Protection & Restoration of Ecosystem Services

Overview

This project is collaboration between CILER, NOAA GLERL, USEPA, and USGS as part of the Coordinated Science and Monitoring Initiative (CSMI) Program to describe the status of Lake Michigan and understand its capacity to deliver important ecological services. The work consists of two subprojects that examine spatial distributions and interaction of benthic and pelagic components of the food web to better understand the movement of nutrients from inshore to offshore and spatial coupling of the food web that has been disrupted by dreissenid mussels.

Project 1: Benthic Surveys for Lake Michigan

CILER has worked with NOAA GLERL to document trends in dreissenid mussel populations and the keystone amphipod Diporeia at 130 sites in the main basin and a subset of 40 sites in the southern basin of Lake Michigan since 1994 and 1998, respectively. In addition to dressenids and Diporeia, the total benthic community (all taxonomic groups) have been sampled/analyzed at the 40 southern basin sites since 1980. This is the longest data set of benthic populations in the Great Lakes that have been consistently collected at the same sites using the same methods. To maintain consistency in both the whole lake data set and the data set in the southern basin, in 2015 GLERL in cooperation with USEPA, USGS and academic partners (including CILER) collected samples at the same 130 sites that were sampled in previous years, process in whole the benthic collections in the southern basin, and analyze mussels and Diporeia in collections from all sites. In addition to densities, a key component of assessing trends in dreissenid populations is accurate estimates of biomass. To estimate biomass, we have developed length-weight regressions and determined size-frequencies of populations during the previous whole-lake surveys; we repeated these analysis again in 2015. In addition to documenting temporal trends in biomass, we used statistical tools to take into account the natural variance of biomass with depth to create better estimates of spatial distributions and total abundance. We have used these new tools to reexamine spatial patterns of biomass in 2000, 2005, and 2010. We applied these statistical tools to biomass estimates in 2015: one method based on organizing stations into transects and fitting depth-dependent models, and a second method based on universal Kriging. These methods allowed us to infer whether there are significant trends in biomass over time, not only at specific stations, but lakewide and within sub-regions of the lake. Again, as with density estimates, it is critical that biomass is determined exactly the same way as in previous years.

Project 2: Temporal and spatial coupling of nutrients and food web—microbes to fish

In support of USEPA/USGS efforts to sample food web components at multiple transects around the periphery of the Lake during two seasons, we proposed to conduct more intensive temporal (including diel sampling) and fine-scale spatial sampling across seasons— nearly monthly—in the Muskegon/Grand River region of Lake Michigan, in an effort to project USEPA/USGS results across time for greater generalization of results and development of spatially-explicit ecosystem models incorporating nutrient movement from inshore to offshore, and impacts of dreissenids and other stressors. We proposed to incorporate the microbial food web (MFW) as part of our study to fully describe connections of the food web. Our approach is similar to Year of Lake Michigan 2010 and Lake Huron 2012, where we have been seasonally (April, July, and September) examining detailed diel spatial coupling of the food web using a variety of advanced tools, including plankton survey system that we tow-yow behind our vessel simultaneously with fisheries acoustics (in moon pool shipboard). We proposed to examine spatial coupling of the food web during May and June to augment our standard seasonal sampling in April, July, and September to understand nutrient flow from inshore to offshore in the Muskegon and Grand River, the largest source of nutrient loading directly into Lake Michigan.

Limited seasonal studies in 2013 indicated that ~ 80% of primary production is now in the picophytoplankton (< 2 μm), which is not available to most mesozooplankton; in contrast in earlier years it constituted ~ 20-30%. However, there is evidence that ciliates, a preferred prey of copepods, are still abundant. Therefore, we proposed to evaluate the sustainability of the pelagic food web in Lake Michigan, with particular emphasis on measuring the link between the MFW and crustacean zooplankton that directly feed fish and the role of mussels in affecting that link. We predicted the MFW is resilient to the quagga mussel-induced ecosystem changes, due to the fast growth rates and ecological plasticity of its major components, so that it may act to stabilize the pelagic system towards a new steady state. Several outcomes will result from this work. First, we proposed to assess the relative importance of the MFW in Lake Michigan by comparing our data collected with measurements made pre-driessenid in 1980-90 and 1998-2000. Second, we proposed to help revise water quality models under development at GLERL by incorporating the MFW into it. Last, we proposed to augment GLERL monitoring of plankton assemblages in 2015 Year of Lake Michigan to fully describe the pelagic system.