The days are getting longer, the beaches more crowded - it’s the bloomin’ algae season but principal research scientist at the Royal Botanic Gardens, Professor Alan Millar, says have no fear, those dreaded seaweeds come in peace….

So you think algae stuffs up our beautiful beaches, fouls our precious swimming pools, dams and water supplies, makes the patio slippery, and pretty much ruins what should be a comfortable existence of antibacterial, squeaky clean heaven? Well - it is time to set the record straight and hand out some serious, sobering and important facts about algae.
The term algae encompasses organisms that are primitive. They include both single-celled and multi-celled plant-like organisms that have been enjoying the delights of this planet for some 2 billion years. They occur in every habitat including the air, soil, rocks, freshwater, saltwater and snow. Take three deep breaths as you read this. The oxygen in two of those breaths was brought to you by the courtesy of marine algae. Think about it. The planet’s surface is 70% covered by seawater.
Every litre of water, has many thousands to millions of marine algal cells happily photosynthesizing – taking up carbon dioxide and using the sun’s energy to produce carbohydrates and oxygen. Almost every coastline on the planet has seaweeds growing on the rocks. We simply could not breathe without them. It is often said that rainforests are the lungs of the earth.
Kelp forests, the giant Macrocystis beds of the northern Pacific and temperate coasts of the southern hemisphere continents, are four times more productive per square metre than any place on earth. Macrocystis pyrifera has been clocked at a staggering growth rate of 50 cm per day. You can actually watch it grow! In the 1970s, 140,000 tons of wet weight were harvested every year from the state-owned kelp beds off the Southern Californian coast for the extraction of alginates, colloids widely used in industry and in the preparation of certain foods.
There are still vast stretches of Australia’s coastline that have not had the seaweeds documented, but we know of about 4000 different species to date, making this continent the richest in biodiversity of any country. Japan is a close second with about 1800 species and the north east coast of North America has about 800 species. The southern seaboard of Australia, the longest longitudinally spanning coast on the planet, from Cape Leeuwin in the west to Cape Howe in the east accounts for a staggering 1400 species. These seaweeds fall into three basic groups, the green algae (such as sea lettuce or Ulva), the brown algae (kelps) and the red algae (e.g. corallines).
There are a group of marine red algae (seaweeds), known as crustose corallines, that form crusts on rocks in the intertidal and in the subtidal regions of the coasts. They make the rocks and pebbles look pink or mauve. These seaweeds produce a different form of calcium carbonate to other organisms, that is known as calcite, not aragonite which is the more usual form. In laying down the chalk in their tissues, and growing over the rocks, they also actively bind sediments to form reefs and shoals. Our coastlines are being changed continuously by their very growth.
While on the subject of red algae, another major misconception is that Red Tides are caused by red algae. Red algae (the phylum Rhodophyta) are multicellular seaweeds that are non-toxic. In fact there are no seaweeds (green, brown or red) that are known to be toxic.
When Captain Cook was exploring the east coast of Australia, his ship’s log mentions many instances of water discolouration (algal blooms) that we now know were probably blooms of the blue-green alga Trichodesmium erythraeum. In New Zealand, the dinoflagellate Noctiluca scintillans causes massive and stunning blooms, bright red tides that are non-toxic and harmless to fish and humans. Seaweeds are also capable of forming huge blooms and in every instance, are non-toxic and harmless.
For all plants, spring is a time of increased daylight and water temperatures, and for the oceans, often subsequent nutrient increases, and thus growth spurts and blooms are often a natural annual phenomenon. Because of the development of our coastal regions (our desire for sea changes), seaweed blooms are being noticed more regularly these days and many people put this down to anthropogenic influences. However, the regular occurrence of blooms over the past 200 years (since European records started), plus our increased knowledge of algal biology lead us to accept the fact that the majority of algal blooms along the coast of Australian are natural occurrences and consist of native, non-toxic and harmless marine algae.
We think nothing of the Frangipani bursting into bloom in spring, or the Jacaranda or the Star Jasmine, or a myriad of many other flowering plants, yet we freak out when those pesky seaweeds have the audacity to wash up on our clean beaches. 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 (this increases their photosynthetic rate) and water temperatures. One of the classic examples of a natural algal bloom caused by natural events was in Jervis Bay in December 1992.
The bloom reached cell densities of 180 million cells per litre (glad I didn’t have the job of counting them) and turned the Bay a dramatic milky blue-green colour.In my 30 years of documenting the seaweeds of the Australian coast, I have witnessed subtidal algal blooms of truly massive proportions that remain completely unnoticed by the beachcomber simply because a storm has not ripped them off the seabed and washed them up on the beach. In 1991, just off Honeymoon Bay in Jervis Bay, the old scallop beds in 12 m of water were covered in a huge bloom of Halymenia kraftii. At the very same site two years later I witnessed a bloom of Ceramium lentiforme, a small red seaweed I had newly discovered elsewhere in NSW. Just off Hole-in-the-wall” on the southern part of Jervis Bay, there was a bloom consisting of three different species of the large bladed red seaweed Kallymenia. In one instance that was noticed in the 1990s, a massive bloom of the multicellular red seaweed, Acrosorium ciliolatum was washed up in tonnes on the beach at Greenpatch and at the same time the red seaweed Rhodymenia caulescens was on the beach at Huskisson. The residents of Jervis Bay and the Council went into catatonic shock – it was nothing short of Armageddon. Acrosorium and Rhodymenia are native on most Australian coasts and are non-toxic and completely harmless. Under the microscope, they are actually quite pretty.We will have to live with and love these seaweed blooms. They are mostly a natural phenomenon, have been occurring in Australia long before we were even thinking about climbing out of the trees, are an excellent affirmation of our fantastically biodiverse seaweed flora in Australia, and if they are not washing up on our beaches, we should be afraid, we should be very afraid. Next time you see seaweed washed up on your beach, relax, take three deep breaths and thank the algae.