Fifteen Fathoms

The ocean.

Vast. Dark.

Unknowable.

It vies with the cosmos beyond our sky for the title of Final Frontier. Both are dangerous to us unless we don oddly similar survival gear. The ocean is closer to home, and is the more frightening of the two, for it is so easy to fall in without trying. But the ocean will only hurt us if we plunge in and stay too long.

Breathe in through your nose. Inhale the wild briny scent that invades your nose and makes you feel as if you've taken a bite of too-salty fish. Taste the trace of it on your tongue. Lick your lips.

Listen to the bubbling, gurgling slap of water on the land. The tide is coming in, and the waves are washing high tonight. Look up, and you will see the reason: the moon is full. Now look down: it's blanketing the beach with water.

Take a step forward to meet the sheet of liquid creeping up the sand. Feel the sand shifting under your bare feet. Be careful; the sun has set, and it’s dark out. All you can see clearly is the faint white foam riding the incoming surge, reflecting the moonlight.

Because of that full moon, something very special is going to happen. Wade into the surf. Dive beneath the waves.

Dark, solid masses rise from the relatively shallow sea floor: a coral reef. They can live nearly forty fathoms down, but thrive from fifteen fathoms to the surface. Reef-building corals require the sunlight found at these depths.

Corals are not plants, but colonies of tiny carnivorous animals, with a need to ingest other creatures to continue living. They have forged an alliance with a particular species of algae. Zooxanthellae reside in their soft tissues and give them their brilliant colors. When the reef is bathed in sunlight, the tiny, brightly-colored algae are busy photosynthesizing and providing the coral with oxygen.

Coral reefs are made of the calcium-carbonate bases built by an innumerable amount of tiny beings called coral polyps. Each fleshy polyp sits in a hard, protective cup called a calyx, and is comprised of a number of tentacles—six for hard corals, eight for soft corals—arrayed around a central opening which both takes in food and releases waste. Each tentacle is covered in nematocysts: minuscule, venomous, biological spring-loaded harpoons. When any living thing of another species makes physical contact with them, the nematocysts fire, incapacitating and anchoring tiny zooplankton prey. The extended tentacle then folds inward, delivering the food to the large stomach chamber.

This feeding only happens at night, and ere morning, the delicate polyps will withdraw into their calyxes. Now, in the nighttime ocean, it is difficult to see their many colors; all sight has faded to shadows. 

The water is warm, 26° Centigrade (78° Fahrenheit), and has been for about a month. The light of the full moon is coming through the water in silvery ripples. It is time. 

Tiny orange orbs are drifting up from the coral polyps, no matter the color of the coral species. This is what consistently warm water coupled with the full moon trigger every October, November, or December on Australia’s Great Barrier Reef: the great coral spawn. 

The tiny gametes are full of fatty lipids, and will rise to the surface to meet. Each individual coral polyp produces both male and female gametes, but eggs and sperm from the same polyp cannot fertilize each other. Instead, the reproductive blizzard will float, and be mingled by the currents. After the eggs have been fertilized, they will continue to float until they hatch into larvae. If the larvae can find a suitable habitat, it will settle down and mature into a single polyp. The polyp will then begin to build a calcium-carbonate skeleton, the shape predetermined by the species. And so a new piece of reef will grow.

The vibrant eggs are dancing and swirling towards the surface. Follow them up. Some will never meet their match. Some will be eaten by fish and zooplankton. Some will be swept out into the deep sea and never find a resting place. But the ones who do will perpetuate these underwater islands of plenty.

Large, round, flattened shapes are rowing towards shore. Travel with them. There are other beginnings of new life to see. 

Here in the Southern Hemisphere, from the month of October through the month of February, female Green sea turtles come ashore to lay their eggs. The high tide tonight will help them get far up the beach, where their eggs will be safer; beyond the reach of the waves, the sea will be unable to excavate the buried treasure of pale, leathery-membraned orbs. 

Join the turtles as they haul out on the sand. Some are already as far up the beach as they are willing to go, and their rear flippers are scooping a nest hole. One hundred and ten eggs might drop into the sandy cradle. This is hard work for the mothers, and they take many rests throughout the night. 

Morning has come, and the turtles are laboring back to the sea. Strings of sandy slime hang from the corners of their eyes. Special glands secrete this fluid to remove excess salt from the turtles’ eyes. On land, it also helps to remove sand. 

Look out at the ocean and the reef beneath. See the orange slick on the surface. That is the next generation of coral.

With the aid of daylight, come under the waves one more time, and look well.

See the white corals. They are missing their algae. Without the symbiotic algae photosynthesizing, the coral tissue and polyps will eventually suffocate and die.

Come to the shore once more, and come inland. See the industrial crop fields spread out in a green patchwork. Know that the runoff of fertilizers from these farms are part of the reason the corals are bleaching.

Far away in Cuba, the coral reefs are some of the healthiest in the world. Core samples were taken from them. A long rod, from the newest growth on the surface to old growth deep inside, was removed. Much as tree rings tell of times of plenty or hardship, coral layers carry a record of all their years. When the age of each layer was examined, it was found that in the years when the Soviet Union had supplied Cuba with chemical fertilizers, the coral had struggled to grow. Once the Soviet Union's financial aid halted, economic hardship set in, and farmers on the biggest island country in the Caribbean turned to more traditional means of growing crops. With the strain of manufactured pesticides removed, the corals rebounded and flourished.

Every night, the flower-like polyps emerge, blooming across their shell-like frames in a riot of splendid color. Tentacles waving in the night currents, they prosper.