US Long-Term Ecological Research Network

Lake Mendota, Wisconsin, USA, Zebra Mussel Body Size and Biomass Biometrics 2018

Abstract
We sampled 98 individuals of the zebra mussel (Dreissena polymorpha) population of Lake Mendota from many littoral zone sites in 2018 to create biometric relationships between several metrics of body size and several metrics of biomass, including length, width, height, living weight, wet weight, dry weight, shell weight, shell-free dry weight, and ash-free dry weight. We selected individuals to span a wide range of body sizes and found strong relationships between most combinations of body size and biomass metrics.<br/>
Dataset ID
395
Date Range
-
LTER Keywords
Methods
In the laboratory, three measurements of body size and seven measurements of biomass were captured. First, any foreign material found adhering to the external surface of specimens was completely removed. Body size directional measurements of shell length (L), width (W), and height (H) were recorded for every specimen with the aid of callipers (0.01 mm). Following this, any excess water was removed from surfaces by drying the external shell with tissue paper. Further, using a scalpel blade and tweezers, excess water was removed from the mantle cavity by gently forcing bivalves to gape, taking care not to cut the adductor muscle or damage tissues. Using high-resolution scales, living-weight (LW) was obtained for each specimen. Then each specimen was fully opened, which in most cases involved cutting of the adductor muscles. To remove additional fluid from the mantle and other cavities, each specimen was then placed with the valve gape (flesh) facing downwards onto absorbent tissue, for ~5-10 minutes. A wet-weight (WW) was obtained for each specimen. Following this, the soft tissue was dissected from the shell, then both soft tissue and shell were dried together within an oven (60-72 degreeC) for ~48 hrs, or until they reached a constant weight. Specimens were cooled to room temperature in a desiccator before final weighing. A combined dry-weight (DW) was recorded, as were weights for the soft tissue and shell separately, i.e. shell free dry-weight (SFDW) and dry shell-weight (SW), respectively. Following the establishment of SW, SFDW was calculated subtracting SW from the total DW (i.e. SFDW = DW–SW). To obtain an ash-weight (AW), the soft and hard tissue structures of specimens were incinerated (500–550 degreeC) together within a muffle furnace for 4–6 hrs. In all cases, the ash free dry-weight (AFDW) was then calculated for the entire specimen (soft tissue and shell) by subtracting the AW from DW, i.e. AFDW = DW–AW.<br/>
Version Number
1

Lake Mendota, Wisconsin, USA, Zebra Mussel Veliger Water Column Density 2016-2019

Abstract
We sampled veliger (larval stage) zebra mussels (Dreissena polymorpha) from 2016-2019.
Zebra mussels are invasive in Lake Mendota and were first detected in November 2015. Samples
were taken at three different sites on Lake Mendota from June to August in 2016, and from
June to November in 2018-2019, using a 0.5 m diameter, 64 micrometer mesh size plankton net
for an 8 m depth tow. This dataset complements adult zebra mussel, zoobenthos, and
phytobenthos data collected during the same time period, for which data is also archived
with EDI.
Core Areas
Dataset ID
392
Data Sources
Date Range
-
Methods
We sampled larval zebra mussels (veligers) using a 64 microm mesh, 0.5 m diameter
plankton net and stored them in 80% ethanol in 200 mL containers at 25degree C for 0-12
weeks until processing. At each site we performed triplicate 8 m depth plankton tows by
pulling a net from 2 m above the lake bottom at the 10 m depth sites of transects A-C
developed for adult zebra mussel collection. We collected samples approximately every 14
days from June to August in 2016, and June to November in 2017-2019. During fall
sampling, poor weather conditions occasionally limited the number of sites or replicates
collected. We also sampled veligers biweekly in 2019 but reduced sampling to one
replicate per site and only sampled at one site after September. Because veligers are
small and difficult to see, enumeration was time consuming. <br/>We sampled larval zebra mussels (veligers) using a 64 microm mesh, 0.5 m diameter
plankton net and stored them in 80% ethanol in 200 mL containers at 25degree C for 0-12
weeks until processing. At each site we performed triplicate 8 m depth plankton tows by
pulling a net from 2 m above the lake bottom at the 10 m depth sites of transects A-C
developed for adult zebra mussel collection. We collected samples approximately every 14
days from June to August in 2016, and June to November in 2017-2019. During fall
sampling, poor weather conditions occasionally limited the number of sites or replicates
collected. We also sampled veligers biweekly in 2019 but reduced sampling to one
replicate per site and only sampled at one site after September. Because veligers are
small and difficult to see, enumeration was time consuming. <br/>We sampled larval zebra mussels (veligers) using a 64 microm mesh, 0.5 m diameter
plankton net and stored them in 80% ethanol in 200 mL containers at 25degree C for 0-12
weeks until processing. At each site we performed triplicate 8 m depth plankton tows by
pulling a net from 2 m above the lake bottom at the 10 m depth sites of transects A-C
developed for adult zebra mussel collection. We collected samples approximately every 14
days from June to August in 2016, and June to November in 2017-2019. During fall
sampling, poor weather conditions occasionally limited the number of sites or replicates
collected. We also sampled veligers biweekly in 2019 but reduced sampling to one
replicate per site and only sampled at one site after September. Because veligers are
small and difficult to see, enumeration was time consuming.
Version Number
1

North Temperate Lakes LTER: Trout Lake Spiny Water Flea 2014 - present

Abstract
Beginning in 2014, 30 meter vertical tows with a special zooplankton net were collected in Trout Lake specifically for the invasive Bythotrephes longimanus (spiny water flea). The net has a 400 micrometer mesh with a 0.5 meter diameter opening. Individuals are simply counted, and density is determined to be the number of individuals divided by the total water volume of each tow.
Additional Information
Related data set: North Temperate Lakes LTER: Zooplankton - Trout Lake Area 1992 - current (37)
Core Areas
Dataset ID
389
Date Range
-
Methods
Two 30-meter vertical tows (0.5m diameter, 400um mesh net) are collected at the deepest part of Trout Lake each time the lake is visited for routine LTER sampling during open water. On occasion, tows are collected on additional dates. Samples are visually scanned in their entirety for number of Bythotrephes present. The samples are not preserved or archived.

Publication Date
Version Number
1

North Temperate Lakes LTER Regional Survey Zooplankton 2015 - current

Abstract
The Northern Highlands Lake District (NHLD) is one of the few regions in the world with periodic comprehensive water chemistry data from hundreds of lakes spanning almost a century. Birge and Juday directed the first comprehensive assessment of water chemistry in the NHLD, sampling more than 600 lakes in the 1920s and 30s. These surveys have been repeated by various agencies and we now have data from the 1920s (UW), 1960s (WDNR), 1970s (EPA), 1980s (EPA), 1990s (EPA), and 2000s (NTL). The 28 lakes sampled as part of the Regional Lake Survey have been sampled by at least four of these regional surveys including the 1920s Birge and Juday sampling efforts. These 28 lakes were selected to represent a gradient of landscape position and shoreline development, both of which are important factors influencing social and ecological dynamics of lakes in the NHLD. This long-term regional dataset will lead to a greater understanding of whether and how large-scale drivers such as climate change and variability, lakeshore residential development, introductions of invasive species, or forest management have altered regional water chemistry. Zooplankton samples were taken at approximately the deepest part of each lake, via a vertical tow with a Wisconsin net. Count of individuals and presence absence data for all lakes in the study region are provided here.
Contact
Core Areas
Dataset ID
381
Date Range
-
Maintenance
ongoing
Methods
One zooplankton sample was collected in June 2015 at the deepest part of each lake, via vertical tow with a Wisconsin net (20cm diameter, 80um mesh). Contents of the net were preserved in the field with cold 95% ethanol. Subsamples of each vertical tow sample were counted for zooplankton species, using enough volume to count at least 300 individuals. A larger volume was then visually scanned to look for presence of additional species not seen in the count volume, until at least 2000 individuals had been seen.

Version Number
1

North Temperate Lakes LTER Zooplankton conversion formulas length to biomass

Abstract
Formulas for calculating zooplankton biomass based on measured length for species encountered in NTL's northern lakes. Formulas are either based on literature reports or measurements in particular research lakes.
Core Areas
Dataset ID
376
LTER Keywords
Maintenance
completed
Methods
formulas are based on data in literature or were determined in samples from research lakes:

Culver D.A. et.al. 1985. Can. J. Fish. Aquat. Sci. Vol 42, 1380-1390.
Biomass of freshwater crustacean zooplankton from length-weight regressions.

Downing, John A. and Frank H. rigler. 1984.
A manual on methods for the assessment of secondary productivity in fresh waters. Second edition.

Dumont, H.J., I. Van de Velde and S. Dumont. Ref??
The dry weight estimate of biomass in a selection of cladocera, copepoda and rotifera from the plankton, periphyton and benthos of continental waters.

Hawkins, Bethany E. and M.S. Evans. 1979. J.Great Lakes Res. 5(3-4):256-263
Seasonal cycles of zooplankton biomass in southeastern Lake Michigan

Lawrence, S.G., D.F. Malley, W.J. Findlay, M.A. MacIver and I.L. Delbaere. 1987. Can J. Fish. Aquat. Sci. 44: 264-274.
Methods for estimating dry weight of freshwater planktonic crustaceans from measures of length and shape.

Pace M.L. and J.D. Orcutt. 1981. Limnol. Oceanogr. 26(5), 822-830.
The relative importance of protozoans, rotifers, and crustaceans in a freshwater zooplankton community.

Yan N.D. and G.L. Mackie. 1987. Can. J. Fish. Aquat. Sci. Vol 44, 382-389.
Improved estimation of the dry weight of Holopedium gibberum using clutch size, a body fat index, and lake water total phosphorus concentration.

Ruttner-Kolisko A. 1977. Arch. Hydrobiol. Beih. Ergebn. Limnol. 8, 71-76.
Suggestions for biomass calculations of plankton rotifers.
Version Number
1

Little Rock Lake Experiment at North Temperate Lakes LTER: Zooplankton length 1988 - 1998

Abstract
The Little Rock Acidification Experiment was a joint project involving the USEPA (Duluth Lab), University of Minnesota-Twin Cities, University of Wisconsin-Superior, University of Wisconsin-Madison, and the Wisconsin Department of Natural Resources. Little Rock Lake is a bi-lobed lake in Vilas County, Wisconsin, USA. In 1983 the lake was divided in half by an impermeable curtain and from 1984-1989 the northern basin of the lake was acidified with sulfuric acid in three two-year stages. The target pHs for 1984-5, 1986-7, and 1988-9 were 5.7, 5.2, and 4.7, respectively. Starting in 1990 the lake was allowed to recover naturally with the curtain still in place. Data were collected through 2000. The main objective was to understand the population, community, and ecosystem responses to whole-lake acidification. Funding for this project was provided by the USEPA and NSF. Zooplankton samples are collected from the treatment and reference basins of Little Rock Lake at at two to nine depths using a 30L Schindler Patalas trap (53um mesh). Zooplankton samples are preserved in buffered formalin and archived. Data are summed over sex and stage and integrated volumetrically over the water column to provide a lake-wide estimate of average length of organisms for each species.
Core Areas
Dataset ID
375
Date Range
-
Maintenance
completed
Methods
We collect zooplankton samples at the deepest part of the lake using two different gear types. We take one vertical tow with a Wisconsin Net (80um mesh), and a series of Schindler Patalas (53um mesh) samples spanning the water column. All samples are preserved in cold 95percent EtOH.
After collection we combine subsamples of the individual Schindler Patalas trap samples to create one hypsometrically pooled sample for each lakeordate. The individual depth samples are discarded after pooling except from one August sampling date per year. The Hypsometrically Pooled sample and the Wisconsin Net sample are archived in the UW Zoology museum.
We count zooplankton in one or two subsamples, each representing 1.8L of lake water, of the hypsometrically pooled samples to calculate zooplankton abundance. We count one sample date per month from the open water season, and the February ice cover sample. We identify individuals to genus or species, take length measurements, and count eggs and embryos.
Protocol log: 1981-May1984 -- a 0.5m high, 31L Schindler Patalas trap with 80um mesh net was used. Two Wisconsin Net tows were collected. Preservative was 12percent buffered formalin.
June1984 -- changed to 53um mesh net on Schindler trap.
July1986 -- began using the 2m high, 45L Schindler Patalas trap. Changed WI Net collection to take only one tow.
2001 -- changed zooplankton preservative from 12percent buffered formalin to 95percent EtOH.
The number of sample dates per year counted varies with lake and year, from 5 datesoryear to 17 datesoryear.
1981-1983 -- pooled samples are of several types: Total Pooled (TP) were created using equal volume subsamples of the Schindler samples. Epi, Meta, Hypo pooled used equal volume subsamples from the Schindler samples collected from each of the thermal strata. Strata Pooled used equal volume subsamples from the Epi, Meta, Hypo pooled samples to create an entire lake sample. Hypsometrically Pooled (HP) is our standard, which uses subsample volumes weighted to represent the hypsometry of the lake.
Version Number
1

Cascade project at North Temperate Lakes LTER - Daily data for key variables in whole lake experiments on early warnings of critical transitions, Paul and Peter Lakes, 2008-2011

Abstract
Peter Lake's food web was altered by adding largemouth bass at a slow rate while monitoring key food web constituents including littoral minnow abundance indexed as catch per trap per hour, zooplankton biomass, and concentration of chlorophyll a. Paul Lake was manipulated and the same variables were measured there.
In Peter Lake, we expected littoral catch of minnows to first increase as minnows moved into the littoral zone due to the threat of bass predation and then decrease due to bass predation. We expected zooplankton biomass to increase as minnows moved into the littoral zone. We expected chlorophyll to decrease due to increased grazing by zooplankton. We expected that variance and autocorrelation of chlorophyll would increase as the food web passed a critical transition.
We expected that the time series in Paul Lake would represent the normal variability of an unmanipulated lake
Dataset ID
374
Date Range
-
Methods
Primary publications that provide more information about taxa, methods, and data are:
Carpenter, S.R., J.J. Cole, M.L. Pace, R.D. Batt, W.A. Brock, T. Cline, J. Coloso, J.R. Hodgson, J.F. Kitchell, D.A. Seekell, L. Smith and B. Weidel. 2011. Early warnings of regime shifts: A whole-ecosystem experiment. Science 332: 1079-1082.
Cline, T.J., D. A. Seekell, S. R. Carpenter, M. L. Pace, J. R. Hodgson, J. F. Kitchell, and B. C. Weidel 2014. Early warnings of regime shifts: evaluation of spatial indicators from a whole-ecosystem experiment. Ecosphere 5:art102. http://dx.doi.org/10.1890/ES13-00398.1
Pace, M.L., S.R. Carpenter, R.A. Johnson and J. T. Kurzweil. 2013. Zooplankton provide early warnings of a regime shift in a whole-lake manipulation. Limnology and Oceanography 58: 525-532.
For an explanation of our rationale and expected results see:
Carpenter, S. R., Brock, W. A., Cole, J. J., Kitchell, J. F., & Pace, M. L. 2008. Leading indicators of trophic cascades. Ecology Letters, 11(2), 128-138. doi:DOI 10.1111/j.1461-0248.2007.01131.x
Version Number
2

Cascade Project at North Temperate Lakes LTER Core Data Zooplankton 1984 - 2016

Abstract
Zooplankton data from 1984-2016. Sampled approximately weekly with two net hauls through the water column (30 cm diameter net, 80 um mesh). There have been over eight zooplankton counters during this period, so species-level identifications (TAX, below) are not as consistent as those for some of the other datasets. Sampling Frequency: varies; Number of sites: 8
Core Areas
Dataset ID
355
Date Range
-
Maintenance
completed
Methods
Sampling:
Zooplankton were sampled approximately weekly with two net hauls through the water column (30 cm diameter net, 80 um mesh). Tows were taken at standard depths for almost all years. The standard depths are as follows: Peter, East Long, West Long, Crampton and Tuesday Lakes: 12m, Paul Lake: 8m, Ward Lake: 6m; exceptions are: for 2012 and beyond Tuesday Lake was sampled at 10m, Peter was sampled at 10m from 1984-1986, Paul was sampled at 7.5m in 1995. Samples were preserved with cold sugared formalin or Lugol's solution.
Version Number
16

North Temperate Lakes LTER Bythotrephes longimanus spiny water flea population monitoring in Wisconsin and Minnesota 2009 - 2014

Abstract
Three data tables are included describing population dynamics for Bythotrephes longimanus, spiny water flea, in Southern Wisconsin during invasion. General monitor took place in Lake Mendota, Lake Monona, Lake Waubesa, Lake Kegonsa, Stormy Lake, Gile Flowage, Lake Gogebic.Accompanying Bythotrephes morphological measurements from Lake Mendota monitoring efforts in 2011 and 2012. Included are individual measurements of body morphology and reproductive status for ~2,500 <em>Bythotrephes </em>collected from Lake Mendota in 2011 and 2012.Sediment cores from Lake Mendota were analyzed for spiny water flea evidence with age of sediment estimated.
Contact
Core Areas
Dataset ID
342
Date Range
-
Maintenance
complete
Methods
general monitoring for spiny water flea:
The dataset contains collected Bythotrephes longimanus monitoring efforts from 8 invaded lakes in Wisconsin that took place over the course of 2009 through 2014 using a zooplankton net. Monitoring efforts were conducted to 1) obtain more accurate estimates of Bythotrephes densities using a more appropriately sized net (50-cm diameter over 30-cm diameter) and 2) obtain detailed demographic measurements of Bythotrephes morphology and reproduction in each lake. Here only Bythotrephes densities are included.
The majority of samples occurred at a lakes deep hole with a 50-cm diameter and 150-micron mesh zooplankton net. Nets are lowered to 2 m off of the lake bottom before being towed to the surface. Samples are processed in their entirety
Exceptions to this are those at sites containing “LTER” (e.g., site IDs LTER-DH and LTER-MB) in their ID which were samples taken according to the Southern Lakes LTER zooplankton collection protocol with a 30-cm and 83-micron mesh. Other exceptions include sites outside the deep hole of the lake (site ID 5m = 5m lake depth north of the Center for Limnology on Lake Mendota; CFL = 15m lake depth north of the Center for Limnology; DH = deep hole but specific to Lake Mendota; MB = 15m lake depth southwest of Maple Bluffs in Madison on Lake Mendota; MO.5m = a 5m lake depth site in Lake Monona; MO.Y = 5m lake depth site at the mouth of the Yahara River on Lake Monona; TL = 15m lake depth west of Tenney Locks in Madison on Lake Mendota; WS = 15m site in northwestern basin of Lake Mendota, east of Picnic Point; WP = 5m site south of Warner Park on Lake Mendota). Several tows were taken using a 200m oblique (i.e., horizontal) net tow with the 50-cm diameter net (DH-ObliqueTow). Efforts in Southern Wisconsin were led by Jake Walsh while efforts in Northern Wisconsin were led by Carol Warden (site ID = CW), Pam Montz (site ID = PM), Sam Christel (site ID = SC), Sam Oliver (site ID = SM), as well as a researcher with initials (site ID) “EM”.
Version Number
8

North Temperate Lakes LTER Madison Wisconsin Lakes Zooplankton 1976 - 1994

Abstract
Zooplankton of the four Yahara River chain of lakes (Mendota, Monona, Waubesa, and Kegonsa) were sampled and analyzed by the Wisconsin Department of Natural Resources (WDNR) during 1976 to 1994 as part of a long-term limnological sampling program directed by Richard C. Lathrop. Methods for zooplankton sampling and laboratory analyses were previously summarized for Lake Mendota (Lathrop 1998); methods were similar for the other three Yahara lakes although Waubesa and Kegonsa were only sampled for zooplankton during 1976-1985. In general, zooplankton were sampled at the deepest location of each lake by pulling a conical net vertically through the water column (i.e., vertical tow sample) during 1976-1994. Sampling was usually done on a biweekly schedule during the open water period and at least once through the ice at the deepest region of each lake, although in some years lakes Waubesa and Kegonsa were only sampled monthly during the open-water period. On a few dates during high winds or during winter, sampling was conducted in slightly shallower water than at the deepest lake location. Tow depths for Mendota and Monona are included in the data set. Tow depths for Waubesa and Kegonsa have not been transcribed yet, but generally ranged between 9.5-10.0 meters and 7.5-8.0 meters, respectively. The conical zooplankton net had a 15-cm diameter opening ("small net") and a net filtering area to opening area ratio of about 11. The net was made of Nitex screening with a mesh size of 75-80 um (#20 net) for all years except for 1976 when the mesh size was about 153 um (#10 net). The smaller-meshed net was initially chosen so that rotifers would be quantitatively collected along with crustacean zooplankton. For the small net, a vertical tow sample was taken from approximately 0.5 m off the lake bottom. The net was pulled to the lake surface at approximately 0.3 m per sec. After the net was raised and the sides rinsed, the sample was transferred to a bottle and preserved with formalin in early years, sugared formalin for a few years, and then formalin plus seltzer water was the preservative used after 1986. For each zooplankton sample obtained by the small net, organisms were identified to species and enumerated in three separate 1-mL subsamples obtained by a Hensen-Stemple pipette. Subsamples were taken directly from the sample bottle (sample volume ca. 150-250 mL), transferred to a 1-mL Sedgewick-Rafter cell and counted using a compound microscope. For each subsample, individual body lengths for all Daphnia encountered were recorded using an eyepiece micrometer; 5-10 organisms of other cladocerans and various life stages of copepods (i.e., nauplii, copepidites, and adults) were also measured. Based on specified size criteria, juvenile and adult Daphnia of each species were recorded separately. These size criteria were given in Luecke et al. (1990) for samples collected in 1976-1989. The criteria varied in subsequent years but were generally 1.3 mm for D. pulicaria, 1.2 mm for D. mendotae, the most common Daphnia species encountered. If smaller Daphnia were encountered with eggs in their brood chamber, then the adult size was adjusted. Thus, the distinction of adult versus juvenile Daphnia densities recorded in each sample must be viewed as only an index of the two age groups. Calanoid and cyclopoid copepodites were counted separately as two distinct groups without regard to species or life stages. All nauplii were counted as a single group with no distinction made between calanoid and cyclopoid species. All densities and length measurements in the three subsamples were then averaged for each species' life stage. Numerical density estimates (N per meter squared) for each species or zooplankton group as reported in the data set were then computed by multiplying the average subsample count by the subsampling dilution factor (i.e., volume of sample in bottle) and then dividing by the net opening area (0.01767 meter squared). Biomass estimates for each species or zooplankton group (gram per meter squared) can then be computed using the average length (mm) recorded in the data set using length-weight relationships published in the literature. One caveat for interpreting the zooplankton data for 1976-1994 is that the net efficiency of the vertical tow net used is less than 100%, and also variable depending on the amount of algae clogging the net (Lathrop 1998). Under clear water conditions (Secchi disc greater than 8 m), the net efficiency of the small net was determined to be approximately 58%. However, net efficiency was only about 42% during a period with moderate blue-green algal densities (Secchi disc 1.8 m). The relatively small mesh size (75-80 um) of the net was initially chosen in order to capture rotifers, which are recorded in the database. Beginning in 1991 a larger 30-cm diameter ("large") net with a 75-80 um mesh size was also used, which became the standard sampling net used in 1995 coincident with the lake sampling program being conducted by the North Temperate Lakes Long-Term Ecological Research (NTL-LTER) Project. After 1994, the "small" net was no longer used for sampling zooplankton on the Yahara lakes. This data set also contains large net data for years 1991 through 1994 for Mendota and for 1994 for Monona. Leptodora counts from the small net are available for Mendota (1976-1989), Monona (1976-1987), Kegonsa and Waubesa (1976-1985). Leptodora counts from the large net are available for Mendota (1991-1993). All Leptodora counts were performed on the entire sample by dumping the sample bottle into a container. Individual length measurements for some zooplankton sampled with the small net are available for Mendota (1988-1989, 1992-1994) and Monona (1994). Individual length measurements for zooplankton sampled with the large net are available for Mendota (1991-1993). Daphnia eggs counts (number of eggs per adult daphnia in the sample) from samples taken with the small net are included for Mendota (1976-1991), Monona (1976-1993 except 1989), and Kegonsa and Waubesa (1976-1985). Egg counts represent the combined number of free eggs found in each subsample plus eggs still remaining in adult Daphnia as many times adult Daphnia had eggs expelled from their brood chambers once the preservative was added (especially in years when the preservative was just formalin). Once the total number of eggs for either D. pulicaria or D. mendotae was counted, then the estimate of the number of eggs per adult Daphnia was calculated while recognizing that the criteria for separating adult versus juvenile Daphnia is not without error. Thus, the number of eggs per adult number is best used as an index to determine if the Daphnia population was increasing or not growing due to food limitation. Number of sites: 4 Sampling Frequency: varies
Core Areas
Dataset ID
262
Date Range
-
LTER Keywords
Maintenance
completed
Metadata Provider
Methods
In general, zooplankton were sampled at the deepest location of each lake by pulling a conical net vertically through the water column (i.e., vertical tow sample) during 1976-1994. Sampling was usually done on a biweekly schedule during the open water period and at least once through the ice at the deepest region of each lake, although in some years lakes Waubesa and Kegonsa were only sampled monthly during the open-water period. On a few dates during high winds or during winter, sampling was conducted in slightly shallower water than at the deepest lake location. Tow depths for Mendota and Monona are included in the data set. Tow depths for Waubesa and Kegonsa have not been transcribed yet, but generally ranged between 9.5-10.0 meters and 7.5-8.0 meters, respectively. The conical zooplankton net had a 15-cm diameter opening ("small net") and a net filtering area to opening area ratio of about 11. The net was made of Nitex screening with a mesh size of 75-80 um (#20 net) for all years except for 1976 when the mesh size was about 153 um (#10 net). The smaller-meshed net was initially chosen so that rotifers would be quantitatively collected along with crustacean zooplankton. For the small net, a vertical tow sample was taken from approximately 0.5 m off the lake bottom. The net was pulled to the lake surface at approximately 0.3 m per sec. After the net was raised and the sides rinsed, the sample was transferred to a bottle and preserved with formalin in early years, sugared formalin for a few years, and then formalin plus seltzer water was the preservative used after 1986. For each zooplankton sample obtained by the small net, organisms were identified to species and enumerated in three separate 1-mL subsamples obtained by a Hensen-Stemple pipette. Subsamples were taken directly from the sample bottle (sample volume ca. 150-250 mL), transferred to a 1-mL Sedgewick-Rafter cell and counted using a compound microscope. For each subsample, individual body lengths for all Daphnia encountered were recorded using an eyepiece micrometer; 5-10 organisms of other cladocerans and various life stages of copepods (i.e., nauplii, copepidites, and adults) were also measured. Based on specified size criteria, juvenile and adult Daphnia of each species were recorded separately. These size criteria were given in Luecke et al. (1990) for samples collected in 1976-1989. The criteria varied in subsequent years but were generally 1.3 mm for D. pulicaria, 1.2 mm for D. mendotae, the most common Daphnia species encountered. If smaller Daphnia were encountered with eggs in their brood chamber, then the adult size was adjusted. Thus, the distinction of adult versus juvenile Daphnia densities recorded in each sample must be viewed as only an index of the two age groups. Calanoid and cyclopoid copepodites were counted separately as two distinct groups without regard to species or life stages. All nauplii were counted as a single group with no distinction made between calanoid and cyclopoid species. All densities and length measurements in the three subsamples were then averaged for each species' life stage. Numerical density estimates (N per meter squared) for each species or zooplankton group as reported in the data set were then computed by multiplying the average subsample count by the subsampling dilution factor (i.e., volume of sample in bottle) and then dividing by the net opening area (0.01767 meter squared). Biomass estimates for each species or zooplankton group (gram per meter squared) can then be computed using the average length (mm) recorded in the data set using length-weight relationships published in the literature. One caveat for interpreting the zooplankton data for 1976-1994 is that the net efficiency of the vertical tow net used is less than 100%, and also variable depending on the amount of algae clogging the net (Lathrop 1998). Under clear water conditions (Secchi disc greater than 8 m), the net efficiency of the small net was determined to be approximately 58%. However, net efficiency was only about 42% during a period with moderate blue-green algal densities (Secchi disc 1.8 m). The relatively small mesh size (75-80 um) of the net was initially chosen in order to capture rotifers, which are recorded in the database. Beginning in 1991 a larger 30-cm diameter ("large") net with a 75-80 um mesh size was also used, which became the standard sampling net used in 1995 coincident with the lake sampling program being conducted by the North Temperate Lakes Long-Term Ecological Research (NTL-LTER) Project. After 1994, the "small" net was no longer used for sampling zooplankton on the Yahara lakes. This data set also contains large net data for years 1991 through 1994 for Mendota and for 1994 for Monona. Leptodora counts from the small net are available for Mendota (1976-1989), Monona (1976-1987), Kegonsa and Waubesa (1976-1985). Leptodora counts from the large net are available for Mendota (1991-1993). All Leptodora counts were performed on the entire sample by dumping the sample bottle into a container. Individual length measurements for some zooplankton sampled with the small net are available for Mendota (1988-1989, 1992-1994) and Monona (1994). Individual length measurements for zooplankton sampled with the large net are available for Mendota (1991-1993). Daphnia eggs counts (number of eggs per adult daphnia in the sample) from samples taken with the small net are included for Mendota (1976-1991), Monona (1976-1993 except 1989), and Kegonsa and Waubesa (1976-1985). Egg counts represent the combined number of free eggs found in each subsample plus eggs still remaining in adult Daphnia as many times adult Daphnia had eggs expelled from their brood chambers once the preservative was added (especially in years when the preservative was just formalin). Once the total number of eggs for either D. pulicaria or D. mendotae was counted, then the estimate of the number of eggs per adult Daphnia was calculated while recognizing that the criteria for separating adult versus juvenile Daphnia is not without error. Thus, the number of eggs per adult number is best used as an index to determine if the Daphnia population was increasing or not growing due to food limitation. Number of sites: 4 Sampling Frequency: varies
NTL Keyword
Short Name
MADZOOP1
Version Number
21
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