Deep Ocean Marine Science I Honors Notes

The Deep Ocean

  • Most of the ocean is cold, dark, and deep.
  • Photosynthesis occurs only down to 100-200m; sunlight disappears altogether at 1,000m or less.
  • The ocean descends to a maximum depth of about 11,000m in the Mariana Trench.
  • Over 60% of the planet is covered by water more than a mile deep; the deep sea is the largest and largely unexplored habitat on Earth.
  • More people have traveled into space than to the deep ocean.
  • 79% of the Earth’s biosphere volume consists of waters deeper than 1,000m.
  • Advances in submersibles and imaging technologies are increasing deep ocean exploration.
  • Deep sea research is vital due to its enormous size.
  • Hydrothermal vents were discovered in 1977, revolutionizing ideas about energy sources and life adaptability.

Studying the Deep Ocean

  • Most deep-sea information comes from advanced technology like submarines, ROVs (remotely operated vehicles), and AUVs (autonomous undersea vehicles).
  • Deep ocean exploration relies on videos and expert commentaries.

Ocean Zones

  • The ocean is divided into two realms: pelagic and benthic.
    • Pelagic: open water with swimming and floating organisms.
    • Benthic: ocean floor and its organisms.
  • Pelagic zones:
    • Epipelagic: less than 200m, photosynthesis occurs.
    • Mesopelagic: 200-1,000m, faint sunlight, no photosynthesis.
    • Bathypelagic: 1,000-4,000m.
    • Abyssopelagic: 4,000-6,000m.
    • Hadopelagic: deep trenches below 6,000m to about 11,000m.

Major Ocean Topography

  • Features include:
    • Shoreline
    • Continental shelf
    • Continental slope
    • Continental rise
    • Abyssal plain
    • Abyssal hills
    • Seamount
    • Guyot
    • Mid-ocean ridge
    • Submarine canyon
    • Trench
    • Rift

Deep Benthic Surfaces

  • Most of the deep seafloor consists of mud (fine sediment) or ooze (mud with high organic remains).
  • Sandy habitats are rare because sand particles are too heavy to be carried to the deep sea.
  • Rocky surfaces occur where sediment cannot stick, such as around islands, continental slopes, or mid-ocean ridges.
  • At mid-ocean ridges, magma creates new rocky surfaces.
  • Chemical reactions can produce unique formations like smoker chimneys at hydrothermal vents.

Challenges to Studying Deep Sea Life

  • Deep-sea exploration presents challenges due to total darkness, extreme cold, and great pressure.

Pressure Challenges

  • Pressure: continuous physical force exerted on an object.
  • Underwater pressure increases about 1 atmosphere for every 10 meters of depth (~32.8 ft).
  • At 5,000 meters, the pressure is approximately 500 atmospheres.
    • This is enough to crush a person.
  • Demonstration with water containers:
    • 20 liters (~5.3 gal) ≈ 44 lbs, similar to 0.5 ft of water.
    • 40 liters (~10.5 gal) ≈ 88 lbs, similar to 1 ft of water.
    • 60 liters (~15.8 gal) ≈ 132.02 lbs, similar to 1.5 ft of water.
  • At 100 m, water weighs about 220,026 lbs.
  • The ocean's potential volume is 538 million cubic miles, weighing about 4.9×10214.9 \times 10^{21} pounds.
  • In the Mariana Trench, the pressure is about 15,750 psi, more than 1,000 times atmospheric pressure.

Temperature Challenges of the Deep

  • The deep ocean (below 200 meters) is cold, with an average temperature of 0-4°C (32-39°F).
  • Cold water is denser and sinks, contributing to the coldness.
  • Seawater doesn’t freeze at this temperature because of salt content.

Advances in Technology for Deep-Ocean Exploration

  • Sophisticated data collection devices have been developed.

Observational Equipment

  • Fiber optics with LED light and low light cameras enhance the understanding of deep-sea creatures.

Remotely Operated Vehicles (ROVs)

  • ROVs are unmanned submarine robots with cables to transmit data.
  • They are fitted with video and still cameras and mechanical tools.
  • AUVs (autonomous undersea vehicles) operate without a cable.
  • The USA’s new Nereus is a hybrid unmanned sub that can switch from ROV to AUV mode, capable of reaching the deepest trenches.
  • ROV Hercules video captured a sperm whale at 598 meters (1,962 ft) in the Gulf of Mexico.
  • Sperm whales typically hunt at depths of 2,000 feet for 45 minutes but can dive to over 10,000 feet for over 60 minutes.

Manned Submersibles

  • Manned deep-sea submersibles are also used to explore the ocean’s depths.
  • Alvin is an American deep-sea submersible built in 1964, carrying 3 people and reaching a maximum depth of more than 4,500 m.
  • Trieste, manned by Jacques Piccard and Don Walsh, reached the bottom of the Mariana Trench at almost 11,000 m in 1960. The windows cracked.
  • James Cameron successfully dove in his commissioned one-man sub to the Challenger Deep in 2012.

Animal Adaptations to the Deep Ocean

  • Physical characteristics that deep-sea life must contend with:
    • Abiotic factors: lack of light, pressure, currents, temperature, oxygen, nutrients and other chemicals
    • Biotic factors: predators, food, mates, competitors, or symbionts
  • Adaptations for sensing, feeding, reproducing, moving, and avoiding predators.

1. Lack of Light Adaptations

  • The deep sea begins below 200 m.
  • The mesopelagic or “twilight” zone extends to 1,000 m, with faint blue light.
  • Below 1,000 m, the ocean is pitch black.
  • Bioluminescence: a chemical reaction creating light without heat, is common.
  • Light is produced by symbiotic bacteria within light-emitting cells called photophores.
  • A luciferin is oxidized to produce light. Animals can make luciferin themselves, or it may be synthesized by symbiotic bacteria inside the photophore.
  • Photophores range from simple clusters of cells to complex organs.
  • Most common light color produced is blue which penetrates furthest through water!
Uses of Bioluminescence:
  • Lures to attract prey (e.g., anglerfish).
  • Protection through counterillumination (e.g., lanternfish, bristlemouth) by breaking up the silhouette of the fish's body.
  • Mate recognition with distinct light patterns.
Eye Adaptations to See Bioluminescence
  • Large eyes capture limited light (e.g., stout blacksmelt).
  • Other animals rely on enhanced senses including smell, touch and vibration (e.g., tripodfishes).
  • Eye size increases with depth before 1,000 m, then decreases in bathypelagic (aphotic) zone.
  • Some fish have night-vision (e.g., Stylephorus chordates).
Functions of Bioluminescence:
  • Headlights (lantern fish).
  • Social signals for attracting mates.
  • Lures to attract prey (anglerfish).
  • Counterillumination to match faint sunlight from above.
  • Confusing predators or prey (squid, green bomber worms).
  • “Burglar alarms” to illuminate attackers.
Interesting Animal Fact:
  • Most bioluminescence is blue or blue-green, which travels farthest in water.
  • Most animals have lost the ability to see red light.
  • Dragonfish can produce red light and use it as a secret “sniper” light.

2. Pressure Adaptations

  • Pressure increases 1 atmosphere (atm) for each 10 m in depth.
  • Deep sea varies in depth 200 m to 11,000 m, with pressure 20 atm to more than 1,100 atm.
  • High pressure can crush air pockets, but does not compress water much.
  • High pressure distorts complex biomolecules, especially membranes and proteins.
  • Life copes with pressure effects on biomolecules in two ways:
    • Pressure-resistant structures that don't work well under low pressure.
    • Piezolytes: small organic molecules that prevent pressure from distorting large biomolecules.
      • Trimethylamine oxide (TMAO) is a piezolyte that gives fish their fishy smell; levels increase with depth.
  • Animals brought from great depth to the surface generally die because their biomolecules no longer work properly at surface pressure or temperature.
  • Rapid pressure as well as temperature changes kill them because their biomolecules no longer work well (high TMAO does not help, as it appears to be too high in deep-sea life for biomolecules to work properly at the surface)

3. Temperature Adaptations

  • Thermoclines: transition layer between warmer mixed water at the ocean's surface and cooler deep water below.
  • In most parts of the deep sea, the water temperature is more uniform and constant (-1 to +4°C or 30.2° F – 39.2°F).
  • Seawater freezes at -1.8°C.
  • Life adapts to the cold with “loose” flexible proteins and unsaturated membranes.
  • Deep-sea animals have cell membranes with high concentrations of cholesterol and unsaturated fatty acids.
    • These maintain the fluidity of the cell membrane.
  • Loose membranes and proteins of cold-adapted organisms readily fall apart at higher temperatures (much as olive oil turns to liquid at room temperature).

4. Lack of Oxygen Adaptations

  • Oxygen enters the ocean through:
    • Surface mixing (wind and waves)
    • Photosynthesis by phytoplankton or macroalgae
  • Cold water can dissolve more oxygen than warm water.
  • Deepest waters originate from shallow polar seas.
  • Thermohaline currents carry oxygen-rich cold water around the globe.
  • Oxygen minimum zones: oxygen-poor environments between 500 – 1,000 m in temperate and tropical regions.
  • Animals and bacteria consume oxygen, which can drop to near zero.
  • Loriciferans, members of an animal phylum first discovered in 1983, are animals living continuously without any oxygen.

5. Nutrition Adaptations

  • Deep sea creatures have evolved some fascinating feeding mechanisms because food is scarce or hard to come by in these zones.
  • Most food consists of detritus (decaying remains) and other organisms (Marine Snow).
  • Scavengers eat detritus (sea cucumbers, brittle stars, grenadier or rattail fish).
  • Marine snow is organic material falling from upper waters to the deep ocean.
    • Includes dead animals and plants, fecal matter, sand, soot, and other inorganic dust.
    • “Snowflakes” grow as they fall, some reaching several centimeters in diameter.
  • The continuous fall of marine snow provides food for many deep-sea creatures. Many animals in the dark parts of the ocean filter marine snow from the water or scavenge it from the seabed.
  • Large corpses such as whales provide infrequent feasts.
    • Eaten by jawless fish (hagfish), scavenger sharks, crabs, and Osedax worms (bone-eaters).
  • Deep-sea pelagic fish have large mouths, hinged jaws, and expandable stomachs (gulper eels).
  • Long fang-like teeth point inward to ensure prey cannot escape.
  • Some species ambush predators using bioluminescent lures (anglerfish, viperfish).
  • Others listen and smell for food sources (rattails or grenadiers).
  • Vertical migration: mesopelagic species migrate to food-rich surface waters at dusk and return to the depths at dawn.

Further Adaptations of Animals in the Deep-Sea

  • Animals’ bodies are often:
    • Transparent (jellies and squids)
    • Black (dragonfish)
    • Red (shrimp and squids)
Reproduction
  • Difficult to find a mate in the vast dark depths.
  • Unique light patterns aid in finding mates.
  • Male anglerfish are tiny compared to females and attach themselves, establishing a parasitic-like relationship for life, providing a reliable sperm source.
Gigantism
  • Tendency for certain types of animals to become enormous in size.
  • Examples: giant squid, colossal squid, giant isopod, king-of-herrings oarfish, giant amphipod.
  • Not fully understood how they achieve such growth in food-poor habitats.
Long Lives
  • Many deep-sea organisms live for decades or even centuries.
  • Examples: rattails or grenadiers and orange roughy.
  • These species reproduce and grow to maturity very slowly.

Hydrothermal Vent Communities and their Unique Extreme Adaptations

  • Life in the deep sea is sparse; exceptions: hydrothermal vent and cold seep communities.

  • Discovered in 1976 – 1977 during a deep-sea expedition with Alvin at a mid-ocean ridge near the Galapagos.

  • Hot springs of mineral-rich water spewing (like continuous geysers) from vents heated by magma, with metal sulfides precipitating in the cold surrounding seawater to form intricate, colorful and often towering chimneys.

  • Hydrothermal vents have high densities of numerous new species, and a new kind of ecosystem flourishing in the dark based on toxic gas.

  • Giant tubeworms (Riftia) have no digestive tract and subsist on energy-rich hydrogen sulfide, harboring chemoautotrophs.

  • Chemoautotrophs use the energy in hydrogen sulfide to convert carbon dioxide into sugars, like plants using sunlight.

  • Ecosystem runs on Earth’s geothermal energy rather than sunlight.

  • Since those first discoveries near the Galapagos, hydrothermal vent communities have been found at depths ranging from about 1,500 m to over 5,000 m.

    • Most vents are along the mid-ocean ridges, where magma is close to seawater.
    • Other animals with bacterial symbionts have been found and undoubtedly many vent communities are yet to be found since many ridge areas have not yet been explored.

  • Water temperature of vents can reach 400°C without boiling due to the high pressure.

    • Most vent life is found between 8 – 25°C, or up to 60°C around some animals such as Pompeii worms (Alvinella).

Cold Seeps

  • High-density deep-sea ecosystems at places where cold methane, hydrogen sulfide, and/or oil seep out of sediments.
  • More energy is locked up in methane hydrates than in all fossil/hydrocarbon fuels combined.
  • Animals with symbiotic bacteria include tubeworms, clams, and mussels. Some mussels harbor methane-using bacteria.

Brine Pools

  • Dense seep communities around deep brine pools, or “lakes within oceans.”
  • Salt deposits under the ocean floor dissolve, forming pools of water so dense they don't mix with seawater.
  • High densities of mussels live around the rim, subsisting on methane gas. No known animal can survive the salt within the pool itself except some microbes.