Modelling growth and form of the scleractinian coral Pocillopora verrucosa and the influence of hydrodynamics

The growth of scleractinian corals is strongly influenced by the effect of water motion. Corals are known to have a high level of phenotypic variation and exhibit a diverse range of growth forms, which often contain a high level of geometric complexity. Due to their complex shape, simulation models represent an important option to complement experimental studies of growth and flow. In this work, we analyzed the impact of flow on coral's morphology by an accretive growth model coupled with advection-diffusion equations. We performed simulations under no-flow and uni-directional flow setup with the Reynolds number constant. The relevant importance of diffusion to advection was investigated by varying the diffusion coefficient, rather than the flow speed in Péclet number. The flow and transport equations were coupled and solved using COMSOL Multiphysics. We then compared the simulated morphologies with a series of Computed Tomography (CT) scans of scleractinian corals Pocillopora verrucosa exposed to various flow conditions in the in situ controlled flume setup. As a result, we found a similar trend associated with the increasing Péclet for both simulated forms and in situ corals; that is uni-directional current tends to facilitate asymmetrical growth response resulting in colonies with branches predominantly developed in the upstream direction. A closer look at the morphological traits yielded an interesting property about colony symmetry and plasticity induced by uni-directional flow. Both simulated and in situ corals exhibit a tendency where the degree of symmetry decreases and compactification increases in conjunction with the augmented Péclet thus indicates the significant importance of hydrodynamics

The effect of local hydrodynamics on the spatial extent and morphology of cold-water coral habitats at Tisler Reef, Norway

This study demonstrates how cold-water coral morphology and habitat distribution are shaped by local hydrodynamics, using high-definition video from Tisler Reef, an inshore reef in Norway. A total of 334 video frames collected on the north-west (NW) and south-east (SE) side of the reef were investigated for Lophelia pertusa coral cover and morphology and for the cover of the associated sponges Mycale lingua and Geodia sp. Our results showed that the SE side was a better habitat for L. pertusa (including live and dead colonies). Low cover of Geodia sp. was found on both sides of Tisler Reef. In contrast, Mycale lingua had higher percentage cover, especially on the NW side of the reef. Bush-shaped colonies of L. pertusa with elongated branches were the most abundant coral morphology on Tisler Reef. The highest abundance and density of this morphology were found on the SE side of the reef, while a higher proportion of cauliflower-shaped corals with short branches were found on the NW side. The proportion of very small L. pertusa colonies was also significantly higher on the SE side of the reef. The patterns in coral spatial distribution and morphology were related to local hydrodynamics—there were more frequent periods of downwelling currents on the SE side—and to the availability of suitable settling substrates. These factors make the SE region of Tisler Reef more suitable for coral growth. Understanding the impact of local hydrodynamics on the spatial extent and morphology of coral, and their relation to associated organisms such as sponges, is key to understanding the past and future development of the reefVersión del editor3,87

Morphometric methods.

<p>(A) A skeleton graph with the increased level of occlusion of the volumetric data in the background, (B–C) Visualization of spheres used for calculating morphometric traits - diameter of a sphere at the terminal branch is defined as terminal branch thickness –<i>dc</i>, (D) A visualization of the volumetric data of TS_002 coral (See <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002849#pcbi-1002849-t001" target="_blank">Table 1</a> for label), (E) Visualization of symmetry angles <i>h_angle</i> and <i>v_angle</i> , (F) Visualization of the associated vectors used for calculation of symmetry vector <i>sm_mag</i>.</p

Schematic diagram of the simulation.

<p>(A) A spherical object represents an initial growth state of the simulation (first growth step) (B) A simulation phase involves solving the Navier-Stokes equations (i) and the advection-diffusion equation (ii). (C) Accretion phase translocates absorbed nutrients from previous simulation phase to a new growth layer hence, after a few consecutive growth steps, spontaneous branching occurs.</p

The simulated growth forms.

<p>(A) Simulated coral in a no-flow condition. (B–F) Simulated corals from various flow simulations (B) <i>Pe_branch</i> = 0.00113, (C) <i>Pe_branch</i> = 0.0105, (D) <i>Pe_branch</i> = 0.0970, (E) <i>Pe_branch</i> = 1.13, (F) <i>Pe_branch</i>∼11.3, Arrow indicates flow direction. The labels of the simulated corals are located on the bottom of each figure (See <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002849#pcbi-1002849-t001" target="_blank">Table 1</a> for labels).</p

An example of three consecutive accretive growth steps.

<p>(A–C) Accretive growth steps; vertex v_i represents a simulated corallite. The new layer is constructed along the direction of normal vector n_i of the vertex v_i. A, B and C are three consecutive growth steps where triangles are inserted once the surface of the object increases.</p