Ecological Drivers of Freshwater Macroalgal Blooms across Trophic Gradients

点击翻译按钮获取中文摘要

The incidence of freshwater algal blooms has been increasing across North America, including regions with no historical record of bloom occurrence. This is a disconcerting trend when considering the negative social and economic impacts of algal blooms. Eutrophication and climate change have been implicated as major drivers of microalgal (i.e., phytoplankton) blooms. In contrast, macroalgal (i.e., visible mat-forming algae) blooms are not consistently explained by nutrients, nor is much known about the role of climate change. Morphologically diverse species of macroalgae bloom across a range of habitats and nutrient conditions (i.e., trophic states), even in systems where nutrients are low. This “nutrient-biomass” paradox may be explained by the shared characteristics of freshwater macroalgae: (1) a colony-matrix; and (2) a benthic or near-bed habitat. One possible driver of macroalgal blooms across trophic gradients involves the microbial community that lives on/within the colony-matrix (i.e., the “epibiome”), which may facilitate or supplement growth when external nutrients are variable or low. Another possible ecological driver is nutrient bioavailability in the benthic zone, whereby blooming species can exploit alternative forms of nutrients (e.g., dissolved organic phosphorus) compared to competing organisms. A likely over-arching driver of macroalgal blooms is climate change, which can either directly or indirectly influence bloom development irrespective of trophic state. As such, there are three main research objectives for this proposed program of study: (1) Determine how climate change directly/indirectly influences macroalgal blooms; (2) Assess the role of organic nutrient supply in macroalgal bloom development; and (3) Evaluate the role of the epibiome in facilitating growth in bloom-forming macroalgae. Three diverse, but representative macroalgal species (Didymosphenia geminata, Nitellopsis obtusa and Cladophora glomerata) with documented nuisance growth in systems representing a broad trophic gradient will be the main study taxa. Overall, this proposed research program will offer new insight on causes of nuisance macroalgal growth, including similarities and differences across taxa and ecosystems. It is anticipated that this information will prove useful to water managers from various levels of government seeking to control nuisance macroalgae outbreaks in their jurisdictions.