Observations on the population distribution and ecology of Branchiostoma (Cephalochordata) lancelets from the Virginia inner continental shelf region, United States

Abstract Lancelets are important model organisms in the study of chordate evolutionary development and are found in abundance in many marine and estuarine environments. The distribution and ecology of Branchiostoma in and around the Chesapeake Bay are particularly understudied, however, as is the case for this genus generally in the Northwest Atlantic. During several sampling events spanning 2022–2024, we collected lancelets using a combination of benthic grabs and epibenthic sled tows from a large sampling regime along with pertinent abiotic conditions such as sediment grain size and bottom water salinity. Our study area covered an inshore-offshore, estuarine-marine gradient, allowing for the assessment of lancelet distribution across variable ecosystem types. Our principal results showed an affinity for coarse-grained, high salinity habitats, which is consistent with previous findings for other species. We also present robust total and seasonally specific length-weight curves, which showed higher mean weight-at-length values in the spring as compared to other seasons. Finally, despite initial identification of samples as Branchiostoma virginiae , supplemental meristic and genetic approaches to speciation applied to a subset of individuals failed to definitively assign those individuals to the species level. We suggest that future studies assess the phylogenetics of Branchiostoma in the Northwest Atlantic use a multilocus approach and (or) improve morphological keys to reduce overlap in the counts of crucial meristic components, potentially investigating hybridization, intergradation, or even the possibility of an extant single Branchiostoma species in this region.