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Algae versus algae

'Red tides' might be staunched by harmless algae.

Diverse species of algae are proving to be unlikely allies in the fight against the lethal toxins created by red tides.

Red tides can kill marine life and ruin beaches. Credit: Alejandro Díaz

Red tides are large algal blooms that can release powerful neurotoxins into both marine and freshwaters. They are a serious problem for conservation, fisheries and tourism, killing wildlife, contaminating shellfish and making otherwise warm and alluring beaches unusable. Controlling them would have obvious benefits. But not knowing what initiates and terminates the blooms has stymied efforts in that direction.

In an attempt to better understand red tides, Julia Kubanek at the Georgia Institute of Technology in Atlanta and her colleagues examined harmless species of algae that grow in the same environment as Karenia brevis, the organism responsible for the red tides that occur off the Florida coast every year. Earlier research had revealed that many of these benign algae can survive in the presence of red-tide toxins, and Kubanek and her team wanted to find out why they were so resilient.

The researchers added five different algal species — all commonly found near K. brevis in the wild — one by one to samples of water with toxins in it, and monitored both their survival and the concentrations of the toxins over the course of 24 hours. One species, Skeletonema costatum, was studied further because of its abundance in the Gulf of Mexico and frequent proximity to K. brevis. It was raised with K. brevis in conditions that allowed both algal species exponential growth, and over the course of nine days the water was regularly analysed for algal population densities of both species and toxins.

The researchers report in Harmful Algae1 that all five species of harmless algae can remove the toxins from water. They found that S. costatum performed the best, growing at a rate that kept pace with K. brevis and reduced waterborne toxin levels by 80%.

"I don't think anybody else has looked at whether algae could do anything like this. That they can is exciting," says ecologist Karin Rengefors at Lund University in Sweden, who was not involved with the study.

Chemical warfare

In a second experiment, Kubanek explored the ability of K. brevis to suppress the growth of many other algal species. The team exposed ten different algal species to chemicals exuded by K. brevis, monitoring algal survival and growth over a period of 1-3 days. The group reports in the Proceedings of the Royal Society2 that some algae were resistant to the chemicals, although several – including S. costatum – were not, and experienced suppressed growth.

But when S. costatum was exposed to K. brevis itself, rather than just its toxins, its growth was barely suppressed at all. This suggests that a complex chemical warfare is playing out between the algae. But Kubanek's team doesn't yet know whether S. costatum is breaking the toxins down, producing a compound to counteract the toxin, or even preventing the toxins being released in the first place.

"The discovery of these complex algal competitive interactions is so important, and has the potential to help us manage red tides when they strike," says Catherine Legrand, a chemical ecologist at the University of Kalmar in Sweden.

It is plausible that the research could lead to new ways of controlling red tides, either by encouraging algal species such as S. costatum or through the development of a targeted way of removing the toxins biochemically. But that is not necessarily the direction Kubanek wants to go in. "Is it even right to contain these [tides]?" asks Kubanek. Red tides have been happening for thousands and, probably, millions of years, she explains. "We don't understand what their role is ecologically and this makes it risky to try to interfere with them," she says.


  1. Myers, T. L. et al. Harmful Algae, doi:10.1016/j.hal.2008.03.001 (2008)

  2. Prince E. et al. Proc. Roy. Soc. B doi:10.1098/rspb.2008.0760 (2008).

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Kaplan, M. Algae versus algae. Nature (2008).

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