Photos by Solvin Zankl / Naturepl.Com

Aliens of the Deep Photos by Solvin Zankl / naturepl.com The deep sea is the largest and most In November 2015, photographer Solvin mysterious habitat on our planet. Taking Zankl accompanied a scientific expe- up 95% of the Earth’s living space, it dition to the Cape Verde Islands in the remains largely unexplored. It’s hard to eastern tropical Atlantic, where his mis- imagine anything surviving in the pitch sion was to document the strange crea- black, icy cold, crushing environment tures living beyond the reach of the sun. of the deep ocean, yet scientists are ‘There is no other place on earth where discovering a habitat rich with life. The you can photograph such interesting- creatures being uncovered are often so looking animals,’ says Zankl, a trained bizarre they might seem, at first glance, marine biologist with a lifelong fascina- like aliens. tion for life under the waves. The MARIA S. MERIAN left the port of Las Palmas, Gran Canaria, on 28 No- vember 2015 and sampled the waters around the Cape Verde Islands in the eastern tropical Atlantic between 30th November and 20th December. The aim of the cruise was to assess the pelagic (open ocean) fauna in the waters around the islands. Solvin Zankl (pictured in the back row, far left) was assigned to photograph samples as they were brought to the surface. All photos were taken in a tank, kept in a cold room at a constant tempe- rature of 4°C. The sampling programme included both netting and optical systems in order to assess a wide variety of species at depths between 150 - 1000 metres. The nets used to capture deep sea organisms [see below] can damage fragile gelatinous species, or even fail to capture them altogether. Therefore, a recently developed optical sam- pler called the PELAGIOS was also deployed [left]. This is a towable observation instrument that consists of an aluminium frame, HD cameras in pres- sure-proof cases, light arrays and LEDs, which illuminate the water around it. Zooplankton play a critical role in main- taining the health and balance of the ocean and its complex food webs. They break down and consume dead plant and animal material that falls through the water column as ‘marine snow’, and in turn, they become food for secondary consumers such as fish. Zooplankton are species that spend their entire life cycle drifting in the water column. They are typically small, and often microscopic, but some (such as jellyfish) are larger and visible to the naked eye. The zooplankton pictured here are not shown to scale. [Below] Juvenile deep water [Right] Deep sea Pram Bug pelagic octopus (Vitreledonella (Phronima sp.) with young in a richardi), also known as the salp house. The pram bug is a glass octopus. Little is known translucent amphipod (a type of about this species. Its body is crustacean). At about 2.5cm in gelatinous and transparent, size, it resembles a shrimp with enabling a clear view of the a head, eyes, jaws and clawed digestive system (the long, nar- arms. This species is only seen row shape above and between in the wild at great depths. the eyes), as well as the gills, Pram bugs hijack salps (barrel- mouth and brain. shaped, gelatinous zooplankton Different life stages seem to which drift throughout oceans) inhabit different depths, and hollow them out to create with individuals gra- mobile nurseries for their young dually moving (the orange larvae can be deeper as they seen inside the salp in this mature. image). [Above] Flatfish larva swim upright and have sym- metrical bodies. But as the larva develops to an adult, it begins to tip on its side and the bones in its skull shift as the right eye migrates to the opposite side of the head. The transformed flatfish sinks and settles on its blind right side. It will spend the rest of its life as a bottomfeeder, with two eyes on the same side of its head and a contorted mouth. [Above and below] Leptocephali are the flat and transparent larval stages of eels and other related fish. They look very different from their adult counterparts, with laterally com- pressed bodies filled with transparent jelly. The rib-like structures are muscle fibres called myomeres. Boxer snipe eel (Nemichthys curvirostris) Depth Range: 0 - 2,000m Snipe eels are characterized by their long body and very slender jaws that separate toward the tips, resembling the beak of a snipe ( a type of wading bird). Deep-sea fish have adapted to their pitch-black environment by evolving eyes that are very good at collecting light. Some species have a tapetum, a reflective layer which bounces light back through the retina, enhancing sensitivity in low light conditions. [Left] Deep Sea Threadtail (Stylephorus chordatus). Depth range: 300-800m This species has tubular eyes with big lenses, capable of detecting even the slightest traces of light. Bioluminescence commonly occurs in deep sea fish, as a result of chemical reactions in light-emitting organs called photophores. This dazzling glow-in-the-dark display can be used for communication, to attract prey, distract predators or even as a defence tactic. [Above] Scaleless black dragonfish (Melanostomias biseriatus) Depth range: 620 - 760 m The barbel hanging below the jaw of this species acts as a bioluminescent lure, drawing prey closer to the fearsome mouth. [Below]: Diaphanous hatchetfish (Sternoptyx diaphana) Depth range 400 - 3676 m Ventral photophores of this species are thought to obscure the body outline from predators, by matching the ambience [Above] The lanternfish’s luminescent of downwelling light. organs are pale green or blue and are located on the fish’s head, underside, and tail. The distribution of their light organs follows a design that is species- specific, with each species lighting up in a different pattern. [Left] The cock-eyed squid is so named because the right eye is normal-sized, whereas the left eye is at least twice the diameter and bulges out of the head. [Below] [Right] Zoea are free-swimming larvae Having passed through various of certain crustaceans. zoea stages, crab larvae moult This crab zoea has rudimen- into the megalopa (or post- tary legs and large spines many larva) stage, as seen here. This times longer than its body, is followed by metamorphosis providing defence against pre- into an immature form, which dators. Owing to the drastic dif- broadly resembles the adult. ference between the larval and After further moults, the adult adult forms, many crustacean form is finally reached. larvae were wrongly classified Megalopa are characterised by when first discovered, thought the use of abdominal appen- to be uinque species as opposed dages (pleopods) for propulsion to larval forms. through the water. Black dragonfish (Malacosteus niger) jaw - which takes up over 20% of the Depth range: 500 - 3886 m fish’s length - to shoot out and impale prey with its sharp fangs. Surprisingly, This species has bioluminescent given these fearsome adaptations, this ‘flashlight’ organs beneath each eye. It is species feeds mainly on copepods - tiny among the small group of deep sea fish crustaceans often less than 1mm in that are able to both emit red light and size. Scientists believe that these small see it, enabling them to lluminate their creatures provide the chemicals that prey without the victims ever knowing M. niger uses in its eyes to see red light. about it – and without ringing the dinner When it gets the chance, however, this bell for other predatory species. predator can still revert to its ancestral Like many of its dragonfish relatives, feeding habits and devour much larger this species has an enormous gape. The organisms, before going back to snac- head can hinge backwards, allowing the king on the copepods. These parasitic copepods (Sapphirina sp.) are known as sea sapphires. Females are translucent, as are the males when they’re not shining. The secret to their shimmer is in the microscopic layers of crystal plates inside their cells, which refract light. Various species of male Sapphirina shine in different hues, from bright gold to deep blue. The colour is dictated by the minute distances between the crystal plates.When the distance matches a particular wavelength of light, the corresponding colour is bounced back. The angle of light reflecting off the crystal layers also changes how the animal looks. At certain angles, the reflectance passes out of the visible light range and into the invisible ultraviolet range, allowing Sapphirina to become nearly invisible. Anglerfish are perhaps the most widely reco- gnised of all deep sea species, typically having at least one long filament sprouting from the middle of their heads (termed the illicium), which is tipped by an irregular fleshy growth (called the esca). Some deep-sea anglerfish emit light from the esca to attract prey, as well as find mates. The luminescence is produced by millions of light-emitting bacteria that breed in the esca. It has been suggested that, Esca in some species, these bacteria are incapable of luminescence outside of the anglerfish, suggesting a symbiotic relationship between the two species. ^ Triplewart Sea Devil (Cryptopsaras couesi) Illicium Depth range: 0 - 3085 m Unlike the female fish, shown here, males of this species are tiny and live parasitically, becoming little more than a sperm-producing appendage. < Johnson’s Abyssal Seadevil (Melanocetus johnsonii) ^ Whipnose anglerfish (Gigantactis vanhoeffeni) Depth range: 0 - 2,100m Depth range: 300 - 5,300m Anglerfish typically have large, crescent-shaped mouths filled Whipnose anglerfish are distin- with translucent teeth. Coupled guished by the presence of a remar- with a pliable body, this allows kably long lure, which may exceed them to swallow prey larger than the body length in some cases.

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