What are all the decomposers in the ocean?

How has biodiversity been affected in areas where green crabs have been introduced? a. additional predators have migrated into the area to feed on the crabs, causing an increase in predator diversity. b. native shellfish populations have dramatically decreased as they are outcompeted by the crabs, causing a decrease in biodiversity. c. the amount of predation on crabs by seabirds has gone up, but biodiversity has not been affected. d. the overall number of crab species has dramatically increased, increasing overall biodiversity.