Mass loss and nutrient release of sloughed Cladophora

Abstract

Cladophora remains a nuisance algae across the Great Lakes region, and although its growth dynamics and nutrient needs are well-researched, little information is available on decomposition dynamics and nutrient release. We conducted a full-factorial laboratory experiment to investigate how wave action and presence of an omnivorous consumer (crayfish) affected the rate of tissue breakdown and subsequent leaching of nutrients back to the water column. Cladophora tissue lost roughly 70% of its wet weight within 20 days in all treatment tanks. Chlorophyl a content and %C declined over time in the tissues, whereas %N and %P in the tissue increased slightly over the experiment duration. Treatments with turbulence resulted in rapid disintegration of the algae, leaving the remaining material in suspension, whereas tissues in the control treatment remained in a single mass at the bottom of each aquaria. Cladophora tissue was shredded in crayfish tanks, but there was no evidence of consumption. Water column nutrient dynamics were complex, with significant time*treatment interactions making conclusions difficult. Overall, there was a reduction in water column SRP concentrations early in the experiment, followed by an increase across all treatments, suggesting that the algae was still absorbing SRP over the first 10 days, but then leaching this nutrient over the remaining 10 days. Collectively, these findings suggest that sloughed Cladophora was still photosynthetically active initially, but within 10 days leached nutrients back to the water column. Further work is needed to quantify the magnitude of this release and determine its potential for fueling late summer benthic or planktonic primary production.