The Great Barrier Reef is part of a larger system of ocean circulation in the Pacific Ocean. This system delivers nutrients and larvae from other regions as well as deep water into the Great Barrier Reef region.

Ocean currents — the movement of water from one location to another — are driven by wind, differences in water density, and the rise and fall of the tide.

They play an important part in regulating heat, connecting biodiversity and transporting fish and other marine life. Currents vary naturally, but climate change now influences them.

Trends

There is increasing evidence of strengthening and accelerated warming in the East Australian Current, which runs south along Australia’s east coast. This current is transporting greater volumes of warmer water southward.

There is little information about the Hiri Current travelling north along the coast in northern Great Barrier Reef waters.

Effects

Changes to ocean currents have the potential to affect entire marine food webs, from microscopic organisms, corals and sponges to top predators such as sharks.

Altered ocean circulation patterns may affect the transport of eggs and larvae within and among coral reefs and other Great Barrier Reef habitats.

Changes to ocean circulation will also affect tiny plants that support the open ocean food web. These microscopic plants (known as phytoplankton) rely on nutrients brought up from deeper in the ocean.

As surface water warms, it becomes less dense and does not mix as readily with the cooler water below. This makes it harder for nutrients to reach the surface, reducing the production of phytoplankton. This, in turn, affects food supply for larger animals, including fish, seabirds, whales and dolphins.

Changes to currents may also result in different species of marine life being more widely distributed or establishing themselves in different areas.