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Chapter 3 - Benthic HabitatsTable 3-1 (continued). A review of literature on seafloor classification and approaches utilized to developour methodology.Physical/BiologicalVariablesEcologicalassociationsSpecies Data type/Comments ReferencesPrincipal Component AnalysisPC1: SST, thermalgradients, stratification,chlorophyllPC2: depth, primaryproduction, chlorophyll,zooplankton, biomass,benthic biomassPC3: substrate type,nekton species richnessspecies abundance andrichnesspelagic (nekton)and benthicbottom trawl; research surveytrawls; bongo nets (for nekton);principal components combinephysical and biological variablesFogarty and Keith2007PC4: nekton biomassPC5: benthic biomassPC6: nekton speciesrichnesBiological Factors: Benthic OrganismsThe map of benthic habitats presented here is based onthe distribution and abundance of benthic organisms inthe Northwest Atlantic. The knowledge of these speciesand their distributions comes largely from seafloorgrab samples described below. In the analysis of this data,groups of species with shared distribution patterns wereidentified, then thresholds in the physical factors wereidentified that correlated with those patterns. Specifically,three basic steps were followed: 1) quantitative analysisof the grab samples to identify distinct and reoccurringassemblages of benthic organisms, 2) recursive partitioningto relate the species assemblages to physical factors(bathymetry, sediment types, and seabed topographicforms), and 3) mapping the habitats based on the statisticalrelationships between the organism groups and thedistribution of the physical factors. Although organismdistributions were used to identify meaningful thresholdsand cutoffs in the physical variables, the final habitat mapsare composed solely of combinations of enduring physicalfactors and are thus closely related to the maps and classificationschemes proposed by others.This study was made possible by access to over forty yearsof benthic sampling data by the National Marine FisheriesService’s (NMFS) Northeast Fisheries Science Center(NEFSC). The NEFSC conducted a quantitative surveyof macrobenthic invertebrate fauna from the mid 1950s tothe early 1990s across the region (Figure 3-1, Table 3-2).Each year, samples of the seafloor were systematically takenduring 25+ individual cruises by five or more researchvessels using benthic grab samplers designed to collect 0.1to 0.6m 2 of benthic sediments. In total, over 22,000 sampleswere collected. Organisms collected in each samplewere sorted and identified to species, genus, or family, andinformation on the sediment sizes, depth, and other associatedfeatures were recorded for each sample. A thoroughdiscussion of the sampling methodology, gear types, history,and an analysis of the benthic dataset, including thedistribution and ecology of the organisms, can be found inthe publications of Wigley and Theroux (1981 and 1998).Recently, new video and remote sensing technologies havearisen to directly assess the seafloor and supplement thesample data (Kostylev et al. 2001). In future iterations ofthe assessment, we hope to integrate data collected usingthese new methods.3-4Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report