Aotearoa's seawater is becoming warmer and more acidic, spelling trouble for the marine species that build their skeletons and shells out of calcium carbonate. When the ocean becomes too acidic, calcium carbonate structures begin to corrode, dissolving shells, exposed coral skeletons and wreaking havoc on creatures like nautiluses, sea stars, crayfish and pāua. If we don't curb emissions, our rich and abundant marine ecosystem may give over to a coral graveyard, patrolled only by jellyfish who thrive in this hostile environment.