Aquatic species, such as mollusks, are most threatened by:
“Habitat destruction and pollution” for aquatic species, such as mollusks, are most threatened by. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Extinction risk rises when abundance, geographic range, or genetic variation becomes small because demographic chance, environmental fluctuations, inbreeding, and rare catastrophes then have disproportionate effects. Correlated losses among subpopulations further weaken regional persistence. The remaining alternatives—“Parasitism”, “Introduced predators
Ref: Conservation Biology, Primack & Sher, 6th Ed., Ch. 7