Habitat Complexity and Functional Ecology of Shallow Glass Sponge Reefs in Howe Sound, British Columbia

  • Author / Creator
    Sergeenko, Nikita
  • The habitat complexity of an aquatic ecosystem plays an important role in niche partitioning and mediating the coexistence of numerous species within a given space. Studying the habitat complexity of glass sponge reefs along the British Columbia (BC) coast provides insight into how and why ecologically and commercially valuable species interact with the reefs. A first step is to establish a set of easily reproducible and accurate protocols for measuring the 3D habitat complexity of the reefs that can subsequently be related to the functional traits of the inhabiting community to determine which aspects of the physical complexity are important to the community. This thesis examines first methodology for quantifying structural complexity and second how structural complexity of sponge reefs influences community (species and traits) composition. The studies took place on several glass sponge reefs in Howe Sound, British Columbia.Chapter 2 of this thesis evaluates the repeatability and reproducibility of two underwater techniques to measure structural complexity, 3D structure-from-motion (SfM) photogrammetry and microtopographic laser scanning (MiLS). The measurement error of both techniques was compared from SCUBA diver surveys of three reef plots on the Inshore (Western) East Defence Islands glass sponge reef, in Howe Sound, BC. The measurement error for both techniques was inconsistent across the three plots and was positively correlated with the habitat complexity metrics rugosity and the ratio of surface area-to-planar area (SAPA). While the coefficient of variation was lower for the metrics derived from 3D photogrammetry, the technique was not necessarily better than MiLS since both were inconsistent in measuring the physical complexity of a static reef plot over different days. These inconsistencies were likely due to the varying ambient light and turbidity conditions of the water, which affected the noise-to-signal ratio in images from which the 3D models (3D photogrammetry) and the 2D height profiles (MiLS) were constructed. Nonetheless, 3D photogrammetry had an advantage over MiLS in that it could disseminate and measure more 3D habitat complexity metrics than MiLS could for the same survey effort. Chapter 3 investigates the relationships between 3D habitat complexity metrics and the functional diversity and community composition of three reefs in Howe Sound, BC. Using a functional traits approach over the traditional biodiversity approach provides insight into which dietary and habitat use traits were linked to 3D complexity metrics for the reefs and enabled the development of hypotheses about the functional role habitat complexity plays in glass sponge reefs. Fifteen sites over three reefs were surveyed using the 3D photogrammetric technique outlined in Chapter 2, and species in the reef sites were counted by divers. The traits analyzed consisted of diet and position in the reef, both of which reflect the importance of trophic interactions in sustaining the productivity of an ecosystem and where those important trophic interactions occur. Surprisingly, functional diversity had a negative relationship with the structural metrics SAPA, relief, slope and curvature. This trend was driven primarily by the invertebrate community, due to the much higher abundances of invertebrate species relative to those of fish species. When individual traits were analyzed, abundance of benthic detritivores was driven by SAPA, while the presence of benthopelagic predators was driven by slope. This analysis provided insight about which structural components of the reefs influence individual traits and how reef structural complexity influences the functional community that inhabits within and over reef patches.

  • Subjects / Keywords
  • Graduation date
    Spring 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.