Oceans Of Life – Creatures Of The Deep
The ocean is a mystifying realm in which beauty and drama are intertwined in a never-ending cycle of life. While reaching for the moon and the stars, scientists and philosophers remind us that our knowledge of the earth and particularly the sea, is still in its infancy. Unlocking the secrets of the sea might turn out to be more vital to the continued viability of Planet Earth than any other human pursuit in the new millennium.
All life originated in the sea and its waters remain Planet Earth’s finest environment for life. 32 out of 33 animal life forms are to be found in marine habitats, with insects being the only ones missing. Of these, 15 phyla are exclusively marine. These include starfish, comb jellies and peanut worms. Sponges too live largely in salt water, where, in an enigmatic environment, dissolved gases and minerals combine with the life-giving powers of the sun to provide the raw materials necessary for life to thrive. The food web of the sea has its origins in silicon-encased unicellular plants or diatoms and works its way upward through microscopic plants and animals to larger creatures such as whales, sharks and seals that humans usually identify with the ocean world.
The sea is a very democratic space. No one species dominates the cycle of life. In fact, if one group were to ‘over-succeed’ it would seriously threaten all the others. This is probably why most marine species have taken to producing prodigious quantities of seed and offspring. The fecundity of most species ensures their survival, even if only an infinitesimal percentage of their eggs or larvae reach maturity. This has been the law of the oceans of life for over three billion years.
1. Giant clam, Tridacna:
These molluscs are efficient filter feeders, drawing in large quantities of water, which is squirted out after retaining organic materials from the ‘sea soup’. Giant clams have been known to grow to such an immense size (200 kg. and two m. across) that when they find a spot to settle, some may never move again for the rest of their lives! Coral often grows on and around such clams, leaving nothing but their soft edges visible.
2. Loggerhead turtle, Caretta caretta:
Related to the crocodiles, the earliest representatives of the testudinates (tortoises and turtles) showed up in the Triassic. Having undergone several evolutionary changes (a flattened carapace and limbs adapted for swimming) that helped them survive a series of natural catastrophes that pushed many reptilians into extinction, all five species of marine turtles now find themselves endangered across the world because of human actions.
3. Lionfish, Pterois volitans:
Amazing to look at, the scorpion fish goes by many names including lionfish, zebrafish, dragonfish, turkeyfish and firefish. The prominent array of spiny fins are supported by glands that produce a powerful venom that can dissuade even the most persistent predators. These fish can grow to lengths of 40 cm. and prefer to swim in shallows near reefs and rocks.
4. Spotted coral grouper or rockcod, Cephalopholis miniata:
This is a dark orange fish, covered from tip to tail with blue dots. Found from the Pacific to the Indian Oceans these fish may grow to a size of just under half a metre. Similar to the wrasse in some ways, groupers are often trapped for display in marine aquariums and this has depleted their populations around many reefs.
5. A mixed shoal of coral fish including the Black Pyramid Butterflyfish Hemitaurichtys zoster, Racoon Butterflyfish Chaetodon inaula and Saddleback Butterflyfish Chaetodon facula.:
Corals have rightly been called the rainforests of the sea. Their diversity is unparalleled, but they are seriously threatened by global warming and other ecological disturbances including pollution. Reef building corals need warm, shallow waters with a minimal silt content. Coral polyps are critical to reef building. Related to sea anemones, these animals however live in close colonies and secrete a hard substance around themselves. They multiply by budding into new individuals, each adding its own skeletal contribution to the coral base.
6. The Featherstar, a Crinoid:
These have an echinoderm ancestry. Their bodies are largely made up of calcium carbonate pieces, or ossicles, bound by ligaments and muscles. These strange creatures generally perch on corals but can also be seen swimming with help from thrashing tentacles, as seen in this image taken in the Lakshadweep waters. Special ‘ambulacral grooves’ are armed with cilia that hydraulically move captured food along the arms to the mouth situated at the base of the arms.
7. A school of trevally fish, (Caranx sp.?):
These fast swimmers are efficient predators and are targetted by the sportsfishing industry. The schooling behaviour of fish is the subject of on-going study. Clearly in the case of trevally, for instance, schooling helps the species to find food and also possibly to tackle prey larger than any one fish might be able to handle. However, the same schooling behaviour also helps smaller fish as predators find it difficult to single out one victim from a conglomerate of thousands. A common advantage is that weak or tired fish can swim in the wake of stronger members within the school.
8. Whitetipped reef shark:
This cartilaginous fish is so superbly adapted to marine life that fossil evidence has been unable to reveal major evolutionary changes over several million years. An apex carnivore, the shark’s existence swings between breeding and feeding. All sharks have an exceptional sense of smell. Using large muscles, especially evolved to provide forward thrust, sharks must swim continually throughout their lives to oxygenate their bodies. Sharks’ skin is a major sensory organ that keeps the fish informed of threats or opportunities around them. Misunderstood and persecuted, these evolutionary miracles are now becoming increasingly endangered.
Photographs: Hugues Vitry/Lacadives, Sanctuary Asia Vol XX No. 1, February 2000.