Abstract
Hornsund is a cold-water fjord in southwestern Spitsbergen, Svalbard Archipelago, with a resident biota that exhibit typical low-temperature Arctic features. Carbon (δ13C) and nitrogen (δ15N) isotopic signatures of macrobenthic fauna and its potential food sources were measured in summer 2008 to delineate the trophic structure of the bottom community and to identify its principal carbon sources. The soft-bottom fauna at a water depth of 100 m was found to rely primarily on detritus, which is supplied by sedimentation of suspended organic matter from the water column and horizontal transport of refractory macroalgae from euphotic coastal habitats. Through resuspension by bottom currents, deposited particles also contributed to the diet of benthic filter-feeders. Since benthic organisms were significantly enriched in 13C compared to epibenthic zooplankton (mainly amphipods and decapods), the stable carbon signature provides a tool to differentiate benthic and pelagic feeding habits. The benthic food web was characterized by a conventional trophic structure with decreasing species numbers in increasing trophic levels. Primary consumers feeding on a mixture of plant matter, fecal pellets, decaying animal tissue, bacteria, and protists accounted for the greatest biomass share (62 % of the total macrobenthic biomass), followed by secondary consumers (38 %). Based on δ15N signatures, three trophic levels were detected, corresponding to the following feeding guilds: filter-feeders and feeding generalists (mainly bivalves, crustaceans, polychaetes, and some fish), mixed detritivore–carnivores (polychaetes, priapulids, crustaceans, and ophiuroids) and obligate carnivores (ascidians). The average food chain length (4.5 trophic levels) suggests that high-quality food is readily available in this Arctic fjord ecosystem.
Highlights
Trophic relationships in marine and estuarine systems of the sub-Arctic and Arctic have been the subject of increasing interest, primarily in order to (1) evaluate the transport of energy and matter, fluxes, and cycles; (2) identify species and feeding links that are most influential in the dynamics of community composition and structure; and (3) define potential contaminant transfer along the food chain and biomagnification (Horton et al 2009; Iken et al 2010; Renaud et al 2011)
Stable isotope ratios of potential carbon sources varied greatly among different components: d13C spanned a range of 11.3 % and d15N spanned a range of 5.1 % (Fig. 2)
Hornsund and Kongsfjorden are both glacial fjords on the west coast of Spitsbergen that are under the influence of the relatively warm Atlantic waters, the former is more affected by the cold Sørkapp Current carrying Arctic waters (Kedra et al 2010)
Summary
Trophic relationships in marine and estuarine systems of the sub-Arctic and Arctic have been the subject of increasing interest, primarily in order to (1) evaluate the transport of energy and matter, fluxes, and cycles (the socalled flow approach); (2) identify species and feeding links that are most influential in the dynamics of community composition and structure (the so-called process– functional approach); and (3) define potential contaminant transfer along the food chain and biomagnification (Horton et al 2009; Iken et al 2010; Renaud et al 2011). The presence of three non-indigenous euphausiid species of typically Atlantic origin in Kongsfjorden (western Spitsbergen) has been linked to enhanced Atlantic water inflow (Buchholz et al 2010). From their extensive survey of long time-series data Wesławski et al (2009) concluded that the advanced propagation of warmer low-latitude waters with the North Atlantic Current to the high European Arctic may be expected to cause a general increase in the overall biodiversity of Arctic biocenoses
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