vertical distribution

2016-10-31T12:39:17Z (GMT) by Rémi M. Daigle Anna Metaxas
We manipulated both the temperature in the bottom water layer (B) and the temperature difference between layers (ΔT) in an orthogonal design. We used, for S. droebachiensis (n = 5): 4 levels of ΔT (0, 3, 6 and 12 °C) and 3 levels of B (3, 6 and 9 °C); for A. rubens (n = 4): 3 levels ΔT (0, 6 and 12 °C) and 2 levels of B (6 and 12 °C); and for A. irradians (n = 4): 3 levels of ΔT (0, 5 and 11 °C) and 2 levels of B (5 and 11 °C). These combinations of factors were chosen to represent the conditions in the local environment. Since there were up to 12 treatment combinations for a particular species and we only had 4 thermocline chambers, not all replicates could be run simultaneously. For S. droebachiensis, different cohorts (from unique parental pairs) were blocked in time and all treatments were completed in 3 randomized groups of 4 within 26 h. For the other species, all replicates of all treatments were conducted in randomized order with a single larval cohort (from multiple parental pairs) within 48 h. Due to limitations of the seawater system at the time, the surface water was ~ 20 °C rather than 21 °C in the treatment combination of ΔT = 12 °C and B = 9 °C for S. droebachiensis. Once the thermoclines were established, 50 ml of seawater containing 250–350 larvae were introduced to each chamber within 1 cm from the bottom of the observation compartment (filled with 0.45 μm-filtered seawater) by gently pouring into a funnel attached to a small tube (2-mm inner diameter). Before being introduced to the experimental chamber, larvae were acclimated to the respective bottom temperature for 15 min. Larval position was visually determined to the nearest cm at 5, 15, 30, 45, 60 and 90 min after introduction for S. droebachiensis and A. irradians, and at 10, 30, 60 and 90 min for A. rubens. Larvae in the entire 50 cm water columns were counted in < 2 min, making repeat counts of individual larvae highly unlikely. Data set includes experimental species, date, temperature of the top and bottom layers of the water column (°C), the temperature difference between layers (°C), time (min), and the number of larvae counted at each depth (cm)