Journal of Great Lakes Research 41 Supplement 3 (2015) 1–6

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Journal of Great Lakes Research

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ComplexinteractionsinLakeMichigan’s rapidly changing ecosystem

Special issue origin areas. Then, looking across all topical areas, we attempt to draw holistic conclusions and identify cross-cutting research themes needing further Over the past 30 years, Lake Michigan's food web has been in a research. One common theme among many of these papers was constant state of transition (Vanderploeg et al., 2002, 2012; Madenjian evaluation of how different components of the food web have et al., 2002; 2015), and it is likely that this emerging system has not responded to the proliferation of nonindigenous dreissenid mussels yet reached a steady state. The proliferation of invasive species at mul- and the predatory cladoceran Bythotrephes longimanus. tiple trophic levels (zooplankton, mussels, fish), coupled with the suc- cess of a nutrient abatement program that has delivered long-term reductions in nutrient inputs, have together contributed to a series of Overview of papers systemic changes to the Lake Michigan ecosystem (e.g., novel trophic interactions, reengineered nutrient cycling, altered physical habitat, We organized the papers in this special issue around topical areas shift from pelagic productivity to enhanced benthic production, and that evaluate status and changes at key levels in the food web: nuisance algal blooms nearshore). Our current understanding and po- (1) Cladophora modeling and nutrient management (Bootsma et al., tential future forecasting of ecosystem-wide consequences of such tran- 2015); (2) quagga mussel status and impacts (Glyshaw et al., 2015; sitions are dependent on describing and understanding changes in the Mosley and Bootsma, 2015; Rowe et al., 2015; Tyner et al., 2015); micro- food web in time and space (i.e., horizontal and vertical), variation of bial food web function and changes (Carrick et al., 2015; Dila and key food web components and linkages with physical habitat, and nutri- Biddanda, 2015); (3) mesozooplankton trends and trophic structure ent cycling. Given that other Laurentian Great Lakes share key members (Driscoll et al, 2015; Engevold et al., 2015; Pothoven and Fahnenstiel, of the Lake Michigan food web as well as changing nutrient and climate 2015); (4) population dynamics and impacts of Bythotrephes dynamics, understanding gleaned from this special issue is highly rele- (Bourdeau et al., 2015; Keeler et al., 2015; Ptáčníková et al., 2015; vant across the basin, especially in Lakes Huron and Ontario. Vanderploeg et al., 2015); (5) fish diet, recruitment, and ecology The idea for the special issue and papers herein originally arose from (Bunnell et al., 2015; Happel et al., 2015-a,b; Houghton and Janssen, a special session we convened at the 56th Annual Meeting of the Inter- 2015; Turschak and Bootsma, 2015; Withers et al., 2015); and finally, national Association for Great Lakes Research (IAGLR; June 2–6, 2013) (6) a synthesis of food web changes (Madenjian et al., 2015). entitled “Tracking and Understanding Changes in Lake Michigan’s Emerging Food Web” that brought together 21 studies assessing various aspects of the Lake Michigan food web from lower to upper trophic Cladophora modeling and nutrient management levels, nearshore to offshore patterns, and the physical, chemical, and biological processes driving these changes. Many of the large-scale The attached filamentous green alga, Cladophora,hasbecomea intensive studies were coordinated, funded, and supported by the US serious management problem in Lake Michigan and other Great Environmental Protection Agency’s Coordinated Science and Monitor- Lakes during the past 10–15 years. Its dense growth in nearshore ing Initiative (CSMI) Year of Lake Michigan 2010. Another stimulus areas and subsequent sloughing fouls beaches and water intakes and source of papers for this special issue came from the Lake Michigan and harbors a variety of pathogens harmful to humans and wildlife Food Web Research Workshop, held on April 1–2, 2014, in Ann Arbor, (Bootsma et al., 2015). Interestingly, Cladophora was a major prob- Michigan sponsored by The Great Lakes Regional Research Information lem during the 1970s owing to phosphorus loading, and as nutrient Network (GLRRIN) and co-organized by three Lake Michigan Sea Grant loading was reduced, the problem largely abated until the expan- programs. This workshop brought federal and academic scientists sion of dreissenid mussel populations. Its recent proliferation was together to discuss the current status and understanding of the Lake unexpected and points to the fact that mussel filtering has in- Michigan food web and also began planning for the 2015 CSMI field creased water clarity and thus permits growth at greater depths. year (http://www.iisgcp.org/research/2014foodwebworkshop.pdf). At the same time, mussels fertilize Cladophora with soluble and When proposing a title for this special issue, we thought “complex particulate nutrients. Given the complex interactions that influ- interactions” was something that would appeal to journal editors and ence Cladophora growth, Bootsma et al. (2015) detail the additional potential readers. Little did we realize how complex and subtle the research needed to model the distribution and abundance of interactions really are. Herein, we begin with an overview of papers Cladophora as a function of nutrient loading, hydrodynamics, and within topical areas and make connections within and across topical ecological processes.

http://dx.doi.org/10.1016/j.jglr.2015.11.001 0380-1330/Published by Elsevier B.V. on behalf of International Association for Great Lakes Research. 2 H.A. Vanderploeg et al. / Journal of Great Lakes Research 41 Supplement 3 (2015) 1–6

Quagga mussel population status and impacts microphytoplankton (N20 μm) greatly decreased. Heterotrophic micro- plankton (ciliates) decreased over the period, whereas heterotrophic Glyshaw et al. (2015) examined factors contributing to seasonal pico- and nanoplankton remained about the same. It is likely that pref- changes in reproductive status and condition index (CI is the ratio of erential grazing and nutrient sequestration by mussels played a role in soft tissue weight to internal shell capacity) of mussels sampled along these changes. High preference for colonial diatoms (Tang et al., 2014; a depth gradient at the GLERL (Great Lakes Environmental Research Vanderploeg et al., 2010) and slow growth rate of large phytoplankton Laboratory) long-term monitoring sites near Muskegon, MI. Quagga would be possible factors here. As Carrick et al. (2015) note, a drop in mussel populations have continued to expand into deep water, but heterotrophic microzooplankton was likely a result of the high feeding overall, the population has stabilized as evidenced by abundance, and preference of mussels for ciliates (Lavrentyev et al., 2014) and loss of di- CI long-term trends indicate mussel biomass has increased at the 93- atoms on which they feed. They further note that the bacteria-flagellate m-deep site but has stabilized at the 25-m and 45-m sites. CI was lowest linkage appears to have remained stable between sampling periods. at the 45-m site, where mussel biomass was highest, and long-term The declines in plankton abundance identified by Carrick et al. trends showed that mussel CI decreased markedly at the 25-m and (2015) and nutrients in the offshore waters (Barbiero et al., 2012) 45-m sites, for which long-term trend data are available. These results point to the fact that nutrient subsidies from nearshore sources may are consistent with mussels having reached carrying capacity, and play a larger role under this current set of conditions in the lake. As they are consistent with lake-wide observations that generally show such, Dila and Biddanda (2015) examined bacterial and gross primary biomass is leveling off (Rowe et al., in press). production (GPP) in interconnected habitats associated with Lake Mich- Tyner et al. (2015), examining dreissenid metabolism, and Mosley igan: A small creek feeding the Muskegon River; the Muskegon River and Bootsma (2015), examining dreissenid phosphorus excretion, dem- that empties into Muskegon Lake; Muskegon Lake, a drowned river onstrated that dreissenid mussels have a major effect on lake-wide C mouth lake; and Lake Michigan into which Muskegon Lake empties. and P dynamics. Tyner et al. (2015) measured O2 consumption of shal- Consistent with their expectation, the ratio of bacterial production to low morph and profunda morph quagga mussels at different tempera- GPP was highest in the creek (i.e., 488%) and declined to 5% in Lake tures. Using this information along with mussel abundance, they Michigan, indicating the importance of terrestrial subsidies. Muskegon calculated lake-wide C consumption and estimated the mussels con- Lake had the highest GPP, and bacterial production: GPP ranged from sumed 54% of annual primary production. Mosley and Bootsma 1 to 110. In Lake Michigan, bacterial production was consistently low (2015) examined both excretion of (soluble) P and egestion (feces and the ratio of bacterial production to GPP was more stable than and pseudofeces) of P for shallow and profundal morph quagga mus- other sites. sels. P egestion has been rarely quantified; the P excretion:egestion ratio was ~3:2, indicating that greater attention needs to be paid to Mesozooplankton trends and trophic structure egestion. In total, P recycled from mussels was 11 times higher than P that settles out of the water column, which highlights the large impact Engevold et al. (2015) described changes in the lower food web at a mussels likely have on P availability in the benthos. deep-water site in western Lake Michigan between 1988–1992 (before Quagga mussels have been hypothesized to have decimated the mussels) and 2007–2009 (after mussels). They reported declines in spring phytoplankton bloom in Lake Michigan; however, an important total P and particulate C, increases in nitrate and silicate, and declines question related to this hypothesis is whether mixing was sufficient to in chlorophyll a N 10 μm; interestingly, C:P seston ratios remained the connect quagga mussel filtration on the bottom with phytoplankton same during both time periods. Total zooplankton abundance and bio- production in the water column above (Fahnenstiel et al., 2010; mass was lower in 2007–2009, with notable declines in cyclopoid cope- Vanderploeg et al., 2010). Rowe et al. (2015) used a biophysical model pods; herbivorous cladocerans and predatory Bythotrephes longimanus to explore this hypothesis. They applied a 3-D finite volume coastal densities were not different between time periods. Although some of ocean model (FVCOM) and atmospheric forcing to generate a 1-D ther- their results (e.g., lack of declines for herbivorous cladocerans or lack mal structure and looked at phytoplankton growth rate and mussel fil- of increases for Limnocalanus macrurus) differed from those on the east- tering impact under two scenarios, a cold year exhibiting winter ern side of the lake reported by GLERL (Vanderploeg et al., 2012)or stratification (surface b 4 ºC), and a warm year exhibiting no stratifica- lake-wide samples by EPA (Barbiero et al., 2012), they argued that tion (surface N 4 ºC). Phytoplankton abundance was higher in the cold those differences were more likely an artifact of differences in temporal year due to retention of phytoplankton in upper well-lit surface waters, comparisons than spatial variability in lower food web dynamics. Over- consistent with the hypothesis that the impact of mussels on phyto- all, they attribute the changes between these two time periods more to plankton is dependent on meteorologically driven stratification and grazing by dreissenid mussels than to planktivory by predatory mixing. cladocerans. Pothoven and Fahnenstiel (2015) extended observations of Status and changes to the microbial food web mesozooplankton in southeastern Lake Michigan by examining season- al dynamics along a nearshore to offshore transect at stations of 15 m, Given the changes observed in the spring diatom bloom, it begs the 45 m, and 110 m depths from 2007 to 2012. There was a decrease of question: have there been alterations (or compensations) in other zooplankton biomass across all depths relative to the 1970s. On a volu- components of the lower food web? As such, Carrick et al. (2015) re- metric basis, biomass was lower at the shallow than at the mid-depth ported remarkable changes in the microbial food web (MFW) that oc- site, but concentrations were similar at nearshore and offshore sites. curred in Lake Michigan between 1987 (before mussels) and 2013 Differences among sites were due in part to species associated with (after mussels) and compared the Lake Michigan community with the metalimnion or hypolimnion being more abundant at offshore that of Lake Superior, a historically ultraoligotrophic system without sites. The predatory cladoceran Bythotrephes was more abundant at dreissenid mussels. The 2013 MFW structure of Lake Michigan resem- mid-depth and offshore sites except during the fall. Relative to observa- bled the Lake Superior MFW more so than the Lake Michigan MFW of tions in 2007 and 2008 (Vanderploeg et al., 2012), there were increases 1987 (see Carrick and Fahnenstiel, 1989, 1990). Over the years in Lake in Daphnia galeata mendotae and Diacyclops, and decreases in Michigan, there has been a decrease in total chlorophyll concentration. Bythotrephes and Limnocalanus in 2010–2012 at the offshore site. Picophytoplankton (b2 μm) numbers were lower in 2013 versus 1987; These changes between time periods would seem consistent with an in- however, there was a 2-fold increase in chlorophyll in the b 2 μm size crease in fish predation (Vanderploeg et al., 2012), selective removal of fraction, with this size fraction constituting N 50% of the chlorophyll. the larger zooplankton, Bythotrephes and Limnocalanus, and possible re- Nanophytoplankton (2–20 μm) remained about the same, and lease of Daphnia and Diacyclops from Bythotrephes predation. Year-class H.A. Vanderploeg et al. / Journal of Great Lakes Research 41 Supplement 3 (2015) 1–6 3 strength of alewives was high during 2010 (Madenjian et al., 2015; the epilimnion, and secondarily in the metalimnion. As a result, spatial Withers et al. 2015); perhaps there was enough alewife biomass during overlap between alewives and Bythotrephes was relatively low, with 2010–2012 to affect these changes. most overlap occurring in the metalimnion at night. Zooplankton com- Driscoll et al. (2015) used stable C and N isotope composition to de- munities were very different at the two sites. Bioenergetics models fine feeding relationships of zooplankton in Lake Michigan. An were used to contrast the predatory impact of Bythotrephes and adult interesting point of this study is that very different food web paths alewives by comparing their consumption with estimates of can lead to the same trophic position defined by stable isotopes. zooplankton production. Offshore, relatively low abundance of alewife Consistent with expectations, the large predatory Limnocalanus and relatively high abundance of Bythotrephes resulted in Bythotrephes macrurus had the highest (tertiary) trophic position, and Daphnia consuming a major portion of zooplankton production and being a mendotae,afilter-feeding cladoceran, the lowest (primary consumer) strong driver of zooplankton community structure. Nearshore, high as defined by stable N stable isotopes. However, stable N isotopes sur- abundance of alewives led to consumption that greatly outpaced prisingly showed that the predatory cladoceran Bythotrephes had the Bythotrephes consumption and had a significant impact on other same trophic position (secondary) as the omnivorous Leptodiaptomus. zooplankton species, leading to a community dominated by small As they hypothesized, this is likely a result of the strong preference of zooplankton such as Bosmina. Bythotrephes for cladocerans (Vanderploeg et al., 1993) and the strong Ptáčníková et al. (2015) examined factors regulating offshore–on- preference of Leptodiaptomus for protozoan microzooplankton (ciliates) shore distribution of the small non-indigenous predatory cercopagid over phytoplankton (Bundy et al., 2005) that would be expected to have Cercopagis pengoi that was hypothesized to be regulated by predation a higher trophic position than phytoplankton. It was not possible for from, or competition with, the larger nonindigenous predatory Driscoll et al. (2015) to measure the isotopic signature of ciliates sepa- cercopagid Bythotrephes longimanus. Temperature and prey abundance rately from other seston. were the other possible factors affecting abundance. They used statisti- cal analyses of Cercopagis abundance, life history traits, and spatio- Population dynamics and impacts of Bythotrephes temporal distribution in conjunction with all these factors to tease apart important relationships and concluded that Bythotrephes abun- Bythotrephes has been a concern of fisheries managers because its dance was the most important factor. Further, they demonstrated that predation on small zooplankton makes it a potential major competitor Bythotrephes consumed Cercopagis at the same rate as a preferred cla- of age-0 fishes. Bythotrephes, primarily found in the epilimnion and sec- doceran prey (Daphnia). Lastly, they showed both species overlapped ondarily in the metalimnion, can also negatively affect its zooplankton vertically with neither species exhibiting any diel vertical migration. prey by inducing them to migrate during the day to deep cooler waters All these results pointed to Bythotrephes predation as the main control- where growth potential is lower (Pangle and Peacor, 2006). The long ler of Cercopagis distribution, but prey availability, temperature, and tail spine of Bythotrephes foils predation by small planktivorous fishes competition were potentially important secondary factors. These results (b100 mm), but it is a preferred prey of large planktivorous fishes imply that invasion success of Cercopagis is limited by the prior invasion (Pothoven et al., 2007). Because of its preference for other cladocerans by Bythotrephes. and other prey with slow escape responses, it has the potential to Keeler et al. (2015) examined whether temperature, zooplankton restructure zooplankton community composition. Therefore, spatial prey density, or top-down control from fishes regulated abundance of and predatory interactions among zooplankton, Bythotrephes,and Bythotrephes at shallow (18 m), mid-depth (46 m), and deep water zooplankton prey are of interest. sites (110 m) in northern Lake Michigan and western Lake Superior. Bourdeau et al. (2015), using a variety of statistical approaches, ex- In Lake Michigan, fish consumption (primarily by alewife) exceeded amined the role of Bythotrephes abundance and other environmental Bythotrephes production only 25% of the time and only in shallow factors affecting daytime mean depth of dominant zooplankton found sites. In Lake Superior, cisco (Coregonus artedi) consumption exceeded in offshore Lake Michigan during 2004–2006 and 2009–2011. They Bythotrephes production 44% of the time at mid-depth and offshore found that daytime depth distribution of Daphnia, Bosmina, Diacyclops, sites. Despite the bioenergetics modeling results, densities of Leptodiaptomus minutus,andL. ashlandi adults increased with Bythotrephes never declined in the month following instances of Bythotrephes abundance, whereas depth distribution of the copepod excessive consumption. Hence, a statistical model explored whether nauplii and diaptomid copepodites did not. Depth of the Bythotrephes densities were best explained by planktivory, preferred metalimnetic–hypolimnetic boundary was an important variable for zooplankton prey, or water temperature; the most parsimonious Bosmina, Daphnia, Diacyclops,andL. ashlandi, and may have set the model identified only temperature. Hence top-down control of lower limit of depth selection by these potential zooplankton prey. Bythotrephes may not be as widespread as previously hypothesized, Vanderploeg et al. (2015) noted that water clarity was sufficiently and is dependent on the density and composition of the fish high during these time periods to enable Bythotrephes to effectively for- community. age at all depths of the 40-m water column they studied; therefore, se- lection of this thermal boundary made sense in terms of vulnerability to Fish diet, recruitment, and ecology predation. Vanderploeg et al. (2015) used a plankton survey system, fisheries Changes in structure and function of nearshore and offshore food acoustics, and opening/closing nets to define nearshore–offshore and webs caused by dreissenid mussels, Bythotrephes, and the round goby fine-scale diel vertical spatial interactions among non-indigenous (e.g., Vanderploeg et al., 2002; Hecky et al., 2004) has stimulated inter- adult alewives, visually preying cercopagids (Bythotrephes longimanus est in documenting fish diets and ecology and their changes in both and Cercopagis pengoi), and indigenous zooplankton in Lake Michigan nearshore and offshore regions of Lake Michigan. In particular, limited on two cruises in August 2004 at 60-m-deep and 10-m-deep sites. Be- attention had been paid to the nearshore zone until these invasions. cause of the radically different thermal structure between cruises, they Bunnell et al. (2015) documented changes in diets of planktivorous were able to observe the effects of thermal structure on diel vertical mi- and benthivorous fishes in northern Lake Michigan from the period be- gration at the 60-m site. Vertical position and overlap between alewives, fore (1994–1995) and after (2010) quagga mussel and round goby pop- Bythotrephes, and Daphnia mendotae were strongly driven by thermal ulation expansions in shallow (18 m), mid-depth (46 m), and offshore structure. Daphnia showed the greatest (29 m) diel vertical migration (91–128 m) sites. This time period also saw a major decrease in the ben- of zooplankton between the epilimnion at night and to a narrow thic amphipod Diporeia. This study was unique in that it identified most depth band at the metalimnion–hypolimnion boundary during the zooplankton prey to the species level. In 2010, large, calanoid day; whereas its major predator, Bythotrephes, generally was found in copepods—Limnocalanus macrurus, Leptodiaptomus sicilis,andEpischura 4 H.A. Vanderploeg et al. / Journal of Great Lakes Research 41 Supplement 3 (2015) 1–6 lacustris—were important diet components of alewives, bloater, and through the lower food web and limit fish abundance and production. rainbow smelt, and when present, Bythotrephes was a major diet item. Although there have been major changes in zooplankton composition, Mysis diluviana was also an important component of the diet of these such as decreases in cyclopoids and filter-feeding cladocerans same planktivorous fishes as well as the benthivorous slimy and deep- (Engevold et al., 2015; Pothoven and Fahnenstiel, 2015; Vanderploeg water sculpins. The diet of round gobies was dominated by Dreissena. et al., 2012) and high variation among years, the general picture Changes in fish diets reflected changes in food web structure; increased drawn by Madenjian et al. (2015) from GLERL’s offshore seasonal mon- consumption of calanoid copepods and Mysis, while decreased con- itoring program (Pothoven and Fahnenstiel, in this issue; Vanderploeg sumption of Diporeia and filtering-feeding cladocerans were seen in et al., 2012) was that there was not a consistent downward trend in zoo- 2010 relative to 1994–1995. plankton biomass. During this time period, there was a major (10-fold) Happel et al. (2015-a,b) reported on the diets of age-0 yellow perch decrease in total pelagic and benthic prey fish abundance, including the and spottail shiners at a variety of nearshore locations around Michigan alewife, which is important for supporting the sport fishery for using stomach contents, fatty acid profiles, and stable C and N isotopes salmonines. Although alewife condition factor has decreased over as diet tracers. The simultaneous use of these three trophic indicators time, consistent with prey limitation, evidence from bioenergetics appears to be a robust approach to overcome some of the biases associ- modeling (Tsehaye et al., 2014a,b) also indicates that abundant Chinook ated with each individual method. Of particular interest in these studies salmon are exerting control of alewife populations. Likewise, the com- were differences between eastern and western nearshore regions of the mercially valuable benthic feeding lake whitefish—formerly Lake Michigan. Demonstrating the likely importance of not only sub- dependent on the benthic amphipod Diporeia—suffered a loss of strate but also lake hydrodynamic patterns (e.g., spatial patterns of up- condition, but population abundance remained high. Madenjian et al. wellings and downwellings), benthos relative to zooplankton was more (2015) hypothesized a number of counterbalancing mechanisms to ex- important prey on the rocky, upwelling-influenced western nearshore plain how salmonines and lake whitefish could maintain high biomass region than in the sandy eastern nearshore region. despite declines at the base of the food web and suggested further re- Turschak and Bootsma (2015) examined the trophic structure of search needs. Lake Michigan’s upper food web, including top piscivores, using stable C and N isotopes at two times, one prior (2002–2003) to and one after Overarching conclusions—major themes expansion of dreissenids into deep water (2010–2012). They were able to separate out the nearshore versus offshore food web using C iso- Historically speaking much of the monitoring on the Great Lakes, tope ratios and trophic level using N isotope ratios. Mixing models of originating from programs in the 1970s, has been focused on measuring isotopic ratios of potential prey items helped identify prey composition. offshore nutrients, chlorophyll, phytoplankton, and zooplankton in Ontogenetic shifts in diet were seen for a variety of fish species, and on- spring and late summer and annual offshore surveys of benthos and for- togenetic diet patterns changed significantly for alewives and bloaters. age fishes. Although this approach effectively captures the lake-wide Conclusions drawn for planktivorous and benthivorous fishes in this trends, papers in this special issue demonstrate how complementary study were consistent in broad terms with observations of Bunnell long-term observations at biweekly to monthly intervals throughout et al. (2015) and Happel et al. (2015-a,b). the year provide further understanding of the dynamics underlying Withers et al. (2015) examined diets and growth potential (GRP) of nutrients and plankton in offshore and inshore regions. Given the early stage larval yellow perch and alewife in nearshore waters at the importance of dreissenid mussels on the Lake Michigan food web, it southern end of Lake Michigan. GRP was highly variable in this general- also seems apparent that benthic surveys at all depth zones should be ly warm dynamic region, characterized by rapid changes in completed on an annual basis. In addition, there has been an implicit temperatures and water clarity. A high percentage of empty stomachs emphasis on the classic food web and an index species approach to suggested that starvation may be a factor in survival of early stage larval monitoring (Fig. 1). The studies reported here also underscore that un- fish. As expected, small diet items were selected, but surprisingly, derstanding and predicting food web response must include the micro- dominant prey were diatoms for alewives and dreissenid veligers for bial food web, especially for understanding Dreissena impacts and lower larval yellow perch. They noted the quality of veligers, in which the food web response (See Carrick et al., 2015). Finally, given ecosystem soft edible parts are incased within a shell, as a food source needs to changes (e.g., decreased phytoplankton production and proliferation be explored. of round goby nearshore), future studies of fishes in Lake Michigan Houghton and Janssen (2015) examined changes in age-0 yellow should place a greater emphasis on the nearshore. perch habitat selection as round goby populations increased in western There is a long-standing appreciation that Lake Michigan is a spatial- Lake Michigan. In regions of high round goby abundance, there was a ly complex system in the vertical dimension. Predatory interactions shift in habitat occupancy from rocky areas to sandy areas. In addition, change throughout the day due to diel vertical migration of zooplankton at rocky sites with high round goby concentrations, benthic prey con- and fish, with zooplankton occurring in narrow depth bands during the centration was reduced, and yellow perch had relatively less benthic day away from predators but in suboptimal conditions for feeding and prey in their stomach contents. These results suggest a niche shift of yel- growth (Bourdeau et al., 2015; Vanderploeg et al., 2015). Moreover, re- low perch with negative consequences to age-0 yellow perch, because cent ecosystem changes have altered vertical gradients and interactions, optimal growth may be related to adequate access to benthic prey. in part owing to increased water clarity. For these reasons, average whole-water column concentrations usually reported for different Synthesis of food web changes prey may have little bearing on food available to predators and trophic transfer and untangling trophic level and predatory prey responses. In part as a follow-up to an earlier review (Madenjian et al., 2002), It may be less well-appreciated that Lake Michigan is also a complex Madenjian et al. (2015) examined time series of multiple trophic levels system in the horizontal dimension. Spatial locations of studies will in the Lake Michigan food web and sought to determine whether any have a strong influence on resulting perspectives. The western near- trends were attributable to the expansion of dreissenid mussels. They shore zone differs from the eastern nearshore zone in terms of substrate considered published literature—including papers in this special and frequency of upwelling with consequences not only to zooplankton issue—on lower food web dynamics and lake-wide changes in fish pop- and benthic communities but also to fish predators (Happel et al., ulations, most of which were sampled in annual USGS (U.S. Geological 2015-a,b). The eastern side of the southern basin receives large nutrient Survey) bottom-trawl surveys. A major question was whether the loading from the major tributaries on that side of the lake. Nearshore large reduction in phytoplankton abundance and production driven by fishes were seen to have diets with more benthic invertebrates on the mussel filtration and nutrient sequestration would propagate up western rocky shore. The degree to which consumption by fish can H.A. Vanderploeg et al. / Journal of Great Lakes Research 41 Supplement 3 (2015) 1–6 5

are courtesy of the Integration and Application Network, University of Maryland Center for Environmental Science.

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Great Lakes Res. 41 (Supplement 3), 86–94. regulate Bythotrephes dynamics varies from nearshore to offshore Fahnenstiel, G., Nalepa, T., Pothoven, S., Carrick, H., Scavia, D., 2010. Lake Michigan lower (Keeler et al. 2015; Pothoven et al., 2007). Likewise, seasonal food web: Long-term observations and Dreissena impact. J. Great Lakes Res. 36, 1–4. – fi Glyshaw, P.W., Riseng, C.M., Nalepa, T.F., Pothoven, S.A., 2015. Temporal trends in condi- onshore offshore sh migrations regulate interactions with tion and reproduction of quagga mussels (Dreissena rostriformis bugensis) in southern Bythotrephes, Cercopagis, and, ultimately, zooplankton community Lake Michigan. J. Great Lakes Res. 41 (Supplement 3), 16–26. structure in offshore and nearshore zones (Ptáčníková et al., 2015; Happel, A., Creque, S., Rinchard, J., Höök, T., Bootsma, H., Janssen, J., Jude, D., Czesny, S., 2015a. Exploring yellow perch diets in Lake Michigan through stomach content, Vanderploeg et al., 2015). fatty acids, and stable isotope ratios. J. Great Lakes Res. 41 (Supplement 3), 172–178. Further research is needed in many areas of ecology to understand the Happel, A., Lafountain, J., Creque, S., Rinchard, J., Höök, T., Bootsma, H., Janssen, J., Jude, D., Lake Michigan food web response and predict its trajectory to a variety of Czesny, S., 2015b. Spatio-temporal description of spottail shiner (Notropis hudsonius) fi fatty acid profiles in Lake Michigan’s southern basin. J. Great Lakes Res. 41 (Supple- stressors such as nutrient loading, new invasive species, sheries ment 3), 179–184. management practices, and climate change. This special issue sought to Hecky, R.E., Smith, R.E.H., Barton, D.R., Guildford, S.J., Taylor, W.D., Charlton, M.N., et al., highlight how nonindigenous species (largely dreissenid mussels, and 2004. The nearshore phosphorus shunt: a consequence of ecosystem engineering – Bythotrephes longimanus to a lesser extent) have directly or indirectly by dreissenids in the Laurentian Great Lakes. Can. J. Fish. Aquat. Sci. 61, 1285 1293. Houghton, C.J., Janssen, J., 2015. Changes in age-0 yellow perch habitat and prey selection influenced multiple trophic levels and highlighted areas ripe for future across a round goby invasion front. J. Great Lakes Res. 41 (Supplement 3), 210–216. research. For example, new insights were made with respect to how Keeler, K.M., Bunnell, D.B., Diana, J.S., Adams, J.V., Mychek-Londer, J.G., Warner, D.M., Yule, mussels influence nutrient availability, primary producers, and the D.L., Vinson, M.R., 2015. Evaluating the importance of abiotic and biotic drivers on Bythotrephes biomass in Lake Superior and Michigan. J. Great Lakes Res. 41 (Supple- microbial food web (Carrick et al., 2015; Mosley and Bootsma, 2015; ment 3), 150–160. Rowe et al., 2015; Tyner et al., 2015). Recent changes in the food web Lavrentyev, P.J., Vanderploeg, H.A., Franze, G., Chacin, D.H., Liebig, J.R., Johengen, T.H., also were detected in the diets of fishes (Bunnell et al., 2015; Driscoll 2014. Microzooplankton distribution, dynamics, and trophic interactions relative to phytoplankton and quagga mussels in Saginaw Bay, Lake Huron. J. Great Lakes Res. et al., 2015; Happel et al., 2015-a,b; Turschak and Bootsma, 2015; Withers 40 (Supplement 1), 95–105. et al., 2015) and can influence predator–prey functional responses Madenjian, C.P., Fahnenstiel, G.L., Johengen, T.H., Nalepa, T.F., Vanderploeg, H.A., Fleischer, (Vanderploeg et al., 2015; Withers et al., 2015) and competitive interac- G.W., Schneeberger, P.J., Benjamin, D.M., Smith, E.B., Bence, J.R., Rutherford, E.S., Lavis, D.S., Robertson, D.M., Jude, D.J., Ebener, M.P., 2002. Dynamics of the Lake Michigan tions (Houghton and Janssen, 2015). Finally, these nonindigenous species food web, 1970–2000. Can. J. Fish. Aquat. Sci. 59, 736–753. have increased water clarity and altered the vertical migration of zoo- Madenjian, C.P., Bunnell, D.B., Warner, D.M., Pothoven, S.A., Fahnenstiel, G.L., Nalepa, T.F., plankton into unfavorable habitats (Bourdeau et al., 2015; Vanderploeg Vanderploeg, H.A., Tsehaye, I., Claramunt, R.M., Clark, R.D. Jr, 2015. Changes in the Lake Michigan food web following dreissenid mussel invasions: a synthesis. J. Great et al., 2015). It will be interesting to follow system trajectories now that Lakes Res. 41 (Supplement 3), 217–231. dreissenid mussel populations may have stabilized or are in decline Mosley, C., Bootsma, H., 2015e. Phosphorus recycling by profunda quagga mussels (Glyshaw et al., 2015). (Dreissena rostriformis bugensis) in Lake Michigan. J. Great Lakes Res. 41 (Supplement 3), 38–48. Pangle, K.L., Peacor, S.C., 2006. Non-lethal effect of the invasive predator Bythotrephes longimanus on Daphnia mendotae. Freshw. Biol. 51, 1070–1078. Acknowledgements Pothoven, S.A., Fahnenstiel, G.L., 2015. Spatial and temporal trends in zooplankton assemblages along a nearshore to offshore transect in southeastern Lake Michigan from 2007 to 2012. J. Great Lakes Res. 52 (Supplement 3), 95–103. This is GLERL Contribution No. 1780, Contribution 1987 of the USGS Pothoven, S.A., Vanderploeg, H.A., Cavaletto, J.F., Kruger, D.M., Mason, D.M., Brandt, S.B., Great Lakes Science Center, and Contribution 61 of the Institute for 2007. Alewife planktivory controls the abundance of two invasive predatory Great Lakes at Central Michigan University. We thank Brian Lantry for cladocerans in Lake Michigan. Freshw. Biol. 52, 561–573. Ptáčníková, R., Vanderploeg, H.A., Cavaletto, J.F., 2015. Big versus small: does Bythotrephes helpful comments that improved the clarity of this manuscript. We longimanus predation regulate spatial distribution of another invasive predatory thank P. Lavrenyev for help with Fig. 1 Plankton symbols used in Fig. 1 cladoceran, Cercopagis pengoi? J. Great Lakes Res. 41 (Supplement 3), 143–149. 6 H.A. Vanderploeg et al. / Journal of Great Lakes Research 41 Supplement 3 (2015) 1–6

Rowe, M.D., Obenour, D.R., Nalepa, T.F., Vanderploeg, H.A., Yousef, F., Kerfoot, W.C., 2015. among visually preying nonindigenous zooplankton and fish in Lake Michigan during Mapping the spatial distribution of the biomass and filter-feeding effect of invasive midsummer. J. Great Lakes Res. 41 (Supplement 3), 125–142. dreissenid mussels on the winter-spring phytoplankton bloom in Lake Michigan. Withers, J.L., Sesterhenn, T.M., Foley, C.J., Troy, C.D., Höök, T.O., 2015. Diets and growth po- Freshw. Biol. http://dx.doi.org/10.1111/fwb.12653 (in press). tential of early stage yellow perch and alewife in nearshore region of southeastern Rowe, M.D., Anderson, E.J., Wang, J., Vanderploeg, H.A., 2015. Modeling the effect of Lake Michigan. J. Great Lakes Res. 41 (Supplement 3), 197–209. invasive quagga mussels on the spring phytoplankton bloom in Lake Michigan. J. Great Lakes Res. 41 (Supplement 3), 49–65. Tang, H., Vanderploeg, H.A., Johengen, T.H., Liebig, J.R., 2014. Quagga mussel (Dreissena Henry A. Vanderploeg rostriformis bugensis) selective feeding of phytoplankton in Saginaw Bay. J. Great Great Lakes Environmental Research Laboratory, NOAA, 4840 S. State Rd., Lakes Res. 40, 83–94. Ann Arbor, MI 48108, USA Tsehaye, I., Jones, M.L., Bence, J.R., Brenden, T.O., Madenjian, C.P., Warner, D.M., 2014a. A multispecies statistical age-structured model to assess predator–prey balance: Corresponding author. Tel.: +1 734 741 2284. application to an intensively managed Lake Michigan pelagic fish community. Can. E-mail address: [email protected] J. Fish. Aquat. Sci. 71, 627–644. Tsehaye, I., Jones, M.L., Brenden, T.O., Bence, J.R., Claramunt, R.M., 2014b. Changes in the David B. Bunnell salmonine community of Lake Michigan and their implications for predator–prey balance. Trans. Am. Fish. Soc. 143, 420–437. U.S. Geological Survey, Great Lakes Science Center, 1451 Green Road, Ann Turschak, B.A., Bootsma, H.A., 2015. Lake Michigan trophic structure as revealed by stable Arbor, MI 48105, USA – C and N isotopes. Great Lakes Res. 41 (Supplement 3), 185 196. E-mail address: [email protected] Tyner, E.H., Bootsma, H.A., Lafrancois, B.M., 2015. Dreissenid metabolism and ecosystem- scale effects as revealed by oxygen consumption. Great Lakes Res. 41 (Supplement 3), 27–37. Hunter J. Carrick Vanderploeg, H.A., Liebig, J.R., Omair, M., 1993. Bythotrephes predation on Great Lakes' Department of Biology & Institute for Great Lakes Research, Central zooplankton measured by an in situ method: implications for zooplankton communi- ty structure. Arch. Hydrobiol. 127, 1–8. Michigan University Biological Station, Central Michigan University, Mount Vanderploeg, H.A., Nalepa, T.F., Jude, D.J., Mills, E.L., Holeck, D.T., Liebig, J.R., Grigorovich, Pleasant, MI 48859, USA I.A., Ojaveer, H., 2002. Dispersal and emerging ecological impacts of Ponto-Caspian E-mail address: [email protected] species in the Laurentian Great Lakes. Can. J. Fish. Aquat. Sci. 59, 1209–1228. Vanderploeg, H.A., Liebig, J.R., Nalepa, T.F., Fanenstiel, G.L., Pothoven, S.A., 2010. Dreissena and the disappearance of the spring phytoplankton bloom in Lake Michigan. J. Great Tomas O. Höök Lakes Res. 36, 50–59. Department of Forestry and Natural Resources, College of Agriculture, Vanderploeg, H.A., Pothoven, S.A., Fahnenstiel, G.L., Cavaletto, J.F., Liebig, J.R., Stow, C.A., Purdue University, 195 Marsteller Street, West Lafayette, IN, 47907, USA Nalepa, T.F., Madenjian, C.P., Bunnell, D.B., 2012. Seasonal zooplankton dynamics in Lake Michigan: disentangling impacts of resource limitation, ecosystem engineering, Illinois-Indiana Sea Grant, 195 Marsteller Street, West Lafayette, IN, 47907, and predation during a critical ecosystem transition. J. Great Lakes Res. 38, 336–352. USA http://dx.doi.org/10.1016/j.jglr.2012.02.005. Vanderploeg, H.A., Pothoven, S.A., Krueger, D., Mason, D.M., Liebig, J.R., Cavaletto, J.F., Ruberg, S.A., Lang, G.A., Ptáčíková, R., 2015. Spatial and predatory interactions