Influence of temperature and congener presence on habitat preference and fish predation in blue (Paralithodes platypus Brandt, 1850) and red (P. camtschaticus Tilesius, 1815) king crabs (Anomura: Lithodidae)

Abstract

Rebuilding fisheries is a difficult process and many stocks that are declared overfished fail to recover even in the absence of fishing pressure. The Pribilof Islands stock of the blue king crab ( Paralithodes platypus Brandt, 1850) in Alaska, USA is one of these recovery failures. To explore how environmental and ecological factors might interact to suppress this stock, we conducted a suite of laboratory experiments to assess the effects of temperature changes and the presence of red king crab ( Paralithodes camtschaticus Tilesius, 1815) on blue king crab habitat preference and fish predation survival. Age-0 blue king crabs exhibited plasticity in habitat preference mediated by changes in water temperature, as well as the presence and density of juvenile red king crabs. While blue king crabs are often associated with shell-hash habitat, increases in water temperature, as well as the presence of red king crab at high densities, caused blue king crab juveniles to shift into habitats with an algal mimic present, a habitat type shown to reduce the predation efficacy of red king crabs. In contrast, red king crabs exhibited fewer changes in habitat preference with changes in water temperature and the presence of a congener. Blue king crabs are therefore behaviorally plastic, switching from strategies of predator avoidance when predator encounter rates are likely low, to predator deterrence strategies when encounter rates are higher. Fish predation trials further support the idea that blue king crabs are more focused on predator avoidance than are red king crabs. In fish predation trials run separately for the two crab species, blue king crabs had higher survival (60%) than red king crabs (33%) when exposed to fish predators. Our results indicate that age-0 blue king crabs can be less vulnerable to fish predation than red king crabs, but future research should assess how fish predation rates change when presented with higher densities of red and blue king crab in mixed assemblages as the observed habitat shifts could affect predation survival.