What invertebrate family would probably be the first to die if the pH of its habitat decreased?

Coral reefs, primarily composed of organisms from the family Scleractinia (stony corals), would likely be among the first invertebrates to suffer from a decrease in pH levels. These corals rely on calcification to build their calcium carbonate skeletons, a process that is negatively affected by ocean acidification. As pH decreases, their ability to maintain and grow their structures diminishes, leading to increased mortality and potential collapse of reef ecosystems.