The crown-of-thorns sea star, acanthaster planci, preys on the flesh of live coral. if coral animals are attacked by these sea stars, then what actually provides nutrition to the sea star, and which chemical (besides the toxin within their nematocysts) do the corals rely on for protection?
a) medusae; silica
b) polyps; silica
c) exoskeleton; calcium carbonate
d) polyps; calcium carbonate

d) polyps; calcium carbonate

Explanation:

The Acanthaster planci It is a kind of invasive starfish, which destroys corals: it has poisonous spines and feeds on coral polyps at the expense of the reef.

On the other hand, CO2 reacts with water, forming carbonic acid and reducing the available calcium carbonate, an essential element so that marine organisms, from clams to hedgehogs, can form their skeletons and shells.