Hintz2021L&O

Title: Changes in spectral quality of underwater light alter phytoplankton community composition
Authors: Nils Hendrik Hintz, Moritz Zeising, Maren Striebel
Institutions: Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg; Alfred-Wegener-Institute, Helmholtz-Centre for Polar and Marine Research
Publication Date: 2021
Journal: Limnology and Oceanography
DOI: 10.1002/lno.11882

Light is essential for phytoplankton as it affects their growth and community structure.
Phytoplankton species use pigments to optimize light absorption, which is essential for efficient light use.
Previous studies focused on light intensity; this study investigates the impact of light spectrum quality (color) on phytoplankton communities.
Experiment conducted in mesocosms with controlled light treatments (blue, green, red), revealing that blue light promotes community growth while red light reduces it.
Community composition changes significantly based on light quality, driven largely by Bacillariophyta and Chlorophyta.
Observed lower species richness and higher evenness under red light compared to full spectrum control.

Light quality affects phytoplankton biomass and community structure.
Light intensity varies spatially in aquatic ecosystems, dependent on factors like water depth and dissolved organic matter (DOM).
Photosynthetically Active Radiation (PAR, 400-700 nm) is crucial for primary producers.
Light spectrum shifts with depth (less blue light in deeper waters) and can be altered by cDOM from terrestrial inputs.
Phytoplankton harvest light using a range of pigments, optimizing absorption strategies based on spectral quality.
This study aims to explore effects of different light spectra on community structure through experimental manipulation.

Location: Coastal North Sea, using natural seawater from German Jade Bight.
Duration: April 2-30, 2019.
Mesocosm Units: 600 liters (Planktotrons).
Each treatment (blue, green, red, full spectrum) conducted in triplicates with comparable light intensity.
Nutrients and vitamins were added to maintain natural conditions and prevent limitations.
Light Treatment: Controlled using LED modules, with distinct spectra achieved via colored filters.

Data analyzed with R software (version 3.6.1).
Parameters like growth rate, final biomass, and community composition analyzed using ANOVA and mixed-effect models.

Growth rates significantly higher under blue light compared to red and green treatments.
Final biomass showed trends favoring blue light, though not statistically significant.

Absorption spectra indicated significant differences based on light treatment.
Communities adapted to the light treatment by altering absorption characteristics.

Relative pigment compositions did not show significant treatment differences.
Chlorophyta and Bacillariophyta dominated under certain light conditions, revealing shifts in community structure.

Species richness was significantly lower in red light treatments compared to full spectrum.
Evenness metrics showed higher evenness under red light, suggesting community stability.

Phytoplankton growth and community composition were influenced by light quality, with specific wavelengths proving more beneficial for growth.
adaptation of communities to light treatments indicates potential ecological implications for nutrient cycling and higher trophic levels.
Observations support the hypothesis that different light qualities influence community sorting more than pigment acclimation.

This study highlights the importance of light spectrum on phytoplankton communities, emphasizing that specific light quality directly impacts primary production and ecological dynamics in aquatic systems.
Future research should consider both light intensity and spectral changes to better understand their combined effects on phytoplankton dynamics.