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Issues Water QualityConditionHarvesting and Marine FarmingGlobal Change |
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At a glance 
The issue Algae are aquatic plants that grow either as single cells or as aggregations. Algal blooms occur when the growth of algae is excessive. When conditions are suitable, algae multiply rapidly until all the available nutrients are used or conditions once again become unfavourable for their rapid growth. Nutrient loads from human settlements may result in increasing numbers of algal blooms in estuaries and marine environments. Sources of nutrients include discharge of sewage waters, urban and agricultural run-off, the use of phosphorous containing detergents, and marine farm organic enrichment. An increase in nutrient levels in estuaries can result in a change in dominant algal species. Certain species of algae (such as blue-green algae and dinoflagellates) produce toxins that are a health hazard to humans and ecosystems. This 'At a glance' section provides an overview of the issue of algal blooms in estuaries and marine environments. More detailed information and references are available in the Algal Blooms Issue Report. Indicators for algal cell and chlorophyll a (referred to as chlorophyll) concentrations are presented in the 'Indicator' section of the Issue Report. Chlorophyll a is a photosynthetic pigment that is a proven indicator of the biomass of microscopic plants such as unicellular algae. While there is no specific recommendation for algal blooms, there are a number of related recommendations provided. Favourable news - New information has been obtained on estuaries with some data relating to eutrophication and algal blooms. A study was conducted by the Tasmanian Aquaculture and Fisheries Institute (TAFI) with funding under the Natural Heritage Trust to assess water quality in Tasmanian estuaries (Murphy et al. 2003). Major objectives of the study were to provide baseline water quality data and determine water quality indicator levels for 22 Tasmanian estuaries.
- The Tasmanian Shellfish Quality Assurance Program provides ongoing monitoring for water quality testing in shellfish growing areas. The Program was set up in the mid-1980s to evaluate and classify all commercial shellfish farming areas in the State by way of routine bacteriological, chemical and biotoxin monitoring. It is applicable to the issue of algal blooms because the program routinely monitors for occurrence of algal species that produce toxins, which may be concentrated in shellfish. Toxic dinoflagellates accumulate in shellfish and if eaten by humans can cause Paralytic Shellfish Poisoning, a potentially fatal condition.
- The Estuarine Health report (Murphy et al. 2003) indicated that for 16 out of 22 estuaries studied in Tasmania, chlorophyll levels were generally in the low to medium range. There are 111 moderate to large estuaries along the coast of Tasmania (Edgar et al. 1999).
- The State of the Derwent Report (Coughanowr 1996) indicated the Derwent estuary did not experience recurrent nuisance algal blooms, despite relatively elevated concentrations of nutrients in the middle and lower reaches of the estuary. However, toxic dinoflagellates bloom periodically in the Derwent (and the Huon) and are sometimes called 'red tides'. The second State of the Derwent Report was released in November 2003.
- The Huon Estuary Study, conducted from 1996-1999 (CSIRO 2000), provided environmental data for integrated catchment management and aquaculture. This included an assessment of algal blooms and the links between algal production and catchment and estuary activities. The study found that the estuary is generally in a good condition.
Unfavourable news- While the CSIRO Huon Estuary Study (1996-1999) found that the Huon estuary is in a good condition, two classes of algal blooms typically characterise the Huon Estuary in the spring to autumn period of most years, one of which includes the toxin-producing dinoflagellate, Gymnodinium catenatum (CSIRO 2000). However, there is some uncertainty about the relative contributions of different nutrient sources to the occurrence of algal blooms in the estuary (see 'Uncertain news').
- The Estuarine Health report for 22 estuaries (Murphy et al. 2003) reported that some estuaries in the north-east of Tasmania are susceptible to eutrophication (including algal blooms) based on high recorded levels of chlorophyll. Ansons Bay regularly recorded high to very high chlorophyll levels and the upstream sections of Little Musselroe estuary and Boobyalla Inlet were medium-high upon occasion. In other parts of the State, the Meredith, Browns and Don River estuaries also showed high to very high chlorophyll levels on some occasions.
Uncertain news - There is considerable variation in the definitions for algal blooms, and without data on natural levels of algal cells in Tasmanian estuaries, it is not possible to report on the occurrence or frequency of 'algal blooms' at the State level.
- Information available on the total algal cell and toxic algal cell concentrations at estuary sites (with no inference for algal bloom frequency) around Tasmania indicated considerable variability between the different sites both over space and time. Without data on the natural algal cell levels it is impossible to say if such variability is a function of natural fluctuations in algal cell levels over time or space, or if variations are indicative of significant ecosystem imbalances due to impacts from human activities.
- An indicator that reports on the number of blooms per estuary may reflect monitoring intensity rather than the actual number of algal blooms relative to other Tasmanian estuaries.
- The 'Report Card' (DPIWE 2000) on the 'Status of the Derwent Estuary' in 2000 indicated that the nutrient and chlorophyll data were difficult to interpret due to a short record and considerable natural variability. Nutrient levels were somewhat elevated at mid-estuary sites, however, chlorophyll levels were usually moderate to low. There were no clear trends for most of the estuary, with the exception of Prince of Wales Bay, where chlorophyll levels have doubled since 1996.
- The study by Murphy et al. (2003) provided information on which estuaries may be more susceptible to eutrophication, but did not provide information on the types of algae (e.g. toxic types). The study was also a 'one-off' to identify baseline conditions and future monitoring is uncertain because there is no formalised program in place.
- There is uncertainty about the relative contributions and impacts of different nutrient sources-land use in catchments, sewage treatment plants, fish farms and the Southern Ocean-in many estuaries.
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