Kelp and smaller algae are the primary producers of the Great Southern Reef. They are the primary biomass that captures the suns energy and creates food through photosynthesis. Organisms such as fish and urchins feed directly on kelp; others such as abalone, graze on drift seaweed (dislodged kelp or blades caught in cracks and crevices) and detritus or; organisms, like sponges, filter decomposed particles floating in the water. Consumers transfer energy through the trophic levels.

Kelps are both a keystone species and a foundation species because:

- without kelp the GSR would not exist as a distinct ecosystem

- kelp creates 3D habitats for a large diversity of marine organisms.

- the physical structure of the reef and the biochemical properties of the seawater (oxygen, carbon dioxide, nutrients) that support life are largely determined by kelp.

The foundation species of the Great Southern Reef is the brown macroalgae known as Golden Kelp. Other large macroalgae include Crayweed, Giant Kelp and Bull Kelp… each is also a foundation species in specific locations.

The high primary productivity of kelp forests supports high levels of biodiversity across all trophic levels. Kelp modifies the environment to create conditions that favour biodiversity.

For example, kelp

- slows water movement providing a sheltered habitat on the sea floor

- shades the seabed for species needing low light

- creates an under-storey below the canopy

- provides habitat for mobile and sessile animals across all levels of the forest including within the holdfast.

- catches drifting larvae making it easier for species such as rock lobster to reproduce and maintain their populations.

COMPLETE a food chain and food web activity using the totem cards provided on the Great Southern Reef website at https://greatsouthernreef.com/resources

The GSR is a designated global biodiversity hotspot with species found nowhere else in the world and more endemic species than the Great Barrier Reef. Of the three groups of algae (brown, green, and red), the Great Southern Reef has the greatest diversity of red algae in the world, more than 800 species with over 75% found nowhere else.

Kelp plays a role in nutrient cycles including the carbon, oxygen, nitrogen and phosphorus cycles. They absorb carbon dioxide and release oxygen. The oxygen rich water supports organisms that feed on the kelp and phytoplankton. Kelps absorb nutrients such as Nitrogen and Phosphorus directly from the water and transfers these nutrients to other consumer organisms through the food web. Nutrients and detritus from decomposed kelp feeds other consumer species such as sponges that feed by filtering water.

Beach wrack consists of decomposing kelp and kelp forest organisms such as sponges and crustaceans that have been washed ashore. The decomposition of wrack recycles nutrients for coastal and marine ecosystems.

*Undertake a Weed Walk in the Virual Fieldwork Activity to learn more about the role of kelp wrack in nutrient cycling and the interconnected coastal ecosystems wrack supports.

There is a fine balance between producer and consumer organisms in a kelp forest ecosystem as well as many unique and specialised relationships between organisms. The balance is easily upset by changes that cause a loss of species or reduced populations. This can occur through through natural events such as storms and floods or human modifications such as pollution, sedimentation, overharvesting, introduced species and anthropogenic climate change.

Kelp forests can become barrens or be replaced by algal turfs.

Kelp is a stationary species that cannot move to avoid a stress event. Once kelp is decimated or lost, reforestation is difficult without sufficient adult population.

When a tipping point is passed, kelp forests and the species they support will not recover naturally and human intervention is needed for restoration.

Examples of kelp forest losses on the Great Southern Reef include Crayweed forests - Sydney, Giant kelp forests -Tasmania, and Golden Kelp - Western Australia.

See Illustrative Examples.

The unique Spotted Handfish in Tasmania was impacted by the overfishing of scallops, the invasion of North Pacific Seastar and loss of the ascidians the fish need for reproduction.

This story illustrates how disequilibrium has consequences for species and ecosystems.

The Great Southern Reef is linked to other ecosystems such as seagrasses, rock platforms, beaches and the deeper ocean. Changes to these ecosystems affects kelp forests.