Coastal and estuarine algal blooms
- What is a bloom?
- Harmful vs nuisance algal blooms
- Common bloom-forming algae
- What causes algal blooms?
Coastal and estuarine algae are protected marine plants in Queensland, playing an important role in aquatic ecosystems. However, when environmental or climatic conditions are favourable their capacity for rapid growth and expansion can lead to large blooms that negatively impact on public health, amenity or the environment. In Queensland, awareness of coastal algal blooms and their impacts has increased following a decade of seasonal Lyngbya blooms in Moreton Bay.
What is a bloom?
Algal blooms refer to the overgrowth of algae (e.g. microalgae, macroalgae or cyanobacteria) in response to natural or human-induced changes to the environment. Algal blooms can have a major detrimental effect on estuarine and marine environments. In addition to some blooms being toxic, they also degrade recreational amenities and fisheries, affect natural ecosystems and potentially impact on the tourism industry.
Harmful vs nuisance algal blooms
Algal blooms can be either ‘harmful algal blooms’ or ‘nuisance algal blooms’ in terms of their impact on public amenity, public health or the environment.
Harmful algal blooms
A harmful algal bloom (also referred to as 'phytoplankton blooms', 'microalgal blooms', 'toxic algae' or 'red tides') is one where the alga species produces toxins that pose a threat to human and/or animal health or the environment.
Potential impacts can include:
- contamination of seafood, aquaculture products and marine species;
- contact with toxins, either dissolved in sea water or present in the algae, during recreational or commercial water activities;
- inhalation of toxins released to the air from algae drying on the shoreline;
- inhalation of harmful or irritant gases released from decomposing algae;
- disruption to recreational and commercial activities that are reliant on good water quality and safe recreational areas (e.g. fishing, aquaculture, seafood and tourism industries).
Nuisance algal blooms
A nuisance algal bloom is one where the alga species is not known to produce toxins and primarily affects public amenity. Impacts can include:
- odours, oxygen depletion and an over-abundance that restricts or excludes other uses in the affected area;
- environmental harm such as damage to seagrass beds from smothering by algae, or fish kills from oxygen depletion;
- potential health effects as a result of odour or particulate/gas emissions from decomposing algae on the shoreline.
Common bloom-forming algae
There are a number of different bloom-forming coastal and estuarine alga species found in Queensland waters including those which may be toxic and algal drifts which are often mistaken for algal blooms. These include red, brown and green macroalgae, cyanobacteria, dinoflagelates and diatoms.
Further information on common bloom-forming species can be found on the South-east Queensland Healthy Waterways Partnership website. This includes:
- A Fact Sheet for Healthy Waterways providing further information on coastal algal blooms in south-east Queensland;
- A Coastal Algal Blooms Field Guide to assist with identifying common algal blooms and drifts in the coastal environments of south-east Queensland.
Any data gathered can be entered into the Algal Bloom Online Observation Registry to track the location of algal blooms in our marine and estuarine environment at <www.algalblooms.org>.
Further information and links to guidelines for collecting, identifying and analysing algal samples are available.
Examples of recent algal bloom occurrences in south-east Queensland’s coastal and estuarine waters are listed below.
Lyngbya majuscula
Lyngbya majuscula (Lyngbya) is a naturally occurring, toxic, marine cyanobacterium. A review of the historical occurrence of Lyngbya blooms, based on anecdotal accounts from fishermen of ‘Lyngbya-like’ blooms, has suggested blooms have occurred in the region for at least the last 100 years. However, since the late 1980s blooms have been recorded with increasing incidence, duration and intensity in the coastal waters of Moreton Bay including southern Pumicestone Passage, northern Deception Bay, southern parts of Moreton Bay, Redland Bay and on the Eastern Banks. Further information on Lyngbya including monitoring updates can be found here.
Lyngbya growing on seagrass in Moreton Bay (courtesy: University of Queensland).
Hinksia sordida
In 2003–2005 Noosa main beach and the Noosa River were affected by large recurring blooms of Hinksia sordida (Hinksia) during the summer months (generally from October through until February). These blooms are not just a local occurrence, but rather a regional phenomenon that affects the coastal area from Fraser Island down to Noosa.
Hinksia bloom at Noosa Beach (courtesy: Sunshine Coast Regional Council).
Trichodesmium
Trichodesmium is a naturally occurring cyanobacteria. Blooms are a common natural event that can occur along Queensland’s coastline, generally between August and December. The foul smelling patches of Trichodesmium can often be mistaken for oil slicks. Generally, Trichodesmium is not visible. However, during extended calm water periods. it can rise to the water surface and form clumps of brown threads that resemble sawdust sprinkled on the ocean surface. Larger patches could be grey, green or purple with streaks, which to the untrained eye can easily be confused with an oil slick or coral spawn.
This type of bloom was documented by Captain Cook’s expeditions in the 1770s and is not caused by pollution or human impacts. It occurs on a similar scale in tropical seas in other places around the world. The blooms can have a putrid fishy smell and, if washed up on shore, the smell will generally disappear within a few days. Blooms of Trichodesmium have been reported along the entire Queensland coastline with suggestion that the intensity and frequency of blooms in recent years is increasing.
Trichodesmium bloom in the Great Barrier Reef Marine Park (courtesy: University of Queensland).
What causes algal blooms?
Whilst algae occur naturally within aquatic ecosystems, the occurrence of an algal bloom can sometimes indicate that processes normally controlling the algal population have failed, for example, a lack of grazers or an increase in nutrient levels. These can be the result of natural processes or changes associated with human activity.
Blooms occur when favourable conditions cause the rapid growth of one (or several) algae species allowing them to dominate the aquatic ecosystem. Environmental conditions influencing algae growth include:
The diagram below compares the environmental conditions of coastal waterways associated with a low and high frequency of algal bloom occurrence.
The environmental conditions of waterways associated with a low and high frequency of algal bloom occurence. Source: Coastal Algal Bloom Action (SEQHWP, 2008).
Nutrients
Elevated nutrient concentrations, particularly nitrogen and phosphorus, in an aquatic environment can promote algal blooms. Nutrients enter waterways through natural processes and as a result of human activity. Major sources of nutrients include sewage effluent, urban run-off, and erosion and run-off from fertilised agricultural areas.
Trace elements (e.g. iron)
The growth of some algal species can depend on the availability of essential trace elements such as iron, molybdenum and zinc. Iron influences the growth of Lyngbya majuscula in Moreton Bay. In other places, iron has influenced Trichodesmium blooms. Typically, the level of ‘bioavailable’ iron in sea water is very low and not enough to support a bloom. However, additional iron entering the waterway via groundwater or surface run-off may lead to an algal bloom. Potential sources of iron include podosol soils (coffee rock), disturbed acid sulfate soils and river sediments. Land uses such as sand extraction, sugar cane production, marinas, aquaculture, bores, cleared catchment, horticulture, dredging and forestry may trigger the release of iron from these sources.
Light
Exposure to increased light levels can lead to algal blooms. However, under low light conditions, blooms can still occur with inputs of high nutrient concentrations. For example, in highly turbid water large amounts of suspended sediment and organic matter limit light availability, but algal growth is enhanced with the input of nutrients. As such, in coastal waters, algal growth is often restricted by a combination of limited light and nutrient availability.
Water flow and circulation
Blooms are less likely to occur in well-flushed waterways as there is a shorter residence time of nutrients and algal biomass. Onshore currents and winds may concentrate algae in embayments, which is thought to be the reason for Hinksia sordida blooms in the surf zone of Noosa main beach in south-east Queensland.
Temperature
Algae respond to water temperatures, with warmer waters often causing accelerated growth leading to algal blooms. The temperature of coastal waters varies with daily and seasonal cycles caused by variations in solar radiation, air temperature and local hydrodynamic processes (e.g. currents).
Season
In sub-tropical areas algae tend to bloom in the warmer months, when water temperatures are higher and when there is increased light. Under stable weather conditions there are low levels of mixing in coastal waters, creating favourable environmental conditions for algal growth.
Last updated 6 July 2011