Corals, and the zooxanthellae algae they contain, form the base of a coral reef ecosystem. organisms like sea urchins feed on microorganisms that grow on the corals. organisms including seahorses feed on plankton and fish that also inhabit the reef. larger animals like sea turtles frequently enter the reef to forage. seaweeds, which are competitors of corals, may grow along the reef bottom. the biodiversity in a coral reef ecosystem can be changed by both natural and human acitivies. what is a natural factor that would most likely decrease the ecosystem's biodiversity? a. the immigration of several new populations of sea urchins into the reef b. the overgrowth of a population of seaweed, which prevents light from reaching the reef c. a sudden increase in the harvesting of corals, which decreases the coral population in the reef d. a decrease in the level of inbreeding in several seahorse populations in the reefnvm ion need nomo ! comment on dis n i will report u !