A high-density multi-species bivalve spawning event in the southern Chukchi Sea

The Pacific Arctic region (PAR) is characterized by high productivity and strong benthic-pelagic coupling, supporting abundant benthic communities. In addition to food availability, persistence of benthic populations is shaped by larval transport and recruitment along the advective pathways which connect patchy benthic hotspots. Here, we describe a chance encounter with an extensive bivalve spawning event on the southeastern Chukchi shelf, initially detected using a shipboard Imaging FlowCytobot in July 2023 and confirmed with discrete sampling. Using integrated taxonomy, larval morphotypes were identified as 2 distinct taxa: Macoma calcarea (trochophores and veligers) and Mya sp. (D shells), both of which are key members of the PAR food web. Larval presence was strongly associated with Bering Summer Water, and morphotypes exhibited vertical partitioning through the water column consistent with behavioral differences across life stages. Densities of both species were orders of magnitude higher than typically recorded in the region (11550 M. calcarea l -1 and 5750 Mya sp. l -1 ), indicating a proximal source population and likely a coordinated spawning event. Benthic biomass data from the southern Chukchi shelf confirm the presence of adult populations of both species. A reverse particle advection model was used to validate this source location, and a forward particle advection projected the dispersal pathway of the larvae, revealing that they likely settled northwest near Herald Shoal. This interdisciplinary approach provides new insight into population connectivity and life history dynamics of both species, as well as general pathways of larval transport in Arctic waters.