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1. Environmental factors affecting chytrid (Chytridiomycota) infection rates on Planktothrix agardhii

   https://doi.org/10.1093/plankt/fbab058  

   McKindles, Katelyn M; Manes, Makayla A; McKay, R Michael; Davis, Timothy W; Bullerjahn, George S (August 2021, Journal of Plankton Research)

   Beisner, Beatrix E (Ed.)

   Abstract Planktothrix agardhii dominates the cyanobacterial harmful algal bloom biomass in Sandusky Bay, Lake Erie (USA) from May until September. This filamentous cyanobacterium known parasites including the chytrid fungal species Rhizophydium sp. C02, which was previously isolated from this region. The purpose of our work has been to establish how parasitic interactions affect Planktothrix population dynamics during a bloom event. Samples analyzed from the 2015 to 2019 bloom seasons using quantitative PCR investigate the spatial and temporal prevalence of chytrid infections. Abiotic factors examined in lab include manipulating temperature (17–31°C), conductivity (0.226–1.225 mS/cm) and turbulence. Planktothrix-specific chytrids are present throughout the bloom period and are occasionally at high enough densities to exert parasitic pressure on their hosts. Temperatures above 27.1°C in lab can inhibit chytrid infection, indicating the presence of a possible upper thermal refuge for the host. Data suggest that chytrids can survive conductivity spikes in lab at levels three-fold above Sandusky Bay waters if given sufficient time (7–12 days), whereas increased turbulence in lab severely inhibits chytrid infections, perhaps due to disruption of chemical signaling. Overall, these data provide insights into the environmental conditions that inhibit chytrid infections during Planktothrix-dominated blooms in temperate waters. 

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2. Deterioration of the Littoral–Benthic Ecosystem Following Recent Expansion of Signal Crayfish (Pacifastacus leniusculus) in the World’s Clearest Large Lake

   https://doi.org/10.1007/s10021-023-00846-0  

   Scordo, Facundo; Girdner, Scott F.; San Pedro, Aldo; Seitz, Carina; Chandra, Sudeep (May 2023, Ecosystems)

   Some biological invasions can result in algae blooms in the nearshore of clear lakes. We studied if an invasive crayfish (Pacifastacus leniusculus) modified the biomass and community composition of benthic macroinvertebrates and therefore led to a trophic cascade resulting in increased periphyton biomass, elevated littoral primary productivity, and benthic algae bloom in a lake with remarkable transparency [Crater Lake, Oregon, USA]. After quantifying the changes in the spatial distribution of invasive crayfish over a 13-year period, we compared biomass and community composition of littoral–benthic macroinvertebrates, periphyton biovolume, community composition, nutrient limitation, and the development of benthic algae bloom in locations with high and low crayfish density. In addition, we determined if the alteration in community structure resulted in directional changes to gross primary production and ecosystem respiration. The extent of crayfish distribution along the shoreline of Crater Lake doubled over a 13-year period, leaving less than 20% of the shoreline free from crayfish. At high crayfish density sites, benthic macroinvertebrate biomass was 99% lower, and taxa richness was 50% lower than at low crayfish areas. High crayfish sites show tenfold greater periphyton biovolume, sixfold higher periphyton biomass (chlorophyll a), twofold higher metabolic productivity, and the presence of large filamentous algae (Cladophora sp.). The invasion of crayfish had negative consequences for a lake protected under the management of the USA National Park Service, with direct impacts on many levels of ecological organization. 

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3. Tracing the active genetic diversity of Microcystis and Microcystis phage through a temporal survey of Taihu

   https://doi.org/10.1371/journal.pone.0244482  

   Pound, Helena L.; Wilhelm, Steven W. (December 2020, PLOS ONE)

   Humbert, Jean-François (Ed.)

   Harmful algal blooms are commonly thought to be dominated by a single genus, but they are not homogenous communities. Current approaches, both molecular and culture-based, often overlook fine-scale variations in community composition that can influence bloom dynamics. We combined homology-based searches (BLASTX) and phylogenetics to distinguish and quantify Microcystis host and phage members across a summer season during a 2014 Microcystis- dominated bloom that occurred in Lake Tai ( Taihu ), China. We found 47 different genotypes of the Microcystis- specific DNA-dependent RNA polymerase ( rpo B), which included several morphospecies. Microcystis flos-aquae and Microcystis wesenbergii accounted for ~86% of total Microcystis transcripts, while the more commonly studied Microcystis aeruginosa only accounted for ~7%. Microcystis genotypes were classified into three temporal groups according to their expression patterns across the course of the bloom: early, constant and late. All Microcystis morphospecies were present in each group, indicating that expression patterns were likely dictated by competition driven by environmental factors, not phylogeny. We identified three primary Microcystis -infecting phages based on the viral terminase, including a novel Siphoviridae phage that may be capable of lysogeny. Within our dataset, Myoviridae phages consistent with those infecting Microcystis in a lytic manner were positively correlated to the early host genotypes, while the Siphoviridae phages were positively correlated to the late host genotypes, when the Myoviridae phages express putative genetic markers for lysogeny. The expression of genes in the microcystin-encoding mcy cassette was estimated using mcyA , which revealed 24 Microcystis- specific genotypes that were negatively correlated to the early host genotypes. Of all environmental factors measured, pH best described the temporal shift in the Microcystis community genotypic composition, promoting hypotheses regarding carbon concentration mechanisms and oxidative stress. Our work expounds on the complexity of HAB events, using a well-studied dataset to highlight the need for increased resolution of community dynamics. 

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4. Convergent photophysiology and prokaryotic assemblage structure in epilithic cyanobacterial tufts and algal turf communities

   https://doi.org/10.1111/jpy.13424  

   Cissell, Ethan C; McCoy, Sophie J (April 2024, Journal of Phycology)

   Abstract As global change spurs shifts in benthic community composition on coral reefs globally, a better understanding of the defining taxonomic and functional features that differentiate proliferating benthic taxa is needed to predict functional trajectories of reef degradation better. This is especially critical for algal groups, which feature dramatically on changing reefs. Limited attention has been given to characterizing the features that differentiate tufting epilithic cyanobacterial communities from ubiquitous turf algal assemblages. Here, we integrated an in situ assessment of photosynthetic yield with metabarcoding and shotgun metagenomic sequencing to explore photophysiology and prokaryotic assemblage structure within epilithic tufting benthic cyanobacterial communities and epilithic algal turf communities. Significant differences were not detected in the average quantum yield. However, variability in yield was significantly higher in cyanobacterial tufts. Neither prokaryotic assemblage diversity nor structure significantly differed between these functional groups. The sampled cyanobacterial tufts, predominantly built byOkeaniasp., were co‐dominated by members of the Proteobacteria, Firmicutes, and Bacteroidota, as were turf algal communities. Few detected ASVs were significantly differentially abundant between functional groups and consisted exclusively of taxa belonging to the phyla Proteobacteria and Firmicutes. Assessment of the distribution of recovered cyanobacterial amplicons demonstrated that alongside sample‐specific cyanobacterial diversification, the dominant cyanobacterial members were conserved across tufting cyanobacterial and turf algal communities. Overall, these data suggest a convergence in taxonomic identity and mean photosynthetic potential between tufting epilithic cyanobacterial communities and algal turf communities, with numerous implications for consumer‐resource dynamics on future reefs and trajectories of reef functional ecology. 

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5. Unusual Hemiaulus bloom influences ocean productivity in Northeastern US Shelf waters

   https://doi.org/10.5194/bg-21-1235-2024  

   Castillo_Cieza, S_Alejandra; Stanley, Rachel_HR; Marrec, Pierre; Fontaine, Diana_N; Crockford, E_Taylor; McGillicuddy_Jr, Dennis_J; Mehta, Arshia; Menden_Deuer, Susanne; Peacock, Emily_E; Rynearson, Tatiana_A; et al (March 2024, Biogeosciences)

   Abstract. Because of its temperate location, high dynamic range of environmental conditions, and extensive human activity, the long-term ecological research site in the coastal Northeastern US Shelf (NES) of the northwestern Atlantic Ocean offers an ideal opportunity to understand how productivity shifts in response to changes in planktonic community composition. Ocean production and trophic transfer rates, including net community production (NCP), net primary production (NPP), gross oxygen production (GOP), and microzooplankton grazing rates, are key metrics for understanding marine ecosystem dynamics and associated impacts on biogeochemical cycles. Although small phytoplankton usually dominate phytoplankton community composition and Chl a concentration in the NES waters during the summer, in August 2019, a bloom of the large diatom genus Hemiaulus, with N2-fixing symbionts, was observed in the mid-shelf region. NCP was 2.5 to 9 times higher when Hemiaulus dominated phytoplankton carbon compared to NCP throughout the same geographic area during the summers of 2020–2022. The Hemiaulus bloom in summer 2019 also coincided with higher trophic transfer efficiency from phytoplankton to microzooplankton and higher GOP and NPP than in the summers 2020–2022. This study suggests that the dominance of an atypical phytoplankton community that alters the typical size distribution of primary producers can significantly influence productivity and trophic transfer, highlighting the dynamic nature of the coastal ocean. Notably, summer 2018 NCP levels were also high, although the size distribution of Chl a was typical and an atypical phytoplankton community was not observed. A better understanding of the dynamics of the NES in terms of biological productivity is of primary importance, especially in the context of changing environmental conditions due to climate processes. 

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