Compared with the colourful sponges of shallow waters, those of the deep sea are not very sponge-like. Some are like empty netting cages or vases with a mesh over the top. These are known as “hexactinellid sponges” and some of them get very complex and intricate. The mesh over the top probably stops large animals from climbing inside and blocking the water flow required by the small filter-feeding cells that make up the sponge. Other types of deep-sea sponge look (and feel) like small cups of rock. These are the stony sponges (family Lithistidae) and they have very complex branching structures in the skin (“spicules”) that interlock to make a very rigid heavy shape. The colour of the one shown is rare as most deep-sea sponges are drab brown or grey. Most sponges have an internal skeleton of spicules. The spicules of most deep-sea sponges are silicate-based. As there is not much tissue on these deep-water forms, they have few predators. As a consequence they don’t need the toxic chemicals that are used by many shallow-water species.
This little shark has a very strange shape. It is triangular in cross section and has a flat underside with two strong keel ridges along the edges. It has a high humped back and a small head. It gets its name from its rough spiky skin. Instead of scales, sharks have small sharp structures in the skin called “denticles”. They are typically about 0.1 mm long and make the skin feel like sand paper. In the prickly shark, the denticles are 10 times larger making it much more prickly. The shape of this shark may be due to its very large liver, which is full of oil. The oil is lighter than water and makes the animal float mid-water. This is called “neutral buoyancy”, which means that it can hang without needing to spend energy swimming. This shark has large nostrils and a small mouth with sharp upper teeth and blade-like bottom teeth. It uses these tools to track down and eat invertebrates and small fish on the seafloor. This shark occurs around New Zealand and southern Australia at depths of 100-800 metres. The other three species of this group (the “rough sharks”, family Oxynotidae) live in the Atlantic Ocean.
This creature looks like a small clam. It is in fact a type of crustacean that makes this clam-like shell. It drives the shell around like a jet ski by paddling hairy legs through the slot on the underside. They are very good swimmers. This ostracod is about the size of a pea and probably scavenges for dead and rotting material that drifts to the seafloor. Both animals shown are females with large eggs being brooded within their shells. Ostracods have been around for hundreds of millions of years and their shells are very common in the fossil record. The largest occurs in the deep sea, reaching a size of 3 cm long. It is a predator, using its antennae to catch crustaceans and even small fish. Some species of ostracods can squirt clouds of blue light as a decoy to predators.
This shark is dreaded by fishermen. Not because of human attacks but because of its capacity to do major damage to a fish catch. It is one of the cookie cutter sharks that take perfect circular plugs out of anything they can reach. They grab on to the sides of passing animals with their front teeth, form a suction with their rubbery lips and use their tail to do a whole body spin. Their head rotates, cutting out a perfect round plug with their sharp bottom teeth. One dead beaked whale was found with more than 20 cookie cutter scars in its sides. Our animal had certainly rammed a lot in before getting to the surface. Seal sharks are found right around the world, usually at depths of 300 to 800 metres.
This fish gets its name from the way it stands on the seafloor, raised up on long stilt-like rays of its pelvic and tail fins. It is a classic sit-and-wait predator, facing into gentle currents with all the fin rays spread out around its head. Its small beady eyes are weak. It feeds on small planktonic invertebrates and fishes that it detects by sensing the slightest vibrations in the water. Its mouth and throat can be opened very wide to engulf the prey, which are then caught on a fine grid of long bones at the back of the throat near the gills (these bones are known as “gill rakers”). Tripodfish are found everywhere in the deep-sea at depths between 200 and 6000 metres.
Sea spiders are not true spiders; they are marine animals in a special group of their own (also known as “pycnogonids”). They have 10 or 12 long legs (depending on the group), a tiny body and long mouthparts. Their body is so small that they store some of their body organs down their hollow legs. They use these stilt-like legs for walking over soft mud and for swimming. These animals feed on attached (“sessile”) invertebrates such as sea anemones, corals, sea pens and hydroids. They use their piercing mouthparts to eat the polyps or suck the fluids out of larger animals. The deep sea is home to the biggest of the sea spiders, some reaching 50 cm across. The one shown was over 30 cm across. The deepest record for a sea spider is 7.4 km deep.
This fish has been the target of massive commercial harvests. It is a popular eating fish as the flesh is firm, it is relatively odourless and it can be filleted boneless. Initially it was very popular for fast food fillet burgers. It is marketed in our region under the names “deep-sea perch” or just “sea perch”. Fishing effort targeted large breeding aggregations on the tops of seamounts taking catches of up to 80 tonnes in a single haul. A million dollars worth of fish could be collected in just a few days. This harvest has lead to dramatic declines in orange roughy stocks. In Australia, the peak year landed 50,000 tonnes of this species in the late 1980’s. The quota has been steadily decreasing since then and is now under 3,000 tonnes per year. These fish are incredibly long-lived, up to 150 years old, which means some of these animals were swimming around before the American Civil War. It is unknown how long orange roughy stocks will take to recover (if they do).
Lantern sharks are a large family of small sharks that range in size from 20 to 80 cm long. They get their name from the dark patches on the undersides of the belly and tail, which are light organs. The light is made using chemicals to hide the shark’s silhouette from predators beneath it. Some researchers have also suggested that light is used for recognising members of the opposite sex of their own species. These sharks live at depths of 100-2500 metres and are always free-swimming, sometimes in mid-water well above the seafloor. They rise every night with other vertical migrators including their prey: lanternfishes, other small fishes and small crustaceans. They have also been found to eat fish eggs. Their upper teeth are pointed with up to 10 cusps (compared with a single cusp in cookie cutter sharks), while the bottom teeth have a continuous blade-like cutting edge. Lantern sharks are ovoviviparous (see 30 May diary) and some species can have up to 20 pups. Seven species have been collected on the NORFANZ cruise, one of which belongs in a new species recently recognised from Australia but yet to be described.
We have found seven species of this great armoured shrimp on the NORFANZ cruise. Between Peter Davie, Rick Webber and myself we agreed that “goblin shrimp” was an appropriate common name due to their great faces. They are bottom dwellers and their heavy armour probably protects them from smaller fish predators. This family of shrimps occurs in all oceans except polar waters and has been collected from 268 m to 6.6 km. The nine caught of this species today were all females carrying eggs, suggesting some separation of the sexes. One of the other species collected had been parasitised by a different crustacean, a pillbug (“isopod”), which had attached in the gill chamber and caused a large swelling in the shrimp’s armour. These parasitic isopods are all females and have their own hitchhikers, a tiny “commensal” male that lives on the body of the female. I don’t know if he has anybody riding on him.