Organisms of the Deep
The deep sea bottom is a rather harsh environment with temperatures hovering at about 4C and very little light. Salinity is slightly higher (remember more salt=more dense=sinks) and pressure is much greater than at the surface. This is similar in the deep oceans world-wide. The cold has its advantages--slowing down organisms' metabolism so they need less food (which also means they grow slower). The majority of food comes from above; bacteria will attack and decompose it while others will eat it.
These animals tend to be smaller but live longer. This applies to MOST but not all deep ocean animals--some keep growing and get fairly large compared to their shallow water counterparts. Many of these organisms do not have skeletons because bones don't handle high pressure well. This makes these animals particularly fragile.
These animals tend to be smaller but live longer. This applies to MOST but not all deep ocean animals--some keep growing and get fairly large compared to their shallow water counterparts. Many of these organisms do not have skeletons because bones don't handle high pressure well. This makes these animals particularly fragile.
Organisms that survive in the deep ocean must adapt. With hardly any light, eyesight is no advantage so other senses are relied upon. For example, the tripod fish uses fins to feel for its food. Some will lie on the bottom with their mouth open-->the prey crawl in looking for a safe place to hide. Some have a strong sense of smell and are able to smell rotting flesh from miles away.
One of the most unique adaptations of the deep is bioluminescence (a chemical reaction in an organism that creates light). Bioluminescence is common in the deep ocean and is used for several different purposes.
One of the most unique adaptations of the deep is bioluminescence (a chemical reaction in an organism that creates light). Bioluminescence is common in the deep ocean and is used for several different purposes.
- Headlights that face forward ex: lantern fish
- Social signals to attract mates
- Lures to attract prey ex: anglerfish
- Counterillumination for camouflage
- Confusing predators or prey ex: squid shooting off bioluminescent material that stuns its prey
- "Turning the tables"--sometimes the animal being attacked will light up so that another predator will see the animal that was attacking the original animal and get eaten. One example is a sea cucumber that will coat its attacker in a sticky glowing mucus so it will be found and eaten.
In order to truly understand the adaptations necessary in the deep ocean, we must look at the adaptations in all of the oceanic zones.
Epipelagic--the uppermost layer that gets sunlight.
Epipelagic--the uppermost layer that gets sunlight.
- Most predators use vision to catch their prey. They have large eyes in order to see their prey.
- One adaptation is small size for prey animals. Most epipelagic fish will have a streamlined shape to allow them to cut through the water more easily, an important adaptation if you are constantly swimming. They also have a lot of muscle mass in order to be strong swimmers. Coloration is another important adaptation.
- Most "upper" fish have countershading--dark on top and silvery on bottom. This helps them blend in depending on whether they are being viewed from above or below. Another is "clear" coloration (think jellies) that makes prey harder to see.
Mesopelagic--the twilight zone that is dimly lit; typically between 350-3000ft.
- While there is not much light, there is still enough to tell the difference between day and night. Many organisms will leave the surface during the day and return at night. These organisms are known as "vertical migrators". This allows organisms to remain at a constant level of low light at all times. These species typically have a swim bladder (buoyancy). They also have well-developed muscles and bones, and are usually somewhat streamlined. Migration behavior is believed to be due to the organism following its food (zooplankton eats phytoplankton at night so fish come up) but the more common theory is this allows organisms to maintain their slow metabolism by remaining in cooler waters. These migrators may be elongated or "skinny" (laterally compressed) to make traveling up and down through the water column more efficient.
- FIsh that are not migrators and are "sit and wait" predators lack a swim bladder, and have flabby muscles and watery flesh. Because they do not go anywhere, streamlining has either not evolved or has disappeared and these organisms are much rounder.
- As you will learn in your light lab, different colors of light are absorbed at different rates. Red wavelengths are absorbed first while blue and green last the longest. This means that, in the darker waters, a red organism will not have a wavelength to reflect back and will appear black. This is why many mesopelagic and abyssopelagic animals are red (because you can't see them).
- Because of the dark water/lack of light many of these organisms have larger eyes in order to allow to absorb as much light as possible. For those organisms in the lower mesopelagic zone (the non-migrators), these eyes may be tubular and directed upward since they are trying to see things silhouetted above them.
- In the upper mesopelagic zone fishes still have silvery upper bodies in order to blend with light coming down; however, as you get deeper many of the fishes have photophores on their belly that are used to camouflage themselves or to confuse predators and/or attract prey.
- Food in this area is not abundant. This has led predators to be opportunistic feeders. Many fish have large mouths so that they can attempt to eat any organism they come across. They also have gill rakers so that small things can't get away. They are very careful not to waste any food!!
- Since these fish are still preyed upon, size typically remains fairly small.
Bathypelagic & Abyssopelagic: DEEP water, below 3000ft, no light.
- These fish are "stuck" in this area as they cannot migrate vertically. Most of these are "sit and wait" predators or they will use bioluminescence to attract their prey.
- At this depth, swim bladders cannot function (gas can't be produced). Most fish in this layer do not have swim bladders or their swim bladders are filled with wax.
- Fish in this environment have difficulties obtaining food which means they have less energy to build muscles; therefore they are weak and flabby. Since food is so hard to come by, fish have very large mouths and teeth and often have "extendable" stomachs to accommodate large prey. Most of these organisms are longer as they have a lateral line that runs down their back. It helps them feel movement in the water caused by other organisms.
- Coloration here includes black, red, transparent or even white as there is no visible light (all wavelengths have been absorbed). Eyes are reduced in size or absent as they are not needed.
- Size in the deep ranges from small to gigantic (think giant squid!).
- Oftentimes, these fishes have a very good sense of smell in order to smell their next meal from miles away.