Influences of Ocean Currents on the Diets of Demersal Fish Communities in the Western North Pacific Revealed by Their Muscle Carbon and Nitrogen Isotopic Compositions

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.

Integrative assessment of amino acid nitrogen isotopic composition in biological tissue samples determined by GC/C/IRMS, LC × EA/IRMS, and LC × GC/C/IRMS

“…The results suggest that the three analytical methods examined in this study return consistent TP output. The TP values are consistent with those expected from their typical diet menu (i.e., large benthos and small fish) and those reported in the previous study (Ishikawa et al 2021). All evidence suggests that these fish are carnivores.…”

“…This study used four fish species: Jelly eelpout Bothrocara tanakae ; Pacific cod Gadus macrocephalus ; Longarm grenadier Abyssicola macrochir ; and Snubnosed eel Simenchelys parasitica collected from the western North Pacific (Ohkouchi et al 2016; Ishikawa et al 2021). One individual per species was used for analysis.…”

Sharing technical knowledge to understand the distribution patterns and migration history of marine organisms

“…This has the advantage over bulk isotopes in that the TP can be estimated solely on the basis of analyses of tissue amino acids (AAs) from the target organism by comparing "trophic AAs" (ex., Alanine, Glutamic acid), which exhibit high isotopic alteration between each trophic position, and "source AAs" (ex., Methionine. Phenylalanine), which exhibit low isotopic alteration through the food web (Popp et al, 2007;Houssard et al, 2017;Ishikawa et al, 2021). Furthermore, "source AAs" can be used as an indicator of the nitrogen source (e.g., d 15 N in phytoplankton) at the base of the food web (Hannides et al, 2009;.…”

“…Generally, both Japanese sardine and mackerel at age-0 migrate shallower than 30 m, but as they grow, mackerel have been reported to migrate to depths of 50-80 m as a school of fish and up to 150 m as individuals in deeper water (Ozawa, 2010;Kamimura et al, 2021;Yasuda et al, 2023). In the Kuroshio-Oyashio transition zone, the Oyashio Current intrudes from a deeper layer below the Kuroshio Current (Itoh and Yasuda, 2010;Ishikawa et al, 2021), suggesting that mackerel are strongly influenced by the food supplied by the Oyashio Current. In fact, reported in their isoscape that the d 15 N of zooplankton (i.e., 6.7 ± 2.1‰ on average) found in the northern region of the Kuroshio-Oyashio transition zone, which is influenced by the Oyashio Current, was greater than that of zooplankton (i.e., 4.6 ± 2.2‰ on average) in the southern region of the zone.…”

Elucidating carbon sources of hydrothermal vent animals using natural 14C abundances and habitat water temperature

“…Natural‐abundance radiocarbon (Δ 14 C) has recently become an increasingly used tool for investigating carbon flows in marine ecosystems (Ishikawa et al 2021). It is useful for investigating carbon sources of vent organisms (Williams et al 1981; Nomaki et al 2019) since it can discriminate between carbon sources such as detrital OM derived from surface primary production (ca.…”