Insights into benthic macroinvertebrate ecology in the northern Bering and southern Chukchi Seas from stable isotope analysis

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In the Pacific Arctic Region, the northern Bering Sea and southern Chukchi Sea support large and diverse communities of benthic macroinvertebrates that provide an important link to the pelagic communities and marine mammals that rely on the benthic populations for food. While the abundance and biomass of these benthic macroinvertebrates are well documented, little is known about how benthic macroinvertebrates interact with each other and how these interactions are affected by climate change. I measured the stable isotope composition (bulk δ15N and δ13C values) of similar species collected in 2014, 2016, 2017, and 2021 in the northern Bering and southern Chukchi Seas. Although there was little change over time in either δ15N or δ13C values, both stable isotope ratios were significantly different between stations with differing production phenologies. The southern Chukchi Sea (a productive set of sites with high chlorophyll concentrations throughout the summer) had lower δ15N values and higher δ13C values, while the northern Bering Sea site with production mostly associated with the period of sea ice breakup had higher δ15N values and lower δ13C values. This pattern was observed across similar species and feeding types. The higher δ15N values in the northern Bering Sea could be due to an extra step in the food chain from bacterial reworking. The contrast between these two regions in δ13C might indicate higher primary production in the southern Chukchi Sea compared to the northern Bering Sea. The differing food web dynamics between these two sites highlight the benthic diversity across small scales and similar organisms in Pacific Arctic food webs.