Local‐ and Regional‐Scale Climate Variability Drives Complex Patterns of Growth Synchrony and Asynchrony in Deep‐Sea Snappers Across the Indo‐Pacific

Climatic variation can play a critical role in driving synchronous and asynchronous patterns in the expression of life history characteristics across vast spatiotemporal scales. The synchronisation of traits, such as an individual's growth rate, under environmental stress may indicate a loss of phenotypic diversity and thus increased population vulnerability to stochastic deleterious events. In contrast, synchronous growth under favourable ecological conditions and asynchrony during unfavourable conditions may help population resilience and buffer against the negative implications of future environmental variability. Despite the significant implications of growth synchrony and asynchrony to population productivity and persistence, little is known about its causes and consequences either within or among fish populations. This is especially true for long-lived deep-sea species that inhabit environments characterised by large-scale interannual and decadal changes, which could propagate growth synchrony across vast distances. We developed otolith growth chronologies for three deep-sea fishes (Etelis spp.) over 65° of longitude and 20° of latitude across the Indo-Pacific region. Using reconstructed time series of interannual growth from six distinct Exclusive Economic Zones (EEZs), we assessed the level of spatial synchrony at the individual-, population- and species-scale. Across five decades of data, complex patterns of synchronous and asynchronous growth were apparent for adult populations within and among EEZs of the Pacific Ocean, mediated by shifts in oceanographic phenomena such as the Pacific Decadal Oscillation. Overall, our results indicate that the degree of synchrony in biological traits at depth depends on life history stage, spatiotemporal scales of environmental variability and the influence of ecological factors such as competition and dispersal. By determining the magnitude and timing of spatially synchronous growth at depth and its links to environmental variability, we can better understand fluctuations in deep-sea productivity and its vulnerability to future environmental stressors, which are key considerations for sustainability.