The Influence of Tidal Phase on Patterns of Ichthyoplankton Abundance in the Vicinity of an Estuarine Front, Botany Bay,

The influence of oceanography on abundance patterns of ichthyoplankton was compared at diVerent phases of the tide in the vicinity of an estuarine front in Botany Bay, Australia. Fronts were observed at high, ebb, low and flood tides, but the most conspicuous colour discontinuities were found on ebb and flood tides. Greatest diVerences in water density were found across the frontal region on ebb tides. Because rainfall was low, density diVerences were primarily due to diVerences in temperature. There was strong advection of drogues into fronts and along frontal margins on ebb and flood tides. Thus, particles are ‘ jetted ’ along fronts. Total ichthyoplankton was always greatest in fronts on low tides (by 1·5–4 times). Rank abundance of ichthyoplankton in the plume, front and ocean, at other phases of the tide (flood, high, ebb), varied among days. Great diVerences in the composition of ichthyoplankton were found between the plume, front and ocean at all phases of the tide, but diVerences were most clear on ebb and low tides. Some types of fish were always most abundant in the front (e.g. Exocoetidae), or the plume and front (e.g. Gobiidae, Pleuronectidae