Habitat structure and fish: assessing the role of habitat complexity for fish using a small, semiportable, 3‐D underwater observatory

Abstract

In contrast to terrestrial ecology, three‐dimensional (3‐D) imaging technology is not well established as a method for studying species‐habitat interactions in aquatic ecology. In this study, we used a semi‐portable, digital, 3‐D underwater observatory designed for long‐term exposure in shallow water habitats to assess fish‐habitat interactions to artificial structures of different complexity. The observatory was mounted on a cable‐car system and was moved along a 50 m transect parallel to five artificial structures of different complexity and one control site. The optical unit took high‐resolution digital images, in pairs, from each structure and the control site at a frequency of 30 min over 24 h and was then moved remotely to the next structure. The system was operated for 2 mo without being recovered and took a total of 2160 stereoscopic image pairs. The system proved highly valuable in assessing small‐scale temporal patterns in fish‐habitat interactions, as well as changes in habitat preferences of fish over the diel cycle. Such small‐scale temporal and spatial patterns are important for a detailed understanding of specieshabitat interactions, not only in fish but also in most aquatic macro‐organisms. Nevertheless, such patterns can hardly be assessed using classical sampling devices due to labor and animal protection restrictions. However, the possibility of a significant increase in quantity of sampling through the use of remote imaging technology is accompanied by a significant increase in labor costs for image analysis. Therefore, further progress in semi‐ and fully automated systems for image analysis is needed, including 3‐D imaging tools, for ecological studies.