Disentangling the relative effects of structural complexity and substrate composition on fish habitat selection in coral reef environments

• Author / Creator

  Garg, Aneri

• Identifying features of biogenic habitats (i.e. made of living plants and animals) that attract and retain resident species is a key theme in ecology with important implications for habitat conservation and restoration. Using corals (class Anthozoa, phylum Cnidaria) —a group of foundational species that provide important habitat for diverse fish communities— as a model biogenic habitat, we designed and tested an integrative method for creating artificial habitat modules to disentangle the relative importance of structural versus compositional features of biogenic habitats hypothesized to affect in the attraction and retention of resident organisms: 3D-SPMC (3D Scan, Print, Mould, Cast; Chapter 2). We then conducted a manipulative field experiment in which we augment a reefscape in Florida, USA over the summer of 2019 with ~ 1m2 replicated habitat patches created using artificial (3D-SPMC) and live corals. Here, we evaluated the relative effects of substrate composition (% living coral) and habitat patch structural complexity on the attraction and retention of resident fish species in two environmental contexts (“high” and “low” reefscape structural complexity at the scale of 100m2; Chapter 3). We found the 3D-SPMC method performed on par with or better than other techniques widely used to create artificial replicas of biogenic habitats in terms of design accessibility, scalability, and ecological realism. Our experiment revealed that augmenting the structural complexity of habitat patches resulted in greater fish attraction (measured as relative recruitment rate and density of juvenile fishes ≤ 3cm total length [TL]) and retention (measured as relative density of larger-bodied [4-6 cm TL] fishes, and richness of fishes ≤ 6cm TL) in low, but not high complexity environments. We suggest non-intuitive cue use may be driving selection processes to habitat patches in low complexity reefscapes, and/or that predator-prey dynamics may mediate selection in high complexity reefscapes. Substrate composition mediated fish attraction and retention to habitat patches, but in an unexpected way: both were consistently lowest at intermediate (i.e. 50%) compared to low (0%) and high (100%) living coral treatments (i.e. non-linear, concave pattern across % living coral treatments) regardless of reefscape complexity, though the effect was dampened at high background complexity reefscapes. Competition for living substrate patches, indirect cues from con/heterospecifics, and/or taxa- or trait-specific habitat selection may have explained these non-linear patterns. In the context of coral reef degradation and restoration, habitat augmentation will likely increase the attraction and retention of juvenile reef fish, primarily when coral patches are placed in low complexity environments. We recommend further investigation into species and/or trait specific responses that may be driving non-linear relationships between fish recruitment and coral substrate composition, and longer-term studies connecting the retention of recruiting fishes at habitats with variable biogenic substrate composition to adult reef fish assemblages.

• Subjects / Keywords

  • Ecology
  • Habitat selection
  • Coral reefs
  • Restoration

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-1qrv-p223

• 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.