Walking With Sharks

              

Epaulette Sharks

   Epaulette sharks are a family of sharks that are known for their peculiar mode of locomotion. They are named so because of the large spot that resembles the insignia worn by soldiers of armed forces. These sharks are nocturnal and are usually found in shallow water, sometimes barely reaching a depth sufficient enough to cover their bodies. They are found in Australia, New Guinea and Indonesia, where a new species was discovered recently. As absurd as it may seem, their primary mode of locomotion is walking. They use their pectoral and pelvic fins to waddle on the sea bed. They swim only to escape a threat and always prefer to walk. These sharks have another interesting ability. They are capable of tolerating extremely low oxygen concentrations. These sharks often get caught in tide pools that get separated from the ocean due to the recession of tides. The amount of dissolved oxygen in the water of these isolated pools drops drastically overnight. So how do these sharks survive in such hypoxic conditions? In such situations, they increase their blood supply to the heart and brain and selectively shut down the unnecessary neural functions. They reduce their blood pressure by dilating their blood vessels. Shutting down the metabolism of certain areas of the brain like the motor nuclei, while keeping the sensory nuclei active, keeps them alert and also saves energy. It has been found that these sharks show this hypoxia tolerance even at high temperatures. This is peculiar because most other organisms that can withstand hypoxic conditions can do so only at low temperatures. These sharks, usually less than a 100 centimetres long, can adapt to and survive in hypoxic environments, which to me is equivalent to any super power flaunted by any comic book hero.

A Decorator Crab's Disguise

Decorator Crab

Decorator crabs, also called Sponge crabs or Dresser crabs, are enthralling creatures. These crabs have successfully found a way to hide from their predators. How do they do this? As their name suggests they decorate and dress themselves with bits of corals, sponges, sea anemone and whatever else they can get their claws on. They have a set of specially adapted legs that they use to cut large sponges and coral into small bits. They place these decorative objects on their shells which bear Velcro-like spines. The objects placed on the crab’s back are fastened by these spines and completely change the appearance of the crab. Their disguises help them hide from their predators because they are now camouflaged with their surroundings. The crabs observe their environment and design their shell accordingly. When they sense the presence of a predator, they freeze. These ‘decorations’ can also provide a form of chemical defence. Some types of decorator crabs place poisonous sea weeds on their shells. Some have sea anemones on their backs. These sea anemones have stinging cells, giving the crabs’ predators another reason to stay away. Some of the crab’s living decorations continue to grow. When they become too big, the crabs simply cut them again. When crabs grow, their shells, which cannot expand enough to accommodate them, are discarded and new ones are formed. Decorator crabs recycle their ornaments, removing them from the old shell and placing them on the new one, once it is fully formed.  These crabs may even use man-made materials, like clothes, slippers and sandals that have found their way into the sea. For these crabs, what they wear is very important because it could potentially save their lives. 

Miniature Stallions Of The Sea

Denise's Pygmy Seahorse

The oceans are usually associated with organisms so enormous that they would put an elephant to shame. But some organisms are so small that they almost always go unnoticed. Pygmy seahorses fit in to the latter category. They are similar to regular seahorses but a few morphological differences and their size sets them apart. Pygmy seahorses can be as small as 1.4 cm. The largest ones are around 2.7 cm in length. So its not surprising that most pygmy seahorse species were discovered only in the 21st century. Unlike the bigger seahorses, pygmy seahorses are found in tropical coral reefs, usually in association with certain corals. A species called Bargibant's pygmy seahorse is very particular about it’s habitat. It spends it’s entire adult life anchored to a single coral. This species is exceedingly specific about the type of coral it chooses. It is always found on Gorgonian corals of the species Muricella paraplectana or Muricella plectana. Some Pygmy seahorses are more accepting of other species of corals. Denise’s pygmy seahorses can be found on several types of Gorgonian corals. These seahorses assume the appearance of the coral they live on, at a very young age. The young of this species, like all other pygmy seahorse species, are released from the male’s brood pouch with considerable force. They are carried away by the current and feed while floating, till they grow. They then settle down on a coral and their dark-coloured bodies change and flaunt more vibrant hues. They not only change colour but also texture, growing bumps or projections on their bodies, donning a new look, to match the corals they will spend the rest of their lives on. Not all pygmy seahorses prefer corals as their home. A species called Pontoh’s pygmy seahorse is seen in pairs or small groups on calcareous algae. The smallest species of seahorse, Satomi's pygmy seahorse, is extremely challenging to find, not only because of it's size but also because it is nocturnal. This also makes it hard to study their behaviour. There is still so much that is not known about Pygmy seahorses. There may be several more species, hidden in the sea, evading discovery. They may be difficult to find but it would, undeniably, be worth the effort. 

Bargibant's Pygmy Seahorse

A Thousand Tiny Tunicates

A Single Salp

There are several transparent and translucent organisms that dwell in the ocean. This transparency helps them blend in with the surroundings and hide from predators. Some are too inconspicuous to be noticed when alone, like the tunicates, Salps. Though they are quite abundantly found in oceans, not many people know about these tiny, transparent creatures. They have small, crystal clear, sac-like bodies with openings at both ends. Though they resemble jellyfish, these salps are actually ancestors of vertebrates, like fish, and even have a heart, gills and a vascular system. In the larval form, they have a primitive backbone, eye and a hollow brain.  They contract their sac-like bodies, taking in water through one end and expelling it out the other. This water, before being dismissed from their bodies, is filtered for food like phytoplankton. Sometimes these salps travel and feed alone and sometimes they form huge colonies by linking themselves to other Salps. Each salp, depending on the species, can grow up to a length of a few inches but Salp colonies can extend up to fifteen feet in length. Some species even exhibit bioluminescence and their colonies appear like long, glowing chains in the oceans. Large salp colonies indicate to fishermen, the presence of Pomfret and Herring as these prized fish feed on them. Salps are significantly more abundant where there are phytoplankton blooms. Large colonies voraciously devour the copious amounts of phytoplankton. The salps even bud off clones of themselves to partake in the feast. They are believed to be the fastest growing multicellular organism because of their ability to clone themselves. Since Salps are filter feeders, they feed on even the tiniest diatoms and protozoa. Scientists find it hard to trap such minute organisms to study. So now biologists catch salps and study the contents of their stomach instead, to get to the microscpoic creatures. These tiny salps are used to catch even smaller organisms. Salps, though small, have a major impact on the ocean’s carbon cycle. When salps die after a bloom, billions of their bodies, along with their faecal pellets, carry colossal amounts of carbon to the ocean floor. So these inconspicuous, unfamiliar, tiny creatures could be affecting a massive global phenomenon like climate change. 

Salp Colony

Ocean's Slugs

Sea Slugs

  

   Sea slugs or Nudibranchs, with their varied colours, shapes and sizes, are significantly more fascinating than terrestrial slugs. The bright colours worn by slugs in the ocean indicate, to their predators, that they are armed with potent toxins. This is just one of their many defence mechanisms. Some slugs are capable of blending into their backgrounds so well that they are barely visible to their predators. Some bioluminescent slugs warn their predators of their toxicity with a hypnotic display of blinking lights. Some change their behaviour to avoid predators by becoming nocturnal and or even staying dormant most of the time, only swimming for short periods when disturbed. The most remarkable defence mechanism of slugs is shown only by a few species of the Aeolids group. These slugs actually steal the defence mechanisms of their predators. Some organisms like sea anemones and jellyfish have special stinging cells along their tentacles. These stinging cells, when triggered, shoot out tiny spear-like structures called Nematocysts, that can attack either their prey or predators. When sea slugs are attacked by creatures with these stinging cells, the chemicals in their slime keep the nematocysts from liberating. This makes sure the slugs don’t get stung. They then ingest the stinging cells with unreleased nematocysts. Some of these cells are digested and excreted out while the younger, immature nematocysts are stored for later use, in pouches called Cnidosacs. When these Aeolid slugs are provoked, they use the pilfered stinging nematocysts to protect themselves from predators. One of the most well-known strategies in any kind of conflict is to take advantage of the enemy’s weakness. What these Aeolid sea slugs have managed to do is use their enemy’s strength to their benefit. 

Where The Stars Fall

Vaadhoo Island in the Maldives

Bioluminescence, one of the most fascinating natural phenomena, can also be caused by tiny, microscopic, single-celled organisms. Dinoflagellates, possibly the most interesting of all phytoplankton groups, are called so because they have two flagellae which are thread-like appendages that help them swim. These microscopic creatures, like other phytoplankton, experience various bloom cycles. When abundant, these Dinoflagellate blooms can show themselves as red tides or as sea water speckled with bioluminescent dots reminiscent of a star filled sky on a clear night. So how do these unicellular organisms mimic the stars that are light-years away? Research has shown that their cells and cell membranes have special channels that allow only protons to go through. The movement of surrounding water creates electrical impulses that trigger or stimulate the proton channels to elicit a chemical reaction. An enzyme called Luciferase reacts with an oxygen-rich compound called Luciferin to form Oxyluciferin. This reaction produces that bright, captivating light that illuminates the Dinoflagellates. Large colonies of these bioluminescent organisms are found in warm water lagoons and can light up the entire beach, especially on windy nights as the phytoplankton get agitated by the movement of water. Dinoflagellates use their bioluminescence to defend themselves from their predators, fish. These organisms are toxic to fish and flash their lights as a warning to them to avoid being eaten. Sometimes this light attracts predators of the fish, like sperm whales, who feed on those fish that were tempted by the phytoplankton. People too take advantage of this bioluminescence to guide them. When a ship travels on water abundant in these Dinoflagellates, they leave behind a trail of luminescence. Aircraft carrier-based jet pilots have been known to use these trails to find their way back in the night. The multitude of these single-celled creatures, like large neon signs, guides the aircraft to the ships and to land. The sight of a million glowing dots in the ocean is one that words cannot express. No picture or movie can capture it.  The ocean is the only place on earth where you can see something as magical a glowing lagoon saturated with fallen stars that have not lost their brilliance. 

A Ship Leaving A Luminescent Blue Trail

Ode To A Sea Snake

“Beyond the shadow of the ship,

I watched the water-snakes:

They moved in tracks of shining white,

And when they reared, the elfish light

Fell off in hoary flakes.

Within the shadow of the ship

I watched their rich attire:

Blue, glossy green, and velvet black,

They coiled and swam; and every track

Was a flash of golden fire.

O happy living things! No tongue

Their beauty might declare:

A spring of love gushed from my heart,

And I blessed them unaware:

Sure my kind saint took pity on me,

And I blessed them unaware.

The self-same moment I could pray;

And from my neck so free

The Albatross fell off, and sank

Like lead into the sea.”

                               - The Rime Of The Ancient Mariner

Yellow-bellied Sea Snake

Sea snakes are the creatures that brought a chance at redemption to the mariner in Coleridge’s poem, “The Rime Of The Ancient Mariner”. It was the deed of appreciating their beauty that liberated him from the weight of his sins. As the mariner conveys in the poem, no description of these snakes can truly do them justice. Different species of sea snakes vary in colours and patterns. Many have alternating rings of black, red, grey, white or blue. Some have a single colour adorning their bodies. Their length ranges from four feet to nine feet depending on the species. These snakes are closely related to cobras and though they have adapted to marine environments, in other ways, still use lungs to breathe. This mean they have to come up to the surface for air occasionally. They can then dive down to a depth of 300 feet and stay without breathing for half an hour. They have valves that keep their nostrils covered under water. Research shows that their skin has adapted to aquatic life such that it can absorb small amounts of oxygen directly from the water. They have laterally flattened bodies and a paddle shaped tail that functions as an oar when the snakes swim. The mesmerising, undulating motion of their bodies propels them in water. They also have specialized sub-lingual glands that help in secreting excess salt from their bodies. When they stick their tongues out, the gland secrets a substance that has a high concentration of sodium chloride. One of the most incredible things about these snakes is their venom which is in the same class as some of the most potent and powerful venom found in the natural world. Their prey, consisting of fish, fish eggs, crustaceans and molluscs, feel the effects of the venom immediately. An enzyme is also secreted that starts the process of digestion as the prey is being swallowed. What is even more incredible than their potent venom is their docile and timid nature. They rarely bite people and bite only when provoked, though it is said that most people don’t even realize they've been bitten till the symptoms start to show. They only use the venom for defence and to eat. Like most animals (other than humans) they kill only when necessary. This docile nature, in spite of being equipped with deadly venom, is where their beauty lies. 

Banded Krait

How Fossil Fuels Can Kill Nemo

Orange Clownfish

If global warming has taught us anything, it’s that our actions however small can have a huge, unexpected impact, locally and globally. The fossil fuels we burn, the energy we waste can set off a chain of destructive reactions that affect even the smallest creatures in a dramatic way. Orange Clownfish, made popular by the Disney movie ‘Finding Nemo’, are coral reef fish that live among anemones with whom they have a symbiotic relationship. These fish live in relatively warm waters and like a lot of other marine species, are severely affected by ocean acidification. The ocean acts like a sink for carbon dioxide as it absorbs a large percentage of it from the atmosphere. A significant increase in the amount of this gas in the atmosphere leads to a corresponding increase in the amount absorbed by the ocean. This in turn is responsible for lowering the pH of water. This acidification is dangerous to clownfish and several other marine species as it alters their ability to perceive sound and smell.  This degrading effect on their auditory and olfactory senses implies that their attempts to respond to and evade predators would be unsuccessful. These fish lose their ability to identify kin and predators by way of smell. Hearing is also important in escaping predators, especially for juvenile clownfish. In an experiment conducted by Dr.Steve Simpson at the University of Bristol, Clownfish were placed in water which contained enough carbon dioxide to mimic today’s conditions. These fish were able to respond to predators successfully. But when placed in water containing carbon dioxide corresponding to the amount expected in 2050, the fish did not respond to the predators and could not evade them. So an increase in this greenhouse gas in the atmosphere comes with a decline in the number of clownfish. Although this species is not listed as threatened due to the large number of eggs they lay, finding Nemo may become much more difficult in the future. 

Now You See Me, Now You Don't

Octopus Camouflage

Fight or flight? These are pretty much the only defence mechanisms humans can use in a dangerous situation. It’s not very impressive when compared to those of other organisms, like octopuses, who have other jaw dropping abilities at their disposal. Octopuses are usually seen as the organism with eight tentacles, a culinary delicacy in some places that has the ability to “predict” and identify the soon-to-be victorious football team in world cup matches. But its abilities extend much further than that. These intelligent cephalopods, like squids and cuttlefish, are masters of camouflage. They are so good at it that they put chameleons to shame. They can change not only the colour of their bodies but also the texture, when they are threatened. This ability, like an invisibility cloak, hides them so well and so quickly that the predator is just left bewildered and hungry. This disappearing act, far superior to that of any magician's, is one of the octopuses’ defence mechanisms.  So what is the secret behind this trick? The skins of octopuses have several thousand sac-like cells called chromatophores. These cells are filled with various coloured pigments. When the chromatophores are stretched or expanded, their colour becomes visible on the surface of the skin. Controlling these chromatophores bring about a colour change in an octopus. They also have reflective cells called iridophores and leucophores that can lend an iridescent appearance to their skin. To modify the texture of their skin, they change the size or height of muscular projections on the skin called papillae. How these octopuses perceive colour is still a mystery because lab tests have shown that they are colour blind. The varied colours of the ocean and it’s organisms are just shades of grey to them. It is believed that they might “see” with their skin as it contains light and colour sensing cells. And if all this doesn’t discourage the predator, the octopus has more tricks up its sleeve.  The mimic octopuses alter the position of their legs, shape of their bodies and their movement to imitate venomous and more dangerous creatures in the ocean like sea snakes and lionfish. This change in appearance successfully scares off predators, leaving the octopus unharmed. If none of these tricks work, the octopus resorts to squirting ink and swimming away swiftly. These eight–legged creatures and their magical acts can captivate any audience and receive standing ovations every time.  

In An Octopus's Garden

Where would you go if you could go anywhere in the universe? Visiting different planets in distant galaxies seems appealing but I would rather go into the oceans of our own planet. The depths of the seas may seem to have as much life as mars, with absolutely no light penetrating through to the bottom. In reality, the dark abyss of every ocean is teeming with life, much of it still undiscovered.  The creatures, whose existence we know of, are fascinating. Saying they are relatively large is an understatement. The Giant Spider Crab can reach a length of 12 feet from claw tip to claw tip. The Giant squid, first captured on screen only in 2013, can be as tall as a two-storey house. In spite of the size of these creatures, they are still difficult to find and often go unnoticed. They seem like creatures that could star in any interesting sci-fi movie. It’s not just their size or their deep-sea gigantism that is fascinating. They have various unique adaptations to survive in a habitat as inhospitable as Pluto. The Anglerfish takes advantage of the darkness to use its bright lure to attract prey. The Fangtooth fish, as the name suggests and the Wolf fish have extremely sharp teeth which are so long the fish find it hard to close their mouths. They too would be perfect for a sci-fi movie. The Vampire squid, named so not because of a thirst for blood but because their tentacles, when extended, resemble the type of cloak vampires (especially Dracula) have been associated with. In the darkness of the deep sea, bio-luminescence has become common in organisms to either attract prey or disorient predators. Their displays of luminescence can match any display of lights on land in big cities. Atolla or Crown jellyfish use bio-luminescence as a last resort or a final plea for help when being attacked. It’s mesmerizing, luminescent display draws the attention of the attacker’s predator that kills and feeds on the attacker giving the Atolla time to escape. In the deep sea too, an enemy’s enemy is a friend. These interesting creatures are just a fraction of what actually exists in that mysterious realm of the ocean. It’s absurd that we’re trying to find life on other planets when we haven’t even discovered all the life on our own. There is still so much left to uncover. Mike deGruy, an underwater cinematographer, described the deep sea as the best place to go to see something you've never seen before or to see something no one has ever seen before. So if I could go anywhere in the universe (and return alive) I would quote the Beatles and say:

           “ I’d like to be,

              Under the sea

              In an Octopus’s garden,

              In the shade. ”