Ecosystem-Based Quality Index in a harbor bay: Assessing the status of a heterogeneous system in a functional framework at a local scale

Abstract The assessment of natural ecosystem status is a fundamental premise to enable environmental management at local scales to maintain ecosystem functioning, services and resilience. Ecologists have developed many biological and environmental indices to inform and support environmental management and policies. To promote efficient use of resources, existing indices would ideally be informative for the widest geographic extent to avoid the development of new but redundant indices. The Ecosystem-Based Quality Index (EBQI), developed for the Mediterranean Sea, may be adaptable to other ecosystems due to its functional approach being closer to a methodological framework than a specialized index. We investigated the adaptability of EBQI beyond its original geographical setting and its applicability to a predefined location rather than a predefined ecosystem. We propose a workflow to apply EBQI to areas without a priori well-defined ecosystems: the shallow subtidal coastal areas of Baie des Sept Iles (Gulf of St. Lawrence, Canada), a major industrial port where the seafloor ranges from soft to mixed substrata (i.e., boulders and gravel in a soft-bottom matrix), creating ecosystem heterogeneity where species typical of different habitats often co-occur. We then tested the index for the assessment of this ecosystem with an explicit consideration of the ecosystem heterogeneity in shallow areas, typically unaccounted for by other indices. Using field sampling and a literature review, we showed that the EBQI can be implemented in areas where little prior information about a given ecosystem is available. Our EBQI implementation, shGSL-EBQI (shallow heterogeneous Gulf of St. Lawrence-EBQI), provided ecosystem status classifications that were robust and consistent with available environmental assessments in the area. We then showed that shGSL-EBQI relates to multiple environmental and anthropogenic drivers and suggest approaches to limit the effect of confounding environmental gradients. Finally, we discuss the potential applicability of shGSL-EBQI to other regions of the Gulf of St. Lawrence and provide advice on how a coastal monitoring initiative could facilitate widespread adoption of EBQI in Canada. As efforts to base future development on sustainability through ecosystem-based management increase both in Canada and internationally, we demonstrate that EBQI is well suited to the Canadian context and thus likely more generally in other jurisdictions.