Vertical distribution and abundance of copepod nauplii and ichthyoplankton in northern Baja California during strong internal tidal forcing

In this study, we explored the changes in the vertical distribution and abundance of copepod nauplii and ichthyoplankton every hour in three different depth strata during a period of strong internal tides, which have been shown to accumulate and transport plankters. In the deeper stratum, the abundance of copepod nauplii was significantly greater, significantly increased during the cold phase of the internal tide, and was significantly correlated with both total and baroclinic current flows in the direction of internal tide propagation. On the other hand, ichthyoplankton abundance was generally low, with no stratification in vertical distribution, no significant changes across the two phases of the internal tide, and no correlation at any depth with any current flows. The cold phases of the internal tide were characterized by a shallow thermocline, a cooler water column, and a significant increase in the abundance of copepod nauplii in the bottom stratum. On the other hand, the warm phases of the internal tide were characterized by abrupt warming in surface waters, a depression of the thermocline, and a significant decrease of copepod nauplii in the bottom stratum. The depth distribution and buoyancy of the different groups of larvae may be responsible for the differences found.