Deep Ocean Marine Science I Honors Notes

The Deep Ocean

The deep ocean is a major part of the ocean biome, characterized by cold, dark conditions.

Introduction to the Deep Ocean

Most people think of the intertidal zone and epipelagic zone when they think of the ocean.
The intertidal zone is where the water meets land.
The epipelagic zone is the upper, sunlit zone of the open ocean.
These zones have abundant life due to sunlight and photosynthesis.
But a small fraction of the ocean biome composes these ocean zones.
The majority of the ocean is cold, dark, and deep.
Photosynthesis occurs down to 100-200 meters.
Sunlight disappears altogether at 1,000 meters or less.
The ocean descends to a maximum depth of about 11,000 meters in the Mariana Trench.

Scale of the Deep Ocean

Over 60% of the planet is covered by water more than a mile deep.
The deep sea is the largest habitat on Earth and is largely unexplored.
More people have traveled into space than to the deep ocean.

Volume of the Biosphere

79% of the entire volume of the Earth’s biosphere consists of waters with depths greater than 1,000 meters.
Until recently, the deep sea was largely unexplored.
Advances in deep-sea submersibles and image capturing and sampling technologies
Increasing the opportunities for marine biologists to observe and uncover the mysteries of the deep ocean realm.

Importance of Deep Sea Research

Deep-sea research is vital because this area is such an enormous part of the biosphere.
The deep ocean is in our backyard.
Human exploration has revealed more about the surface of the moon and Mars than the deep sea!
The hydrothermal vents and their unique organisms were discovered in 1977.
Hydrothermal vents revolutionized our ideas about energy sources and the adaptability of life.
Possibilities of life-altering discoveries to be found at the bottom of the ocean.

Studying the Deep Ocean

Most of the information we have learned/seen from the deep is from advanced technology.
Submarines, ROVs (remotely operated vehicles), and AUVs (autonomous undersea vehicles).
These technologies captured videos, photos, and samples from this mysterious world.
We will be watching a lot of videos to see what is happening.
We will also be listening to commentaries from the people who specialize and are experts in this area of study!
This is a place that we don’t recognize as well, or know, the same way we know the sandy shores of our beaches or the lighted part of the ocean we interact with.
Keep an open mind as we explore this mysterious world!

Ocean Zones

The oceans are divided into two broad realms: the pelagic zone and the benthic zone.
- Pelagic: The open water in which swimming and floating organisms live.
- Benthic: The ocean floor and the organisms that live there.
We divide the pelagic into the following zones (remember the last three zones have no sunlight at all)
- Epipelagic zone: Less than 200 meters where there can be photosynthesis.
- Mesopelagic zone: 200 – 1,000 meters, the “twilight” zone with faint sunlight but no photosynthesis.
- Bathypelagic: 1,000 – 4,000 meters.
- Abyssopelagic: 4,000 – 6,000 meters.
- Hadopelagic: The deep trenches below 6,000 meters to about 11,000 m or 36,000 feet deep.

Major Ocean Topography

Continental shelf
Continental slope
Continental rise
Abyssal plain
Abyssal hills
Seamount
Guyot
Mid-ocean ridge
Submarine canyon
Trench

Deep Benthic Surfaces

Most of the deep seafloor consists of mud (very fine sediment particles) or “ooze” (mud with a high percentage of organic remains).
The mud and ooze are due to the accumulation of pelagic organisms that sink after they die.
Sandy habitats are rarely found in the deep sea.
Sand particles are created by wave action on coral and rocks at shorelines which are too heavy to be carried by currents to the deep.
If benthic areas are too steep for sediment to stick, like around the flanks of islands, they are covered in rocks.
At the mid-ocean ridges, even flat surfaces are rocky because these areas are too geologically new to have accumulated much mud or ooze.
In some areas certain chemical reactions produce unique benthic formations.
“Smoker” chimneys created by hydrothermal vents.

Challenges to Studying Deep Sea Life

Exploration of the deepest ocean zones has been a challenge for decades, and much remains to be discovered.
Life in the deep sea must withstand total darkness (except for bioluminescence), extreme cold, and great pressure.

Pressure Challenges

Pressure is defined as the continuous physical force exerted on an object by something in contact with it.
The pressure underwater increases about 1 atmosphere for every 10 meters of water depth (~32.8 ft).
At a depth of 5,000 meters the pressure will be approximately 500 atmospheres or 500 times greater than the pressure at sea level.
That’s enough pressure to crush a person!
The third container was only 60 L, but it weighed 132.02 lbs!
1 liter of water weighs 1 kilogram or 1000 grams.
At about 100 m below the ocean’s surface, water weighs about 220,026 lbs.
Our ocean has a potential volume of 538 million cubic miles, so it weighs about $4.9x10^{21}$ pounds!
In the Mariana Trench, it weighs about 15,750 lb or above for every square inch.
The pressure at the bottom is… 15,750 psi, more than 1,000 times the atmospheric pressure at the surface!

How Deep Can We Scuba Dive?

-300 METERS (964 FEET)
-301 METERS (987 FEET)
302 METERS (996 FEET)

Temperature Challenges of the Deep

The deep ocean (below about 200 meters depth) is cold, with an average temperature of only 0-4°C (32-39°F)
No sun = no heat
Cold water is also more dense, and as a result heavier and therefore sinks below the warm water at the surface, which contributes to the coldness of the deep ocean.

Advances in Technology for Deep-Ocean Exploration

Sophisticated data collection devices have been developed to collect samples and observations from the deep.

Observational Equipment

Advances such as fiber optics that use LED light and low-light cameras have increased our understanding of the behaviors and characteristics of deep-sea creatures in their natural habitat.

Remotely Operated Vehicles (ROVs)

Remotely operated vehicles (ROVs) have been used underwater since the 1950s.
ROVs are unmanned submarine robots with cables used to transmit data between the vehicle and researcher for remote operation in areas where diving is constrained by physical hazards.
ROVs are often fitted with video and still cameras as well as with mechanical tools such as mechanical arms for specimen retrieval and measurements.
Other unmanned submarine robots include AUVs (autonomous undersea vehicles) that operate without a cable, and the USA’s new Nereus, a hybrid unmanned sub which can switch from ROV to AUV mode, and which is currently the world’s only unmanned submarine capable of reaching the deepest trenches.

Sperm Whales and ROVs

The ROV Hercules captured the following video at 598 meters (1,962 ft) below the Gulf of Mexico off the coast of Louisiana.
The sperm whale circled the ROV Hercules several times and gave their cameras the chance to capture some incredible footage of this beautiful creature!
Encounters between sperm whales and ROVs are incredibly rare!
Sperm whales typically hunt for food during deep dives that routinely reach depths of 2,000 feet and can last for 45 minutes.
They are capable of diving to depths of 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 that has been used extensively over the past 4 decades to shed light on the black ocean depths.
This sub, which carries 3 people (typically a pilot and 2 scientists), has been used for more than 4,000 dives, reaching a maximum depth of more than 4,500 m.

Trieste Submarine

Until 2012, only one manned submarine device, the bathyscaphe Trieste manned by Jacques Piccard and Don Walsh, has ever reached the bottom of Mariana Trench at almost 11,000 m.
During the Trieste’s single dive in 1960, its windows began to crack.
It has never been used since due to the intense pressure that deep.
52 years later, on March 25, 2012, James Cameron successfully dove in his commissioned one-man sub to the Challenger Deep.

Animal Adaptations to the Deep Ocean

Abiotic (non-living) factors: lack of light, pressure, currents, temperature, oxygen, nutrients and other chemicals
Biotic ones: other organisms that may be potential predators, food, mates, competitors or symbionts.
All these factors have led to fascinating adaptions for sensing, feeding, reproducing, moving, and avoiding being eaten by predators

Lack of Light Adaptations

The deep sea begins below about 200 m, where sunlight becomes inadequate for photosynthesis.
From there to about 1,000 m, the mesopelagic or “twilight” zone, sunlight continues to decrease until it is gone altogether.
This faint light is deep blue in color because all the other colors of light are absorbed at depth
The deepest ocean waters below 1,000 m are as black are completely pitch black.

Bioluminescence

People who dive deep in a submersible (with its lights off) are often mesmerized by an incredible “light show” of floating, swirling, zooming flashes of light.
This is bioluminescence, a chemical reaction in a microbe or animal body that creates light without heat, and it is very common in the deep sea for a variety of reasons.

How Bioluminescence Light is Released

The light is produced by symbiotic bacteria within light-emitting cells called photophores.
It's produced by a chemical reaction when a substance called a luciferin is oxidized. When the light is released, the luciferin becomes inactive until it is replaced by the animal.
Some animals can make luciferin themselves, or it may be synthesized by symbiotic bacteria inside the photophore.
The photophores, or light-emitting cells, range from simple clusters of cells to complex organs surrounded by reflectors, lenses, color filters and muscles.
The most common colored light produced by marine organisms is blue - this is because it is the color that penetrates furthest through water!

What is Bioluminescence Used For?

In the dark of the ocean, bioluminescence can help organisms to survive.
Several deep-sea fish, such as anglerfish, and viperfish use bioluminescence as a lure to attract prey.
The dangling appendage that extends from the head of the anglerfish has a light organ at the end
Which attracts small animals to within striking distance for nutritional needs in the deep.
Deep-Ocean animals can turn their photophores on and off.
Bioluminescence is used for a variety of offensive and defensive strategies ranging from avoiding predators to finding their next meal — or even a mate.

Bioluminescent Protection

Other fish, such as lanternfish (myctophids), have light organs on their sides and bellies.
Lights on the underside of a fish such as a lanternfish or bristlemouth break up the silhouette of the fish's body.
This makes the fish harder to see from below and helps protect it from predators.
Light organs also help fish to recognize mates. Each species of lanternfish has a distinct pattern of lights.

Large Eyes Adapted to See Bioluminescence

Bioluminescent light is low compared to sunlight, so animals here — as well as those in the mesopelagic zone — need special sensory adaptations.
Many deep-sea fish such as the stout blacksmelt have very large eyes to capture what little light exists.
Other animals such as tripodfishes are essentially blind and instead rely on other enhanced senses including smell, touch and vibration.

Deep-Sea Eye Adaptations

Eye size increases with depth before 1,000 m, then decreases in bathypelagic (aphotic) zone
Some deep-sea fish have even evolved to have night-vision

Six Functions of Bioluminescence

Headlights, such as the forward-facing light organs (called photophores) of lantern fish
Social signals such as unique light patterns for attracting mates
Lures to attract curious prey, such as the dangling “fishing lures” of anglerfish
Counterillumination, in which rows of photophores on the bellies of many mesopelagic fish produce blue light exactly matching the faint sunlight from above (making the fish invisible to predators below them)
Confusing predators or prey, such as bright flashes that some squid make to stun their prey, and decoys that divert attention, such as the glowing green blobs ejected by green bomber worms
“Burglar alarms” in which an animal being attacked illuminates its attacker (the “burglar”) so that an even bigger predator (the “police”) will see the burglar and go after it. Some swimming sea cucumbers even coat their attackers with sticky glowing mucus so the “police” predators can find them many minutes later.

Interesting Animal Fact

Most bioluminescence is blue, or blue-green, because those are the colors that travel farthest in water.
As a result, most animals have lost the ability to see red light, since that is the color of sunlight that disappears first with depth.
But a few creatures, like the dragonfish, have evolved the ability to produce red light!
This light, which the dragonfish can see, gives it a secret “sniper” light to shine on prey that do not even know they are being lit up!

Pressure Adaptations

Pressure increases 1 atmosphere (atm) for each 10 m in depth.
The deep sea varies in depth from 200 m to about 11,000 m, therefore pressure ranges from 20 atm to more than 1,100 atm.
High pressures can cause air pockets, such as in fish swim bladders, to be crushed, but it does not compress water itself very much.
High pressure distorts complex biomolecules — especially membranes and proteins — upon which all life depends.
Their membranes and proteins have pressure-resistant structures that work by mechanisms not yet fully understood, but which also mean their biomolecules do not work well under low pressure (shallow waters)
Some organisms may use “piezolytes” - small organic molecules that somehow prevent pressure from distorting large biomolecules.
One of these piezolytes is trimethylamine oxide (TMAO).
TMAO is found at low levels in shallow marine fish and shrimp that humans routinely eat, but TMAO levels increase linearly with depth and pressure in other species.

Consequences of Pressure Change

Animals brought from great depth to the surface generally die.
In the case of some deep-sea fishes, their gas-filled swim bladder expands to a deadly size.
The vast majority of deep-sea life has no air pockets that would expand as pressure drops during retrieval (non-vertebrae organisms like arthropods or echinoderms)
Rapid pressure as well as temperature changes kill them because their biomolecules no longer work well

Barotrauma and Recompression

Animals from deep sea can experience barotrauma, damage to body tissues caused by a difference in pressure between an air space inside or alongside the body and the surrounding fluid.

Temperature Adaptations

Except in polar waters, the difference in temperature between the photic zone and the deep aphotic zone can be dramatic because of thermoclines
A thermocline is the transition layer between warmer mixed water at the ocean's surface and cooler deep water below. It is the separation of water layers of differing temperatures.
In most parts of the deep sea, the water temperature is more uniform and constant.
With the exception of hydrothermal vent communities where hot water is emitted into the cold waters, the deep sea temperature remains between about -1 to about +4°C (30.2° F – 39.2°F)
Water never freezes in the deep sea (seawater freezes at -1.8°C).

Adaptations to the Cold Temperatures

Life in the deep is thought to adapt to this intense cold in the same ways that shallow marine life does in the polar seas
By having “loose” flexible proteins and unsaturated membranes which do not stiffen up in the cold.
It has been found that deep-sea animals have cell membranes with high concentrations of the steroid molecule cholesterol and a high percentage of unsaturated fatty acids in it.
These two lipids’ function is to maintain the fluidity of the cell membrane
ensuring that cells still function and can get things in/out even in extreme cold temperatures!
There is a tradeoff: loose membranes and proteins of cold-adapted organisms readily fall apart at higher temperatures.

Lack of Oxygen Adaptations

Oxygen has two main ways of entering the ocean:
- surface mixing (where air meets the water through wind and waves)
- photosynthesis by microscopic phytoplankton or macroalgae that produce oxygen.
Cold water can dissolve more oxygen than warm water, and the deepest waters generally originate from shallow polar seas.
In certain places in the northern and southern seas, oxygen-rich waters cool off so much that they become dense enough to sink to the bottom of the sea.
These so-called thermohaline currents can travel at depth around the globe, and oxygen remains sufficient for life because there is not enough biomass to use it all up!

Oxygen-Poor Environments of the Deep

Oxygen-poor environments in intermediate zones, wherever there is no oxygen made by photosynthesis and there are no thermohaline currents.
These areas, called oxygen minimum zones, usually lie at depths between 500 – 1,000 m in temperate and tropical regions.

Nutrition/Food Adaptations

Deep sea creatures have evolved some fascinating feeding mechanisms because food is scarce or hard to come by in these zones.
In the absence of photosynthesis, most food consists of detritus — the decaying remains of microbes, algae, plants and animals from the upper zones of the ocean — and other organisms in the deep (also known as Marine Snow)
Scavengers on the seafloor that eat this “snow” of detritus include sea cucumbers (the most common benthic animal of the deep), brittle stars, and grenadier or rattail fish.

Marine “Snow”

Marine snow is a shower of organic material falling from upper waters to the deep ocean.
As plants and animals near the surface of the ocean die and decay, they fall toward the seafloor
In addition to dead animals and plants, marine snow also includes fecal matter, sand, soot, and other inorganic dust.
The decaying material is referred to as “marine snow” because it looks a little bit like white snow as it falls.
The “snowflakes” grow as they fall, some reaching several centimeters in diameter. Some flakes fall for weeks before finally reaching the ocean floor.

Importance of Marine Snow

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.
NOAA scientists and others have measured the amount of useable material in marine snow and found that there is plenty of carbon and nitrogen to feed many of the scavengers in the deep sea.
About three-quarters of the deep ocean floor is covered in this thick, smooth ooze. The ooze collects as much as six meters every million years.

Large Falling Meals

The corpses of large animals such as whales that sink to the bottom provide infrequent but enormous feasts for deep sea animals and are consumed by a variety of species.
This includes jawless fish such as hagfish, which burrow into carcasses, quickly consuming them from the inside out; scavenger sharks; crabs; and a newly discovered group of worms (called Osedax, meaning bone-eater) which grow root-like structures into the bone marrow!

Large Mouths and Teeth Adaptations

Deep-sea pelagic fish such as gulper eels have very large mouths, huge hinged jaws and large and expandable stomachs to engulf and process large quantities of scarce food.
Many deep-sea pelagic fish have extremely long fang-like teeth that point inward.
This ensures that any prey captured has little chance of escape.

Ambush Predators in the Deep

Some species, such as the deep-sea anglerfish and the viperfish, are also equipped with a long, thin modified dorsal fin on their heads tipped with a photophore lit with bioluminescence used to lure prey.
Many of these fish don’t expend much energy swimming in search of food; rather they remain in one place and ambush their prey using clever adaptations such as these lures and projections from their bodies.
Others, such as rattails or grenadiers cruise slowly over the seafloor listening and smelling for food sources failing from above, which they engulf with their large mouths.

Vertical Migration

Some mesopelagic species have adapted to the low food supply with a special behavior called vertical migration.
At dusk, millions of lantern fish, shrimp, jellies and other mobile animals migrate to the food- rich surface waters to feed in the darkness of night.
Then, to avoid being eaten in daylight, they return to the depths at dawn to digest.
Some of the species undergo large pressure and temperature changes during their daily migrations.

Further Adaptations of Animals in the Deep-Sea

Animals of the deep-sea have evolved to cope with their harsh environment

Body Color Adaptations

In the deep sea, animals’ bodies are often:
- Transparent (such as many jellies and squids)
- Black (such as dragonfish), or even
- Red (such as many shrimp and other squids).
The absence of red light at these depths keeps them concealed from both predators and prey.

Reproduction Adaptations

Consider how hard it must be to find a mate in the vast dark depths. For most deep sea species, we do not know exactly how they achieve this.
Unique light patterns may aid in this.
Deep-sea anglerfish may use such light patterns as well as scents to find mates, but they also have another interesting reproductive adaptation.
Males are tiny in comparison to females and attach themselves to their mate using hooked teeth, establishing a parasitic-like relationship for life.
The blood vessels of the male merges with the female’s so that he receives nourishment from her.

Gigantism Adaptations

This is the tendency for certain types of animals to become truly enormous in size.
A well-known example is the giant squid, but there are many others such as the colossal squid, the giant isopod, the king-of-herrings oarfish (which may be the source of sea-serpent legends), and the recently captured giant amphipod from 7,000 m in the Kermadec Trench near New Zealand.

Long-Lives Adaptation

Many deep-sea organisms, including gigantic but also many smaller ones, have been found to live for decades or even centuries!
Long-lived fishes include rattails or grenadiers and the orange roughy.
These species reproduce and grow to maturity very slowly, such that populations may take decades to recover (if at all) after being overfished.

Hydrothermal Vent & Cold Seep Communities

Life in the deep sea is relatively sparse compared to the epipelagic and intertidal zones, however there are TWO exceptions— hydrothermal vent and cold seep communities.
These amazing formations were first discovered in 1976 – 1977 during a deep-sea expedition with Alvin at a mid-ocean ridge near the Galapagos.
These dives to depths of about 2,700 m revealed hot springs of far greater complexity: hot 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 Vent Communities

High densities of numerous new species new kind of ecosystem flourishing in the dark that had never been imagined by scientists — an ecosystem based on toxic gas!
The most amazing of the new species was a giant tubeworm, named Riftia.
Growing rapidly in dense clusters, these 2-meter-tall worms were found to have no digestive tract.
Hydrogen sulfide (rotten-egg gas) is normally toxic to animals, but these worms avoid the problem because they harbor bacteria known as chemoautotrophs, which can use the energy in hydrogen sulfide to convert carbon dioxide into sugars, just as plants do using sunlight.
The worm’s blood picks up and delivers sulfide, carbon dioxide and oxygen to these bacterial symbionts, which in turn “feed” their hosts with the excess sugars they make (while turning the sulfide into a non- toxic waste product).
The ecosystem was found to run on the Earth’s geothermal energy rather than sunlight. Many scientists now think that life on Earth began at such vents over 3 billion years ago.

Hydrothermal Vent Locations

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.
The water temperature of vents is much warmer than normal for the deep sea (about 2°C), reaching as high at 400°C without boiling due to the high pressure.
The communities of vent life are mostly found between about 8 – 25°C, but may reach perhaps 60°C around some animals such as Pompeii worms (Alvinella).
Some archaea have been found living at temperatures of over 120°C!

Cold Sleeps/Seeps

After the first vent discoveries, other high-density deep-sea ecosystems were found named cold sleeps.
These occur at places (mostly along continental margins) where cold methane (which at depths below 500 m forms methane- hydrate “ice”), hydrogen sulfide, and/or oil seep out of sediments to provide abundant energy.
Animals with symbiotic bacteria were found, different from but related to vent species, including tubeworms, clams, and mussels.

Brine Pools

Dense seep communities have also been found around deep brine pools, or “lakes within oceans.”
These form where salt deposits under the ocean floor dissolve to form pools of water so dense from their salt content that they do not mix with the overlying seawater.
High densities of mussels live around the rim, subsisting (using symbionts) on methane gas seeping from the pool.
No known animal can survive the salt within the pool itself except some microbes.