INFLUENCE OF SENESCENT ALGAE, TEMPERATURE, TIDES, CURRENTS, AND EMBRYO DETACHMENT ON CHIONOECETES OPILIO (SNOW CRAB) LARVAL RELEASE

On the Scotian Shelf (SS), Chionoecetes opilio (snow crab) larval releases are spread out over at least a 12-week period in the spring. This large spread in the timing of snow crab larval release may be caused by the large variability in the timing of the spring phytoplankton bloom found on the SS, or complex oceanographic factors. It has been reported that C. opilio release their larvae in response to post bloom senescent algae exposure, and that the release may also be timed with the high spring tide. Objectives of this study include exploring the possibility of tidal, current, and senescent algae induced larval release in ovigerous C. opilio from the SS population; temperature influences were also examined. Another objective was to determine if the female or the embryos themselves control the hatching process. The average duration of hatching was 9.6 d for the warmer treatment and 12.3 d for the cooler treatment. A mixed-effects model using a logistic regression indicated no significant influence of senescent algae upon the larval release patterns (P > 0.5); and a statistically significant temperature influence upon larval release patterns (P < 0.0001). Detached embryos still hatched 14 days post removal, and throughout the duration of hatching were relatively synchronous with those still attached to the female (two-sided KS, D = 0.308, P > 0.5). Larval release did coincide with local high tide and the associated higher current speeds. The results of this study indicate that C. opilio embryos are not receiving chemical cues from the female or senescent algae, but rather, are under endogenous control. Whether they rely on internal pressure, some type of internal biochemical cue or external physical factor such as hydrostatic pressure from high tides or increased current speed warrants further study.