Diving With Marine Life
Marine life is far more diverse than life on land. At present, scientists have described nearly 200,000 species of marine plants and animals, and new ones are discovered all the time. Most inhabit the sea. About a tenth of all plants — namely brown, red, green, and other kinds of algae — are found in salt water; the 3,000 species of ocean chordates (animals with backbones) roughly equal those on land and in fresh water combined.
But it's the invertebrates that really rule the sea: 130,000 species of everything from corals to chitons to sea cucumbers, comprising nearly a tenth of all known life on Earth.
Few divers have trouble imagining themselves descending through clear, azure water to a sun-dappled reef, vivid in color and vibrant with life. Although tropical rain forests, the closest terrestrial counterpart to coral reefs for biological diversity, harbor many more species, tropical reefs are nonetheless one of the richest repositories of life on the planet.
Though often mistaken for plants, reef-building corals are animals resembling and related to sea anemones. Corals include four distinct groups of animals: stony corals, hydrocorals, octocorals, and black corals. Only stony corals construct reefs, but most corals live in colonies and possess some form of rigid outer skeleton. Not all corals are tropical; some thrive in deep or cold water, even close to the poles. But corals occur at their most lavish in the warm, clear, shallow water straddling the equator.
It's amazing to think that such massive structures as Australia's Great Barrier Reef and the barrier reef off the coast of Belize are the handiwork of a tiny, stationary animal, the coral polyp, which resides in a cup-shaped pore in a reef by day and emerges at night. The tentacled polyp takes in calcium and carbon dioxide from surrounding seawater to make its external castle of calcium carbonate. Reefs could not be built, however, without the single-celled algal tenants living within the gut of each polyp. Known as zooxanthellae, the algae nourish the coral and enable the reef to grow. Individual coral structures can look like giant brains, mushrooms, lettuce leaves, and deer antlers, but together they create an intricate maze of shapes and textures that characterizes a coral reef.
Baleen whales are the biggest creatures in the ocean, but divers rarely encounter them. Two exceptions among them are the humpback whales that winter near the Hawaiian island of Maui and the Atlantic humpbacks that winter on the Silver and Mouchoir banks in the Turks and Caicos. Lucky divers may see newborn calves swimming beside their mothers and feel the rumbling, resonating vibrations from the whales' high-pitched calls. Each year, the whale song picks up where it left off the previous winter and advances with a new series of stanzas.
More commonly seen marine mammals are seals and sea lions. Divers may observe sea otters in Monterey Bay and manatees in Florida, although both remain very rare and are protected by the Endangered Species Act. Also remember that from sea otters to blue whales, all ocean mammals have the federal government behind them in the form of the Marine Mammal Protection Act. This law prohibits any harm or harassment of marine mammals on land or at sea, and anyone even approaching a marine mammal closer than 50 feet can be fined. Curious sea lions may investigate a diver — and almost certainly will if the diver has been spearing fish — and perform a few acrobatics before quickly vanishing, but don't pursue them. Besides, they have the home-field advantage and will be gone with a few flaps of their flippers.