Question

it is largely thanks to the physical impact that kelp species have on their environment that kelp forest ecosystems are able to provide food and shelter to such a wide variety of plants and animals. when these foundation species are disturbed, however, there can be cascading effects impacting the entire ecosystem.
among the many organisms that live in kelp forests are primary consumers that feed on the kelp. sea urchins are particularly voracious consumers of kelp. in an undisturbed kelp forest ecosystem, predators like sea otters, sea stars, and california sheephead fish keep the sea urchin population in check. but when predator populations are diminished, sea urchin grazing increases. when sea urchins graze in large numbers, they can eat away at a kelp forest until theres almost nothing left. this creates a deforested area called an urchin barren.
biodiversity refers to the variety of life in a given area. one measure of the biodiversity within an ecosystem is its species richness—that is, the number of different species it contains. which sentence from the passage best supports the claim that kelp forest ecosystems have a high amount of biodiversity?
it is largely thanks to the physical impact that kelp species have on their environment that kelp forest ecosystems are able to provide food and shelter to such a wide variety of plants and animals.
when sea urchins graze in large numbers, they can eat away at a kelp forest until theres almost nothing left.
because of their dependence on light for photosynthesis, kelp forests form in shallow, open waters.
foundation species are species that heavily influence their biological community through the physical impact they have on the environment.

Explanation:

The claim is about high biodiversity in kelp forest ecosystems. Biodiversity involves variety of life. The sentence "It is largely thanks to the physical impact that kelp species have on their environment that kelp forest ecosystems are able to provide food and shelter to such a wide variety of plants and animals" directly mentions a wide variety of plants and animals (indicating many species, which is related to species richness - a measure of biodiversity). The other sentences are about sea - urchin grazing (negative impact, not about biodiversity), kelp forest formation (due to light, not biodiversity), and foundation species definition (not directly about biodiversity in kelp forests).

Answer:

It is largely thanks to the physical impact that kelp species have on their environment that kelp forest ecosystems are able to provide food and shelter to such a wide variety of plants and animals.