Chapter 5, Problem 24A

Summary Introduction

Introduction:

Kelp forests are found about 2 m-30 m of the depth in the ocean in nutrient-rich water. For many of them, it acts as a habitat, some feed on the kelps while some take refuge during the storm. Sea urchins feed on the kelps while sea otters keep a check on their population to prevent the kelp forest from overexploitation.  The plankton-eating whales and fishes, on the other hand, are the source of food for sea lions and harbor seals. The killer whales feed on these harbor seals and sea lions.  All these organisms are dependent on each other for their food.

Answer to Problem 24A

Correct answer:

Option (C) overharvesting of plankton-eating whales

Explanation of Solution

Explanation/justification for the correct answer:

Option (C) overharvesting of plankton-eating whales. Sea urchins and sea otters act as keystone species in the kelp forests. Sea urchins feed on kelp and keep a check on their number, but they graze so rapidly that the kelp forest may permanently be destroyed. To check on the population of sea urchins, sea otters play crucial roles. They feed on sea urchins to protect the kelp forest from overgrazing. When the number of the primary food source of a killer whale that is sea lion and harbor seal decreases, they shift to sea otters. As they start feeding on sea otters, the number of sea otters starts to decline. In the absence of sea otters, sea urchins grow rapidly, leading to the over-exploitation of the kelp forest.

Explanation for incorrect answer:

Option (A) a decrease in the amount of plankton. The reason behind the shift of killer whales from their primary food source to sea otters was due to a decreased number of sea lions. Killer whales do not feed on planktons. Thus, it is an incorrect answer.

Option (B) an increase in the number of sea otters. An increased number of sea otters will help to reduce the number of sea urchins that feed on kelps. It will not lead to the deterioration of the kelp forest. Thus, it is an incorrect answer.

Option (D) pollution caused by pesticides. Pollution caused by pesticides had no role in the disruption of the kelp forests.