The World Beneath. Richard Smith

The World Beneath - Richard  Smith


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      Detail of a giant clam’s mantle. Great Barrier Reef, Australia.

      Not all corals contain zooxanthellae, and it tends to be simple to tell which ones do. Zooxanthellae typically have a beige coloration, so corals containing these algae tend to be beige. Non-zooxanthellate corals (those corals without intracellular algae) tend to be much brighter in color. Most of the bright colors you might associate with coral reefs come from organisms that do not have symbiotic algae. These animals obviously do not benefit from contributions of a symbiont; however, as they do not require access to sunlight (a key ingredient in Darwin’s Paradox), these corals are not as limited in where they can grow. They will often proliferate inside large overhangs or caves that receive little natural light.

      Detail of non-­zooxanthellate soft coral polyps. Raja Ampat, West Papua, Indonesia.

      Rather than deriving nutrition from their symbionts, non-zooxanthellate corals mostly filter feed and usually situate around parts of the reef where nutrient-­rich currents hit. Nutrient-rich water tends to be rather murky, which explains why—in that setting—the vibrant colors of soft corals, sponges, and other filter feeders truly come alive.

      At 100 feet beneath the surface, filter-­feeding organisms proliferate. Komodo Island, Indonesia.

      Triton Bay in West Papua, Indonesia, experiences localized seasonal upwellings of cool, nutrient-rich water that turn the existing water into a green soup. The first time I dived there, descending with a little hesitation into the eerie water, I wasn’t sure what to expect. When I reached the seafloor I was taken aback by the profusion of growth and riot of color. Without having to compete with light-loving corals, other organisms had been able to proliferate. Soft corals in reds, pinks, yellows, and purples covered every inch of the reef. In an illogical contradiction, most color exists in the gloom.

      In plankton-­rich waters, invertebrate life grows in profusion. Triton Bay, West Papua, Indonesia.

      Soft corals do not produce a ridged calcium carbonate skeleton like hard corals do; rather their structure is based on a mesh of tiny calcareous rods, known as “spicules.” During the parts of the day when currents aren’t flowing, soft corals shrink, forming small spiky balls. As currents begin to pick up, they swell and expose their polyps, which can then begin to trap plankton from the passing water. These corals, which live without zooxanthellae, are also found in the deep, lightless sea where individual colonies grow extremely slowly for thousands of years. Twenty thousand feet below the surface, in water of 30 degrees Fahrenheit, life continues at a slower pace. Without the volatile climatic conditions experienced in shallower waters, the corals here have created rich but fragile ecosystems that are home to their own unique fauna.

      Where Corals Grow

      With the symbiotic coral-algal powerhouse facilitating growth of corals in clear tropical seas, few other organisms in this habitat are able to compete. However, corals do have specific environmental requirements; where these are not met they can be outcompeted by other organisms that are more tolerant of the particular conditions. On the whole, corals have a few basic ecological requirements to maintain meaningful reef building growth.

      I have seen firsthand how this extension of the warm East Australian Current has had an unfortunate impact on the historically cool waters of southern Australia. In 2011, I visited the Tasman Peninsula in southeast Tasmania to dive the giant kelp beds. Much like the famed kelp beds of California, these giant algae form huge dense and towering forests. These kelp beds were known as being similarly impressive as their northern Pacific counterparts, and it was the only time I have had the chance to experience this amazing ecosystem. The kelp beds were previously so dense and widespread as to allow commercial harvesting but have gradually dwindled over the years. I dived one of their last real strongholds, Waterfall Bay, in southeast Tasmania—where colorful weedy seadragons and a wide variety of other unique creatures exist.

      Robust coral growth enduring crashing waves. Egyptian Red Sea.

      Huge and elaborate coral growth can take many decades or even centuries to grow. Egyptian Red Sea.

      Competition


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