Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…the expansion of artificial structures in coastal waters might be an important driver of the increase in Aurelia spp. populations due to the resultant increase in the availability of suitable benthic habitats for polyp proliferation (Duarte et al., 2012; Purcell, 2012; Makabe et al., 2014).
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