Spatial heterogeneity in mussel larval abundance across fjord systems of northern Chilean Patagonia

Abstract

Climate change is reshaping marine ecosystems by altering the timing, intensity, and predictability of key biological processes. In northern Chilean Patagonia, where mussel aquaculture depends on wild seed collection, variability in oceanographic and climatic conditions may affect mussel larval abundance at local scales. Here, we analyze a decade of monthly data on mussel larvae collected at seven sites distributed across contrasting fjord and channel systems. We assess phenological patterns, extreme events, and long-term trends in larval abundance, and evaluate their associations with local hydrography and large-scale climate indices (ENSO, PDO, SAM) and local hydrographic variability. Larval peaks varied in timing and duration across sites, and we identified extreme positive and negative events. Extreme positive larval abundances were concentrated at mid-latitude sites and occurred during strong negative PDO phases, often combined with La Niña or positive SAM. In contrast, decreasing trends were detected at the southernmost sites, while a positive trend emerged at one mid-latitude site. These contrasting patterns suggest that larval dynamics are primarily shaped by large-scale climate forcing, with local hydrographic conditions modulating site-specific responses. These contrasting patterns highlight strong spatial heterogeneity in larval dynamics, suggesting that local hydrographic conditions and geomorphological setting play a key role in modulating the effects of large-scale climate variability. Our results emphasize that larval abundance cannot be generalized across the region and must be interpreted within the context of site-specific processes. Understanding these local dynamics is critical for predicting variability in seed availability and supporting the sustainability of mussel aquaculture under changing environmental conditions.