Flora Collection - Harmful algal blooms and why they matter

Flora Collection - Harmful algal blooms and why they matter

Discover the inspiration behind the Flora Collection. Algae are a large and diverse collection of organisms living almost everywhere on the planet where there is water. They range from microscopic individual organisms invisible to the naked eye, to the more familiar coastal seaweed. Like plants, algae have the ability to photosynthesise, or put simply, make energy from the sun.

An algal bloom occurs when the algae have a rapid increase in growth. Just like us humans, algae thrive when the environmental conditions are perfect for their growth. These conditions include: nutrient (food), clear water for light availability, and generally warmer temperature.

Algal blooms are a natural phenomenon and are mostly beneficial to our planet. In the oceans, algae produce much of the world’s oxygen, absorb excess carbon dioxide and store it in the deep ocean sediments. They are at the base of the oceanic food chain, fuelling important fisheries and populations of large marine mammals we love to watch.

In fresh water, algal blooms provide food for fish and can help clean up pollution in waterways.

About harmful algal blooms

Harmful algal blooms or HABs occur when the growth of algae becomes detrimental to humans or other organisms either through excess growth or toxin production. Too many algal cells in water can irritate fish gills causing suffocation or may result in a sharp decrease in water oxygen content which can lead to fish kills and “dead zones”. Cell densities can reach millions per litre and turn the water’s surface into a variety of colours including red, white, green, orange, brown and yellow.

HABs are often referred to as “Red Tides” but this implies that blooms are very dense, red in colour and somehow related to the tide. The name is enigmatic and evokes biblical scenes of the sea turning red as blood, and when you see a red algae bloom it’s easy to see where the scene may have come from.

However, some species don’t have to be particularly numerous in the water to cause problems – one in particular, Alexandrium tamarense can cause the rather nasty paralytic shellfish poisoning (PSP) and shellfish harvesting areas are closed at cell densities of only 40 cells in a litre of seawater. Given that one litre of seawater can contain 100 million algal cells of many different species, the power of these small toxic algae to cause problems for humans is immense.

The costs of harmful algal blooms to fisheries, aquaculture and tourism can be high. Toxins produced by some algae can lead to mass mortality of marine life and shellfish poisoning syndromes in humans.

Supported by the International Society for the Study of Harmful Algae, the Flora Collection aims to explore the natural process of algal blooms, which is often beneficial, but can also cause so much harm.

Our designs focus on five mechanisms as five themes in which a HAB can be detrimental:

  1. Damage to fish gills;
  2. Water discolouration;
  3. Anoxia;
  4. Slime or foam formation and
  5. Biotoxin production.

Damage to fish gills

Diatoms are a group of microscopic algae with external glass skeletons (exoskeletons) made of silica. The diatom Chaetoceros has long, elegant spines, which increase the diatom surface area and help it stay in the sunlit surface waters where it can carry out photosynthesis. When this diatom blooms in high numbers the spines littering the water can cause damage to fish gills. Most fish can swim away from the area of the bloom, however, if the bloom occurs in a contained environment such as a lake or aquaculture farm, the fish cannot escape. The detached or broken spines clog the gills, causing inflammation, mucus production and haemorrhaging of gill tissue. The result is a fish kill by suffocation, where many fish die at once. This is one of the most dramatic displays of the power of an algal bloom.

Water discolouration

In summer 2016, beaches in Florida turned green. A harmful algal bloom in nearby Lake Okeechobee was discharged into waterways which transported the toxic green slime to the shore. The photosynthesising bacteria responsible, cyanobacteria, also known as blue-green algae, is one of the oldest and most important bacteria on earth. But some scientists believe its harmful blooms are being intensified by human activity, such as runoff from farms and city sewer systems. Climate change may also play a role. The 2015 massive bloom was Florida’s eighth since 2004. Appearing as swirls of scum or marbled paint, the water discolouration caused by a harmful algal bloom is rightfully a cause for alarm. Some blooms can even be seen from space and be visually striking, and strangely beautiful.


In Lake Erie, the Chesapeake Bay and the Gulf of Mexico, among other places, scientists are monitoring “dead zones”, areas with little or no oxygen resulting from harmful algal blooms. When algae in a bloom are growing rapidly, they are photosynthesising and producing large amounts of oxygen. But after a high-density bloom has grown to form a slick and discoloured the surface water, the growth rate slows as nutrients and space runs out. Cells begin to die off, dead algae sink out of the surface layer, and bacteria break down the organic matter resulting from the bloom growth and death. The bacteria respire – that is, they use oxygen and produce carbon dioxide, as humans do, and rapidly deplete the surrounding water of oxygen. Anoxia – the absence of oxygen – can be the result, which literally suffocates other organisms in the water body, causing the death of fish and invertebrates. Water circulation in the ocean helps to re-oxygenate the waters. In lakes and enclosed areas, however, anoxic waters can persist. Sometimes you will see large amounts of silvery fish floating dead in the water, a sad depiction with a raw serene beauty.

Slime and foam formation

Phaeocystis species are a group of algae that are ubiquitous in the world’s oceans, and are even found in sea ice. They are unique in forming colonies which are stuck together with a polysaccharide gel matrix. Blooms can be extremely dense, turning the water thick and gloopy, with the biggest blooms occurring in polar regions. Sometimes the blooms are frothed up by waves, creating huge quantities of thick and noxious smelling foam, which can blow onshore and engulf coastal areas. They can be unpleasant, but these blooms sequester a huge amount of carbon from the atmosphere due to the high carbon cost of the algae’s gelatinous homes. Phaeocystis blooms also produce vast quantities of a compound called 3-dimethylsulphoniopropionate (DMSP), the precursor to another compound, dimethyl sulphide (DMS). This gas helps to form clouds in the atmosphere, raising the Earth’s albedo or reflectiveness and thereby helping to regulate the global climate by reflecting the sun’s heat back into space – the power of small at its best.

Biotoxin production

Most shellfish eaten by humans are filter feeders; they sieve tiny organisms, including micro-algae, from seawater and will accumulate any toxins they ingest within themselves. There is no evidence this harms the shellfish: it is when humans eat the contaminated flesh that there may be very serious results. Cooking and other treatments don’t break down the toxins and the effects can be fatal – there are no antidotes to counteract the ingestion of algal toxins. In countries with economically important shellfish industries, such as Scotland, routine monitoring of shellfish and the waters they live in is typically in place. The Scottish Association for Marine Science (SAMS) near Oban is responsible for testing water samples from all around the Scottish coast for toxin-producing species. Shellfish samples are analysed for toxins by the Centre for Environment, Fisheries and Aquaculture Science in Weymouth. Increasingly, scientists are getting a stronger hold on this complex and yet fascinating issue.

The Flora Collection was inspired by science from The Scottish Association for Marine Science. 

It was developed in collaboration with Dr Ruth Paterson and The Scottish Association for Marine Science (SAMS). 

SAMS is Scotland’s largest and oldest independent marine science organisation, dedicated to delivering marine science for a healthy and sustainable marine environment through research, education and engagement with society.

The International Society for the Study of Harmful Algae

The development of the Flora Collection was generously supported by a grant from the International Society for the Study of Harmful Algae. The society was founded in 1997, in response to a request from the Intergovernmental Oceanographic Commission (IOC) of UNESCO for an international programme on harmful algae. The overall mandate of the society is to promote and foster research and training programmes on harmful algae, and to co-sponsor meetings on this topic at the national, regional, and international level.

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