UTILIZING MODERN OSTRACODE ECOLOGY AND BIOGEOGRAPHY IN THE SOUTHEAST CHUKCHI SEA AS A MEANS TO ENHANCE PALEOECOLOGICAL RECONSTRUCTIONS

Changing climate and ocean conditions throughout the past three decades have strongly impacted the Chukchi Sea ecosystem. We conducted a repeat quantitative analysis of benthic ostracode assemblages from surface sediment samples collected along a transect in the southeast Chukchi Sea to monitor changes and to establish a baseline for interpreting ecological conditions. Ostracode species distributions are controlled primarily by environmental conditions such as seawater temperature, salinity, food availability, and substrate. This study reexamines the ostracode species distributions reported in Gemery et al. 2021, and thus represents bio-indications of changing ocean conditions over the past decade. Our goals were to (1) define the current ostracode distribution across the Chukchi shelf; (2) determine if ostracode assemblages have changed during the period 1984-2023, (3) analyze the ecological preferences of ostracode species using environmental measurements (temperature, salinity, sediment size, and food type and availability) by using those data collected concurrently at each station; and (4) assess the influence of these environmental parameters on the distribution of ostracode species through time. Our results indicate that Pacific-affiliated cold-temperate species Patagonacythere dubia, and Munseyella kiklukhensis have increased in abundance in the Chukchi Sea during 2019-2023. We have documented the first occurrences of Muellerina abyssicola and Celtia palmensis in the southern Chukchi Sea and we found the highest abundance and diversity of ostracode species at near-shore stations in warmer, less saline summer waters. Since 2017, we documented a dramatic decline in ostracode populations at offshore sites. This study continues to build upon our understanding of modern species ecology and distributions, which will enhance paleoecological record interpretation by verifying species-environment relationships from modern records.