COSEE Summer Workshop: Teaching Science by Ocean Inquiry

Energy & Food Webs

Energy comes in many forms and can be transferred from one form to another. For example, in our everyday life we eat food (stored chemical energy) so that our body can function (perform work). Vegetables have converted the sun's radiant energy (i.e., light) to chemical energy associated with the bonds of its organic material. But even if the form of energy is changing, the energy itself is conserved. Thus energy is neither created nor destroyed. All energy transfers -- gains and losses within and between systems -- should be accounted for in an energy balance.

ANOTHER "SPIN" ON THIS TOPIC
Solar energy reaches Earth's surface in the form of radiation. Absorbed energy can be re-radiated as longwave radiation in the form of heat. This process contributes to a habitable planet climate-wise. However, to sustain life, the energy from the sun also must be converted to metabolically useful compounds. In other words, organisms need heat *and* something to eat! (Contributed by Adam Casey, workshop TA)

What can energy tell us about the ocean & marine food webs?

When energy is being transferred between components of a system, not all of it is converted to a usable form. To understand this, consider the example system depicted at left, is the simplified marine food chain. Phytoplankton use sunlight to grow, converting light energy to chemical energy. Not all the light energy absorbed by phytoplankton is converted into biomass; however, much of it is lost to respiration and heat. Phytoplankton, in turn, serve as chemical energy sources for their grazers, zooplankton. But some of phytoplankton's available energy is lost due to "sloppy" feeding by zooplankton, some to respiration, and some as heat. In general, only a small fraction of energy is available between subsequent trophic levels (e.g., from phytoplankton to zooplankton, from zooplankton to small fish, etc.). On average, the energy transfer efficiency between trophic levels in an ecosystem is only 10%.

In addition to the chemical energy sources within the marine food chain, Earth's ocean basins are home to large deposits of petroleum and natural gas that are buried beneath the seafloor. The world ocean also has potential sources of reusable mechanical energy in the forms of waves, tides, and currents. In recent years, there has been growing interest in harnessing tidal and wave energy from the oceans. Small scale energy plants that showcase this potential already exist in Western Europe and Canada.

How might this workshop benefit my students?

The following activity allows students to measure the caloric energy of common food items. This information is used to understand the energy transfer process in marine ecosystems. Full details and explanations of this station is available by clicking here (1.5 MB PDF file).