Behavioral Responses to Changes in Hydrostatic Pressure and Light During Larval Development of the Lobster Homarus americanus

Abstract

Larvae of the lobster Homarus americanus hatched and reared under laboratory conditions in shallow water responded to changes in hydrostatic pressure in a depth-regulatory manner. Responsiveness to instantaneous pressure increments ranging from 1 to 20 psi increased linearly up to 10 psi but varied little at higher pressures. Sensitivity to pressure changes was retained throughout larval life up to and including stage IV (megalopa) but stage III and IV larvae were much less responsive than stage I and II. Stage V (1st juvenile) lobsters were nonresponsive to pressure changes. Larvae were much less responsive (in terms of vertical movements) to changes in light intensity than to changes in pressure, and there were no clear, sustained phototactic or photopathic responses in the vertical plane.In the sea, stage I, II, and III larvae showed limited downward movement when released at the surface and generally upward movement when released below the surface. Newly-molted stage IV larvae generally remained at the surface when released there and swam to the surface when released at the bottom; those 14–15 days after molting also tended to remain at the surface but when released at the bottom they generally remained there and found shelters. Newly-molted stage V juveniles generally remained where they were released, both at the surface and at the bottom, but those 13–15 days after molting when released at the surface generally swam to the bottom and found shelters, and when released at the bottom, remained there.