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Blue King Crab, Paralithodes platypus, Development of Larval Cultivation Techniques

Dorsal view of a blue king crab
Red king crab female with eyed eggs
blue king crab embryo at the four cell stage
Eyed red king crab embryos just prior to hatching

The blue king crab (Paralithodes platypus) once supported lucrative fisheries in the eastern Bering sea. Two distinct populations and fisheries occur, one at St. Matthew Island, and another near the Pribilof Islands. Since 1997, both populations have declined drastically, and fisheries have been closed.

Blue king crabs (link to enlarged photos of adults) have a 2-year reproductive cycle. In January-February of their spawning year, female crabs moltand mate, and extrude about 150,000 eggs that are then fertilized and attached to the female's abdomen. The females carry the developing fertilized embryos for approximately one year. The next year, larvae are released or hatched, but the crab do not molt or mate again, unlike red king crabs, which hatch, molt, mate, and extrude each year.

In 2003, Dr. Bradley Stevens received a grant from the North Pacific Research Board (NPRB) to study the early life history of blue king crab. In July and October 2003, 21 female blue king crabs were captured from the Bering Sea and returned to the Kodiak Fishery Research Center, where they were maintained in seawater at 3 ˚C. Most females were new-shelled and ovigerous, carrying eyed eggs, and thus still in their spawning year. Two crabs had old shells encrusted with barnacles, and carried empty egg cases, evidence that they had released larvae the previous spring. Pictured at right are embryos of blue king crab, prior to hatching. The large black patch is the eye; yellow region is yolk; red splotches are chromatophores (color cells). Larval appendages can be seen at the top of the egg case.

In January 2004 one of the old-shell females molted, mated, and extruded a new clutch of eggs. Embryos were photographed at daily intervals. The first cell division occurred on Day 4; the 4-cell stage (pictured here) occurred on Day 7. Subsequent divisions occurred at 1-2 day intervals. Several embryonic stages, at the 64 and 256-cell stage, can be viewed by clicking on the 4-cell stage photo to the left.

The first priority of this study was to develop cultivation techniques for the embryos and larvae, in order to insure a supply of crab for future research. For this purpose, larvae hatched in the spring of 2004 were used. The goals in 2004 were to conduct three separate experiments to determine optimal diet, temperature, and density for cultivation of the larvae to the first crab stage. Four diets, three experimental temperatures (3, 6, and 9 ˚C), and three different densities (10, 20, and 40 liter beakers) were tested.

In the second year of this study, four females are being studied at each of three temperatures (2,4, 6 ˚C) to look at the effects of temperature on the embryonic development. Starting at fertilization, and at weekly intervals thereafter, a small number of eggs from the clutch were photographed and then measured. Dr. Stevens was interested in understanding the impacts of climate change, especially seawater warming, on the reproduction of the blue king crab.

From this work several posters and papers have been presented so far:

Sara Persselin currently oversees this project.

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