An initiative of Earthwatch Institute

  1. Bull_kelp_on_rocks_arthur_chapman Bull kelp on rocks by A. Chapman

Bull Kelp

Durvillaea potatorum


  • Bull kelp is a very large brown seaweed (algae)
  • It has dark brown leathery, strap-like branches (thallus). 
  • It attaches to the substrate by a large disc or conical-shaped holdfast. 
  • Usually there is a single leathery frond (stalk) from the holdfast, which divides into long segments or fronds.
  • Size: up to 8 m long, holdfast up to 25 cm across.

What to Observe

Search area for 30 minutes and record under the following categories:

  • Abundant - found easily with little searching
  • Frequent - found with minimal searching
  • Rare - only 1 or 2 individuals found with intensive searching
  • Not found - not present during search

ClimateWatch Science Advisor

As a result of climate change, warm tropical ocean currents are expected to strengthen and persist for longer periods in southern coastal area normally dominated by cooler waters. The consequent increases in water temperature are likely to result in unfavourable growing conditions for cool water algae species, causing a loss of seaweed in some areas.

When To Look

Throughout the year.

Where To Look

  • Around the low tide mark on exposed coastlines, particularly where there is rough water or considerable wave action. It has been seen at depths of up to 30 metres but is usually seen clinging to rocks.
  • Washed up on beaches after storm events 
  • In southern Australia from Robe in South Australia to Bermagui in New South Wales, including the west, south and east coasts of Tasmania and King Island in Bass Strait.
 Bull Kelp distribution map - GBIF

Bull Kelp distribution map - GBIF


  1. Search Species

  1. What Else?

    Durvillaea antarctica, the dominant species in shallow waters around Macquarie Island, may occasionally be found washed ashore in southern parts of Tasmania.

  1. Did You Know?

    It is also found along the coasts of Chile and New Zealand.

    Its strong holdfast often pulls a piece of granite off when detched during storms and this can remained attached when washed up on beaches.

    Plants can reach 200 kg in weight.

    Kelp can live up to 14 years and can grow at the rate of 10 – 14 cm a day.