Oceanography 10, T. James Noyes, El Camino College 10B-1. Deep-Sea Life

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1 Oceanography 10, T. James Noyes, El Camino College 10B-1 Deep-Sea Life The Deep-Ocean Environment and Food Supply The deep ocean is the largest habitable space on the Earth. Most of the sunlight is absorbed near the surface, so the deep ocean is eternally cold and dark. Animals who live here are squeezed by the enormous pressures, 400 times greater (or more) than the pressure that we experience at the surface of the Earth. Even though these conditions many seem inhospitable, life thrives in the deep ocean, because the animals who live there are well adapted to these conditions. Many deep-ocean animals have a gelantinous ( jelly-like ) body, something that scientists only began to realize in the 1970s. National Oceanic and Atmospheric Administration, Department of Commerce, except for the lower left: Courtesy of Uwe Kils (CC BY-SA 3.0). Most life in the ocean lives in the sunlit waters near the surface, because there is little food in the deep ocean. Most of the animals who do not live at the surface live pretty close to the surface. Many swim up to the surface at night to feed when it is harder to be seen (and eaten themselves), and then swim down again during the day. This is called diurnal vertical migration. Oceanography 10, T. James Noyes, El Camino College 10B-1

2 Oceanography 10, T. James Noyes, El Camino College 10B-2 Diurnal vertical migration was discovered during World War II while scientists were testing SONAR systems. SONAR determines the depth of the ocean or how far away enemy ships are by sending out a pulse of sound and listening for the echo. The echoes kept returning too early, as if the bottom of the ocean was much shallower than it should be. This false bottom changed depth, becoming deeper Day Night during the day and shallower at night. By taking samples at different depths and at different times, scientists determined that the sound was bouncing off large groups of small animals who were migrating up at night to feed. Today, fishermen use SONAR to pinpoint the location of schools of fish. We can scarcely imagine the vast three-dimensional boundlessness of the open sea, in which gravity loses its importance and the only surfaces are other animals. Nothing in outer space could be more alien to us that that. And above all we cannot comprehend a place so utterly permeated with randomness, a place in which there really are no fixed places at all. When you jump in the ocean, you never know what you re going to see Because the water is not the same water you jumped in yesterday. And for the animals that are vertically migrating, they never go up into the same water they were in the day before. Living in the ocean, you don t have the predictability that you do on land Now if you re a planktonic animal your environment is constantly new. You never know what you re going to find. Robert Kunzig & Richard Harbison, The Restless Sea Gelatinous zooplankton ( jellies, see previous page) are especially abundant. Out in the middle of the ocean, there are no hard surfaces (aside from other animals) to run into that would break their delicate bodies. Their bodies can also be vulnerable to violent waves and other motions near the surface of the ocean. Some of them have bodies strong enough to resist the surface turbulence (e.g., a Portuguese man-o-war), while others live deep enough that this is not a problem. Although a gelatinous ( jelly ) body may be delicate and limits their ability to swim quickly, it also has considerable advantages, including transparency and floating easily. In a sense, transparency is the ultimate camouflage in the open ocean, allowing an organism to blend in with the background no matter what color it is. Of course, this is a trade-off: a solid body capable of resisting predators teeth cannot Portuguese man-o-war, NOAA. be transparent; a gelatinous body helps a jelly remain hidden 1 instead. Jellies are transparent because they are primarily made of water (over 95% in some cases), so their density is very close to that of water. Jellies may not be able to gather food as quickly as a fish, but they require less food, in part because they do not need to spend a lot of energy trying to float or swim. 1 This may seem unimportant in the deep, dark ocean, but as we shall see in a moment, there is lots of light in the deep ocean owing to bioluminescence. Oceanography 10, T. James Noyes, El Camino College 10B-2

3 Oceanography 10, T. James Noyes, El Camino College 10B-3 Most true deep-ocean animals those that live there entire lives in the deep ocean eat dead, decaying material (or animals that eat dead, decaying material) that sinks down from the surface of the ocean. The majority of the dead, decaying material (called detritus ) is recycled near the surface of the ocean; only about 10% sinks into the deep ocean. Sinking material tends to clump together, which helps speed its fall and allows explorers to see it with their own eyes. It gleams like little jewels when deep-sea explorers shine their lights on it, and oceanographers have nicknamed it marine snow. It includes dead bodies, Marine Snow, National Oceanic and Atmospheric Administration. mucus, and fecal matter. Bacteria grow on this material on the way down, and some animals will eat fecal pellets, digest the bacteria, and excrete the fecal pellet. Thus, a fecal pellet may go through several digestive tracks before reaching the bottom! Deposit Feeders: Sea Cucumbers & Sand Stars Suspension / Filter Feeder: Sea Fan National Oceanic and Atmospheric Administration Only about 1% of the detritus reaches the bottom and becomes sediments. Most of the detritus is decomposed by bacteria, dissolved by the ocean water, or eaten by animals on the way down. Some benthic organisms (organisms who live on the bottom of the ocean) grab the material before it reaches the bottom (suspension or filter feeding). Others eat the sediments ( deposit feeding ). Their digestive tracks extract the nutritious material, and they excrete the cleaned sediments back onto the ocean floor. Since a very small portion of the sediments that they eat contain organic material, they have to ingest vast amounts 2 of sediments. The amount of food available in the deep ocean can change dramatically with time. Whenever there is a bloom at the surface, more material sinks towards the bottom, so there is a deep-sea bloom as well. However, food in the deep ocean is often a good deal less predictable: the remains of large animals (e.g., fish, whale) can sink to the bottom at any time. Many deep-sea animals specialize in smelling these bodies and gobbling them up first, before others arrive. A fish will be gone in a few hours, a whale in a few months. Your remains would remain for no more than a few days. 2 This churning of the sediments by animals, called bioturbation, causes problems for people who study ocean sediments hoping to learn about life or climate in the past. These organisms disturb the layers that these people study, reducing the accuracy of their measurements. Oceanography 10, T. James Noyes, El Camino College 10B-3

4 Oceanography 10, T. James Noyes, El Camino College 10B-4 Light in the Deep Ocean There is very little sunlight in the deep ocean. At a depth of about 500 feet (150 meters), only 1% of it remains, and sunlight is almost completely gone at 3300 feet (1000 meters). Blue light penetrates deepest, because the other colors 3 (especially red) are absorbed more quickly by the ocean water. Even though sunlight does not penetrate deeply into the ocean, the ability to see or at least sense light in some way is an important adaptation for deep-sea life, because most deep-sea animals are bioluminescent (90% or more!). Many deep-ocean organisms are red. National Oceanic and Atmospheric Administration. Left: GFDL. Right and Center: National Oceanic and Atmospheric Administration. Bioluminescence is light made by living organisms. Deep-sea animals mix the chemical luciferin with oxygen, which produces blue-green light via the same chemical reaction used by fireflies and glow sticks. Some animals have their own special cells called photophores, where the chemicals are mixed to produce light. Others have symbiotic, glowing bacteria that live inside them. The bacteria can be covered by a skin flap (like an eye lid or shutters) that is lifted when the animal wants to glow. Some animals have to eat other organisms to get luciferin, because they cannot make it themselves. Bioluminescent Ctenophore. (NOAA) Chemical Light. Courtesy of David Muelheims (CC BY SA 2.5). 3 Violet is absorbed more slowly than blue light, but there is so much more blue light to begin with that the blue light still dominates. Oceanography 10, T. James Noyes, El Camino College 10B-4

5 Oceanography 10, T. James Noyes, El Camino College 10B-5 Bioluminescence has a variety of uses, and different animals use it for very different purposes. In the movie Finding Nemo, the anglerfish lures Marlin and Dory towards its jaws by lighting the end of one tentacle, making it look as if there was a small zooplankton there instead of a large predator. Some fish simply have glowing headlights above their eyes that work like flashlights for finding food. There is one group of fish, the loosejaws, that have a special filter that changes the light from blue-green to red before emitting it. Most red light deep-sea animals cannot see the color red, but the loosejaws can, so they have a red flashlight that they can use to see other fish, but the other fish cannot see them. Some may light up when attacked to illuminate their attacker, hoping to blind them or that some other animal nearby will attack their attacker (kind of like saying, If I m going down, I m going to take you with me. ), while others send down precisely the same amount of sunlight as that streaming from above, so they will not cast a shadow visible to animals below them (an ingenious form of countershading ). Some cause a non-essential body part to glow (e.g., a tentacle) and detach it, so that a predator will chase after the body part, giving them a few moments to try to get away. Light Shadow Since populations are low in the deep sea, it can be hard to find that special someone to mate with, so animals may glow in particular patterns to say that they are available. (In these species, you tell a lady that you re interested by flashing her.) Have you ever been to the beach at night and seen flashes of light in the crashing waves? You are watching glowing dinoflagellates, a kind of phytoplankton with whiplike tails. Most bioluminescent organisms light up when they run into something, when they make physical contact. The crashing waves exert enough pressure to trigger this response. There are always dinoflagellates like these in the water, but you can only see them flash during blooms (e.g., red tides ) when there are a lot of them in the water. If you see flashing waves, a fun thing to do is to go down to edge of the water and wave your hands back and forth across the surface of the wet sand. Dinoflagellates washed ashore will glow because of the pressure of your hands, so you will create glowing patterns (and footprints) in the sand. You could also take home some water samples, shake them in a (very dark) room, and watch them light up. Bioluminescent algae in breaking waves during a red tide. Courtesy of Catalano82 and Yikrazuul (CC BY 2.0). Oceanography 10, T. James Noyes, El Camino College 10B-5

6 Oceanography 10, T. James Noyes, El Camino College 10B-6 Hydrothermal Vents and Chemosynthetic Communities In the 1970s, scientists discovered that life is enormously abundant on the deep-ocean floor near hydrothermal vents, deep-ocean hot springs where hot water laced with volcanic chemicals pours out of the ocean floor. Stunningly, some of the animals did not have stomachs. In this section, we will examine what hydrothermal vents are and how the animals in these environments obtain the energy that they need to maintain their bodies. Fissures and cracks open in the ocean floor by the midocean, because of earthquakes, volcanic activity, and uneven heating of the crust 4. Cool ocean water seeps down into the cracks and is warmed by the hot rock deep beneath the ocean floor. This makes the water expand, lowering its density and causing it to rise out the hydrothermal vent. It then mixes with the cold water on the bottom of the ocean and cools down again. The cool water can seep down into the cracks again and repeat the cycle, known as hydrothermal circulation (notice that it is a convection cell see topic 8A). Hydrothermal Vent. National Oceanic and Atmospheric Administration. As the water goes down into the cracks and out through the vents, it interacts chemically with the rocks of the crust. The water picks up some dissolved substances from the rock of the crust, and the rock absorbs other substances from the water, altering the water s salinity. For example, sodium and chloride Vent ordinary salt are removed from the water and other substances including potassium, silicon, and calcium are added to the water. Sulfate is of particular interest. The sulfate in ocean water is transformed into hydrogen sulfide as it travels through the ocean crust. Hydrothermal vents are common, so a lot of water goes through them. Thus, they probably have had a strong influence on the ocean s salinity. As some sulfides and other substances come out of vent, they are cooled by contact with the cold ocean water in the deep ocean, which makes some of them precipitate ( solidify ). Not only does this give the water pouring out of some hydrothermal vents a black, cloudy appearance, but the resulting sediments slowly drift to the bottom of the ocean near the vents. These sediments pile up over time, slowly building tall, rock chimneys around the vents. 4 Cooler areas contract more than other areas, causing them to split from the warm areas. Vent When substances are dissolved in a liquid state, they are not sediments. When the water cools and the substances solidify into small particles, they become sediments. Oceanography 10, T. James Noyes, El Camino College 10B-6

7 Oceanography 10, T. James Noyes, El Camino College 10B-7 It is the hydrogen sulfide at the hydrothermal vents that is the key to the abundance of life in their vicinity. Some bacteria ( archaea 5 ) use hydrogen sulfide as an energy source to make food (carbohydrates) in a process we call chemosynthesis: Hydrogen Sulfide + Water + Carbon Dioxide + Oxygen These bacteria are at the bottom of the food chain near hydrothermal vents. In other words, the animals eat the bacteria or eat animals that eat the bacteria. Many bacteria are plankton, and animals strain them out of the water as they drift by. Other animals graze on bacteria that grow in mats or webs on the ocean floor and the chimneys. Many animals have symbiotic bacteria that live inside their bodies. These animals take in hydrogen-sulfide rich water for their bacteria sometimes by diving through scalding hot water coming out of the vents and the bacteria give the animals some of the carbohydrates that they make using the hydrogen sulfide. As a result, animals like tube worms do not need a stomach to breakdown prey into carbohydrates! (See pictures of tube worms on the next page.) In general, the water is almost entirely still at the bottom of the ocean, and organisms are responsible for most of the motion in the deep ocean. In fact, the small amount of mixing caused by deepocean animals is responsible for helping deep-sea nutrients get mixed back up towards the surface so that phytoplankton can use them. (This is a VERY slow process, but would be much slower without them.) There are exceptions of course. Hydrothermal vents stir the water surrounding them. Some places have deep ocean currents, and if the currents are fast or distorted by the bottom, they can become quite turbulent. Carbohydrates + Sulfuric Acid ("Sugars") If we were to eat animals who lived near hydrothermal vents, we would be poisoned by the high levels of sulfur in them. Minerals spewing from the ocean floor. National Oceanic and Atmospheric Administration. Bacteria Mat. National Oceanic and Atmospheric Administration. 5 Technically speaking, archaea are species of microorganisms that diverged from bacteria long ago, but they are similar enough to the non-specialist that we will not worry about the technical differences. Oceanography 10, T. James Noyes, El Camino College 10B-7

8 Oceanography 10, T. James Noyes, El Camino College 10B-8 Tube Worms. National Oceanic and Atmospheric Administration. The term chemosynthetic community is used to describe a food chain in which the organisms at the bottom of the food chain use chemicals, not the energy of sunlight, to make food for themselves. The discovery of chemosynthetic communities near hydrothermal vents in 1977 was a major scientific discovery. Prior to this time, scientists knew of many forms of chemosynthesis used by a variety of bacteria. However, they also thought that all large, complex animals like ourselves ultimately relied on plants, algae, and the energy of the Sun to survive. The discovery of chemosynthetic communities in 1977 showed that this is not the case; even if the Sun went out, big, complex animal life would still survive on the Earth. The discovery of chemosynthetic communities has important implications for several areas of fascinating-but-highly-speculative research. The discovery of chemosynthetic communities showed us that we cannot just look for photosynthetic organisms when we explore other planets. Volcanic activity, after all, is or has been fairly common throughout the solar system. Not only should we look for chemosynthetic organisms as well as photosynthetic ones, but now that we know that there is one alternative to photosynthesis, why couldn t there be 2, 3, or more? The earliest forms of life on the Earth may have begun at hydrothermal vents on the bottom of the ocean. Volcanism would have been common worldwide on the early Earth, and the associated hydrothermal vents would have provided a rich source of energy for early bacteria. In addition, living on the bottom of the ocean would have helped protect these early bacteria from the stillcommon impacts of giant asteroids and the harmful effects of solar radiation (since there was little or no atmosphere to reduce it). If life did begin at the bottom of the ocean at hydrothermal vents, that would help explain why life got started so quickly after the Earth cooled and solidified. A final thought: bacteria have been found living very deep inside the Earth s crust. They use processes like chemosynthesis to survive. As we continue to learn about the microscopic life that lives deep within the Earth, we may learn that a significant amount of the planet s biomass if not most of it actually lives beneath the planet s surface! Oceanography 10, T. James Noyes, El Camino College 10B-8

9 Oceanography 10, T. James Noyes, El Camino College 10B-9 There are places in the world where there are no volcanoes, but chemical-rich water seeps out of the ocean floor for other reasons. These places also have chemosynthetic communities with bacteria at the bottom of their food chains. The two primary chemicals used by bacteria at these cold seeps are hydrogen sulfide and methane 6. Cold Seep Tube Worms. Courtesy of Charles Fischer (CC BY 2.5). Cold Seep Chemosynthetic Communities. National Oceanic and Atmospheric Administration. Oil and other hydrocarbons naturally leak from the bottom of the ocean in some places, including along the coast of southern California. Although many of my students assume that adding oil to the ocean is a bad thing, life is abundant near these seeps. Chemosynthetic bacteria break down the hydrocarbons and are eaten by animals. Oil only becomes a bad thing for the ocean when released in huge quantities (e.g., an oil spill). 6 The methane is probably produced when bacteria in the Earth partially-decompose dead, decaying matter in the sediments or sedimentary rock. This dead matter was almost certainly made via photosynthesis originally, and thus these communities could not exist without photosynthesis. Oceanography 10, T. James Noyes, El Camino College 10B-9

10 Oceanography 10, T. James Noyes, El Camino College 10B-10 Oceanography 10, T. James Noyes, El Camino College 10B-10