How phytoplankton protects itself from different predators
Phytoplankton exhibit a species-specific response
The behaviour could impact global climate change
DENCE RESPONSES are often seen in higher plants, but now comes a report of a complex and species-specific response in marine phytoplankton. Scientists suspect they may find other examples of complex defensive strategies when they look more closely at other single-celled organisms.
The behaviour could have implications for global climate change because the phytoplankton Phaeocystis, the species studied, plays a key role in the carbon cycle of cold oceans, accounting for up to 85 per cent of local productivity during some time periods.
Complex behaviour
This complex defensive behaviour also shows how environmental factors can affect even simple organisms.
In a paper published June 11 in the online version of Proceedings of the National Academy of Sciences, researchers of the Georgia Institute of Technology report the first evidence that the phytoplankton can change form to protect i
tself against attack by predators that have very different feeding habits.
Boosting survival
To boost its survival chances, Phaeocystis globosa will enhance or suppress the formation of colonies based on whether nearby grazers prefer eating large or small particles, according to a Georgia Institute of Technology press relea
se.
Chemical signals
“Based on chemical signals from attacked neighbours, Phaeocystis globosa enhances colony formation if that’s the best thing to do for survival, or it suppresses the formation of colonies in favour of growing as small sol
itary cells if that’s the best thing to do,” said Mark E. Hay, Teasley Professor of Biology at the Georgia Institute of Technology. Phaeocystis has two primary predators: small grazers such as ciliates, which prefer to eat
small solitary cells that are four to six microns in diameter, and the larger shrimp-like copepods, which prefer to eat large, ball-shaped colonies.
When copepods are attacking the phytoplankton, therefore, the best survival strategy of Phaeocystis is to form solitary cells.
When ciliates are attacking, the best strategy is to form colonies that are too large for those predators to consume.
Chemicals that signalled attacks from copepods suppressed the formation of colonies by 60 to 90 per cent, while signals from ciliates enhanced colony formation by more than 25 per cent.
Experimentally, the researchers attempted to separate the chemical signals from the actual predators. They grew Phaeocystis in the presence of either ciliates or copepods. They then filtered out both the phytoplankton and predators,
leaving only water containing the chemical signals of attack. Water samples containing signals from the two predators were then separately introduced into Phaeocystis cultures that had not been attacked.
Survival advantage
The scientists then studied how the different chemical signals affected the percentage of Phaeocystis living in colonies or as solitary cells.
Finally, they examined whether this response affected how much the predators ate to determine if the change conferred a survival advantage.
The response of Phaeocystis could be important to scientists studying climate change because the predator that ultimately consumes the phytoplankton determines the fate of the carbon it contains.
If eaten by copepods, the carbon becomes part of faecal packages that sink into the deep ocean where a portion of that carbon is sequestered — thereby reducing atmospheric carbon dioxide, a leading greenhouse gas.
If consumed by smaller creatures like ciliates, less of the carbon sinks to the deep sea and more remains in the surface waters. — Our Bureau
Printer friendly
page
Send this article to Friends by
E-Mail
Sci Tech
