Indicator description

Why is it indicative

What does the data show

Data

Acknowledgment

Indicator description

The frequency of algal blooms, and dominant species of algae responsible for them.

This specified National SoE indicator description cannot be report on in Tasmania because of significant differences in the definitions for algal blooms (see 'Data' section below). Instead, information is presented on the total concentrations of algal cells and toxic algal cells for sampling periods at various sites around Tasmania, with no inference made as to the number of algal blooms occurring.

Why is it indicative

Water has many environmental values including recreation and the protection of aquatic ecosystems. The maintenance of these values is a critical environmental issue.

The frequency of algal blooms is usually related to land based sources of nutrients. A reduction in inputs of nutrients, leading to fewer algal blooms, is the desired target for Australian waters. Nutrient concentrations alone are inadequate for understanding nutrient conditions. The calculations of nutrient loads are more useful but are expensive to measure. Chlorophyll a concentrations are a more direct indicator of algal biomass while algal bloom events may indicate algal species outbreaks that can directly threaten biodiversity, water quality and human health.

What does the data show

• The data indicates high variability in total algal cell and toxic algal cell concentrations between the different sites both over space and time. Due to the lack of a single definition for algal blooms, it is impossible to say if such variability is a function of natural fluctuations in algal levels or if variations demonstrate significant ecosystem imbalances due to the impact of human activities.
   


• In August 2001, the Mercury reported the detection of the toxin producing dinoflagellate, Pfiesteria piscicida. Little is know about the history of the organism in Tasmanian waters and recent findings seem to be the result of increased detection capability of new molecular techniques. The species has been known to affect human health, and fisheries in mid-Atlantic and south-eastern estuaries. The issue is raised as relevant to this indicator, given the organism's potential toxicity, even though concentrations of the dinoflagellate in Tasmania were not at bloom levels. The organism may have actually been present in Tasmanian waters at such low levels for a long period of time with no serious deleterious effects due to the unsuitable conditions within Tasmanian waters (low temperatures) for the initiation of blooms.
   


• A non-toxic dinoflagellate, Noctiluca scintillans, causing pink water colouration was found in bloom conditions at Triabunna and Nubeena in 2000. This may have moved with ocean currents from eastern Australia.
   

Data

Data are collected by the Department of Health and Human Services (DHHS) as part of the Tasmanian Shellfish Quality Assurance Program, which assesses shellfish growing areas for public health risk. Therefore, data collection was limited to estuaries with marine farming taking place. Sampling is concentrated around the time of year when blooms are imminent.

The number of cells defining an algal bloom was not outlined within this indicator. Such a sweeping definition is difficult to derive for the following reasons:

1. The concentration of algae that defines an algal bloom varies widely between species. This is significantly affected by the different sizes and growth rates of particular species.
    


2. Concentrations are also specific to particular water bodies. For example, species may occur naturally at significant levels in some estuaries, while in others the same levels may not be natural and may instead indicate ecosystem imbalances or nutrient enrichment. In order to derive algal bloom definitions for particular water bodies, data must be related to background levels typically found within each estuary, so that interpretation can be related to the conditions in each estuary that are considered 'normal'.
    


3. Different definitions of algal blooms are required for non-toxic and toxic algal species as only a small number of toxic algae/mL may result in a health risk.
    

As a result a number of definitions have been derived to quantify algal blooms but these vary greatly. To illustrate the point, a selection of these definitions used within Australia are listed below:

1. For cyanobacterial blooms the NSW Blue-green Algal Taskforce report (1992) recommends 15,000 cells/mL as an alert level for recreation and also for stock watering. No specific criteria were defined for the protection of aquatic ecosystems (ANZECC 1992).
    


2. Water and Rivers Commission in Western Australia defined algal blooms: for moderate to large algal cells (greater than 15 to 20 microns in diameter) as bloom conditions if there were > 15,000 cells per mL of water. For small microscopic non-toxic cells (less than 1-5 microns) at around 100,000 cells per mL, and even densities of 500-2,000 cells per mL require action by managers. The Commission, however, also suggests that a bloom of a toxic species in a shellfish harvesting area could pose a threat at densities as low as 5 cells per mL.
    


3. The Australian Water Quality guidelines for fresh and marine waters gave a primary contact recreation guideline for non-toxic algae of <5,000 cell/mL.
    

As a consequence, it was impossible to report on the indicator as it was expressed above. Data collected within the State are presented below as total concentrations of both total algal cell and toxic algal cell concentrations for all sampling periods, but no inference is made as to the number of algal blooms occurring.

Total number of algal cells/mL

SITE	DATE	Cells/mL
Blackman Bay	20/3/01	58
		22
Cloudy Lagoon	18/12/00	23
	23/10/96	127
Cygnet	21/2/01	313
Deep Bay	10/12/00	814
	17/1/01	1,526
	17/12/01	1,372
	19/2/01	7,069
	25/3/01	365
	26/3/01	235
	28/1/01	1,943
	25/10/96	262
	12/6/96	2,538
	28/2/97	2,481
Deep Bay	27/2/97	1,759
Duck Bay	25/3/01	47
Dunalley	21/3/01	1,731
Esperance	12/9/96	264
G.Swanport	21/3/01	242
Georges Bay	27/3/01	14
Georges Bay Site 8	11/6/96	231
Great Oyster Bay Lease 119	25/11/96	8
Hastings	13/12/00	215
	15/1/01	147
	12/6/96	176
Little Swanport	14/12/00	100
	21/3/01	517
	17/10/96	168
Little Taylors	23/10/96	25
Little Taylors Bay	18/12/00	471
Long Bay	25/3/01	546
	16/12/96	677
Norfolk Bay	12/3/96	348
Pipe Clay	18/12/01	68
	6/3/01	24
	23/1/01	168
	27/11/00	484
	20/3/01	69
Pittwater	18/12/01	48
	20/3/01	49
	6/3/01	176
	22/1/01	667
Pittwater 4	25/11/96	6
Port Arthur	15/10/96	84
Port Esperance	15/1/01	118
Recherche Bay	15/1/01	31
	12/9/96	27
Swan River	12/12/00	26
Triabunna	17/10/96	386

Check dates

Total toxic algal cells/mL

SITE	DATE	Cells/mL
Blackman Bay	21/3/01	22
Cloudy Lagoon	18/12/00	11
	23/10/96	47
Cygnet	21/2/01	2,841
Deep Bay	10/12/00	758
	17/1/01	1,256
	17/12/00	1,253
	19/2/01	6,985
	25/3/01	32
	26/03/01	16
	28/01/01	1,645
	25/10/96	4
	6/12/96	2,448
	28/2/97	2,139
	27/2/97	1,588
Dunalley	21/3/01	50
Esperance	9/12/96	241
G/Swanport	21/3/01	52
Georges Bay	27/03/01	1
	6/11/96	8
Hastings	13/12/00	171
	15/1/01	1,161
	9/12/96	115
Little Swanport	21/3/01	31
	17/10/96	2
Little Taylors Bay	23/10/96	4
	18/12/00	409
Long Bay	25/3/01	47
	16/12/96	575
Norfolk Bay	3/12/96	246
Pipe Clay Lagoon	18/12/00	53
	6/3/01	2
	23/1/01	1,462
	20/3/01	33
Pittwater	18/12/00	12
	20/3/01	59
	6/3/01	233
	22/1/01	595
	25/11/96	2
Port Arthur	15/10/96	1
Port Esperance	15/1/01	1,033
Recherche Bay	15/1/01	4
	9/12/96	14
Swan River	12/12/00	7

Acknowledgment

Core Indicators for State of the Environment Reporting E+S9 (ANZECC 2000)