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<p>In freshwater ecosystems, variation in light quantity is a determinant of production that causes bottom-up effects in food webs. Most research has only explored the effects of light on system metabolism and primary producers. In contrast, multitrophic effects of light availability – including fluctuations in light availability – remain understudied. Using outdoor mesocosms, we examined how changes in the average quantity and temporal fluctuations of light alter lake food webs. We hypothesized that reduced average light should decrease the quantity but increase the quality of primary production for consumers, thereby promoting secondary production. We also hypothesized that regular fluctuations in light should increase production by promoting species coexistence, whereas irregular fluctuations should have the opposite effect. To test these hypotheses, we constructed communities containing periphyton, phytoplankton, zooplankton, and snails and exposed these communities to three constant light treatments (90%, 40%, and 10% of ambient sunlight) and two fluctuating light treatments (regular and irregular fluctuations) that had an average 40% ambient sunlight. We discovered that the phytoplankton abundance (i.e. chlorophyll a concentration) doubled under constant low-light conditions compared to constant highlight conditions. However, we did not detect a change in abundance of the zooplankton that consume phytoplankton. The standing crop of periphyton biomass exhibited no change, but the periphyton-consuming snails experienced large population increases under constant, low-light and under fluctuating irregular-light conditions, suggesting they experienced a higher quantity or quality of periphyton. These results indicate that variation in light availability can have large, multi-trophic effects.</p>

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Shedding Some Light on Lake Communities: Impacts of Light Level and Light Variability

  • 期刊论文

  • 发表日期：

    2025年2月19日

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  • Aaron B. Stoler,
  • Kayla Coldsnow,
  • Rick A. Relyea

摘要

In freshwater ecosystems, variation in light quantity is a determinant of production that causes bottom-up effects in food webs. Most research has only explored the effects of light on system metabolism and primary producers. In contrast, multitrophic effects of light availability – including fluctuations in light availability – remain understudied. Using outdoor mesocosms, we examined how changes in the average quantity and temporal fluctuations of light alter lake food webs. We hypothesized that reduced average light should decrease the quantity but increase the quality of primary production for consumers, thereby promoting secondary production. We also hypothesized that regular fluctuations in light should increase production by promoting species coexistence, whereas irregular fluctuations should have the opposite effect. To test these hypotheses, we constructed communities containing periphyton, phytoplankton, zooplankton, and snails and exposed these communities to three constant light treatments (90%, 40%, and 10% of ambient sunlight) and two fluctuating light treatments (regular and irregular fluctuations) that had an average 40% ambient sunlight. We discovered that the phytoplankton abundance (i.e. chlorophyll a concentration) doubled under constant low-light conditions compared to constant highlight conditions. However, we did not detect a change in abundance of the zooplankton that consume phytoplankton. The standing crop of periphyton biomass exhibited no change, but the periphyton-consuming snails experienced large population increases under constant, low-light and under fluctuating irregular-light conditions, suggesting they experienced a higher quantity or quality of periphyton. These results indicate that variation in light availability can have large, multi-trophic effects.