Not the usual suspect: Understanding the cyanobacteria responsible for January fish kill
FOOTAGE of cod, bream and perch clogging the Darling River in western New South Wales hit headlines in January, stirring fresh debate over water management and climate change. It was a perfect storm of conditions that helped one tiny organism thrive. Strangely, it wasn’t the usual suspect.
Samples were taken and are now being studied by researchers at the Australian National Algae Culture Collection in Hobart which holds samples from previous algal events.
It makes for fascinating insights under the microscope.
Blue-green algae is an imprecise catch-all for a diverse range of ancient, photosynthetic microbes. For one thing, not all of them are blue, or green, or even half-way between. Many aren’t even algae, but rather a distinct phylum of prokaryotes about as distinct from kelp and pond scum as we are from E. coli.
Though the more accurate term is ‘cyanobacteria’ any time a population of these microbes explodes in numbers, it’s usually blamed on ’algal blooms’, regardless of the culprit’s identity.
“Blooms are defined as excessive growth of an algae above the normal background level,” says Anusuya Willis, a research scientist with the Australian National Algae Culture Collection in Hobart.
“Multiple cyanobacteria species will be present in water systems but they only become a problem if a bloom occurs.”
Remote satellite sensing and probes that detect specific pigments in the water help keep us alert to cyanobacterial levels in our waterways. But to tease out which species are responsible once a bloom appears, researchers need to head out to collect samples for a closer look.
Individual species have their own unique pool of talents for taking advantage of conditions in their environment. Some have a knack for scumming the surface to take advantage of the warmer water. Others can differentiate roles in their colony, harvesting nitrogen or sending ‘sleeper cells’ to lie dormant in the muck. As conditions change, some find the going easier than others.
While we can predict with relative ease when a bloom is likely to occur, we still have a long way to go in forecasting which bacteria and algae will dominate.
“One of the interesting things about the bloom in the Darling River is that the dominant species has changed,” says Willis.
“During the large blooms in the early nineties, the species blooming was a type of Dolichospermum. Now it appears to be Chrysosporum ovalisporum, a species that is not known to cause such massive blooms in Australia.”
Pending research on the genetics of this potential new bloomer will help confirm the identity as a Chrysosporum. But knowing as much as we can about how different cyanobacteria adapt to shifts in their ecosystem is vital if we’re to strike the right balance when it comes to water management.
Cyanobacteria have to compete with other photosynthesising organisms swimming in their habitat. Like plants, they require a decent amount of light for energy and warmth. They also require the kinds of nutrients found deep down in the cool shadows of the sediment, creating a potential hurdle when it comes to accessing all of the necessities of life.
“Some cyanobacteria have the ability to move up and down in the water between the high light and high temperature conditions at the top and the high nutrients at the bottom, so they can get everything they need to grow fast and bloom,” says Willis.
On occasion, conditions are just right and provide a sure-fire way to help cyanobacteria numbers explode. A drop in water levels brings the sunlit surface and nutrient-rich depths close together, while also making for lazy currents that warm in the summer heat.
“Cyanobacteria grow faster than other algae at higher temperatures, so that when the water temperatures are higher than usual, the ‘good’ algae grow slower and the cyanobacteria grow even faster and overwhelm the phytoplankton,” says Willis.
For non-aquatic species relying on the water source for hydration, the blossoming blue-green algae can whip up a potentially deadly soup. Liver-destroying hepatotoxins, nerve-breaking neurotoxins, and skin-itching endotoxins produced by various species can sicken and kill livestock.
Cyanobacteria’s role in life cycle of others
That’s not what decimated the Darling River’s fish numbers, though. It was the death of these cyanobacteria that triggered devastation for other species. Once countless microscopic lives come to their inevitable end, a haze of tiny corpses fuels those microbes that drain their environment of oxygen as they burn their way through the feast.
Cyanobacteria’s talent for generating excessive amounts of oxygen has not only driven sensitive species to the brink of extinction and beyond in the distant past, but might also have contributed to the genesis of complex life.
Where oxygen’s reactivity once played havoc with ancient biochemistry, evolution quickly adapted it as a novel way to harvest energy. Our own dependence on aerobic respiration may have even evolved in the wake of photosynthesising microbes exploding in numbers and ‘polluting’ the globe with their toxic breath.
Cyanobacteria give and take life on dramatic scales, making them a focus for researchers across a number of fields. At the CSIRO’s Australian National Algae Culture Collection more than 1000 strains representing some 300 species of both algae and cyanobacteria are stored alive in liquid cultures, available for researchers all around the globe to study for their threats and uses.
“Most of the algal strains have been targeted because of research interest within CSIRO in species that have a proven or possible positive or negative economic and social impact,” says the collection’s director, Ian Jameson.
The very characteristics that make them such a nuisance in our water systems also make them an attractive biological resource. Species of cyanobacteria grow quickly under optimal conditions, churning out products that could be used in novel materials or as a fuel or food source, or consuming potential pollutants in their environment.
Research into cyanobacteria can take the form of either a problem to solve or a solution to explore.