Trophic relationships in early spring along the Okhotsk coast of Hokkaido, Japan, as traced by stable carbon and nitrogen isotopes

Abstract

Abstract:We measured stable carbon and nitrogen isotope ratios ( N) of organic matter sources and consumers, including fishery resources, along the Okhotsk coast of northern Hokkaido, Japan, in early spring to characterize the food web. Phytoplankton and benthic detritus, including ice algae, fecal pellets, and benthic microalgae, constituted the main food sources for primary consumers (zooplankton and small benthic invertebrates, respectively); seagrass and terrestrial plant debris served no trophic function for consumers. Planktivorous and benthivorous fish species could be differentiated using stable carbon isotope ratios. Differences in stable nitrogen isotope ratios revealed speciesspecific feeding habits of crustacean groups: copepods were separated into three groups as herbivorous, omnivorous, or omnivorous-carnivorous, and benthic amphipods were divided into two groups as either omnivorous or omnivorous-carnivorous. We distinguished four levels of both pelagic and benthic trophic linkages. The d 13 C values were enriched by 0.9-1.3‰ at the linkage between each pelagic trophic level except between the 1st and 2nd levels; d15 N values were enriched by 2.2-2.9‰ at each level. For benthic trophic linkages, the enrichment for d C and d 15N values between each level ranged from 0.6‰ to 1.0‰ and from 1.6‰ to 2.6‰, respectively. Trophic positions of copepod, mysids, and sand lance appeared between pelagic and benthic linkages. This suggests that those species have fed on both pelagic and benthic diets.

Cryptic Zooplankton Diversity Revealed by a Metagenetic Approach to Monitoring Metazoan Communities in the Coastal Waters of the Okhotsk Sea, Northeastern Hokkaido

“…The proportional contribution of meroplankton to sequence read counts was greater than that detected in a metagenetic study in Tosa Bay, off Japan, (Hirai et al, 2017a) or in reefs in the Red Sea (Pearman et al, 2014). Furthermore, stable isotope analyses in the coastal waters of northeastern Hokkaido indicated an interaction between planktonic and benthic organisms (Hiwatari et al, 2011). As observed for zooplankton diversity, environmental factors such as water temperature, driven by water mass exchange, and a strong bentho-pelagic interaction in coastal waters, acted together to influence seasonal changes in dominant taxa.…”

Reconstruction of diachronic changes in human fishing activity and marine ecosystems from carbon and nitrogen stable isotope ratios of archaeological fish remains

“…First, it seems that fishing locations did not change between the Epi-Jomon and Okhotsk periods, as there was no significant chronological difference in the δ 13 C values of the five fish species, except for rockfish from the Initial Okhotsk phase (Table 4; Figure 3). The δ 13 C values of inshore fish are typically higher than those of offshore or pelagic fish (Bas et al 2020;France 1995;Hiwatari et al 2011;Misarti et al 2009), but no difference between the time periods was seen here. Although the Okhotsk had ocean-going vessels (Amano 1977;Nomura & Utagawa 2003;Oba 1955), and zooarchaeological evidence that suggests that Okhotsk communities did fish somewhat further from the coast than in the Epi-Jomon, relatively speaking both can still be considered as inshore fisheries (Nishimoto 1985).…”

“…Higher nutrient concentrations and thus higher productivity can be typically seen in inshore and benthic systems resulting in enriched 13 C for biota compared to pelagic systems (France 1995). Such inshore/pelagic differences can be seen in modern fish species in the Okhotsk Sea and Pacific Ocean (Hiwatari et al 2011;Misarti et al 2009). This provides the basis for differentiating between inshore and offshore fishing using δ 13 C values.…”

“…Inter-species differences in δ 13 C and δ 15 N values are consistent with the species-specific diet and habitat of the analyzed fish with ≥3 individuals. Migrating fish species that seasonally come near the coast, such as cod, Okhotsk atka mackerel, and Pacific herring (Table 2; Fisheries Agency 2019, 2020), exhibit lower δ 13 C values, consistent with more time spent feeding in offshore waters (Bas et al 2020;France 1995;Hiwatari et al 2011;Misarti et al 2009). The δ 15 N values of these species can be classified into higher (i.e., cod) and lower (i.e, Pacific herring and Okhotsk atka mackerel) groups, reflecting their diets (Table 2; Chikaraishi et al 2014;Minagawa & Wada 1984;Schoeninger et al 1984).…”

“…The main prey of adult cod are fish, crustaceans, and molluscs resulting in a relatively high trophic level with elevated δ 15 N values, while adult Pacific herring and adult Okhotsk atka mackerel focus on plankton, small fish, and crustaceans from relatively low trophic levels and hence exhibit lower δ 15 N values (Table 2; Fisheries Agency 2019Agency , 2020. Fish species living in the inshore benthic system (i.e., flatfish, pufferfish, rockfish, and sculpin) show higher δ 13 C values, a signature of the inshore/benthic ocean (Bas et al 2020;France 1995;Hiwatari et al 2011;Misarti et al 2009;Szpak et al 2013). The typical δ 15 N values of these species are intermediate between the higher and lower groups, suggesting that their prey are mainly from the middle trophic levels.…”