The influence of temporally heterogeneous copper stress on mothers and their offspring

Environmental stresses are common, but their effects can be complex and depend on the nature of the stress. While individuals may experience multiple stresses during their lifetime, the impact of each exposure to stress may... [ view full abstract ]

Environmental stresses are common, but their effects can be complex and depend on the nature of the stress. While individuals may experience multiple stresses during their lifetime, the impact of each exposure to stress may vary with its timing (relative to the life-history stage of the organism), duration (i.e. the total length of exposure), intensity (i.e. the relative strength) and frequency (i.e. the recurrence of stress, including the interval between bouts of stress). The pollutant copper was used to stress Watersipora subtorquata, a common bryozoan, in the field. Its timing, duration and frequency were manipulated and the growth, reproduction and quality of resultant offspring of Watersipora colonies were assessed.

When the timing of a short exposure (1 wk) was varied, colonies exposed to copper grew less than unexposed colonies, regardless of the timing of the exposure. While no effect of copper was observed on the size of larvae, it was latently manifested as the reduced settlement success of larvae. Exposure to copper only at the earliest time interval influenced whether any larvae would be released (‘spawned’) and the number of larvae; copper stressed colonies were less likely to release any larvae and those that did spawn larvae, released fewer than unstressed colonies.

When colonies were exposed to stress that varied in duration and frequency, an interval of no stress between bouts of stress was important. Individuals stressed for one or two weeks with no opportunity to subsequently recover were less likely to spawn and released fewer larvae. Furthermore, colonies stressed for two weeks continuously produced larvae that were smaller in size and had reduced settlement success. Individuals exposed to stress for the longest duration (3 wk) released the fewest larvae, with each colony only releasing one larva.

Exposure to copper adversely affected colonies and depended on the temporal nature of the stress. When stressed, colony growth and/or reproduction were affected in an integrated way, influencing the number, size and viability of larvae produced. This is likely due to the partitioning of finite energy in the face of stress.