As with many Argument Part questions, the stimulus starts with other people's argument. Some people think sinking big, obsolete pieces of equipment in coral areas provides habitats for marine life, and that therefore the practice of sinking these kinds of equipment in coral areas is ecologically sound.

(We know the first two sentences describe other people's argument, because of the phrases "is said" and "proponents say.")

The author's argument begins in the third sentence. She concludes that this practice—referring to the sinking of big, obsolete pieces of equipment in coral areas—is ecologically unsound even if it provides the habitats that other people say it does. We know that's the author's conclusion, because the next part of the sentence uses "for" as a support indicator. This signals that the claim "the practice might upset an area's ecological balance in unknown ways" is designed to provide support to the claim that the practice is ecologically unsound.

(By the way, note that the phrase "even if" does not introduce a conditional statement. "Even if" just means that the other part of the sentence is still true, regardless of whether the part after "even if" is true.)

The question stem asks us for the role of the claim that happens to follow the "for" in the second half of the last sentence. As explained in the Stimulus Summary above, that claim provides support to the author's conclusion. We know it provides support because it follows the word "for," which, in this context, means the same thing as "because" or "since."

Also, although this isn't required to identify the role of the claim, it may help to think about cost/benefit method of reasoning. The proponents of the practice point out what they view to be a benefit of sinking the equipment in coral areas. Because of this alleged benefit, they think the practice is ecologically safe. The author pushes back and points out a risk of that practice. The author assumes this risk outweighs the alleged benefit cited by the proponents. That's why the author believes the practice isn't ecologically safe. The claim we're asked about is the claim that points out a risk of the practice.