Vertical positioning and swimming performance of lobster larvae (Homarus gammarus) in an artificial water column at Helgoland, North Sea

The vertical distribution and swimming ability of the three larval stages (Zoea I, II, and III) of Homarus gammarus were determined in laboratory experiments. In an artificial water column, newly hatched larvae were positively phototactic to white light at intensities near 0.6 mmol m 2 s . The positive phototactic behaviour decreased with increasing larval age and stage. Accordingly, older larvae were mostly distributed away from the light source in deeper layers and near the bottom. The measured vertical swimming speed of newly hatched larvae was 4.690.5 cm s . Lobster larvae were positively rheotactic and thus able to swim against the current direction. The horizontal swimming ability of the larvae increased with stage from 0.791.0 cm s 1 (Zoea I) to about 1.590.9 cm s 1 (Zoea II) and 2.290.7 cm s 1 (Zoea III). Implications for the persistence of the small, isolated lobster population around the island of Helgoland are discussed.