Under the Tropical Keel
by Charles LoBue
You’re sailing along a tropical coast as it transitions from the turquoise waters of the sand and coral shallows to the rich indigo deep. The water beneath you is too clear to imagine. Under your keel, areas of lush sea grasses are preened to a rich beauty by the active feeding of thriving turtle populations, as shoals of juvenile fish dance and dart to the kinetic rhythm of survival among feeding predators. Mountains of colorful and varied coral structures create ridges, castles, bridges, corridors, and canyons in the transition to the deep. Every color imaginable is displayed by the thousands of reef fish throughout. A goliath grouper the size of a treasure chest stands watch inside a cave stalking its fishy prey. Schooling fish, barracuda, sharks, rays, and sea mammals cruise their fertile territory, in this bustling, beautiful, vital, valuable habitat, the coral reef.
This is the splendor of the Caribbean . . . about 80 years ago. Today’s coral reefs pale by comparison, impacted by any number of stressors caused by increasing human presence such as over fishing, land-based sources of pollution, ship groundings, ocean discharges, rising water temperatures, anchor damage, physical contact, invasive species, and so on. As these stressors were introduced over time, the early reefs were able to adapt in the short term; however, as the assaults build the current reefs are being overwhelmed and are showing signs of decline throughout the world. How does this happen? First, let’s understand the coral reef.
What is a coral reef? It is a very complex and sensitive living habitat that is built upon the physical structure created by stony coral. There are hard (or stony) and soft corals, but it is the stony corals that are bedrock of the reef. Coral is a class of colonial animal that lives throughout the world’s clear warm tropical oceans. Stony coral colonies, also referred to as coral heads, comprise hundreds to thousands to millions of little living individual polyps. At its minimum, coral is a polyp smaller than the size of your pinky nail. This miraculous little organization of cells is capable of drawing dissolved calcium from the ocean, and solidifying it into concrete structure for the polyp to live in. These structures grow into heads of various size and form. When you look at a coral head, only a thin veneer on its surface is live coral, the rest of the mass beneath is the rock-hard remains of years and even decades of living coral structure.
Sitting within its concrete housing, the coral polyp uses tiny tentacles to collect floating food into its gut for digestion. More significant to its nutrition, within the tissue of the polyp live symbiotic algae. These algae use the waste from the coral polyp’s digestion and energy from sunlight to manufacture food, by photosynthesis, for itself and subsequently the coral polyp. These symbiotic algae exist in all coral species, and give colonies their variety of colors. Corals can reproduce both sexually and asexually. Asexual budding of polyps allow a coral colony to grow in size. Sexual reproduction allows coral colonies to expel gametes into the water where they fertilize and ride ocean currents to new locations to spread their progeny. All species of stony coral make pretty much the same living eating, building shelter, preying and reproducing. The diversity of stony coral species accounts for a very large variety of coral head shapes and colony forms, such as elkhorn, boulder, leaf, and brain corals.
Colonies of various stony coral species grow together in aggregations to form reefs. As these reefs expand, they create larger areas of hard bottom upon which new corals can settle and grow, thus perpetuating the reef expansion. As coral reefs recruit more and more species, they grow in size and biological diversity. The expanding reef structure becomes a platform for other sessile organisms such as sponges, anemones, soft corals, tube worms, bryozoans, and assorted algae species. This growing biological and structural complexity creates habitat, stony holes, spaces, perches, and gaps, thus opportunities for more mobile animals to seek shelter. This complexity also creates a more diverse menu for animals to graze upon. Sea stars, worms, nudibranchs, shrimp, sea urchins crawl and graze upon this fertile biological realm. Lobsters, crabs, octopus, small fish vie for space within the reef structure to avoid their predators. Contrary to the reef’s sheltering design for these smaller critters, larger predatory fish are now attracted to this growing aggregate that’s brimming with tasty morsels. Over time the coral reefs amass magnificent structure painted with myriad biological communities, cemented by the vital balance of predator and prey relationships among all the reef’s organisms from the smallest plants to the apex predators, sharks.
In full splendor, coral reefs are complex spur and groove reefs, coral ridges separated by sandy grooves. They are magnificent walls starting near the surface and plunging into the depths of offshore trenches. They are broad barrier reefs, immense expanses of coral life that can extend hundreds of square miles around continents. They are low relief fields of simpler biodiversity; they are high relief networks of caves, cuts, and mounds of immense biodiversity and beauty. The stony remnants of coral reefs accumulating over geologic time have become the foundation for many tropical land masses and islands. Coral reefs provide many beneficial services to the human populations. The coral structure provides protection for land masses from damaging storm and ocean surge forces. The biological productivity provides vast fishing grounds for food supply. Biological diversity harbors organisms that can be harvested to produce pharmaceuticals. Many island economies are anchored by the immense tourism dollars brought in by masses attracted to the beauty of coral reefs. Coral reefs are valuable resources.
What’s harming the reefs? Perhaps the early stresses started with over fishing. Subsistence populations were first attracted to these areas by the abundant food production of the coral reef fisheries. As fishermen take the more attractive larger and schooling species, the overall impact of removing the apex predators could be profound on the fish populations beneath them in the food chain. Perhaps smaller herbivorous fish populations would grow. This could increase grazing on the sea vegetation. This change in the biological balance of species population dynamics within the reef may not doom the reef, but the natural course of reef development is altered, making them less resilient to the forces of change to come.
The real assault escalates as populations increase on the lands up slope from the coral reefs. By-products of this increasing development always flow downhill, ultimately to the reefs. The two most significant land-based items that currently plague the reefs are runoff sediments and human wastes. As the land is cleared for development, the natural vegetation that stabilizes the soils is lost, thus rainfall flushes these soils to the coastal waters. Corals require clear clean water, and are easily smothered by this foreign cover. Human wastes flowing into coastal waters cause a number of problems. Pathogens in the waste cause disease in corals. The chemical nature of the waste is fertilizer to aquatic vegetation. Over fertilization of coral reef waters leads to blooming of algae on the reef. Over blooming algae begins to grow on thriving coral heads. Those parts of the coral head covered by the algae die off. To add to the problem, many natural herbivores, such as fish and urchins, have been lost to over fishing and disease. With added nutrients and reduced grazing, algae easily over competes the coral heads. When living surface area of coral head dies off, the structure of the head begins to erode. As a once-thriving reef dies off, it is rendered to piles of stony rubble, and eventually all its structure will erode away.
As boat traffic increases, ship grounding and anchors physically damage the reef. Drop an anchor on a reef and corals will be broken. As the boat sits at anchor and the wind swings it back and forth, the anchor chain sweeps a wedge of devastation to the coral reef. To add to this, people swim and snorkel amidst the reef, and their touch and fins contribute to the physical damage. Although this may not seem significant over a vast area of reef, increasing boat traffic and population can incur death of the reef by a thousand cuts.
In recent years, global climate change has caused sea surface temperatures to rise to levels often critical to corals. When the sea water gets too warm, the corals eject all those symbiotic algae that are living within. Externally, the color of the coral disappears making them look white, or bleached. Internally the corals are starving as their photosynthetic food supplier is lost. When the water temperature returns to its natural condition, the algae return and the coral may revive. More often, however, corals are weakened by this bout of starvation, and become more susceptible to the other stressors in their presence. In 1998, a massive bleaching event in the western Pacific destroyed an exceeding large area of coral reefs throughout the Maldives and Micronesia. Those areas have not yet fully recovered to conditions prior to the bleaching. In 2005, a massive bleaching event occurred in the Caribbean. When the bleaching subsided, corals continued to die for two year following. The U.S. Virgin Islands lost more than 50 percent of their coral cover in those two short years.
A new threat has literally just arrived in waters of this hemisphere, the lionfish. Although invasive species is not a new phenomenon, the arrival of this Indo-Pacific species has exploded in the Atlantic and Caribbean. This fish has venomous spines and a voracious appetite for reef fish. Lionfish are beautiful, and in ecological harmony in their natural habitats; however, they’re proving to be devastating to reef fish populations of local waters, where those fish have no natural mechanisms to avoid their predation by lionfish.
What can we do? First, visit coral reefs, but do so gently. Witness the beauty that still exists. Awareness of this magnificent resource increases sensitivity and understanding of their great value and need. Notice how animals coexist: a clownfish living symbiotically within an anemone; a trumpetfish hanging vertically within the limbs of a sea rod soft coral; territorial reef fish skittering about their particular coral area.
As individuals, we can indirectly contribute to coral preservation by embracing standard environmentally friendly practices such as economical fuel consumption, reducing, reusing and recycling the materials that we consume, using environmentally responsible hotels at our tropical paradises, and supporting coral conservation efforts. We can more directly contribute to preservation of coral reefs in a number of ways. When sailing in coral waters, avoid shallows. Always use moorings and avoid any anchoring where coral may exist. Seek out proper pump-out facilities for boat wastes, and never discharge into coastal areas. Prevent trash or other ship-board items from going overboard. When dining out and ordering seafood, order those species that are considered sustainable. A helpful pocket guide to sustainable fish can be found at the following website:
www.montereybayaquarium.org/cr/cr_seafoodwatch/download.aspx. When snorkeling or diving, watch those fins and don’t touch anything. Don’t limit your conservation efforts to these few suggestions, but always be aware of how your presence or activities could possibly hurt the delicate reefs.
The beautiful and vital coral reefs of the world are under great siege these days.
Their decline can be slowed and maybe even reversed. The difference between recovery and losing them forever will be determined by how well we people respond to the challenge of its conservation. As typical of sound environmental response, it requires a balance of needed economic drivers with vital ecological requirements. It will take increased awareness of this challenge and sincere determination to maintain this resource that we can’t afford to lose.
Photographs © Copyright Charles LoBue
© Copyright Charles LoBue and Black Laser Learning, Inc. 2008-2013