Botanic Gardens Trust, Sydney, Australia

Marine algae

Dr Alan J.K. Millar, Principal Research Scientist & Yola Metti

My research work with the Royal Botanic Gardens & Domain Trust has resulted in the discovery of more than 50 new species of seaweeds. When you're in the Royal Botanic Garden look over the wall into Farm Cove and if it’s low tide you may be able to spot the seaweeds below - especially one that looks like green fettucini, called Caulerpa filiformis, and also a brown kelp called Ecklonia radiata. These are just two of the 2000 different species of seaweeds we have in Australia - the continent with the richest seaweed flora on earth.

Why is it that we think nothing of the Frangipani bursting into bloom in spring, or the Jacaranda or the Star Jasmine, or a myriad other flowering plants, yet we freak out when those pesky seaweeds have the audacity to wash up on our clean beaches? Seaweeds are the most important organisms along our spectacular coastline. They help to bind sediments to make shoals and rocky reefs, they oxygenate the waters for fish and invertebrates that don’t have the capacity to photosynthesize, and they take up a lot of carbon dioxide in this process and thus help reduce our footprint. Nutrient fluxes are often seasonally driven, but can also be catalysed by heavy rains after long dry spells. The nutrients flushed into the oceans from rivers, creeks and streams generally disperse and are rapidly diluted as they enter the vast open oceanic coasts. Not all algae bloom when exposed to increased nutrients. Much like eastern suburbs humans and their coffee preferences, some algae like a latte, or a macchiato, or flat white, or short black or sometimes bloom due to no effective input at all (a skinny decaf). Algae are not responding necessarily to increased nutrients, but to increased day lengths and water temperatures. Recent research by Dr Alan Millar at Roscoff on the Britany coast of France, where he was invited to help teach a course on marine algal biodiversity, has shown that there are some coastal regions where algae bloom almost continually throughout the year. Thirty years documenting the marine algae of the NSW coastline by Dr Millar is starting to produce long term evidence of naturally occurring algal blooms that are not always associated with ocean outfalls that dot the entire coast. What is interesting is that the algal species involved in these regular blooms are different each time. One year it may be a red alga such as Ceramium lentiforme, a species newly described by Dr Millar in the 1990s. More recently around the southern coast of NSW it was the brown filamentous alga Hinksia sordida. Only in these instances does the term ‘seaweeds’ take on a more noxious meaning.

Read reports for Marine algae 2012-2013Marine Algae 2011-2012, Marine Algae 2010-2011 and Marine Algae 2008-2009

Did you know?

  • Seaweeds are plants - they are marine algae.
  • Seaweeds use sunshine to convert carbon dioxide into carbohydrates (photosynthesis).
  • Seaweeds and their relatives (phytoplankton)  produce more than half the world’s oxygen.
  • Without marine algae, the seas would be sterile and there would be no animals on land (even humans).
  • Some seaweeds grow up to 30 cm a day.
  • Kelp forests are more productive than rainforests.
  • We use a by-product of seaweeds (called agar) every day - in toothpaste.
  • Scientists who study seaweeds are called ‘phycologists’ from the Greek phykos for seaweed.

Genetics of Caulerpa taxifolia

In March 2000, the marine macroalga Caulerpa taxifolia was discovered in NSW waters. This species is a pan tropical native and its appearance in temperate waters has been causing massive problems in the Mediterranean, California and now NSW and South Australia. Using genetic ‘markers’ or DNA fingerprinting, we can now trace the invasive strain’s travels around the globe. Native, naturally occurring specimens from Queensland were sent to the Stutgart Aquarium in Germany in the 1970s. Over the period of about 15 years, they inadvertently managed to develop a cold tolerant, fast growing strain, which looked excellent in aquaria and was almost impossible to kill. Through a market driven demand, the invasive strain was sold to many aquaria in Europe and around the world. The Oceanographic Institute in Monaco accidentally released it into the Mediterranean (where it now covers 11 000 hectares of ocean seabed), Aquaria in California did likewise, and its appearance in NSW and South Australia was via a similar vector. So the strain started in Queensland, went to Europe, then was brought back to Australia.  Rock or Sea salt is being used by NSW Fisheries to eradicate the alga. The rapid blast of high salinity appears to kill the alga but do minimal damage to the seagrasses and associated invertebrates.  

New Caledonia

Through a joint French/Australian Government initiative, we have been able to collect marine plants from coral reef areas of the outer lagoon near Noumea, New Caledonia. While our collections have added 40 new records to the region, we have also discovered several new species and genera to science.  Apart from typical tropical algae growing on the reefs (species commonly found on the Great Barrier Reef), there were also some very interesting and unusual range extensions discovered.  At least three formerly southern Australian endemic species were found growing quite healthily in deep water off the reef edges.  Molecular sequencing of these particular genera and species will more clearly demonstrate the true relationships between these disjunct populations.

Threatened species

Could marine plants be threatened with extinction? We believe there is a real risk and ascertaining which species are rare and vulnerable. This was the subject of a symposium held in Ireland at the European Phycological Congress in July 2003.

Aussie marine algae

Marine algae include the tiny microscopic phytoplankton of the oceans as well as the larger seaweeds that we see washed up on our beaches. This website deals only with the seaweeds, although links to other databases that cover plankton are suggested. General information on reproduction and life histories is covered and this will be expanded and updated. It is hoped this will aid primary, secondary and University students to better understand marine plants.

For the phycologist and scientist, this database will allow you to search for all the seaweed genera and species we have in our collection here at the National Herbarium of NSW at the Royal Botanic Garden in Sydney. It will also allow you to find what species may grow in your area, especially the NSW coast, but also to a lesser extent the Australian continent. Because this search facility is directly linked to our database, the information is live and thus updated every time a new voucher specimen is inserted.


Marine Algae
Intertidal seaweeds of Ile de Batz, Roscoff on the Britany coast of France Photo: A Millar


Alan diver



Dr Alan Millar

Our team

Some species of marine red algae

Dasya cystocarps
Dasya cystocarps

Ceramium juliae
Ceramium juliae

Cepalocystis leucobotrys
Cepalocystis leucobotrys


Dicroglossum crispatulum
Dicroglossum crispatulum

Claudea elegans
Claudea elegans

Hemineura frondosa
Hemineura frondosa