Download 1 One thing that all the diverse forms of life found in the oceans have

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