Habitat zonation on coral reefs: Structural complexity, nutritional resources and herbivorous fish distributions

Abstract

Distinct zonation of community assemblages among habitats is a ubiquitous feature of coral reefs. The distribution of roving herbivorous fishes (parrotfishes, surgeonfishes and rabbitfishes) is a particularly clear example, with the abundance of these fishes generally peaking in shallow-water, high-energy habitats, regardless of the biogeographic realm. Yet, our understanding of the factors which structure this habitat partitioning, especially with regards to different facets of structural complexity and nutritional resource availability, is limited. To address this issue, we used three-dimensional photogrammetry and structure-from-motion technologies to describe five components of structural complexity (rugosity, coral cover, verticality, refuge density and field-of-view) and nutritional resource availability (grazing surface area) among habitats and considered how these factors are related to herbivorous fish distributions. All complexity metrics (including coral cover) were highest on the slope and crest. Nutritional resource availability differed from this general pattern and peaked on the outerflat. Unexpectedly, when compared to the distribution of herbivorous fishes, none of the complexity metrics had a marked influence in the models. However, grazing surface area was a strong predictor of both the abundance and biomass of herbivorous fishes. The strong relationship between grazing surface area and herbivorous fish distributions indicates that nutritional resource availability may be one of the primary factors driving the distribution of roving herbivorous fishes. The lack of a relationship between complexity and herbivorous fishes, and a strong affinity of herbivorous fishes for low-complexity, algal turf-dominated outer-flat habitats, offers some cautious optimism that herbivory may be sustained on future, low-complexity, algal turf-dominated reef configurations.

Warming Alters the Relationship Between Benthic Cover and Herbivores on Hawaiian Reefs

“…shows that in warm years, herbivores are responding to spatial patterns in algal distributions where grazing surface area is a strong predictor of the abundance of herbivorous fishes (Tootell and Steele, 2016;Oakley-Cogan et al, 2020).…”

Trade‐off between number and length of remote videos for rapid assessments of reef fish assemblages

“…The reason for a higher efficiency of several shorter videos may lie in the uneven distribution of fishes within the reef (Belmaker et al ., 2007). Reef communities comprise a large range of environmental conditions, as wide depth ranges and patches of distinct complexity, implying a heterogeneous distribution of species within the reef area (Oakley‐Cogan et al ., 2020). By performing more spatial replicates, the chances of detecting a given species would increase simply by covering a larger area.…”

Reefscape Genomics: Leveraging Advances in 3D Imaging to Assess Fine-Scale Patterns of Genomic Variation on Coral Reefs

“…The power of SfM in resolving 3D structure has enabled the study of structural complexity in relation to species diversity, competition, and coexistence. Structural complexity can be characterized through various metrics: linear and surface rugosity (Dustan et al, 2013;Ferrari et al, 2016aFerrari et al, , 2018, fractal dimension (Tokeshi and Arakaki, 2012;Leon et al, 2015;Young et al, 2017), crevice or refuge density (González-Rivero et al, 2017;Agudo-Adriani et al, 2019;Oakley-Cogan et al, 2020), viewshed (González-Rivero et al, 2017Urbina-Barreto et al, 2020), and surface height range (Torres-Pulliza et al, 2020). Broader-scale environmental parameterization (e.g., through the deployment of sensors) has the potential to enable fine-scale modeling of further abiotic variables that cannot be inferred directly from .…”