Bottom-up effects on freshwater bacterivorous nematode populations: a microcosm approach
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PRIMARY RESEARCH PAPER
Bottom-up effects on freshwater bacterivorous nematode populations: a microcosm approach A. Gaudes • I. Mun˜oz • T. Moens
Received: 7 June 2012 / Revised: 18 November 2012 / Accepted: 1 December 2012 / Published online: 28 December 2012 Ó Springer Science+Business Media Dordrecht 2012
Abstract Nutrient enrichment may alter population dynamics of species in different ways depending on their life strategies. The aim of this study was to test the effect of different nutrient concentrations on the population development of two bacterivorous freshwater nematodes, Bursilla monhystera and Plectus aquatilis. Microcosms with autoclaved natural sand from a pristine stream (Fuirosos, NE of Spain) were enriched with different levels of phosphate, nitrate and ammonia as inorganic nutrients and glucose as a biodegradable dissolved organic carbon source. Although leaching of carbon and nutrients from the detritus fraction in the sediment initially may have overruled differences between treatments, later samplings revealed bottom-up control, with Bursilla monhystera abundances positively correlated to bacterial abundances at high nutrient concentrations.
Electronic supplementary material The online version of this article (doi:10.1007/s10750-012-1421-5) contains supplementary material, which is available to authorized users.
Nevertheless, there were several indications that nematodes in turn affected microbial abundance, most likely through excretion of ammonia and through grazing. In contrast to B. monhystera, Plectus aquatilis at high nutrient concentrations showed a unimodal abundance curve, while not increasing in abundance at low nutrient concentrations. Glucose enrichment did not have any stimulatory effect on either microbial or nematode abundances, probably as a result of unfavourable C:N:P stoichiometry. P enrichment, by contrast, stimulated microbial and Bursilla abundances. Our results indicate that episodic nutrient enrichment may affect populations of bacterial-feeding nematodes in the short term. Their longer-term dynamics may, however, be more dependent on leaching of carbon and nutrients from the pools of sediment-bound detritus. Keywords Eutrophication Nematodes Bacteria Bottom-up Top-down control
Handling editor: Stefano Amalfitano
Introduction
A. Gaudes I. Mun˜oz Departament d’Ecologia, Facultat de Biologia, Universitat de Barcelona, Avgda. Diagonal 645, 08028 Barcelona, Spain
Nematodes are often the most abundant metazoans in the soft sediments of freshwater bodies. Their ecological significance in terms of productivity, food-chain relationships and the remineralisation of organic substances may be substantial (Ingham et al., 1985). Compared with soil and marine habitats, relatively little is known about the ecology of freshwater
A. Gaudes (&) T. Moens Marine Biology Lab, Biology Department, Ghent University, Krijgslaan 281 (S8), 9000 Ghent, Belgium e-mail: [email protected]
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nematodes, especially those in lotic systems (Traunspurger, 2002; Gaudes et al., 2006;
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