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Dylan Baker, James Lauer, Anna Ortega, Sara L. Jackrel, Vincent J. Denef

Phytoplankton is fundamental to life on Earth. Their productivity is influenced by the microbial communities residing in the phycosphere surrounding algal cells. Expanding our knowledge on how algal-bacterial interactions affect algal growth to more hosts and bacteria can help elucidate general principles of algal-host interactions. Here, we isolated 368 bacterial strains from phycosphere communities, right after phycosphere recruitment from pond water and after a month of lab cultivation and examined their impacts on growth of five green algal species. We isolated both abundant and rare phycosphere members, representing 18.4% of the source communities. Positive and neutral effects predominated over negative effects on host growth. The proportion of each effect type and whether the day of isolation mattered varied by host species. Bacteria affected algal carrying capacity more than growth rate, suggesting that nutrient remineralization and toxic byproduct metabolism may be a dominant mechanism. Across-host algal fitness assays indicated host-specific growth effects of our isolates. We observed no phylogenetic conservation of the effect on host growth among bacterial isolates. Even isolates with the same ASV had divergent effects on host growth. Our results emphasize highly specific host-bacterial interactions in the phycosphere and raise questions as to which mechanisms mediate these interactions.

Nikesh Dahal, Paul Glyshaw, Glenn Carter, Henry A Vanderploeg, Vincent J Denef

Bacteria represent most of the biodiversity and play key roles in virtually every ecosystem. In doing so, bacteria act as part of complex communities shaped by interactions across all domains of life. Here, we report on direct interactions between bacteria and dreissenid mussels, a group of invasive filter-feeders threatening global aquatic systems due to high filtration rates. Previous studies showed that dreissenids can impact bacterial community structure by changing trait distributions and abundances of specific taxa. However, studies on bacterial community effects were conducted using water from Lake Michigan (an oligotrophic lake) only, and it is unknown whether similar patterns are observed in systems with differing nutrient regimes. We conducted ten short-term dreissenid grazing experiments in 2019 using water from two eutrophic lake regions—the western basin of Lake Erie and Saginaw Bay in Lake Huron. Predation by dreissenids led to decline in overall bacterial abundance and diversity in both lakes. However, feeding on bacteria was not observed during every experiment. We also found that traits related to feeding resistance are less phylogenetically conserved than previously thought. Our results highlight the role of temporal, spatial, and genomic heterogeneity in bacterial response dynamics to a globally important invasive filter feeder.

Bopaiah Biddanda, Deborah Dila, Anthony Weinke, Jasmine Mancuso, Manuel Villar-Argaiz, Juan Manuel Medina-Sánchez, Juan Manuel González-Olalla, Presentación Carrillo

Who’s cooking, who’s cleaning, and who’s got the remote control within the waters blanketing Earth? Anatomically tiny, numerically dominant microbes are the crucial “homemakers” of the watery household. Phytoplankton’s culinary abilities enable them to create food by absorbing sunlight to fix carbon and release oxygen, making microbial autotrophs top-chefs in the aquatic kitchen. However, they are not the only bioengineers that balance this complex household. Ubiquitous heterotrophic microbes including prokaryotic bacteria and archaea (both “bacteria” henceforth), eukaryotic protists, and viruses, recycle organic matter and make inorganic nutrients available to primary producers. Grazing protists compete with viruses for bacterial biomass, whereas mixotrophic protists produce new organic matter as well as consume microbial biomass. When viruses press remote-control buttons, by modifying host genomes or lysing them, the outcome can reverberate throughout the microbial community and beyond. Despite recognition of the vital role of microbes in biosphere housekeeping, impacts of anthropogenic stressors and climate change on their biodiversity, evolution, and ecological function remain poorly understood. How trillions of the smallest organisms in Earth’s largest ecosystem respond will be hugely consequential. By making the study of ecology personal, the “housekeeping” perspective can provide better insights into changing ecosystem structure and function at all scales.

Matthew Jurjonas, Christopher A. May, Bradley J. Cardinale, Stephanie Kyriakakis, Douglas R. Pearsall, Patrick J. Doran

The Great Lakes Restoration Initiative (GLRI), designed to restore and protect the ecology of the Laurentian Great Lakes, is one of the largest environmental funding programs in the United States. Over 5,400 grants have been awarded in the last 11 years (2010–2020), representing over $3.5 billion in federal spending. A publicly available database that contains a written description about each grant is available online. However, analysis cannot easily be performed given that the descriptions are only textual. Therefore, we applied a modified version of the Conservation Action Classification (CAC 2.0), an established framework from the Open Standards for the Practice of Conservation, to synthesize the number of restoration actions, target species, and specific threats mentioned using thematic content analysis. The framework was modified to expand the CAC 2.0 by adding actions specific to GLRI. For example, we created typologies for the monitoring performed, site stewardship actions, and maritime ballast management practices. Based on this tally, we provide a summary of all the GLRI efforts to date. In addition to the more widely known restoration actions, we also describe the extent of educational, capacity building, and the non-monetary value projects that considered human wellbeing and/or focused on traditional ecological knowledge, recreation, or public outreach and engagement. Finally, we conclude with a discussion about the state of GLRI, the extent of the social or community-oriented efforts, and possible areas for adaptive management. This systematic coding process, and our shared supplementary data, can assist future GLRI research and strategic planning.

Tian Guo, Victoria Campbell-Arvai, Bradley J. Cardinale

This research examines public acceptability of regulations to reduce agricultural nutrient runoff and curb Harmful Algal Blooms (HABs). We tested the effects of two novel policy specific beliefs including support for farmers’ autonomy and support for external accountability. We also simultaneously tested the direct and indirect effects of political orientation and environmental worldview through a Direct Effect Model and a Mediation Model using structural equation modelling. Survey data were collected from 729 Ohio residents collected in November 2018. The specific regulatory policy measure we targeted is fines on excessive agricultural runoff. As hypothesized, autonomy beliefs negatively affect, and accountability positively affect support for fines. Both models revealed good fits. the direct effects of environmental worldviews political orientation were not supported. Instead, environmental worldviews indirectly increased support for fines through increased accountability beliefs and diminished autonomy beliefs. From the results, we suggest that when proposing suitable regulations for specific sites, policy makers and interest groups should be aware of differences in public support for farmer autonomy and external accountability, and that such differences are likely rooted in environmental worldviews. The study also suggests a need for coupled ecological and social studies that assess the likelihood of regional agricultural producers voluntarily adopting conservation practices and forecast the effectiveness of potential accountability measures.

Qiongqiong Cai, Jia Wang, Dmitry Beletsky, James Overland, Moto Ikeda, Liying Wan

The 168 year trends of summer (July–September) sea ice area (SIA) variations in six Arctic regions during 1850–2017 are analyzed. SIA has been significantly decreasing in most Arctic regions since 1850. The rate of retreat for the period of 1948–2017 accelerated multi-fold. For the nearly four decades since 1979, most Arctic regions are experiencing the highest reduction rate. Besides the increasing surface air temperature, the key drivers to the accelerated summer Arctic sea ice decline are found to be the combined global warming and the regional Arctic warming exerted simultaneously by the Arctic Oscillation, North Atlantic Oscillation, Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation during the last several decades. The dynamical and thermodynamical warming, driven by the internal variability of the teleconnection patterns, occurred in the last several decades, in particular on the multidecadal timescales. This leads to Arctic amplification that accelerates the positive ice/ocean albedo feedback loop, resulting in accelerating summer sea ice decline.

Hanna S. Anderson, Thomas H. Johengen, Casey M. Godwin, Heidi Purcell, Peter J. Alsip, Steve A. Ruberg, Lacey A. Mason

Lake Erie’s central basin experiences seasonal anoxia, contributing to internal sediment phosphorus (P) loading and exacerbating eutrophication. The precise conditions required for internal loading are poorly understood. This study constrains the timing and rates of internal P loading using continuous in situ temperature, dissolved oxygen (DO), and soluble reactive P (SRP) observations from two sites. SRP concentrations remained low during normoxia (>2 mg of DO L–1) and hypoxia (0–2 mg of DO L–1) but increased abruptly after anoxia for 12–42 h. SRP flux rate estimations varied, likely due to advection and hypolimnion thickness variation, but could still be reasonably quantified. Flux rates and standard errors during anoxia averaged 25.67 ± 5.5 mg m–2 day–1 at the shallower site and 11.42 ± 2.6 mg m–2 day–1 at the deeper site. At the shallower site, the anoxic hypolimnion was displaced with normoxic water, causing cessation of P flux until anoxia returned, and higher flux rates resumed immediately (89.1 ± 8.6 mg m–2 day–1), suggesting rapid, redox-controlled P desorption from surface sediments. On the basis of our rate and onset findings, the expected anoxic area and duration in the basin could yield an annual internal SRP load comparable to the annual central basin TP tributary load of 10000–11000 metric tonnes.

Freya E. Rowland, Craig A. Stow, Thomas H. Johengen, Ashley M. Burtner, Danna Palladino, Duane C. Gossiaux, Timothy W. Davis, Laura T. Johnson, Steve Ruberg

Despite the initial success of extensive efforts to reduce phosphorus (P) loading to Lake Erie as a part of the Great Lakes Water Quality Agreement, Lake Erie appears to be undergoing a re-eutrophication and it is plagued by harmful algal blooms. To offer insights into potential lake responses under differing Maumee River loads and reveal recent changes with time, we explored patterns in phosphorus and chlorophyll a data from 2008 to 2018 collected in western Lake Erie near the mouth of the Maumee River. We found high, but relatively stable Maumee River and lake concentrations of total P (TP) and soluble reactive P (SRP) with no discernable annual or seasonal patterns. Maumee spring TP load was not strongly related to lake TP, and lake SRP concentrations were positively but weakly related to SRP loads. Lake TP was a strong predictor of chlorophyll a, but the relationship was weaker at sites closer to the Maumee. These results highlight spatial differences both in P concentration and the relationship between TP and chlorophyll a, and these indicate that spring phosphorus loads are a weak algal biomass predictor in the portion of the western basin of Lake Erie represented by these sampling stations.

Jia Wang, Yang Ting-Yi, James Kessler

This report investigates interannual variability in ice coverage (Bai et al., 2012; Assel et al., 1998; Assel et al., 2013). We conduct analyses of the ice coverage records—freeze-up date, break-up date, duration and annual maximum ice coverage (AMIC)—with air temperature —cumulative freezing degree days (FDD), winter severity index (WSI)—and atmospheric teleconnections—El Niño–Southern Oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO). In addition, we use scatter plots and linear / non-linear regression, to determinate whether they have linear or quadratic relationships. The purpose of this report is to provide users with the Great Lakes environmental parameters and in depth analyses that are easily digested and applied to resources management, projection, and planning.

Craig A. Stow, Qianqian Liu, Eric J. Anderson

The “phosphorus loading concept,” or more generally the “nutrient loading concept,” arose from Richard Vollenweider’s work in the 1960–1970s that showed correlations between phosphorus loads and various eutrophication symptoms. The initial success of target loads developed for the Great Lakes solidified the concept that nutrient loading causes eutrophication, and load targets have become common tools to reduce eutrophication. Using concepts from the field of causality, we offer additional context to the nutrient loading concept to show that the correlation between nutrient load and eutrophication is spurious; load and eutrophication have common drivers, tributary flow and tributary nutrient concentration, but load itself is not causal. Consequently, in-lake conditions are not invariant to the same load delivered at differing flow-concentration combinations. We then use a simulation model to evaluate the consequences of delivering the same load at various flow-concentration combinations from the Maumee River into Lake Erie. We show that load reductions under increased tributary flows may cause in-lake phosphorus concentration increases, potentially offsetting the anticipated effect of the load reduction. Thus, particularly under a scenario where climate change may cause systematic flow changes, it will be important to expand the nutrient loading concept to consider the independent effects of tributary flow and nutrient concentrations, to assess the effectiveness of nutrient reduction strategies.