In order to withstand tidal currents, juvenile horseshoe

Question

In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles from clinging to their shells. When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles. Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow.

Which of the following, if true, most helps to explain the surprising finding?

(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs.
(B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest.
(C) The strength of the tidal currents in a given location varies widely over the course of a day.
(D) A very large barnacle population can significantly decrease the ability of a horseshoe crab to find food.
(E) Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.

Anonymous · Accepted Answer

E
The question statement first establishes a cause and effect relationship: burrowing causes lack of barnacles. The question then states an observation that non-burrowing crabs do not have barnacles. The observation is inconsistent with the cause and effect relationship that was previously stated. Thus, we must find a new cause for a crab's lack of barnacles in order to explain the surprising finding. Answer "E" establishes a new cause: frequent shell shedding.

jananijayakumar · Answer

This is an OG Question Q No: 59, OG12.
We are apparently asked to resolve the paradox that although the tidal currents are weak and crabs don't burrow, the barnacle population is weak.
A. this gives a reason y there is significant barnacles in crabs that do not burrow. We are not looking out for this answer. Rather we want an answer that explains why there is less barnacle population.
B. This gives an additional premise for the argument and triggers more intrigues as to y there is less population of barnacles even though there are weak tidal currents.
C. Out of scope.
D. Out of scope. Nowhere in the argument, Food comes into picture.
E.  Correct answer.  This explains why Juvenile crabs have less barnacle population. When they shed their shells regularly, they also shed the barnacles that cling to them regularly. Thus, this explains the surprising finding.

Correct me if I'm wrong.

Thanks.

amit22 · Answer

i am still not able to stand why E is correct answer.the statement E have same effect whether horseshoe crabs stay in strong tide current region or weak tide current region.how it explain the low population of barnacle in weak tidal current area.

amithravindra · Answer

This is a Resolve the paradox Question.The Paradox is when the tides hit the Adult Crabs there will be barnacles attched to them But in weak tide (this is a decoy)areas even though the tides hit Juvenile crabs there are not more barnacles.The correct ans choice must allow both the facts to be true and explain the paradox.Only Option E tells how the Juveniles shed the shell and hence have no barnacles if Adults they wud have had clusters of Barnacles too

chris558 · Answer

This is an Explain the Paradox question type!

Premises: 
- juvenile horseshoe crabs frequestly burrow in sand to withstand tidal currents
- burrowing discourages barnacles from clinging to juvie's shells
- fully grown horseshoe crabs can readily withstand tidal currents without burrowing and therefore acquire substancial populations of barnacles

Conc:
- in areas where tidal currents are weak, juvenile horshoe crabs found not ot have significant barnacle populations, even though theyy seldom burrow

a) we already know that BURROWING does. this does not explain anything.
b) then there should be MORE barnacles on their shells.. opp direction
c) tempting but doesn't FULL explain... what is the range of this strength? doesn't really answer our discrepancy
d) out of scope.
e) bingo! if horse shoe crabs are shedding their shells and growing new ones, this w ould explain why we didnt find significant barnacles on their shells even though they weren't burrowing.

Answer is E

dpvtank · Answer

I had a really hard time understanding Choice A. I'm wondering if my thought process is correct in disqualifying A now.

Here's how I understand the argument:
- high tidal waves --> more burrowing for juvenile horseshoe crabs --> decreased barnacles
BUT ALSO
- low tidal waves --> less burrowing for juvenile horseshoe crabs --> decreased barnacles
how can this be?

A. Tells us that the water tides don't matter. So the less or more barnacle populations have to do with burrowing then (given the premises). So we are left with the situation where:
 - more burrowing --> less barnacle population
 - less burrowing --> less barnacle population 
So...we still have a paradox.

Is this accurate?

avrgmat · Answer

Let me take a dig at trying to explain the answer choice.

Choice A says that the tidal ways do not dislodge the barnacles from the crab-shells. Thus high or low tidal waves should not make a difference in the population of barnacles, instead burrowing should make all the difference i.e. less burrowing = more barnacles and vice-versa.

Hence in low tidal waves areas the juvenile crabs would burrow less hence ideally the population of barnacles on the juvenile crabs should be larger. However this is contrary to the observed phenomenon i.e. in low tidal areas the barnacle population on juvenile crabs was not found to be larger. Thus option A does not help us resolve the paradox. Hence A can be eliminated.

Hope this helps.

JarvisR · Answer

My 2 cents:

In order  to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand . Such  burrowing discourages barnacles from clinging to their shells.  
When fully grown,  however , the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles.
 Surprisingly , in  areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow .

Which of the following, if true, most helps to explain the surprising finding?
 
(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs.
 >>Evident from argument "burrowing discourages barnacles from clinging". Doesn't help in answering the paradox.
 (B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest.
 >>But juvenile horseshoe crabs are found not to have significant barnacle populations in such areas. Doesn't help. 
 (C) The strength of the tidal currents in a given location varies widely over the course of a day.
 >> I found this one intriguing. but this means Barnacle population shouldnt vary much because of variation in tidal strength.
 (D) A very large barnacle population can significantly decrease the ability of a horseshoe crab to find food.
 >>Irrelevant.
 (E) Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.
>>Now apart from sand borrowing this is anther reason for low barnacle population. This answers bth part of argument.

OptimusPrepJanielle · Answer

In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles from clinging to their shells. When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles. Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow.

Which of the following, if true, most helps to explain the surprising finding?

The question to answer is, why do juvenile horseshoe crabs have sparse barnacle populations although they aren't burrowing (Burrowing decreases barnacle accumulation)?

(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs.  doesn't answer the question 
(B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest.  This would have the opposite effect. 
(C) The strength of the tidal currents in a given location varies widely over the course of a day.  not relevant to our question 
(D) A very large barnacle population can significantly decrease the ability of a horseshoe crab to find food.  also out of scope 
 (E)  Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.  This explains why they don't have barnacles although we would think they would because they don't burrow. They shed the barnacles along with their shells.

deddex · Answer

OFFICIAL EXPLANATION:

Argument Construction

Situation - Juvenile horseshoe crabs withstand tidal currents by burrowing in the sand.
This action makes barnacles less likely to cling to their shells. Adult horseshoe crabs can
withstand currents, so they do not burrow, and barnacles become more likely to cling to
their shells. Surprisingly, however, juvenile horseshoe crabs that do not burrow, because
tidal currents do not threaten them, do not have significant numbers of barnacles clinging
to their shells.

Reasoning - What would most help explain the finding that nonburrowing juvenile
horseshoe crabs do not have significant barnacle populations? The finding suggests that
there is some way in which nonburrowing juvenile horseshoe crabs either discourage
barnacles from clinging to their shells, or get rid of the barnacles that do cling to their
shells. Identifying how this is accomplished will explain the finding.

A. This gives a reason why juvenile horseshoe crabs that do not burrow would have
significant barnacle populations.

B. If barnacles in areas of weak tidal currents readily attach themselves to horseshoe
crabs, then it would be more likely for juvenile horseshoe crabs in such areas to
have significant barnacle populations.

C. The areas under discussion are those where tidal currents are very weak. The
strength of currents may vary widely there, but presumably they are still weak
compared to other areas.

D. The surprising finding under discussion is why certain juvenile horseshoe crabs do
not have significant barnacle populations, despite failing to engage in behavior that
dislodges barnacles. That a very large barnacle population can hurt a horseshoe crab
does not help explain such a finding.

E. Correct. This statement properly identifies something that helps explain the
surprising finding: If juvenile horseshoe crabs regularly shed their shells, they also
regularly shed the barnacles that cling to those shells. Thus juvenile horseshoe
crabs would most likely be found not to have significant barnacle populations.

The correct answer is E.

peanuts · Answer

In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles from clinging to their shells. When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles. Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow.

Surprising finding: on juvenile crabs, significant barnacle populations are not found. To explain this finding, a connection between juvenile crab and lack of observable barnacle in areas with weak tidal current should be established

Which of the following, if true, most helps to explain the surprising finding?

(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs.  Nothing relevant 
(B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest.  This one makes the finding even weirder as there should be more observable barnacles  
(C) The strength of the tidal currents in a given location varies widely over the course of a day.  so what? 
(D) A very large barnacle population can significantly decrease the ability of a horseshoe crab to find food.  not relevant to the finding 
(E) Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.  yes. Juvenile = not fully grown. This answer says that young crab shred their shells several times, so barnacle could not stay on for long

ef1988 · Answer

GMATNinja

Wouldn't you have to know that barnacles permanently attach to the shell to answer this question? I don't think the words "cling" and "adhere" can infer that the barnacles are permanent. Couldn't they technically "cling to"/"adhere to" the shell only during the tidal currents?

Please let me know if I'm missing something.

DmitryFarber · Answer

ef1988 
The text tells us that adult horseshoe crabs acquire "substantial populations" of barnacles, so that tells us that it isn't just a temporary phenomenon, like flies on cattle. E gives us a reason that juveniles would be different from adults, so it helps clear up the mystery. But sure, having said all that, it helps to know what barnacles are. Although the GMAT will usually explain needed vocabulary words, we may need to lean on our own knowledge when no explanation is given.

uttonio · Answer

C is a trap answer that is very mind-boggling.
The explanation for why C is not the answer.

"Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow."
--> The surprising finding is that these very juvenile horseshoe crabs don't have significant barnacle populations (like their fully grown brothers?) in areas of very weak tidal currents. They even seldom burrow in the sand.

"In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand." --> the juvenile crabs only "withstand tidal currents" if these currents are strong. They don't have to deal with the weak tidal currents and therefore, seldom burrow in the sand.

C. The strength of the tidal currents in a given location varies widely over the course of a day.
Assuming that "varies widely" means the currents can be strong and then "very weak", when the currents are strong, the juvenile horseshoe crabs will definitely burrow in the sand. Since the answer says "over the course of a day", the crabs have to burrow in the sand every single day, which contrasts with "they seldom burrow" at the end of the text. And the case of strong currents is not really valid because the text already says "in areas where tidal currents are very weak".

It leaves us with the assumption that "varies widely" means having a wide range of different weak tidal currents. Throughout a day, the juvenile crabs might acquire a small number of barnacles since the water is so weak that it cannot bring a lot of barnacles to the shore. This will answer the question of why it is surprising that the juvenile crabs don't have significant barnacle populations. However, another scenario is the juvenile crabs might acquire a significant amount of barnacles because even though the currents are weak, there are a lot of barnacles in the water. So we are unsure of the number of barnacles that the juvenile crabs acquire.

If I have to do a painstaking analysis for this answer, this answer is not the correct answer. The right answer tends to be more straightforward and very comprehensive so once you choose it, you have a gut feeling that it's correct. I don't mean that we guess based on our feelings. I have total belief in reading the text carefully and choose an answer based on the text.

This trap answer will waste most of our time and from time to time, I still have the thinking that oh, there is something about it that makes it correct

DmitryFarber · Answer

uttonio 
I'm not sure we need to do that much analysis to cut C. The argument states that the juvenile crabs in these areas seldom burrow AND don't have significant barnacle populations. Since the strength of the tide was only discussed as the reason for burrowing, and we know that not much burrowing is occurring here, there's nothing further we can do with the information in C. As you've surmised, any variation we do see is clearly not enough to cause much burrowing. We can't speculate about any other possible results of this variation, since we haven't been given any means to do so. So we should toss this out as a "variation trap" and move on. The GMAT loves to get us wondering about some difference that we don't have the information to assess. As you've said, we shouldn't fall for the trap and use up our time!

EatMyDosa · Answer

GMATNinja ,  GMATNinja ,  ChiranjeevSingh ,  AnishPassi

Hi,

I was confused b/w option D and E and chose D eventually. My reasoning for selecting D and rejecting E is as follows:

Option E  (rejected): Horseshoe Crabs (HCs) which are growing shed their shells several times a year. But this phenomenon is applicable to both types of HCs - ones in strong-tide areas and others in weak-tide areas. Further, HCs in strong-tide areas also burrow, so they also shouldn't have significant barnacles population (In fact, they should have less barnacles population as they are burrowing and shedding shells). On the other hand, HCs in weak tide areas on have one counter-measure against barnacles (i.e. shedding shells). Therefore, option E doesn't help us resolve the paradox.

Option D  (selected): Although, this option does not specficially talk about juvenile HCs and rather presents a general observation on HCs, it is applicable to juvenile HCs also. If excessive barnacles grow on juvenile HCs, latter would struggle to find food. If the host (HC) is weak and not getting food, the parasite (barnacles) wouldn't be able to sustain on the host for long. Therefore, barnacles keep their population growth in check on juvenile HCs in weak-tide areas. Therefore, D explains the paradox.

DmitryFarber · Answer

EatMyDosa

We know that the juveniles who burrow already have a reason not to be covered in barnacles. The surprising finding is that even those who do NOT burrow are still not covered in barnacles. E solves that by giving us another reason for juveniles to be different. The fact that this applies to ALL juveniles is not a problem at all. It still helps us to understand what we need to understand--why the non-burrowers don't have substantial barnacle populations.

D requires some assumptions from us. We have no reason to suspect that barnacles tailor their strategy to reduce the mortality of the host. Whether this would be a conscious strategy (unlikely, since barnacles are relatively simple organisms) or a behavior shaped by evolution, we still just have no indication that such an adjustment would happen. Also, it's clear that many adult crabs do survive with "substantial populations" of barnacles, so we still don't know from E why juveniles couldn't have similarly significant populations (relative to their size). The fact that there is such as thing as too many barnacles just doesn't explain much about what's going on.

kdk21 · Answer

Understanding the argument is tough here because of many marine terminology. If you understand what the argument says as a whole this is a pretty simple question. Problem here is tough vocab and terminology.

What does arguments say?
When crabs are juvenile, they go under the sand because currents are too heavy. Now, because they are under the sand, crabs avoid barnacles from clinging. When they grow they don't need to burrow, hence barnacle cling. Now, here we assume that avoidance of barnacles is because of burrowing. But the second half of the passage suggests that even when there are no current and no burrowing, barnacles never clung the juvenile crabs. (Please notice the word juvenile crab)

"Question ask why did they not cling to juvenile crabs even when there was no current and no burrowing?" ---Focus on this point when evaluating options

(A) Tidal currents do not themselves dislodge barnacles from the shells of horseshoe crabs.
This option doesn't explain anything about why barnacles didn't cling when there no current and no burrowing. -- Out

(B) Barnacles most readily attach themselves to horseshoe crabs in areas where tidal currents are weakest.
If this is the case then why did barnacles not cling to juvenile crabs when there was no currents? Doesn't answer our question- Out

(C) The strength of the tidal currents in a given location varies widely over the course of a day.
This option only talks about strength of the current throughout the day. Nothing else is implied here. Doesn't answer our question- Out

(D) A very large barnacle population can significantly decrease the ability of a horseshoe crab to find food.
This option talks about what a very large population can do to crab's ability to find food. But it doesn't talk about clinging to juvenile crabs in no currents. Doesn't answer our question- Out

(E) Until they are fully grown, horseshoe crabs shed their shells and grow new ones several times a year.
Now, this is interesting. It says that until crabs are fully grown, crabs shed shells i.e. as long as crabs are juvenile, they shed shell.
Let's say barnacles do cling to the shell of the crabs, then what will happen next? This option says crabs shed shell so as they shed the shell they loose the barnacles that are clung to the shell as well. Hence this addresses our problem. Because 
This option says that absence of barnacles on juvenile crabs has nothing to do with currents or burrowing. Because younger crabs always shed shells, crab can avoid barnacles as well.

Option (E) is the answer

AvijitDey · Answer

why option D can not be th right answer. Both Option D & E talk about something that inhibits the formation of large barnacles even at low tide. Both the option have additional information. Then wnhy Option D can not be the right answer?

In order to withstand tidal currents, juvenile horseshoe

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In order to withstand tidal currents, juvenile horseshoe

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