Zones of the Open Ocean Marine Biology

The Zones The Ocean Zones are: Sunlit Zone (Epipelagic) Photic Twilight Zone (Mesopelagic) Dark Zone (Bathypelagic) Aphotic Abyssal Zone (Abyssopelagic) Hadal Zone (Hadopelagic)

Conditions of the Ocean Vary with depth Light and temperature changes occur quickly Pressure increases incrementally Each zone produces very different conditions for living things

Life in these zones are linked to the amount of plankton and light intensity

Deep Sea Exploring

The Surface Layer The top one meter of the ocean (part of sunlit zone) Richest in nutrients Amino acids, fatty acids, and proteins excreted by plants and animals float, as do oils from decomposing bodies of dead animals

The Surface Layer Gas exchange takes place between the ocean and atmosphere Phytoplankton gather here in daylight, as do the animals that feed on them Highly susceptible to chemical pollution and floating litter, which can be deadly for marine life

The Sunlit Zone (0~200m) Seawater rapidly absorbs sunlight, so only 1% of light reaches 200m below the surface Phytoplankton use the light to photosynthesize, forming the base of food chains This zone drives all ocean life More than 90% of all marine life lives here

The Sunlit Zone Nearly all red light is absorbed within 10 meters, so red animals look black below this depth Green light penetrates much deeper in clear water, to around 100 meters, and blue light to 200 meters Due to presence of chlorophyll, phytoplankton preferentially absorb red and blue portions of the light spectrum for photosynthesis and reflect green light

Sunlit Zone (in cloudy water) In cloudy water, the sunlit zone is shallower because light is absorbed more quickly Accumulation of phyto- and zooplankton in fertile waters absorb sunlight, reducing the depth of the sunlit zone Phytoplankton must stay here during the day to photosynthesize, zooplankton follow them to feed, along with animals that feed on zooplankton

Nocturnal and Diurnal Distribution The sunlit zone is dangerous for animals because they become conspicuous to hunters, so many stay in the twilight zone by day and only go up at night

Living in the Sunlit Zone Phytoplankton need to remain in the sunlit zone to photosynthesize, but don’t want to expend huge amounts of energy to stay afloat They may use/be: buoyancy bubbles, droplets of oil, or stores of light fats to keep afloat covered in spines to increase surface area and buoy them up In colonial chains to produce more drag in water and slow sinking rate threadlike flagella to swim weakly

Adaptations of vertical migrators like Lanternfish on left as opposed to non-migrators like Dragonfish on right Well developed muscles and bones Swim bladder of air or fat Withstand extreme temperature changes

The Twilight Zone (200~1000m) Too dark for photosynthesis, but just light enough for animals to see…and be seen Many species are almost totally translucent or camouflaged with countershading to avoid casting even a faint shadow (dark on top, light on bottom) Others are reflective to disguise themselves against the light from above To cope with dim light, many have large eyes

Midwater Trawl to Collect Mesopelagic Organisms Remote-controlled net opens only at certain depths

“Invisible” Octopus at Night

The Twilight Zone Main source of food is detritus (organic matter from dead organisms) Many animals migrate up into the sunlit zone where food is plentiful at night, and return to twilight zone as the sun rises 30% of the total marine biomass make this daily trek (the largest migration of life on Earth) Some planktonic animals less that 1mm long may migrate 20m, but larger shrimp travel 600m each way, every day

Spookfish Found at depths up to 1,000m, on boundary of dark zone Bones are so thin its almost transparent, and large eyes look up to spot predators attacking from above

Typical Mesopelagic Fish

The Dark Zone (1000~4000m) Almost no light penetrates No plants can grow and virtually only food source is “snow” of waste from above Temperatures are 35~39°F (2~4°C) Extreme pressure so only adapted animals can survive Liquid filled bodies are almost incompressible compared to gas-filled bodies of surface-living birds and mammals Only light comes from bioluminescent animals

Typical Deep Sea Fish

Bioluminescence Living light is used for: Counter-illumination to mask silhouette Escape from predators with confusing light Attract or see prey Communication and courtship

Vampire Squid

Abyssal Zone (4000~6000m) Beyond the continental slope Around 30% of total seabed area lies here Animals are typically slow-moving (to save energy), slow-growing, and long-lived (up to 100 years) Conserve energy by waiting for food to come to them, many therefore have massive mouths and powerful teeth Use tricks to catch prey- bioluminescent lures and other glowing structures

Viperfish Accomodates large prey with large, hinged jaw

Aliens of the Deep Sea

Hadal Zone (6000m~) Only in few deep ocean trenches Less than 2% of total seafloor area Only three human beings have ever visited this zone (James Cameron who directed Titanic is the third) Pressures are so high (14,700psi) only a few un-manned submersibles are able to operate here We know very little about what lives here, but few have been photographed Tough to visit and bring fish back alive

Fangtooth Fish Has been recorded at depths of 4,992m Like many deep-water fish, has a large head and massive teeth. Sensory organs along its body detect prey movement in dark Has to grab food in short time they float past