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Evaluating the role of 3D complexity in shaping animal distributions and nutrient hotspots in coral reef environments

  • Author / Creator
    Helder, Noelle
  • Three-dimensional (3D) habitat complexity is a primary driver of species distributions and biodiversity across ecosystems. Animal communities, in turn, provide key ecological services that reciprocally modify habitat structure and heterogeneity, such as creating create ‘hotspots’ of biogeochemical activity via nutrient recycling. To better define hotspots of ecological services from animal communities and identify conditions under which they form in habitats characterized by continuous measures of complexity, we studied relationships between 3D complexity, animal distribution, and nutrients on coral reefs— one of the most structurally complex and biologically diverse ecosystems on the planet. From May to July 2019, we measured large- and small-scale intra-habitat structural complexity (25 m2), surveyed the abundances of fish functional groups, and quantified nutrient composition of macroalgae across eight reefscapes (~2500 m2) within the Florida Keys, FL, USA. We first used these data in a hierarchical clustering analysis to group 80 species by five traits (diet, social level, body size, cryptic, activity period) related to species habitat use and feeding guild rather than taxonomic structure to generate mechanistic insights into consumer-habitat complexity relationships (Chapter 2). We evaluated relationships between the resulting trait-based functional groups (k=9) and four metrics of habitat complexity (large-scale: vertical relief, linked to prey refuge space; small-scale: vector ruggedness [VRM at 1cm], VRM deviation, and profile curvature, linked to availability of fish recruitment habitat and attachment sites for foraging resources). We found that functional groups respond variably to complexity. For example, schooling herbivores (Cluster 7) respond strongly to increases in small-scale complexity across reefscapes, but this effect is seen only in shoaling herbivores (Cluster 5) when small-scale complexity occurs in low-relief habitat. The general relationships we identified using species traits could provide a iii predictive framework for understanding fish community responses as reefs lose or gain structural complexity globally, particularly to predict functional responses to small-scale habitat augmentation such as through coral restoration. Next, we explored the shape and magnitude of relationships between habitat complexity, fish-derived nutrient supply (nitrogen [N] and phosphorous [P]), and producer nutrient uptake (macroalgal %N and %P) across six of the reefscapes in the Florida Keys (Chapter 3). We found that intra-reef complexity influenced N and P supply across reefscapes but identified a threshold (~2.8 m of relief) above which this effect dampens. Macroalgal nutrient content was also non-linearly related to nutrient supply from fishes, with supplies exceeding ~250 mg N m-2 day-1 and ~35 mg P m-2 day-1 having no measurable effect on macroalgal content. Taken together, our findings demonstrate the importance of habitat structural complexity in shaping abundances of fish functional groups and as a driver of nutrient heterogeneity within reefs. Preserving 3D habitat complexity by protecting or augmenting (through restoration) foundational organisms that provide physical structure is critical to supporting diverse animal communities and the important functions they provide.

  • Subjects / Keywords
  • Graduation date
    Fall 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.