The unique characteristics of kelp forest ecosystems  

What is kelp?

Kelp is the most common type of seaweed which attaches to the sea floor. Kelp is actually a type of brown algae and is a very simple aquatic plant.  Kelp generally grows between 30cm to 10 metres long. Although it can be green, red or brown in colour, common kelp is part of the brown algae family. The seaweed which is washed up on the beach is usually kelp and when kelp is found  on the surface of the water or on the beach it is called 'wrack'.  

What is a kelp forest ecosystem?

Kelp ecosystems are marine ecosystems in which  kelp (which are the larger seaweeds ) grow and dominate to form an underwater community, made up of smaller seaweeds, algae, fish, crustaceans and other species. 

What is the difference between kelp and seaweed ?  

Seaweed is the common name given to all multi-celled macro-algae in the seas and oceans. Macro-algae simply means larger algae. Seaweed can range from microscopic in size to very large. Whilst kelp is a type of seaweed,  kelp is the name given to the larger seaweeds that form canopies or beds or forests, eg, Golden/brown Kelp ('Ecklonia radiata') and 'Giant kelp'. 

Most seaweed (macro-algae) fall into three basic groups:

1. the green algae family - often found in shallow waters, eg, rock-pools.

2. the brown algae family that include kelps and giant kelps .

3. the red algae family - often found growing in low light conditions eg, under a kelp forest.

Look at the photos of the  Range of Kelp  plants here.

Watch the first part of the video by the Royal Botanic Gardens to learn about different seaweeds.

Kelp ecosystems should not be confused with  seagrass and coral ecosystems.

This case study will focus on the larger and most common type of seaweed known as  kelp.

The kelp forest ecosystem

A kelp forest is formed when individual kelp grow together and cover a large area of the sea floor.  A kelp forest is like a forest on the land, in that the kelp plants form a canopy which usually shades the other species of plants and animals that thrive in and below the canopy.  When kelp grows together and is much shorter in height (less than approximately 30cm), it is often referred to as a kelp bed. However, the term kelp forest can be  used to describe both kelp forest and kelp bed ecosystems.

See figure 5 which shows the structure of a KELP plant. 

Watch Youtube  Golden Kelp: Foundation species or click on the YouTube video 'Golden Kelp'.

Healthy kelp forests contain a network of food chains and food webs and support high levels of biodiversity. Kelp is considered a foundation species by scientists. This means that kelp is necessary to the whole ecosystem as it provides food, habitat and shelter for many other species, for example, sponges, sea squirts, corals and barnacles. The essential role that kelp plays in an ecosystem is shown in figure 6. 

Where are kelp forests found ?

Kelp  forests are found on rocky reefs in marine waters below the high tide mark, where water is shallower.  However kelp forests can grow in water up to a depth up of approximately 30 metres. 

A rocky reef is simply an outcrop of rocks and boulders on the sea floor.

Kelp forests are found in temperate areas across the world, where the marine waters are on average less than 20 degrees Celsius. 

In  Australia kelp forests are found off the coast of south- east, south and southwestern Australia. 

What conditions determine the growth of kelp forests?

There are many important aspects of the abiotic environment  which are essential for the survival of kelp forests. These include-

1. Cooler water temperatures, ie, Kelp forests are found in areas where marine waters are on average less than 20 degrees Celsius. In some cases kelp can grow in areas where the sea temperature reaches 26 degrees celsius.

2. Sunlight  - access to sunlight is important so that photosynthesis can occur. 

3. Shallow water is important so sunlight can be absorbed. Some kelp can grow in waters up to 30 metres in depth.

4.  Marine salinity levels should be in the normal range. Kelp is not found in fresh water.

5.  Water quality should be in the normal range - importantly, this includes clear water (not turbid).

6. Waters should be nutrient rich - Kelp thrives in cold-water ecosystems where nutrient-rich water from the deep sea makes it up to the surface, a process known as upwelling. Abundant nutrients allow some types of kelp to grow up to almost a metre a per day.

7. Marine waters which have 'medium energy' are most ideal - high energy waters (strong waves) can destroy kelp.

Importance of kelp forest ecosystems 

The kelp forests along the east coast of Australia are significant to the functioning of the whole marine environment and are valuable to the Australian economy.  

Kelp forests provide a complex habitat for many species including abalone, crabs, sea dragons, fish and sharks. Kelp forests support coastal food webs and therefore support the Australian fishing, tourism and recreation sectors. Kelp forests are important as marine 'sinks' of carbon dioxide and are part of an emerging 'blue carbon' economy.

In the document written for the United Nations  the importance of seaweed and kelp forests are recognised. 

Kelp forests at risk

In many countries across the world and in Australia there has been a significant decline in the size and density of kelp forests over recent decades. 

Scientists suggest some reasons for this decline include ocean warming, 'tropicalisation', overgrazing and pollution. Along the NSW  coast the decline has most likely been caused by polluted water and the strengthening of the Eastern Australian Current. 

The main strategies which have been developed to manage the decline in kelp forests are government established marine parks and reserves,  restoration and replanting projects  and community education programs.  

Kelp forests are part of larger aquatic and marine ecosystems. The Department of Primary Industries (DPI) manages most of the aquatic ecosystems of NSW.