Fine-scale habitat use by larval fishes in the Swartkops Estuary, South Africa
Information regarding the use of habitats in estuaries is often geared toward the juvenile stages and rarely toward the earlier larval stages. In some cases, postflexion larvae and early juveniles may be constituted as hyperbenthos over these habitats and their contributions are rarely considered. The fine scale habitat use of larval fishes was assessed in the lower reaches of the warm temperate, permanently open Swartkops Estuary in the Eastern Cape, South Africa. Habitat use and seasonal trends were assessed by counting and measuring larval fishes obtained from larval seine net catches in four habitat types sampled twice per season from February 2013 to January 2014. Results showed that habitat preferences did not exist in the larval stages of most species with no species showing a significant difference in occurrence or abundance among habitat types (p > 0.05). However, multivariate analyses indicated that temperature was a strong seasonal driver influencing the recruitment of marine spawned species into estuarine nurseries, thereby affecting the species composition. Additionally, general additive models indicated that high catches in many of the dominant larval taxa were related to high temperatures, low salinities and high turbidities. Consequently, it is confirmed that environmental drivers may be more important in determining larval composition in estuaries than habitat type.
KeywordsIchthyofauna Nursery habitats Physico-chemical variables Species composition
Gratitude is expressed to the National Research Foundation for financial and bursary support (Grant number 79733, held by N.A. Strydom). Much appreciation is expressed to the field assistants for their practical assistance and support. Special mention and thanks to Dr. Paula Pattrick (South African Institute for Aquatic Biodiversity) for her editing assistance and comments on the draft of this paper. All research was approved by the Research Ethics Committee: Animals (RECA), Nelson Mandela University.
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