Thermal effects on embryonic development and hatching for blue king crab Paralithodes platypus (Brandt, 1850) held in the laboratory, and a method for predicting dates of hatching

Climate change may affect crab populations via thermal effects on embryo development and hatching. To test this, we measured the duration of development and hatching for the embryos of 11 blue king crabs Paralithodes platypus held at 2.3 ± 0.45, 4.3 ± 0.31, and 6.1 ± 0.61°C. Embryo area, length, and width, eye length and width, and percent yolk were measured biweekly from digital images, and hatching larvae were collected daily from individual crabs. Data were compared between eggs of identical age (weeks since fertilization). Temperature did not have a significant effect on embryo measurements, but did affect development indices (percent yolk and eye size). Hatching was significantly delayed at colder temperatures with about a 46-day difference from 2.3°C to 6.1°C. Length of development was related to temperature via a power function, and ranged from 410 ± 8 days at 6.1°C to 434 ± 11 days at 2.3°C. Length of hatching increased from 40 ± 4.6 days at 2.3°C to 55 ± 6.2 days at 6.1°C. A model for predicting hatching dates from an eye index was developed using a quadratic equation. Embryo development at 4.3 and 6.1°C was arrested between weeks 35 and 50; this evidence, plus other behavioral observations, suggests that crabs may be able to adjust development rates to partially compensate for temperature changes.