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Shellfish Assessment Program - Recruitment: Past Research


Red and Blue King Crab Species Interactions

Graph of historial mature male abundance
			of Pribilof Islands red and blue king crab. Blue line represents blue king crab, red line represents red
			king crab. Click image to enlarge.
Historial mature male abundance (millions) of Pribilof Islands red and blue king crab. Click image to enlarge.
 
Graph of proportion of blue king crabs eaten by predators at each prey ratio. Points are the
			average predation at each density, which are offset slightly to prevent error bar overlap. Lines 
			represent the model estimates for the predator preference model in cobble (solid line) and shell
			(dashed line). Click image to enlarge.
Proportion of blue king crabs (BKC) eaten by predators at each prey ratio. Points are the average (± SE) predation at each density, which are offset slightly to prevent error bar overlap. Lines represent the model estimates for the predator preference model in cobble (solid) and shell (dashed). Click to enlarge.

An apparent shift in predominance from blue king crab to red king crab occurred around the Pribilof Islands in the late 1990s.

To help understand this shift, researchers in the Shellfish Assessment Program at the Kodiak Laboratory explored intra-guild predation between red and blue king crabs as a possible mechanism for limiting the recovery of the blue king crab population.

Laboratory studies were used to help understand possible large-scale effects on population abundance.

Predation rates of year-1 red king crab (predator crabs) on year-0 blue and red king crabs (prey crabs) were compared in shell and cobble habitat.

Year-0 red king crabs were preferentially consumed over blue king crabs in shell habitat but not cobble, likely because the smaller interstitial spaces in shell reduced predator foraging efficiency and predator-prey encounter rates.

Blue king crab light, mottled coloration and relatively smooth, flat carapace is well adapted for visual and physical crypsis in shell, implying shell material may provide blue king crabs a competitive advantage over red king crabs.

This research suggests the extent of shell habitat may be an important factor for survival for early benthic phase blue king crabs around the Pribilof Islands.

Scientists hope to assess the current status of habitat composition and associated benthic species assemblages around the Pribilof Islands in future research, as very little habitat work has been done in nearshore waters around the Pribilof Islands since the 1980s.






            Photo of a juvenile red king crab 
			depicting more pronounced spines and monochromatic coloration. Click image to enlarge.             Photo of juvenile blue king crab
			depicting light, mottled carapace coloration and a smooth, flat carapace. Click image to enlarge.

Juvenile red (Paralithodes camtschaticus, left photo) and blue (P. platypus, right photo) king crabs. Morphological differences between species occur in the early benthic phase, including the larger size, more pronounced spines, and monochromatic coloration of red king crabs. Click images to enlarge.


Blue King Crab Cannibalism

Graph of average predator crab activity
			in sand and shell habitat. Motionless is defined as crabs not moving, walking as crabs moving 
			laterally, and foraging as crabs consuming prey or crabs with repeated movements of chelae from the
			substrate to the mouth. Different letters indicate statistical significance between habitats for each
			behavior. Click image to enlarge.
Average (± SE) predator crab activity in sand and shell habitat. We define "motionless" as crabs not moving, "walking" as crabs moving laterally, and "foraging" as crabs consuming prey or crabs with repeated movements of chelae from the substrate to the mouth. Different letters indicate statistical significance between habitats for each behavior. Click image to enlarge.

In laboratory experiments, researchers evaluated the effects of habitat type on the cannibalistic behavior of early juvenile blue king crabs. Compared to sand habitat, predation rates in shell material were low regardless of predator size or prey density.

Predator foraging activity was reduced in shell and may be an adaptive behavior to balance foraging efficiency and susceptibility to larger predators.

Results demonstrate that early benthic phase blue king crabs are cannibalistic between cohorts in the laboratory and that shell material is extremely effective for reducing encounter rates with conspecific predators.

Cannibalism between cohorts may be a source of mortality limiting recruitment success in wild populations and may play a role in fluctuating blue king crab population abundances.

This laboratory study highlights the importance of the distribution and abundance of shell material for recruitment success in blue king crab populations.





Photo of juvenile blue king crab in shell material
Juvenile blue king crab in shell material


Shellfish Assessment Program - Recruitment Research CURRENT RESEARCH


Related Publications

  • DALY, B., and W. C. LONG. 2014. Intra-guild predation among early benthic phase red and blue king crabs: Evidence for a habitat-mediated competitive advantage. J. Exp. Mar. Biol. Ecol. 451:98-104.

  • DALY, B., and W. C. LONG. 2014. Inter-cohort cannibalism of early benthic phase blue king crabs (Paralithodes platypus): Alternate foraging strategies in different habitats lead to different functional responses. PLoS ONE 9(2):e88694. doi:10.1371/journal.pone.0088694 Online


See the publications and poster databases for additional listings.

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