134
E. Wolanski . B. King . S. Spagnol
the fringing mangroves near high tide. The currents vary smoothly spatially and
temporally (Anim. 16), calculated from the model of Wolanski et al. (1990). The complex topography and the location of distinct sand patches and mud patches result
in suspended sediment distribution that is also highly patchy temporally and spatially (Anim. 17). Further patchiness is introduced by the wind because some areas
are sheltered by sand banks while other areas are exposed to wind and waves (Anim. 18).
In turn this patchiness is reflected in a patchy distribution of sedimentation zones
in the fringing mangroves. Presumably this patchy suspended sediment concentration is reflected in patchiness of the plankton abundant in this channel. Seagrass
forms rich meadows along the shallow mangrove-fringed coast and somehow they
survive repeated events of high turbidity and sedimentation (Wolanski et al. 1997C).
If high concentrations of suspended sediment concentration (1000-5000 ppm)
were prolonged, the meadows would not survive (OnuiI994; Schoellhamer 1996).
The response of seagrass to chaotic events of high sedimentation and turbidity is unknown.
7.5
Coral, Fish and Prawn Larvae
On the Great Barrier Reef most hard corals spawn once a year in a synchronized event
called mass spawning. Mass spawning can release millions of eggs that float around a
single reef, such as Bowden Reef on the Great Barrier Reef (Fig. 14). Yet as this cloud of
eggs is advected and mixed by the currents, the egg plume is extremely patchy
(Anim. 19), with no apparent correlation spatially (from site to site) or temporally (at
a given site from daily samples). The distribution is chaotic, with the standard deviation from the triplicate samples having the same magnitude as the mean at a given site.
In such cases the mean values are probably meaningless. Patchiness develops quickly
after the release of eggs into the water (Fig. 15). These patches usually take the form of
slicks, a few metres in width and several hundreds of metres to a few kilometres in
length (Wolanski and Hamner 1988). Clearly the distribution the concentration of eggs
is chaotic.
The distribution of coral fish larvae is also patchy. At Bowden Reef, for example,
fish larvae occur in patches for a few days. Patches of weakly motile larvae are located
generally downstream of the reef (Anim. 20) and patches of highly mobile fish upstream of the reef (Anim. 21) (Wolanski et al. 1997a). There is thus no smooth distribution.
The distribution of prawn larvae in shallow, mangrove-fringed waters is also patchy
and highly variable from species to species. This is shown in Anim. 22 for the case of
Klang Strait on the west coast of Malaysia. No spatial or temporal correlation exists.
Scientists cope with such spatial and temporal patchiness by calculating the mean
over triplicate samples and the ensemble-average of the data (e.g. Oliver et al. 1992, for
coral eggs and Chong et al. 1996, for prawn larvae). With this technique the only parameter retained to characterize patchiness is the standard deviation. However, in these
chaotic flows the standard deviation has a magnitude comparable to the mean
(e.g. Anim. 19). This makes the mean and standard deviations meaningless. These parameters indicate only that there are either plenty of larvae or there are none; no useful statistics remain.
E. Wolanski . B. King . S. Spagnol
the fringing mangroves near high tide. The currents vary smoothly spatially and
temporally (Anim. 16), calculated from the model of Wolanski et al. (1990). The complex topography and the location of distinct sand patches and mud patches result
in suspended sediment distribution that is also highly patchy temporally and spatially (Anim. 17). Further patchiness is introduced by the wind because some areas
are sheltered by sand banks while other areas are exposed to wind and waves (Anim. 18).
In turn this patchiness is reflected in a patchy distribution of sedimentation zones
in the fringing mangroves. Presumably this patchy suspended sediment concentration is reflected in patchiness of the plankton abundant in this channel. Seagrass
forms rich meadows along the shallow mangrove-fringed coast and somehow they
survive repeated events of high turbidity and sedimentation (Wolanski et al. 1997C).
If high concentrations of suspended sediment concentration (1000-5000 ppm)
were prolonged, the meadows would not survive (OnuiI994; Schoellhamer 1996).
The response of seagrass to chaotic events of high sedimentation and turbidity is unknown.
7.5
Coral, Fish and Prawn Larvae
On the Great Barrier Reef most hard corals spawn once a year in a synchronized event
called mass spawning. Mass spawning can release millions of eggs that float around a
single reef, such as Bowden Reef on the Great Barrier Reef (Fig. 14). Yet as this cloud of
eggs is advected and mixed by the currents, the egg plume is extremely patchy
(Anim. 19), with no apparent correlation spatially (from site to site) or temporally (at
a given site from daily samples). The distribution is chaotic, with the standard deviation from the triplicate samples having the same magnitude as the mean at a given site.
In such cases the mean values are probably meaningless. Patchiness develops quickly
after the release of eggs into the water (Fig. 15). These patches usually take the form of
slicks, a few metres in width and several hundreds of metres to a few kilometres in
length (Wolanski and Hamner 1988). Clearly the distribution the concentration of eggs
is chaotic.
The distribution of coral fish larvae is also patchy. At Bowden Reef, for example,
fish larvae occur in patches for a few days. Patches of weakly motile larvae are located
generally downstream of the reef (Anim. 20) and patches of highly mobile fish upstream of the reef (Anim. 21) (Wolanski et al. 1997a). There is thus no smooth distribution.
The distribution of prawn larvae in shallow, mangrove-fringed waters is also patchy
and highly variable from species to species. This is shown in Anim. 22 for the case of
Klang Strait on the west coast of Malaysia. No spatial or temporal correlation exists.
Scientists cope with such spatial and temporal patchiness by calculating the mean
over triplicate samples and the ensemble-average of the data (e.g. Oliver et al. 1992, for
coral eggs and Chong et al. 1996, for prawn larvae). With this technique the only parameter retained to characterize patchiness is the standard deviation. However, in these
chaotic flows the standard deviation has a magnitude comparable to the mean
(e.g. Anim. 19). This makes the mean and standard deviations meaningless. These parameters indicate only that there are either plenty of larvae or there are none; no useful statistics remain.