Isabel Schmalenbach

Effects of temperature on the moulting and locomotory activity of hatchery-reared juvenile lobsters (Homarus gammarus) at Helgoland (North Sea)

Abstract Optimized release conditions of hatchery-reared juvenile lobster (Homarus gammarus) can reduce loss in the field. The effect of seasonal temperature on the behavioural and physiological activity of lobsters was examined, observing the timing of moulting and locomotory activity in juvenile lobsters maintained at increasing temperatures under standardized laboratory conditions. The juveniles of three different year and size classes mostly moulted when a threshold temperature between 12 and 14°C was reached. In addition, the locomotory activity of lobsters showed significant responses to seasonal temperatures between 12 and 15°C in the dark-phase. The knowledge about the temperature-dependent activity of lobsters may be helpful to explain behaviour in the field and in assessing the chances of a future large-scale stock enhancement programme.

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

Abstract 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 µmol m−2 s−1. 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 4.6±0.5 cm s−1. 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 0.7±1.0 cm s−1 (Zoea I) to about 1.5±0.9 cm s−1 (Zoea II) and 2.2±0.7 cm s−1 (Zoea III). Implications for the persistence of the small, isolated lobster population around the island of Helgoland are discussed.