The surf zone ichthyoplankton adjacent to an intermittently open estuary, with evidence of recruitment during marine overwash events

The composition, structure and seasonality of ichthyoplankton in the surf z one adjacent to the mouth of the intermittently open East Kleinemonde Estua ry (33 degrees 32'S, 27 degrees 03'E) were investigated over a period of 2 years. Altogether 451 fishes, representing at least 21 taxa from 14 familie s, were collected. The assemblage was dominated by postflexion larvae of eu ryhaline marine species that are dependent on estuaries as nursery areas. T he sparid Rhabdosargus holubi was the most abundant taxon and constituted m ore than 77% of the total catch. A distinct modal size class was identified for R. holubi, while the mean individual size of this and other abundant t axa was comparable to the observed recruitment size range reported from a w ide variety of estuarine nursery habitats in southern Africa. Periodic regr ession analyses revealed significant peaks in abundance of larval R. holubi during late winter (August), at down and dusk, at new and full moon (sprin g tides), and on the flood stage of the tidal cycle. Evidence for estuarine immigration during marine overwash events (surging rough seas that enter t he estuary) is provided by (1) the stranding of postflexion larvae in the r egion of the closed estuary mouth following these events, and (2) back extr apolation from length modes within the estuary to coincide with such an eve nt. The advantages and disadvantages of such a recruitment strategy are dis cussed. (C) 2001 Academic Press.