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<p>The light climate is a fundamental factor shaping autotrophic communities in stratified aquatic ecosystems. This study investigates three coastal lakes—Lagoon, Elovoe, and Trekhtzvetnoe—situated along the White Sea coast and representing successive stages of postglacial isolation. Field measurements of underwater illuminance, light spectra, and chromophoric dissolved organic matter (CDOM) were combined with analyses of phytoplankton composition, chlorophyll-<i>a</i> fluorescence, and pigment characteristics. With increasing isolation, three consistent trends were observed: (1) a progressive narrowing of the spectral range of underwater light; (2) a reduction in the depth of the photic zone; and (3) a shift in dominant spectral niches—from green in the slightly isolated Lagoon, to orange-red in Elovoe, and to red-far red in the fully meromictic Trekhtzvetnoe. These optical changes result from rising CDOM concentrations, which dim the underwater environment and selectively absorb short wavelengths. Consequently, phototrophs with different pigment systems occupy depth layers matching their optimal light range: eukaryotic phototrophic taxa prevail near the 1% light boundary, whereas anoxygenic phototrophic bacteria dominate deeper layers illuminated by less than 0.1% of surface light. The observed succession of color niches and phototrophic assemblages along the isolation gradient demonstrates that CDOM-controlled spectral composition serves as a key selective force in meromictic lakes. These systems provide a natural model for understanding brownification-driven optical and biological transformations in Arctic and subarctic aquatic environments.</p>

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Sequence of spectral niches for phototrophic communities in the White Sea meromictic lakes

  • 期刊论文

  • 发表日期：

    2026年7月9日

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  • Elena Labunskaya,
  • Valentin Lobyshev,
  • Dmitry Matorin,
  • Svetlana Patsaeva,
  • Nikita Sidochenko,
  • Julia Sokolovskaya,
  • Dmitry Voronov,
  • Elena Krasnova

摘要

The light climate is a fundamental factor shaping autotrophic communities in stratified aquatic ecosystems. This study investigates three coastal lakes—Lagoon, Elovoe, and Trekhtzvetnoe—situated along the White Sea coast and representing successive stages of postglacial isolation. Field measurements of underwater illuminance, light spectra, and chromophoric dissolved organic matter (CDOM) were combined with analyses of phytoplankton composition, chlorophyll-a fluorescence, and pigment characteristics. With increasing isolation, three consistent trends were observed: (1) a progressive narrowing of the spectral range of underwater light; (2) a reduction in the depth of the photic zone; and (3) a shift in dominant spectral niches—from green in the slightly isolated Lagoon, to orange-red in Elovoe, and to red-far red in the fully meromictic Trekhtzvetnoe. These optical changes result from rising CDOM concentrations, which dim the underwater environment and selectively absorb short wavelengths. Consequently, phototrophs with different pigment systems occupy depth layers matching their optimal light range: eukaryotic phototrophic taxa prevail near the 1% light boundary, whereas anoxygenic phototrophic bacteria dominate deeper layers illuminated by less than 0.1% of surface light. The observed succession of color niches and phototrophic assemblages along the isolation gradient demonstrates that CDOM-controlled spectral composition serves as a key selective force in meromictic lakes. These systems provide a natural model for understanding brownification-driven optical and biological transformations in Arctic and subarctic aquatic environments.