Benthic algae compensate for phytoplankton losses in large aquatic ecosystems

Area of Science:

• Aquatic ecology
• Limnology
• Ecosystem function

Background:

• Anthropogenic activities cause trophic shifts in aquatic systems, impacting ecosystem function and primary production (PP).
• Phytoplankton biomass and production in the Laurentian Great Lakes have declined due to reduced nutrients and invasive mussels.
• Increased water clarity from phytoplankton decline may enhance benthic PP.

Purpose of the Study:

• To investigate if Laurentian Great Lakes experienced oligotrophication or a shift in autotrophic structure.
• To quantify the contribution of benthic PP to overall ecosystem production.
• To assess the resilience of large aquatic ecosystems to trophic shifts.

Main Methods:

• Calculations based on productivity rates from the Laurentian Great Lakes.
• Analysis of phytoplankton and benthic primary production.
• Comparison of production data from the 1970s to the 2000s.

Main Results:

• Benthic contributions to ecosystem PP can be substantial, reaching up to 50% in Lake Huron.
• Phytoplankton production declined by 5-45% in the Great Lakes from the 1970s to 2000s.
• Benthic PP increased by up to 190%, potentially compensating for phytoplankton losses.

Conclusions:

• Large aquatic ecosystems demonstrate resilience in autotrophic productive capacity despite trophic shifts.
• Production can be redirected to the near-shore benthic zone, maintaining overall ecosystem PP.
• Large lakes may exhibit regime shifts in autotrophic structure, similar to shallow lakes.