Southeastern Lake Michigan Research Articles

Large-Lake Responses to Declines in the Abundance of a Major Fish Planktivore—the Lake Michigan Example

Alewife abundances declined dramatically in southeastern Lake Michigan over 1973–77, several years before the lakewide decline occurred. The regional effects of this decline on adult copepod abundances, zooplankton biomass, and water clarity are examined. In the offshore region, the two largest copepods, Limnocalanus macrurus and Diaptomus sicilis, increased in abundance during the mid-1970's, reflecting the decrease in alewife predation. Limnocalanus macrurus abundances declined in later years, reflecting increased prédation pressures from the increasing bloater population. The small-bodied D. minutus and the medium-bodied D. ashlandi exhibited no apparent response to the decline in alewife abundance. Large-bodied D. oregonensis and small-bodied C. bicuspidatus thomasi declined in abundance. Size-selective fish prédation pressures continued to remain high in the inshore region: increased abundances of yellow perch and rainbow smelt apparently compensated for the alewife decline. Zooplankton biomass, zooplankton mean dry weight, and water clarity apparently were not affected by the decline in alewife abundance in either the inshore or offshore region. The results of this study are evaluated in terms of the lakewide decline in alewife abundance, the summer 1983 dominance of Daphnia pulicaria in offshore waters, the 1983 marked improvement in offshore water clarity, and later changes in summer offshore D. pulicaria populations.

Mysis relicta in Lake Michigan: Abundances and Relationships with their Potential Prey, Daphnia

Mysis relicta were sampled at a 100-m reference staton in southeastern Lake Michigan (43°N 86°40′W) from 1985 to 1989, to quantify nighttime water column abundances and to compare vertical distributions with those of Daphnia. Diel vertical migration produced maximum concentrations in the thermocline at night of 1 to 10 mysids∙m−3. Variation among replicates averaged 28% with a 3-net Tucker trawl and 19% with Puget Sound vertical closing nets. Mean areal abundances over 5 yr averaged 110 mysids∙m−2 (SE = 20; n = 30; range = 25 to 645) based on nighttime vertical and oblique net tows at 1–3-wk intervals during summers at the reference station. Synoptic cruises from 43°N to 45°N during August indicated that densities were considerably greater offshore than inshore, and greater in the north than in the south. Hypothesized long-term changes in mysid abundances were not detected. Although Mysis is potentially an important predator on Daphnia, differences in nighttime vertical distributions reduce encounters between Mysis and Daphnia during summer in Lake Michigan, such that Mysis exert mortality rates on Daphnia of < 1.5% per day; the latter are in general less than 10% of the birth rates of Daphnia populations, estimated from fecundities.

Changes in Mysis and Pontoporeia populations in southeastern Lake Michigan: A response to shifts in the fish community

Changes in Mysis and Pontoporeia populations in southeastern Lake Michigan: A response to shifts in the fish community

Mass Flux and "Nutritional Composition" of settling Epilimnetic Particles in Lake Michigan

A series of sediment-trap samples, collected at a 30-m depth in southeastern Lake Michigan, was analyzed to evaluate the seasonal flux and nutritional value of settling epilimnetic particles as potential food for benthic organisms. Flux was highest in the spring (due in part to resuspension), lowest in the summer during stratification, and intermediate during autumn months. Organic content of the particles ranged from 10% ash free dry weight (AFDW) in March through May samples to 17–19% in July–August samples. During the summer, microbial degradation of organic materials occurred in the trap bottles without added preservative, as evidenced by less AFDW in nonpreserved trap bottles than in similar chloroform-preserved bottles. The percentage of AFDW occuring as lipid ranged from 3.5% in April–May up to 14% during May through August. Dominant lipid classes were hydrocarbons, polar lipids including phospholipids and chlorophyll a, and free fatty acids. The ratio of n-alkane C-17 (algal indicator) to n-alkane C-29 (terrestrial or resuspension indicator) and the ratio of biogenic silica to AFDW in preserved samples both reached a maximum in May, shortly before lipid content peaked in the benthic amphipod, Pontoporeia hoyi. This observation agrees with the hypothesis that P. hoyi receives much of its nutrition from the spring algal bloom.

Dynamics of Lake Michigan Phytoplankton; Relationship to Nitrogen and Silica Fluxes

We describe rates of nitrogen and silica concentration change during May–August 1983 and 1984 in southeastern Lake Michigan and compare those rates with measured plankton processes. Epilimnetic dissolved inorganic nitrogen depletion, compared with total phytoplankton demand, suggests that about 44% of the nitrogen demand is recycled. Epilimnetic diatom production, calculated from soluble silica depletion, is a relatively small fraction (< 20%) of total primary production, even when diatoms dominate. Sedimentation of epilimnetic diatom silica, compared with total silica depletion, suggests that a large portion (approximately 43%) of epilimnetic particulate silica sedimentation is due to nonliving diatoms.

Gut Fullness of the Deposit-Feeding Amphipod, Pontoporeia hoyi, in Southeastern Lake Michigan

Pontoporeia hoyi Smith, a deposit-feeding amphipod and a prominent member of the Great Lakes macrobenthic community, was collected at a 45-m-deep site in southeast Lake Michigan during October 1983 and March, May, June, August, and September 1984. Substantial numbers of animals with empty or partially-full guts indicated that P. hoyi feeds intermittently, unlike other continuous-feeding amphipods which routinely maintain uniformly full guts among all members of a population. The incidence of animals with empty, partially-full, and full guts also varied significantly with animal size and sampling date and implied that aspects of the amphipod's life history, and seasonality, were primarily responsible for changes in feeding rates. Overall, P. hoyi gut fullness was greatest in spring and, secondarily, in autumn, reflecting an opportunistic feeding strategy that exploited newly-deposited detritus generated from spring and autumn phytoplankton blooms. This strategy, in association with P. hoyi's known capacity to store energy as lipids may largely explain P. hoyi's exclusive and widespread distribution in profundal areas of the upper Great Lakes, compared to other amphipods.

Changes in the abundance of blue-green algae related to nutrient loadings in the nearshore of Lake Michigan

Nutrient loadings to the nearshore of southeastern Lake Michigan have undergone a remarkable reduction. This reduction can affect the nutrient supply and result in biological changes. Changes in phytoplankton community, particularly the blue-green algae, can be related to nutrient changes. After thermal stratification, sudden increases in the blue-green algae population were significantly correlated to soluble reactive phosphorus concentrations. Phosphorus-stimulated low dissolved silica and phosphorus limitations after stratification appear to be primary factors contributing to the success of these algae.

Diet and Selection of Major Prey Species by Lake Michigan Salmonines, 1973–1982

Abstract To elucidate prey preferences, we quantified stomach contents of 1,231 salmonines collected from inshore (21 m or shallower) southeastern Lake Michigan during 1973–1982. Predators ate 12 species of fish. Alewife Alosa pseudoharengus made up 48–79% by weight of the diet of brown trout Salmo trutta, chinook salmon Oncorhynchus tshawytscha, coho salmon Oncorhynchus kisutch, lake trout Salvelinus namaycush, and rainbow trout Salmo gairdneri. Alewives eaten ranged from 23 to 245 mm total length; 46% were 150–200 mm. Rainbow smelt Osmerus mordax eaten were 21–245 mm long and made up 4–11% of the salmonines' prey. There were significant direct linear relationships between lengths of alewives and rainbow smelt eaten and lengths of the five predators. Alewives are currently declining in Lake Michigan. If their population collapses, there should be a shift to alternative prey species. We have seen no such shift through 1982, although more recent data of other investigators show a decline in the importance ...

Near-Bottom Currents and Suspended Sediment Concentration in Southeastern Lake Michigan

In a study of sediment transport at the edge of the coastal shelf (28 m depth) in southeastern Lake Michigan we used an instrumented tripod to make continuous observations of horizontal current velocity, temperature, and turbidity within 1 meter of the bottom for 4 weeks during October 1981. The concentration of total suspended material (TSM) 0.9 m above the bottom varied from 1 to 5 mg/L in response to coastal upwelling, surface waves, and currents that exceeded 0.28 m/s (0.7 m above the bottom) on occasion. Advection of the Grand River plume also contributed significantly to the variations in the observed TSM concentration. Currents near the bottom were well correlated with surface winds and, although upwelling currents transported sediment upslope, the net horizontal sediment flux during the period of observation was west-southwestward, almost directly offshore. The magnitude of the horizontal sediment flux was approximately 1,000 times the magnitude of the vertical flux estimated from sediment traps deployed as part of earlier studies. We infer that local resuspension occurred roughly 20 percent of the time and the critical mean flow speed (at 0.7 m) for resuspension of the local silty sands was estimated to be about 0.18 m/s.

Acid Rain Stimulation of Lake Michigan Phytoplankton Growth

Three laboratory experiments demonstrated that additions of rainwater to epilimnetic lake water collected in southeastern Lake Michigan stimulated chlorophyll a production more than did additions of reagent-grade water during incubations of 12 to 20 d. Chlorophyll a production did not begin until 3–5 d after the rain and lake water were mixed. The stimulation caused by additions of rain acidified to pH 3.0 was greater than that caused by additions of untreated rain (pH 4.0–4.5). Our results support the following hypotheses: (1) Acid rain stimulates the growth of phytoplankton in lake water; (2) phosphorus in rain appears to be the factor causing this stimulation. We conclude that acid rain may accelerate the growth of epilimnetic phytoplankton in Lake Michigan (and other similar lakes) during stratification when other sources of bioavailable phosphorus to the epilimnion are limited

Alewife (Alosa pseudoharengus) Survival During the First Growth Season in Southeastern Lake Michigan

Alewife (Alosa pseudoharengus) survival from newly hatched larvae to fall young-of-the-year (YOY) was calculated using data collected in southeastern Lake Michigan, June–November 1974–82. Alewife YOY density (number per 1000 m3) was estimated from trawl catches. Larval alewife densities, derived from plankton net samples at trawling stations and from power plant entrainment samples, were averaged each year for length intervals which represented yolk-sac and post-yolk-sac larvae. Survival (ratios of YOY to larval alewife densities) varied considerably among years, but mean survival over all years from yolk-sac larvae to YOY was 1% calculated from either field-larvae or entrained-larvae data. Mean survival from post-yolk-sac larvae to YOY was higher, 2.2–4.6%. Daily mortality rates were 12–27% for larvae through yolk absorption, decreasing to 2–5% for juveniles. Differences in survival among years may be due to timing of sampling, distribution of larvae and YOY, or actual survival differences, perhaps related to predator abundance.

The effects of power plant passage on zooplankton mortalities: Eight years of study at the Donald C. Cook nuclear plant

Zooplankton mortalities resulting from passage through the Donald C. Cook Nuclear Plant (southeastern Lake Michigan) were studied over an 8-year (1975–1982) period. The power plant operated at a low ΔT (< 12°C) and discharge water temperatures did not exceed 35°C (except September 1978). While zooplankton mortalities were significantly greater in discharge than intake waters, differences were small, averaging < 3%. There was no evidence of additional delayed effects on zooplankton mortality following plant passage. Calanoid copepods ( Diaptomus spp, Eurytemora affinis and Limnocalanus macrurus) were most sensitive to plant passage, cyclopoid copepods least sensitive, while cladocerans ( Daphnia spp, Eubosmina coregoni) were intermediate in sensitivity. There was no relationship between zooplankton mortalities and temperature ( ΔT, discharge water temperature), suggesting that thermal stresses were not the major source of mortality. The single exception was September 1978 when discharge water temperatures exceeded 35°C and there were large differences between intake and discharge water zooplankton mortalities (net mortality differences of 14–22% for the two units). Mechanical stresses appeared to be the major cause of zooplankton mortality. However, there was only a weak relationship between mortality as a result of plant passage and zooplankton size. Based on our long-term preoperational (1970–1974) and operational (1975–1982) ecological studies in the vicinity of the power plant, we hypothesize that fish predation, rather than power plant operation, probably was the major source of zooplankton mortality in inshore waters during much of the year.

Production of planktonic bacteria in Lake Michigan

Bacterial production rates were estimated for the surface waters of a station 100‐m deep in southeastern Lake Michigan during 1984. Production was calculated from incorporation of [3H‐methyl]thymidine and from empirical conversion factors determined from dilution experiments performed throughout the study. The conversion factors (with typical C.V. &lt;40%) varied between 4.7 and 18.3 × l09 cells produced per nanomole of thymidine incorporated into ice‐cold trichloroacetic acid extracts. Our estimates yielded bacteria exponential growth rates between 0.05 and 0.24 h‐1 (C.V. typically &lt;50%) based on the empirical conversion factors. The growth estimates are much lower (0.004–0.020 h‐1) when based on measured 47% thymidine incorporation into DNA and a theoretical conversion factor. The higher growth estimates appear more consistentwith estimated grazing losses. Carbon flux estimates are less certain, due to the possible range of bacterial carbon content and growth efficiencies, but most of the higher growth estimates imply a bacterial carbon demand higher than concurrent 14C‐based primary production measurements. This may mean that a source other than recent primary production is needed to meet this demand.

Intervention Analysis of Power Plant Impact on Fish Populations

Alewife (Alosa pseudoharengus) and yellow perch (Perca flavescens) abundances, estimated from monthly gillnet and trawl catches at two transects, were monitored before (1973–74) and during (1975–82) operation of the D. C. Cook Nuclear Power Plant, southeastern Lake Michigan. Intervention analysis, a technique which accounts for autocorrelated observations, and analysis of variance (ANOVA) were applied to the monitoring data to assess any plant impact beginning in 1975. Both analyses disclosed no significant power plant impacts except for gillnetted yellow perch adults. The ANOVA indicated a significant decrease in abundance at the plant-discharge transect relative to the reference transect as plant operation began, which established a plant effect; intervention analysis showed no change. When April and May catches (months of low abundance) were deleted, this plant effect was insignificant. Monte Carlo simulation showed that as the first-order autoregressive coefficient increased positively, type I error of the ANOVA F-test increased. However, ANOVA was more powerful than intervention analysis when a first-order autoregressive component was included. Impact assessment based only on ANOVA can result in detection of impact when actually there was no effect (type I error) when observations are serially correlated (lack independence).

Free Amino Acid Pools of Five Species of Freshwater Oligochaetes

The concentrations of free amino acids (FAA) were measured in five species of freshwater Oligochaeta (Limnodrilus hoffmeisteri, Tubifex tubifex, Potamothrix moldaviensis, Potamothrix vejdovskyi, and Stylodrilus heringianus) collected from southeastern Lake Michigan. Alanine represented between 23.1 and 41.8% of the total FAA pool and was the most abundant amino acid in all species. Leucine, valine, and glutamic acid were, respectively, the next most abundant and had similar relative concentrations in all species except T. tubifex. In T. tubifex, glutamic acid, asparagine, and aspartate were the second, third, and fourth most abundant FAA, respectively. Relative to other freshwater invertebrates, the total FAA pool of Lake Michigan oligochaetes was small. Differences in innate physiological and/or biochemical processes, dietary intake, and reproductive status may have contributed to the quantitative and qualitative differences observed among species. Identification of individual oligochaetes to species was accomplished by multivariate statistical analysis of the FAA profiles. A potential exists for the application of this technique for identifying immature oligochaetes.

Food of Deepwater Sculpin, Myoxocephalus Thompsoni, from Southeastern Lake Michigan

Pontoporeia hoyi was the major food consumed by most sizes of deepwater sculpins ( Myoxocephalus thompsoni) during spring and summer, 1981–82, at a 100-m station in southeastern Lake Michigan. There was no apparent seasonality in choices of food or volumes consumed. Mysis relicta made up less than 9% of the total food volume and averaged second to Pontoporeia volumetrically—a result which differed from previous investigations for Lake Michigan. Reduced consumption of Mysis in our study compared to previous work may be a function of lower prey density or station depth; mysids may have been farther above the lake bottom than at previously studied, more shallow stations. Ostracods were important in 6- and 7-cm fish diets. Mysis, chironomids, and fish eggs were only found in sculpins larger than 8 cm. Chironomid larvae, which typically burrow into sediments, and copepod and cladoceran zooplankton constituted a small percentage of the diet of all sculpins. These results indicated that the deepwater sculpins examined were primarily epibenthic predators at the sediment-water interface and apparently did not burrow for food or feed higher up in the water column.

Seasonal variations in copepod size: effects of temperature, food abundance, and vertebrate predation

Seasonal dry weights of female and male Cyclops bicuspidatus thomasi, Diaptomus ashlandi and Diaptomus minutus were studied in southeastern Lake Michigan during 1975-1981. Smallest animals oc- curred during summer and early fall, and largest animals in winter and spring, a pattern reported for other copepods. The range of weights for the species and sexes decreased from winter to summer, and converged in summer to a value of approximately 2 /tg/animal. Surface water temperature and abundances ofyoung- of-the-year (YOY) fish were inversely correlated with weights of males and females of the three copepod species. Standing stocks of important phytoplankton groups, especially pennate diatoms and flagellates, were positively correlated with copepod weight. Seasonal change of copepod body size appears to be more than simply a function of temperature; seasonal predation by YOY fish may be a factor influencing sizes of adult copepods.

Recent shifts in Daphnia community structure in southeastern Lake Michigan: A comparison of the inshore and offshore regions1,2

Before 1982, Daphnia retrocurva and Daphnia galeata mendotae were the dominant species of Daphnia in Lake Michigan. Between 1972 and 1981, Daphnia community structure in the offshore region shifted toward greater dominance of the larger D. galeata mendotae, with Daphnia pulicaria, another large species, dominating by 1982. This continued through summer 1984. Shifts in offshore Daphnia community structure appear to be related to a reduction in predation pressure by declining alewife (Alosa pseudoharengus) populations and a hypothesized increase in relative predation pressure by Mysis relicta. From 1972 to 1984, Daphnia community structure changed only slightly in the inshore region; D. retrocurva generally remained the summer and autumn dominant. However, summer Daphnia abundances decreased after 1980 as yellow perch (Perca flavescens) and bloater (Coregonus hoyi) increased. From an examination of historic data we conclude that inshore region Daphnia populations probably have changed little since the late 1880s. The 1982–1984 offshore Daphnia complex, however, differed markedly from the earliest (mid‐1950s) record of zooplankton community structure in this region of southeastern Lake Michigan.

Depth Distribution, Diet, and Overwinter Growth of Lake Trout ( Salvelinus Namaycush) in Southeastern Lake Michigan Sampled in December 1981 and March 1982

Lake trout were collected in graded-mesh gill nets and forage fishes were collected in trawls in mid December 1981 and late March 1982. The length ranges of 317 lake trout caught in December and 138 in March were 280–767 and 286–857 mm, and the age ranges I–XI and II–XIV, respectively. Three year classes (1977–79) made up almost 80% of the catches of lake trout in both sampling periods. Lake trout were most abundant at depth of 18 to 37 m in December (water temperatures, 5.5–6.8°C) and at 28–64 m in March (water temperatures, 1.0–1.3°C). Fish of the 1977–79 year classes completed 9 to 24% of their annual growth in length, and 14 to 39% of their growth in weight, between mid December and late March. Lake trout ate mainly alewives ( Alosa pseudoharengus) especially young-of-the-year, in December, but primarily slimy sculpins ( Cottus cognatus) in March, when alewives were mainly at depths of greater than those occupied by most lake trout. Other important food items were rainbow smelt ( Osmerus mordax) and, in deeper water, deepwater sculpins ( Myoxocephalus thompsoni) Bloaters ( Coregonus hoyi) were eaten only sparingly, although they were abundantly available in both sampling periods. Perhaps this species, which coevolved with the lake trout in Lake Michigan and was important in the native trout's diet, is better able to avoid capture by the trout than are the exotic alewife and rainbow smelt. It may not again become a major forage species unless the other food sources become scarce.

Recent Major Declines in Zooplankton Populations in the Inshore Region of Lake Michigan: Probable Causes and Implications

Summer Zooplankton communities in the inshore region of southeastern Lake Michigan were dominated by small species during the 1970s, suggesting that size-selective fish predation pressures were intense. Abundances of alewife (Alosa pseudoharengus), the dominant planktivore in the 1970s, declined in recent years, especially over 1982–84. Despite decreased alewife predation, small zooplankton taxa continued to predominate. Moreover, zooplankton standing stocks declined 10-fold during 1982–84, suggesting that predatory pressures had intensified. Concurrent with the alewife population decrease was a major increase in yellow perch (Perca flavescens) abundances. As a probable consequence of intense predation pressures exerted by abundant yellow perch, zooplankton standing stocks were severely reduced. Yellow perch populations may have been adversely affected by food limitation, especially in summer 1984 when zooplankton standing stocks were only 3% of their average level over 1975–81.