A human impact metric for coastal ecosystems with application to seagrass beds in Atlantic Canada

Abstract

Coastal biogenic habitats are particularly vulnerable to cumulative human impacts from both terrestrial and marine realms. Yet the broad spatial scale used in current global or regional approaches of quantifying multiple anthropogenic stressors are not relevant to the local or baywide scales affecting most coastal biogenic habitats. To fill this gap, we developed a standardized human impact metric to quantify the magnitude of anthropogenic impacts to coastal ecosystems more broadly, and biogenic habitats in particular. We applied this metric to 180 seagrass beds (Zostera marina), an important biogenic habitat prioritized for marine protection, across Atlantic Canada. Our impact metric includes five bay-scale and four local-scale terrestrial and marine-based impacts. Results show that seagrass beds and coastal bays in Atlantic Canada exist across a wide gradient of human impacts. Considerable differences in the range and intensity of impacts within and between regions provide insight into where coastal bays and seagrass ecosystems are expected to be most and least affected by individual or cumulative human threats. We discuss implications for management and conservation planning, and the general application of our impact metric to other coastal regions and habitats in Canada and beyond.

Response and Recovery of Eelgrass (Zostera marina) to Chronic and Episodic Light Disturbance

“…In particular, we evaluate how the relative importance of both types of light disturbance is influenced by varying degrees of light reduction and durations of light stress. Z. marina is the dominant seagrass species in Atlantic Canada, where in certain areas it is susceptible to chronic light limitation from nutrient loading (i.e., Southern Gulf of St. Lawrence; Hitchcock et al 2017;Murphy et al 2019). However, in many areas of Atlantic Canada, nutrient loading is minimal (Murphy et al 2019), and episodic light reduction from storms or nearby human activities is the more prevalent type of light disturbance for Z. marina.…”

“…Z. marina is the dominant seagrass species in Atlantic Canada, where in certain areas it is susceptible to chronic light limitation from nutrient loading (i.e., Southern Gulf of St. Lawrence; Hitchcock et al 2017;Murphy et al 2019). However, in many areas of Atlantic Canada, nutrient loading is minimal (Murphy et al 2019), and episodic light reduction from storms or nearby human activities is the more prevalent type of light disturbance for Z. marina. Light attenuation coefficients (K d ) ranging from 0.3 to 7 m −1 or even 12 m −1 during extreme weather events have been observed in various Z. marina beds in the region (Wong, unpublished data;Krumhansl et al 2020).…”

Ecosystem-based management of seaweed harvesting

“…Another consideration involves cumulative human impacts from activities both on land and in the sea. The growth and survival of seaweeds can be affected by nutrient loading and chemical pollution from land-based sources or aquaculture activities, sediment runoff, physical disturbance from fishing, boating or constructions, shading from overwater structures, and invasive species to name a few (Rangeley and Davies 2000, Worm and Lotze 2006, Murray et al 2015, Murphy et al 2019). Because wild seaweeds are harvested directly from the ocean, they are often considered and marketed as "organic" without evaluation of their tissue content or environmental conditions they were grown in; however, seaweeds are known to accumulate chemical substances and toxins (Chen et al 2018, Falace et al 2018.…”

“…Also, because many species are impacted by a suite of human activities, the protection of important marine habitats is a growing priority for marine management and conservation worldwide (European Commission 2008, Cullen-Unsworth and Unsworth 2016, Murphy et al 2019. Essential fish habitats, for example, which many seaweeds and seagrasses provide, are often conservation priorities which is counter to the continued harvesting of canopy-forming seaweeds.…”

“…Essential fish habitats, for example, which many seaweeds and seagrasses provide, are often conservation priorities which is counter to the continued harvesting of canopy-forming seaweeds. In Atlantic Canada, seagrass (Zostera marina L.) has been identified as an Ecologically Significant Species (ESS; DFO 2009) because of the important roles it plays in coastal ecosystems, and management efforts aim to reduce or prevent harmful human disturbances (Murphy et al 2019). In contrast, rockweed and kelp play similar roles in marine environments, yet have not received similar recognition and commercial harvesting continues (DFO 2013).…”