Diversity in life histories within species profoundly influences biological interactions and resonates throughout food webs, yet quantifying these intricate processes is challenging. To explore the impact of intraspecific diversity on food web functioning, we applied century-long observational dataset of the fish community in the coastal Skagerrak to an allometric trophic network model. Representing fish, zooplankton, and phytoplankton taxa as 148 guilds interlinked by 2054 feeding links, we constructed the Skagerrak food web and quantified the roles of two Atlantic cod (Gadus morhua) ecotypes. Our results revealed a compelling dynamic: the coastal Fjord cod ecotype had a pronounced intraspecific influence on the biomass growth of the offshore North Sea cod ecotype, whereas the North Sea cod ecotype exerted stronger interspecific top-down control on other fish species. The coexistence of these ecotypes enhanced ecosystem robustness and connectivity. These findings highlight the critical importance of incorporating intraspecific diversity into sustainable fisheries management practices.

Regime shifts are increasingly prevalent in the ecological literature. However, definitions vary, and many detection methods are subjective. Here, we employ an operationally objective means of identifying regime shifts, using a Bayesian online change-point detection algorithm able to simultaneously identify shifts in the mean and(or) variance of time series data. We detected multiple regime shifts in long-term (59-154 years) patterns of coastal Norwegian Atlantic cod (>70% decline) and putative drivers of cod productivity: North Atlantic Oscillation (NAO); sea-surface temperature; zooplankton abundance; fishing mortality (F). The consequences of an environmental or climate-related regime shift on cod productivity are accentuated when regime shifts coincide, fishing mortality is high, and populations are small. The analyses suggest that increasing F increasingly sensitized cod in the mid 1970s and late 1990s to regime shifts in NAO, zooplankton abundance, and water temperature. Our work underscores the necessity of accounting for human-induced mortality in RS analyses of marine ecosystems.