Composition, abundance, distribution and seasonality of larval fishes in the Mngazi Estuary, South Africa

Abstract

We investigated the larval fish assemblage in the intermittently-open Mngazi Estuary, in the subtropical/warm-temperate biogeographic boundary region of South Africa. Larvae were collected by means of boat-based plankton tows in summer and winter for a period of three years between 2003 and 2005. Within the Mngazi Estuary, salinity ranged from 10.1–37.4, temperature ranged from 15.5°C–27.3°C, pH ranged from 6.8–8.3ppt and oxygen ranged from 2.6mg l–1–8.8mg l–1. In total, 8 343 larval fishes were collected, representing 18 families and 31 species. Clupeidae and Gobiidae were the dominant fish families whilst the dominant species was the estuary — resident Gilchristella aestuaria (Clupeidae). Estuary-resident larvae were the dominant group in the system. Larval fish density ranged from 0–38 600 individuals per 100m3 in summer and from 0 to 638 individuals per 100m³ in winter. Species diversity also varied seasonally. Salinity zones played a significant role in terms of species distribution. The euhaline zone supported the highest species diversity while the mesohaline zone supported the highest densities of larval fishes. Salinity, temperature and turbidity were identified as important variables governing larval fish dynamics in the system.

African Journal of Aquatic Science 2007, 32(2): 113–123