Climatic forcing modulates non-stationary environmental synchrony in shellfish production regions

Coupled fluctuations between ecological and environmental processes — i.e., synchrony — have been documented in marine ecosystems across multiple spatial and temporal scales. To investigate multiscale synchrony, we applied Wavelet Coherence (WC) and Partial Wavelet Coherence (PWC) analyses to disentangle nonstationary associations between local and regional environmental variables that are critical for shellfish aquaculture along the southeastern Pacific. Specifically, we examined and controlled the effects of local associations between sea surface temperature (SST) and shellfish food supply, represented by normalized fluorescence line height (nFLH), in relation to the regional El Niño–Southern Oscillation (ENSO). Using MODIS-Aqua satellite time series (2003–2022) and the Multivariate ENSO Index (MEI), we assessed temporal changes in the coupling between SST and nFLH in two bivalve aquaculture regions: Tongoy Bay (north-central Chile) and northern Chiloé (southern Chile). Our analyses revealed that SST exhibited a stationary annual cycle explaining over 95% of total variance, while nFLH showed a dominant annual mode accounting for more than 60% of variance. However, the second mode of nFLH in both Tongoy Bay and northern Chiloé reflected the influence of local drivers — such as freshwater discharge events — that were not synchronized with the dominant pattern. PWC analyses identified significant intra- and interannual synchrony between nFLH and ENSO within the 1.5–2.5 yr and 3–5 yr bands, after removing the influence of SST. These results demonstrate that large-scale climatic forcing modulates local environmental synchrony through differential regional coupling strengths. Consequently, the predictability of environmental conditions relevant to shellfish aquaculture in both regions appears to be strongly constrained by ENSO-driven variability operating across multiple temporal scales.