Modelling and analysis of growth and form of sponges and stony corals and the influence of the physical environment

Jaap Kaandorp

The growth form of many marine sessile organisms, as for example sponges, stony-corals, and hydro-corals, is influenced strongly by the physical environment. Most of these organisms use light, filter-feeding by trapping suspended material from the environment or a combination of both as an energy source. In the case exclusively light is being used for the photosynthesis, only light and inorganic substances are required for the growth process. In the case filter-feeding is the only energy input, the growth process is influenced by the local concentration of (organic) suspended material. The distribution of suspended material in a marine environment is determined by a combination of flow and diffusion. In many of these organisms (e.g. many stony-corals) a combination of both energy sources is used.

A method for modelling a nutrient distributions, caused by a combination of diffusion and flow, will be discussed. The method is based on a ``particle-based'' approach: the lattice Boltzmann method. With this method it is possible to simulate the nutrient distributions in complex geometries in three dimensions. From the nutrient distributions it is possible to model different types of growth processes, which are driven by the local amount of available nutrients. The influence of light, required in the growth process of photosynthetic organisms, can be represented in the growth model by a three dimensional model of underwater light intensities.

Several types of growth models for marine sessile organisms will be discussed: aggregation models in which growth is modelled by the addition of individual particles and growth by accretion in which growth is represented by the addition of layers of material on top of the previous growth stages. In the accretive growth models examples will be shown of growth processes driven by the local available amount of (simulated) food particles and of growth processes driven by the local light intensities.

Methods will be discussed for the morhological analysis and comparison of actual and simulated growth forms. The availability of these methods is crucial for the verification and testing the predictive value of the simulation models mentioned above. A potential application area of morphological simulation models in combination with methods for the morhological analysis of growth forms, is in bio-monitoring studies in which the growth form is being used to assess the state of the physical environment.

Jaap Kaandorp
Section Computational Science
Faculty of Mathematics, Computer Science, Physics & Astronomy
University of Amsterdam
Kruislaan 403
1098 SJ Amsterdam
The Netherlands
Phone: +31 20 5257539 / +31 20 5257463
fax: +31 20 5257490