Abstract
To study the influence of different ocean currents on the trophic spectra found in a sympatric fish community, we analyzed the radiocarbon contents (Δ14C) and stable carbon (δ13C) and nitrogen (δ15N) isotopic compositions in their bulk muscle tissues and the δ15N of individual amino acids in 26 species of demersal fish collected from off Tohoku (Pacific coast), northeastern Japan. The Δ14C values of the fish varied from –42 to +41‰, consistent with the Δ14C of the dissolved inorganic carbon in the cold Oyashio Current (typically about –50‰) and the warm Kuroshio Current (typically about +50‰). The trophic positions (TPs) of the fish estimated from the δ15N values of amino acids increased from 3.1 to 4.5 with increasing snout length. A negative correlation was observed between Δ14C and TP in gadiform fish and flatfish, suggesting that the Oyashio Current delivers a high TP diet to these fish groups. These results suggest that the trophic ecology of marine fish in the coastal western North Pacific is primarily controlled by the two major surface water currents, but is also significantly influenced by a combination of species-specific feeding and migration strategies.
Highlights
Surface ocean currents play an important role in controlling primary production, ecosystem structures, and fisheries resources (Ganachaud and Wunsch, 2000; Toggweiler and Russell, 2008)
We found no significant relationship between sampling depth, latitude, or longitude and δ13CBulk (n ≥ 42, r2 < 0.02, p > 0.41) or δ15NBulk (n ≥ 44, r2 < 0.06, p > 0.10), except for the effect of longitude on δ15NBulk (n = 47, r2 = 0.11, p = 0.04)
The lowest 14CBulk values were found in Laemonema longipes, whereas the highest 14CBulk values were found for Dexistes rikuzenius, Glyptocephalus stelleri, and Alcichthys elongatus (Elkhorn sculpin) (+35 to +41, n = 4) (Figure 4)
Summary
Surface ocean currents play an important role in controlling primary production, ecosystem structures, and fisheries resources (Ganachaud and Wunsch, 2000; Toggweiler and Russell, 2008). The interfrontal regions in which different currents meet and mix are important sites for local fishery grounds, because their high primary production is supported by different temperature, 14C & Trophic Positions in Marine Fish salinity, and nutrient profiles (Yatsu et al, 2013). Oyashio Current (of the northwestern subarctic gyre) meets the warm northward Kuroshio Current (of the western subtropical gyre) around middle latitudes. The warm Tsugaru Current, which originates in the Kuroshio Current, contributes significantly to the water masses, especially nearshore on the Sanriku coast (Hanawa and Mitsudera, 1987; Itoh et al, 2016; Figure 1). Understanding ecosystem structures and functions is essential for sustainable fisheries and resource use, and yet fundamental information is still largely unavailable, including the sources of carbon and nitrogen in the benthic ecosystems off the Sanriku region
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