The vertical zonation of sessile marine species in the intertidal zone

Question

The vertical zonation of sessile marine species in the intertidal zone is a long-examined phenomenon. A particular tide-cycle study examined the incidence of two sessile animal species, the common mussel (Mytilus edulis) and the acorn barnacle (Semibalanus balanoides), in plots of increasing altitude in the intertidal zone of a beach preserve in coastal Massachusetts. Results showed that incidence of Mytilus increased as height decreased, and incidence of Semibalanus increased as height increased, up to the high-tide line or "barnacle line." This distribution suggests competition between the two species, with the mussel successfully outcompeting the barnacle for more time underwater and the barnacle evincing more ability than the mussel to reside in less ideal conditions.

The study also indicates that barnacles display numerous adaptations that equip them for life in the upper tide zone.

Which of the following, if true, would best strengthen the study's results?
 
A.  In tropical waters where there are no mussels, barnacles live predominantly close to the high-tide line.
B.  Barnacle concentration decreases as the high-tide mark decreases in height.
C.  Mussels can survive in air-only environments three times longer than barnacles.
D.  Barnacles are able to feed on land-based flora, while mussels can only gain nutrition from underwater species.  
E.  When a larger geographical area is studied, the incidence of mussels matches that of barnacles.

Feb2024 · Answer

Bunuel   KarishmaB   GMATNinja   CrackverbalGMAT   MartyMurray

Hello Experts! Please provide your insights here.

How could the answer be Option (D) when nothing is mentioned about their dietary habits in the passage. By POE, I believe the answer should be Option (A).

Thanks in Advance.

bangadg99 · Answer

The reason I selected option D is because the conclusion of the argument primarily focuses on two things
1) High population of mussels
2) Higher adaptive ability of barnacles than mussels

Since it’s asked to strengthen it, we can look for something which enhances barnacles adaptation which option D does.

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ShresthKhandelwal · Answer

The best answer choice to strengthen the argument is the one that explains the high incidence of both mussels and barnacles at a particular level or zone. Option A focuses only on barnacles and fails to account for mussels, which weakens its overall relevance. On the other hand, Option D provides a more complete explanation that supports why both species are found in high numbers at that specific zone. Remember, when evaluating answer choices, prioritize the one that best supports the core observation or pattern, not just isolated details like diet.

Feb2024

Bunuel KarishmaB GMATNinja CrackverbalGMAT MartyMurray

Hello Experts! Please provide your insights here.

How could the answer be Option (D) when nothing is mentioned about their dietary habits in the passage. By POE, I believe the answer should be Option (A).

Thanks in Advance.

jayagr · Answer

Option  A  actually weakens the study by stating that barnacles are predominantly found at high tide levels even in areas where there are no mussels. This runs against the explicitly stated hypothesis in the passage: " This distribution suggests competition between the two species, with the mussel successfully outcompeting the barnacle for more time underwater and the barnacle evincing more ability than the mussel to reside in less ideal conditions." If, even without competition, the barnacles are concentrated at higher elevations, it would invalidate this hypothesis.

sdas80923 · Answer

Why is the answer not E?

The conclusion states that it is the competition between the two species that is leading to one species taking underwater and the other the available option.
Answer E supports this by saying that when there's a bigger geography (and space enough for both to co-exist at the same depth), they do.

sdas80923 · Answer

Doesn't E do a better job here?

Edit: BB has answered below why E isn't a better choice.

bb · Answer

E) does not tell us anything about enough space for them to coexist. It just says a larger study of a larger area. It’s not critical for this component but just clarifying, that he does not mean there’s more space for both it means the study studying more areas.

The reason E. is not the correct answer choice is that it tells there is a equal number of both which doesn’t really tell us anything because we do not know what the numbers are or how they compare. There’s something that we’re looking forward tell us that barnacles live above the barnacle line and muscles live below the barnacle line.

Hope this clarifies it a bit more.

bb · Answer

A) does not provide sufficient information to support the conclusion and the study. We are only told about barnacles in that case and that Mrs. half of the argument so a cannot be the correct answer even if you can eliminate unfortunately

The vertical zonation of sessile marine species in the intertidal zone

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The vertical zonation of sessile marine species in the intertidal zone

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