Winter food utilisation by sympatric mysids in the Baltic Sea, studied by combined gut content and stable isotope analys
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ORIGINAL PAPER
Winter food utilisation by sympatric mysids in the Baltic Sea, studied by combined gut content and stable isotope analyses Maiju Lehtiniemi · Mikko Kiljunen · Roger I. Jones
Received: 3 July 2008 / Accepted: 5 December 2008 / Published online: 20 December 2008 © Springer-Verlag 2008
Abstract We studied the winter dietary characteristics of two sympatric mysid species, Mysis mixta and M. relicta, which exploit both benthic and pelagic habitats during diel vertical migrations. Samples collected before and after the ice-covered period in the northern Baltic Sea were investigated using both stomach content analyses and stable isotope analyses of carbon and nitrogen. Both of the mysid species were omnivorous during winter and utilised both benthic and pelagic food sources. The main food source before the ice period was calanoid copepods (40 and 36% for M. mixta and M. relicta, respectively), and after ice-out calanoid copepods (23%) and zooplankton resting eggs (23%) for M. mixta and diatoms (44%) and calanoids (25%) for M. relicta. Their patterns of food utilisation broadly followed seasonal Xuctuations in the abundance of the main prey groups. Although pelagic food availability is low in winter both mysid species utilised pelagic prey widely. We also show that when combining these diVerent diet analysis methods it is important to take into account the time lag in isotopic signatures, otherwise the obtained results do not correspond but instead show the feeding history at diVerent times.
Communicated by X. Irigoien. M. Lehtiniemi (&) Finnish Institute of Marine Research, P.O. Box 2, 00561 Helsinki, Finland e-mail: [email protected] M. Kiljunen · R. I. Jones Department of Biological and Environmental Science, University of Jyvaskyla, P.O. Box 35, 40351 Jyväskylä, Finland
Introduction Mysid shrimps (Malacostraca, Peracarida, Mysidacea) are common crustaceans, inhabiting various aquatic environments. Most species (»95%) are marine, some live in brackish water and a few species occur in freshwater environments (Mauchline 1980). Mysids are general omnivores utilising widely diVerent zooplankton prey, algae and benthic animals as well as detritus as food during their life cycles (e.g. Mauchline 1980; Grossnickle 1982; Viherluoto et al. 2000; Winkler et al. 2007; Lehtiniemi and Nordström 2008; Taylor 2008). They have species-speciWc feeding modes, and some species can switch from one feeding mode to another when food availability changes. They either feed on small particles by creating a suspension feeding current, or feed raptorially, selectively capturing prey (Viitasalo and Rautio 1998). Co-occurring species have diVerences in their diets indicating niche partitioning (Winkler et al. 2007; Lehtiniemi and Nordström 2008; Vilas et al. 2008) and some species are important in linking energy transfer between pelagic and benthic environments (Viherluoto et al. 2000; Taylor 2008; Vilas et al. 2008). Mysids are prey for many larger predators, such as invertebrates, various Wshes (Thiel 1996; Gal et al. 2006;
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