1. Pond bloom monitoring & management
“Characterising and managing harmful algal blooms that cause production loss on Australian prawn farms”
FRDC #2013/231
David Mann
Bribie Island Research Centre

2. Heterosigma Identification Occurrence Mechanism of harm
Control options

3. 1. Identification Identification is not straight-forward
Apical groove & flagella
‘Potato’
‘Cornflake’
1. Identification
Microscopic ID features
two flagella & groove near front
swimming corkscrew or similar to dinoflagellate
killed cells form ‘raspberry’ - good diagnostic
Identification is not straight-forward
one farm strain – 5 cell morphologies observed
‘cornflake’ replaced with ‘potato’ last season
‘Snot’ test
is a strong diagnostic tool
can give false negative
Two species of Heterosigma
4 strains isolated from 4 farms DNA sequenced
1x H. akashiwo &
1x Heterosigma species undescribed
Raspberry form of fixed cells
Mucus aggregations
Differentiation of Heterosigma species impossible in fixed samples
(Demir-Hilton, Hutchins et al. 2012)
This characteristic of H. akashiwo has resulted in the assignment of several different names to this organism over the years
Can change shape in response to the physiochemical characteristics of its environment
This is not unusual – eg Hara and Chihara 1987 – observed five to six different H. akashiwo morphologies in cultures
Identification of raphidophyte species in environmental samples is challenging because they lack a cell wall and specimens are poorly preserved with common fixatives.
Different morphologies and different behaviours)
Heterosigma is pleomorphic (can change size & shape)
swimming similar to dinoflagellate (rotates as moves forward); some difference among shapes
two flagella – one forward and one trailing, both arising from a groove back from the top
killed cells (eg Lugols, acid) form ‘raspberry’
acidification causes mucus development which aggregates into threads or clumps

4. 2. Occurrence Heterosigma can occur any time, anywhere
Rapid bloom development
high growth rate potential
ability to form resting cells and cysts
synchronous ‘hatch’  rapid bloom
Heterosigma can occur any time, anywhere
north to south; crop start to finish
blooms recorded 23°C to 33°C
blooms unpredictable
regular pond monitoring
Resting cell
Cyst
Kok The study observed that H. akashiwo strains grew well under the pulsed supply of three N-sources— ammonium, nitrate, and urea.
Growth rate values suggest its ability to out-grow diatom species.
Light experiments also demonstrated the ability of H. akashiwo to tolerate decreased light conditions, which allow it to thrive at depth.
The ability to accumulate intracellular stores of N-nutrients was also demonstrated and can be important for sustaining cell productivity.
Bloom occurrences of the H. akashiwo species might be driven by its ability to form cysts or resting cells when environmental conditions are not suitable for growth
(note global distribution – Iceland through the tropics to Tasmania)

5. 3. Mechanism of harm H. akashiwo strain is toxic
‘Snot’ gill fouling
water quality shock may trigger
rapid ‘snot’ release from live cells
H. akashiwo strain is toxic
killed fish larvae (20-30mm) in hours
reduced fish gill cell viability
P. monodon juveniles not affected over days
However...
field evidence indicates potential
other toxins or circumstances ?
Fish larvae killed rapidly
Juvenile prawns no symptoms
Live cell within ejected mucus (stained blue)
Heterosigma known for its variability in cell physiology and behaviour, and
may produce more than one toxic compound
as indicated by field evidence (impacts on other biota)
Therefore not sure about toxin relevance to prawns
mucopolysaccharide)

6. 4. Control options Heterosigma-specific management tools
Alternative controls that do not cause pond destabilisation
Inhibit growth or kill cells
Reduce release and impact of mucus
Options being tested
Surfactant compounds
safe, biodegradable (used in soaps etc)
LDAO, CAPB (derived from coconut oil)
Ultrasound
Heterosigma lacks a robust cell wall
Clay
eg bentonite
2ppm CAPD for 1h
2ppm LDAO for 1h
Heterosigma is versatile so basic WQ manipulation less likely to be a viable option.

7. More information... Refer to APFA website project reports
Algal Directory Online -
Contact me
Bribie Island Research Centre ;