Declines in the energy content of yearling non‐native alewife associated with lower food web changes in Lake Michigan

Juveniles of non‐native alewife, Alosa pseudoharengus (Wilson), were collected in Lake Michigan in 1998, 1999, 2010, 2011 and 2013 to evaluate changes in energy content during a period of major ecosystem changes. Consistent with historical data, energy content of yearling alewife declined from late winter into late spring and was at its lowest point in June. Energy density and length‐adjusted, entire‐body energy were lower in 2010, 2011 and 2013 than in 1998 and 1999. Energy losses over the first winter in the lake were more severe for the 2010 year class (56% decrease) than for the 1998 year class (28% decrease). Alewife diets in late spring of 2010–2013 reflected the loss of major prey such as Diporeia spp. and a shift towards lower energy prey. The recent decline in energy content of yearling alewife can be linked to recent changes in productivity and abundance of key components of the lower food web of Lake Michigan following the dreissenid invasion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109567/1/fme12092.pd

Benthic algae compensate for phytoplankton losses in large aquatic ecosystems

Anthropogenic activities can induce major trophic shifts in aquatic systems, yet we have an incomplete understanding of the implication of such shifts on ecosystem function and on primary production (PP) in particular. In recent decades, phytoplankton biomass and production in the Laurentian Great Lakes have declined in response to reduced nutrient concentrations and invasive mussels. However, the increases in water clarity associated with declines in phytoplankton may have positive effects on benthic PP at the ecosystem scale. Have these lakes experienced oligotrophication (a reduction of algal production), or simply a shift in autotrophic structure with no net decline in PP? Benthic contributions to ecosystem PP are rarely measured in large aquatic systems, but our calculations based on productivity rates from the Great Lakes indicate that a significant proportion (up to one half, in Lake Huron) of their whole-lake production may be benthic. The large declines (5–45%) in phytoplankton production in the Great Lakes from the 1970s to 2000s may be substantially compensated by benthic PP, which increased by up to 190%. Thus, the autotrophic productive capacity of large aquatic ecosystems may be relatively resilient to shifts in trophic status, due to a redirection of production to the near-shore benthic zone, and large lakes may exhibit shifts in autotrophic structure analogous to the regime shifts seen in shallow lakes

Carbon Fixation Trends in Eleven of the World’s Largest Lakes: 2003–2018

Large freshwater lakes provide immense value to the surrounding populations, yet there is limited understanding of how these lakes will respond to climate change and other factors. This study uses satellite remote sensing to estimate annual, lake-wide primary production in 11 of the world’s largest lakes from 2003–2018. These lakes include the five Laurentian Great Lakes, the three African Great Lakes, Lake Baikal, and Great Bear and Great Slave Lakes. Mean annual production in these lakes ranged from under 200 mgC/m2/day to over 1100 mgC/m2/day, and the lakes were placed into one of three distinct groups (oligotrophic, mesotrophic, or eutrophic) based on their level of production. The analysis revealed only three lakes with significant production trends over the study period, with increases in Great Bear Lake (24% increase over the study period) and Great Slave Lake (27%) and a decline in Lake Tanganyika (−16%). These changes appear to be related to climate change, including increasing temperatures and solar radiation and decreasing wind speeds. This study is the first to use consistent methodology to study primary production in the world’s largest lakes, allowing for these novel between-lake comparisons and assessment of inter-annual trends

Impacts of suspended sediment on the ecosystem in Lake Michigan: A comparison between the 1998 and 1999 plume events

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95095/1/jgrc9241.pd

Mapping the spatial distribution of the biomass and filter‐feeding effect of invasive dreissenid mussels on the winter‐spring phytoplankton bloom in Lake Michigan

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/115963/1/fwb12653.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/115963/2/fwb12653_am.pd

REJUVENATION OF MELOSIRA GRANULATA (BACILLARIOPHYCEAE) RESTING CELLS FROM THE ANOXIC SEDIMENTS OF DOUGLAS LAKE, MICHIGAN. I. LIGHT MIGROSCOPY AND 14 C UPTAKE 1

Resting cells of Melosira granulate (Ehr.) Ralfs were collected from the anoxic sediments of Douglas Lake, Michigan. Sediment containing M. granulata was inoculated into distilled water and incubated in a growth chamber for one week during which observations were made on the cytological differentiation process. Cells classified as “condensed,” i.e. containing a dark brown cytoplasmic mass were identified as resting cells. The differentiation process consisted of a series of gradual cytological changes that included elongation of the cytoplasmic mass and recognition of definable organelles to the point where the cells were non-distinguishable from water column vegetative cells. Differentiating cells accumulated large polyphosphate and lipid granules. However, these granules disappeared just prior to cell division. The complete differentiation or rejuvenation sequence occurred in some cells in less than 24 h. However, not all dormant cells rejuvenated at the same time and it was observed that the lag period for rejuvenation increased with resting cell age (depth of burial in sediments). In the 14 C uptake studies, label was initially observed in condensed state cells. The label gradually progressed to the more differentiated forms. Total carbon uptake during the rejuvenation process was initially lower in the rejuvenating cells, but roughly equal to water column populations after 8 h, indicating a period of high metabolic activity in the rejuvenating cells between 1 and 8 h.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66031/1/j.1529-8817.1986.tb02510.x.pd

Small‐scale nutrient patchiness: Some consequences and a new encounter mechanism

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109816/1/lno19842940785.pd

Impacts of a Recurrent Resuspension Event and Variable Phytoplankton Community Composition On Remote Sensing Reflectance

In order to characterize the impact of turbidity plumes on optical and biological dynamics, a suite of environmental parameters were measured in southern Lake Michigan during the springtime recurrent sediment plume. In-water measurements of inherent optical properties (IOPs) were entered into the Hydrolight 4.2 radiative transfer model and the output was compared with measured apparent optical properties (AOPs) across a wide range of optical conditions. Hydrolight output and measured underwater light fields were then used to clarify the effects of the sediment plume on primary production, phytoplankton community composition, and nearshore remote sensing ocean color algorithms. Our results show that the sediment plume had a negligible effect on the spectral light environment and phytoplankton physiology. The plume did not significantly alter the spectral quality of available light and did not lead to light limited phytoplankton populations compared to non-plume conditions. Further, the suspended sediment in the plume did not seriously impact the performance of ocean color algorithms. We evaluated several currently employed chlorophyll algorithms and demonstrated that the main factor compromising the efficacy of these algorithms was the composition of phytoplankton populations. As phycobilin-containing algae became the dominant species, chlorophyll algorithms that use traditional blue/green reflectance ratios were compromised due to the high absorption of green light by phycobilin pigments. This is a notable difficulty in coastal areas, which have highly variable phytoplankton composition and are often dominated by sharp fronts of phycobilin and non-phycobilin containing algae

Lake Michigan lower food web: Long-term observations and \u3ci\u3eDreissena\u3c/i\u3e impact

Lake Michigan has a long history of non-indigenous introductions that have caused significant ecological change. Here we present a summary of eight papers that document recent changes and the current state of the lower food web of southern Lake Michigan after the establishment of large dreissenid populations. Results are based on long-term data sets collected by federal and academic research and monitoring programs that place recent changes into a historic context. Dramatic and significant changes in the lower food web, such as the loss of the spring diatom bloom, large declines in phytoplankton productivity, and a decline of Mysis populations, were directly or indirectly attributed to the expansion of Dreissena rostriformis bugensis. Total phosphorus concentrations and loadings also have decreased in the last 20 years. Changes in the Lake Michigan ecosystem induced by D. r. bugensis have produced conditions in the offshore pelagic region that are similar to oligotrophic Lake Superior. The future state of the lower food web in southern Lake Michigan is difficult to predict, mainly because population trends of D.r. bugensis in cold, offshore regions are unknown. Hence, monitoring programs designed to collect long-term, consistent data on the lower food web of Lake Michigan are essential

The importance of zooplankton‐protozoan trophic couplings in Lake Michigan

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109824/1/lno19913671335.pd