Assessing and quantifying variations in the functioning of marine food webs across scales.

Abstract

The mismatch between the scale of ecological processes and management decisions represents a significant challenge in marine conservation. This misalignment can result in ineffective conservation measures and compromise the sustainability of marine ecosystems. The large spatial resolution commonly used to analyze food webs may obscure key ecological processes and their functioning, leading to inaccurate conclusions with important consequences for management and governance. To address this gap, we used a food web indicator, the survey-based mean trophic level (MTL), covering an entire bentho-demersal community across four subregions of the Northeast Atlantic. The indicator was developed at two spatial resolutions, subregional and local (0.2° × 0.2° cells), and we used a long-term dataset to assess food-web status. A set of 18 ecological scenarios, based on different trophic level (TL) thresholds and depth ranges, were established for each subregion, and linear models were applied to the historical series for each scenario. At the subregional scale, the results indicated potential recovery of top predators in the northern area; however, the stable patterns under various scenarios may have been attributable to ongoing fishing pressure rather than to true ecosystem stability or a genuinely balanced state. At the finer spatial resolution, local declining trends were revealed that had been masked in the broader-scale analysis. These contrasting patterns underscore the importance of spatial resolution when assessing the status of marine food webs and highlight the need to consider multiple ecological scenarios. We recommend aligning management strategies with the natural processes that govern marine ecosystems to enhance the resilience and long-term sustainability of ocean environments.