fully. We beached on a mud flat and marveled at the rivulets formed by the outgoing tide flowing full of the dawn's rose-gold light.

Mangroves along the Estero River grow in a compacted peat substrate, and are somewhat stunted. When I first saw the majestic trees lining the Joe River in Everglades National Park years later, I didn't even realize at first that they were mangroves. Living in Miami, my husband and I loved to trailer our 16-foot motorboat to Flamingo, the southernmost tip of the park, and explore its rivers and trails. Whitewater Bay, the Joe, Roberts, and Shark Rivers were ours to discover. Often once away from the boat ramp, we would be the only boat around, especially in summer. Alligators loved to sun on the concrete ramp, so during the summer you had to take the best place to put in that was available.

Nearly 30 years later, after Hurricane Andrew blew us out of Miami and onto Florida's west coast, we still love the watery world bounded by the mangroves. By now we've acquired enough local knowledge to find our way, but we still carry a chart.  It never gets boring. Each trip reveals something new. We've gotten too old to sail, which is a blow, but we still can putt around in the backwaters. My parents moved to north Florida, along the Suwannee River, in the early 1970's. SW Florida had become too crowded. The Suwannee River has its own beauty, and my father loved it, but he never forgot the strange, flat world of the mangrove forests.