A new study has shown that growth patterns stored in the cementum tissue structure of marine mammal teeth provide unique insight into climate–growth histories of marine mammal populations over long time series.
Mammal teeth form regular growth increments, referred to as growth layer groups (GLGs), within the cementum and dentine tissue structure of the tooth, analogous to tree rings. Using these tooth growth chronologies, researchers from the Gillanders Aquatic Ecology Lab at the University of Adelaide reconstructed long-term growth histories of male and female New Zealand fur seals from southern Australia. These growth histories were then related to key climate variables, such as sea surface temperature, the Southern Oscillation index, the Southern Annular Mode, and the El Niño-Southern Oscillation index.
The results of the study indicated a net negative effect of increasing sea surface temperature on growth for this population, with the strength of the relationship stronger for females. The authors suggest that the impacts of sea surface temperature on growth is likely explained by the indirect affect that climate has on abundance, distribution or energy content of prey, as New Zealand fur seal diets are largely dependent upon primary ocean productivity driven by climate. Male New Zealand fur seals often travel farther than females, as maternal provisioning mothers are more likely to be restricted in foraging range, which they suggest may also explain why females appear to be more sensitive and males more resilient to some climatic variables.
With ocean temperatures off the southeast coast of Australia predicted to increase by more than 3 °C by the end of this century, there is a growing need for accurate predictions of the ecological response of natural populations to patterns of climatic variability. This study highlights the underutilised potential of mammal teeth to develop these long-term, indirect records of climate–growth relations that would otherwise prove very difficult and expensive to acquire using traditional sampling techniques.
Reference: Wittmann TA, C Izzo, ZA Doubleday, J McKenzie, S Delean, BM Gillanders. 2016. Reconstructing climate-growth relations from the teeth of a marine mammal. Marine Biology 163, article 71.
Image: Jame McKenzie