Habitat structure as an alternative explanation for body-size patterns in the deep sea

Patterns in body size are important to study as the size of an organism correlates with many biological traits of the organism. Changes in the size distribution of a community can be indicative of environmental change and/or anthropogenic impacts. What structures body size is, however, still poorly understood, with many factors proposed and shown to influence body size, including energy, which is likely a major driver. The deep sea is a good test bed to explore the relationship between body size and the
availability of energy as it is an energy-poor system, and strong responses to energy changes are expected. Here, we test the increased packing hypothesis that states that the modal size class should increase with energy, while other size classes reduce in abundance, resulting in less variance in the distribution. This has been demonstrated to be the case in a system with discrete food resources, but here we test what happens when energy is not discretely distributed. Furthermore, we test for alternative explanations using habitat structure to explain patterns in body size. We find no support for the increased packing hypothesis for the two energy variables used, but we did find strong patterns with habitat structure. Only when habitat structure was included did we find a small effect of particulate organic carbon on the mean body size. It is likely that how energy is partitioned in an ecosystem influences its structuring effect; when energy is not distributed in a discrete way, this can obfuscate the relationship. Habitat structure influences how energy is distributed in a system, and studying body size in relation to both habitat structure and energy may further our understanding in what structures this aspect of benthic communities.