Factors affecting Cladophora growth in the eastern basin of Lake Erie: Analysis of a monitoring dataset (2012–2019)

Abstract

Cladophora is a naturally occurring benthic alga in the Great Lakes which can reach nuisance levels in the nearshore, leading to beach closures and other impacts. A monitoring program was initiated in 2012 in the eastern basin of Lake Erie to identify ecological factors driving its growth. Inflows from the Grand River, the largest river to the north shore, were generally positively associated with phosphorus concentrations in the nearshore and negatively associated with light reaching the lakebed. At the depths sampled (3 m–18 m), Cladophora was strongly influenced by light availability, and due to shading by the Grand River plume, an overall negative association was found between Cladophora biomass and phosphorus inputs. Phosphorus limitation was only observed at shallow sites farthest from the Grand River. Positive associations between dreissenid mussel coverage and both Cladophora biomass and tissue phosphorus suggest that nutrient cycling by dreissenids supports Cladophora growth. Our results indicate that i.) the Grand River has a strong influence on nearshore nutrient levels and water clarity; and ii.) Cladophora is limited by both phosphorus and light to varying degrees within the study area, although light appears to be the dominant factor, at least at these depths, years, and locations. The implication that phosphorus reductions could lead to increased Cladophora biomass by improving light conditions will need to be considered carefully against the known historical success of controlling nuisance algae through nutrient management.