Naturalist: The decline of coral reefs has various causes. One contrib

Question

Naturalist: The decline of coral reefs has various causes. One contributing factor is predation on coral by organisms such as the crown-of-thorns sea star, whose preferred food source is coral polyps. Human fishing practices have decreased the sea star's predators, such as the harlequin shrimp. It is also possible that runoff containing nutrients for phytoplankton has resulted in larger phytoplankton blooms: the crown-of-thorns sea star gladly eats phytoplankton.

Indicate in the table which cause-and-effect sequence would most likely, according to the naturalist, result in coral reef decline. Make only two selections, one in each column.

ID: 100398

AnishPassi · Accepted Answer

I want to focus on the phrase at the start of the last sentence of the passage: "It is also possible that"

It is also possible that  runoff containing nutrients for phytoplankton has resulted in larger phytoplankton blooms: the crown-of-thorns sea star gladly eats phytoplankton.

Why has the naturalist used the word 'also;

1. Is it another cause for decline of coral reefs?

No.
The first mentioned contributing factor is predation on coral by organisms such as the CoT sea star.
Then the mention of something that CoT sea star thrive on doesn't seem to be a separate cause.

2. Then what does the phrase "it is also possible" go with?
The previous sentence.

Human fishing practices have decreased the sea star's predators, such as the harlequin shrimp. It is also possible that runoff containing nutrients for phytoplankton has resulted in larger phytoplankton blooms: the crown-of-thorns sea star gladly eats phytoplankton.

In the harlequin shrimp sentence, the naturalist is giving a reason for why CoT sea star population might have increased. When I read the last sentence with this piece in my mind, it becomes more clear that the author is giving another possible reason for the CoT sea star population increase.

And why would the naturalist mention possible reasons for the growth of CoT sea star population?

To support why coral reefs decline could be caused by CoT sea star.

Not a perfect analogy, but I'm thinking:

Say a nice famous cafe opens next to one that wasn't doing well. The whole area would get more footfall. And that could get the older cafe to do better than before, even though there's competition next door now.

Sajjad1994 · Answer

Official Explanation

We are asked to provide a sequence of cause and effect that would (according to the naturalist) result in coral reef decline. The question suggests that the answers will be dependent on one another, in that the correct answer for Cause will depend on the correct answer for Effect, and vice versa.

The passage states that one factor contributing to coral reef decline is predation on coral by organisms such as the crown-of-thorns sea star. The preferred food source for this organism is coral polyps, and so a causal sequence that has as its effect an increase in crown-of-thorns sea stars may be likely to produce a decline in coral reefs. This suggests that the third option may be the correct response for Effect. However, this depends on whether one of the other statements in the table describes a cause suggested by the naturalist to produce this effect.

The last sentence of the naturalist’s statement indeed suggests, in the context of the passage, that an increase in phytoplankton blooms would result in greater numbers of crown-of-thorns sea stars. This suggests that the first option may be the correct response for Effect. And indeed, according to the naturalist, the crown-of-thorns sea star’s preferred food source is coral polyps. All of the naturalist’s statement is about possible explanations of the decline of coral reefs. The passage therefore indicates that the naturalist would take an increase in phytoplankton to produce an increase in crown-of-thorns sea stars, and that this causal sequence would result in coral reef decline.

The correct answer is An increase in phytoplankton.
The correct answer is An increase in crown-of-thorns sea stars.

Apt0810 · Answer

Cause: An increase in phytoplankton so that sea star population increased

Effect: An increase in crown-of-thorns sea stars,making the consumption of more coral reefs

Posted from my mobile device

maikikiuu · Answer

I think there are 2 pairs of answers:

1st as the OA: increase of phy; increase of sea stars

2nd: increase of shrimp, decrease of sea stars.

What is the base to reject the 2nd?
In my opinion the cause-and-effect relation of the shrimp and sea stars are closer (clearly stated that the shrimp decrease THEN stars increase.) than that of the OPTIONAL food choice (phytoplankton, because the stars feed on both phy AND coral polyps) and sea stars.

Tanchat · Answer

Dear Experts,  KarishmaB

Why An increase in harlequin shrimp (Cause) does not affect A decrease in crown-of-thorns sea stars (Effect) ?

KarishmaB · Answer

An increase in shrimp will cause a decrease in sea stars but will it cause the coral reef to decline? No. We need a cause-effect which will ultimately lead to decline of coral reef. Since sea stars eat coral polyps, a decline in their number will let coral polyps thrive and hence coral reefs should do well.

laragarg · Answer

How did you draw the correlation between   phytoplankton(phytop)   and   crown-of-thorns sea stars(COT)  ? Since COT gladly eats phytop, apart from coral reefs, if phytop increases, coral reefs should also increase as COT would be more likely to eat COT instead of preying upon coral reefs.

Sahana3115 · Answer

Isn't it the case that decrease in polyplankton --> Sea stars feeding on more coral reefs --> result in coral reef decline?

chetan2u · Answer

You have to think from the perspective of the Naturalist. He nowhere mentions the sequence of decrease in pp, resulting in sea star feeding on coral reef.

So, we have to stick to what has been mentioned in the argument, as the argument gives the thought process of the naturalist. The Naturalist talks of larger pp blooms, so more food, resulting in more sea stars, who in turn feed on coral polyps, the preferred foof source.

Badsha5796 · Answer

this question has a faulty understanding. it is notfull proof. 
author is two directional in his reasoning and contradicting is line of reasoning

Gemmie · Answer

https://gmatclub.com/forum/download/file.php?id=82742 GMAT-Club-Forum-mvm7h650.png

mm92325 · Answer

Can anyone explain this?, Same confusion.

adithya000 · Answer

IMO, if  2nd  case is true, then that would affect the fact that corals are declining

cheshire · Answer

We are asked to find the cause and effect that would show a  decline  in coral reef health. As sea stars are a predator of coral, their numbers declining would not cause a decline in coral, rather an increase.

Anish27 · Answer

Hello  GMATCoachBen , Could you please explain this?

MohdZaidKhan · Answer

The explainations fail to explain why an increase of phytoplankton will cause a decrease in coral reef . As CoT star will gladly eats phytoplankton instead of coral reef.

cheshire · Answer

"preferred food source" is coral reefs.

bb · Answer

I feel this is a slightly weird question. I misunderstood it as well.

The key with TPA's is that the answer choices are super important, so you have to make the answer choices work and fit the question. Here the ideal answer would have been: 
Decrease in shrimp predator --> Increase in Sea Stars --> More reef gets eaten up

But this is not one of the options, so we have to look for what makes the most sense after that, which makes this question difficult. You have to recognize that you have pick an imperfect answer combination.

We know that the  effect  has to be (sort of has to be) the increase in the sea star population, so the effect is fixed.  
 Now we have to find the  cause  out of 3 remaining options (since increase/decrease of seastars would not play) 
 
 The Shrimp increase has the opposite effect 
 Decrease in phytoplankton would drive the sea stars to eat the corral reef so it would decrease corral reef but it would probably not increase the sea star population if it decreased 
 Increase in phytoplankton would on the other hand increase the sea star population but would not potentially increase the reef damange/eating with exception that the sea stars prefer the reefs, so perhaps it would - this is scraping at the bottom of the barrel to get methodically to something.

At this point, you could guess between these 2. I sort of had to as it felt too weak to make the whole question judgement to be based on it. 
I am personally not thrilled with the question - not a very black and white one it seems and not very cause-effect so to speak. Just something you would need to print out and diagram out so you remember the marker patterns and the importance of the word  preferred .

Naturalist: The decline of coral reefs has various causes. One contrib

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Cause	Effect	Statements
		An increase in phytoplankton
		A decrease in phytoplankton
		An increase in crown-of-thorns sea stars
		A decrease in crown-of-thorns sea stars
		An increase in harlequin shrimp

GMAT Two-part Analysis (TPA) Questions

Naturalist: The decline of coral reefs has various causes. One contrib

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