Of the many organisms found in marine ecosystems

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Of the many organisms found in marine ecosystems, sea otters play a uniquely significant role in maintaining their environments. Sea otters (Enhydra lutris) are a keystone species, a species whose effect on their environment is disproportionately great relative to their size in numbers or weight. Keystone species keep the growth of populations of other species in check and are thereby a determining factor of the type and number of other species in a community; keystone species are so named because their role is analogous to that of a keystone in an arch: while keystones bear the least amount of pressure among the components of an arch, the arch collapses without them.

The sea otter's reputation as a keystone species is largely a consequence of its affinity for sea urchins. Sea otters are known to prey upon over 100 different species, but the bulk of their diet consists of sea urchins and other marine invertebrates. Sea urchins are such highly preferred prey that sea otters have been known to significantly deplete urchin populations. In marine ecosystems at equilibrium, however, sea otters are often the primary force that keeps populations of sea urchins in check. Without sea otters, sea urchins and other seafloor herbivores would graze on kelp holdfasts, causing kelp to drift away from their substrates and die. The aggregate result of many such events leads to the destruction of entire kelp beds, resulting in a loss of habitat and nutrients for other organisms in the ecosystem. The extended consequences include local extinction of other species and vast urchin barrens: subtidal areas where the unchecked population growth of sea urchins has caused a dearth of kelp and, therefore, other marine species.

This ecological cascade effect of secondary extinctions resulting from a decrease in otter populations and corresponding growth in urchin populations was observed throughout the 19th century along the Pacific coast of North America. Sea otters had been aggressively hunted for their rich pelts since before the 1600s, and this practice was not outlawed until an international treaty was signed in 1911 to prevent further exploitation. Prior to the enforcement of the treaty, hunters caused sea otter populations to decline; this in turn caused sea urchin populations to explode. Consequently, the urchin populations overexploited their primary food source, kelp, creating a preponderance of urchin barrens


The author's tone towards sea otters could best be described as

A disdainful

B dispassionate

C concerned

D critical

E jovial


my concern: i feel that the author is indeed concerned about "sea otters", especially in the last paragraph. in fact i strongly feel that had this passage been continued further then he would have taken the topic of conserving "sea otters" .i am just not able to eliminate option C .[spoiler]why the answer is D and not C?[/spoiler]

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by David@GMATPrepNow » Sun Sep 07, 2014 11:09 am
Hi aditya8062,

In this passage, we are presented with a lot of information about sea otters and their relationship with the environment in which they live. Various facts are presented, including the direct impact of too many sea otters in the environment, and too few. Essentially, we are presented with a critical review of the sea otter's role in the environment.

I bolded critical above to highlight the way in which "critical" is being used in the answer choices. Critical has two meanings. The first meaning, the one I think you assumed, means to express adverse or disapproving comments or judgments. The passage does not do that, which is why you selected C instead of D. However, the second - and in this case correct - meaning of critical is not at all negative. It means to express an analysis of the merits and faults of something (often a work of art, but not always, as is the case in this passage).

I hope this helps.

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by yogesh_gmat » Thu Nov 13, 2014 12:49 pm
Thanks Dave,

May you please explain why "dispassionate" is not the correct choice ?

Thank You,
Yogesh