13.4 Larval Settlement and External Fertilization
411
Transport of various matter and biochemical interactions within the river
plumes are the key factors for primary production and global geochemical cycling. This transport controls the input of land-derived natural and pollutant
chemicals into shelf seas (Morris et al., 1995). In some locations in the tropics, such as the northern east coast of Australia, river catchments are small
and major flood events are associated with the activity of monsoonal depressions or tropical cyclones. As tropical cyclones move onto the continental shelf
and coastal regions, the whole water column is extensively mixed, and bottom
sediments are resuspended together with dissolved and particulate nutrients.
Nutrients mineralized by bacteria trigger regional phytoplankton blooms. The
resulting plankton biomass and primary productivity can increase 5-10 times
within a few days after a cyclone (Furnas, 1996).
The Burdekin River, Australia, is the largest river in the Great Barrier Reef
region with mean annual discharge of 9.7x 10 9 m 3 into the Great Barrier Reef
lagoon (Wolanski, 1994). The river runoff is highly variable and limited to occasional flood events, usually occurring during the Australian summer months
of December to March. The Burdekin River peak discharges are of the order
of 10,000 m 3 /s to 30,000 m 3 /s (see Fig. 13.5).
Data on the fate of flood waters during and after large discharge events of
the Burdekin River are limited. King et al. (1997) used the data set on
salinity distribution after the 1981 flood event, reported by Wolanski and van
Senden (1983), to calibrate and verify a three-dimensional hydrodynamic model
of the Burdekin River in flood. They used the NOAA MECCA model which
incorporates river plume dynamics into the governing equations. The model
predicts flows due to tides, winds and density difference forcing, as well as the
salinity and temperature distributions. The entire 1981 flood event period (90
days) has been simulated and compared with experimental data. Agreement
between the observed and predicted salinity distribution was very good.
Detailed information on the fate of the Burdekin River plume is of particular
importance for the determination of the impact of low salinity waters on the
adjacent coral reefs. Low salinity water affecting corals for prolonged periods of
time may cause irreversible coral damage. Therefore, a risk assessment analysis
is needed to quantify the impact of river floods on the Great Barrier Reef. In
Fig. 13.6, an example of preliminary results of the risk analysis is given. Isolines
in the figure indicate the particular return periods (in years) of events when
the exceedance of 10% freshwater is of the duration of 120 hours. Thus, close
to the Burdekin River mouth, a return period of such event is about 3 years,
while for reefs close to the Fitzroy Island it is about 30 years.
13.4 Larval Settlement and External Fertilization
13.4.1 Settlement of Larvae
In Chap. 11, we have examined various mechanisms used by aquatic organisms
to move through the water column. Basically, organisms generate the thrust
411
Transport of various matter and biochemical interactions within the river
plumes are the key factors for primary production and global geochemical cycling. This transport controls the input of land-derived natural and pollutant
chemicals into shelf seas (Morris et al., 1995). In some locations in the tropics, such as the northern east coast of Australia, river catchments are small
and major flood events are associated with the activity of monsoonal depressions or tropical cyclones. As tropical cyclones move onto the continental shelf
and coastal regions, the whole water column is extensively mixed, and bottom
sediments are resuspended together with dissolved and particulate nutrients.
Nutrients mineralized by bacteria trigger regional phytoplankton blooms. The
resulting plankton biomass and primary productivity can increase 5-10 times
within a few days after a cyclone (Furnas, 1996).
The Burdekin River, Australia, is the largest river in the Great Barrier Reef
region with mean annual discharge of 9.7x 10 9 m 3 into the Great Barrier Reef
lagoon (Wolanski, 1994). The river runoff is highly variable and limited to occasional flood events, usually occurring during the Australian summer months
of December to March. The Burdekin River peak discharges are of the order
of 10,000 m 3 /s to 30,000 m 3 /s (see Fig. 13.5).
Data on the fate of flood waters during and after large discharge events of
the Burdekin River are limited. King et al. (1997) used the data set on
salinity distribution after the 1981 flood event, reported by Wolanski and van
Senden (1983), to calibrate and verify a three-dimensional hydrodynamic model
of the Burdekin River in flood. They used the NOAA MECCA model which
incorporates river plume dynamics into the governing equations. The model
predicts flows due to tides, winds and density difference forcing, as well as the
salinity and temperature distributions. The entire 1981 flood event period (90
days) has been simulated and compared with experimental data. Agreement
between the observed and predicted salinity distribution was very good.
Detailed information on the fate of the Burdekin River plume is of particular
importance for the determination of the impact of low salinity waters on the
adjacent coral reefs. Low salinity water affecting corals for prolonged periods of
time may cause irreversible coral damage. Therefore, a risk assessment analysis
is needed to quantify the impact of river floods on the Great Barrier Reef. In
Fig. 13.6, an example of preliminary results of the risk analysis is given. Isolines
in the figure indicate the particular return periods (in years) of events when
the exceedance of 10% freshwater is of the duration of 120 hours. Thus, close
to the Burdekin River mouth, a return period of such event is about 3 years,
while for reefs close to the Fitzroy Island it is about 30 years.
13.4 Larval Settlement and External Fertilization
13.4.1 Settlement of Larvae
In Chap. 11, we have examined various mechanisms used by aquatic organisms
to move through the water column. Basically, organisms generate the thrust