Lesson II: Animal Adaptations and Distributions I

Key words: Photosynthesis, topography, phytoplankton, nutrients, phytoplankton blooms, buoyant, cilia, fusiform, lunate, caudal peduncle, deep scattering layer, diel migrations, euphotic, metabolism, pupil, rods, cones, retina, photophores, ventral, microhabitat, food-poor, opportunistic, gill rakers

During this program we will discuss organisms of the epipelagic and mesopelagic zones focusing on the adaptations that allow them to live in these environments. Included in this show will be the vertical migrators.

Organisms of the Epipelagic Zone

The Epipelagic zone is the nutrients have phytoplankton uppermost layer of the ocean; it is blooms. Zooplankton, (small located between the surface and animals that float with the currents 600 feet in depth. It is in this thin that we think of as fish food) feed layer that all photosynthesis takes on phytoplankton and are present place. The epipelagic zone only in higher numbers where blooms represents 2-3% of the entire occur. ocean, beyond this, light is too dim for photosynthesis to occur. In In the well-lit epipelagic-zone, fact, in all the world’s oceans, 65% most predators use vision to seek of the plankton are in the top 500 out prey. There are several meters. adaptations that allow prey organisms to survive here. One Not all surface waters are adaptation is small size. The most productive and much is featureless. numerous organisms of the sunlit Therefore in the surface waters, zone, the zooplankton, are small. temperature, light, topography, When you are small, not only are and distance from land tend to you hard to see, but it is easier it is determine organism distribution. to stay afloat. If an organism is Phytoplankton need nutrients small and light it can stay up in the (fertilizer) in addition to lots of water column longer. Larger sunlight. Much of the open ocean gelatinous organisms, like jelly- is nutrient poor and there is little fish are also very hard to see phytoplankton growth. Areas close because they are transparent and to land tend to have higher nutrient they have a density close to that of content because of runoff from water; this allows them to be both land. These areas with higher hard to see and neutrally buoyant. Some of these organisms have locomotion, touch, or to sense cilia, tiny hairs on their body, this water movement. increases their resistance to sinking, and can also be used for A diatom A comb jelly

Most epipelagic fishes have narrow caudal peduncle. They streamlined or fusiform bodies also have a lot of muscle mass, (spindled-shaped like a which enables them to be strong submarine), that allow them to swimmers. Good examples of slide through the water more these adaptations can be seen in a easily, which is important if you tuna fish, shown below. This are swimming continuously. Many picture also shows water flow over have adaptations that help them the fusiform shape. swim fast such as a lunate tail or a countershading

terminal mouth

narrow, caudal lunate tail peduncle

Generalized Fusiform Body Shape

These large visual predators often mouths. The oceanic plankton have terminal mouths (see above) feeders often have superior because they use their speed to mouths, so they can pick on the ram their prey right into their large plankton at the surface of the water.

superior

mouth

Atlantic Bumper

Coloration, or countershading is them from below, they blend into another important adaptation in the the lighted surface above! Often, epipelagic zone. Most epipelagic their colors are silvery; this reflects organisms have countershading and scatters incoming light making (see the tuna on the previous their silhouettes difficult to see. As page): dark on top, and silvery mentioned above, zooplankton of below. For anything swimming the epipelagic zone are usually above (predator or prey) they small and hard to see. If they are blend into the darker water below larger, they are transparent, like and for anything looking up at jellyfish.

Organisms of the Mesopelagic Zone

If we proceed in our journey important issue governing life in through the water column, the next the twilight zone is that we lose the zone that we encounter is the air-water interface; it becomes an mesopelagic or twilight zone. It is entirely three-dimensional world! called the twilight zone because it We have nothing to compare it to is dimly lit. The amount of light is in our terrestrial existence. Even insufficient for plants to carry out birds have to land on the ground or photosynthesis yet it is bright in a tree sometime! Organisms of enough to tell the difference the mesopelagic zone may never between night and day. The see a physical boundary of any mesopelagic zone ranges from kind. This makes it very difficult about 600 feet to about 3000 feet for researchers to study organisms in depth, depending on how far of the mesopelagic zone. When sunlight can reach. The amount of held in captivity they tend to ram suspended material, in the water, themselves into the sides of their like silt or algae can determine aquarium until they kill how deep sunlight can reach and themselves. They are unable to which wavelengths are absorbed deal with boundaries. first. First, a short discussion on The mesopelagic zone is also what light is may help. Sunlight is where we encounter the permanent actually composed of many thermocline (see diagram), a different wavelengths, each of region of marked vertical which is a different color; you can temperature change. Temperature see this when you pass light decreases from near surface through a prism. Long temperatures to about 4-8°C at wavelengths are red. Short about 1000 meters (3280 feet). The wavelengths are blue. When you temperatures encountered by look at the ocean, it appears to be mesopelagic organisms are blue or green, that is because the therefore a function of how deep shorter wavelengths are being they live. reflected. The longer red wavelengths are being absorbed in Pressures are far greater than in the the surface waters; at depth red epipelagic zone. Pressure increases wavelengths are no longer present. by one atmosphere with every A red organism will not have a thirty feet of depth. Pressure in the wavelength to reflect and will mesopelagic zone ranges from therefore appear black. Another about 300 pounds per square inch These vertical migrations are (psi) to 1500 psi. known as diel migrations, because the journey has two parts: up at The fact that many organisms dusk and down at dawn. Vertical leave the surface waters during the migrators occur at all latitudes in daylight hours and then return at all oceans. Different organisms night has been known since the migrate at different times to Challenger expedition in the different depths. This migration 1860’s. However, it wasn’t until allows organisms to remain at a the development of sonar and the constant level of low light at all increasing use of submarines in times. Zooplankton migrate up at warfare that it attracted large night to feed on phytoplankton, amounts of scientific interest. This which always stay in the euphotic is because there are so many of zone and small fish follow the these vertical migrators that they zooplankton. Then, around sunrise create what is known as a deep they migrate back to the depths to scattering layer. The animals avoid daylight. There are several reflect sound waves and appear on theories as to why this might an echogram as a phantom bottom, occur. It may be that in the because it moves around absence of light they are less depending on the time of day! The visible to predators or possibly, navy was of course interested their metabolism slows when they because they wanted to hide their return to cooler, darker waters. submarines beneath it. Many Since they are cold blooded, the researchers speculated as to what cold temperature at depth allows could possibly cause it. Some them to burn up the food they have thought giant squid, and others just consumed more slowly! It is thought shrimp or fish. Well, the easy to see how this helps to bring fish and shrimp camp won. Tows food to the food-poor depths. were made at the exact depth and Some organisms do not make the time of the deep scattering layer. migration, they simply wait for the They brought up many small food to come back to them! euphausiid shrimp, lanternfishes (myctophids) and large shrimp.

Vertical Migrations

We have already discussed the dim (light sensitive layer located inside light that reaches the twilight or rods and cones in their retina the mesopelagic zone as you might back of the eye), the rods absorb guess it has profound effects on light and cones allow them to see the adaptations of the organisms color. Fishes of the mesopelagic living here. The eyes of layer and deeper only have rods, mesopelagic organisms are well with a few exceptions. Not only do developed and though they may they have all rods but the actual look similar to eyes of an part of the rod that absorbs the epipelagic organism, if we look light is longer. Many fish of the closer, we find important mesopelagic zone have eyes that differences. Often the eyes are are outwardly different, tubular larger, but even if they are not, the eyes that are upwardly directed are pupil, the part of the eye that lets a common adaptation; this may in the light, is larger. Also, fishes help to see things above them that of the epipelegic zone have both are silhouetted in the dim light.

tubular, upwardly directed eyes

photophore

The hatchetfish- Argyropelecus i and yet be able to make In the upper mesopelagic zone themselves known to mates. fishes tend to still have silvery upper bodies to help them blend Not only is the mesopelagic zone with light coming down from the dark, it is food poor. The surface. But in the mesopelagic inhabitants of the twilight zone zone many fishes also have must be able to utilize a wide photophores on their ventral range of prey items in order to surface. There are many theories survive, or in ecological terms, as to the function of the they must be opportunistic. photophores such as blending with Therefore, in comparison with the surface light, species most surface dwelling organisms identification (to aid in finding a their mouths are pretty large. If mate), flashing to confuse a they happen upon another predator or to attract prey. Maybe organism they may try to eat it, no depending on the circumstances matter how large. They also have a they fill all of these functions! All set of fine gill rakers so that really of these would be useful in the small things cannot slip away deep sea, as there are no either. In surface dwelling fish the microhabitats; that is, there are no gill rakers can be very finely bushes to hide behind or caves to spaced for those that filter duck into. Animals must carry plankton to widely spaced for their own concealment with them carnivores. But in the twilight zone nothing is wasted!

Earlier, we discussed the adaptation of being red. However, distribution of light through the there are also fish in the water column. Long wavelengths mesopelagic zone that have a (red light) are absorbed in the special adaptation to allow them to upper ten meters therefore any see these red crustaceans. A few of organism that is red in the the fish have a special cheek light mesopelagic zone is functionally organ that emits light in the far-red black! There is no red light to portion of the spectrum, this reflect the red color back. There allows them to see these invisible are many crustaceans in the shrimp! twilight zone that have the special

In our next show we journey even deeper in the ocean, to a place where the sun’s rays never reach, the Bathypelagic Zone.

Fun Facts • Some shampoos contain oils from the orange roughy fish. The orange roughy is a deep-sea species from New Zealand. • Sea-serpent sightings are attributed to the oarfish. It is the longest bony fish in the world with a magnificent red fin along its 50-foot length, horse-like face, and blue gills. • Some deep ocean fish have organs below their eyes, which give out both red and ordinary light. The fish can then see red animals that are invisible otherwise, and illuminate others with the red light only they can see. Discussion Topics/Questions 1. What are some advantages to being small in the epipelagic zone? 2. Why is proximity to land important in determining animal distributions? How might this affect the deep sea? 3. Plants need sunlight. Why is productivity low in some areas where there is a lot of sunlight? 4. Compare and contrast some of the adaptations for living in the epipelagic zone with those for living in the mesopelagic zone. Why are these adaptations important? 5. What are some advantages and disadvantages of vertical migrations?

Activity II-1. Seeing Red

1. Buy a red light bulb and put it in a small lamp. Give the students red pencils and have them write a note or a word. Make sure the room is totally dark then turn on your red lamp. Have the students read their words. Can they see them? Ask them why they think this is so? How does being red help organisms that live in the mesopelagic zone?

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Organisms of the Epipelagic Zone

The Epipelagic zone is the use vision to seek out prey. There uppermost layer of the ocean; it is are several adaptations that allow located between the surface and prey organisms to survive here. 600 feet in depth. It is in this thin One adaptation is small size. The layer that all photosynthesis takes most numerous organisms of the place. The epipelagic zone well-lit zone, the zooplankton, are represents 2-3% of the entire small. ocean, beyond this, light is too dim for photosynthesis to occur. Coloration, or countershading is another important adaptation in the Not all surface waters of the ocean epipelagic zone. Most epipelagic are productive. Therefore in the organisms have countershading: surface waters, temperature, light, dark on top and silvery below. for topography, and distance from anything swimming above land tend to determine organism (predator or prey) they blend into distribution. Phytoplankton need the dark water below, for anything nutrients (fertilizer) in addition to looking up at them from below, lots of sunlight. they blend into the silvery surface above! In the well-lit (photic) or epipelagic-zone, most predators

Organisms of the Mesopelagic Zone

The amount of light is insufficient photosynthesis yet it is bright for plants to carry out enough to tell the difference between night and day. The look similar to eyes of an mesopelagic zone ranges from epipelagic organism, if we look about 600 feet to about 3000 feet closer, we find important in depth depending on how far differences. Fishes of the sunlight can reach. The amount of epipelegic zone have both rods suspended matter in the water, like and cones in their retina, the rods silt and algae can determine how absorb light and cones allow them deep sunlight can reach and which to see color. Fishes of the wavelengths are absorbed first. mesopelagic layer and deeper only have rods with a few exceptions. The mesopelagic zone is also where we encounter the permanent Not only is the mesopelagic zone thermocline, a region of marked dark, it is food poor. The vertical temperature change. inhabitants of the twilight zone Temperature decreases from near must be able to utilize a wide surface temperatures to about 4- range of prey items in order to 8°C at about 1000 meters (3280 survive. feet). Pressures are far greater than in the epipelagic zone. Pressure increases by 1 atmosphere with every thirty feet of depth.

The fact that many organisms leave the surface waters during the daylight hours and then return at night has been known since the Challenger expedition in the 1860’s. These vertical migrations are known as diel migrations, because the journey has two parts: up at dusk, down at dawn.

We have already discussed the dim light that reaches the twilight or mesopelagic zone. As you might guess, it has profound effects on the adaptations of the organisms living here. The eyes of mesopelagic organisms are well developed and though they may