LIFE HISTORY OF ARCHITEUTHIS DUX REVEALED BY SIMS ANALYSIS OF CARBON AND OXYGEN ISOTOPES IN STATOLITHS

The giant squid (Architeuthis dux) is the largest living marine invertebrate. Genetic evidence suggests there is a single, globally distributed species. In order to sustain a globally connected population, dispersal of individuals must happen regularly. In many other deep-sea cephalopods, juvenile dispersal though a planktic phase is critical. Although charismatic and of considerable interest, direct study of the entire life history of A. dux is difficult because adults live in deep, inaccessible waters and juveniles are morphologically similar to other squids. Recently, some authors have suggested that juvenile A. dux may inhabit shallower water than adults.

Here we use secondary ion mass spectrometry to analyze the carbonate statoliths of 5 A. dux individuals that were collected near Aotearoa (New Zealand). Statoliths are small (~150 µm in maximum length) and incrementally precipitated within statocysts, a balance and acceleration sensing organ. Statoliths are analogous to fish otoliths and record conditions like temperature and metabolic rate in geochemical proxies across the entire lifespan of the individual. In the core of each statolith δ¹⁸O values plateau near -3‰ and indicates early life stages were spent in a warm, shallow habitat. There is a gradual shift towards higher δ¹⁸O values (+2‰ VPDB) from the edge of the plateau towards the rim of the statolith suggesting a gradual transition to cooler water. The core of the statolith has uniform δ¹³C values near -7‰ towards the rim there is a gradual increasing trend to +2‰. Assuming a uniform metabolic δ¹³C and a consistent dissolved inorganic carbon δ¹³C, we calculate the change in the proportion of metabolic carbon incorporated into the statoliths. In the core of the statolith, >50% of the carbon may be metabolic and towards the rim, < 30% is metabolic, which implies that metabolic rate decreases through ontogeny.

In total, these data provide insight into the life history of these ocean giants and highlight potential vulnerability to environmental change in shallow waters during the earliest parts of their lives.