Seasonal zooplankton dynamics in Lake Michigan: Disentangling impacts of resource limitation, ecosystem engineering, and predation during a critical ecosystem transition

Abstract

Fahnenstiel, Gary L.; Cavaletto, Joann F.; Liebig, James R.; Stow, Craig A.; Nalepa, Thomas F.; Madenjian, Charles P.; and Bunnell, David B., "Seasonal zooplankton dynamics in Lake Michigan: Disentangling impacts of resource limitation, ecosystem engineering, and predation during a critical ecosystem transition" (2012 We examined seasonal dynamics of zooplankton at an offshore station in Lake Michigan from 1994 to 2003 and 2007 to 2008. This period saw variable weather, declines in planktivorous fish abundance, the introduction and expansion of dreissenid mussels, and a slow decline in total phosphorus concentrations. After the major expansion of mussels into deep water (2007)(2008), chlorophyll in spring declined sharply, Secchi depth increased markedly in all seasons, and planktivorous fish biomass declined to record-low levels. Overlaying these dramatic ecosystem-level changes, the zooplankton community exhibited complex seasonal dynamics between 1994-2003 and 2007-2008. Phenology of the zooplankton maximum was affected by onset of thermal stratification, but there was no other discernable effect due to temperature. Interannual variability in zooplankton biomass during 1994 and 2003 was strongly driven by planktivorous fish abundance, particularly age-0 and age-1 alewives. In 2007-2008, there were large decreases in Diacyclops thomasi and Daphnia mendotae possibly caused by food limitation as well as increased predation and indirect negative effects from increases in Bythotrephes longimanus abundance and in foraging efficiency associated with increased light penetration. The Bythotrephes increase was likely driven in part by decreased predation from yearling and older alewife. While there was a major decrease in epilimnetic-metalimnetic herbivorous cladocerans in 2007-2008, there was an increase in large omnivorous and predacious calanoid copepods, especially those in the hypolimnion. Thus, changes to the zooplankton community are the result of cascading, synergistic interactions, including a shift from vertebrate to invertebrate planktivory and mussel ecosystem impacts on light climate and chlorophyll.

Non-stationary recruitment dynamics of rainbow smelt: The influence of environmental variables and variation in size structure and length-at-maturation

“…More recently, lake levels have declined to record-low levels, which may be influencing habitat availability along shorelines, within tributaries, and affecting lake hydrological dynamics (Gronewold and Stow, 2013). The myriad physical, chemical, and biotic changes to Great Lakes ecosystems have resulted in benthification of energy pathways and altered zooplankton and macroinvertebrate species composition and abundance Fahnenstiel et al, 2010;Nalepa et al, 2009;Pothoven et al, 2013;Vanderploeg et al, 2012).…”

Comparing seasonal dynamics of the Lake Huron zooplankton community between 1983–1984 and 2007 and revisiting the impact of Bythotrephes planktivory

“…One could speculate, however, that because alewife densities had dropped to nearly zero by autumn 2003, and alewife consumption of Bythotrephes has been demonstrated to exceed Bythotrephes production in nearshore Lake Michigan waters , Bythotrephes densities may have increased following the alewife collapse. Note, however, that similar zooplankton community composition changes have occurred in Lake Michigan without a collapse of the alewife population (Barbiero et al, 2009b;Barbiero et al, 2012;Vanderploeg et al, 2012). Clearly, greater understanding of these putative bottom-up and topdown mechanisms is required for ecologists and managers in the Great Lakes to have some level of certainty regarding whether these changes in the Lake Huron zooplankton community are indicative of a new regime or are a shorter-term response to the multiple perturbations within the food web.…”

“…For example, more frequent (at least monthly) monitoring in nearby lakes Michigan and Erie has provided a better understanding of zooplankton dynamics for species that exhibit high seasonal variability (e.g., Conroy et al, 2005;Dettmers et al, 2003;Vanderploeg et al, 2012). To facilitate more intensive sampling of zooplankton (and other trophic levels) at regular intervals, the US Environmental Protection Agency (USEPA) and Environment Canada coordinate a year of intensive sampling on one Laurentian Great Lake per year.…”

Remotely-Sensed Early Warning Signals of a Critical Transition in a Wetland Ecosystem

“…These state variables also are increasingly temporally autocorrelated and show high variability [10]. Therefore, autocorrelation [11,12], and standard deviation [13] are both expected to increase as resilience is lost prior to a transition. In some cases, disturbances push the state of an ecosystem toward near-tipping-point values, and therefore, the distribution of the time series also becomes asymmetric [5].…”

“…Lack of such observations imposes limitations because, in practice, it is difficult to measure high-frequency time series of the right variables at the appropriate scale. For instance, the data to explore the state of an ecosystem may need to be collected through long-term fieldwork [2,8,10,13]. As an alternative, remote sensing datasets with high temporal resolution may provide relevant ecosystem variables that can be used to retrieve indicators of critical transitions through time.…”