Rapid response of the nearshore round goby population to temperature declines associated with upwelling events in Lake Ontario

Upwellings occur in all the Great Lakes in response to prolonged wind events. Several studies have modeled or measured changes in abiotic conditions associated with upwellings, but few direct observations of fish responses have been documented. Video-capture techniques were used in conjunction with moored temperature loggers to link the disappearance of benthic round gobies to temperature declines during upwelling events along the southern Lake Ontario nearshore in summer of 2019. Benthic water temperatures declined by as much as 18 °C within 18 h over as many as nine events. Round goby density estimates were as high as 50/m² prior to upwellings, but declined to as low as 0/m² during the events. Using just nine observation dates, ARMA trend analysis suggested a relationship between benthic temperature and round goby abundance (AIC = 78.7, t = 2.21, P = 0.063). Although the actual response of gobies to rapidly declining temperatures was unknown, this population was unobservable in our sample area during upwellings, yet returned to pre-upwelling densities within days. Understanding the magnitude and frequency of fish responses to these events can improve our understanding of the potential for this non-native benthic fish to affect the nearshore environment.     

Diet shift of double-crested cormorants in eastern Lake Ontario associated with the expansion of the invasive round goby

The proliferation of the invasive round goby (Apollonia melanostoma) in the Great Lakes has caused shifts in the trophic ecology in some areas. We examined the diet of double-crested cormorants (Phalacrocorax auritas) prior to, and immediately after, round goby population expansion at two colonies, Pigeon and Snake Islands, in eastern Lake Ontario from 1999 to 2007. Cormorant diet was determined from the examination of 10,167 pellets collected over the nine-year period. By the second year round gobies were found in the diet (2002 at Snake Island and 2003 at Pigeon Island) they were the main species consumed by cormorants at each colony. The dominance of round goby in cormorant diets had a significant effect on both daily fish consumption and seasonal trends in fish consumption compared to the pre-goby years. Seasonal differences that were observed during the pre-goby years were lost once gobies became the main diet component of cormorants. The rapid switch to a benthic prey such as round goby, from a largely limnetic fish diet demonstrates the adaptive foraging ability of cormorants. Round goby may act as a buffer for yellow perch and smallmouth bass, two sport fish impacted by cormorant predation in eastern Lake Ontario.     

Density and habitat use by the round goby (Apollonia melanostoma) in the Bay of Quinte,Lake Ontario

We assessed round goby (Apollonia melanostoma) density and size structure in two sections of the Bay of Quinte (Lake Ontario) that had been invaded by this species two years apart. Round goby density was assessed with 50 m linear transects, recorded with an underwater video recording apparatus developed for this study that included a depth sounder for maintaining a fixed distance above the substrate. The highest mean round goby densities were observed in the shallowest depth zone (1.5–3 m) at both sites, but there were differences between the sites in the habitat types where the highest densities occurred and there were no significant density differences among habitat types at either site (rock with sparse vegetation, mud with sparse vegetation, sand/mud with moderate vegetation cover). In the upper bay, mean body length of round gobies declined with depth, whereas in the lower bay, mean round goby length was greatest in the deepest zone. Mean body length of round gobies did not differ significantly by habitat type in either section of the bay.     

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 species has resulted in major ecological shifts in the Great Lakes, but the abundance and impacts of these species 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 presence of round gobies, dreissenid mussels, or aquatic vegetation, and for dominant substrate type. We compared DLE classification results to expert classification of the same videos to evaluate accuracy. DLE had the lowest agreement with expert classification for hard substrate (77%), and highest agreement for vegetation presence (90%), with intermediate agreement for round goby and mussel presence (89% and 79%, respectively). Video quality in the application, video processing, abundance of species of interest, volunteer experience, and task complexity may have affected accuracy. We provide recommendations for future crowdsourcing projects like DLE, which can increase timeliness and decrease costs for classification but may come with tradeoffs in accuracy and completeness.     

Impacts of the Introduced Round Goby (Apollonia melanostoma) on Dreissenids (Dreissena polymorpha and Dreissena bugensis) and on Macroinvertebrate Community between 2003 and 2006 in the Littoral Zone of Green Bay,Lake Michigan

We show that the invasion of round gobies (Apollonia melanostoma) in Green Bay, Lake Michigan, has changed the benthic food web in fundamental ways related to their impact on invasive dreissenid mussels. Dreissenid mussels are of specific interest because they are one of the primary dietary items for round gobies. In this study, we collected rocks from each of 10 study sites along approximately 60 km of the eastern shoreline of Green Bay, Lake Michigan, to assess a temporal change in macroinvertebrate abundance related to the northward movement of the round goby invasion front from a point about midway along the shoreline in 2003 to the entire coast in 2006. The pattern of macroinvertebrate abundance in 2003 suggested that round gobies had already caused significant decreases in macroinvertebrate abundances south of the invasion front (interpretation of the data could have been compromised by confounding environmental gradients). In subsequent sampling in 2006 macroinvertebrates were picked off of sampled rocks in the field and underwater transects were videotaped to estimate round goby abundance at each site. Round gobies were collected for stomach analysis to assist in determining which invertebrates would likely be impacted by goby predation. Our results indicated that by 2006, round gobies had become abundant at those sites where they were absent in 2003 and zebra mussels (Dreissena polymorpha), quagga mussels (Dreissena bugensis), isopods, amphipods, trichopterans, and gastropods in the newly invaded sites had significantly decreased at the newly invaded sites.     

Piscivory in recovering Lake Michigan cisco (Coregonus artedi): The role of invasive species

Contemporary conditions in Lake Michigan where cisco (Coregonus artedi) populations are expanding are vastly different from those encountered by the historic fish community. Invasive species introductions have substantially altered the Lake Michigan ecosystem in the last half century. Successful management efforts for cisco in Lake Michigan hinge on our ability to understand their contemporary ecology, especially diet. We collected 725 cisco stomachs opportunistically from commercial fisheries (2%) and in agency surveys (98%) over six years (2014–2019). The majority (70%) of stomachs were from East Grand Traverse Bay and 96% of these were collected at Elk Rapids. Additional samples were collected from Charlevoix (8%), Little Traverse Bay (11%), other sites in northern Lake Michigan (4%), Central Lake Michigan (6%), and Green Bay (1%). Our results indicated a high degree of piscivory, in contrast to historical and contemporary accounts of planktivory for cisco in the other Laurentian Great Lakes. The top three prey items by mass were not native to the Great Lakes and these accounted for 87% of all observed prey mass consumed: round goby (Neogobius melanostomus) (58%), Bythotrephes longimanus (15%), and alewife (Alosa pseudoharengus) (14%). Round goby dominated the prey in the spring and summer, while B. longimanus and alewife occurred more in summer and fall diets. The contemporary population of cisco in Lake Michigan has been able to uniquely capitalize on abundant invasive prey resources, which may be less limiting and more energy-rich than a more typical planktivorous cisco diet.     

Phenology and species diversity in a Lake Huron ichthyoplankton community: Ecological implications of invasive species dominance

Ichthyoplankton communities are dynamic and vary spatiotemporally based on factors such as wind, water currents, and phenology. Nonetheless, ichthyoplankton are an indicator of spawning success in fish populations and examining their community diversity and composition can serve to provide information on ecosystem integrity. Although some ichthyoplankton species may be transient, understanding their distribution in space and time provides information on species composition, abundance, and habitat use during critical early life stages. We sampled the spring-summer ichthyoplankton community during 2008 and 2009 in northern Lake Huron to determine species succession, abundance, and species diversity along physical and environmental gradients. Seasonal succession of species was similar during both years, indicating well-defined patterns in spawning by northern Lake Huron fish populations. Invasive alewife, rainbow smelt, and round goby were the dominant species during both years, with native stickleback species also abundant. Shannon Entropy (H′) increased with increasing water temperature until late summer when H′ declined. H′ decreased with increasing bottom depth and distance to tributary mouth indicating the important ecological role of these habitat features during early life stages. Although ichthyoplankton diversity was comparable to or higher than that reported for other areas of the Great Lakes, the prominence of invasive species in our study is reflective of the disturbed state of the Lake Huron fish community, despite large reductions in invasive planktivorous fish since 2004. Continued monitoring of ichthyoplankton communities will be important for measuring the impacts of species invasions or other ecosystem stressors on fish community structure in the Great Lakes.     

Developing and monitoring an innovative NNBF to nourish a bay bar: An example from the southeast shore of Lake Ontario

This project tests a cost-effective, innovative dredged sediment placement technique targeted to nourish an eroded barrier bar. The dredged sediment was placed in the nearshore in a Cobble Bell, a form designed to allow for efficient dispersal and migration of sediment by natural processes in this location (such as predominant waves and longshore transport) in a desired direction along the bar. We describe the regional and site assessment undertaken, and explain the way design parameters including technical feasibility, assumptions about wave climate, and constructability were accounted for. A monitoring protocol was designed and implemented to measure the vertical and horizontal accretion on the barrier bar. This included survey transects using RTK equipment and surface analysis of beach volume and morphology change via drone images and photogrammetry. Field measurements of the bar indicated that within the first few days, the piled material eroded rapidly, and over the next few months, migrated downshore, widening the previously breached area. This suggests that the cobble bell nature-based feature has the potential to both accelerate and slow down natural processes in ways that enhance the performance and attractiveness of the beach while minimizing costs. In addition to the monitoring results, we describe a monitoring protocol that is both simple and effective which can be adapted by local entities interested in the management of their coastal landscapes.     

Ecological tracers track changes in bird diets and possible routes of exposure to Type E Botulism

Dreissenid mussels have become important components of the Great Lakes biological community since their introduction in the 1980s, but much remains to be understood regarding their effect on energy and nutrient flows in pelagic systems. Here, we report a new method that tracks incorporation of resources of molluskan origin into food webs used by aquatic birds. Biochemical tracers (fatty acids and stable carbon isotopes) are used to characterize species associated with pelagic and benthic food webs in Lake Ontario. Our focus is on the polymethylene-interrupted fatty acids (PMI-FAs) because previous research identified mollusks as their primary source. We found that PMI-FA mass fractions were greater in organisms associated with benthic (e.g. round goby) versus pelagic (e.g. alewife) food webs. Double-crested cormorants that had recently consumed benthic prey fish, i.e. goby, had greater proportions of PMI-FAs in their blood plasma than birds which showed no signs of recent goby ingestion. We did not detect an increase in mass fractions of PMI-FAs in cryogenically archived cormorant eggs following expansion of dreissenid mussels in Lake Ontario. However, following the introduction and expansion of round goby in the lake, PMI-FAs were detected at greater levels in cormorant eggs. These results illustrate how only after dreissenid mussel-facilitated establishment of round goby was the full extent of exotic species disruption of food webs manifested in fish-eating birds. These food web changes may be contributing to negative impacts on aquatic birds exemplified by the emergence of Botulism Type E as a significant mortality factor in this ecosystem.     

Seasonal variation in the influence of environmental drivers on nearshore water quality along an urban northern Lake Ontario shoreline

We examined drivers of water quality during 2007–2013 in a region of Lake Ontario influenced by various anthropogenic inputs and natural influences. Nutrient concentrations generally declined from shoreline to offshore, with mean concentrations approaching background after 1 km from shore. N species were an exception to this overall pattern, often with higher concentrations coincident with a mid-nearshore Water Pollution Control Plant outfall (WPCPo). The WPCPo, however, did not appear to be a major contributor to shoreline total phosphorus (TP) or ammonia + ammonium. Shoreline TP variability increased in dry years, while E. coli and conductivity variability increased in wet years. The influence of environmental drivers on water quality differed seasonally. In summer, cross-shore winds causing resuspension appeared to be drivers of elevated nearshore TP and suspended solids (SS), while precipitation, light, and water column stability were related to E. coli. Summer biological activity was evident in higher shoreline total Kjeldhal N contributions and lower NO₃ + NO₂ and dissolved inorganic N. In fall and spring, TP, SS, and conductivity were elevated within 400 m of the shore, suggesting tributary inputs were an important P delivery mechanism to the nearshore in addition to spring resuspension events. Fall, however, represented a transitional period representing a shift from drivers dominant in summer to those in spring. The analytical approach used here reveals generalizable patterns in nearshore water quality and their drivers and may be applicable to other regions where there is a confluence of varying drivers of water quality to a nearshore region.     

Status of Mysis diluviana in Lake Ontario in 2013: Lower abundance but higher fecundity than in the 1990s

Mysis diluviana is a major component of prey fish diets in the Great Lakes, so annual production of M. diluviana is important for understanding and modeling energy flow through Great Lakes food webs. However, only three lake-wide measurements of M. diluviana annual production in Lake Ontario are currently available (1971, 1990, 1995). During 2013, lake-wide coverage of Lake Ontario was achieved during four periods from April to November. Annual mean density and biomass of M. diluviana in 2013 were 99?#/m² (SE: 8) and 318?mg?dw/m² (SE: 28) – approximately half of values observed in 1990s. M. diluviana comprised 13–30% of offshore zooplankton biomass in each period. Reproduction peaked in fall, with mean brood size of 32 embryos (range: 11–49), at least 10% larger than in 1990s. Generation time was two years from embryo to initial reproduction. Growth rates were 0.052?mm/d for the age-0 cohort and 0.027?mm/d for the age-1 cohort. Age-0 growth rate was significantly higher than in 1980s–90s (0.035?mm/d). Annual production in 2013 was 0.85?g?dw/m²/yr (SE: 0.03) which was 30–40% of values observed in 1990 and 1995 (2.23 and 2.53?g/m²/yr). Annual production to biomass ratio (P/B) in 2013 was 2.65?/yr which was 80–85% of values observed in 1990 and 1995 (3.24 and 3.11?/yr), but this difference was not statistically significant. Our results suggest that changes in annual production over time can be estimated using changes in biomass over time and a mean P/B ratio.     

DNA metabarcoding of the phytoplankton of Great Salt Lake’s Gilbert Bay: Spatiotemporal assemblage changes and comparisons to microscopy

The Great Salt Lake (GSL) is a unique hypersaline system with an understudied phytoplankton assemblage supporting a productive open water ecosystem in the largest embayment of the lake, Gilbert Bay. Determination of phytoplankton by microscopy has practical limitations that can constrain the scope of a study, but DNA metabarcoding may improve upon this through higher taxonomic resolution and the capacity to generate a large volume of assemblage data in comparatively little time. To determine if metabarcoding could replicate microscopy and expand the assessment of GSL phytoplankton, a 23S SSU rRNA metabarcoding and microscopy survey of Gilbert Bay was conducted in 2017 and 2018. Assemblage composition and relative abundances from each method were compared, and spatial and temporal assemblage changes from metabarcoding data were investigated using non-metric multidimensional scaling. Metabarcoding differed from microscopy in multiple taxonomic assignments and relative abundances, with poor correlation for most categories. Diatoms were overrepresented by metabarcoding relative to microscopy, and chlorophytes underrepresented. However, metabarcoding revealed seasonal and spatial patterns in assemblage, detected seasonal patterns within phytoplankton sequences of very low abundance, and detected potential cryptic speciation within the lake’s dominant Dunaliella viridis. Phylogenetic analysis revealed greater phytoplankton diversity than observed before in GSL, but demonstrated the need to improve taxonomic assignment of the resulting sequences, particularly within the diatoms. The expansion of detectable diversity and isolation of DNA sequences that can be traced through time and analyzed against environmental variables make metabarcoding a potentially effective tool for parallel use with microscopy in future GSL research.     

Spatial ecology of Bay of Quinte walleye (Sander vitreus): Annual timing,extent, and patterns of migrations in eastern Lake Ontario

Walleye (Sander vitreus) are the top nearshore predator in the Bay of Quinte and eastern Lake Ontario, where they have strong ecological and socio-economic impacts. The population is known to migrate seasonally; however, the precise timing and extent are not well defined. This study used acoustic telemetry to provide a fisheries-independent measure of timing, extent, and seasonal distribution of migration in Lake Ontario and to examine the influence of sex, spawning river, size, and year. Annual detection histories were used to determine the timing of migrations into and out of the spawning rivers, departure from the Bay of Quinte post-spawn, and the pre-spawn return to the Bay of Quinte. Sequence analysis was subsequently used to examine how fish occupy defined regions of eastern Lake Ontario annually and identify patterns in migration strategy. Spawning site fidelity was high for both rivers (91–97%) and annual residency within the Bay of Quinte was low (9.5%). Females spent less time in spawning rivers, migrated to the main lake earlier, and generally travelled further than males. Larger fish also migrated to the main lake first and travelled further, and differences in timing between spawning rivers were minor. Annual differences in timing were observed and were most likely related to environmental differences between years. Cluster analysis was used to identify groups of fish which utilized unique annual migration strategies and demonstrated sex and size had an important influence on the variability in annual spatial occupancy, but the importance of spawning river and year was minimal.     

Examining 20th century water quality and ecological changes in the Lake of the Woods, Ontario, Canada: A paleolimnological investigation

Comparisons between diatom assemblages preserved in modern and pre-industrial sediments were made to provide a lake-wide paleolimnological assessment of environmental change in 17 sites located throughout the Ontario portion of the Lake of the Woods (LoW). Diatom changes were consistent across all sites, although the magnitude of these changes varied along a trophic gradient (i.e., main channel sites versus isolated bays). The most notable taxonomic shift was towards a higher relative abundance of small, centric Cyclotella taxa and other planktonic, pennate diatoms (e.g., Asterionella formosa, Fragilaria crotonensis) in the modern sediments, with corresponding lower relative abundances of heavily silicified Aulacoseira taxa and small benthic Fragilaria taxa. To aid in determining whether changes in nutrients can explain the diatom trends, weighted-averaging partial-least-squares (WA-PLS) techniques were used to develop a diatom-based inference model to reconstruct changes in total phosphorus (TP) concentrations. Diatom-inferrred TP (DI-TP) reconstructions revealed that 88% of the sites showed either no change or a slight, but not significant decline in DI-TP since pre-industrial times. Diatom-based inferences suggest that TP concentrations at many sites in the Ontario portion of the LoW were moderately elevated in nutrients prior to any major human disturbances (i.e., pre-1850). Results suggest that substantial increases in temperature over the last few decades, and the associated changes to ice cover and water column properties, have likely exacerbated the effects of existing stressors on the system and were key factors influencing a lake-wide restructuring of the diatom communities over the past ca. 150 years.     

Historical changes of a large river in an urban area: The Garonne river,Toulouse, France

Man-made structures have greatly modified the flow pattern of the Garonne River at Toulouse (France) since at least the 12th century. The first of many small dams was constructed in 1182. Destructive floods regularly destroyed the dams, flooded protions of the city, changed the river course, and destroyed the wooden bridges, the first of which was probably built during the first half of the 13th century. The first stone bridge was completed in 1660, after a 100 year period of constuction. After 1680 attempts to control the river led to a variety of river responses: increased sedimentation in some locations and erosion in others, a reduction in the number of islands from seventeen to four, and a 63 per cent reduction in the length of shoreline in the urban area of Toulouse.     

Sea lamprey wounding in Canadian waters of Lake Huron from 2000 to 2009: Temporal changes differ among regions

Lake Huron has undergone a number of substantial changes in recent years, including changes to management of the parasitic sea lamprey, Petromyzon marinus. While control strategies of lamprey involving lampricides have had some success, lamprey spawning in St. Marys River has been a major and persistent problem and has led to intensified treatment beginning in 1998. The objective of our study was to broadly examine lamprey spatial wounding dynamics of lake whitefish (Coregonus clupeaformis) and lake trout (Salvelinus namaycush) within the Canadian waters of Lake Huron from 2000 to 2009. Temporal trends were evident and these differed among regions (North Channel, northern Main Basin, southern Main Basin, northern Georgian Bay, and southern Georgian Bay). There was a monotonic annual increase in probability of wounding for both lake trout and lake whitefish in three of the five regions, with high increases seen in both northern and southern Georgian Bay. The increases in three of the five regions are unexpected given the ongoing treatment of St. Marys River.