Abstract
Coastal biogenic habitats are vulnerable to human impacts from both terrestrial and marine realms. Yet the broad spatial scale used in current approaches of quantifying anthropogenic stressors is not relevant to the finer scales affecting most coastal habitats. We developed a standardized human impact metric that includes five bay-scale and four local-scale (0–1 km) terrestrial and marine-based impacts to quantify the magnitude of anthropogenic impacts to coastal bays and nearshore biogenic habitats. We applied this metric to 180 seagrass beds ( Zostera marina), an important biogenic habitat prioritized for marine protection, in 52 bays across Atlantic Canada. The results show that seagrass beds and coastal bays exist across a wide human impact gradient and provide insight into which are the most and least affected by human threats. Generally, land alteration, nutrient loading, and shellfish aquaculture were higher in the Gulf of St. Lawrence, whereas invasive species and fishing activities were higher along the Atlantic coast. Sixty-four percent of bays were at risk of seagrass decline from nitrogen loading. We also found high within-bay variation in impact intensity, emphasizing the necessity of quantifying impacts at multiple spatial scales. We discuss implications for management and conservation planning, and application to other coastal habitats in Canada and beyond.
Highlights
Over past decades and centuries, the magnitude, spatial extent and variety of human impacts have substantially increased in coastal ecosystems around the world (Lotze et al 2006, Halpern et al 2008)
Prince Edward Island (PEI) watersheds had the greatest land alteration for urban (Fig. 3b) and agricultural uses (Fig. 3c), urban land use was similar between PEI and Atlantic Nova Scotia (NS) (8.3 ± 1.49% and 7.1 ± 2.23%, respectively), but significantly greater than Gulf New Brunswick (NB)+NS (3.5 ± 1.35%)
When developing our human impact metric, we focused on impacts that are relevant for biogenic habitats but where similar data to quantify the extent of each impact is obtainable for other provinces and coasts in Canada, as well as other countries
Summary
Over past decades and centuries, the magnitude, spatial extent and variety of human impacts have substantially increased in coastal ecosystems around the world (Lotze et al 2006, Halpern et al 2008) Nearshore biogenic habitats, such as seagrass meadows, kelp forests, rockweed beds, and oyster reefs, are especially vulnerable as they are subject to anthropogenic threats from both the terrestrial and marine realms (Orth et al 2006, Worm and Lotze 2006, Waycott et al 2009, Beck et al 2011, Krumhansl et al 2016). Metrics of anthropogenic stressors used to inform management and conservation have previously been applied to ocean ecosystems across broad global and regional scales (Halpern et al 2008, Ban and Alder 2008, Murray et al 2015). These assessments are not relevant at smaller spatial scales, such as specific coastal bays, nearshore ecosystems or biogenic habitats
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