More Like this

1. Temporal changes in diatom valve diameter indicate shifts in lake trophic status

   Siver, Peter A.; Sibley, Joel; Lott, Anne M.; Marsicano, Larry (January 2021, Journal of paleopathology)

   null (Ed.)

   When diatoms undergo vegetative cell division the new siliceous wall components are slightly smaller than those of the parent because they are produced within the confines of the parent wall. Thus, with continued growth the mean size of cells in a population declines. Given this unique feature of diatom cell division, if the growth of a species in a lake increases (decreases) under more (less) favorable conditions, then the mean size of the resulting population will decline (increase). Numerous paleolimnological investigations rely on shifts in the relative abundances of diatom species over time to infer lake conditions. Although relative abundance data yield information about the dominance of species in the community, they do not necessarily provide evidence about growth of a given species. For instance, a species could have increased in growth, but simply to a lesser extent than other taxa, resulting in a decline in relative abundance. In a similar fashion, relative abundance values can be misleading when used to infer environmental change, such as trophic status change in lakes. We propose that including data on mean size of diatom valves can yield greater insight into changes in growth and improve observations and conclusions based on relative abundance data. To test this concept, we examined changes in the mean diameter of Aulacoseira ambigua (Grunow) Simonsen valves relative to known shifts in lake trophic status in a core from Bantam Lake, Connecticut, representing * 130 years of sediment accumulation. The mean valve diameter of A. ambigua declined from 9.7 to 7.6 lm, with the largest declines clearly tracking significant increases in trophic status. We conclude that changes in the mean size of diatom frustules over time can provide valuable information for understanding long-term environmental changes. 

   more » « less
2. Time-series metagenomics reveals changing protistan ecology of a temperate dimictic lake

   https://doi.org/10.1186/s40168-024-01831-y  

   Krinos, Arianna I.; Bowers, Robert M.; Rohwer, Robin R.; McMahon, Katherine D.; Woyke, Tanja; Schulz, Frederik (July 2024, Microbiome)

   Abstract BackgroundProtists, single-celled eukaryotic organisms, are critical to food web ecology, contributing to primary productivity and connecting small bacteria and archaea to higher trophic levels. Lake Mendota is a large, eutrophic natural lake that is a Long-Term Ecological Research site and among the world’s best-studied freshwater systems. Metagenomic samples have been collected and shotgun sequenced from Lake Mendota for the last 20 years. Here, we analyze this comprehensive time series to infer changes to the structure and function of the protistan community and to hypothesize about their interactions with bacteria. ResultsBased on small subunit rRNA genes extracted from the metagenomes and metagenome-assembled genomes of microeukaryotes, we identify shifts in the eukaryotic phytoplankton community over time, which we predict to be a consequence of reduced zooplankton grazing pressures after the invasion of a invasive predator (the spiny water flea) to the lake. The metagenomic data also reveal the presence of the spiny water flea and the zebra mussel, a second invasive species to Lake Mendota, prior to their visual identification during routine monitoring. Furthermore, we use species co-occurrence and co-abundance analysis to connect the protistan community with bacterial taxa. Correlation analysis suggests that protists and bacteria may interact or respond similarly to environmental conditions. Cryptophytes declined in the second decade of the timeseries, while many alveolate groups (e.g., ciliates and dinoflagellates) and diatoms increased in abundance, changes that have implications for food web efficiency in Lake Mendota. ConclusionsWe demonstrate that metagenomic sequence-based community analysis can complement existing efforts to monitor protists in Lake Mendota based on microscopy-based count surveys. We observed patterns of seasonal abundance in microeukaryotes in Lake Mendota that corroborated expectations from other systems, including high abundance of cryptophytes in winter and diatoms in fall and spring, but with much higher resolution than previous surveys. Our study identified long-term changes in the abundance of eukaryotic microbes and provided context for the known establishment of an invasive species that catalyzes a trophic cascade involving protists. Our findings are important for decoding potential long-term consequences of human interventions, including invasive species introduction. 

   more » « less
3. Coexisting picoplankton experience different relative grazing pressures across an ocean productivity gradient

   https://doi.org/10.1073/pnas.2220771120  

   Landry, Michael R.; Stukel, Michael R.; Selph, Karen E.; Goericke, Ralf (October 2023, Proceedings of the National Academy of Sciences)

   Picophytoplankton populations [Prochlorococcus,Synechococcus(SYN), and picoeukaryotes] are dominant primary producers in the open ocean and projected to become more important with climate change. Their fates can vary, however, with microbial food web complexities. In the California Current Ecosystem, picophytoplankton biomass and abundance peak in waters of intermediate productivity and decrease at higher production. Using experimental data from eight cruises crossing the pronounced CCE trophic gradient, we tested the hypothesis that these declines are driven by intensified grazing on heterotrophic bacteria (HBAC) passed to similarly sized picophytoplankton via shared predators. Results confirm previously observed distributions as well as significant increases in bacterial abundance, cell growth, and grazing mortality with primary production. Mortalities of picophytoplankton, however, diverge from the bacterial mortality trend such that relative grazing rates on SYN compared to HBAC decline by 12-fold between low and high productivity waters. The large shifts in mortality rate ratios for coexisting populations are not explained by size variability but rather suggest high selectivity of grazer assemblages or tightly coupled tradeoffs in microbial growth advantages and grazing vulnerabilities. These findings challenge the long-held view that protistan grazing mainly determines overall biomass of microbial communities while viruses uniquely regulate diversity by “killing the winners”. 

   more » « less
4. Trophic niche dynamics of two fish mesoconsumers in adjacent coastal habitats with varying nutrient regimes

   https://doi.org/10.1007/s00442-025-05680-w  

   Santos, Rolando O; James, W Ryan; Rehage, Jennifer S; Eggenberger, Cody W; Lesser, Justin S; Madden, Christopher J (March 2025, Oecologia)

   Changes of consumers’ trophic niches, the n-dimensional biotic space that allows a species to satisfy its minimum requirements for population growth, are driven in part by shifts in the degree of individual resource use specialization within a population. Individual specialization results from complex trade-offs in inter- and intraspecific competition as organisms reduce niche overlap within a population or with heterospecifics. It is vital to build empirical knowledge on the trophic niche dynamics of consumers, given the role that niche dynamics play in food web stability, species coexistence, and population resilience, especially quantifying the trophic niche’s expansion and contraction of coastal fish populations experiencing increasing frequency of environmental disturbance and habitat transformation. In coastal ecosystems, disturbances alter the connectivity, productivity, and nutrient regimes of aquatic habitats, which could lead to significant shifts in consumers’ trophic niches. We investigated the trophic niche dynamics of two fish species Centropomus undecimalis (Common Snook) and Megalops atlanticus (Atlantic Tarpon), across two adjacent coastal lake systems of varying nutrient regimes (eutrophic vs. mesotrophic) and hydrological connectivity. In both systems, Snook had larger trophic niches than Tarpon. Also, the trophic niche size in the eutrophic system was larger than the mesotrophic system for both species. Snook and Tarpon used different prey resources, resulting in low niche overlap between species in both systems. Our results highlight how altered hydrological connectivity, and nutrient regimes can shift trophic niche dynamics of higher trophic-level consumers, likely due to changes in prey landscapes and shifts in the foraging ecology of species. 

   more » « less
5. Density Dependence in Three Snake River Sockeye Salmon Nursery Lakes in Central Idaho

   https://doi.org/10.1002/nafm.10835  

   Griswold, Robert_G; Kohler, Andre_E; Tardy, Kurt_A; Griswold, Kitty_E; Taki, Doug (October 2022, North American Journal of Fisheries Management)

   Abstract Snake River Sockeye Salmon Oncorhynchus nerka, listed as an endangered species in 1991, currently inhabit three nursery lakes (Redfish, Pettit, and Alturas lakes) in the Sawtooth Valley, Idaho. Conspecific kokanee (lacustrine Sockeye Salmon) are also present in the lakes. Snake River Sockeye Salmon recovery efforts, initially focused on genetic conservation, are now attempting to rebuild naturally spawning populations using hatchery supplementation. However, in Sockeye Salmon nursery lakes, density dependence is frequently observed when elevated O. nerka abundance leads to declines in zooplankton biomass, body size, and shifts in community composition. In turn, these changes lead to reductions in juvenile O. nerka growth rates, survival, and adult returns. We examined a long-term data set of O. nerka population metrics and associated zooplankton community metrics. We found evidence of density dependence within and among nursery lakes. We detected differences in zooplankton biomass, lengths of preferred zooplankton prey (Daphnia spp. and cyclopoid copepods), parr growth rates, and age-1 smolt size among the three lakes. We found negative relationships between O. nerka density and zooplankton biomass and size. We identified positive relationships between zooplankton biomass and two response variables: smolt size at migration and growth rates of hatchery parr. The relationships were generally similar among lakes. Variable outcomes were a result of differences in O. nerka density (or zooplankton biomass), controlled primarily by the relative proportion of spawning and rearing habitat in each lake. Understanding unique lake habitats, ecological interactions, and the role of density dependence is germane to management of Snake River Sockeye Salmon populations. 

   more » « less