Nature and rate of change affecting ecosystem functioning

Nature of change

Kelp forests have adapted to changes in the marine environment over thousands of years. The drivers of change are the causes, or factors, which drive the change. Some of the drivers of change operate on a local and regional level, and others operate on a global level. Some changes in kelp forest ecosystems have happened over the long term and other changes have happened over a shorter period of time.

Kelp forests of south eastern Australia are experiencing change which is not consistent across the region. Some kelp forests have disappeared, others are reducing in size and density whilst most are showing signs they are under threat.

Global scale change

Sea levels have changed at various times in the earth's history. The peak of the most recent ice age in Australia was approximately 21 000 years and by 6 000 years ago the sea level was close to its current level. Marine ecosystems were able adapt to these changing conditions partly because the change happened slowly, and there was time for natural change to occur.

The rocky reefs which form the basis of the Great Southern Reef have been geologically stable for thousands of years and it is this stability which has contributed to the GSR's diversity.

Local/regional scale change

Kelp forest ecosystems have also constantly experienced change due to natural drivers/forces on a local scale, for example when storms have occurred. In the past kelp forests have modified and adapted to this change, partly because most kelp forests are resilient that is, they are able to regrow after relatively minor disruptions.

In some cases, local drivers which are due to human activities can cause a kelp forest to disappear. For example, large sections of the kelp forests off Sydney's coast actually disappeared in the 2000's. Sewage from sewerage pipes was discharged close to the coast and is considered to be the likely cause of this disappearance.

For more information on how local drivers can destroy as well as rejuvenate a local kelp forest, see the section on 'Operation Crayweed' in the Traditional and Contemporary Management and the website of the Sydney Institute of Marine Science .

Whilst there has always been change in kelp forest ecosysytems due to natural forces the impacts of human induced forces eg, rising ocean temperatures may be may be too widespread and the rate of change too fast for kelp forests and ecosystems to respond and adapt.

The recent State of the Environment report (2016) found that "Australia's biodiversity is under increased threat and has, overall, continued to decline." Human impacts on many ecosystems including kelp forests have been responsible for modifications and damage to ecosystems.

Refer to the map of Australia, figure 11, to see how change is occurring in most ecosystems in Australia. The Climate Council is a non government organisation and the map it produced shows that the extent of change is significant and widespread.

Rate of change

In recent decades the changing climate has increased the rate of change in most ecosystems. The rate of change refers to how fast (or slow) something changes.

A recent global study of kelps across the world has "found that 38% of the world's kelp forests have declined over the past 50 years." The same study also found some kelp forest (about 25%) have increased in size in some parts of the world, but not in Australia. Given there is huge variation in how kelp forests are changing across the world, the nature of change in kelp forests is varied, widespread and is happening on a variety of scales.

Human factors which cause change are referred to as drivers or threats. Impacts from human factors both locally/regionally and globally have caused changes in kelp forest ecosystems.

Refer to the Human impacts - both positive and negative for more information on all drivers which have caused change.

However, the primary driver of significant change at a global level to kelp forests has been rising ocean temperatures.

Scientists such as Dr Thomas Wernberg state that "There has been a doubling in the frequency and duration of these marine heatwaves, and this is something that's been linked to the extreme heating of the Earth's temperature,"

How fast are kelp forests changing ?

There are two global warming hotspots in the Great Southern Reef - southwestern WA and eastern Australia. In eastern Australia, the ocean is warming at rates twice as fast as the global average. The main reason for this is the strengthening of the East Australia Current which pushes warm tropical water southwards. As the ocean is warming at such a fast rate, the change in kelp forests is also happening at a fast rate. There have been dramatic changes across all life on the GSR.

Read about the rate of change in kelp forests across the world including off the coast of Sydney, reflecting the how quickly kelp forests are changing.

Read the article by a scientist in Western Australia about how some kelp is moving southwards and some is disappearing in response to changing ocean temperatures.

The concepts of resilience and vulnerability are also relevant when analysing change in kelp forests. Some kelp forests are able to expand into areas which were previously unfavourable (usually too cold) and are considered somewhat resilient. However, many kelp forest ecosystems off the Australian coast including those around north - east Tasmania and those near Sydney were unable to regrow or expand without human intervention. The kelp forests in north -east Tasmania are now considered endangered and some kelp forests in Sydney disappeared. These kelp forests would be considered vulnerable.

In 2016 a team of international experts, in a global study analysed data that measured kelp abundance from more than 1,000 sites across 34 regions around the globe.

This was the first study to provide a global “health check” for kelp forests. Whilst the authors found a small average decline across the globe, there was huge variation across the globe in the percentage change in kelp forest abundance. Globally, 38% of kelp forests experienced a decline in abundance, 27% of kelp forests experienced an increase in abundance (but not in Australia) and for 35% there was no detectable change.

The authors found that kelp forests' growth and decline varied markedly across the world. So the nature of change in kelp forests is varied, it is widespread and is happening on a variety of scales.

The study was also helpful in recognising the drivers of change in kelp forests across the globe.

The authors found that both local and global drivers caused change in kelp forests, and there were huge regional differences in how much change each driver made to each kelp forest.

For south eastern Australia it is the impact of the East Australian current which is the cause of the significant change in this region.

Where kelp forests have increased in size, local factors and human intervention have usually played a part. For example a restoration project in Sydney called 'Operation Crayweed' lead to the rejuvenation of kelp off the coast of Sydney, and the reintroduction of otters lead to the regrowth of the kelp forests off the Californian coast.

Refer to the Human impacts - both positive and negative for more information.

Change in kelp forests is predicted to continue. Ocean temperatures are predicted to warm even more quickly than they did in the 20th century.

The global study states that "Climate projections estimate that ocean isotherms will continue to shift poleward at a rate seven times faster in the 21st century than the 20th century."

With warmer oceans, 'tropicalisation' will continue and the impact of tropical fish will continue to threaten the valuable temperate kelp forest ecosystems.

The article in 'theconversation.com' refers to the global study mentioned above and has links to the two scientific journal articles published.