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Mantis shrimp, particularly the more colorful varieties like the peacock mantis, are popular subjects for underwater photographers and are welcome sights on dives throughout the Indian and Pacific Oceans. Usually seen in rock crevices or in the burrows that they create for themselves in the sea bed, mantis shrimp are exceptionally territorial. They are relatively small crustaceans, with the largest of the 400 species currently known only measuring around twelve inches in length. However, the mantis shrimp’s small size is by no means reflective of its identity both as a lethal predator and as one of the most fascinating of all marine creatures. There are many unique aspects about this shrimp, one of the most significant of which is how they catch and kill their prey.
There are two kinds of mantis shrimp; those equipped with spear-like appendages that they use to stab their prey, and those more advanced specimens that possess a developed club for smashing their food. These clubs are exceptionally powerful, enabling the mantis shrimp to strike at speeds of over 50 miles per hour, and pack a punch with the acceleration of a .22 caliber bullet. The power behind the strike is so extreme that larger species of mantis shrimp are able to shatter aquarium glass with a single blow, and are consequently rarely kept in captivity. The victim of a mantis shrimp’s blow is struck with a staggering force of approximately 1,500 newtons.
The devastating effect of the mantis shrimp’s club is compounded by the cavitational bubbles caused as a result of the sheer speed with which the animal strikes. The bubbles create a kind of shockwave that follows directly in the wake of the initial blow. The primary prey of the mantis shrimp species equipped with this incredible club include crabs and mollusks, while the spearing mantis favor fish due to their softer flesh. Amazingly, despite the level of impact that the club absorbs each time it strikes, a mantis shrimp can punch 50,000 times between molts without sustaining any damage to the club. Scientists are attempting to replicate this level of resilience by modeling military body armor on the design of the mantis shrimp’s cell structure.
For many years, experts believed that mantis shrimp could detect colors that the human brain is unable to process, due to the fact that mantis shrimp possess 16 different photoreceptors in their eyes, in comparison to the three possessed by humans. However, recent studies suggest that in reality, mantis shrimp encode color in a way that is completely unique to all other animals. For example, when the human brain looks at an object, it can determine the color by using its three color receptors (red, blue and green) in conjunction. Our brain understands that an object is yellow, for instance, because of the level of responsiveness it triggers in each of our receptors. A mantis shrimp, on the other hand, uses its sixteen receptors to pick up sixteen colors- they do not work in conjunction to allow the shrimp’s brain to process the mid-hues in between.
However, while the mantis shrimp may not inhabit as technicolor a world as we once thought, its eyes are still among the most complex in the animal kingdom. They are capable of moving independently of one another, and can detect polarized light, multispectral images and ultraviolet light. Certain species can even detect circularly polarized light, an ability that scientists are trying to harness in order to apply it to the next evolutionary stage in high definition technology. Why the mantis shrimp needs such advanced eyesight is uncertain, although it seems likely to pertain to mating and hunting advantages. Whatever the reason, the mantis shrimp’s miraculous vision combined with its incredible hunting technique make it one of the deadliest (and most intriguing) creatures in the sea.
There are so many wondrous things about scuba diving in the Galapagos that it’s hard to pick highlights. The remote archipelago is uniquely positioned at the point where the frigid Humboldt Current clashes with the warm waters of the Equator; as a result, each island is its own microcosm, and each one differs hugely from the next. It is possible in the Galapagos to dive with penguins one morning, and schooling hammerheads the next; it is a world of extremes where strange creatures found nowhere else in the world rule by day and at night the stars of both hemispheres cast their glow upon the ocean. The Galapagos Islands are rightfully known as one of the world’s premier dive destinations, thanks to the incredible productivity boasted by the 28,000 square miles of protected waters that surround the archipelago. I remember the diving there as a constant procession of incomparable experiences; a dizzy blur of consecutive ‘best dives ever’. Looking back, there are many exceptional encounters written indelibly upon my memory- coming face-to-face with an enormous Galapagos shark; watching penguins dart hungrily through a silvery curtain of baitfish; rubbing noses with a family of sea lions; entering a cavern filled with so many resting female turtles that I swiftly lost count. One creature in particular however managed to capture my imagination and my heart, and that was the peculiarly bewitching marine iguana.
As the planet’s only extant marine reptile, these iguanas are a complete anomaly; like many of their island neighbors, they are endemic to the Galapagos. On the islands, they make up for their absence elsewhere in the world by basking on the shoreline in their hundreds like a scaly, reptilian carpet. While the hours that iguanas spend sunbathing may seem luxurious, they are in fact vital to their survival. Because their diet consists solely of seaweed and algae, the iguanas spend much of their time in the ocean searching for food. When they surface, their cold-blooded bodies are so chilled that the lizards become lethargic and clumsy, and only the sun’s heat can restore them to normal functionality.
They are found on all of the Galapagos Islands, although experts have distinguished six distinct sub-species throughout the region. On land, the air resonates to the sound of the iguanas’ sneezing; a continuous cacophony as first one and then the next expunges the salt ingested during their time in the water from their nasal glands. This method of coping with their unusual habitat is not the only evolutionary trait that iguanas display- in addition, they possess laterally flattened tails and spiked dorsal fins ideally suited to life in the water. Their claws are longer and sharper than those of terrestrial lizards, to aid in clinging to rocks in strong current; and their flattened snouts allow for easier purchase when feeding on algae beds.
Seeing an iguana on land is one thing, but to see them underwater for the first time is mind-boggling. It is such an incongruous sight- a meter long lizard grazing along the seafloor as calmly as a cow put out to pasture. Capable of diving to depths of up to nine meters, iguanas are proficient swimmers, and to see them in the water is to witness a masterclass in streamlined efficiency and diving prowess. For me, marine iguanas define what is so special about the Galapagos- a place unrestricted by the boundaries and expectations of the rest of the world, and where absolutely anything is possible.
Last Friday, spectators onboard a whale-watching vessel in Canada’s Strait of Georgia witnessed the homecoming of the world’s oldest known orca. Affectionately known as Granny, the whale is estimated by the Center for Whale Research to have been born in 1911, making her a staggering 103 years old. Granny is the matriarch of the J-pod, one of three pods that make up the southern resident group of orcas that reside predominantly in Puget Sound, the Strait of Georgia and San Juan de Fuca during the summer, and head into open ocean during the winter. When she was spotted last week she was leading her family home, having been most recently sighted prior to that off the coast of California eight days previously. The distance between California and the Strait of Georgia is approximately 800 miles, and the fact that Granny seemed to have completed the journey with ease proves that although she’s a great-great grandmother she is still just as fit and healthy as the other whales in her pod.
Granny’s reappearance in her Canadian home waters is eagerly anticipated each year by the researchers that have been documenting the lives of her family since 1970, making them the most studied group of orcas in the world. She was identified last Friday by Captain Simon Pidcock of Ocean EcoVentures, who recognized her immediately thanks to a distinctive half-moon shaped notch on the edge of her dorsal fin. Just as Granny’s lifetime has seen countless human tragedies including the sinking of the Titanic and two World Wars, she had to survive through her own period of fear and unrest. In the 60s and 70s the capture of wild orcas from the waters of Puget Sound for sale into captivity was a common occurrence, and although the practice of taking orcas from the wild has since stopped, Granny’s family did not escape unscathed from those years of persecution. Although Granny herself managed to avoid capture, her relative Lolita was taken from Puget Sound in 1970 and sold into captivity. Seventeen years later, Lolita was the only survivor of approximately 58 whales captured around the same time. She still resides in Miami Seaquarium, in a concrete pen only 35 feet wide.
The comparisons between captive orcas like Lolita and wild ones like Granny underline once and for all why a life in captivity is not a humane option for animals as sociable and intelligent as these whales. Unlike Lolita, Granny does not have to perform tricks for a living; instead, her role is the passing down of knowledge to her extensive family. Granny spends all her time with 25 of her family members, while Lolita has lived alone for over 30 years – while Lolita’s every movement is restricted, Granny can travel hundreds of miles every day. Perhaps the most obvious comparison is in the life expectancy between captive and wild orcas. Although SeaWorld maintains that the lifespan of orcas kept by the entertainment industry is comparable to those in the wild, the evidence strongly suggests that this is not the case. While the average life expectancy for male orcas in the wild is between 40 and 60 years, and for females between 60 and 80 years, more than 60% of the orcas that have died in captivity were younger than ten years old according to the Center for Whale Research.
Granny’s incredible age serves as a testament to how long orcas can survive in the wild, and should not necessarily be regarded as an anomaly. Other whales from the southern resident group have reached equally impressive birthdays, including one individual that died in 2008 aged 98, and another female that is currently believed to be 87 years old. Ultimately, Granny’s reappearance last week should trigger bittersweet emotions- joy at the full and enriched life that she has led in the wild, and sadness at the plight of captive orcas, whose reduced years continue to be defined by boredom, humiliation, trauma and loneliness.
Sandtiger sharks are an aquarium favorite thanks to their ferocious appearance; with rows of crooked teeth and eyes of glinting gold, they certainly fulfill our expectations of the ocean’s most famous apex predator. Also known variously as ragged-tooth or grey nurse sharks, these animals are even more impressive in their natural environment, and those that have gone scuba diving in South Africa, Australia or the eastern coast of the United States may have been lucky enough to encounter them in the wild. Despite their fearsome façade, sandtigers are rarely aggressive towards humans, and can be seen in aggregations numbering tens of individuals during mating season. They are fascinating animals, with several strange characteristics that combine to make them a truly unique species.
The most famous of these characteristics is connected with the sandtiger’s method of reproduction. The female sandtiger has two uteri, which after impregnation may each contain as many as fifty embryonic babies. In a phenomenon known as intrauterine cannibalism, the first of these embryos to reach a certain size (usually around 10 centimeters) consumes all of its smaller siblings. After all of the other embryos have been eaten, the remaining baby shark in each embryo subsists on unfertilized eggs for the duration of its eight to twelve month gestation period. As a result of intrauterine cannibalism, the female sand-tiger will only ever give birth to two pups- one from each uterus. Thanks to its robust diet, the baby sandtigers emerge from the womb fully developed- at approximately 1 meter in length, they are immediately capable of fending for themselves against possible predators.
Known as embryophagy, this form of intrauterine cannibalism only occurs in sandtiger sharks. Although the embryos of other shark species consume unfertilized eggs in the womb in a process called oophagy, sandtigers are the only species in which embryos prey on other embryos. According to legend, the phenomenon was discovered by a researcher in 1948, who was bitten on the hand whilst probing the uterus of a pregnant sandtiger. Despite the fact that the perpetrator was yet to be born at the time, this incident was later recorded in shark attack records for that year. Researchers have several theories as to why sandtigers reproduce in this unique and slightly grisly way, the first of which relates to the large size of the surviving pup at birth. Sandtigers only reproduce once every two to three years, and with just two pups born each time they have one of the slowest rates of reproduction of all shark species.
As a result, it is imperative that both pups survive to reach sexual maturity if sandtiger populations are to be maintained. Whereas most shark species produce multiple young in the hope that probability will allow at least a few to make it to adulthood, the sandtiger chooses instead to produce babies that are already strong enough to cope with life in the ocean. Their unusual diet prior to their birth is undoubtedly the source of their unparalleled size and development. Other scientists theorize that intrauterine cannibalism is a struggle for paternity within the womb, due to the fact that female sandtigers mate with several males each breeding season. This habit results in embryos with different fathers, and experts hypothesize that intrauterine cannibalism is a mechanism for ensuring that the offspring of only one male survive. In a series of tests conducted on sandtiger embryos in various stages of development, researchers found that in the overwhelming majority of cases, the final two pups were full siblings.
Whatever the reason, the next time you come face to face with a sandtiger (whether it’s in an aquarium or in open ocean), remember to treat it with respect. After all, this is an animal that has been fighting for survival since before it was born.
From the Philippines to Micronesia, lionfish are a common sight throughout the Indo-Pacific, where their delicate beauty and charismatic nature have made them firm favorites for divers and underwater photographers alike. There are ten species of lionfish, most of which originate in either the Indian or Pacific oceans. Although each species varies slightly in size, coloration and appearance, all of them have several characteristics in common. These include fan-like pectoral and dorsal fins, bodies adorned with bands of vivid color, and highly venomous spines. As is often the case in Nature, a lionfish’s mesmerizing beauty serves as a warning of its toxicity- the venom in its spines is potent enough to put off any would-be predators, meaning that lionfish have very few natural enemies. Instead, lionfish are themselves the apex predators of the reef, using their large pectorals to fan prey towards them that they then swallow whole. They are perfectly adapted for their role, equipped with bilateral swim bladders that allow them to achieve flawless buoyancy whilst approaching their quarry.
The effect of lionfish venom on humans can be severe, with symptoms including vomiting, fever, convulsions, and in extreme cases, heart failure and even death. However, lionfish are rarely aggressive towards humans, preferring instead to focus their attention on the creatures that make up their diet. They are proficient hunters, preying predominantly upon juvenile fish, molluscs and invertebrates. In their native waters, this considerable appetite is a functioning part of the marine ecosystem that causes no issue. However, in the past twenty years lionfish have expanded beyond their natural habitat and are now found off the East coast of the United States and throughout the Caribbean. There, their presence has become a major cause for concern and has created a phenomenon known as the Great Lionfish Invasion. Exactly how lionfish were introduced into the Atlantic is a subject of much debate- some experts blame the aquarium trade, suspecting that the first specimens were discarded into the ocean by irresponsible owners, while others believe that lionfish were transported in the bilge pumps of long-distance container ships.
Whatever their origin, lionfish are now creating havoc upon the reef systems of the Western Atlantic and the Caribbean. Native fish species are not equipped to deal with the sudden invasion of such a successful predator, and the damage they have wreaked upon juvenile fish nurseries is devastating. In addition, the complete absence of any natural enemies combined with the favorable conditions of their new home means that lionfish populations have expanded by 700% in some areas over a four year period. As a result of the invasion, reef diversity in the Atlantic could be reduced by 80%. This is due in part to the removal of native species into less favorable conditions in an attempt to escape lionfish predation, and partly as a result of decimated juvenile fish populations. In an attempt to restore the balance, dive centers and conservation groups throughout the southern States and the Caribbean are introducing drastic measures in an attempt to control lionfish populations; including organized culls, the promotion of lionfish as an edible source of seafood and lionfish hunting derbies.
Ironically, while lionfish have come to be perceived as a dangerous pest in the Americas, they continue to delight divers in countries like Indonesia and Thailand. This animal that embodies both the beauty and the beast provides a constant source of debate – which side are you on?