Figure 3.
Heterogeneous O2 dynamics emerge in egg clusters. (a) Representative cross section of flow velocity from a CFD simulation (flow = 0.04 cm s−1, T = 15°C) mimicking the natural rearing environment of salmon eggs. The black and grey circles are egg and gravel cross-sections, respectively. The random packing configuration of eggs and gravel resulted in highly variable flow conditions within the egg cluster. (b) This variability in flow in turn led to highly variable local O2 conditions, where slow-flowing regions were more heavily depleted of O2. Additionally, O2 was depleted as it flowed from the front to the back of the egg cluster. (c) Measured O2 concentrations within experimental egg clusters were highly variable even at spatial scales as small as 1 cm. Shown are absolute differences in O2 concentrations between paired O2 probes within the same egg pocket as a function of the distance between probes. (d) The degree of O2 limitation for eggs within the cluster in the CFD model depended on flow and temperature. Each point represents one egg within the cluster, lines show the mean O2 limitation of eggs within a treatment. The black horizontal line represents a critical O2 limitation, above which mortality increases rapidly with further O2 limitation (figure 2c). (Online version in colour.)