Can a rapid underwater video approach enhance the benthic assessment capability of the national coastal condition assessment in the great lakes?

Rapid assessment of Dreissena population in Lake Erie using underwater videography

Dreissenid bivalves (Dreissena polymorpha and D. rostriformis bugensis) are considered the most aggressive freshwater invaders inflicting profound ecological and economic impacts on the waterbodies that they colonize. Severity of these impacts depends on dreissenid population sizes which vary dramatically across space and time. We developed a novel method that analyzes video recorded using a Benthic Imaging System (BIS) in near real-time to assess dreissenid distribution and density across large waterbodies and tested it on Lake Erie. Lake Erie basins differ dramatically in morphometry, turbidity, and productivity, as well as in Dreissena distribution, density, and length-frequency distribution, providing an excellent model to test the applicability of our method across large and dynamic environmental gradients. Results of rapid assessment were subsequently compared with dreissenid density obtained from Ponar grab samples collected at the same sites. In the eastern and central basins, the differences in basin-wide density estimations from BIS and Ponar were 3% and 23%, respectively. In the western basin, this method had limited application due to high turbidity and abundance of small (< 10 mm length) mussels. By substantially reducing the time required to assess dreissenids across large areas, rapid assessment could be a useful and cost-effective addition for monitoring their populations.

Deep Lake Explorer: A web application for crowdsourcing the classification of benthic underwater video from the Laurentian Great Lakes

Underwater video is increasingly used to study aspects of the Great Lakes benthos including the abundance of round goby and dreissenid mussels. The introduction of these two species have resulted in major ecological shifts in the Great Lakes, but the species and their impacts have heretofore been underassessed due to limitations of monitoring methods. Underwater video (UVID) can "sample" hard bottom sites where grab samplers cannot. Efficient use of UVID data requires affordable and accurate classification and analysis tools. Deep Lake Explorer (DLE) is a web application developed to support crowdsourced classification of UVID collected in the Great Lakes. Volunteers (i.e., the crowd) used DLE to classify 199 videos collected in the Niagara River, Lake Huron, and Lake Ontario for the following attributes: round goby, Dreissena, and aquatic vegetation presence, and dominant substrate type. We compared DLE classification results to expert classification of the same videos to evaluate accuracy. Depending on the attribute, DLE had 77% (hard substrate) to 90% (vegetation presence) agreement with expert classification of videos. Detection rates, or the number of videos with an attribute detected by both volunteers and an expert divided by the number where only the expert detected the attribute, ranged from 62% (hard substrate) to 95% (soft substrate) depending on the attribute. Many factors affected accuracy, including video quality in the application, video processing, abundance of species of interest, volunteer experience, and task complexity. Crowdsourcing tools like DLE can increase timeliness and decrease costs but may come with tradeoffs in accuracy and completeness.

Biomonitoring Using Invasive Species in a Large Lake: Dreissena Distribution Maps Hypoxic Zones

Due to cultural eutrophication and global climate change, an exponential increase in the number and extent of hypoxic zones in marine and freshwater ecosystems has been observed in the last few decades. Hypoxia, or low dissolved oxygen (DO) concentrations, can produce strong negative ecological impacts and, therefore, is a management concern. We measured biomass and densities of Dreissena in Lake Erie, as well as bottom DO in 2014 using 19 high frequency data loggers distributed throughout the central basin to validate a three-dimensional hydrodynamic-ecological lake model. We found that a deep, offshore hypoxic zone was formed by early August, restricting the Dreissena population to shallow areas of the central basin. Deeper than 20 m, where bottom hypoxia routinely develops, only young of the year mussels were found in small numbers, indicating restricted recruitment and survival of young Dreissena. We suggest that monitoring Dreissena distribution can be an effective tool for mapping the extent and frequency of hypoxia in freshwater. In addition, our results suggest that an anticipated decrease in the spatial extent of hypoxia resulting from nutrient management has the potential to increase the spatial extent of profundal habitat in the central basin available for Dreissena expansion.

Benthic video image analysis facilitates monitoring of Dreissena populations across spatial scales

In contrast to marine systems where remote sensing methods in studies of benthic organisms have been widely used for decades, these methods have experienced limited use in studies of freshwater benthos due to the general lack of large epifauna. The situation has changed with the introduction of dreissenid bivalves capable of creating visible aggregations on lake bottoms into North American freshwaters in the 1980s and 1990s. The need for assessment of Dreissena densities prompted exploration of videography as a potentially cost-effective tool. We developed a novel sampling method that analyzes video recorded using a GoPro camera mounted to a benthic sled to estimate Dreissena coverage, density, and biomass over relatively large areas of the lake bed in the Laurentian Great Lakes compared to traditional sampling methods. Using this method, we compared quagga mussel coverage, density, and biomass estimates based on three replicate Ponar grabs vs. 500 m-long video transects across 43 stations sampled in Lake Michigan in 2015. Our results showed that analysis of images from video transects dramatically increased the bottom area surveyed compared to Ponar grabs and increased the precision of Dreissena density and biomass estimations at monitoring stations. By substantially increasing the ability to detect relatively small (<20%) changes between years within a particular station, this method could be a useful and cost-effective addition for monitoring Dreissena populations in the Great Lakes and other freshwater systems where they occur.