Weather and climate influence the features of the Great Southern Reef.

Air temperatures influence the water temperature kelp requires for optimum growth (around 20 degrees C). Heatwaves contribute to marine heatwaves that cause kelp forests loss. Atmospheric change (warming) is increasing the stresses on kelp forests.

Nutrient cycling and energy flows.

Sunlight is essential for photosynthesis. Kelp uses solar energy to produce food (primary biomass). Kelp maximises access to sunlight through adaptations such as gas chambers or ‘floaties’, and wide spreading blades. Kelp is the primary biomass and the bottom level of food chains and food webs. See Fact Sheet

Weather and climate influence water temperature and therefore the distribution of kelp forests in Australia’s.

Carbon cycle, oxygen cycle and water cycle. Kelp absorbs carbon dioxide and releases oxygen. Kelp forests are ‘carbon sinks’, permanently removing carbon from the atmosphere and sequestering it into the deep sea or coastal sediments. It is estimated that 11% of global kelp is permanently sequestered in the ocean with about 90% of that in the deep sea. Oxygen released by kelp is used by consumer organisms at higher trophic levels.

Global wind circulations (prevailing winds) drive the ocean currents and upwelling, that determine water temperature and nutrient supplies. Upwelling, a natural process in which currents bring cold, nutrient-rich water to the surface, is caused by wind and earth’s rotation. Coastal upwelling supports the growth of seaweed and plankton providing food for fish, marine mammals, and birds and generating some of the world’s most fertile ecosystems.

La Nina and El Nino events alter normal trade winds and subsequent ocean current conditions including the EAC, Leeuwin Current and upwelling events .

Climate change

Anthropogenic climate change is placing increased stress on the Great Southern Reef and has caused significant kelp forest losses. Changes in kelp forest ecosystems attributed to a warming atmosphere and subsequent marine warming include:

• tropicalisation and migration of herbivorous species of fish and urchins

• kelp bleaching reduces the ability of algae to photosynthesise and reproduce, makes them more susceptible to grazing

• marine heatwaves - temperatures exceed the threshold for kelp to grow

• ocean acidification impacts organisms with shells or skeletons e.g., lobsters. Shells dissolve in acidic water and organisms’ reduces ability to produce Calcium Carbonate structures - smaller creatures with thinner shells, slower growth and reproduction rates result with repercussions for food webs.

• Deoxygenation: Warm water holds less oxygen. Some species need highly oxygenated water.

See Human Impacts for more on climate change.