Spring rotifer community structure in the Alcantara River (Sicily, Italy), using different mesh size nets: relation to environmental factors

Abstract

-The present study focus on some aspects of zooplankton structure in the Alcantara River (Sicily, Italy), in relation to environmental factors. Zooplankton samplings were performed in spring in four sites, located from up-to downstream along the river course. Four low-flow velocity station points were chosen along a transversal river section in each site. Samples were taken from all station points in the four sites by two different mesh sizes (55 and 100 mm) rectangular nets. Rotifer abundances were an order of magnitude higher in 55 mm mesh size samples than in 100 mm mesh size ones. The two communities also resulted significantly different (ANOSIM test, r = 0.212; P = 0.1%). Generally, low abundances (from 3470 ¡ 5133 to 422 ¡ 474 ind.m x3 ) were explained by low chlorophyll a concentration and the highflow regime of this river. Rotifer dominated the zooplankton community. Cladocerans, copepods and nauplii occurred with considerably lower abundances than rotifers. However, the relative contributions of these taxa to total abundances depended on the mesh sizes used. Euchlanis and Adineta genera exhibited the highest abundances in the rotifer assemblage. Conductivity alone or in association with temperature and dissolved oxygen was the most important environmental factor affecting rotifer community distribution. Cephalodella sp., Lepadella sp. and Trichotria pocillum showed a high positive relation to pico-plankton, showing this fraction as a possible rotifer food item. This paper demonstrated a higher efficiency of the finest net to characterize riverine zooplankton community that increases from up to downstream in terms of abundances and diversity.

Body size in relation to rotifer abundance underestimation using a net of large mesh size in a tropical reservoir

“…While the efficiency of zooplankton sampling is affected by the number and spatial distribution of samples, type of sampling equipment and methods of preservation and enumeration (Bottrell et al 1976, Ruttner-Kolisko 1977, de Bernardi 1984, McCauley 1984, Nie & Vijverberg 1985, James 1991, Wetzel & Likens 1991, Pinto Coelho 2004, Mack et al 2012, Suthers et al 2019, Appel et al 2020, the role of net mesh size must be considered of baseline importance. Figure 4 can be considered as a general indication of sampling efficiency based on body size, dependent on mesh size, and could perhaps be extrapolated to evaluate the efficiency of other mesh sizes not analyzed here (Rodrıguez et al 2013). I emphasize that knowledge of the body size of the taxa under study is of importance not only with regard to analysing ecosystem structure and function (Gianuca et al 2016., Hébert et al 2017, Kwong & Pakhomov 2021, but also when choosing sampling methodology.…”