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Discovery - Virtual tours of the underwater world
Mark Norman, Museum Victoria
This specimen of this thin lanternfish came up in especially good condition. These small fishes usually lose their scales very easily. Lanternfishes belong in the family Myctophidae, a large of family of hundreds of species of small fishes, typically less than 10 cm long. They are so abundant in the oceans that some people suggest that they are the most common sort of fish in the sea. Lanternfishes are recognised by their small light organs dotted along the undersides of their bodies. They are very important food for many animals from fish and squid to seals and whales. Some species have extra light organs for attracting mates and possibly for seeing their prey. The lights can be turned on and off. These fish migrate up through the water every night, moving into shallower waters to feed under the cover of darkness. Some of the deeper forms have swim bladders full of oil instead of air to make them buoyant. They feed on small invertebrates in the plankton.
These two deep-sea animals have come to a very agreeable arrangement. Hermit crabs have long soft bodies that must be protected. So they like to live safe inside other objects, typically shells. As shells can be rare in the deep sea, these hermit crabs have worked out a way to live inside a relative of anemones and corals known as “zonathid”. Most corals and anemones need a hard surface on which to settle and grow. Most of the deep sea is mud and sand, so hard surfaces are rare. By these two animals getting together, they both benefit. The crab has a safe home in the tough leathery body of the zonathid, it may even be protected by the coral’s stinging tentacles. In return the coral gets carried to new places that might have more food, including the sorts of foods that the hermit crab scavenges. It is not known how this union starts but it’s possible that the two get together from a small size and grow up helping each other out.
Stargazers are a family of muscular bulldog-like fishes that typically bury in the seafloor and ambush passing prey. This deep-sea species is a bit different. It was originally described from a flabby looking animal (like the one shown) with eyes towards the top of its head and scales embedded in the soft skin. Around 20 years ago, Martin Gomon and Peter Last (both on board) discovered a very different looking stargazer, square in shape with eyes on the sides of its head, large spiked scales, horn-like ridges on the head and a silver blue colour along its sides. They thought they had discovered a second species in this poorly known deep-sea genus. At about the same time, a Japanese colleague made a similar discovery and found that he had specimens that connected these two different looking animals as growth stages of the same species. It turns out that around 28 cm long, members of this species suddenly go flabby and their spikiness disappears (are there parallels with humans here?). In their publication describing the large juvenile, Gomon and Last made the radical suggestion that the juveniles must be swimming off the sea floor and living a pelagic lifestyle, behaviour unheard of in stargazers of that size. Criticized at the time, their prediction proved true when long-lining fishermen started catching the large spiky juveniles hundreds of metres off the seafloor. It turns out that all stargazers have a pelagic juvenile stage but in other species they settle out at a very small size.
Hatchetfishes live in open water as one of the vertical migrating species. They get their name from their axe-like shape. Last night we caught an excellent specimen of the largest species in this distinctive family (family Sternoptychidae). This species reaches about 12 cm long. Members of this type of hatchetfish have telescopic eyes that aim upwards and give a clue to how they hunt. As with many creatures of the ocean’s mid-depths, one way of finding food is looking for the shadows of animals passing overhead. The slightest silhouette would allow these animals to shoot up and swallow their prey. So they need to swim where there is just enough light to see shadows above. This can be very dangerous as they might also be seen. As a consequence they have evolved numerous complicated light organs on the undersides of their bodies, seen as rows of silver oblong patches. The silver tissue strips are reflectors. The lights are at the top, are pink and face down. They use the chemical enzyme luciferase, which gives of light when it is broken down. Just enough light is given off to hide their silhouette.
These jelly-like octopuses only occur in the deep sea. They differ from other octopuses in that they have a pair of fins on their body that they flap to glide through the water. It makes them look like the cartoon character Dumbo the Flying Elephant. They have a very soft jelly body and deep webs between the arms that can be spread out to glide looking like a frisbee, powered by the flapping fins. They are often found near the seafloor where they glide just above the surface using rows of little sensory hairs along their arms to sense prey buried in the mud. These sorts of octopuses have been found down to at least 5 km deep. Some reach large sizes, more than three metres from armtip to armtip. Operators of research submarines have been shocked by large ones swimming past the portholes and blocking out the light.
These small eel-like animals are not eels, they’re actually related to blennies. Their name comes from their eel shape and big pouty lips. This group of fishes is very common in the northern hemisphere with hundreds of species, some getting very large like the 2 metre long Wolf Blennie of the northern Pacific Ocean. In the southern hemisphere, this family is represented by only a few small species mainly from the deep sea. The bottom-living forms like the one shown are very rare, there are only a handful of specimens in New Zealand collections and only one specimen in all of Australia ’s research collections. There is still very little known about these rare fishes.
Specimens of this large pointy nosed rattail were captured last night. This species was named several years ago by the day shift team leader Peter MacMillan, a NIWA research scientist who is onboard. These sorts of rattails feed in the muddy seafloor by gliding along head down and tail up, powered by gentle undulations of a long fin under the tail. The triangular head has sensory cells underneath that help detect animals buried in the mud or sand. The tough scale armour on the head protects them from anything that might leap out and try to eat them. The mouth faces down and can be pushed deep into the mud. The common name comes from the black edges around the mouth. As in other rattails there is a small light organ on the underside of the body that is fuelled by glowing bacteria. The function of this light is unknown as it is too small to hide the fish’s silhouette.
Spineback eels are fairly primitive fishes that are related to true eels in that they share a similar juvenile form. They both have “leptocephalus larvae”, planktonic young that look like a swimming transparent gum leaf with a tiny pinhead stuck on the end. The name, leptocephalus, comes from the Greek words for leaf and head. These fishes get their name from the row of collapsible spines midway along their back. They have a distinctive rounded head and small mouths that they use to feed on small invertebrate s on the seafloor including crustaceans and worms. Some spineback eels have been reported as feeding on sea pens, soft coral colonies that stick out of the mud. The head has a special sensory system of mucus-filled canals visible as rows of dots on the face.
Most sea urchins have a hard skeleton known as a “test” that holds their round shape and anchors their spines. They often wash up on beaches as round hollow balls after the urchin has died. Some deep-sea urchins use fluid pressure instead of a rigid skeleton to hold their shape. When these sorts of urchins are caught in the net, they collapse and the water leaks out. By the time we see them they are soggy leathery pancakes. These sorts of urchins have poison sacks on the tips of their short tentacles. When an animal pushes on to a spine the poison sac ruptures. It is not known what these animals eat as their intestines are also lost when the body fluids escape. Using fluid pressure to maintain shape is a good idea as it uses less energy than making a skeleton. Many soft corals use the same trick, holding themselves up by internal water pressure, compared with their hard coral relatives that have to slowly grow their own rigid skeleton.
For me, this bizarre fish (the size of a tennis ball) is one of the most fascinating creatures in the deep sea. It has it all, it’s black, has big savage teeth, little nasty pin eyes, a big flabby stomach ready to fit in anything it can catch (irrelevant of size) and a rod lure off the top of its head with a glowing tip to coax in stupid prey. It doesn’t stop there: its flesh is watery, its bones are very light (barely coated by a thin layer of calcium carbonate) and it can barely swim (there’s not much of a tail).
This animal just hangs mid-water waving its little lure and waiting to chomp. And this is only what the female looks like! The male is completely different. He’s very small and looks like a black jellybean with fins. He has no lure, has big eyes, huge nostrils and a fairly small mouth with curved hooked teeth. His body is made of strong red muscle for swimming long distances. Why the difference? She’s looking for food, he’s looking for her. She releases anglerfish-type perfumes into the water and he spends all his time swimming around looking and smelling for her. When he eventually finds her (in the dark), he latches on to her side (with his hooked teeth) and drinks her food-rich blood in return for producing the sperm she needs when it comes time to release her eggs.
These long thin fishes are related to the seahorses and pipefishes in that they share fused mouthparts and bony plates in the body. Bellowsfish are named after their long-snouted shape, similar to a set of fire bellows. These fishes occur in mid-depth waters, too deep for divers, so there is little known about their behaviours. They form large schools and can be caught in huge numbers. Adults appear to feed near the seafloor, probing for and vacuuming up small crustaceans and other invertebrates with their long snouts. Juveniles have been found in large numbers in the stomachs of true pelagic fishes such as tuna, indicating that these early life stages are spent swimming in open ocean.
It takes a lot of time and energy to make a shell. The familiar coiled seashells are made by molluscs known as “gastropods” (meaning “stomach-foot”, as their stomach is inside their foot). Their shells are not simple structures. They are laid down in alternating layers of flexible protein and hard calcium carbonate. These layers make the shell strong but not brittle. The hard layer is further strengthened by laying down the crystals of carbonate at different angles. Karen Gowlett-Holmes from CSIRO describes it as being the same process as used to make laminated safety glass, crossing the crystal grains make them strong but flexible. Carrier Shells are sneaky and bypass a lot of this hard work by just using the shells of other snails. From a tiny size, they glue on any shells they can find (irrelevant of the occupant!) and start building armour made of other shells. All they have to do is build the coiled centre and keep looking for a new addition the right size for their works of art.
