30
2. ENVIRONMENTALLY DRIVEN PLASTICITY
serve as a means of dampening fluctuations in ambient flows (Chamberlain
and Graus 1977, Sebens et al. 1997, Helmuth et al. 1997).
Measurements of particle capture by corals have also shown that the location of capture on a colony, and within aggregations, can vary consistently
depending on local flow conditions. For example, several studies have shown
that particle capture at low flow speeds tends to be highest on upstream regions of colonies. As flow speed increases, areas of maximum capture rate
are shifted to the downstream region of the colony or aggregation (Patterson
1984, Helmuth and Sebens 1993, Sebens et al. 1997). In Fig. 2.6 the capture
rates of a single branch of a Madracis mirabilis colony at the front and rear
sites are compared; for high flow speeds the maximum capture rate is shifted
to the downstream region of the branch. However, most of these studies were
conducted under conditions of unidirectional, low-turbulence flow, and it
is unclear whether or not these patterns remain under conditions of highly
turbulent flow. Patterson (1984) found highly asymmetrical patterns of particle capture by a soft coral under conditions oflaminar flow; however, these
differences disappeared under higher levels of turbulence. Hunter (1989)
studied feeding by a hydroid under oscillatory flow, and found that patterns
in intracolony particle capture disappeared when compared with those observed during feeding in unidirectional flow, but also that capture rates under
conditions of alternating flow could not be predicted given measurements in
unidirectional flow. While both oscillatory and unidirectional flows occur on
coral reefs (Sebens and Johnson 1991,Helmuth and Sebens 1993), the relationship between colony morphology and particle capture under highly complex
flow regimes requires much more detailed study before we can explicitly
relate patterns in flow over large scales to patterns in food uptake by corals.
50
1 "'--+----;/-'
/
/
/
/
/
1
{
100
10
20
30
40
Flow speed (cm/s)
Fig. 2.6. Capture rates of a singlebranch
ofaMadracis mirabi/is colony atthefront
(upstream) and the rear (downstream)
region (after Sebens et al. 1997)
2.2 The Case Studies
In this section the different organisms, used as case studies, will be discussed
in more detail. Information will be provided regarding the growth processes,
which will be later used in the simulation models. This section will focus
on the level of organization varying from molecular genetics to the level of
the modules and give an overview of the morphological plasticity of each
organism.
2.2.1 Case Studies of Environmentally Driven Plasticity: Seaweeds
Seaweeds include a vast variety of evolutionarily distant organisms with the
single unifying feature of being macroscopic algae which live in the sea. Their
myriad variety of growth forms is produced by a number of very different
growth processes which are, in general, associated with different evolutionary
lines.
Seaweeds occur in three different divisions, or phyla: reds (Rhodophyta),
browns (Phaeophyta), and greens (Chlorophyta). The three groups are not
closely related to each other and one, the green algae, are more closely related
to land plants than they are to other seaweeds. Red and green seaweeds are
evolutionarily ancient, first appearing in the midproterozoic, 1600 million
years ago, before the earliest traces of invertebrates. Brown seaweeds are
part of a very large and diverse group which includes unicellular algae such
2. ENVIRONMENTALLY DRIVEN PLASTICITY
serve as a means of dampening fluctuations in ambient flows (Chamberlain
and Graus 1977, Sebens et al. 1997, Helmuth et al. 1997).
Measurements of particle capture by corals have also shown that the location of capture on a colony, and within aggregations, can vary consistently
depending on local flow conditions. For example, several studies have shown
that particle capture at low flow speeds tends to be highest on upstream regions of colonies. As flow speed increases, areas of maximum capture rate
are shifted to the downstream region of the colony or aggregation (Patterson
1984, Helmuth and Sebens 1993, Sebens et al. 1997). In Fig. 2.6 the capture
rates of a single branch of a Madracis mirabilis colony at the front and rear
sites are compared; for high flow speeds the maximum capture rate is shifted
to the downstream region of the branch. However, most of these studies were
conducted under conditions of unidirectional, low-turbulence flow, and it
is unclear whether or not these patterns remain under conditions of highly
turbulent flow. Patterson (1984) found highly asymmetrical patterns of particle capture by a soft coral under conditions oflaminar flow; however, these
differences disappeared under higher levels of turbulence. Hunter (1989)
studied feeding by a hydroid under oscillatory flow, and found that patterns
in intracolony particle capture disappeared when compared with those observed during feeding in unidirectional flow, but also that capture rates under
conditions of alternating flow could not be predicted given measurements in
unidirectional flow. While both oscillatory and unidirectional flows occur on
coral reefs (Sebens and Johnson 1991,Helmuth and Sebens 1993), the relationship between colony morphology and particle capture under highly complex
flow regimes requires much more detailed study before we can explicitly
relate patterns in flow over large scales to patterns in food uptake by corals.
50
1 "'--+----;/-'
/
/
/
/
/
1
{
100
10
20
30
40
Flow speed (cm/s)
Fig. 2.6. Capture rates of a singlebranch
ofaMadracis mirabi/is colony atthefront
(upstream) and the rear (downstream)
region (after Sebens et al. 1997)
2.2 The Case Studies
In this section the different organisms, used as case studies, will be discussed
in more detail. Information will be provided regarding the growth processes,
which will be later used in the simulation models. This section will focus
on the level of organization varying from molecular genetics to the level of
the modules and give an overview of the morphological plasticity of each
organism.
2.2.1 Case Studies of Environmentally Driven Plasticity: Seaweeds
Seaweeds include a vast variety of evolutionarily distant organisms with the
single unifying feature of being macroscopic algae which live in the sea. Their
myriad variety of growth forms is produced by a number of very different
growth processes which are, in general, associated with different evolutionary
lines.
Seaweeds occur in three different divisions, or phyla: reds (Rhodophyta),
browns (Phaeophyta), and greens (Chlorophyta). The three groups are not
closely related to each other and one, the green algae, are more closely related
to land plants than they are to other seaweeds. Red and green seaweeds are
evolutionarily ancient, first appearing in the midproterozoic, 1600 million
years ago, before the earliest traces of invertebrates. Brown seaweeds are
part of a very large and diverse group which includes unicellular algae such