24
2. ENVIRONMENTALLY DRIVEN PLASTICITY
diffusion alone. Sh is related to St as
Sh = StSc Re
where:
where m is the metabolic rate or uptake rate per unit area. As a result, either
Sh or St can be used to examine relationships between metabolism and water
motion.
These engineering correlations are for mass transfer to hydrodynamically smooth surfaces. However, seaweeds and corals often have projections
(e.g. hairs, bullae, calices) on their surfaces .
For rough surfaces, a more appropriate formulation of St is given by
Kays and Crawford (1993). Alternatively, in the cases where a detailed estimation is required of the local mass transfer at the surface of complex -shaped
growth forms and to be able to include mass transfer in simulation models
of growth processes, estimates of the local mass transfer in a simulation of
hydrodynamics can potentially be made, by estimating local flow velocities
and concentration gradients from a simulation. In Sections 4.3.1, 4.5, and 4.6,
methods will be discussed for approximating flow fields and concentration
gradients through simulation.
EFFECTS OF THE FLOW ENVIRONMENT ON ORGANISMAL METABOLISM: ExAMPLES. Several previous studies have quantified the effect of increasing
water flow on rates of nutrient uptake and rates of organismal and community metabolism (Parker 1981, Carpenter et al. 1991, Patterson et al. 1991).
A fewstudies have also examined how organismal morphology interacts with
flowto alter boundary layer dynamics and mass flux (Koehl and Alberte 1988,
Hurd et al. 1996, Hurd and Stevens 1997).
Patterson and Sebens (1989) used an engineering approach to examine the effects of water flow on rates of respiration of a temperate species
of octocoral (Alcyonium) and a species of sea anemone (Metridium). For
both species they found a positive relationship between water flow and Sh
(based on respiration rate), suggesting that mass transfer of gas exchange
limits the metabolic rate. They concluded that organism shape, the local flow
environment, and the resulting boundary layer dynamics were important
determinants of organismal function.
Seaweeds vary in morphology, both within and between species. Koehl
and Alberte (1988) investigated the effects of morphological variation in the
bull kelp, Nereocystis luetkeana, on boundary layer thickness and rates of
photosynthesis of low and high flow morphs under different flow environments. Nereocystis has strap-like blades that might be expected to develop
thick boundary layers under low flow conditions. Their results indicate that
variation in blade morphology allows the low flow morph to flap at a lower
flowspeed, thereby increasing the flowrelative to the blade, resulting in higher
rates of photosynthesis. The narrow, flat blades of the high flow morph collapse into a bundle more readily, reducing the drag force experienced, but
likely also reducing rates of photosythesis due to self-shading and perhaps
increased boundary layer thickness between the blades. This study provides
a good example of how seaweed morphology is often a trade-off between the
costs and benefits of interaction of the thallus with the physical environment.
2. ENVIRONMENTALLY DRIVEN PLASTICITY
diffusion alone. Sh is related to St as
Sh = StSc Re
where:
where m is the metabolic rate or uptake rate per unit area. As a result, either
Sh or St can be used to examine relationships between metabolism and water
motion.
These engineering correlations are for mass transfer to hydrodynamically smooth surfaces. However, seaweeds and corals often have projections
(e.g. hairs, bullae, calices) on their surfaces .
For rough surfaces, a more appropriate formulation of St is given by
Kays and Crawford (1993). Alternatively, in the cases where a detailed estimation is required of the local mass transfer at the surface of complex -shaped
growth forms and to be able to include mass transfer in simulation models
of growth processes, estimates of the local mass transfer in a simulation of
hydrodynamics can potentially be made, by estimating local flow velocities
and concentration gradients from a simulation. In Sections 4.3.1, 4.5, and 4.6,
methods will be discussed for approximating flow fields and concentration
gradients through simulation.
EFFECTS OF THE FLOW ENVIRONMENT ON ORGANISMAL METABOLISM: ExAMPLES. Several previous studies have quantified the effect of increasing
water flow on rates of nutrient uptake and rates of organismal and community metabolism (Parker 1981, Carpenter et al. 1991, Patterson et al. 1991).
A fewstudies have also examined how organismal morphology interacts with
flowto alter boundary layer dynamics and mass flux (Koehl and Alberte 1988,
Hurd et al. 1996, Hurd and Stevens 1997).
Patterson and Sebens (1989) used an engineering approach to examine the effects of water flow on rates of respiration of a temperate species
of octocoral (Alcyonium) and a species of sea anemone (Metridium). For
both species they found a positive relationship between water flow and Sh
(based on respiration rate), suggesting that mass transfer of gas exchange
limits the metabolic rate. They concluded that organism shape, the local flow
environment, and the resulting boundary layer dynamics were important
determinants of organismal function.
Seaweeds vary in morphology, both within and between species. Koehl
and Alberte (1988) investigated the effects of morphological variation in the
bull kelp, Nereocystis luetkeana, on boundary layer thickness and rates of
photosynthesis of low and high flow morphs under different flow environments. Nereocystis has strap-like blades that might be expected to develop
thick boundary layers under low flow conditions. Their results indicate that
variation in blade morphology allows the low flow morph to flap at a lower
flowspeed, thereby increasing the flowrelative to the blade, resulting in higher
rates of photosynthesis. The narrow, flat blades of the high flow morph collapse into a bundle more readily, reducing the drag force experienced, but
likely also reducing rates of photosythesis due to self-shading and perhaps
increased boundary layer thickness between the blades. This study provides
a good example of how seaweed morphology is often a trade-off between the
costs and benefits of interaction of the thallus with the physical environment.