In a new study published in Global and Planetary Change, researchers have used the shell of a giant clam (Tridacna gigas) from Jiigurru (also known as the Lizard Island Group) to reconstruct climate conditions in the northern Great Barrier Reef at a monthly resolution.
Giant clams, the world's largest living bivalves, can reach 1.2 metres in length and weigh more than 200 kilograms, living for over a century. As they grow, the cycle of day and night produces microscopic daily lines in their shells, while changing seasons produce broader annual bands, creating what researchers describe as an autobiographical shell diary.
The chemistry of each new layer is shaped by the surrounding seawater, allowing climate researchers to decode how the reef environment changed during the clam's lifetime. The study's findings indicate that before industrial-era warming, summer temperatures at Jiigurru were cooler than today, while winter temperatures were surprisingly similar.
The research addresses a gap in the southern hemisphere's climate records. Today, instruments on land provide detailed weather data, but such records extend back only about a century in many regions. The giant clam shell offers a longer-term perspective on natural climate variability in the reef environment.