Larval accumulation and transport in the nearshore support the fundamental role of thermal stratification

Larval transport in the nearshore plays a central role in larval dispersal and connectivity of shallow water species; however, few studies have resolved the relevant scales of larval transport and patterns of larval distribution in this region. To better understand the physical-biological mechanisms that determine larval transport, we combined high-resolution physical measurements (temperature, currents and pressure) with vertically-stratified sampling of barnacle larval distributions in a nearshore region within 1km from adult, rocky intertidal habitat, in depths from 4 to 12m. We sampled larvae from 2014-2016, using a semi-vortex pump to determine how larval vertical distributions varied spatially and temporally with changing hydrodynamic conditions. Barnacle nauplii and cyphonautes larvae were vertically distributed above the thermocline, while brachyuran zoeae and barnacle cyprids were slightly deeper and more associated with the depth of the thermocline. Additionally, barnacle cyprids were distributed closer to shore when thermal stratification was greatest. Our data suggests that cyprids are transported by the internal tide and accumulate at a well-mixed nearshore station, where stratification breaks down.