Swimming velocities and patterns of Bugula californica larvae through the early stages of development

The larval swimming patterns prior to settlement play an important role in geographic dispersal and genetic connection for sessile marine organisms. This study examined how swimming patterns and size change with age for larvae of the bryozoan, Bugula c.f. californica. We observed three different swimming patterns, including upward swimming, downward swimming, and sinking which were observed every hour post hatch for four hours until the onset of settlement each day. We used analysis of digital photographs to measure the body length and width of larvae within the same cohort. Almost all early stage larvae swam up to the top in the first hour, but in later stages larvae changed their swimming pattern to swim down or sink. Upward velocity averaged at about 2mm per second and decreased over time, and in the fourth hour the larvae started to sink at about 2mm per second. In addition, there is no significant difference among the values of the lengths or widths of the larvae over time, but these phenotypic characteristics did vary within the age cohorts