title: Microbial Food-Web Drivers in Tropical Reservoirs.
abstract: Element cycling in aquatic systems is driven chiefly by planktonic processes, and the structure of the planktonic food web determines the efficiency of carbon transfer through trophic levels. However, few studies have comprehensively evaluated all planktonic food-web components in tropical regions. The aim of this study was to unravel the top-down controls (metazooplankton community structure), bottom-up controls (resource availability), and hydrologic (water residence time) and physical (temperature) variables that affect different components of the microbial food web (MFW) carbon stock in tropical reservoirs, through structural equation models (SEM). We conducted a field study in four deep Brazilian reservoirs (Balbina, Tucuruí, Três Marias, and Funil) with different trophic states (oligo-, meso-, and eutrophic). We found evidence of a high contribution of the MFW (up to 50% of total planktonic carbon), especially in the less-eutrophic reservoirs (Balbina and Tucuruí). Bottom-up and top-down effects assessed through SEM indicated negative interactions between soluble reactive phosphorus and phototrophic picoplankton (PPP), dissolved inorganic nitrogen, and heterotrophic nanoflagellates (HNF). Copepods positively affected ciliates, and cladocerans positively affected heterotrophic bacteria (HB) and PPP. Higher copepod/cladoceran ratios and an indirect positive effect of copepods on HB might strengthen HB-HNF coupling. We also found low values for the degree of uncoupling (D) and a low HNF/HB ratio compared with literature data (mostly from temperate regions). This study demonstrates the importance of evaluating the whole size spectrum (including microbial compartments) of the different planktonic compartments, in order to capture the complex carbon dynamics of tropical aquatic ecosystems.
authors.affiliation: Museu Nacional, Laboratório de Ficologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 20940-040, Brazil. carolina.ddomingues@gmail.com.
authors.forename: Carolina Davila
authors.initials: CD
authors.lastname: Domingues
authors.affiliation: Museu Nacional, Laboratório de Ficologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 20940-040, Brazil.
authors.forename: Lucia Helena Sampaio
authors.initials: LH
authors.lastname: da Silva
authors.affiliation: Museu Nacional, Laboratório de Ficologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 20940-040, Brazil.
authors.forename: Luciana Machado
authors.initials: LM
authors.lastname: Rangel
authors.affiliation: Museu Nacional, Laboratório de Ficologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 20940-040, Brazil.
authors.forename: Leonardo
authors.initials: L
authors.lastname: de Magalhães
authors.affiliation: Laboratório de Limnologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 21940-590, Brazil.
authors.forename: Adriana
authors.initials: A
authors.lastname: de Melo Rocha
authors.affiliation: Laboratório de Ecologia Aquática, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais, 36036-900, Brazil.
authors.forename: Lúcia Meirelles
authors.initials: LM
authors.lastname: Lobão
authors.affiliation: Laboratório de Ecologia Aquática, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais, 36036-900, Brazil.
authors.forename: Rafael
authors.initials: R
authors.lastname: Paiva
authors.affiliation: Laboratório de Ecologia Aquática, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais, 36036-900, Brazil.
authors.forename: Fábio
authors.initials: F
authors.lastname: Roland
authors.affiliation: Departamento de Hidrobiologia, Laboratório de Processos Microbianos e Biodiversidade, Universidade Federal de São Carlos, São Carlos, 13565-905, Brazil.
authors.forename: Hugo
authors.initials: H
authors.lastname: Sarmento
mesh_terms: D000818:Animals; D001419:Bacteria / Q000378:metabolism*; D001938:Brazil; D016798:Ciliophora / Q000378:metabolism*; D033361:Cladocera / Q000378:metabolism*; D033342:Copepoda / Q000378:metabolism*; D017753:Ecosystem; D005068:Eutrophication; D020387:Food Chain; D005618:Fresh Water / Q000382:microbiology; D009584:Nitrogen / Q000378:metabolism; D010933:Plankton / Q000378:metabolism*; D013696:Temperature; D014871:Water Microbiology
chemical_list: D009584:Nitrogen
keywords: Carbon stock; Degree of uncoupling; Grazing; Structure equation models