Transport in the Nearshore: Linking Larval Vertical Distributions and Coastal Hydrodynamics

Recent studies suggest that larval transport in the nearshore zone plays a central role in larval dispersal and connectivity of shallow water species. Such transport can be mediated by behavioral responses to environmental conditions that result in larval vertical movement within the water column. To better understand the biophysical mechanisms that enhance transport, we combined high-resolution physical measurements (temperature, currents and pressure) with measures of barnacle (Chthalamus spp. and Balanus glandula) larval distributions in a nearshore region in La Jolla, California, USA. We sampled larvae during six different days in June-July 2015, at a fixed nearshore station (5m depth, within 200m of the adult rocky intertidal habitat), using a semi-vortex pump that filtered water through a 112µm mesh net. Samples were collected from 5 depth intervals every 1-2 hours to determine if larval vertical distributions varied temporally with changing oceanographic conditions. Barnacle nauplii were less abundant than cyprid-stage larvae in most samples, and were primarily found near the surface. Cyprids were most abundant below the thermocline in mid-depths, except during certain frontal conditions when they moved to surface waters. We will examine the relationship between the hydrodynamic conditions during our study and larval distributions, discussing the implications for nearshore larval transport.