The correlation of downwelling irradiance and staggered vertical igration patterns of zooplankton in Wilkinson Basin, Gulf of Maine

Field studies on the characteristics of light that influencevertical migrations in the mesopelagic realm are sparse, dueto the difficulty in simultaneously monitoring changes in speciesdistributions with changes in downwelling irradiance. Usingthe Johnson-Sea-Link submersible as a platform, in situ measurementsof the changes in downwelling irradiance at sunset were madesimultaneously with observations on changes in animal distributionpatterns in Wilkinson Basin, Gulf of Maine. The results indicatethat the vertical migrations for several species of large zooplanktonare staggered, with euphausiids (Meganyctiphanes norvegica)migrating first, cydippid ctenophores (Euplokamus) migratingnext, and two species of caridean shrimp (Dichelopandalus lepiocerusand Pasiphaea multidentata) migrating last Data collected ondaytime dives indicate that the daytime depth distribution isnot solely responsible for the migration order, and that differentspecies may be responding to different cues, or have differentthresholds for the same cue.