Development of biochemical measures of age in the Alaskan red king crab Paralithodes camtschaticus (Anomura): Validation, refinement and initial assessment

Abstract

Age determination of marine organisms is a central metric for understanding the timing and magnitude of spawning, recruitment and habitat use, juvenile duration, and population age structure. For crustaceans, however, age determination has been a challenge because they lack permanent hard structures and thus easily identified increments of chronology. For the commercially important red king crab Paralithodes camtschaticus, size and shell condition have been used in lieu of accurate age information for estimating population dynamics. Our goal for this validation study was to evaluate an alternative approach based on analysis of specific metabolic products. These “age pigments” collectively termed lipofuscins (LF) were used to assess P. camtschaticus age and provide a more robust metric of age than size measurements alone. For LF measurements, we relied on solvent extraction followed by HPLC separation and fluorometric quantification over histological microscopic analysis to allow higher throughput of samples for practical application in fisheries management where significant numbers of analyses are required. LF accumulation in crabs of known age reared in the laboratory under controlled conditions was tracked for calibration, with testing on P. camtschaticus from wild populations. Initial analysis showed that the P. camtschaticus fluorescence properties were broadly similar to other crustaceans but also had properties unique to this high latitude species. P. camtschaticus accumulated LF in a highly predictable manner during first four years of their lifespan consistent with observations of their increase in body size. The impact of temperature on LF accumulation was also examined in juvenile crabs 3–20 months after hatching and showed positive albeit highly variable results. Estimates of age of young P. camtschaticus from the wild population in Southeast Alaska based on LF content was in close agreement with estimates based on the population size structure and time of the spawning in the region, supporting the feasibility of the technique to provide valuable demographic information for future P. camtschaticus studies.