Postlarval settling behavior, substrate preference, and time to metamorphosis for red king crab Paralithodes camtschaticus

Swimming behavior was observed and substrate preference determined for glaucothoe stage postlarvae of the red king crab Paralithodes camtschaticus in the laboratory. One hundred 1 d old glaucothoe were placed into each of 3 replicate 10 l aquaria, each containing a choice of 3 substrates: sand. gravel, or synthetic fiber mesh. Glaucothoe began settling on the first day, and <10% remained swimming after Day 6. Glaucothoe showed a significant preference for the structurally complex mesh substrate. Occupancy of mesh increased from 49% on Day 2 to 75% by metamorphosis to the first crab (C1) instar, with a mean of 62 +/- 11%. Glaucothoe rejected sand, and only 1% were observed on it. Settlement was also tested in aquaria with only sand, gravel or mesh substrates. Glaucothoe in gravel- or mesh-only aquaria settled rapidly, whereas 40% of glaucothoe in the sand-only aquarium continued swimming until metamorphosis to C1 instar. In addition, mean time-to-metamorphosis in the sand-only aquarium (17.6 d) was significantly greater than in other experimental aquaria (16.8 d). Glaucothoe in the sand-only aquarium exhibited marked diurnal swimming behavior; 66% were swimming at 14:00 h (vs a maximum of 12% in other aquaria), but only 5% (vs 1%) were swimming at 02:00 h. Daytime swimming probably allows glaucothoe to avoid nocturnal predators while searching for preferred substrates, i.e. those which are structurally complex, can be easily grasped, and provide a high degree of interstitial space.