Morphological models of radiate accretive growth and the influence of hydrodynamics

In many marine sessile organisms (for example sponges and stony corals) the skeleton is formed by an accretive growth process, where layers of materia l are secreted on top of each other in a surface normal deposition process. In many of these organisms the growth process exhibits a strong morphologi cal plasticity due to differences in exposure to water movement. In general , many of these organisms tend to form thin-branching growth forms under sh eltered conditions, while the growth form gradually transforms into a more compact shape when the exposure of water movement increases. In this paper, we investigate this phenomenon by combining a three-dimensional simulation model of radiate accretive growth driven by the local availability of simu lated food particles and a model based on the lattice Boltzmann method, for simulating food particle distributions caused by a combination of flow and diffusion. In the simulations two different models of a suspension feeder with accretive growth were compared. In the first model, the deposition pro cess is exclusively driven by the local availability of food particles, in the second model the deposition process was determined by the combination o f local amount of contact to the environment and availability of food parti cles. In the simulations it was found that hydrodynamics has a strong impac t on the overall morphologies which develop in the accretive growth process . In the model exclusively driven by the local availability of food particl es, column-shaped objects emerged under diffusion conditions, while more sp herical and lobed abject were found for the flow-dominated case. In the sim ulations, the Peclet number was varied independently from the Reynolds numb er, which was kept at a relatively low constant value. In a range of increa sing Peclet numbers, indicating an increasing influence of hydrodynamics, t he simulated morphologies gradually transformed from thin-branching ones in to more spherical and compact morphologies in the model where deposition wa s controlled by the local availability of food particles and the local amou nt of contact with the environment. (C) 2001 Academic Press.