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Chapter 3 - Benthic Habitats© SBNMSDiscussionIn the Gulf of Maine/Georges Bank/Scotian Shelf region,World Wildlife Fund and the Conservation LawFoundation conducted an earlier analysis of the seafloor,resulting in “seascapes,” a concept similar to EMUs(World Wildlife Fund and Conservation Law Foundation2006). In their approach, they used fixed depth, bottomtemperature and salinity, and sediment type to definea seascape. Our approach was influenced by their work,with some differences. This analysis extends to the entireNorthwest Atlantic region and depth and sediment classeswere not pre-assigned, but as described above, the clusteranalysis of grab samples was used to determine the ecologicallyrelevant splits. Seabed forms were also correlatedwith the benthic invertebrate assemblages. In addition,temperature and salinity were explored as variables, butnot used in this analysis. The assumption was that thesetwo factors may not be geographically stable over longtime periods, especially in light of climate change, and thegoal was to understand the importance of enduring physicalplaces on benthic habitats.The thresholds used to define depth, grain size, and seabedforms for the EMUs were extracted directly fromthe organism data. This step was important in ensuringthat the EMUs represent truly different environments asperceived by the benthic macrofauna. Moreover, this approachallowed us to sidestep the problem of determiningwhich of the many proposed physical factor classificationsis best for a given region. Finding the most importantphysical thresholds for each organism group in order todetermine a meaningful number of EMUs to which wecould link a clear organism group or set of groups wasan important part of this process. The results presentedhere range from 108 to 168 EMUsper subregion with correspondinglydifferent thresholds for eachsubregion. Because this approachused the actual types and amountsof seafloor structures, the results arenot generalizable to other regions. Inother words, the patterns uncoveredare ecological, not physiological, andpresumably somewhat different relationshipsbetween depth and grainsizeand benthic assemblages wouldbe observed in other regions.The use of habitat complexity as ametric for separating among examplesof the same habitat type is still beingexplored. The complexity of ahabitat can affect whether an animalsurvives predation. It also affectsthe number of available niches. To date, habitat complexityhas been shown to be correlated with a number ofbiological variables, including species richness, diversity,abundance, and community composition. Other variablesunder consideration for distinguishing and prioritizingamong examples of the same habitat type include: confirmedrare species such as corals, diversity (phyla to species),size of the feature, intactness relative to human uses,and confirmed importance from other sources. As it willnot be possible to conserve all examples of every benthichabitat type, these metrics are intended to help focus conservationon the most critical examples of each type.3-52Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report