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HOW DOES LIFE IN THE OCEAN DEPEND ON ENERGY? O ne thing that all the diverse forms of life found in the oceans have in common is their need for energy. Plant life derives its energy from sunlight through the process of photosynthesis. Since all other organisms feed on plants or other organisms that feed on plants, virtually all life on Earth is sustained by energy from the Sun. Various forms of energy are identified in nature: chemical energy such as that contained in the chemical bonds of molecules, electromagnetic energy from sunlight for example; and kinetic energy, which is the energy of motion and is also known as mechanical energy. All life requires energy to sustain its vital processes. The complete set of processes is known as metabolism. Life in the ocean is strongly affected by the dynamic nature of its fluid environment which is in constant motion. Unlike life on land, any consideration of marine life must include the adaptations made to withstand or perhaps take advantage of the physical forces of the oceans’ constant motion. This theme (Life- Energy) describes the role of energy in ocean life. Related Themes: • For more information on the overall size and organization of ocean life and physical factors that support ocean life, see Life - Scale and Structure. • The oceanic food chain is addressed in Life - Systems and Interactions. • The oceans’ photic zone is discussed in Life - Scale and Structure. • How fisheries harvest the oceans is covered in Life - Human Interactions. • El Niño’s effect on ocean ecology is presented in Life - Systems and Interactions. • The exchange of energy between the ocean and atmosphere and the important role the oceans play in regulating local and global climate are discussed in Climate Energy. • The origin and dynamics of winds and currents are covered in Oceans - Energy. • The effect of salinity, temperature, and density on the ocean’s vertical structure is featured in Oceans - Scale and Structure. • Ocean eddies and coastal upwelling are also addressed in Oceans - Systems and Interactions. • The El Niño phenomenon is examined in Oceans - Process and Change. Related Activities: • Bioluminescence from Ostracods • Growing Chemosynthetic Bacteria INTRODUCTION All living organisms require energy to exist. This is an important and fundamental fact of life on the surface of Earth, and in the ocean. Metabolism is the word used by biologists to describe the sum of energetic processes that sustain living organisms. 1 ENERGY CONSIDERATIONS FOR LIFE IN THE OCEAN Solar Energy The Sun is the primary source of energy for Earth and its oceans. Energy is generated in the Sun’s core through the process of nuclear fusion. The nuclei of hydrogen atoms in the Sun’s hot core are in constant motion and continually collide, occasionally fusing to form helium nuclei and releasing energy in the process. The energy created in the Sun’s core eventually migrates to the surface, where it is released in the form of electromagnetic radiation. Light from the Sun provides energy to plants through a process called photosynthesis. In photosynthesis, light energy is stored and converted into chemical energy contained in the bonds of an organic sugar molecule called glucose. Chlorophyll, which often gives plants their green color, enables plants to carry out this conversion process. The vast majority of plants, on the land as well as in the ocean, get their energy from sunlight through the action of photosynthesis. Therefore virtually all life on Earth depends on photosynthesis. This is because animals derive energy for metabolism by eating plants (or other animals that eat plants), which obtained their metabolic energy through photosynthesis. Sunlight freely penetrates Earth’s atmosphere. Even on the most overcast days, some light makes its way through the cloud cover down to the surface. In the oceans, however, the situation is different because light is absorbed by water and can only penetrate to, at most, a few hundred meters depth. Below this depth, the ocean is perpetually dark. The area of the ocean through which sunlight can penetrate is called the photic zone [Fig. 1], or illuminated zone. The bottom of the photic zone is defined as the depth where the intensity of light is about 1% of the intensity of sunlight at the ocean surface. Because the oceans are on average a few kilometers deep, they can be thought of as deep bowls of very dark water with a very thin illuminated top layer. Most life depends on photosynthesis and light, so the photic zone is the most populated part of the ocean. Figure 1. The photic zone. The photic zone is the upper Many animals live at great depth, how- ocean in which the presence of sunlight, or solar radiation, ever, despite the lack of light. is detectable. Volcanism and Hydrothermal Vents Other sources of energy exist below the photic zone. Hydrothermal vents are cracks in the ocean floor that release hot material. Note that hydrothermal vents make up only a small component of the total energy available in the ocean. Found along volcanically active mid-ocean ridges, these hydrothermal vents release heat and various chemicals, such as sulfur, that can be used by living organisms. 2 Black smokers are tall, thin structures, similar to seafloor geysers. They produce thick plumes of hot chemicals that rise upward because the hot water is less dense than its surroundings. As the plume hits the cold ocean water, heavier minerals precipitate to form chimney-like structures. Black smoker chimneys can reach several tens of meters in height [Fig. 2]. Recently, scientists discovered an astonishing variety of life near hydrothermal vents, well below the photic zone. Some species have adapted to the absence of light, the great pressure at this depth, and a sulfur-rich chemical environment that is toxic to most Figure 2. Black Smoker. Submarine hydrothermal ocean life. In the Pacific, giant red worms up vents have water temperatures around 350°C (662°F). to three meters in length live near smokers. These waters are rich in black particles of metallic sulSulfur-eating bacteria provide food for the fides. worms. Black smokers are somewhat like oases in the desert when compared to the typically barren deep ocean floor. LIFE AND ENERGY IN THE OCEAN Photosynthesis Photosynthesis is the process through which plants convert sunlight into chemical energy using the molecule chlorophyll. Chlorophyll can absorb light energy and rearrange its electrons to trigger a chain that transfers electrons from one molecule to another. Ultimately, carbon dioxide (CO2) receives the hydrogen atoms from water to form glucose, a simple sugar with the chemical formula of C6H12O6 , and oxygen is released. Bioluminescence Some ocean creatures use chemical energy to produce light in a process called bioluminescence. Although many bioluminescent animals live in the deep light-free ocean, others live at or near the surface. One example is the very small (0.5 - 5 mm) class of crustaceans known as ostracods. Luminescent ostracods create two chemicals which they release into the water. When these chemicals mix, one product of the reaction is a blue-green light. Also, stirring up water in where ostracods live can produce a green glow, often visible at night in the wake of ships or in the crashing surf. Currents and Eddies The electromagnetic energy of sunlight and the mechanical energy of Earth’s rotation are converted into wind and current energy. This energy is important for ocean life. For example, the distribution of organisms is largely controlled by the current patterns and ocean water mixing rates. Also, heating by the Sun and wind-driven mixing control the vertical distribution of temperature and density of the surface waters. 3 One of the most important aspects of wind and ocean currents for marine life is how they help to distribute and mix organic materials and nutrients. For example, plankton growth is stimulated by the upward transport of nutrients near the edges of ocean eddies. Increased availability of plankton, which forms the bottom of the ocean food chain, helps to boost the number of larger animals such as fish. Greater overall food availability near the edges of some ocean eddies attracts marine mammals and thus they tend to congregate in these areas. This has been verified by comparing TOPEX/Poseidon satellite observations of ocean eddies in the Gulf of Mexico with the locations of some species of dolphins and whales [Fig. 3]. Figure 3. TOPEX/Poseidon image of sea surface height plotted with sightings of sperm whales. Blue and purple areas correspond to lower-than-average sea surface height. Eddies in these areas spin counterclockwise and bring nutrient-rich cold water toward the surface. Note that whales (shown as black diamonds) are concentrated near the edges of such eddies. 4 Upwelling Winds that blow parallel to coastlines cause surface waters to flow either toward or away from shore. This is the result of Ekman transport, the motion of water at right angles to the wind, caused by Earth’s rotation. When surface waters move away from a coast, they are replaced by deep water which rises in a process called upwelling. Such upwelling is enhanced near irregularly-shaped coastal features, such as near capes. Deep waters are usually colder than surface waters because they have not been heated by the Sun. They also tend to be richer in the nutrients that support ocean plant life. When transported to the surface, these nutrient-rich waters warm up and plant growth is stimulated. Rapid growth rates of microscopic plants at the base of the food chain cause these regions to be heavily populated by many forms of marine life. In fact, upwelling regions often support fifty to one hundred times more marine life than surrounding waters. These areas provide bountiful fish habitats that are tracked and used by the fishing industry. Sea surface temperature maps from satellites show upwelling as regions of relatively cool water [Fig. 4]. Figure 4. Satellite thermal image of California coastal upwelling. Cooler regions (blue) indicate upwelling as well as contributions from cold north-to-south flowing currents. 5 Upwelling can also change as a result of disruptions to ocean currents and wind patterns. Such changes can have a major impact on the distribution of marine life. For example, El Niño can temporarily halt upwelling by displacing cold, nutrient-rich water with warm equatorial water. The subsequent depletion of nutrients can decrease plankton growth rates and plankton population. This can under-nourish or kill zooplankton, and force fish to either migrate or starve. Eventually, other marine life that depends on these organisms for food, such as sea lions or birds, also die out or relocate. CONCLUSION Energy is necessary for the existence of life. Metabolism is the word used to describe biological processes that utilize or convert energy in living organisms. Plant life derives most of its energy from sunlight through the process of photosynthesis. Marine life also takes advantage of energy sources not directly related to the Sun. For example, bioluminescent creatures use chemical energy to produce light. Mechanical energy from Earth’s rotation, coupled with swirling winds, helps to stir ocean waters and stimulate plankton growth. some of the most biologically productive waters on Earth--zones of upwelling--are a direct result of these precesses. VOCABULARY black smoker chemical energy dynamic electromagnetic radiation glucose metabolism nuclei photic zone species bioluminescence chlorophyll eddy El Niño hydrothermal vents mid-ocean ridge nutrients photosynthesis upwelling 6 cape crustacean Ekman transport food chain kinetic energy nuclear fusion organic plankton