We explored the use of statolith diameter as an age indicator for the larvacean Oikopleura vanhoeffeni.
Laboratory studies indicated that variability in statolith diameter-at-age is substantially lower than that of
trunk length-at-age, and that variability in statolith diameter-at-age remains constant as statolith diameter
increases with age, while variability in trunk length-at-age increases with age. These results suggest that
statolith diameter is the better indicator of age at all body sizes and ages. Using statolith diameter as a proxy
for age, trunk length-at-age of O. vanhoeffeni was observed in Conception Bay, Newfoundland, for two years.
Seasonal variation in trunk length-at-age was observed in older age groups, and this variability increased
with age, suggesting that body size is not a reliable indicator of age in field populations. Length-at-age
increased in older individuals during the spring phytoplankton bloom, suggesting variation of age-specific
growth in relation to food availability. This new method to determine age of animals in the field provides
opportunities to define age structure and age-specific life history characters that are essential for
understanding the population dynamics of larvaceans.