♻️AP Environmental Science
1. Kelp forests are highly productive marine ecosystems found in cold, nutrient-rich coastal waters. Sea otters are secondary consumers that prey on sea urchins, which are primary consumers that graze on kelp. The energy flow in a simplified kelp forest food chain is shown below.
Describe one characteristic of the marine (ocean) biome where kelp forests are located.
Based on the food chain provided, explain how an increase in sea urchin populations would affect kelp abundance through resource competition.
Figure 1. Sea Otter Population Density (individuals per km²) and Kelp Forest Coverage (%) from 2000 to 2020
Based on the data in Figure 1, identify the sea otter population density in the year 2010.
Figure 2. Biomass (kg/m²) at Three Trophic Levels in a Healthy Kelp Forest Ecosystem (means with error bars)
Describe the trend in biomass as energy moves from producers to secondary consumers in the kelp forest ecosystem. Scientists use the data in Figure 2 to calculate energy transfer efficiency between trophic levels.
Describe your calculation of the energy transfer efficiency from primary consumers to secondary consumers. Using the biomass data from Figure 2, calculate the percentage of energy transferred from sea urchins (primary consumers) to sea otters (secondary consumers). Show all work.
Primary productivity is essential for supporting kelp forest food webs. A group of students was interested in investigating factors that affect phytoplankton productivity in marine ecosystems. They collected water samples from two sites: a nutrient-rich coastal area near a kelp forest and an offshore open ocean area. The students measured dissolved oxygen concentrations in sealed bottles containing the water samples. Each site had three light bottles (exposed to light) and three dark bottles (wrapped in foil to block light). Students measured initial dissolved oxygen and final dissolved oxygen after 24 hours.
Identify a testable hypothesis for the students' investigation of phytoplankton productivity.
Identify the independent variable in the students' investigation.
Site | Species A | Species B | Species C | Species D | Species E | Species F |
|---|---|---|---|---|---|---|
Coastal water | X | X | X | X | X | |
Open ocean | X | X |
The students also collected phytoplankton samples to assess biodiversity at each site. The data from the biodiversity investigation are shown in the following table. An 'X' in the table indicates that the species was present at that site.
Explain why the phytoplankton community in the coastal water would be more resilient to environmental stress, such as temperature increase or pollution, than the phytoplankton community in the open ocean would.
Explain how the nutrient cycling in a kelp forest ecosystem differs from nutrient cycling in a terrestrial tropical rainforest ecosystem.
Describe one step in the nitrogen cycle that makes nitrogen available to kelp as a usable nutrient. The nitrogen cycle is important for supporting primary productivity in kelp forests. Nitrogen enters the ocean through various pathways including atmospheric deposition and upwelling of deep, nutrient-rich water.
