2022 Role of crayfish and invertebrate food web dynamics in controlling algae in Lake Tahoe

No Project associated with this Finding

Finding Details

Algae affects Lake Tahoe’s clarity and visual quality. Excessive amounts of algae can reflect imbalances in the ecosystem, declines in water quality and excessive pollutants (N and P). Periphyton is an unsightly algae attached to rocks in Lake Tahoe’s scenic nearshore. Signal crayfish are a non-native aquatic species that live along the bottom of the lake in the nearshore where periphyton is proliferating. The goal of this study was to understand the interactions between crayfish, nutrients, microorganisms and periphyton.

A few of the findings from this work:  

  • Nutrient cycling, distribution and concentration controlled by biota may be more important to certain periods of periphyton growth than tributary and groundwater inputs.  

  • Lake Tahoe periphyton is nitrogen-limited, which means that controlling inputs and distribution of nitrogen is important in controlling its growth.  

  • The effects of crayfish on periphyton vary seasonally. In autumn, crayfish excrete nitrogen that promotes growth of periphyton. Increased periphyton can lead to the dominance of epithemia, a diatom associated with nitrogen-fixing cyanobacteria.   

  • Crayfish eat small aquatic creatures (midges and snails), leading to reduced biodiversity. This reduction of biodiversity has thereby changed how much, when and which algae is consumed. 

  • Larger crayfish contribute larger pools of nitrogen than smaller crayfish.  

  • Methods were developed to be able to use sensor data to estimate metabolism of gross primary production, respiration and ecosystem production; this means that methods were developed that can be used to monitor metabolic processes (algae, bacteria, zooplankton, fish) associated with water quality.     

  • Crayfish migrate to deeper water in the winter and toward the shoreline in summer.  

  • Crayfish eat native invertebrates; 90+ years of crayfish establishment has reduced native invertebrates to a very high degree, which affects the algae they would otherwise consume.  

  • Algae species were catalogued. (This is important because the effects of algae on clarity, nutrient uptake and nutrient cycling vary by algae species. This is also important to provide a baseline reference to understand changes in the ecosystem over time, which has a direct effect on algae.) 

  • Large lakes around the world are exhibiting nearshore nuisance periphyton blooms; drivers of these periphyton blooms include changes in water temperature, change in ice phenology with earlier ice out, land-use change, pollution, and changes in invasive species). 

How this work was accomplished:  

  • Thousands of data points from sensors (light, temperature, oxygen) were analyzed. 

  • >1000 environmental samples were analyzed, including water, algae and invertebrate samples.  

  • >10 in-situ experiments were conducted.  

  • 18 crayfish density transects were surveyed. 

  • >2,000 articles were evaluated. 

  • 25 lakes were researched through a literature review. 

  • New methods were developed to understand primary production.   

Article: Algal blooms emerging threat to clear lakes worldwide

Article: methods development

Final Report - Crayfish and Algae