Reconstructing climate–growth relations from the teeth of a marine mammal

Abstract

Sclerochronological analysis of growth increment patterns (growth layer groups; GLG) in marine mammal teeth offers a unique opportunity to reconstruct climate– growth relations of marine mammal populations over long time series. We developed sclerochronologies from GLG width measures in the cementum of male and female New Zealand fur seal (Arctocephalus forsteri) post-canine teeth collected from southern Australia. Tooth growth chronologies spanned 15 years and encompassed the period from 1987 to 2001. We also developed a rigorous analytical framework for assessing species suitability for sclerochronological analyses. Suitability assessments indicated that GLG clarity and relative width measures were variable among regions within individual teeth, and therefore, measurements were standardised to a consistent tissue type. Deposition of cementum in post-canine teeth was also correlated with body size, suggesting tooth growth measures were a suitable proxy of somatic growth. Inter-annual patterns of tooth growth were negatively correlated with mean annual sea surface temperature and the Southern Oscillation Index (both lagged by 1 year), but the strength of the relationships differed between the sexes. These results suggest both local- and regional-scale physical processes influence variations in growth and provide the first evidence of an environmental effect on cementum growth in a marine mammal. This study demonstrates the underutilised potential of marine mammal teeth to provide extended time series of growth, critical information which facilitates predictions of future ecological response to environmental change.