Temperature affects growth rates while dietary lipid influences condition metrics in juvenile Tanner crab (Chionoecetes bairdi)

Tanner crab (Chionoecetes bairdi) populations in Alaska have declined since the 1980s. Increasing ocean temperatures have been hypothesized to be a driver of regional crab declines, both via direct thermal effects on their metabolic rates and through indirect effects on predatory-prey interactions and available food quality. Lower juvenile crab energy storage and higher metabolic rates may make early life stages more vulnerable to warming-induced starvation than adults. To characterize the potential synergistic influence of temperature and diet quality (% lipid) on juvenile Tanner crab survival, growth, lipid composition and condition metrics, we collected age-0 crab from nursery grounds in Kodiak, Alaska, during the summer of 2022. We performed an 11-month growth experiment in which crab were reared in individual cells under three temperatures (2, 5, and 9 °C) and on two dietary lipid levels (low and high). Morphometric data were collected within one week of molting and whole-body lipid samples were taken at mid-molt following the second full molt cycle, or at the end of 11 months of culture. Results show that temperature significantly impacted growth and survival, with shorter intermolt periods and high mortality observed at 9 °C. Morphometric-based condition was highly variable and not significantly differ between treatments. In contrast, lipid-based condition metrics revealed that crab fed high dietary lipids had elevated triacylglycerols and total lipids per weight relative to crab fed low-lipid diets. Crab reared in elevated temperatures had higher proportions of sterols and saturated fatty acids than crab at low culture temperatures. Our findings in this fully crossed experiment suggest that increasing temperatures in Alaska waters have the potential to impact juvenile crab populations both directly through accelerated growth and indirectly via declining lipid content available in the benthic food web.