  Vertical migrations of zooplankters have been widely described, but their
active movements through shallow, highly dynamic water columns within the inner
shelf may be more complex and difficult to characterize. In this study,
invertebrate larvae, currents, and hydrographic variables were sampled at
different depths during and after the presence of fronts on three different
cruises off the southern coast of South Africa. Internal wave dynamics were
observed in the hydrographic data set but also through satellite imagery,
although strong surface convergent currents were absent and thermal
stratification was weak. During the first two cruises, fronts were more
conspicuous and they preceded strong onshore currents at depth which developed
with the rising tide. Vertical distributions of larvae changed accordingly,
with higher abundances at these deep layers once the front disappeared. The
third cruise was carried out during slack tides, the front was not conspicuous,
deep strong onshore currents did not occur afterward and larval distributions
did not change consistently through time. Overall, the vertical distributions
of many larval taxa matched the vertical profiles of shoreward currents and
multivariate analyses revealed that these flows structured the larval
community, which was neither influenced by temperature nor chlorophyll. Thus,
the ability to regulate active vertical positioning may enhance shoreward
advection and determine nearshore larval distributions.
