PRIMARY RESEARCH PAPER Impacts of turbidity on an epibiotic ciliate in the St Lucia Estuary, South Africa Salome Jones . Nicola K. Carrasco . Andre Vosloo . Renzo Perissinotto Received: 9 January 2017 / Revised: 11 January 2018 / Accepted: 8 February 2018 / Published online: 6 March 2018 Ó Springer International Publishing AG, part of Springer Nature 2018 Abstract Ciliate epibionts inhabit aquatic systems globally and may exert negative impacts on their hosts. Evidence of the environmental drivers of these epibionts is lacking. This study aimed to test the effects of turbidity on the attachment success of the ciliate Epistylis sp. on the copepod Pseudodiaptomus stuhlmanni in the turbid St Lucia Estuary, South Africa. Epistylis sp. was exposed to P. stuhlmanni individuals for 24 h under six turbidity treatments (range 8–1,500 NTU). The prevalence and density of Epistylis sp. exposed to inorganic silt decreased significantly across the turbidity range in both runs of this experiment. In the natural silt treatments, prevalence increased with turbidity up to 500 and 250 NTU in the first and second experiment, respectively. Beyond these peaks, prevalence decreased. Density peaked at 250 NTU in both experiments. High prevalence and density in the natural silt experiments is directly related to the high organic matter content in this treatment. Association of Epistylis sp. with turbidity may impact negatively P. stuhlmanni, as the longevity of this copepod is negatively related to heavy cover by Epistylis sp. and to turbidity. These findings show that environmental factors may play a key role in modulating epibiotic interactions. Keywords Epistylis sp. Á Nutrition Á Peritrich epibionts Á Suspended silt Á Zooplankton hosts Introduction Ciliate epibionts are common components of aquatic ecosystems, where they are found attached to a diverse range of metazoans (Henebry & Ridgeway, 1979; Green & Shiel, 2000; Fernandez-Leborans, 2010). These organisms may benefit by feeding on the host’s excreta and in the host’s feeding current, hiding from predators and dispersing at little energetic cost (Barea- Arco et al., 2001; Fernandez-Leborans, 2010). The hosts may also possibly benefit by being camouflaged from predators (Stoecker, 1978). However, most studies have shown that ciliate epibionts generally have a negative impact on zooplankton hosts (Gilbert & Schro ¨der, 2003; Visse, 2007; Souissi et al., 2013). Epibionts can be metabolically costly as they impose a physical burden on zooplankton (Xu & Burns, 1991; Handling editor: Mariana Meerhoff S. Jones (&) Á N. K. Carrasco Á A. Vosloo Á R. Perissinotto School of Life Sciences, University of KwaZulu-Natal, Westville Campus, P. Bag 54001, Durban 4000, South Africa e-mail: salomemandyjns@gmail.com R. Perissinotto DST/NRF Research Chair in Shallow Water Ecosystems, Nelson Mandela University, P.O. Box 77000, Port Elizabeth 6031, South Africa 123 Hydrobiologia (2018) 815:37–46 https://doi.org/10.1007/s10750-018-3545-8