Abstract
Benthic habitat maps, including maps of seabed sediments, have become critical spatial-decision support tools for marine ecological management and conservation. Despite the increasing recognition that environmental variables should be considered at multiple spatial scales, variables used in habitat mapping are often implemented at a single scale. The objective of this study was to evaluate the potential for using environmental variables at multiple scales for modelling and mapping seabed sediments. Sixteen environmental variables were derived from multibeam echosounder data collected near Qikiqtarjuaq, Nunavut, Canada at eight spatial scales ranging from 5 to 275 m, and were tested as predictor variables for modelling seabed sediment distributions. Using grain size data obtained from grab samples, we tested which scales of each predictor variable contributed most to sediment models. Results showed that the default scale was often not the best. Out of 129 potential scale-dependent variables, 11 were selected to model the additive log-ratio of mud and sand at five different scales, and 15 were selected to model the additive log-ratio of gravel and sand, also at five different scales. Boosted Regression Tree models that explained between 46.4 and 56.3% of statistical deviance produced multiscale predictions of mud, sand, and gravel that were correlated with cross-validated test data (Spearman’s ρmud = 0.77, ρsand = 0.71, ρgravel = 0.58). Predictions of individual size fractions were classified to produce a map of seabed sediments that is useful for marine spatial planning. Based on the scale-dependence of variables in this study, we concluded that spatial scale consideration is at least as important as variable selection in seabed mapping.
Highlights
Marine ecosystems provide a broad range of services to humans, including food, extractive resources, and cultural identity [1,2]
Eleven variables were selected to model the response of ALRms at five different scales (Fig 4): broad benthic position index (BPI) (175 m), eastness (5 m), backscatter (45 m), plan curvature (5 m), rugosity (275 m), northness (275 m), Δbackscatter (5 m), Δbackscatter (105 m), distance from the coast, plan curvature (105 m), and plan curvature (275 m)
ALRms was most strongly influenced by broad BPI at 175-m scale, the eastness component of aspect at 5-m scale, and backscatter at 45-m scale, together which contributed over 73% to model building
Summary
Marine ecosystems provide a broad range of services to humans, including food, extractive resources, and cultural identity [1,2]. These systems are being threatened and profoundly impacted on local and global scales by a suite of anthropogenic stressors such as climate change, overfishing, and pollution [3,4]. As pressures on marine systems intensify, there is an urgent need to monitor and mitigate impacts to ensure ecosystem viability and sustainable ecosystem services. Multiscale mapping seabed sediments funding and ship time from ArcticNet The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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