Quantifying the in situ 3-dimensional structural complexity of mangrove tree root systems: Biotic and abiotic implications at the microhabitat scale

The structural complexity of mangrove root systems provides multifunctional ecological habitats that enhance ecosystem processes and ensure the provision of services. To date, the ecological implications and roles of these microstructures at fine scales are overlooked. Here, the complexity among the root systems of three mangrove tree species; Rhizophora mucronata, Avicennia marina and Bruguiera gymnorhiza at two mangrove forests in South Africa, was empirically assessed using 3D scanning techniques to address the biotic and abiotic implications of such structures relative to the occurrence of marine larval communities within the system. Complexity was assessed using three metrics from 3D models; fractal dimension D, the area-volume (AVR) ratio index and Blender interstitial volume. Results indicated that fractal dimensions are not good parameters to determine the structural complexity of mangrove root systems due to the insensitivity to detect differences in the spatial patterns of visibly distinct structures. Additionally, A. marina is the most complex in the AVR index and least for interstitial space, while the inverse is true for R. mucronata. Measuring the comparative complexity of these indices could be advantageous for approximating how boundary layer dynamics change at alternate states of the tide for larval transport and inorganic particle retention (AVR) and providing refuge for organisms while avoiding predators who are too large to navigate among the intricate structures (interstitial space). The incorporation of these metrics at relevant scales is therefore crucial to understand how fine-scale habitat complexity emerges to drive ecosystem services that regulate organic and inorganic cycles and provide multifunctional habitats to ecologically and commercially important taxa.