Habitat structural complexity in the 21st century: measurement, fish responses and why it matters

Abstract

The physical shape or structure of a habitat is a key driver of species’ distributions and central to maintaining diversity through ecological niche differentiation. Anthropogenic influences are changing the structure of habitats and the assemblages of associated organisms globally. Understanding the links between the physical shape of habitats and the organisms they support will be essential to predicting and mitigating anthropogenic impacts. In marine ecosystems climate change, bottom trawling and marine infrastructure drive changes to the structure of habitats. While many of the observed and forecast changes to structure are incidental (e.g. loss of coral or addition of shoreline armouring), there are also concerted efforts to create ecologically beneficial structures. Ecologically informed engineering presents an opportunity to augment local ecology through changes to the physical structure of an environment. Yet much of the hard earned knowledge from past studies is not applicable to the design of habitats because structurally vague summary metrics are the standard. This aim of the research described in this study is to improve the mechanistic understanding of fish responses to structure, both natural and man-made, providing advice for the creation of future habitat and insight into the underlying ecological processes. These improvements in understanding the mechanistic relationships between fish distribution and habitat structural complexity bring us closer to actively managing habitats in the Anthropocene. By creating links between the metrics used for measuring habitat complexity and those used to create it, this thesis paves the way for further insight into building environments to augment local biota.