A Novel Method to Map and Quantify a Slow-growing Freshwater Alga, Heribaudiella fluviatilis (Aresch.) Sved

Gillian Cohen Barker, Fordham University


Non-random sampling and visual estimates, despite poor spatial resolution, are routinely employed in river studies to collect ecological data. Yet the technological capacity to overcome the shortcomings of these methods is available. This project aimed to establish randomized, spatially-explicit, observation-based field methods for the study of benthic, crust-forming algae in rivers. Methods were developed to investigate the spatial distribution, cover, and microhabitat preferences of Heribaudiella fluviatilis (Aresch.) Sved., in a second-order stream in Macedonia State Park, CT. H. fluviatilis is infrequently reported worldwide, but is the most common freshwater species within the brown algae (Phaeophyceae). It has been suggested, but unconfirmed, that abiotic factors, such as sunlight or current velocity, impact this species more strongly than biotic factors, such as grazing. These factors may together account for its apparently slow growth, compared to other stream-dwelling species. To evaluate these and other ecological questions, random, spatially-explicit sampling and photographic image analysis methods were developed to quantify fine-scale abundance and growth patterns. These methods are readily adaptable and easy to implement for any sessile species at a range of spatial scales, making randomized, quantitative, spatially-explicit methods more accessible. Using data gathered through these methods, I built a detailed map of H. fluviatilis distribution and canopy cover within a 40-m stream reach to determine whether canopy cover may influence H. fluviatilis presence and cover. Regions in which H. fluviatilis was found were significantly shadier than regons in which H. fluviatilis was not found, although within the range of canopy cover in locations in which H. fluviatilis did occur, the areal cover of colonies was greater in more open-canopy microhabitats. A sun-shade transplant study (confirmed by microscopy) conducted over a ten-month period (July 2018 – May 2019), determined that H. fluviatilis growth averaged 33.7 mm2/day in a highly shaded (ca. 90% cover) section of the stream, but only 1.95 mm2/day in a more open (ca. <40% cover) stream section. Analysis colonies photographed October 2018 and May 2019, demonstrated that colonies exhibited both thallus loss and growth, with an overall average increase of 0.11 mm2/day.

Subject Area

Ecology|Limnology|Physical geography

Recommended Citation

Barker, Gillian Cohen, "A Novel Method to Map and Quantify a Slow-growing Freshwater Alga, Heribaudiella fluviatilis (Aresch.) Sved" (2019). ETD Collection for Fordham University. AAI22618551.