Strahler Ordering Analyses on Branching Coral Canopies: Stylophora pistillata as a Case Study

Yaniv Shmuel,Yaron Ziv,Baruch Rinkevich

doi:10.3390/jmse10010121

Abstract

The three-dimensional structural complexities generated by living sessile organisms, such as trees and branching corals, embrace distinct communities of dwelling organisms, many of which are adapted to specific niches within the structure. Thus, characterizing the build-up rules and the canopy compartments may clarify small-scale biodiversity patterns and rules for canopy constituents. While biodiversity within tree canopies is usually typified by the vertical axis that is delineated by its main compartments (understory, trunk, crown), traditional studies of coral canopy dwelling species are evaluated only by viewing the whole coral head as a single homogeneous geometric structure. Here, we employ the Strahler number of a mathematical tree for the numerical measurements of the coral’s canopy complexity. We use the branching Indo-Pacific coral species Stylophora pistillata as a model case, revealing five compartments in the whole coral canopy volume (Understory, Base, Middle, Up, and Bifurcation nods). Then, the coral’s dwellers’ diel distribution patterns were quantified and analyzed. We observed 114 natal colonies, containing 32 dwelling species (11 sessile), totaling 1019 individuals during day observations, and 1359 at night (1–41 individuals/colony). Biodiversity and abundance associated with Strahler numbers, diel richness, abundance, and patterns for compartmental distributions differed significantly between day/night. These results demonstrate that the coral-canopy Strahler number is an applicable new tool for assessing canopy landscapes and canopy associated species biodiversity, including the canopy-compartmental utilization by mobile organisms during day/night and young/adult behaviors.

Highlights

Coral reefs and tropical forests, two of the most biodiverse ecosystems on earth [1,2,3,4], rely on the three-dimensional (3D) structural complexity generated by their operational building units, the corals and trees, respectively [5,6,7]
A total of 32 species were identified dwelling in the 114 S. pistillata canopies surveyed at the Japanese Gardens site, eight of them were considered to be rare (Supplementary Table S1)
Canopy dwelling species assemblages were numerically dominated by the sessile bivalve Leiosolenus lessepsianus, recorded from 95 canopies and reaching up to 90% abundancy of total sessile species

Summary

Introduction

Coral reefs and tropical forests, two of the most biodiverse ecosystems on earth [1,2,3,4], rely on the three-dimensional (3D) structural complexity generated by their operational building units, the corals and trees, respectively [5,6,7]. Branching organisms are the key building units in forests and coral reefs. The canopies create a wide diversity of habitats that are enclosed within one of three major organismal compartments, the crown, trunk, and understory [6,13]. These categorizations that considers functional properties of the tree’s 3D structures could be harnessed for the study of the enclosed spaces within branching coral canopies. An additional vital ecological service is that the overall 3D structure generated by an individual tree or a coral colony (termed here as a canopy) harbors a distinct community of organisms at any dynamic space and time dimension [17,18]

Methods

Results

Conclusion