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Red, Black and White Mangroves - Ecology


Kayak the mangrove lagoons canls through the red mangrove forest and laggons


THE MANGROVE HABITAT: A variety of organisms utilize mangrove habitats. All ocean fish and shellfish caught commercially, and by recreational means, utilize mangrove habitat at some point in their life cycle. Amphipods, fiddler crabs, killifish and minnows live in mangroves and eat detritus. Lobster larvae floating in the plankton, migrate to the roots of red mangroves. They consume both plant and animal material. The sea trouts (from the croaker family) tolerate higher turbidity and feed on fish in mangroves and sea grass beds. Terrestrial organisms and birds utilize the forest floor, root complex and the canopy. Mangroves provide habitat for a number of threatened and endangered species.

Mangroves reproduce by dropping their 'propagules' into the water which float across the oceans until they lodge into the ground, on perhaps a distant seashore. There they take root and form a new plant, if allowed to grow. Propagules contain no seeds. They have already matured on the plant and are 'ready to go' plants that only need lodge themselves to send out their roots and leaves. They are viable, floating in the ocean, for up to a year.

Red mangrove roots with oysters

The mangroves shed leaves copiously all year long, creating the basic source of food. Bark, twigs, root material, guano from birds roosting in the trees, and organic matter of all kinds including dead animals and loose sea grass trapped in the maze of roots add to it. All decompose to begin the food chain. Bacteria and fungi are the agents that produce edible detritus and are themselves eaten by marine animals often too small to see. They in turn are eaten by larger animals. And finally, larger predators, including humans, come along to harvest the bounty.

THE MANGROVES OF PUERTO RICO

Puerto Rico has three types of mangroves: Red mangroves (photo above) , Black mangroves, White mangroves and Buttonwood which is related and sometimes called a mangrove. All of these line the lagoons and shorelines, where there is no wave action

bio.uminescent lagoon Mosquito bay in Vieques

Why is The Vieques Mosquito Bay so brightly Bioluminescent?

A Delicate Balancing Act:

To create a Bioluminescent bay you need a lagoon surrounded by Red Mangroves. The roots of the red mangroves release tannins that are rich in Vitamin B12, one of the important nutrients for these light emitting dinoflagellates. The decomposing mangrove leaves release many other nutrients which add to the nutrient rich environment.

The Bay must also be relatively free of pollution, which generally requires protected lands surrounding the bay.

The Bay requires enough size and depth to enable the water to stay relatively cool in the daytime, it does, however, remain warmer than the ocean outside. It also requires a restrictive channel to the ocean, with a relatively small tidal exchange. This Biobay has the channel to the ocean at the windward end of the bay allowing sufficient water exchange to avoid overheating and stagnancy.

Any alterations to the size of the channel to the ocean (such as shallower or deeper or wider) can destroy a Biobay. Pollution flowing into the bay from chemicals in groundwater and flood waters can ruin a Biobay. Sufficient fluorocarbons from motorboats adversely affects the Bioluminescent dinoflagellates, as would waste from any boats anchored in the bay. People swimming, who have sprayed themselves with DEET, adversely affect the Biobay.

Lights seen from the bay and ambient light in the sky ( reflected from clouds) greatly reduce the visibility of the Bioluminescent at night. It is a real treat to be in the Biobay when the electricity goes out on the island! It is also considerably better to see the Biobay when there is no moon visible in the sky.

So why is this particular Biobay (perhaps) the brightest in the world? Because all these factors are perfectly balanced, creating ideal circumstances for a constant 'super bloom' of Pyrodinium bahamense dinoflagellates, over 700,000 per gallon of water!

How fragile is this ecosystem? Well, the factors being constant, this bay recreates itself continuously (for now). A recent rainfall, of over 30 inches, poured sediment into the bay turning it into a giant mud puddle... and killed most of the dinoflagellates. The sediment flushed out with the tides over a few weeks period, the dinoflagellates reproduced like crazy, and repopulated themselves, and the bay became, just as bright all over again.

THE BIOBAY HABITAT

The Bioluminescent dinoflagellates Pyrodinium bahamense are a photosynthesis using plankton. They are one celled and measure about 1/500 th of an inch. The tiny burst of light it gives off is a hundred times bigger than itself. ( Above is merely an artists depiction of the glow) Each dinoflagellete bursts into light when it feels pressure against its cell wall. The light is given off in an instantaneous process; when you add the light bursts of 750,000 dinoflagellates per cubic foot of water together the effect is spectacular!

Almost all marine Bioluminescent is (greenish) blue in color, for two related reasons. First, blue-green light (wavelength around 470 nm) transmits furthest in water. The reason that underwater photos usually look blue is because red light is quickly absorbed as you descend. The second reason for bioluminescence to be blue is that most organisms are sensitive only to blue light.
The luminescence of a single dinoflagellate is readily visible to the dark adapted human eye. Most dinoflagellates emit about 6e8 photons in a flash lasting only about 0.1 second. Much larger organisms such as jellyfish emit about 2e11 photons per second for sometimes tens of seconds. The intensity of luminescence by photosynthetic dinoflagellates is strongly influenced by the intensity of sunlight the previous day. The brighter the sunlight the brighter the flash! Which is only emitted at night.