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4. SIMULATING GROWTH AND FORM
4.5 Growth by Aggregation
4.5.1 Morphological Plasticity and the Influence of Hydrodynamics
In Sect. 3.3 the morphological plasticity of some marine sessile organisms, for
example the sponge Haliclona oculata, the hydrozoan Millepora alcicornis,
and the stony coral Pocillopora damicornis, were related to the impact of
hydrodynamics. There is a strong impact of hydrodynamics on the growth
process . In a number of cases it is possible to arrange growth forms of
sponges, hydrocorals, and stony corals along a gradient of the amount of
water movement, as shown in Figs. 2.16 and 1.1. In the case of the stony
coral, the growth form gradually transforms from a compact shape under
exposed conditions, to a thin-branching one under sheltered conditions.
In growth forms of the sponge Haliclona oculata, plate-like, more compact
shapes emerge at exposed sites. This shape gradually transforms into a thinbranching form when the exposure to water movement decreases. A similar
trend can be observed in growth forms of the hydrozoan Millepora alcicornis
(de Weerdt 1981). In this species the shape changes from plate-like forms at
shallow and exposed sites, to thin-branching forms at deeper and sheltered
locations.
Water flow has a strong influence on the local supply of food particles in suspension feeders . In Sect. 2.1.1 the effects of hydrodynamics on
particle capture by suspension-feeding invertebrates was discussed in detail. In several studies (Frechette et al. 1989, Buss and Jackson 1981, Pile et
al. 1997) it has been demonstrated that locally around a sessile suspension
feeder, exposed to various flow velocities, areas may occur which are depleted from food particles. It has been found by several authors that there
exists an asymmetric type of food capture. Patterson (1984) demonstrated
that the largest amount of food capture is found at the upstream side of
the octocoral colony for low flow velocities, while the situation reverses
for higher flow velocities where the largest amount of food is captured at
the downstream side of the colony. A similar phenomenon was observed
by Sebens et al. (1997) for the stony coral Madracis mirabilis (see Fig. 2.5),
where the largest amount of food particle capture was found at the upstream
side of the colony for low flow velocities (below 15cm -s'"), while the situation again reverses for higher flow velocities (see Fig. 2.6). In studies on
branching stony corals (Sebens et al. 1997, Chamberlain and Graus 1977)
and the influence of hydrodynamics it is demonstrated that branch spacing
is a crucial morphological property which determines the microflow pattern inside the colony. The flow direction will basically reverse twice a day
due to the tidal movements (see also Sect. 2.1.1) and in branching sessile
suspension feeders growth forms emerge which have a roughly radial symmetry or show a tendency to develop a flattened growth form (see also
Sect. 2.2.3 on octo corals, Johnson and Sebens 1993, Stearn and Riding 1973,
Wainwright and Dillon 1969). In the last case most branches will develop
in a plane perpendicular to the governing flow direction. Local food particle absorption patterns which are determined by the direction and the
velocity of the flow, local areas which surround the organism and which
are depleted from food particles, as well as microflow patterns in branching organisms have important consequences for the growth process and the
resulting morphology.
4. SIMULATING GROWTH AND FORM
4.5 Growth by Aggregation
4.5.1 Morphological Plasticity and the Influence of Hydrodynamics
In Sect. 3.3 the morphological plasticity of some marine sessile organisms, for
example the sponge Haliclona oculata, the hydrozoan Millepora alcicornis,
and the stony coral Pocillopora damicornis, were related to the impact of
hydrodynamics. There is a strong impact of hydrodynamics on the growth
process . In a number of cases it is possible to arrange growth forms of
sponges, hydrocorals, and stony corals along a gradient of the amount of
water movement, as shown in Figs. 2.16 and 1.1. In the case of the stony
coral, the growth form gradually transforms from a compact shape under
exposed conditions, to a thin-branching one under sheltered conditions.
In growth forms of the sponge Haliclona oculata, plate-like, more compact
shapes emerge at exposed sites. This shape gradually transforms into a thinbranching form when the exposure to water movement decreases. A similar
trend can be observed in growth forms of the hydrozoan Millepora alcicornis
(de Weerdt 1981). In this species the shape changes from plate-like forms at
shallow and exposed sites, to thin-branching forms at deeper and sheltered
locations.
Water flow has a strong influence on the local supply of food particles in suspension feeders . In Sect. 2.1.1 the effects of hydrodynamics on
particle capture by suspension-feeding invertebrates was discussed in detail. In several studies (Frechette et al. 1989, Buss and Jackson 1981, Pile et
al. 1997) it has been demonstrated that locally around a sessile suspension
feeder, exposed to various flow velocities, areas may occur which are depleted from food particles. It has been found by several authors that there
exists an asymmetric type of food capture. Patterson (1984) demonstrated
that the largest amount of food capture is found at the upstream side of
the octocoral colony for low flow velocities, while the situation reverses
for higher flow velocities where the largest amount of food is captured at
the downstream side of the colony. A similar phenomenon was observed
by Sebens et al. (1997) for the stony coral Madracis mirabilis (see Fig. 2.5),
where the largest amount of food particle capture was found at the upstream
side of the colony for low flow velocities (below 15cm -s'"), while the situation again reverses for higher flow velocities (see Fig. 2.6). In studies on
branching stony corals (Sebens et al. 1997, Chamberlain and Graus 1977)
and the influence of hydrodynamics it is demonstrated that branch spacing
is a crucial morphological property which determines the microflow pattern inside the colony. The flow direction will basically reverse twice a day
due to the tidal movements (see also Sect. 2.1.1) and in branching sessile
suspension feeders growth forms emerge which have a roughly radial symmetry or show a tendency to develop a flattened growth form (see also
Sect. 2.2.3 on octo corals, Johnson and Sebens 1993, Stearn and Riding 1973,
Wainwright and Dillon 1969). In the last case most branches will develop
in a plane perpendicular to the governing flow direction. Local food particle absorption patterns which are determined by the direction and the
velocity of the flow, local areas which surround the organism and which
are depleted from food particles, as well as microflow patterns in branching organisms have important consequences for the growth process and the
resulting morphology.