Human impacts -  positive and negative

Figure 28 : Kelp forests along Sydney's coasts.

Source: John Turnbull  www.marineexplorer.org

   Approximately 80 % of Australia's total population lives on or near the south east coastal region.  The rising population, its associated activities and threats such as, overfishing and pollution have impacted negatively on the existence, health  and functioning of kelp forest ecosystems.

Kelp forest ecosystems are generally resilient to normal storm damage but are  vulnerable to change from human activities. Kelp forest ecosystems are important habitats for fish and invertebrates and when kelp forests are destroyed the diversity and abundance of fish and other species may decline on the coast or in nearby estuaries. 

(Read the fact sheet  produced by the DPI )

Kelp forests can be negatively impacted directly and indirectly by humans through a number of threatening actions and  processes which drive change.

Direct Negative Impacts

Kelp forests can be impacted directly and indirectly by humans through actions and processes which occur due to coastal development, pollution and climate change. Human activities create threatening processes to ecosystem functioning and the threatening processes create negative impacts. 

Some negative impacts which have occurred in Kelp forests in south eastern Australia are : 

• the existence of some kelp species are  now threatened, eg, in Tasmania's north - east kelp forests have been placed on the endangered species list,  and a species of marine brown algae off the coast northern NSW has been placed on the threatened species list. 

• local extinction of some kelp species, eg, disappearance of a species of kelp called  Bennetts seaweed in Sydney harbour. 

• there have been other changes  in abundance (numbers of species), changes in distribution (where kelp is found) and changes in reproduction rates.

Some negative human threats and impacts include 

1. Physical  damage -  Kelp plants and forests can be directly damaged and destroyed by boats and their anchors, moorings and rubbish. When harbours, bays and estuaries are dredged or reclaimed, kelp forests are often directly cleared from the sea floor and destroyed. When construction occurs along the coast e.g. for a harbour marina or for an aquaculture farm, or when even simple foreshore structures such as jetties and pontoons are built, kelp is usually cleared and destroyed. Even minor structures have an ongoing impact as they shade the water and seafloor below and block access to sunlight which kelp requires to function. 

2. Poor water quality - The quality of ocean water near the coast is affected by many pollutants . The type of pollution can be categorised according to where it comes from that is, whether it comes from a 'point source' (one location) or a 'non point source ' (many locations).  Both point and non-point sources contribute; 

• toxic pollutants, eg, heavy metals 

• pathogens like bacteria  

• nutrients e.g. nitrogen and phosphorus, and 

• soil which creates siltation.

a. Point sources -  these are sources of pollution that can be traced back to a specific  location  eg, a sewerage treatment works or an aquaculture farm.

Kelp forests off the coast of Sydney are a good example of macro-algae forests that have been affected by poor water quality. In this case, in the 1980's and 1990's, the three main sewage treatment works in Sydney (Malabar, North Head and Bondi - which are considered point sources),  were discharging large quantities of sewage effluent into the ocean just off the coast. Beachgoers and community members protested and eventually the NSW government  invested in new sewerage pipeline technology. Scientists have suggested that the high levels of E.coli bacteria and nutrients such as nitrogen in the discharged sewage water contributed  to the death of these kelp forests.

Read about how and when the Kelp forests off the Sydney coast disappeared in  'Operation Crayweed' on the SIMS website. 

b. Non-point  sources - these are sources of pollutants which are widespread. eg, stormwater run-off from roads, gardens and farms.

Both point sources and non -point sources contribute to a process called 'eutrophication'. This process  begins when large amounts of nutrients, usually nitrogen or phosphorous are washed into a water body eg, a coastal bay. 

Phosphorus and nitrogen  are examples of chemicals which act as nutrients and are found in  household garden fertilisers, detergents and sewage. Stormwater picks up the chemicals  from hard surfaces like roads or from the soil, which are washed into stormwater drains and discharged into oceans.

Large amounts of nutrients encourage the growth of algae and even the growth of algal blooms. Algal blooms  can be toxic to both fish and kelp. Even non- poisonous algal growth can be detrimental to kelp forests as the algae inhibits sunlight reaching the sea floor, which reduces the kelp's ability to photosynthesise.   Recently Sydney's coastal waters were inundated with polluted floodwaters. Read  about the  effects here  .

3. Siltation -  is the  process whereby silt (dirt or soil) is washed into  waterways and is either suspended in water or deposited on  the bottom of the sea floor.  Siltation usually reduces water quality because it produces water which is murky and unclear. The measure of the clarity or murkiness of water is known as turbidity.  High levels of siltation can interfere with photosynthesis as a silt layer can form on the kelp plant, or suspended silt can create murky water and reduce sunlight, which in turn may affect photosynthesis.

4. Alteration of food webs, such as overfishing.

The balance in any kelp forest ecosystem is easily disrupted or destroyed by human activities. Overfishing and over harvesting by humans of fish or other species can interrupt food chains and food webs. The loss of one species can lead to a modification of the ecosystem and/or an invasion by another species. A good example of this,  are the complex changes in the kelp forests of eastern Tasmania when the over- harvesting of lobsters complicated the effects of 'tropicalisation'. 

 Tasmanian lobsters were over-harvested during the 1990's which meant that there were not enough of these top predators to keep  the numbers of spiny black urchins in check. The numbers of spiny black urchins increased due to the EAC and 'tropicalisation'. The impact of both over-harvesting and 'tropicalisation' was the reduction of the Tasmanian kelp forests by 95%. (See  below for more information on 'tropicalisation'). 

Indirect Negative Impacts

Recently, the changing climate and warming oceans have increased the negative impacts by humans on kelp forests through indirect cause and effect processes. 

What are the threats and impacts of the changing 

climate ?    

The DPI and Environment NSW  have outlined how climate change has affected temperatures, currents, oceans and aspects of the marine environment that kelp live in. There are a number of reports which discuss the impact of the changing climate   on ecosystems and communities.

The following are the threatening drivers/processes associated with climate change and in turn, it is these threats which negatively impact kelp forests.

1. Increasing ocean temperatures 

  Sea surface temperatures have been increasing as well as the temperature of ocean water up to 500 metres in depth. The increase in temperature has led to the death of some kelp forests for eg. in Western Australia after extreme heat events between 2011-2015. Read about Impact of heatwaves on kelp .

John Turnbull (from www.marineexplorer.org) explains that warmer ocean water also holds fewer nutrients than cooler ocean water. As kelp likes water to be cooler and higher in nutrients the conditions for kelp forests becomes less favourable. 

Increased sea temperatures are predicted to change ocean currents and increase El Nino events along the east coast of Australia. This in turn is projected to increase the number of  extreme weather  events and lead to more physical destruction of coastal environments including individual kelp and kelp forests. 

Changing patterns of storms and rainfall events can lead to fluctuations in rainfall discharge to estuaries which affect salinity levels and siltation. This can impact the turbidity (clarity) of the water which has implications for the optimal growth conditions of kelp forests.

2. Changes to ocean currents and circulation 

 A rise in ocean temperatures  has lead to changes to ocean currents and circulation which in turn, has lead to a process known as 'tropicalisation'.  This process can be seen along the south east coast of Australia.  

The East Australian Current (EAC) has become warmer, stronger and, as a result now travels further south to Tasmania.  Tropical fish from further north travel in the EAC and  have invaded the kelp forests of north - east Tasmania.  It is the tropical fish, which are new to the temperate kelp ecosystem that consume the kelp plants.  Consequently, there are not enough adult kelp plants to produce enough young plants to rejuvenate and thus, the kelp forest disappears. 

At the same time a species of spiny black urchin also moved into the kelp forest and consumed whatever was left on the rocky surface. This created urchin barrens. The urchins were able to 'take over' because the natural predator, the lobster, was over-harvested, so there were not enough lobsters to keep the urchin numbers in check. 

Thus, a change in ocean temperature changed the ocean current which lead to 'tropicalistion' and the disappearance of most of the Tasmanian kelp forest.  Over-harvesting of the lobster species in Tasmania also played  a part in the disappearance of the kelp forest. 

Read about the impacts from urchin invasion here. 

3. Increase in average sea level  

 Global warming may impact the depth of the sea water that is above each kelp forest. Scientists from  'The Australian Academy of Science' predict that  -  

" By 2100, it is projected that the oceans will rise by a global average of 28 to 61 centimetres relative to the average level over 1986–2005 if greenhouse gas emissions are low, and by 52 to 98 centimetres if emissions are high." 

Kelp grows both sub-tidally ie, on the sea floor which is below the effects of the tide, and inter-tidally which is that part of the sea floor between the high tide and low tide. Given that kelp needs to be able to reach sunlight, an increase in the depth of seawater over a particular kelp forest may reduce its ability to photosynthesise. 

4. Change in seawater chemistry

The increase in Co2 emissions also affect the seawater chemistry. When carbon dioxide meets the surface of the water it dissolves and becomes carbonic acid.  The presence of carbonic acid reduces  the pH of ocean water from a normal level of between 8-9 (alkaline ) to a lower alkalinity of around 8. (Given pH is a log scale this is a significant change). This is called ocean acidification and it has implications for the survival of many parts of a kelp forest ecosystem. For example, young crustaceans eg, lobsters cannot form their shells in acidic seawater because the hydrogen ions present in acidic seawater interfere with the uptake of  calcium carbonate needed to form their shells.  Fewer crustaceans in a kelp forest may affect kelp forest ecosystem functioning.   

Refer to the Contemporary management  section to read about how different types of kelp can be used to manage ocean acidification.

Find out more about threats to kelp forests

Figure 32 : Shows the main threats to kelp forests in Sydney 

Source : John Turnbull www.marineexplorer.org

Sydney's changing reefs  webinar I YouTube I  57:03

 ReefLifeSurvey Transcript 

https://www.youtube.com/watch?v=t6NbjglbYGo

Figure 33 : Kelp growing on pylons at Chowder Bay, Sydney

Source : Observatory Hill EEC

Activities 

1. Watch  episode two of ABC's  Ocean Odyssey.

Or simply watch the section between 9 minutes and sixteen minutes. This part of the documentary illustrates the changes to kelp forests that have happened around the Solitary islands, near Coffs harbour NSW.  

Discuss the impacts of climate change on the kelp forests of the Solitary Islands in NSW. 

For more information watch 

ABC -  episode two  and other episodes of ABC's Ocean Odyssey  or 

Official trailer of Ocean Odyssey ABC .

2. Figure 32 outlines 6 main drivers (or threats) to kelp forests along the coast of Sydney. Outline how these threats  affect kelp forests.

3. 'Sydney's changing reefs' Youtube video and webinar takes 57:03 minutes to view however, John Turnbull from Reef Life Survey connects fish, invertebrate and kelp survey data to climate change,  tropicalisation and other threats like overfishing. Examine the slide titled 'climate winners' and 'climate losers' and explain why fish species can be categorised like this.

4. The NSW government recognises the key threatening processes to all ecosystems in the government's threatened species document. 

Name the two threatening processes which are relevant to the kelp forest ecosystem.

RLS Lap of Australia and Sydney I YouTubeI 4:55

Transcript 

Reef Life Survey of Australia and Sydney https://www.youtube.com/watch?v=3I4V9iRKCBE

Fieldwork to investigate human impacts 

1. Follow the earlier guidelines which help you think about the fieldwork and inquiry process. Choose a safe area along a beach or on a rock platform where kelp can be observed to be growing. 

2. Locate your area of study on a map - use your google map, Reef Life survey, DPI or SEED map to outline it's location and to describe the human activities, land uses, stormwater outlets, constructions and buildings near the foreshore in the area/catchment surrounding your fieldwork site.

3.  Draw a field sketch of your site and make note of significant natural features and human features such as break walls, jetties, wharves and so on.

4. Photograph areas where kelp is growing and not growing and outline possible reasons for the presence and absence of kelp eg, stormwater pipe, recent storms.

5. Outline possible positive and negative human impacts on the kelp forest.

6. BIOTIC environment - Use  transects or quadrats along the high tide mark or on the rock platform to observe elements of the kelp ecosystem. 

Observe and record elements which reflect evidence of invasion and modification and the kelp forests' resilience and vulnerability.

In each case you can use the methodologies referred to in biology online to count the number of species eg, kelp, urchins. 

7. ABIOTIC environment - Use instruments to measure water quality indicators and assess whether conditions  are optimal.

Observe and record elements which reflect evidence of invasion and modification and the kelp forests' resilience and vulnerability.

For example, take a water sample and 

• measure the turbidity 

• measure pH

• dissolved oxygen (proxy for bacteria ) 

• temperature 

8. For more information refer back to Using Fieldwork to investigate biophysical interactions 

9.  Use the photos in the carousel below to describe what fieldwork techniques and methodologies can be used to investigate kelp forest ecosystems and human impacts on kelp forests.

10. Read and view the video from biology online  to view two methods (methodologies ) which demonstrate how to use  quadrats and transects to collect data collection in the field. 

11. Using one of the methodologies outlined above ,can you calculate the number of kelp in an area and connect its numbers (or abundance) it to an abiotic or biotic (human) activity or threat?

Figure 34 : Identify the species of kelp located at your fieldwork site.

Source : Observatory Hill EEC

Figure 35 : Evidence of storm impact.

Source : Observatory Hill EEC

Figure 36 : Evidence of human activities and impacts.

Source : Observatory Hill EEC