The Algal Ecophysiology Laboratory, School of Biological Sciences, Monash University http://www.biolsci.monash.edu.au/staff/beardall/index.html
The overall interests in our laboratory centre on the ecophysiology and biochemistry of algae. Currently we are running projects on the effects of climate change (elevated CO 2 and UV-B radiation) on performance of microalgae, and on interactions between nutrient uptake and photosynthesis in macro- and micro-algae. In addition to work on Nodularia (factors influencing growth, akinete formation and germination) we are also examining the role of environmental factors in controlling the growth and toxicity of Cylindrospermopsis , a toxic cyanobacterium that impacts sub-tropical and tropical freshwater systems. We also have strong links with the Water Studies Centre in the School of Chemistry and will be doing some work related to the Synechococcus bloom in conjunction with Perran Cook and Mike Grace.
We have put our knowledge about algal ecophysiology to good use in the following major field studies:
Port Phillip Bay Environmental Study – the Beardall lab was responsible for studies on
phytoplankton distributions and productivity (R. Royle and Simon Roberts);
benthic microalgal distributions and productivity (B. Light, PhD project) and
grazing rates (Rick Royle, Anna Redden and Gillian Beattie)
Primary production, phytoplankton nutrient status and bacterial production in the Derwent River, Tasmania (for Norske Skog )
Port Phillip Bay Channels Deepening Environmental Effects Statement – Marine Microphytobenthos and seagrass and algal productivity studies (for Matt Edmunds - Australian Marine Ecology )
Jackie Myers has just completed a PhD project, funded by ARC and DPI, examining factors controlling the onset of blooms and vegetative growth of Nodularia spumiginea in the Gippsland Lakes The lab therefore has a range of skills and expertise to contribute to studies of bloom initiation and their persistence in freshwater, brackish and saline environments. Samal Say is studying factors controlling phytoplankton and benthic microalgal productivity and their role in supporting fisheries in Tonle Sap, Cambodia. We have recently carried out studies on the environmental impacts of mining on the Ok Tedi and Fly Rivers in Papua New Guinea
Based on studies in other Australian systems, conditions in the Lakes in the summer months meet the requirements for blooms to occur, however blooms do not always form.
To date Nodularia sp . from the Gippsland Lakes has not been well described and data on its environmental requirements are lacking.
Clearly the strain of Nodularia from the Gippsland Lakes is tolerant of a range of salinities, though growth is less at extremes. Growth is increased by increasing phosphorus levels in the water, but relatively unaffected by nitrogen as nitrate.
Toxin production follows the effect of salinity on growth, with less toxin at very high or very low salinities. Toxicity is stimulated by N, but not by P, levels
Blooms of Synechococcus – what do we know? Synechococcus is a genus of cyanobacterium which is distributed widely in the oceans, although there are also some freshwater species. Synechococcus is an important organism across all marine environments, where it can be found at concentrations ranging from 5 x 10 5 to 1.5 x 10 9 cell L -1 , which translates into approximately 7.5 to 12 g chlorophyll a L -1 Blooms dominated by Synechococcus can attain chlorophyll concentrations up to 150 g chlorophyll a L -1 Cultures of some strains have been reported as being capable of producing compounds with neurotoxic and hepatotoxic effects but there is no evidence that the bloom in the Gippsland Lakes is toxic
In some studies, Synechococcus has been found as two distinct morphotypes distinguishable by size. In Florida Bay for instance, a size class of larger cells was dominant whenever cyanobacteria reached bloom proportions. This size class was consistently phycocyanin (PC)-rich. Some studies suggest PC-rich strains occur closer to the surface in salinities <20 PSU, and the ratio of PC:PE-rich cells in a population decline at salinities >20PSU. Significant blooms have been described from Pensacola Bay (Florida) from Florida Bay , San Franciso Bay , the Mediterranean Sea, the Baltic Sea and the Black Sea.
Irradiance should be considered a significant driving force in sustaining Synechococcus blooms. The genus is certainly tolerant of high light In Florida Bay, N 2 fixation has been suggested as a significant factor sustaining blooms of Synechococcus . However, the Gippsland Lakes N:P ratios range from 19:1 to 24:1 (Webster et al 2001) implying that N is not a limiting factor unless there are large inputs of P into the system. The N 2 -fixing capacity of Synechococcus would thus be unlikely to have a significant impact on bloom formation and persistence unless, as is the case with Nodularia blooms, P inputs increased and N became limiting Synechococcus is also found in regions with elevated inorganic nutrients , especially nitrogen and ammonium addition will stimulate growth of Synechococcus in mixed populations . Synechococcus is found in highly eutrophic waters in the Gulf of Naples and is capable of utilizing dissolved organic nitrogen compounds (DON) such as urea Wawrik and Paul (2004) and Wawrik et al (2004) have clearly demonstrated the importance of N inputs from the Mississippi River in stimulating algal (including Synechococcus ) blooms in the Gulf of Mexico. It is likely therefore that high nitrogen (DON and inorganic N) loadings, together with the elevated levels of other nutrients such as P, in the Gippsland Lakes are contributing to the persistence of Synechococcus blooms
Temperature is undoubtedly a very important driver of Synechococcus growth. Significant relationships between Synechococcus growth rates and biomass accrual have been reported by a number of authors working on a variety of systems Optimal growth of Synechococcus in the Mediterranean has been reported at ~24 o C with no growth when water temperatures were <11 o C Cyanobacterial abundance (dominated by Synechococcus ) in Penascola Bay, Florida was greatest when water temperatures were 28-30 o C Data of Jonathan Smith provide good evidence that there is a strong relationship, in the Gippsland Lakes, between cyanobacterial biovolume and temperature, with lower cyanobacterial numbers as temperatures drop below ~20 o C.
Salinity can be a contributing factor to growth of Synechococcus . In Penascola Bay in Florida, the proportion of phycocyanin-rich to phycoerythrin-rich strains of Synechococcus decreased dramatically from ~ 20 PSU to 28 PSU, i.e. PC-rich cells were an order or magnitude higher in abundance in the upper, lower salinity, part of this estuary. But there was a decline in picoplankton populations at low (< 5 PSU) salinities compared with higher salinity stations in the Ebro River estuary (Spain). Given the salinity gradients that exist in the Gippsland Lakes, salinity may be one of the drivers behind the genesis and persistence of Synechococcus blooms. However, as discussed above, such effects may well be secondary to those of temperature. There is evidence that cyanobacterial blooms in the Gippsland Lakes show a strong positive correlation with temperature but high temperatures will not necessarily lead to elevated Synechococcus numbers if the salinity is low .
Grazing Synechococcus populations frequently show high growth rates in nature. However, extensive blooms are not always found and it is believed that grazing exerts a strong influence on population size. Bloom formation has thus been suggested to occur when top-down control from grazers breaks down. The Future…… Synechococcus is a much smaller organisms than Nodularia . It therefore stays suspended in the water column and does not readily sink out. This may be one reason for the persistence of the bloom.
The overseas experience is that blooms of Synechococcus will persist. However, nutrient levels in the Lakes are not as high this year as last, suggesting that a bloom, if it occurs, might be smaller However, a summer flush of nutrient laden freshwater would a) reduce the salinity and b) bring in extra nutrients --- these are ideal conditions for Nodularia blooms, which could be seeded from resting cells in sediments