The Great Southern Reef kelp forests are influenced by

- water temperature, depth, and clarity.

- waves, tides, ocean currents and upwelling.

Kelp forests need cool, clear, shallow, nutrient rich water with the average pH and salinity levels of seawater.

Two Australian Ocean Currents, the East Coast Current (EAC) and Leeuwin Current influence the spatial distribution (location) and functioning of kelp forests.

Currents mix warm and cold water to create the temperatures that suit kelp, adding several degrees of temperature to coastal waters in temperate latitudes.

Ocean currents also cause upwelling, a process bringing cold nutrient rich water to the surface, fertilising surface waters and contributing to primary productivity.

During upwelling, displaced surface waters are replaced by cold, nutrient-rich water that “wells up” from below.

Source: https://oceanservice.noaa.gov/facts/upwelling.html

Warm currents such as the EAC and Leeuwin Current are nutrient poor and can reduce kelp growth.

Warm water results in tropical species migrating southwards. The tropicalisation of species into temperate kelp forests is linked to a stronger EAC on Australia's east coast. Invading herbivorous tropical species feed on kelp and compete for habitat and food.

The impact of warming waters include:

• Tropical fish numbers are increasing in temperate waters

• Migrating fish and sea urchins are eating more kelp

See 'Human impacts' for more on climate change and tropicalisation.

Storms created by weather events such as East Coast Lows and intense cold fronts, produce high energy waves that damage kelp. This is evidenced by large amounts of wrack on the seashore after storms.

Usually kelp recovers quickly by -

• recolonising exposed surfaces where kelp has been ripped off the surface

• having high primary productivity - new blades grow quickly.

Floods increase ocean turbidity and may smother smaller species like seaweeds and sponge gardens through sedimentation.

Turbidity interrupts solar energy transmission through the water column. Once clarity returns however, normal processes will resume.