Abstract
Abstract. This study examines the resource use and trophic position of nematodes and harpacticoid copepods at the genus/species level in an estuarine food web in Zostera noltii beds and in adjacent bare sediments using the natural abundance of stable carbon and nitrogen isotopes. Microphytobenthos and/or epiphytes are among the main resources of most taxa, but seagrass detritus and sediment particulate organic matter contribute as well to meiobenthos nutrition, which are also available in deeper sediment layers and in unvegetated patches close to seagrass beds. A predominant dependence on chemoautotrophic bacteria was demonstrated for the nematode genus Terschellingia and the copepod family Cletodidae. A predatory feeding mode is illustrated for Paracomesoma and other Comesomatidae, which were previously considered first-level consumers (deposit feeders) according to their buccal morphology. The considerable variation found in both resource use and trophic level among nematode genera from the same feeding type, and even among congeneric nematode species, shows that the interpretation of nematode feeding ecology based purely on mouth morphology should be avoided.
Highlights
Seagrass meadows form unique, productive and highly diverse ecosystems throughout the world (Hemminga and Duarte, 2000)
Chemoautotrophic bacteria were added as an additional resource based on the δ13C obtained here for the nematode genera Terschellingia and Sabatieria and for the copepod family Cletodidae and on literature information; we adopted an average δ13C of −35 ± 5 ‰ for this resource and an average δ15N of 4 ± 0.5 ‰, based on our own data for the three aforementioned taxa, since we found no information on the δ15N of sulfide-oxidizing bacteria in the literature
The present study includes δ13C data of 20 nematode taxa, 16 of which were identified to the genus level and two to the family level, as well as four harpacticoid copepod families (Canuellidae, represented here by the genus Sunaristes, Cletodidae, Ectinosomatidae and Harpacticidae, this last taxon being present only in deeper sediments) (Tables 1 and 2)
Summary
Seagrass meadows form unique, productive and highly diverse ecosystems throughout the world (Hemminga and Duarte, 2000). Seagrass beds typically support higher biodiversity and faunal abundance compared to the adjacent unvegetated areas (Edgar et al, 1994) due to both increased food supply and reduced predation risks (Heck et al, 1989; Ferrell and Bell, 1991). They strongly influence the associated fauna by modifying hydrodynamics (Fonseca and Fisher, 1986) and by altering the energy flux either directly, through release of dissolved organic carbon into the water column, or indirectly, by contributing to the detritus pool after decomposition (Boström and Bonsdorff, 1997). The few studies using natural isotope abundances to unravel food resources of coastal meiofauna at this level (Carman and Fry, 2002; Moens et al, 2002, 2005, 2013; Rzeznik-Orignac et al, 2008) do not examine seagrass habitats
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