Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss Sampling planktonic cnidarians with paired nets: Implications of mesh size on community structure and abundance Everton Giachini Tosetto a,* , Sigrid Neumann-Leitão a , Miodeli Nogueira Júnior b a Departamento de Oceanografia, Universidade Federal de Pernambuco, Avenida Arquitetura, S/N, 50670-901, Recife, PE, Brazil b Departamento de Sistemática e Ecologia, Universidade Federal da Paraíba, Cidade Universitária, 58051-900, João Pessoa, PB, Brazil ARTICLE INFO Keywords: Hydromedusae Siphonophores Mesh selectivity Zooplankton Amazon River Plume ABSTRACT Mesh selectivity is an important factor to be considered when sampling zooplankton. Selectivity may differ according to the environment and taxon, but his has not been evaluated for cnidarians in neritic and/or oceanic ecosystems. In this study, efficiency of plankton nets with two different mesh sizes (120 and 300 μm) were compared to assess the cnidarian assemblage from neritic and oceanic habitats in the equatorial Atlantic Ocean. No statistical differences between meshes were observed in species richness, total and most dominant taxa abundance, or taxonomic and size structure of the community in both oceanic and neritic habitats. Only for the small (0.5–2 mm) neritic Persa incolorata did the meshes differ, with higher abundances in the finer one. Despite small particularities, our results show that the 120 and 300 μm meshes produce similar results. 1. Introduction Marine planktonic animals have a wide variability in size and swimming ability, constituting a quite heterogeneous community which, together with the typical patch distribution, makes it difficult to establish standard sampling protocols in ecological studies and quan- titative assessments (Omori and Hamner, 1982; Harris et al., 2000). The accuracy of a particular sampling instrument typically is related to species size, morphology, flexibility, behavior and distribution, and environmental characteristics (Vannucci, 1968; De Bernardi, 1984). Among the many factors that may influence zooplankton sampling, mesh size selectivity is one of the most important (Skjodal et al., 2013). While a small mesh may filter high rates of unwished particles, ob- structing water passage and rapidly clogging the mesh, a coarse one may lose smaller species and early life stages (Riccardi, 2010; Vannucci, 1968). Mesh selectivity and catch efficiency is a controversial subject. For copepods, where mesh size effect is relatively well understood, 200 μm meshes may lose a significant proportion of small species, copepodites and nauplii abundance (up to 90%) and biomass (up to 50%; Hopcroft et al., 1998; Hwang et al., 2007; Di Mauro et al., 2009; Favareto et al., 2009; Riccardi, 2010; Wu et al., 2011). However, the reported under- estimation of larger species and individuals by smaller meshes due to the bow wave effect and mesh obstruction (Vannucci, 1968; Hopcroft et al., 2001; Favareto et al., 2009) is not ubiquitous (Antacli et al., 2010; Miloslavić et al., 2014). The effects of different mesh sizes on other invertebrate zooplank- tonic taxa are poorly known. Few particular information is available considering appendicularians, chaetognaths, mollusks, polychaetes, cnidarians and non-copepod crustaceans (Almeida Prado, 1962; Vidjak, 1998; Di Mauro et al., 2009; Riccardi, 2010; Skjodal et al., 2013; Miloslavić et al., 2014; Nogueira Júnior et al., 2015). Despite most of this literature showing that specific groups and/or sizes are better es- timated by particular mesh sizes, the lack of detailed information, such as seasonality and habitat variability, hinders the development of standard sampling protocols. Given the requirement of precise methods to estimate zooplankton abundance, detailed information of taxa-spe- cific mesh size effects considering habitat heterogeneity is a matter of great importance. Planktonic cnidarians have aroused recent interest in the scientific community due to their high feeding rates and unexpected population blooms (e.g. Purcell et al., 2007). For a complete understanding of these processes, precise quantitative methods need to be established. Al- though the choice of the mesh size will depend on particular targets in each study, the 500 μm mesh, frequently used in planktonic cnidarian sampling (e.g. Gili et al., 1991; Loman-Ramos et al., 2007; Segura- Puertas et al., 2010), was found to largely underestimate hydrozoan estuarine assemblages (Nogueira Júnior et al., 2015). Since the es- tuarine cnidarian community usually is dominated by small-sized hy- dromedusae (Xu and Huang, 1983; Nogueira Júnior et al., 2015), the https://doi.org/10.1016/j.ecss.2019.02.027 Received 6 November 2018; Received in revised form 15 January 2019; Accepted 9 February 2019 * Corresponding author. E-mail addresses: evertontosetto@hotmail.com (E. Giachini Tosetto), sigridnl@uol.com.br (S. Neumann-Leitão), miodeli@gmail.com (M. Nogueira Júnior). Estuarine, Coastal and Shelf Science 220 (2019) 48–53 Available online 21 February 2019 0272-7714/ © 2019 Elsevier Ltd. All rights reserved. T