Aging of the sea urchin Centrostephanus rodgersii using demi-pyramid microstructure

Abstract

We investigate a novel aging method that utilizes parallel ridges and grooves on the surface of demi-pyramids of the sea urchin Centrostephanus rodgersii. Analysis of marginal increments from sea urchins tagged with oxytetracycline confirmed that ridges form in the mid to late Austral spring, as seawater begins to warm. After known periods of up to three years, counts of ridges from tagged sea urchins showed that the ridges were formed annually. Differences between observed and expected counts of ridges were mostly related to readers’ inability to distinguish adjacent ridges at the growing margin of the demi-pyramid. This resulted in a higher probability of underestimating age for individuals ≥ 6 yr. Counts of the ridges on the same demi-pyramid by the same reader, and comparisons among different readers, provided estimates of random error and bias. Estimates of aging error and bias in distinguishing ridges were modeled and used to estimate ‘true’ age and age structure. Maximum estimated age was 27 yr but most individuals were estimated to be 10–15 yr. We discuss the relevance of our findings to the fishery and the broader applicability of our method to correct ages estimated from other hard parts in marine species.