Molting, growth, and energetics of newly-settled blue king crab: Effects of temperature and comparisons with red king crab

Abstract

Populations of blue king crab (BKC) (Paralithodes platypus Brandt, 1850) have declined in Alaskan waters over recent decades, and substantial effort is being made to rehabilitate the once important fishery with releases of hatchery-reared juveniles. However, little is known about the species' first year of post-settlement life. This study was conducted to evaluate how temperature mediates growth and energy allocation beginning with the first benthic instar (stage C1). Juvenile BKC were reared in four temperatures (1.5 to 12°C) for a period of 60days in low-density populations (150crabsm−2) and 120days in individual cultures. Growth rate increased rapidly up to 8°C, and then leveled off. At 60days, most of the crabs in 1.5°C remained at stage C1, most in 4.5°C were C2, and most in 8°C were C3, while those in 12°C were highly variable and ranged from C2 to C5. Growth records for individuals revealed an inverse exponential relationship between water temperature and intermolt period (up to 8°C). A small decrease in molt increment at 12°C resulted in crabs 6% smaller than those at 8°C. Total lipid content increased with temperature in C2 BKC, but the response was variable and not significant in later stages. The proportion of storage class lipids (triacylglycerols) increased with an increase in temperature and polar lipids decreased. Concentrations of essential fatty acids were relatively constant over all temperature treatments, indicating that temperature and growth rate did not affect the biochemical condition of juvenile BKC. Survival rates of BKC (>95%) were similar across temperatures and were much higher than rates observed for red king crab (RKC) (Paralithodes camchaticus Tilesius 1815) (65–72%) in identical experiments. Growth rates of the two species were nearly identical up to 8°C, but RKC grew faster than BKC at temperatures greater than 8°C, with more molts resulting in larger individuals. Fatty acid (FA) signatures supported the lipid class data and showed that BKC had higher proportions of FA associated with energy storage while RKC had higher proportions of polyunsaturated FAs associated with membranes. These results indicate that BKC are the hardier species, and it shows little sign of cannibalism in culture (unlike RKC), but RKC grow faster at high temperature and are less vulnerable to warming climate. These data help to model temperature-dependent recruitment processes in the field and assist in the design of diets and hatchery conditions for production of seed stocks intended for field release.