BIO3021 Lecture Notes - Lecture 15: Brown Algae, Red Algae, Ecophysiology
25 May 2018
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Lecture 15 – Ecophysiology of Primary Producers, Adaptations to Stresses in
Intertidal Region
Light harvesting
• All primary producers are photosynthetic
• Light is major driver
• Photosynthesis is major determinant of primary productivity
• Light availability is environmental factor most likely to limit primary
productivity
1. Light harvesting pigments in different algal groups and their role
• All algal groups have chlorophyll a
• Dinoflagellates → form peridinin
• Brown algae and chrysophytes → fucoxanthin
• Accessory pigments have different light absorption properties
compared to chlorophylls
o Increases range of wavelengths algae can use available to
power photosynthesis
• Green window: green algae not absorbed
o Very low absorbance
• Action spectra reflect absorption spectra (flat)
o Thick
o Except in red algae chlorophyll – silent
▪ Red algae are dominant at low light
2. Range of photon flux for growth and photosynthesis in different groups
• Light compensation point
• Beta / alpha
• Ik – light imaging
• Most commonly see adaptation to low light brought about my increase
in cellular light harvesting pigments
• Acclimation: adapt to low light: make more light pigments
• Photosynthesis in saturated region is controlled by levels of carbon
fixing enzymes
3. Ways in which algae can adapt/acclimate to different light intensities
• Increased capacity to use low light can be accompanied by a lower
Pmax
o Microalgae: can see reduction in photosynthetic capacity
(maximal rate)
▪ Energetically expensive to algae to make all the enzyme
for carbon fixation → reduce investment and lower
rates of maximal photosynthesis
o Macroalgae: low light → leads to increased Pmax as well as
increased capacity to use low light
▪ Low light responses to upregulate of photosynthetic
capacities → cant disconnect upregulate systems of
harvesting
▪ Higher rates of photosynthesis → advantage of
intertidal organism: low tide will see high light
• Other adaptive responses
o Reduction in respiration rates
o Light induced chloroplast movements
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