Biogeographic, ontogenetic, and environmental variability in larval behaviour of American lobster Homarus americanus

Through laboratory observations we evaluated the influence of natal origin, onto geny, and environment (light, temperature) on the vertical and horizontal swimming behaviour of larval American lobster Homarus americanus. We quantified several behavioural indices including vertical water position, average swim speed, and linearity, and measured how these factors interacted to determine horizontal diffusivity. Larval swimming behaviour varied significantly for all behavioural indices as a function of natal origin, ontogeny, temperature, and light. Across treatments, post-larvae exhibited fastest swim speeds (5.96 cm s(-1)), horizontal diffusivities (9.97 cm(2) s(-1)), and highest position in the water column compared to earlier stages. We observed significantly lower (similar to 60%) swimming speed and vertical position in intermediate developmental stages compared to early and late stages. Within stage I larvae, swim speed averaged 2.1 cm s(-1) with a horizontal diffusivity of 3.31 cm(2) s(-1), and although swim speed did not vary with maternal origin we observed a significant interaction between origin and temperature. Larvae from different geographic regions, reared in common garden conditions, differed in behavioural response to temperature; warm origin larvae swam significantly faster (similar to 25%) in warm water, as did cold origin larvae in cold water (similar to 43% faster), relative to each other. Our results detail potential novel sources of variability in larval behaviour and provide one of few direct measures of swimming behaviour of larval American lobster. Collectively, our results provide a biological-behavioural context to parameterize biophysical models with broad applicability to meroplanktonic species, and a powerful tool to potentially improve accuracy of dispersal models and advance understanding of larval transport.