Local shear and mass transfer on individual coral colonies: Computations in unidirectional and wave-driven flows

Abstract

Flows through single coral colonies were simulated with an implementation of the Immersed Boundary (IB) method in Large-Eddy Simulation (LES). The method was first validated with magnetic velocimetry experiments, which demonstrated that computational results were within approximately 7% of flow measurements. The algorithm was then applied to simulate unidirectional and wave-driven flow conditions through two morphologically distinct coral colonies that naturally grow in very different hydrodynamic environments, with detailed analysis on spatial hydrodynamic and mass transfer variability. When the hydrodynamics of each coral's native environment was simulated, the dynamics in the interior of both branching species appeared to converge, in spite of vast differences between the hydrodynamic conditions and morphologies. A correlation between local surface shear and mass transfer was derived from simulated data. The results suggest that the corals grew in such a way that mass transfer characteristics are similar despite of vast differences in their physical shapes and hydrodynamic conditions.

Coral Microcosms: Challenges and Opportunities for Global Change Biology

“…Defined and controlled light conditions are also important for assuring reproducible results obtained from coral-microcosm experiments. Among others, light (1) affects density and photosynthetic activity of hermatypic corals [29], (2) increases calcification rates in hermatypic corals [30], (3) influences the activity of associated faunas such as diurnal fishes [31,32], (4) affects the metabolic efficiency of corals and thus survival [33,34] and (5) influences the phenotype of scleractinian corals [35].…”

“…Under controlled microcosm conditions, it is therefore important to meet the requirements of the study species for achieving near-natural growth rates and physiological responses [37]. Too little light may, for example, decrease the metabolic efficiency and growth rates in stony corals, or may cause shifts in phenotype morphology [35]. Too much light could burn the zooxanthellae or cause coral bleaching [38].…”

“…A controlled movement is also critical for obtaining reproducible results in global-change studies using microcosm setups. Among others, water movement increases the exchange rate of gases and thus photosynthetic efficiency [42], increases mass-transfer of materials across the tissue-water interface [43,44], increases food capture and thus energy supply to the coral [43,45], facilitates cleaning of corals and prevents build-up of detritus [46], and influences the phenotype of scleractinian corals [35].…”

Effects of coral colony morphology on turbulent flow dynamics

“…Similarly, Chindapol et al [35] used COMSOL Multiphysics to analyze 63 the effects of flow on coral growth only in a laminar framework. Chang et al [36] were 64 the first (according to the authors' knowledge) to introduce immersed boundary method 65 with large-eddy simulation on real coral geometry while computing the velocity profile 66 at the inside of the coral, but the analysis was mainly focused on local shear and mass 67 transfer on the coral structure. In a recent paper, Hossain and Staples et al [37] 68 computed the flow profile on the inside of coral, and showed that the mass transfer flow conditions.…”

“…Similar to Chang et al [36], Dirichlet boundary conditions were applied at the inlet, But, within the coral, the overall magnitude of velocity was higher in P. eydouxi than in 360 P. meandrina through the complete length of the coral. In terms of food, the interior of 361 the coral has a strong chance of starving if the velocity is not sufficiently high.…”