The Ocean Depths The ocean depths include a number of distinct habitats: – Epipelagic zone - upper 200 meters; the photic zone – Mesopelagic zone – m “middle” zone; some light penetrates but insufficient for photosynthesis – Bathypelagic zone – m; “deep” zone; aphotic, perpetually cold – Abyssopelagic zone – m; deepest, at or near the bottom

The Ocean Depths

Deep Sea Communities Without primary producers to support photosynthesis, most of the communities in the deep sea depend on food produced in the surface layers above – Life is much less abundant below the photic zone Organisms in the deep sea evolved special adaptations for surviving darkness, sparse food and mates, cold temperatures, and immense pressures

Animals of the Mesopelagic Many of the characteristics of the midwater (mesopelagic) zone is directly related to the lack of food Since animals need a lot of food to grow large, animals in the mesopelagic are small (~<10 inches) and have large, usually hinged, extendible jaws equipped with fearsome teeth – Must be able to eat a broad range or prey; don’t have to pass up any meal that is ‘too large’ to eat

Animals of the Mesopelagic Most midwater animals are “sit and wait” predators, gulping down anything that comes within range Midwater animals also have a slow metabolism to conserve energy, and flabby, watery bodies instead of energy-consuming muscle

Animals of the Mesopelagic To fill their air bladder, fishes must produce a gas pressure inside the bladder that matches the external water pressure Because water pressure is greater at depth than at the surface, filling the swim bladder requires more energy in the mesopelagic – As a result, most midwater fishes have lost their swim bladder – To compensate, they evolved soft, weak bones, making them ~neutrally buoyant

Animals of the Mesopelagic To help them see in the dim light, midwater fishes characteristically have eyes that are not only large, but unusually sensitive Many midwater fishes have upward-looking eyes to detect subtle changes in the negligible light above – Can detect silhouettes of prey moving above them

Animals of the Mesopelagic Because midwater fish cannot afford the energy costs of fast swimming, or heavy defensive spines and scales, camouflage is perhaps more important in the mesopelagic than the epipelagic Midwater fishes have evolved ways to make their silhouettes from potential predators below – Red coloration, transparency, bioluminescence

Anyone got a light? Many midwater fish possess bioluminescent photophores, which produce light that breaks up the silhouette and help the animal blend in with the background light – Found primarily on underside (ventral surface)

Animals of the Mesopelagic

Animals of the Mesopelagic: Lanternfish Lanternfish belong to family Myctophidae Myctophids are believed to be the most abundant of all fishes! – As much as 65% of all deep sea biomass – Migratory; they ‘are’ the deep scattering layer!

Animals of the Mesopelagic: Dragonfish Small body size Extendable, hinged jaw Bioluminescent barb Photophores on underside of body Dark body coloration

Animals of the Mesopelagic: Hatchetfish Small body size Large, upward-facing eyes Photophores on underside Large, extendable mouth Silver body coloration

The world of perpetual darkness Below the mesopelagic lies the little-known world of the deep sea: the bathypelagic and abyssopekagic Here, environmental conditions change very little – It’s always dark – It’s always cold (~1-2°C) – Salinity is also remarkably constant

Animals of the Deep Sea In the darkness of the deep sea, there is no need for camouflage – Deep sea fishes are generally black; shrimp are often bright red Bioluminescence is very common, but is not used for counter-illumination – Used for prey attraction, communication, and courtship

Animals of the Deep Sea The large eyes of midwater animals are not needed in the deep sea Not completely dark here though, because of all the bioluminescence!

Midwater vs deep sea fishes

Animals of the Deep Sea In shallow water organisms, the enzymes that control metabolism are strongly affected by pressure, and would cease to function at pressures of the deep sea Deep sea organisms have much more pressure-resistant enzymes, and high amounts of a chemical that helps to stabilize the enzymes – Pressure still limits the depth range of fishes

Animals of the Deep Sea

Animals of the Deep Sea: Anglerfish Bioluminescent angler (lure) Small body size Black body Extendable jaw Watery composition Parasitic sexual reproduction!

Animals of the Deep Sea: Fangtooth Small body size Black Large, extendable jaw Sensory systems along body

Sex in the Deep Sea Food is not the only thing that is sparse in the deep sea Finding a mate here can be extremely difficult; has to be the right species and the right sex! Many deep sea fishes are hermaphrodites Some species of anglerfish have evolved an extreme solution to the problem of finding mates – Parasitic reproduction!

And you thought your boyfriend was clingy Because mates are few and far between, the male anglerfish is equipped with specialized olfactory organs to detect and find a female When he does, he bites into her skin, fusing with the female and atrophies; loses digestive system, brain, heart and eyes, but not gonads! Parasitic male!