The role of estuarine type in characterizing early stage fish assemblages in warm temperate estuaries, South Africa

Abstract

Assemblages of early stage fishes (larval and early juvenile stages) were investigated and compared in seven permanently open and five intermittently open estuarine systems on the warm temperate Eastern Cape coast of South Africa. Estuarine type, by virtue of mouth state and prevailing physico chemical conditions, played a defining role in the structure of these fish assemblages. Clupeidae and Gobiidae were the dominant fish families in both estuarine types. Permanently open estuaries were characterized by the predominance of larvae and early juveniles of estuary dependent marine fish species while estuary resident fishes dominated intermittently open estuaries. Seasonal changes were observed in species density and diversity in both estuarine types. Species richness and diversity were highest in the permanently open Swartkops Estuary that is characterized by large nursery habitat availability. Species diversity was high in estuaries with a good supply of freshwater, that results in good recruitment of estuary dependent marine species. Similarly, freshwater deprived estuaries also displayed high species diversity and this was due to the higher incidence of marine straggler species in these systems. Salinity zones appeared to play a significant role in both species density and the presence or absence of species in both estuarine types. Mesohaline zones were found to be the most productive in terms of accumulator regions for larval stages.

A multidisciplinary study of a small, temporarily open/closed South African estuary, with particular emphasis on the influence of mouth state on the ecology of the system

“…Although certain marine species may decline in abundance under prolonged closed-mouth conditions due to predation and the lack of new recruits, the dominant estuarine-resident species G. aestuaria breeds during this phase and attains maximal abundance and biomass (Strydom et al 2003). Although the actual numbers of marine species may decline during the closed phase, growth of these fish ensures that the overall ichthyofaunal biomass actually increases (Cowley and Whitfield 2002).…”

“…Research includes descriptions of the fish community (Cowley and Whitfield 2001a, Strydom et al 2003, Vorwerk et al 2003, quantification of fish population sizes (Cowley and Whitfield 2001b), fish biomass and production estimates (Cowley and Whitfield 2002), composition of larvae in the marine environment adjacent to the estuary mouth , and estuary recruitment strategies by marine-spawning species .…”

Seasonal relative abundance of fish larvae in Helleh River estuary (north of the Persian Gulf, Iran)

“…Clupeidae family was dominant and present family in all seasons; Gobiidae, Engraulidae, Sillaginidae, Platycephalidae, Teraponidae, Siganidae, Synodontidae, Sphyraenidae, Cynoglosside, Soleidae and Carangidae families were observed in 3 seasons; Sparidae, Gerridae, Lutjanidae, Mugulidae, Hemiramphidae, Scorpaenidae, Belonidae families were observed in 2 seasons during study period (Table 1). Estuary environment is a very important nursery for many fish larvae and juveniles of other estuarine species (Strydom et al 2003). Most marine fishes which are dependent on estuary environment enter these ecosystems within the postflexion phase of their larval stage (Strydom and Whitfield 2000).…”

“…Salinity as an effective factor in development, growth and stress level of marine fish is well known (Chesalina et al 2013). Water salinity and temperature are two main factors affecting fish distribution among and within estuarine environments and have been shown to play an important role in the occurrence, density and growth of the larval stages of fishes (Rakocinski et al 1996;Strydom et al 2003). The changes in salinity range and other water factors such as temperature, dissolved oxygen, pH and conductivity happen for the reasons of the effects of tides and mixing of fresh water and marine water (Marshall and Elliott 1998).Temperature as the primary abiotic parameter is controlling the physiological and biochemical processes during fish life period and influences the utilization of estuaries ecosystems by fish species (Harrison and Whitfield 2006).…”

Influence of oceanographic seasonality and dredging activities on the fish larvae assemblage in the Port of Aratu, Todos os Santos Bay

“…Furthermore, salinity and temperature has been shown as important variables that control the distribution and abundance of planktonic organisms (Mouny & Dauvin, 2002;Tackx et al, 2004;Strydom et al, 2003).…”