Management implications of Cladophora resurgence in the Great Lakes

Document Type

Conference Paper/Presentation

Publication Date



Cladophora growth is limited by phosphorus (P). P limits in WWTP effluents in the 1970s apparently helped curb previously excessive algal growth, but nuisance conditions have returned since the invasion of dreissenids in the 1990s. The literature speaks of the 'resurgence' of Cladophora, but there is no widely accepted definition of this phenomenon. Nuisance growth, defined here as the amount of biomass available for deposition on beaches, depends on both the growth rate and the colonizable area. Both are ecosystem engineering outcomes of dreissenids, but only P is manageable. Management depends on the dominating factor. Here, we look at biomass densities, tissue P (directly related to the growth rate by Droop), and areal extent as shown by satellite imagery over three time periods: 1) pretreatment, pre-dreissenids (early 1970s); 2) post-treatment, pre-dreissenids (1980s); and 3) post-treatment, post-dreissenids (2000s). Lake Ontario shows no change in biomass density, decreasing tissue P, and increasing colonizable area since the dreissenid invasion. Resurgence is more a function of colonization than nutrient enrichment in this lake, but it is urban influences that allow increases in colonizable substrate to cause the resurgence; the alga does not benefit from increasing available area in P poor regions.

Publisher's Statement

© 2014 The authors.

Publication Title

IAGLR 57th Annual Conference on Great Lakes Research