The oceanography and marine ecology of Ningaloo, a World Heritage Area
2020
The Ningaloo coast of north-western Australia (eastern Indian Ocean) hosts one of
the world's longest and most extensive fringing coral reef systems, along with
globally significant abundances of large marine fauna such as whale sharks. These
characteristics – which have contributed to its inscription on the World Heritage
list – exist because of the unique climatic, geomorphologic and oceanographic
conditions. The region is hot and arid, so runoff of water from land is low,
facilitating clear water that allows corals to grow close to the shore. The
poleward-flowing Leeuwin Current is an important influence, bringing warm water
and generally suppressing coastal upwelling. During the austral summer, strong
southerly winds generate the equatorward-flowing Ningaloo Current on the inner
shelf – this current facilitates sporadic upwelling events that enhance
concentrations of nutrients, which in turn enhance pelagic primary productivity
that supports the reef's biota. The coast has experienced several marine heatwaves
since 2011 that have caused mortality of corals and probably seagrass, albeit
relatively less than elsewhere along the coast. Wind-generated surface waves break
over the fringing reef crest, causing cooling currents that tend to dampen warming
– although this mechanism seems not to have prevented some areas from experiencing
damaging heat, and corals in places that do not receive the wave-generated
currents have experienced substantial mortality. Herbivores, from fish to green
turtles, are abundant, and in the lagoon, extensive stands of large brown algae
provide an important habitat for newly recruited fish. There has been a decline in
abundance of some fish. Predictions of future pressures include a weaker but more
variable Leeuwin Current and increased human use. The ability of Ningaloo's
144ecosystems to withstand
growing pressures will depend partly on the rate and magnitude of global warming
but also on actions that manage local pressures from increasing human use. These
actions will rely on continued science to provide the evidence needed to identify
the pressures, the changes they create and the ways that we can mitigate them.
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