Mangroves are a special form of vegetation as they exist at the boundary of terrestrial and marine environment. They have a special role in supporting ÿsheries and in the stabilizing the tropical coastal zones. Biochemical and trophodynamic processes in the mangroves are strongly linked to water movement, due to tides and waves. In this paper we present the theoretical attempt to predict the attenuation of wind-induced random surface waves in the mangrove forest. The energy dissipation in the frequency domain is determined by treating the mangrove forest as a random media with certain characteristics determined using the geometry of mangrove trunks and their locations. Initial nonlinear governing equations are linearized using the concept of minimalization in the stochastic sense and interactions between mangrove trunks and roots have been introduced through the modiÿcation of the drag coe cients. The resulting rate of wave energy attenuation depends strongly on the density of the mangrove forest, diameter of mangrove roots and trunks, and on the spectral characteristics of the incident waves. Examples of numerical calculations as well as preliminary results from observation of wave attenuation through mangrove forests at Townsville (Australia) and Iriomote Island (Japan) are given.

[1] The role of waves, tide, and wind on the circulation of a fringing reef system was investigated using data collected during a 6 week field experiment in a section of Ningaloo Reef off Western Australia. The high correlation observed between current velocities and wave height throughout the system revealed the dominant role wave breaking plays in driving the overall reef-lagoon circulation, whereas the modulation of the currents at tidal frequencies suggested that the wave-driven currents responded to tidal variations in the mean water level over the reef. The influence of the various forcing mechanisms on the current field was investigated for both high-and low-frequency bands. Wave breaking was found to be the dominant forcing mechanism for the low-frequency (subtidal) currents, with the subtidal flow pattern consisting of a cross-reef flow over the reef, alongshore flow in the lagoon, and water exiting back to the ocean through the main channel. The tides controlled the high-frequency current variability via two mechanisms: one associated with the ebb-flood cycle of the tides and the second associated with tidal modulations of the wave-driven currents. Wind-forcing and buoyancy effects were both found to be negligible in driving the circulation and flushing of the system during the observation period. Flushing time scale estimates varied from as low as 2 h to more than a day for the wide range of observed incident wave heights. The results suggest that the circulation of Ningaloo Reef will be strongly influenced by even a small mean sea level rise.

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This study focuses on a mesoscale eddy feature, the 'Capricorn Eddy', that typically forms within an indentation of the continental shelf in the southern GBR system. Satellite data at moderate resolution (1 km) are used to examine relevant mesoscale and sub-mesoscale sea surface dynamics. Available in situ measurements and model data are used to validate the satellite observations and to specify the nature of the processes occurring within the water column itself. The characteristic features are identified and physical theory employed to develop an understanding of associated processes. In particular, the effect of the eddy in raising cooler, nutrient-enriched oceanic subsurface water and transporting it to the reef zone, and eventually into the lagoon, is shown. This study demonstrates that the linkages between large-scale oceanography and the meso-and sub-mesoscale patterns are crucial to determining biologic responses on the scale of reef communities and may be key to understanding climate change impacts at the relevant spatial scales.

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[1] Surface velocity observations from satellite tracked drifters made between 1987 and 2008 were used to resolve the surface circulation of the western Coral Sea, west of 158°E, and the Great Barrier Reef (GBR). The mean surface current map depicts well the major circulation patterns of the region, such as the position of the north Vanuatu and north Caledonia jets (NVJ and NCJ) and the western boundary currents. The North Queensland Current (NQC) and the East Australian Current (EAC) are well defined, flowing at speeds greater than 50 cm s −1 to the north, south of 15°S and 19°S, respectively. The NQC/EAC is mainly formed by the NVJ/NCJ flows, respectively. The presence of the Queensland Plateau greatly affects the westward flow, causing a zone of weak and highly variable currents that extends from 15°S to 18°S between the Queensland Plateau and the GBR shelf. Of the 235 drifters that crossed the western Coral Sea, 75 entered the GBR. Analysis of the drifter trajectories inside the GBR reveals the presence of a northwestward circulation at speeds of 22 cm s −1 north of 18°S and 0.5 cm s −1 south of 18°S. Drifter travel times used to evaluate the water residence times within the GBR indicate residence times of a few weeks for most of the lagoon.

[1] The circulation and temperature variability on the inner shelf near the North West Cape of Australia off Ningaloo Reef was investigated using field data obtained from two moorings deployed from 2004 to 2009. The results revealed that alongshore currents on the inner shelf were, on average, only weakly influenced by the offshore poleward (southward) Leeuwin Current flow, i.e., monthly averaged alongshore current velocities were $0.1 m s À1 or less. The presence of a consistent summer-time wind-driven equatorward (northward) counter flow on the inner-shelf (referred to in the literature as the Ningaloo Current) was not observed. Instead, the shelf waters were strongly influenced year-round by episodic subtidal current fluctuations (time scale 1-2 weeks) that were driven by local wind-forcing. Analysis of the current profiles showed that periods of strong equatorward winds were able to overcome the dominant poleward pressure gradient in the region, leading to upwelling on the inner-shelf. Contrary to prior belief, these events were not limited to summer periods. The forcing provided by these periodic wind events and the associated alongshore flows can explain much of the observed temperature variability (with timescales < 1 month) that influences Ningaloo Reef.

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