Diatom assemblages promote ice formation in large lakes.

Area of Science:

• Aquatic Ecology
• Microbiology
• Limnology

Background:

• Phytoplankton, particularly diatoms, form blooms in the Laurentian Great Lakes during winter.
• The role of ice formation in the life cycle and survival of these ice-covered lake plankton remains poorly understood.
• Attachment to ice may offer a survival advantage by maintaining diatoms in the photic zone.

Purpose of the Study:

• To investigate the directed formation of ice by planktonic communities dominated by filamentous diatoms.
• To explore the potential role of diatoms and their associated bacteria in ice nucleation.
• To understand the ecological implications of ice-diatom-bacteria interactions in seasonal ice-covered lakes.

Main Methods:

• Sampling of planktonic communities from ice-covered Laurentian Great Lakes.
• Scanning electron microscopy to identify associations between diatoms and bacterial epiphytes.
• Isolation and characterization of bacteria from phytoplankton to determine ice nucleation activity and crystallization temperatures (T(c)).

Main Results:

• Filamentous diatoms were observed in association with ice formation.
• Bacterial epiphytes were found on dominant diatoms, with some bacteria exhibiting ice nucleation activity at temperatures as high as -3 °C.
• While Pseudomonas species showed ice nucleation activity, their abundance was insufficient to fully explain the observed freezing.

Conclusions:

• Ice nucleation activity, potentially from bacterial epiphytes, may facilitate diatom attachment to frazil ice.
• This ice-recruitment mechanism could enhance diatom survival and fitness in winter conditions.
• The study proposes a novel winter life cycle stage for meroplanktonic diatoms and a model for other seasonal ice-covered aquatic ecosystems.