Lesson Plan - Get It!
Why has there been an increase in shark attacks at Surf Beach?
Surf Beach, California, as it's name suggests, is a prime location for surfers. However, every two years in October, you might think twice about going into the water. The surfers and community members of Surf Beach noticed an increase in shark attacks beginning in October 2008 and continuing like clockwork every two years.
Watch Serial Killer | Shark Week from Discovery Canada:
In this lesson, you will follow the research and do your own exploration of the shark's ecosystem at Surf Beach.
To understand what is causing the increase in shark attacks, you need to investigate the lifestyle and relationships, known as the ecology, of the organisms at Surf Beach.
Ecology is a branch of biology that deals with the relations of organisms to one another and to their physical surroundings. Ecologists use food webs — a series of food chains — to diagram the relationships of organisms in a community.
A food chain is a hierarchical series of organisms, each dependent on the next as a source of food. A simple food chain starts with the primary producers. Primary producers are autotrophic organisms that are able to synthesize their food from organic compounds. There are two types of autotrophs: photoautotrophs and chemoautotrophs.
Photoautotrophs such as plants use energy from the sun, combined with carbon dioxide and other nutrients from the soil, to make sugar for food. Plants store the extra sugar, which makes them a perfect start to a food chain. Other common photoautotrophs include algae and cyanobacteria.
Chemoautotrophs use chemosynthesis, a process that requires energy from chemicals to build organic compounds. Bacteria found near deep sea vents where there is no sunlight are chemoautotrophs.
The other organisms in this food chain are all heterotrophs, organisms that must consume food in order to survive. Heterotrophs are more commonly referred to as consumers. You are a consumer! Consumers are differentiated by their relationship to the producer in categories called trophic levels. In the food chain pictured above, you can see that the worm is the primary consumer, the owl at the top of the food chain is the final consumer, and there are several other trophic levels of consumers in between.
- Can you think of anything that is missing from this food chain?
There are several things that you could have added to the food chain. Think about your own diet.
- Do you only eat one thing?
Most likely, you eat a variety of things. Even if you only eat hamburgers, you are eating beef, which is a primary consumer, and lettuce or bread, which come from producers. Most consumers eat from a variety of trophic levels. That’s why ecologists use food webs to show the more complex interactions that happen in nature. A food web is a compilation of interconnected food chains that show organisms' interactions.
Another reason why ecologists use food webs is to trace energy and other compounds as they move through the environment. In physics, Newton's first law is the Law of Conservation of Energy, which more or less states that energy cannot be created or destroyed.
Energy is important to trace in a food web because it is the limiting factor in the length of a food chain. When one organism consumes another, they gain energy; however, the transfer of that energy is inefficient. Once energy enters a trophic level, it can be used or stored as biomass. Only the stored energy can be transferred to the next trophic level. As you move up the food chain, the rule is that only 10% of the energy from the previous trophic level can be passed on to the next trophic level.
In addition to energy transfer, other compounds can be transferred between trophic levels.
The compounds of most concern to ecologists are the toxic pollutants, such as pesticides. Pollutants are of no value to the consumer, and are therefore excreted or stored as part of the biomass. Bioaccumulation occurs when a pollutant is absorbed faster than it is excreted, and therefore becomes more concentrated and more toxic in organisms as you move up the food chain. Organisms that live at the top of the food chain, like sharks and humans, are most impacted by bioaccumulation; so it is important to monitor and maintain safe levels of pollutants.
Continue on to the Got It? section to examine the links in the food chain.