NOAA Technical Memorandum GLERL-172 

____________________________________________________________________________ 

ABUNDANCE AND DISTRIBUTION OF BENTHIC 

MACROINVERTEBRATES IN THE LAKE HURON SYSTEM: SAGINAW 

BAY, 2006-2009, AND LAKE HURON, INCLUDING GEORGIAN BAY 

AND NORTH CHANNEL, 2007 AND 2012. 

Thomas F. Nalepa1, Catherine M. Riseng2, Ashley K. Elgin3, Gregory A. Lang4 

1 Water Center, University of Michigan, Ann Arbor, MI 48104 

2 School for Environment and Sustainability, University of Michigan, Ann Arbor, MI 48109 

3 Lake Michigan Field Station, Great Lakes Environmental Research Laboratory, NOAA, 

Muskegon, MI 49441 

4 Great Lakes Environmental Research Laboratory, NOAA, Ann Arbor, MI 48108 

NOAA Great Lakes Environmental Research Laboratory 

4840 S. State Road, Ann Arbor, Michigan 

Published: Friday, August 03, 2018 

____________________________________________________________________________ 

UNITED STATES NATIONAL OCEANIC AND 

DEPARTMENT OF COMMERCE ATMOSPHERIC ADMINISTRATION 

Wilbur L. Ross, Jr., Secretary RDML Tim Gallaudet, Ph.D., USN Ret., 

 Acting Administrator 
ii

NOTICE 

Mention of a commercial company or product does not constitute an endorsement by the NOAA. 

Use of information from this publication concerning proprietary products or the tests of such 

products for publicity or advertising purposes is not authorized. This is GLERL Contribution 

Number 1889. 

This publication is available as a PDF file and can be downloaded from GLERL’s web site: 

www.glerl.noaa.gov or by emailing GLERL Information Services at oar.pubs.glerl@noaa.gov. 
iii

TABLE OF CONTENTS 

1.0 INTRODUCTION .................................................................................................................................. 8

2.0 DESCRIPTION OF LAKE HURON SYSTEM ..................................................................................... 9

3.0 STATION LOCATIONS AND FIELD PROCEDURES ..................................................................... 10

4.0 LABORATORY PROCEDURES ........................................................................................................ 10

5.0 DATA PRESENTATION ..................................................................................................................... 13

6.0 STATION GROUPINGS AND ANALYSIS ....................................................................................... 13

7.0 TEMPORAL TRENDS IN SAGINAW BAY ...................................................................................... 14

7.1 Dreissena .......................................................................................................................................... 14

7.2 Non-Dreissenid Taxa ........................................................................................................................ 15

8.0 TEMPORAL TRENDS IN LAKE HURON, GEORGIAN BAY AND NORTH CHANNEL ............ 16

8.1 Dreissena .......................................................................................................................................... 16

8.2 Non-Dreissenid Taxa ........................................................................................................................ 17

9.0 SUMMARY .......................................................................................................................................... 18

10.0 ACKNOWLEDGEMENTS ................................................................................................................ 19

11.0 REFERENCES ................................................................................................................................... 19

12.0 APPENDICES – EXCEL DATA FILES ............................................................................................ 21
iv

LIST OF TABLES 

Table 1. Location (latitude, longitude), water depth, and dominant substrate type at each of the stations 

sampled for benthic macroinvertebrates with a Ponar grab and with SCUBA divers in Saginaw Bay, 

Lake Huron in 2006-2010. Also given are the year and season of collection. For samples collected 

with a Ponar, the season of collection is given as: Sp = spring, S = summer, F = fall. Stations 

sampled for Dreissena by divers are designated with a “D”; all diver samples were collected in fall.22

Table 2. Stations sampled in the main basin of Lake Huron in 2000, 2003, 2007, and 2012. Also given are 

the location and dominant substrate of each station. Given in parenthesis is the water depth each time 

the station was sampled. Blank space means not sampled. ................................................................. 23

Table 3. Stations sampled in Georgian Bay and North Channel in 2002, 2007, and 2012.. Also given are 

the location, water depth, and dominant substrate of each station. Blank space means not sampled. 26

Table 4. Relationships between shell length (SL, mm) and tissue ash-free dry weight (AFDW, mg) for 

Dreissena polymorpha and Dreissena rostriformis bugensis at sites in Lake Huron and Saginaw Bay. 

The AFDW/SL relationship is defined as logeAFDW = b + a*logeSL. Also given are the number of 

individuals used to define the relationship (n) and their median shell length (range in parentheses). 

Included is the AFDW of a standard 15-mm individual as derived from the determined relationship. 

#Weights in 2009 were not measured directly; regression values were derived by combining data 

collected in 2008 and 2010. ................................................................................................................ 27

Table 5. List of taxa collected in Saginaw Bay, 2006-2009, and in Lake Huron, 2012. The four-letter code 

identifies taxa in Excel files given in the appendices. ........................................................................ 28

Table 6. Mean (±SE) density (no./m2) and biomass (gAFDW/m2) of Dreissena at sites with different 

substrates in inner and outer Saginaw Bay in 1991-1996 and in 2008-2010. Samples collected by 

SCUBA divers in the fall of each year. Inner bay- cobble = Stations 5, 6 and 15; Inner baysand/gravel = Stations 13, 14, and 16; Outer bay- cobble = Station 27. Station 13 was not sampled in 

1991, Station 16 was not sampled in 2008 and 2009, and Station 27 was not sampled in 2010. ....... 30

Table 7. Mean (±SE) density (no./m2) of major taxonomic groups at sites with different substrates and 

depths in inner and outer Saginaw Bay during three periods: 1987-1990, 1994-1996, and 2006-2009. 

All samples collected with a Ponar grab. Sources of variation are yearly (multiple stations) or 

seasonal means (single station). Differences between periods were tested with ANOVA (p-value 

given). If the P-value was ≤ 0.05, Fisher’s LSD was used for pairwise comparisons. Results of such 

comparisons are provided by subscripts; values with the same subscript were not significantly 

different (P > 0.05).. Inner bay-sand/ gravel = Stations 13, 14, and 16; Inner bay-silty sand (Station 

11); Inner bay- silt = Stations 4, 7 and 10; Outer bay- 12 m = Station 24; Outer bay- 16 m = Station 

20; Outer bay-28 m = Station 23. ........................................................................................................ 31

Table 8. Mean (±SE) biomass (gAFDW/m2) of Dreissena and non-dreissenid taxa at sites in inner and 

outer Saginaw Bay with different substrate types and depths. Relevance of the three periods is given 

in the text. Samples collected with a Ponar grab. Differences between periods were tested with 

ANOVA (P-value given). If the P-value was ≤ 0.05, Fisher’s LSD was used for pairwise 
v

comparisons. Results of such comparisons are provided by subscripts; values with the same subscript 

were not significantly different (P >0.05).. Inner bay-sand/ gravel = Stations 13, 14, and 16; Inner 

bay-silty sand (Station 11); Inner bay- silt = Stations 4, 7 and 10; Outer bay-12 m = Station 24; Outer 

bay-16 m = Station 20; Outer bay-28 m = Station 23. ........................................................................ 33

Table 9. Mean (±SE) density (no./m2) of major taxa at sites in the 18-30 m, 31-50 m, 51-90 m, and > 90 

m intervals in the main basin of Lake Huron in 2000, 2003, 2007, and 2012. See Table 2 for the 

number of sites per year per interval. Differences between years were tested with ANOVA (P-value 

given). If the P-value was ≤ 0.05, Fisher’s LSD was used for pairwise comparisons. Results of such 

comparisons are provided by subscripts; values with the same subscript were not significantly 

different (P > 0.05). ............................................................................................................................. 34

Table 10. Mean (±SE) density (no./m2) of major taxa at sites in the 18-30 m, 31-50 m, and 51-90 m 

intervals in Georgian Bay and North Channel in 2002, 2007, and 2012. See Table 2 for the number 

of stations in each interval in each of the three sampling years. Differences between years were 

tested with ANOVA (P-value given). If the P-value was ≤ 0.05, Fisher’s LSD was used for pairwise 

comparisons. Results of such comparisons are provided by subscripts; values with the same subscript 

were not significantly different (P > 0.05ND = not determined. ........................................................ 35

Table 11. Mean (±SE) biomass (gAFDW/m2) of major taxa at sites in the 18-30 m, 31-50 m, and 51-90 m 

intervals in the main basin, Georgian Bay and North Channel in 2012 See Table 2 for the number of 

stations in each interval in each of the three sampling years. ............................................................. 36

 
vi

LIST OF FIGURES 

Figure 1. Location of sampling sites in Lake Huron, Georgian Bay, and North Channel, 2000, 2002, 2003, 

2007, and 2012. See Table 2 for those sites specifically sampled in 2007 and 2012. ........................ 37

Figure 2. Location of sampling sites in Saginaw Bay in 2006-2010. These were the same sites sampled in 

1987-1996. Dashed line separates the inner bay from the outer bay. Depth contours given in meters. 

An “x” indicates sites sampled with SCUBA divers and a circled black dot indicates sites sampled 

with a Ponar grab. ............................................................................................................................... 38

Figure 3. Mean (± SE) density (no./m2) of major macroinvertebrate groups at stations in inner Saginaw 

Bay with water depths of > 6 m and with a substrate of silt (Stations 4, 7, and 10). Densities in 1987-

1996 were taken from previous surveys (Nalepa et al. 2002). Note different scales of the Y-axis. ... 39

Figure 4. Mean (± SE) density (no./m2) of major macroinvertebrate groups at stations in inner Saginaw 

Bay with water depths of < 6 m and with a substrate of sand/gravel (Stations 13, 14, and 16). 

Densities in 1987-1996 were taken from previous surveys (Nalepa et al. 2002). Note different scales 

of the Y-axis. ....................................................................................................................................... 40

Figure 5. Mean (± SE) density (no./m2) of major macroinvertebrate groups at a station in inner Saginaw 

Bay with a substrate of silty sand (Station 11). Densities in 1987-1996 were taken from previous 

surveys (Nalepa et al. 2002). Note different scales of the Y-axis. ...................................................... 41

Figure 6. Mean (± SE) density (no./m2) of major macroinvertebrate groups at a station in outer Saginaw 

Bay with water depth of 12 m (Station 24). Densities in 1987-1996 were taken from previous 

surveys (Nalepa et al. 2002). Note different scales of the Y-axis. ...................................................... 42

Figure 7. Mean (± SE) density (no./m2) of major macroinvertebrate groups at a station in outer Saginaw 

Bay with water depth of 16 m (Station 20). Densities in 1987-1996 were taken from previous 

surveys (Nalepa et al. 2002). Note different scales of the Y-axis. ...................................................... 43

Figure 8. Mean (± SE) density (no./m2) of major macroinvertebrate groups at a station in outer Saginaw 

Bay with water depth of 28 m (Station 23). Densities in 1987-1996 were taken from previous 

surveys (Nalepa et al. 2002). Note different scales of the Y-axis. ...................................................... 44

Figure 9. Yearly mean (± SE) biomass (g AFDW/m2) of non-dreissenid taxa for the various stations and 

station groups in the inner (upper panel) and outer (lower panel) portions of Saginaw Bay during the 

periods 1987-1996 and 2001-2009. Inner Bay: silt = solid line, solid point; silty sand = dashed line, 

open point; sand/gravel = dashed line, solid point. Outer Bay: 12 m = solid line, solid point; 16 m = 

dashed line, solid point; 28 m = dashed line, open point. ................................................................... 45

Figure 10. Mean density (no./m2) of D. r. bugensis in the main basin of Lake Huron in 2000, 2003, 2007, 

and 2012. ............................................................................................................................................. 46

Figure 11. Mean density (no./m2

) of D, polymorpha in the main basin of Lake Huron in 2000, 2003, 2007, 

and 2012. ............................................................................................................................................. 47
vii

Figure 12. Mean density (no./m2) of Diporeia in the main basin of Lake Huron in 2000, 2003, 2007, and 

2012..................................................................................................................................................... 48

Figure 13. Mean density (no./m2) of Oligochaeta in the main basin of Lake Huron in 2000, 2003, 2007, 

and 2012. ............................................................................................................................................. 49
8

Abundance and distribution of benthic macroinvertebrates in the Lake 

Huron system: Saginaw Bay, 2006-2009, and Lake Huron, including 

Georgian Bay and North Channel, 2007 and 2012. 

Thomas F. Nalepa, Catherine M. Riseng, Ashley K. Elgin, Gregory A. Lang

1.0 INTRODUCTION 

This technical report provides results of benthic macroinvertebrate surveys conducted in Saginaw Bay in

2006-2009, and in Lake Huron, including Georgian Bay and North Channel, in 2007 and 2012. The 

objective of these surveys was to update the status of the benthic community and thereby extend temporal 

assessments of previously-defined trends in these lake regions. Previous surveys were conducted in 

Saginaw Bay in 1991-1996, in Lake Huron in 2000 and 2003, and in Georgian Bay and North Channel in 

2002. Based on these previous surveys, benthic macroinvertebrate communities in both Saginaw Bay and 

Lake Huron had undergone major changes since the late 1960s and early 1970s (Nalepa et al. 2003, 

2007a). Factors driving community changes in Saginaw Bay were primarily attributed to phosphorus 

abatement and the introduction and expansion of invasive zebra mussels (Dreissena polymorpha) (Nalepa 

et al. 2003), while community changes in Lake Huron were mainly attributed to both zebra mussels and 

quagga mussels (Dreissena rostriformis bugensis) (Nalepa et al. 2007a). 

While published papers summarized and interpreted results of these previous surveys, the basic, raw data 

were provided in two technical reports, one for Saginaw Bay (Nalepa et al. 2002), and one for Lake 

Huron (Nalepa et al. 2007b). These reports also included details of station locations, collection methods, 

and laboratory procedures. Similar to these previous technical reports, the purpose of this technical report 

is to provide basic data and supporting information of the most recent surveys; that is, to provide collected 

data in its simplest form (i.e., number of each taxon in each replicate sample), and to provide additional 

details of study design, station locations, sampling methods, and laboratory procedures. In addition, this 

report also provides summary tables and figures that link previous and recent surveys, thereby giving 

some perspective of current temporal trends. Further and more detailed analyses, including community 

shifts and interpretations of trends, will be provided in future publications. 
9

2.0 DESCRIPTION OF LAKE HURON SYSTEM 

There are several distinct regions of the Lake Huron system that are defined by broad differences in 

physical characteristics and benthic features. Hence, the benthic macroinvertebrate data are reported and 

summarized separately for each region. Saginaw Bay is a warm, shallow regional-extension of the 

western shoreline of the lake that can be functionally separated from the main basin by a line extending 

from AuSable Point to Point Aux Barques (Figure 1). The bay can be further sub-divided into inner and 

outer regions by a line extending along its narrowest width (21 km) from Sand Point to Point Lookout 

(Figure 2). Differences in physical and chemical features of the inner and outer bay are distinct. The inner 

bay has a mean depth of only 5.5 m, is well-mixed, and nutrient rich; it is heavily influenced by organic 

input from the Saginaw River, which accounts for 70% of tributary flow into the bay. The outer bay has a 

mean depth of 16.4 m and is more influenced by the colder, nutrient-poor waters of Lake Huron. Surface 

areas of the inner and outer bay are 1,625 km2 and 1,255 km2, respectively. Bottom substrates in the inner 

bay grade from mostly cobble/rock in shallow areas to silt in deeper areas. The inner bay has two shallow 

sand bars that extend along the southeastern and northwestern shorelines. Both sand bars have irregular 

areas of cobble with patches of gravel and pebbles. Water depth between the two sand bars gradually 

increases to a maximum of 14 m. The proportion of fine-grained material gradually increases along this 

depth gradient as a function of sediment deposition. At depths > 6 m, the substrate consists mostly of silt 

and clay. Overall, proportions of substrates by area in the inner bay are: sand/cobble = 57%, silty sand = 

16%, and silt = 27% (Nalepa et al. 2003). In the outer bay, the east shore is rocky, as is the area around 

Charity Island. The western shore has extensive sandy areas, with rock and clay near Point Lookout. Most 

substrate in the outer bay consists of sand with varying amounts of overlying silt. 

As a region, the main basin of Lake Huron has a mean depth of 85 m, a maximum depth of 245 m, and a 

surface area of 41,475 km2. A till-covered, bedrock escarpment (Six-Fanthom Scarp) extends from Point 

Clark to Alpena and divides the lake into northern and southern portions (Figure 1). In the southern 

portion another escarpment (Ipperwash Scarp) extends along a southeast-to-northwest line and further 

divides the lake into an east (Goderich Basin) and a west basin (Port Huron Basin). Maximum depths of 

these basins are 119 m and 88 m, respectively. The northern portion is also divided into two major basins 

by a sill (Thunder-Duck Sill) that extends southwest to northeast from near Alpena to the northern end of 

Manitoulin Island. The basin north of the sill (Mackinac Basin) has a maximum depth of 137 m and the 

basin south of the sill (Manitoulin Basin) has a maximum depth of 227 m. In general, these four basins 

serve as zones of sediment deposition. Sand and bedrock dominate the substrate in nearshore regions and 

on the escarpments, while fine substrates (silts and muds) dominate in the depositional basins. Overall, 

areas with fine substrates` account for 58% of the total lake bottom (Thomas et al. 1973). Highest 

sedimentation rates in the lake occur in the Goderich Basin in the southeastern end of the lake between 

Goderich and Ipperwash (Thomas et al. 1973; Robbins 1980). Maximum sedimentation rates in this area 

are about 100 mg/cm2

/yr (Robbins 1980). 

Georgian Bay and North Channel are regions that lie north and east of the main basin, separated from the 

lake by land components of the Niagara Escarpment (Manitoulin Island and Bruce Peninsula) (Figure 1). 

Mean depth, maximum depth, and surface area are 44 m, 165 m, and 15,111 km2for Georgian Bay and 22 

m, 85 m, and 3,950 km2 for North Channel. Nearshore areas of both water bodies are dominated by 

bedrock, rock, and cobble. Beyond that, substrates in Georgian Bay are a complex pattern of glacial tills 

(mixture of sand, gravel, silt, and clay), lacustrine clays, and basin muds. The latter occur in offshore 

depositional regions that are interconnected and occur as troughs throughout the bay resembling a residual 

drainage system. Sedimentary muds are more prominent in the North Channel as a result of material 

carried by the St. Mary’s River and then deposited. 
3.0 STATION LOCATIONS AND FIELD PROCEDURES 

In Saginaw Bay, ten stations were sampled using a Ponar grab in fall 2006, in spring, summer, and fall 

2007 and 2008, and in fall 2009 (Figure 2, Table 1). These were the same ten stations sampled in 

1987-1996 (Nalepa 2002). Of these stations, seven were located in the inner bay and three were in the 

outer bay. Some stations were not sampled in all years because of weather conditions or technical/

scheduling issues; notably, most stations in the outer bay were not sampled in 2006 and 2009 (Table 1). 

In the main basin of Lake Huron, samples were collected using a Ponar grab in late July/early August at 

80 stations in 2007 and at 83 stations in 2012, and these stations were mostly the same stations sampled 

in 2000 and 2003 (Table 2). The three stations sampled in 2012 but not sampled in 2007 (GLERL18, 

GLERL30, GLERL45) were located along a transect near Alpena, MI and were part of a larger 

ecosystem study that was conducted only in that year. These three stations are not shown in Figure 1, but 

were in close proximity to stations near Alpena sampled in 2003 (AL20, AL30, and AL45; see Table 2, 

Figure 1). In Georgian Bay and North Channel, samples were collected using a Ponar grab at 17 and 13 

stations, respectively, and these were the same stations sampled in 2002 (Table 3). Two stations in 

Georgian Bay (GB11 and GB26) were not sampled in 2012 because of poor weather conditions. 

In all surveys regardless of region or year, triplicate grab samples were taken at each station. Each 

replicate sample was washed into an elutriation device (a funnel-shaped hopper) that was fitted with a 

nitex sleeve having 0.5-mm mesh openings. Grab contents were placed into the elutriation device, gently 

stirred, and then washed through the sleeve. Retained material (organisms and coarse substrate material) 

was then washed into a collection jar and immediately preserved in 5% buffered formalin containing rose 

bengal stain. Jars were labeled with the station, replicate number, and date. 

In addition to the Ponar samples, samples for only Dreissena were collected at seven stations in Saginaw 

Bay using SCUBA divers in September 2008, 2009, and 2010 (Figure 2, Table 1). These stations were the 

same as those sampled by divers in fall of 1991-1996 (Nalepa et al. 2003). Four stations were located in 

areas with cobble that could not be effectively sampled with the Ponar grab (Stations 5, 6, 15, and 27), 

while three stations had sand/gravel substrates that were sampled by both divers and the Ponar grab 

(Stations 13, 14, and 16). At each station, divers randomly placed a 0.5 m2

 or 1.0 m

2

 frame on the bottom, 

and hand-collected all hard material within the frame area. Frames were subdivided such that a smaller 

portion could be sampled if desired, but the minimum area sampled was 0.25 m2. In 1991-1996, after all 

hard material in the sampled area within the frame was removed, divers used a suction device fitted with 

nitex net (0.5-mm openings) to re-sample the original area sampled (see Nalepa et al. 2003). In 2008-

2010, this suction re-sampling procedure was not conducted since few if any Dreissena were collected by 

this procedure in 1991-1996. In all years, three replicate samples were collected by divers at each station 

except in 2009 when four replicates were collected. Divers moved directionally 2-3 m between replicates 

to ensure each sample was taken in an undisturbed area. 

4.0 LABORATORY PROCEDURES 

In the laboratory, material collected by the Ponar grab and retained in the 0.5-mm sleeve was placed into 

a white enamel pan or a large petri dish, and organisms were removed and counted under a 1.5x magnifier 

lamp, or under low-power of a binocular microscope. Organisms were sorted, counted, and placed into 

separate vials by major taxonomic groups: Amphipoda, Oligochaeta, Sphaeriidae, Chironomidae, 

Dreissena polymorpha, and Dreissena rostriformis bugensis, and “others”. Individuals in the “others” 

category included Gastropoda, Isopoda, Hirudinea, Ephemeroptera, and Tricoptera. Taxonomic groups 

observed in the samples but not counted were: turbellarians, nematodes, nemertea, and Mysis. 

10
11

After being sorted and counted, organisms were identified to the lowest practical taxonomic level. For 

identification of oligochaetes, up to 75-100 individuals in a given replicate (proportionately split with a 

Folsom plankton splitter when numbers were higher) were mounted in CMC9 on microscope slides and 

their images were either projected onto a sheet of paper using a camera lucida and then traced, or captured 

with a microscope-mounted camera and recorded. Subsequently, individuals were identified and 

taxonomic designations placed alongside the respective image. Only oligochaetes with a prostomium 

were identified and counted; individuals without a prostomium were identified as fragments and not 

included in the final count. For chironomids, up to about 50 individuals were identified per replicate 

sample. The sample was proportionately split as described above when numbers were higher. Chironomid 

head capsules were removed from bodies and mounted in CMC9 on microscope slides with mentum side 

up. Corresponding bodies were mounted alongside respective head capsules and images recorded as 

described for oligochaetes. 

For samples collected in 2007 from Lake Huron, Georgian Bay and North Channel, oligochaetes and 

chironomids were not identified beyond the group level, hence abundances were derived from the sorted 

counts. Since oligochaete fragments (without prostomium) were included in these counts, total abundance 

of oligochaetes at each station in 2007 was corrected based on the mean proportion of fragments found at 

the same station in 2012. For the two stations sampled in 2007 but not in 2012 (GB11 and GB26), a mean 

proportion of all stations in the same depth interval (see below for depth intervals) was used as the 

correction factor. A similar correction process was followed for oligochaete abundances in 2003 when 

oligochaetes were not identified (Nalepa et al. 2007a). In this case, abundances in 2003 were corrected 

based on the proportion of fragments found in 2000 when oligochaetes were identified. 

Biomass (ash-free dry weight) of the benthic macroinvertebrate community in Saginaw Bay was 

determined for all years (2006-2009). Methods were the same as those used to determine biomass in 

Saginaw Bay in 1987-1996 (see Nalepa et al. 2002). Biomass in Lake Huron, Georgian Bay, and North 

Channel in 2012 was determined using the same methods as for Saginaw Bay. Biomass in previous 

surveys in these three water bodies in 2000, 2002, and 2003 was not determined (Nalepa et al. 2007b), nor 

was biomass determined in the 2007 survey. 

As noted, details regarding methods to determine biomass, including length-weight relationships and 

direct conversion factors, are given in Nalepa et al. (2002). In brief, lengths of all traced oligochaetes and 

oligochaete fragments were measured using a digital map measurer or an imaging software program. For 

Saginaw Bay, total length was then converted to ash-free dry weight by multiplying it by a conversion 

factor of 0.25 mg dry weight per cm (Nalepa and Quigley 1980) and then assuming ash-free dry weight to 

be 90 % of dry weight (Johnson and Brinkhurst 1971). For Lake Huron, Georgian Bay, and North 

Channel, total oligochaete length was multiplied by 0.342 mg ash-free dry weight per cm (Nalepa and 

Quigley 1985). The former conversion value was determined from oligochaete communities in a shallow, 

nearshore region of Lake Michigan. This value would be more realistic for the community in Saginaw 

Bay. On the other hand, the latter conversion value was determined from oligochaete communities mostly 

in offshore regions of Lake Michigan, and this value would be more realistic for the community in open 

waters of Lake Huron. For chironomids, lengths were determined as given above and then converted to 

dry weights using length-weight relationships given in Nalepa et al. (2002). Ash-free dry weight was 

assumed to be 90% of dry weight (Johnson and Brinkhurst 1971). 

For Dreissena, length-weight relationships used to determine biomass were derived from freshlycollected individuals. In Lake Huron, individuals for length-weight determination were collected during 

the 2012 survey at 13 stations: GB3, GB8, GB35, FI3, HU27, HU32, HU429, MZ44, MZ93, MZ123, 

SR6, PT5, and TN3. Selection of these stations was not pre-determined; that is, station selection depended 

on the number of mussels found at the time of sampling and by a visual estimate of the size range (shell 

lengths) of the population. For the latter, a broad size range of individuals was a requirement (10 mm to > 
12

20 mm) so a representative relationship could be obtained. Also, an effort was made to collect at stations 

located throughout the lake and at various depths. Immediately after collection of mussels with a Ponar 

grab, soft tissues of about 25 individuals of various sizes were removed from shells, placed individually 

into pre-weighed aluminum planchets, and dried at 60oC for a minimum of 48 h. After drying, planchets 

were placed and kept in a desiccator. Upon completion of the survey cruise and return to the laboratory, 

soft tissues were weighed, ashed at 550oC for 1 h, and then re-weighed to obtain ash-free dry weights. 

Corresponding shell lengths were measured to the nearest 0.5 mm. Overall, 227 individuals from the 13 

stations were weighed and measured. All weighed individuals from the 2012 survey were D. r. bugensis

since D. polymorpha was rarely found. In Saginaw Bay, Dreissena were collected for determination of 

length-weight relationships at either Station 5 (in 2008) or at Stations 6 and 15 (in 2010) at the same time 

divers conducted quantitative sampling. Individuals were immediately placed in coolers, overlaid with 

damp towels, and kept at 4

oC. Within 48 h of collection, mussels were sorted by size, and ash-free dry 

weights and shell lengths were determined as given above. Separate length-weights were determined for 

D. polymorpha and D. r. bugensis in 2008, but weights of D. polymorpha were not determined in 2010

due to minimal numbers and limited size ranges of individuals.

Shell lengths (SL) and ash-free dry weights (AFDW) were used to develop length-weight relationships 

according to the allometric equation: logeAFDW (mg) = b + a*logeSL (mm). For Lake Huron, two 

relationships were developed based on weighed mussels from the 13 stations, one for mussels from 

stations < 50 m, and another for mussels from stations > 50 m (Table 4). To determine biomass for 

mussels in the diver-collected samples in Saginaw Bay in 2008, 2009, and 2010, the relationship 

determined for D. polymorpha in 2008 was also used for any D. polymorpha collected in 2009 and 2010, 

while the composite relationship for D. r. bugensis in 2008 and 2010 was used for D. r. bugensis collected 

in 2009 (Table 4). For mussels in the Ponar-collected samples in 2006-2009, the relationship for D.

polymorpha in 2008 was used for D. polymorpha in all years, while the relationship for D. r. bugensis in 

2008 was used for individuals of this species collected in 2006 and 2007, while the relationship used for 

those collected in 2009 was determined as given above.

Biomass of Dreissena populations was calculated using determined length-weight relationships as given 

above and size frequencies of the population. To determine the latter, shell lengths of mussels in each 

replicate sample were measured, and then binned into 1-mm size categories ranging from 5 to 33 mm. 

Individuals < 5 mm were binned into a single category (1-5 mm). To determine biomass, the number of 

individuals in each size category was multiplied by the AFDW of an individual in that category as derived 

from the length-weight regression (calculated from the mid-shell length within each size bin). All 

category weights were then summed. 

To determine AFDW of the amphipod Diporeia, body lengths (base of rostrum to base of telson) of all 

individuals were measured and dry weights (DW) determined from the allometric equation: logeDW (mg) 

= -6.889 + 3.404*logeSL (mm) (Johnson 1980). Ash-free dry weight was assumed to be 90% of dry 

weight. Ash-free dry weights of Sphaeriidae, Gastropoda, Isopoda, Hirudinea, Ephemeroptera, and 

Amphipoda (excluding Diporeia) were determined by multiplying numbers of each taxa group by the 

mean weight per individual as determined from previous surveys in Saginaw Bay in 1987-1996 (Nalepa 

et al. 2002). For example, the mean weight of Sphaeriidae over all sites and dates in 1987-1996 was 0.08 

mg AFDW. This mean weight was then multiplied by the number of Sphaeriidae in each sample collected 

in Saginaw Bay in 2006-2009 and in Lake Huron in 2012. While not as precise as direct measurements, 

the error introduced to overall biomass was considered minor given the relatively low abundance of these 

groups. Further, mean weights derived in this manner were generally similar to mean weights measured 

directly and reported previously (Nalepa and Quigley 1980). For instance, the mean weight of 0.08 mg 

per individual for Sphaeriidae was comparable to the 0.07 mg per individual measured directly (small and 

medium individuals). Also, the mean weight of Gastropoda was 4.72 mg per individual, which compared 

to 6.62 mg per individual measured directly. Other mean weights were: Amphipoda (Gammarus and 
13

Hyalella)= 0.478 mg, Isopoda= 0.678 mg, Hirudinea = 0.917mg, Ephemeroptera = 8.45 mg, and 

Tricoptera = 0.203 mg. 

5.0 DATA PRESENTATION 

Benthic macroinvertebrate data collected in each survey are provided as Excel files within the following 

designated Appendices: Appendix 1 Density and Biomass in Saginaw Bay, 2006-2009 (Ponar-collected); 

Appendix 2 Density and Biomass of Dreissena in Saginaw Bay 2008-2010 (diver-collected); Appendix 3 

Density in Lake Huron, 2007 and 2012; and Appendix 4 Biomass in Lake Huron, 2012. For all files, 

densities are given as the number per square meter, and biomass is given as mgAFDW per square meter. 

To convert from number per grab to number per square meter, values in 2012 were multiplied by 20.70, 

while values in all other years were multiplied by 21.42. Variables in the files include year, station, 

replicate number, and taxa. Season of sampling (spring=1, summer=2, fall=3) is provided as a variable 

only for data collected in Saginaw Bay (Appendix 1) since these data were often collected over several 

seasons (see Table 1). Individual taxa within the data files are identified by four letter codes, and these 

codes are consistent across all surveys (Table 5). 

6.0 STATION GROUPINGS AND ANALYSIS 

For analysis, stations within the various lake regions were grouped based on substrate type or water depth 

as in previous publications (Nalepa et al. 2003, 2007a). In the inner portion of Saginaw bay, station 

groups were: cobble (Stations 5, 6, 15), sand/gravel (Stations 13, 14, 16), silty sand (Station 11), and silt 

(Stations 4, 7, 10). Stations in the first two groups were in shallow regions (< 6m) that were considered to 

be non-depositional, while stations in the latter two groups were deeper (> 6 m) and considered to be 

transitional and depositional, respectively (see Nalepa et al. 2003). As noted earlier, stations in the cobble 

group and the sand-gravel group were specifically sampled for Dreissena using SCUBA divers, while 

stations in the sand-gravel, silty sand, and silt groups were sampled for the entire benthic community 

using the Ponar grab. In the outer bay, stations sampled using the Ponar grab were functionally separated 

by water depth: 12 m (Station 24), 16 m (Station 20), and 28 m (Station 23). These stations all had a 

substrate consisting of silty sand, but were not grouped because of their wide range of water depths, 

which contributed to great differences in community composition (Nalepa et al. 2003). In Lake Huron, 

Georgian Bay, and North Channel, stations were grouped based on water depth: 18-30 m, 31-50 m, 51-90 

m, and > 90 m (main basin only). These depth categories are consistent with prior characterization of 

depth-macroinvertebrate associations in Lake Huron (Nalepa et al. 2007a). 

Since the main objective of recent surveys was to define long-term trends, data from previous surveys 

were included in summary tables and figures. For Saginaw Bay, temporal trends in Dreissena and major 

non-Dreissena taxa groups are shown in figures that summarize data collected each year during the 

periods 1987-1996 and 2006-2010. To more closely analyze temporal changes between these time 

periods, yearly data in the former period were further divided into distinct periods based on prior 

examination of population trends in Dreissena and observed Dreissena impacts on other taxa (Nalepa et 

al. 2003). During the initial years after Dreissena became established in 1991, there were wide-scale 

variations (both temporal and spatial) in both dreissenid density and biomass as the population spread and 

colonized the bay (Nalepa et al. 2003). The population subsequently stabilized at a lower level after 1993. 

Hence, while the dreissenid population was surveyed every year between 1991 and 1996, the 1994-1996 

period represented the most realistic (and conservative) baseline to assess if any population changes 

occurred in 2006-2010. For examining trends in non-dreissenid taxa, the three periods were: 1987-1990, 

1994-1996, and 2006-2009, which represented the pre-Dreissena period, the short-term, post-Dreissena 

period, and the long-term, post-Dreissena period, respectively. Prior surveys in 1987-1996 showed that 

the major groups of non-dreissenid taxa had different responses to Dreissena, and these responses varied 
14

depending on bay region (inner, outer), substrate, and time lag after Dreissena introduction and 

subsequent peak (Nalepa et al. 2003). Thus, densities of non-dreissenid taxa in 1994-1996 should be 

considered with this caveat in mind. 

For statistical analysis of trends in Saginaw Bay, mean annual density or biomass at each station within a 

station group was considered a replicate for a given time period. For instance, for the category of inner 

bay-sand/gravel as sampled by divers, mean values of Dreissena at Stations 13, 14, and 16 in 1994-1996 

(n=9; 3 stations x 3 years) were compared to mean values for the same stations in 2008-2010 (n=9; 3 

stations x 3 years). In cases where a defined category had only one station (e. g., inner bay-silty sand), the 

seasonal mean was considered a replicate. Differences between periods were tested using a t-test or 

ANOVA after loge+1 transformation. Separate tests were performed for each major taxonomic group. If 

differences were significant (P ≤ 0.05), Fisher’s LSD was used for pairwise comparisons. 

For the main basin of Lake Huron, differences in mean densities in 2000, 2003, 2007, and 2012 in each of 

the four depth intervals were examined by ANOVA after loge+1 transformation. As above, each major 

taxonomic group was tested separately. For Georgian Bay and North Channel, mean densities in 2002, 

2007, and 2012 were compared. 

7.0 TEMPORAL TRENDS IN SAGINAW BAY 

7.1 Dreissena

As noted, trends in Dreissena in Saginaw Bay were derived from samples collected with both divers and 

the Ponar grab. Both collection methods indicated that Dreissena populations on hard substrates (cobble, 

sand/gravel) in the inner bay declined substantially between 1994-1996 and 2006-2010. For divercollected samples, mean densities in 2008-2010 declined by 80.6% and 79.9% compared to 1994-1996 at

sites with cobble and sand/gravel substrates, respectively, and biomass declined by 79.9% and 85.6% 

(Table 6). These declines were significant (P ≤ 0.05) for the cobble sites, but not significant for the 

sand/gravel sites (P > 0.05). For samples collected with the Ponar grab at sites with sand/gravel, mean 

densities in 2006-2009 were 78.4% lower when compared to mean densities in 1994-1996 (Table 7). This 

decline found in the Ponar samples was thus similar to the 79.9% decline found at the same sites as 

sampled by divers; however, unlike the diver-collected samples, the difference between periods was not 

significant (P > 0.05). Differences between 1994-1996 and 2006-2009 at sites with silt and silty sand 

were also not significant (P > 0.05). At sites with silt, mean densities were consistently low (< 50/m2 in 

both periods). At the site with silty sand, mean densities were 10 times greater in 2006-2009 than in 

1994-1996, but year-to-year variation within periods was substantial. For instance, the range in yearly 

means at this site in 1994-1996 was 0/m2 to 50/m2, whereas the range in 2006-2009 was 0/m

2

to 2,209/m2. 

Over all sites in inner Saginaw Bay, only D. polymorpha was collected in 1994-1996, whereas D. r. 

bugensis was the dominant dreissenid in 2008-2010, accounting for 75% of abundance and 80% of 

biomass of all dreissenids > 5 mm. 

In the outer bay, density and biomass of Dreissena at the site with a cobble substrate (diver-collected; 

Station 27) were 94.7% and 94.8% lower in 2008-2010 than in 1994-1996, respectively, and these 

differences were significant (P ≤ 0.05; Table 6). In contrast, at the three sites with silty sand substrate at 

12 m, 16 m, and 28 m depths (Ponar-collected), mean densities remained the same or increased in 

2006-2009 compared to 1994-1996 (Table 7). For these three sites, the extent of the temporal change 

appeared positively related to station depth. Mean densities at 12 m remained < 5/m2 in both periods, 

mean densities at 16 m increased from 3/m

2

 to 77/m

2

, and mean densities at 28 m increased from 7/m2 to 

173/m2. All dreissenids collected in the outer bay in 1994-1996 regardless of substrate or depth were D. 

polymorpha, whereas all dreissenids collected in 2006-2010 were D. r. bugensis. 
15

7.2 Non-Dreissenid Taxa 

Temporal trends in the following major, non-dreissenid taxa groups were examined: Oligochaeta, 

Chironomidae, Sphaeriidae, and Amphipoda. To provide an overall perspective of temporal trends of 

these groups in Saginaw Bay, yearly mean densities over the entire 1987-2009 period are given for each 

substrate type (inner bay) and depth (outer bay) (Figure 3). When densities within the three distinct 

temporal periods were compared (1987-1990, 1994-1996, 2006-2009) for each group, temporal changes 

were evident, and these changes varied by substrate and depth (Table 7). 

Among the most notable temporal patterns were the large fluctuations in oligochaete densities at sites 

with a silt substrate in the inner bay (Figure 3). At these sites, mean densities of oligochaetes were 

greatest in 1987-1990 (19,423/m2), decreased 8-fold between 1987-1990 and 1994-1996 (down to 

2,727/m2), and then increased 3-fold between 1994-1996 and 2006-2009 (up to 6,055/m2). Mean 

densities in each of these three periods were significantly different from each other (P ≤ 0.05; Table 7). 

These temporal changes appear to further support the hypothesis that oligochaete densities in the portion 

of the inner bay with a silt substrate were negatively associated with dreissenid densities in portions with 

a hard substrate (i.e., sand/gravel, cobble) (Nalepa et al. 2003). For example, oligochaete densities in the 

silt portion were greatest before Dreissena became established in the bay (1987-1990), greatly decreased 

just after Dreissena became widespread and abundant (1994-1996), and then increased after Dreissena 

declined from population peaks (2006-2009). Since Dreissena was never abundant in the silt portion of 

the inner bay during the entire 1991-2009 period, the hypothesis suggests that Dreissena populations in 

hard-substrate, non-depositional portions of the inner bay divert organic material from the silty, 

depositional portion, thereby decreasing available food for oligochaetes (Nalepa et al. 2003). 

The most consistent, directional trend in the inner bay was an increase in the abundance of amphipods 

after Dreissena became established. This increase was most evident when the period just after Dreissena

became established (1994-1996) was compared to the period before Dreissena (1987-1990) (Table 7). 

While mean densities of amphipods were lower in 2006-2009 compared to 1994-1996, densities were still 

greater than in 1987-1990. Amphipods in the inner bay in 1987-2009 were almost exclusively Gammarus 

(98%). This amphipod genera typically increases in abundance after Dreissena becomes established; it

utilizes dreissenid biodeposits as a food source and inhabits dreissenid clusters which offer a refuge from 

fish predation (Ward and Ricciardi 2014). 

Sphaeriids progressively declined at sites with sand/gravel and silty sand substrates in the inner bay, with 

lowest densities in the 2006-2009 period (Table 7). Differences between periods were significant for each 

substrate (P ≤ 0.05). In contrast, sphaeriid densities did not decrease at sites with a silt substrate but 

actually increased, although differences between periods were not significant (P > 0.05). In general, 

sphaeriids are negatively impacted by Dreissena, likely as a result of food competition (Ward and 

Ricciardi 2014). Consistent temporal patterns in chironomid densities relative to Dreissena were not 

evident for any of the three substrate types in the inner bay. While densities in 2006-2009 were 

significantly lower (P ≤ 0.05) than in 1987-1990 and 1994-1996 at sites with gravel/sand substrates, 

differences between periods were not significant for the other two substrate types (P > 0.05). 

Temporal trends in non-dreissenid biomass (total biomass of all non-dreissenid taxa) in the inner bay 

were not apparent at sites with sand/gravel and silty sand substrates (Table 8). At these sites, biomass in 

1987-1990, 1994-1996, and 2006-2009 was generally similar, and differences between these three periods 

were not significant (P > 0.05). In contrast, non-dreissenid biomass at sites with a silt substrate gradually 

declined over time. Biomass was about 2-fold lower in 2006-2009 compared to 1987-1990 (Table 8). 
16

When mean densities between the three temporal periods at sites in the outer bay were compared, 

differences were apparent in some of the major non-dreissenid groups, and in some cases these 

differences were a function of depth. The most striking example was the depth-defined temporal pattern 

in oligochaete densities. Between 1987-1990 and 2006-2009, oligochaete densities declined 3.6-fold at 

12 m, remained generally stable at 16 m, and increased 16.6-fold at 28 m (Table 7). The difference 

between time periods at 28 m was significant (P ≤ 0.05). Reasons for the decline at the 12-m site are not 

clear, whereas the increase at 28-site was consistent with similar increases at sites in the 18-30 m interval 

in the main basin of Lake Huron in 2007 and 2012 as discussed below. Trends in amphipods in the outer 

bay were mostly defined by declines in Diporeia. At 28 m, mean densities of Diporeia were 819/m2 in 

1987-1990, 168/m

2

 in 1994-1996, and 0/m2 in 2006-2009. Diporeia accounted for 99.6% of all 

amphipods at this depth in 1987-1996. At 12 m and 16 m, mean densities of amphipods were < 20/m2 in 

each of the three time periods and meaningful trends could not be discerned. In 1987-1996, the 

amphipod population at these two depths consisted of Gammarus (73%), Diporeia (22%), and Hyalella

(5%); in 2006-2009, only Gammarus was collected. Sphaeriid densities declined at 12 m and 16 m (P ≤

0.05), but remained stable at 28 m (P > 0.05). On the other hand, chironomid densities declined at 28 m 

(P ≤ 0.05), but did not change at 12 m and 16 m (P > 0.05). 

In the outer bay, temporal trends in mean biomass of non-dreissenid taxa (i.e., total biomass of all nondreissenid taxa) at 12 m and 16 m were not apparent (P> 0.05) (Table 8). However, at 28 m biomass in 

2006-2009 was about 2.5 and 4.9 times greater than in 1987-1990 and in 1994-1996, respectively, and 

this difference was significant (P ≤ 0.05). This increase in biomass occurred despite the loss of Diporeia

and can be attributed to the great increase in density of oligochaetes at the 28-m site in 2006-2009 (Table 

7). 

8.0 TEMPORAL TRENDS IN LAKE HURON, GEORGIAN BAY 

AND NORTH CHANNEL 

8.1 Dreissena

Between 2000 and 2012, densities of D. r. bugensis in the main basin increased in each of the four depth 

intervals (Table 9, Figure 10). When comparing more recent changes between 2007 and 2012, mean 

densities of D. r. bugensis in 2012 were 1.6, 0.7, 6.1, and 5.5 times those densities found in 2007 at the 

18-30 m, 31-50 m, 51-90 m, and > 90 m intervals, respectively. Although greatest increases occurred at 

the two deepest intervals and an actual decline occurred at 31- 50 m, mean densities at 31-50 m were 

similar to or great than densities at the other intervals in both 2007 and 2012. Differences in mean 

densities between 2007 and 2012 were only significant at the > 90 m (P ≤ 0.05). In contrast to D. r. 

bugensis, D. polymorpha was rarely found at any depth interval in 2007 and 2012 (Table 9, Figure 11). In 

2012, this species was only collected at 2 of 83 stations in the main basin and accounted for only 3 of 

17,960 dreissenids collected. 

In Georgian Bay, densities of D. r. bugensis increased in each depth interval between 2002 and 2007, but 

in 2012 densities were lower than in 2007 at 18-30 m and 31-50 m, perhaps indicating the population may

have peaked at these depths (Table 10). In contrast, at 51-90 m densities in in 2012 were greater than in 

2007, indicating the population continued to expand. As in the main basin, D. polymorpha was rarely 

collected in 2012, accounting for only 13 of 442 dreissenids collected. These 13 individuals were 

collected at just one station (GB9). Dreissena was not collected at any of the stations in North Channel in 

2007 and 2012. 
17

Biomass of D. r. bugensis in both the main basin and Georgian Bay was lowest at 18-30 m, increased to a 

maximum at 31-50 m, and then declined as depth increased (Table 11). Low biomass at 18-30 m could 

partly be explained by the dominance of small individuals in this depth interval compared to deeper 

intervals. For instance, in the main basin, the mean percentage of individuals < 5 mm in shell length was 

94 % at 18-30 m compared to 54%, 49%, and 43% in the 31-50 m, 51-90 m, and > 90 m intervals, 

respectively. 

8.2 Non-Dreissenid Taxa 

Of the four major non-dreissenid taxa in the main basin of Lake Huron (Diporeia, Oligochaeta, 

Sphaeriidae, and Chironomidae), temporal trends in the amphipod Diporeia were the most consistent and 

pronounced (note: all amphipods in the main basin, Georgian Bay, and North Channel were Diporeia).

Declines in Diporeia were first noted when densities in 2000 were compared to densities in 1972 (Nalepa 

et al. 2007a). Subsequently, in each of the survey years after 2000 (i.e., 2003, 2007, and 2012), mean 

densities of Diporeia progressively declined at each of the four depth intervals (Table 9, Figure 12). By 

2012, Diporeia was not collected at any sites < 50 m and, while it was still present at sites in the 51-90 m 

and 90-m intervals, mean densities had declined by 96% and 85%, respectively, compared to 2000. The 

complete disappearance of Diporeia from the shallowest depth intervals in the main basin is consistent 

with similar findings in outer Saginaw Bay in 2006-2009 (see Table 7). The decline of Diporeia is 

temporally linked to the introduction and expansion of Dreissena in all the other Great Lakes except Lake 

Superior, however, the exact mechanism for the negative response remains unclear (Nalepa et al. 2006). 

Temporal trends in the other major taxa (Oligochaeta, Sphaeriidae, and Chironomidae) in the main basin 

varied as a function of depth. For oligochaetes, mean densities increased 4.9-fold at 18-30 m and 2-fold 

at 31-50 m between 2000 and 2012, but similar increases were not evident at 51-90 m and > 90 m (Table 

9). These increases at the two shallowest depth intervals, particularly apparent at the 18-30 m interval, 

may be a result of organic material being retained in this shallowest interval by dreissenids, a process 

termed the “nearshore shunt” (Heckey et al. 2004). In brief, primary producers (mainly phytoplankton) in 

shallow, nearshore regions are filtered by dreissenids and unassimilated organic material is subsequently 

deposited in the benthic zone in the form of feces and pseudofeces. These organic biodeposits serve as a 

food source for oligochaetes. In addition, dreissenid filtration of phytoplankton and other particulate 

material from the water column increases light penetration to the bottom, which, in turn, stimulates 

benthic macro-algae. Upon decay, this material also increases food availability for oligochaetes. While 

relative increases in oligochaete densities at sites in the 18-30 m depth interval were apparent throughout 

the main basin, most noteworthy were increases in the southeastern portion of the lake (Figure 13). Of the 

three stations in the 18-30 m interval in this portion of the lake that were sampled in 2003, 2007, and 

2012 (TN1, TN7, TN10), mean oligochaete densities in each of these years were 5,154 ± 539/m2

, 21,143 

± 7,088/m2, and 27,345 ± 14,025/m2, respectively. Mean densities at all other sites in this interval were 

only 1,060 ± 153/m2, 4,205 ± 1,526/m2, and 4,536 ± 1,100/m2in the same three years. The southeastern 

portion of the lake has the highest sedimentation rates and likely the highest inputs of organic material 

(Thomas et al. 1973, Robbins 1980). The dominant current patterns undergo a major reversal in this 

portion of the lake (south to north) likely leading to high deposition (Beletsky et al. 1999). 

Mean densities of sphaeriids tended to be lower at the 18-30 m, 31-50 m, and 51-90 m intervals after 

2000, but a clear, distinct declining trend was not apparent between 2003 and 2012 (Table 9). Temporal 

trends in chironomids were not apparent at any of the depth intervals. 

In Georgian Bay and North Channel, temporal trends in the major non-dreissenid taxa were generally 

similar to those in the main basin with some noted exceptions. Similar to the main basin, Diporeia

densities declined in both Georgian Bay and North Channel, but the severity of the decline varied. In 
18

Georgian Bay, the decline of Diporeia was consistent across all depth intervals and by 2012 was rarely 

found. Mean densities at the 18-30 m, 31-50 m, and 51-90 m intervals in Georgian Bay in 2002 ranged 

from 1,400 to 1,700/m2, but in 2012 Diporeia densities were ranged from 0/m2 to 3/m2 (Table 10). In

North Channel, declines in Diporeia were severe at 18-30 m and 51-90 m, with densities declining 83 % 

and 96 % respectively between 2002 and 2012, but a declining trend was not evident at 31-50 m. It is 

noteworthy that, overall, Diporeia declined in North Channel even though Dreissena was rare in 2002 

and not collected in 2007 and 2012. 

Oligochaete densities in Georgian Bay and North Channel remained relatively stable at sites in the 18-30 

m interval between 2002 and 2012, which contrasts to great increases observed in this depth interval in 

the main basin. There were no significant differences in oligochaete densities in any of the depth intervals 

in both regions (P > 0.05). Also, distinct trends in sphaeriid and chironomid densities in Georgian Bay 

and North Channel were not apparent. Densities of the former taxa tended to be lower in more recent 

years, but distinct trends between 2002 and 2012 were not significant (P > 0.05). 

In 2012, total mean biomass of non-dreissenid taxa in the main basin and North Channel was greatest at 

the 18-30 m interval, but in Georgian Bay greatest biomass occurred at 31-50 m (Table 11). Mean nondreissenid biomass ranged from 0.18 g/m2

 to 1.52 g/m2across all depth intervals within regions. 

9.0 SUMMARY 

Benthic surveys were conducted in various regions of the Lake Huron system (Saginaw Bay, main basin, 

Georgian Bay, and North Channel) in 2006-2012 to assess temporal trends. Compared to earlier surveys 

in each of these regions, trends in the major macroinvertebrate taxa (Dreissena, Diporeia, Oligochaeta, 

Sphaeriidae, and Chironomidae) varied widely as a function of substrate and water depth. Dreissena 

densities declined by 80% in areas with hard substrates (cobble, gravel, coarse sand) in the inner portion 

of Saginaw Bay as compared to densities in the mid-1990s. In contrast, Dreissena densities in the main 

basin of Lake Huron continued to increase at all depths during the period between 2000 and 2012. Recent 

increases have been particularly apparent at depths >50 m. Dreissena densities remain low in areas with 

soft substrate (silt) in inner Saginaw Bay, and Dreissena was not found at any sampled sites in North 

Channel in 2007 or 2012. Over the entire lake Huron system, maximum biomass of Dreissena in 2012 

occurred at the 31-50 m depth interval in the main basin. D. r. bugensis has replaced D. polymorpha as 

the dominant species in all regions of the lake, accounting for 80% of Dreissena in Saginaw Bay, and 

accounting for nearly all Dreissena in the main basin and Georgian Bay. 

The amphipod Diporeia progressively declined at all depths throughout the Lake Huron system. It was 

not found in Saginaw Bay in 2006-2009 and in 2012 was rarely collected at depths < 50 m in the main 

basin and Georgian Bay, and at depths > 50 m in North Channel. Although still present at depths > 50 m 

in the main basin, densities declined by > 80% between 2000 and 2012. 

Densities of oligochaetes fluctuated widely in depositional areas with soft substrates in inner Saginaw 

Bay, and this variation appeared negatively associated with densities of Dreissena in non-depositional 

areas with hard substrates in the inner bay. The hypothesis to explain this negative association posits that 

Dreissena in hard-substrate regions reduce deposition of organic material in deeper-soft substrate regions, 

thereby diminishing food for oligochaetes. Oligochaete densities increased in the main basin at depths < 

50 m, and this increase was particularly apparent at the 18-30 m depth interval; densities in this interval 

increased 5-fold between 2000 and 2012. This increase was likely a result of increased deposition of 

organic material in the form of Dreissena biodeposits which served as a food source for oligochaetes. 

Maximum oligochaete densities in the Lake Huron system occurred at the 18-30 m interval in the 

southeastern portion of the lake where deposition rates of organic material are the highest. Over the Lake 
19

Huron system, oligochaetes accounted for most non-dreissenid biomass. Densities of Sphaeriidae and 

Chironomidae varied widely from year-to-year, and clear temporal, long term trends were not evident in 

any of the lake regions.

10.0 ACKNOWLEDGEMENTS 

Given the extent of these surveys over time and space, there are many to thank for their assistance, 

advice, and support over the years. Foremost, we are especially grateful to Don Schloesser for his efforts 

in the Saginaw Bay surveys, both in field collections and in sample processing. We also thank Katie 

Birkett, Laurie Cummins, Lauren Eaton, Dave Fanslow, Paul Glyshaw, Derek Lamarand, and Kerrin 

Mabrey for their dedication in sample collection and processing. We are grateful to the Great Lake 

National Program Office, EPA, for use of the R/V Lake Guardian and the support/ assistance of the crews 

of the Lake Guardian and the NOAA R/V Laurentian. Finally, we thank Russ Green from the NOAA 

Marine Sanctuary in Alpena, MI for his support and coordination of diving activities to collect Dreissena. 

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Nalepa, T. F., D. L. Fanslow, S. A. Pothoven, A. J. Foley III, G. A. Lang, S. C. Mozley, and M. W. 

Winnell. 2007b. Abundance and distribution of benthic macroinvertebrate populations in Lake Huron in 

1972 and 2000-2003. NOAA Technical Memorandum GLERL-140. Great Lakes Environmental Research 

Laboratory, Ann Arbor, MI. https://www.glerl.noaa.gov/pubs/tech_reports/glerl-140/tm-140.pdf

Robbins, J. A. 1980. Sediment of southern Lake Huron: elemental composition and accumulation rates. 

EPA-600/3-80-080, Environmental Protection Agency, Duluth, MN. 

Thomas, R. W. 1988. Distribution and composition of the surficial sediments of Georgian Bay and North 

Channel. Hydrobiologia 163: 35-45. 

Thomas, R. W., A. L. Kemp, and C. F. M. Lewis. 1973. The surficial sediments of Lake Huron. Can. J. 

Earth Sci. 10: 226-271. 

Ward, J. M. and A. Ricciardi. 2014. Impacts of Dreissena on benthic macroinvertebrate communities: 

predictable patterns revealed by invasion history. In Quagga and Zebra Mussels: Biology, Impacts, and 

Control, 2nd edition. T. F. Nalepa and D. W. Schloesser, eds., pp. 599-610. Boca Raton, FL: CRC Press. 
21

12.0 APPENDICES – EXCEL DATA FILES 

Appendix 1. Density and Biomass in Saginaw Bay, 2006-2009 

https://www.glerl.noaa.gov/pubs/tech_reports/glerl-172/tm-172-Appendix1-SaginawBayAbundance_and_Biomass_2006-2009.xlsx

Appendix 2. Density and Biomass of Dreissena in Saginaw Bay 2008-2010 

https://www.glerl.noaa.gov/pubs/tech_reports/glerl-172/tm-172-Appendix2-SaginawBayDreissena_Density_and_Biomass_2008-2010.xlsx

Appendix 3. Density in Lake Huron, 2007 and 2012 

https://www.glerl.noaa.gov/pubs/tech_reports/glerl-172/tm-172-Appendix3-LakeHuronAbundance_2007_2012.xlsx

Appendix 4. Biomass in Lake Huron, 2012. 

https://www.glerl.noaa.gov/pubs/tech_reports/glerl-172/tm-172-Appendix4-LakeHuronBiomass_2012.xlsx
22

Table 1. Location (latitude, longitude), water depth, and dominant substrate type at each of the stations sampled for 

benthic macroinvertebrates with a Ponar grab and with SCUBA divers in Saginaw Bay, Lake Huron in 2006-2010. 

Also given are the year and season of collection. For samples collected with a Ponar, the season of collection is 

given as: Sp = spring, S = summer, F = fall. Stations sampled for Dreissena by divers are designated with a “D”; all 

diver samples were collected in fall. 

Sampling Year

Station Depth (m) Latitude Longitude Substrate 2006 2007 2008 2009 2010

4 6.7 43 44.65 -83 52.07 silt F Sp, S, F Sp, S, F F

5 3.0 43 53.72 -83 51.63 cobble, sand D D D

6 4.0 43 53.08 -83 49.25 cobble, sand D D D

7 7.0 43 50.28 -83 47.57 silt F Sp, S, F Sp, S, F F

10 11.0 43 56.50 -83 37.43 silt F Sp, S, F Sp, S, F F

11 9.0 44 01.23 -83 34.42 silty sand F Sp, S, F Sp, S, F F

13 3.0 43 57.57 -83 29.32 sand, gravel F Sp, S, F Sp, S, F, D F, D D

14 3.6 43 44.30 -83 38.45 sand, gravel F Sp, S, F Sp, S, F, D F, D D

15 5.0 43 45.67 -83 31.58 cobble, gravel D D D

16 3.0 43 50.82 -83 33.75 sand, gravel F Sp, S, F Sp, S, F, D F,D D

20 16.0 44 07.57 -83 30.00 silty sand Sp, S, F Sp, S, F

23 28.0 44 13.25 -83 15.75 sand, some silt Sp, S, F Sp, S, F

24 12.5 44 00.08 -83 17.00 silty sand F Sp, S, F Sp, S, F

27 5.5 44 02.33 -83 06.66 cobble, rocks D D
23

Table 2. Stations sampled in the main basin of Lake Huron in 2000, 2003, 2007, and 2012. Also given are the 

location and dominant substrate of each station. Given in parenthesis is the water depth each time the station was 

sampled. Blank space means not sampled. 

Sampling Year

Station Substrate Latitude Longitude 2000 2003 2007 2012

AL20 sand 44 57.140 -83 16.250 X (20)

AL30 silty sand 44 56.070 -83 14.810 X (30)

AL45 silty sand 44 55.080 -83 11.460 X (45)

AL60 sandy silt 44 51.740 -83 06.780 X (60)

AL80 silt 44 49.120 -83 01.910 X (80)

AP1 sand 45 25.000 -83 42.730 X (23)

FI2 sand, some clay 45 29.987 -81 56.495 X (30) X (30) X (33) X (33)

FI3 silty clay 45 29.975 -82 02.776 X (46) X (46) X (45) X (44)

FI4 silty clay 45 29.999 -82 16.687 X (61) X (61) X (69) X (61)

FI5 silt 45 30.008 -82 20.383 X (82) X (90) X (86) X (85)

GLERL18 sand 44 57.315 -83 16.620 X (18)

GLERL30 silty sand 44 56.324 -83 14.430 X (30)

GLERL45 silty sand 44 53.947 -83 08.978 X (46)

HB1 sand 45 36.830 -84 10.190 X (20) X (12) X (12)

HB3 silty clay 45 38.156 -84 07.764 X (45) X (44) X (42)

HB4 silt 45 39.600 -84 05.300 X (58) X (55) X (54)

HB5 silty loam 45 43.373 -83 58.820 X (80) X (74) X (73)

HU6 silt 43 27.970 -82 00.020 X (51) X (52) X (51) X (49)

HU9 silt 43 38.020 -82 13.008 X (59) X (60) X (59) X (57)

HU12 silt 43 53.393 -82 03.371 X (90) X (90) X (88) X (87)

HU15 silt 43 59.991 -82 21.023 X (66) X (69) X (65) X (65)

HU27 silty sand 44 11.919 -82 30.169 X (57) X (61) X (55) X (53)

HU32 silt 44 27.205 -82 20.471 X (80) X (82) X (84) X (78)

HU37 sandy silt 44 45.658 -82 46.974 X (72) X (72) X (74) X (72)

HU38 silty clay/loam 44 44.393 -82 03.583 X (133) X (132) X (138) X (135)

HU45 clay, some sand 45 08.203 82 59.059 X (91) X (99) X (100) X (94)

HU48 silty clay 45 16.673 -82 27.188 X (112) X (113) X (112) X (107)

HU53 silty clay 45 27.010 -82 54.885 X (91) X (93) X (92) X (88)

HU54 silty clay/loam 45 30.990 -83 24.952 X (139) X (125) X (127) X (140)

HU61 silty loam 45 44.989 -83 54.980 X (116) X (120) X (116) X (115)

HU93 silt 44 05.988 -82 07.055 X (87) X (90) X (89) X (88)

HU95 sandy silt 44 19.994 -82 49.954 X (66) X (69) X (67) X (65)

HU97 silty sand 44 54.953 -83 09.973 X (45) X (45) X (44) X (42)

HU325 sandy clay 45 48.996 -84 23.258 X (58) X (60) X (57) X (55)

HU329 silty sand 45 54.760 -84 18.126 X (37) X (38) X (37) X (37)

HU429P silty sand 45 49.311 -84 26.219 X (19)
24

Sampling Year

Station Substrate Latitude Longitude 2000 2003 2007 2012

HU429 silty sand 45 49.447 -84 26.208 X (33) X (33) X (43) X (41)

KB472 silty clay 45 13.503 -81 49.555 X (44) X (44)

KB479 silty sand 45 41.070 -82 33.020 X (34) X (34)

KB480 silty sand 45 44.420 -82 49.190 X (31) X (32)

KB482 sand, some clay 45 48.290 -83 09.560 X (48) X (42)

MZ12 silty sand 43 16.181 -82 25.705 X (21) X (21) X (21) X (20)

MZ13 silty sand 43 16.170 -82 20.439 X (31) X (31) X (29) X (28)

MZ14 silty sand 43 16.188 -82 12.044 X (29) X (28) X (28) X (27)

MZ22 silty sand 43 30.303 -82 30.155 X (19) X (20) X (21) X (21)

MZ23 silty sand 43 30.419 -82 27.265 X (33) X (33) X (33) X (34)

MZ24 silty clay 43 30.601 -82 23.268 X (43) X (44) X (42) X (43)

MZ25 silty clay 43 31.180 -82 12.250 X (52) X (53) X (51) X (51)

MZ34 silty sand 43 52.617 -82 31.737 X (45) X (48) X (45) X (45)

MZ43 coarse sand 44 04.009 -82 44.775 X (30) X (30) X (30) X (30)

MZ44 silty sand 44 05.705 -82 43.063 X (39) X (40) X (39) X (39)

MZ45 silty sand 44 14.505 -82 32.993 X (58) X (60) X (58) X (56)

MZ72 sand 44 24.279 -83 12.484 X (24) X (24) X (24) X (23)

MZ73 sand 44 25.397 -83 10.515 X (32) X (32) X (31) X (30)

MZ74 sand 44 26.304 -83 08.802 X (42) X (42) X (40) X (40)

MZ75 silty sand 44 30.924 -83 00.174 X (67) X (67) X (65) X (63)

MZ76 silty loam 44 43.487 -82 35.500 X (79) X (80) X (71) X (76)

MZ87 loam 45 05.854 -83 03.497 X (55) X (58) X (55) X (50)

MZ88 sandy silt 45 05.341 -83 04.643 X (47) X (46) X (49) X (47)

MZ89 silty sand 45 04.771 -83 05.781 X (32) X (32) X (33) X (32)

MZ93 silty sand 45 26.469 -83 44.591 X (32) X (32) X (32) X (31)

MZ94 silty sand 45 26.304 -83 44.304 X (40) X (38) X (32) X (38)

MZ95 silt 45 28.688 -83 42 208 X (64) X (61) X (61) X (62)

MZ96 silt 45 40.641 -83 28.575 X (129) X (139) X (125) X (122)

MZ123 silty sand 45 53.661 -84 09.611 X (54) X (55) X (45) X (45)

MZ125 Silt 45 50.712 -84 11.575 X (81) X (81) X (80) X (78)

PT2 sand 45 00.049 -81 32.991 X (30)

PT3 silty clay 45 00.057 -81 35.192 X (45) X (45) X (46) X (43)

PT5 silty clay 44 59.998 -81 40.479 X (80) X (80) X (77) X (77)

PT6 silt 45 00.023 -81 42.495 X (136) X (135) X (137) X (133)

SB23 silty sand 44 13.306 -83 15.761 X (28) X (28)

SO2 sand 44 34.992 -81 23.478 X (31) X (31) X (31) X (30)

SO3 silty sand 44 35.036 -81 29.993 X (40) X (48) X (47) X (45)

SO4 sandy silt 44 35.002 -81 31.978 X (67) X (68) X (67) X (65)

SO5 silt 44 35.007 -81 34.983 X (81) X (80) X (78) X (78)
25

Sampling Year

Station Substrate Latitude Longitude 2000 2003 2007 2012

SR3 silt 45 19.203 -83 25.323 X (32) X (35) X (30)

SR4 sandy clay 45 19.203 -83 22.707 X (45) X (45) X (43)

SR5 sandy clay 45 19.203 -83 20.165 X (55) X (56) X (55) X (58)

SR6 sandy clay 45 19.203 -83 14.503 X (77) X (75) X (72)

SR10 sandy silt 44 49.482 -83 06.555 X (56) X (57) X (56) X (54)

TA20 sand 44 09.154 -83 20.739 X (20)

TA45 sandy silt 44 18.107 -83 11.055 X (45)

TN1 silt 43 16.343 -82 00.361 X (21) X (21) X (20) X (21)

TN2 silt 43 41.800 -82 25.000 X (51) X (51) X (51) X (51)

TN3 silt, clay/sand 43 41.782 -81 55.995 X (66) X (65) X (64) X (61)

TN4 coarse sand 44 13.344 -81 50.480 X (48) X (45) X (47) X (49)

TN5 silty clay 45 12.447 -82 42.492 X (170) X (173) X (171) X (164)

TN6 silt 43 30.002 -81 53.489 X (31) X (29) X (28)

TN7 silt 43 30.037 -81 50.558 X (21) X (21) X (20)

TN8 sandy silt 43 41.800 -81 53.734 X (44) X (44) X (43)

TN9 silt 43 41.800 -81 52.421 X (32) X (31) X (30)

TN10 silt 43 41.800 -81 50.366 X (22) X (22) X (21)

TN11 coarse sand 44 13.406 -81 39.987 X (30) X (29) X (28)

TN12 sand 44 13.458 -81 39.121 X (20) X (18) X (18)
26

Table 3. Stations sampled in Georgian Bay and North Channel in 2002, 2007, and 2012.. Also given are the location, 

water depth, and dominant substrate of each station. Blank space means not sampled. 

Sampling Year

Station Substrate Depth (m) Latitude Longitude 2002 2007 2012

Georg.Bay

GB1 silt 89.0 44 43.05 -80 51.40 X (89) X (88) X (89)

GB3 silty coarse sand 32.0 44 43.50 -80 37.00 X (32) X (31) X (35)

GB4 sandy silt 57.0 44 38.75 -80 10.00 X (57) X (57) X (57)

GB5 sandy clay 57.6 44 47.80 -80 14.60 X (58) X (58) X (58)

GB6 sandy silt 86.0 44 44.20 -80 26.10 X (86) X (87) X (87)

GB8 silty clay 51.0 44 57.16 -80 08.93 X 51) X (51) X (51)

GB9 sandy clay 32.0 44 52.30 -79 58.08 X 32) X (27) (31)

GB11 sandy clay 61.0 44 55.25 -80 36.35 X (61) X (62)

GB12 silty clay 87.0 44 55.20 -80 52.50 X (87) X (87) X (87)

GB17 silt/clay/loam 77.5 45 14.70 -80 52.50 X (78) X (78) X (76)

GB24 silty sand, clay 39.0 45 44.73 -80 50.33 X 39) X (40) X (31)

GB26 sand, some clay 26.0 45 50.00 -80 54.00 X (26) X (21)

GB29 silty clay loam 42.0 45 35.00 -81 05.00 X (42) X (43) X (42)

GB35 silty sand,some clay 33.4 45 31.65 -81 40.17 X (33) X (36) X (37)

GB36 loam, coarse sand 52.0 45 42.50 -81 37.20 X (52) X (53) X (56)

GB39 silty sand 28.0 45 52.40 -81 15.50 X (28) X (28) X (28)

GB42 silty clay 26.0 45 54.77 -81 35.70 X (26) X (26) X (26)

N. Channel

NC68 sandy silt 16.7 46 02.50 -83 51.20 X (17) X (17) X (16)

NC70 silt 21.5 46 08.20 -83 40.30 X (22) X (22) X (22)

NC71 silt 35.0 46 14.00 -83 44.80 X 35) X (35) X (35)

NC73 course sand 18.7 46 11.20 -83 21.30 X (19) X (17) X (20)

NC76 silt 58.0 46 00.00 -83 26.00 X 58) X (58) X (57)

NC77 silt 77.8 45 58.20 -83 11.90 X (78) X (78) X (76)

NC79 silt 25.4 46 07.40 -82 53.15 X 25) X (25) X (27)

NC82 silt 27.2 45 56.20 -82 45.50 X (27) X (29) X (28)

NC83 silt 30.4 46 00.00 -82 33.00 X (31) X (30) X (32)

NC84 silty clay 35.3 46 05.50 -82 33.40 X (35) X (36) X (36)

NC87 silty clay 32.0 46 03.67 -82 11.83 X 32) X (37) X (44)

NC88 silt 33.9 46 03.33 -82 00.00 X (34) X (34) X (36)

NC89 silt 38.8 45 55.00 -82 09.67 X 39) X (38) X (38)
27

Table 4. Relationships between shell length (SL, mm) and tissue ash-free dry weight (AFDW, mg) for Dreissena 

polymorpha and Dreissena rostriformis bugensis at sites in Lake Huron and Saginaw Bay. The AFDW/SL 

relationship is defined as logeAFDW = b + a*logeSL. Also given are the number of individuals used to define the 

relationship (n) and their median shell length (range in parentheses). Included is the AFDW of a standard 15-mm 

individual as derived from the determined relationship. #Weights in 2009 were not measured directly; regression 

values were derived by combining data collected in 2008 and 2010. 

Region (year) a b n R

2 Median SL 15 mm 

Lake Huron (2012) 

<50 m 2.589 -5.060 140 0.759 19.4 (9.6-36.3) 7.0

>50 m 2.899 -5.915 87 0.916 19.1 (9.8-26.9 6.9

Saginaw Bay

D. polymorpha (2008) 2.027 -3.948 25 0.795 15.0 (10.0-22.0) 4.7

D. r. bugensis (2008) 2.775 -5.836 27 0.903 16.0 (11.0-22.0) 5.4

D. r. bugensis (2009)#2.316 -4.697 76 0.793 --- 4.8

D. r. bugensis (2010) 2.094 -4.144 49 0.774 16.9 (9.9-23.6) 4.6
28

Table 5. List of taxa collected in Saginaw Bay, 2006-2009, and in Lake Huron, 2012. The four-letter code identifies 

taxa in Excel files given in the appendices. 

Taxa Code Taxa Code

Amphipoda AMPH Oligochaeta (continued)

Pontoporeiidae Naidinae

Diporeia spp. DIPO Arcteonais lomondi ALOM

Gammaridae Chaetogaster sp. CHAE

Gammarus sp. GAMM Dero sp. DERO

Hyalellidae Dero nivea DNIV

Hyalella sp. HYAL Nais sp. NAIS

Isopoda ISOP Nais bretscheri NBRE

Hirudinea HIRU Nais communis NCOM

Glossiphoniidae Nais eliguis NELI

Helobdella stagnalis HSTA Nais pardalis NPAR

Piscicolidae Nais pseudobtusa NPSE

Piscicola sp. PISC Nais simplex NSIM

unidentified Hirudinea HIRU Nais variabilis NVAR

Oligochaeta OLIG Opistonais serpentina OSER

Enchytraeidae ENCH Piguetiella blanchi PBLA

Lumbriculidae Piguetiella michiganensis PMIC

Stylodrilus heringianus SHER Pristina sp. PRIS

Naididae Slavina appendicula SAPP

Tubificinae Specaria josinae SJOS

 Aulodrilus americanus AMME Stylaria fossularis SFOS

 Aulodrilus limnobius ALIM Stylaria lacustris SLAC

 Aulodrilus pigueti APIG Uncinais uncinata UUNI

 Aulodrilus pluriseta APLU Vejdovskyella intermedia VINT

 Branchiura sowerbyi BSOW Diptera

 Ilyodrilus templetoni ITEM Chironomidae TCHI

 Isochaetides freyi IFRE Chironominii

 Limnodrilus cervix LCER Chironomus spp. CHIR

 Limnodrilus claparedianus LCLA Cladopelma sp. CLAD

 Limnodrilus hoffmeisteri LHOF Cryptochironomus sp. CRYP

 Limnodrilus profundicola LPRO Demicryptochironomus sp. DEMI

 Limnodrilus maumeensis LMAU Dicrotendipes sp. DICR

 Limnodrilus spiralis LSPI Dicrotendipes neomodestus DNEO

 Limnodrilus udekemianus LUDE Harnischia sp. HARN

 Potamothrix bavaricus PBAV Hydrobaenus sp. HYDR

 Potamothrix moldaviensis PMOL Microtendipes sp. MPED

 Potamothrix vejdovskyii PVEJ Paracladopelma nereis PNER

 Rhyacodrilus coccineus RCOC Paracladopelma undine PUDI
29

Taxa Code Taxa Code

 Spirosperma ferox SFER Paracladopelma winnelli PWIN

 Spirosperma nikolskyi SNIK Paralauterborniella nigrohalteralis PNIG

 Tasserkidrilus superiorensis TSUP Paratendipes albimanus PALB

 Tubifex tubifex TTUB Polypedilum sp. POLY

 Varichaetadrilus angustipenis VANG Polypedilum halterale grp. PHAL

 Immatures Polypedilum scalaenum PSCA

 without hair setae IMWO Polypedilum tuberculum PTUB

 with hair setae IMWH Pseudochironomus sp. PSEU

Diptera (continued) Pelecypoda

Sticochironomus sp. STIC Sphaeriidae SPHA

Tribelos sp. TRIB Dreisseniidae

Tanytarsinii Dreissena polymorpha DPOL

Cladotanytarsus sp. CTAN Dreissena rostriformis bugensis DBUG

Micropsectra sp. MICR Gastropoda GAST

Paratanytarsus sp. PARA Hydrobiidae

Tanytarsus sp. TANY Amnicola limnosa ALMO

Orthocladiinae Bythinia tentaculata BTEN

Heterotrissocladius changi HCHA Valvatidae

Heterotrissocladius oliveri HOLI Valvata sincera VSIN

Othocladius sp. ORTH Ephemeroptera EPHE

Psectrocladius simulans PSMI Ephemeridae

Parakiefferiella sp. PKIE Hexagenia sp. HEXA

Tanypodinae TAYP Tricoptera

Ablabesmyia spp. ABLA Leptoceridae

Coelotanypus sp. COEL Ocetis sp. OECE

Procladius sp. PROC Zygoptera ZYGO

Thienemannimya grp. THIE Other (biomass only) OTHE

Diamesinae

Monodiamesia sp. MONO

Monodiamesia tuberculata MTUB

Potthastia longimanus PLOG

Protanypus sp. PROT

Unidentified Chironomidae UNDE
30

Table 6. Mean (±SE) density (no./m2) and biomass (gAFDW/m2) of Dreissena at sites with different substrates in 

inner and outer Saginaw Bay in 1991-1996 and in 2008-2010. Samples collected by SCUBA divers in the fall of 

each year. Inner bay- cobble = Stations 5, 6 and 15; Inner bay-sand/gravel = Stations 13, 14, and 16; Outer baycobble = Station 27. Station 13 was not sampled in 1991, Station 16 was not sampled in 2008 and 2009, and Station 

27 was not sampled in 2010. 

Year Inner Bay-Cobble Inner Bay-Sand/Gravel Outer Bay- Cobble

Density Biomass Density Biomass Density Biomass

1991 25,271 ± 11,260 16.34 ± 9.07 18 ± 91 0.05 ± 0.04 3,408 0.73

1992 28,157 ± 23, 576 41.45 ± 32.71 35,519 ± 16,040 82.29 ± 34.50 4,695 19.49

1993 3,712 ± 2,052 3.43 ± 1.89 4,238 ± 2,080 5.56 ± 3.18 5,813 15.29

1994 7,803 ± 2,439 11.59 ± 3.12 2,160 ± 905 5.07 ± 1.92 9,925 32.55

1995 3,345 ± 1,731 5.90 ± 2.12 945 ± 811 2.28 ± 1.89 3,824 27.10

1996 6,909 ± 5,415 13.59 ± 10.27 4,186 ± 2,067 13.59 ± 6.79 6,981 57.54

2008 695 ± 205 2.27 ± 0.45 239 ± 116 1.22 ± 0.30 356 2.11

2009 516 ± 130 2.17 ± 0.64 494 ± 2 0.47 ± 0.23 366 1.97

2010 2,289 ± 1,929 1.79 ± 0.60 1,514 ± 998 1.26 ± 0.44
31

Table 7. Mean (±SE) density (no./m2) of major taxonomic groups at sites with different substrates and depths in 

inner and outer Saginaw Bay during three periods: 1987-1990, 1994-1996, and 2006-2009. All samples collected 

with a Ponar grab. Sources of variation are yearly (multiple stations) or seasonal means (single station). Differences 

between periods were tested with ANOVA (p-value given). If the P-value was ≤ 0.05, Fisher’s LSD was used for 

pairwise comparisons. Results of such comparisons are provided by subscripts; values with the same subscript were 

not significantly different (P > 0.05).. Inner bay-sand/ gravel = Stations 13, 14, and 16; Inner bay-silty sand (Station 

11); Inner bay- silt = Stations 4, 7 and 10; Outer bay- 12 m = Station 24; Outer bay- 16 m = Station 20; Outer bay-28 

m = Station 23. 

Period

Region/Taxa 1987-1990 1994-1996 2006-2009 P-Value

Inner Bay-Sand/Gravel

 Amphipoda 66 ± 17a

296 ± 86b126 ± 42ab

0.04

 Oligochaeta 653 ± 113 716 ± 89 679 ± 127 0.73

 Chironomidae 106 ± 24a

148 ± 73a38 ± 10b

0.02

 Sphaeriidae 27 ± 9

a

7 ± 3

b

1 ± < 1c<0.01

 Dreissena 0 ± 0

a

2,247 ± 1,038b480 ± 185b<0.01

Inner Bay-Silty Sand

 Amphipoda 6 ± 4 51 ± 4 26 ± 18 0.21

 Oligochaeta 6,799 ± 2,379 3,268 ± 710 5,281 ± 1,107 0.36

 Chironomidae 6,942 ± 4,256 2,145 ± 576 2,072 ± 963 0.33

 Sphaeriidae 535 ± 66a

116 ± 55ab37 ± 13b

0.04

 Dreissena 0 ± 0 54 ± 31 630 ± 528 0.07

Inner Bay-Silt

 Amphipoda 1 ± <1a

12 ± 2

b

10 ± 6

b <0.01

 Oligochaeta 19,423 ±

1,466a

2,727 ± 775b6,055 ± 966c < 0.01

 Chironomidae 1,507 ± 170 1,901 ± 487 1,654 ± 312 0.96

 Sphaeriidae 93 ±22 151 ± 57 284 ± 69 0.09

 Dreissena 0 ± 0

a

10 ± 6

ab 46 ± 25b

0.03

Outer Bay-12 m

 Amphipoda 9 ± 2 19 ± 13 2 ± 2 0.27

 Oligochaeta 3,089 ± 1,305 2,246 ± 1,077 823 ± 225 0.18

 Chironomidae 965 ± 299 1,645 ± 1,094 344 ± 174 0.23

 Sphaeriidae 42 ± 17a

6 ± 5

b

2 ± 2

b

0.03

 Dreissena 0 ± 0 3 ± 1 2 ± 2 0.32

Outer Bay-16 m

 Amphipoda 3 ± 2

ab

10 ± 2

a

0 ± 0

b

0.03

 Oligochaeta 1,894 ± 548 2,582 ± 814 1,241 ± 213 0.48

 Chironomidae 1,382 ± 116 1,797 ± 661 637 ± 451 0.32

 Sphaeriidae 373 ± 162a

86 ± 13a1 ± 1

b <0.01

 Dreissena 0 ± 0 3 ± 2 77 ± 73 0.07

Outer Bay-28 m

 Amphipoda 819 ± 189a

168 ± 102b0 ± 0

c <0.01

 Oligochaeta 387 ± 88a727 ± 155a6,421 ± 143b< 0.01
32

Period

Region/Taxa 1987-1990 1994-1996 2006-2009 P-Value

 Chironomidae 218 ± 49ab

515 ± 144a62 ± 43b

0.04

 Sphaeriidae 228 ± 68 202 ± 70 216 ± 43 0.93

 Dreissena 0 ± 0

a

7 ± 7

a

163 ± 4

b

<0.01
33

Table 8. Mean (±SE) biomass (gAFDW/m2) of Dreissena and non-dreissenid taxa at sites in inner and outer 

Saginaw Bay with different substrate types and depths. Relevance of the three periods is given in the text. Samples 

collected with a Ponar grab. Differences between periods were tested with ANOVA (P-value given). If the P-value 

was ≤ 0.05, Fisher’s LSD was used for pairwise comparisons. Results of such comparisons are provided by 

subscripts; values with the same subscript were not significantly different (P >0.05).. Inner bay-sand/ gravel = 

Stations 13, 14, and 16; Inner bay-silty sand (Station 11); Inner bay- silt = Stations 4, 7 and 10; Outer bay-12 m = 

Station 24; Outer bay-16 m = Station 20; Outer bay-28 m = Station 23. 

Period

Region/Taxa 1987-1990 1994-1996 2006-2009 P-Value

Inner Bay-Sand/Gravel

 Dreissena 1.87 ± 0.67

 Non-Dreissena 0.10 ± 0.01 0.47 ± 0.24 0.21 ± 0.05 0.13

Inner Bay-Silty Sand

 Dreissena 2.40 ± 1.88

 Non-Dreissena 2.15 ± 0.43 1.60 ± 0.63 1.35 ± 0.32 0.47

Inn Bay-Silt

 Dreissena 0.01 ± <0.01

 Non-Dreissena 5.50 ± 0.79a2.97 ± 0.72

b

2.58 ± 0.31

b <0.01

Outer Bay-12 m

 Dreissena <0.01 ± <0.01

 Non-Dreissena 0.50 ± 0.18 0.55 ± 0.34 0.24 ± 0.06 0.60

Outer Bay-16 m

 Dreissena 0.01 ± 0.01

 Non-Dreissena 0.48 ± 0.03 0.74 ± 0.24 0.36 ± 0.10 0.39

Outer Bay-28 m

 Dreissena 0.05 ± 0.01

 Non-Dreissena 0.38 ± 0.06

ab

0.19 ± 0.03a0.92 ± 0.42b

0.05
34

Table 9. Mean (±SE) density (no./m2) of major taxa at sites in the 18-30 m, 31-50 m, 51-90 m, and > 90 m intervals 

in the main basin of Lake Huron in 2000, 2003, 2007, and 2012. See Table 2 for the number of sites per year per 

interval. Differences between years were tested with ANOVA (P-value given). If the P-value was ≤ 0.05, Fisher’s 

LSD was used for pairwise comparisons. Results of such comparisons are provided by subscripts; values with the 

same subscript were not significantly different (P > 0.05). 

Interval/

Year

Taxa

Diporeia Oligochaeta Sphaeriidae Chironomidae D. polymor D. r. bugensis

18-30 m

2000 244 ± 237 a1,648 ± 410 a457 ± 196 883 ± 451 386 ± 342 3 ± 2 a

2003 97 ± 92 ab1,783 ± 417a47 ± 21 238 ± 55 297 ± 209 297 ± 180a

2007 1 ± 1

b

8,114 ± 2,742b183 ± 64 754 ± 210 0 ± 0 850 ± 283b

2012 0 ± 0b8,138 ± 2,854b66 ± 25 228 ± 57 19 ± 19 1,332 ± 780b

P-value <0.01 0.01 0.30 0.28 0.08 <0.01

31-50 m 

2000 876 ± 287 1,196 ±314a237 ± 37a379 ± 140a6 ± 2a2 ± 1a

2003 248 ± 103a1,460 ± 368a67 ± 13b62 ± 14b7 ± 4ab 1,469 ± 757b

2007 17 ± 10b3,076 ± 824b113 ± 25

b

256 ± 52

a

1 ± 1bc 2,217 ± 664b

2012 0 ± 0b2,403 ± 412b137 ± 31

b

472 ± 164a0 ± 0c1,619 ± 513b

P-value <0.01 <0.01 <0.01 <0.01 <0.01 <0.01

51-90 m

2000 1,908 ± 183a805 ± 89

a

335 ± 44a71 ± 11a0 ± 0 0 ± 0a

2003 914 ± 133

b

383 ± 42

b

109 ± 17

bc 28 ± 5b

18 ± 18 72 ± 45

ab

2007 170 ± 57c489 ± 60bc 128 ± 14

b

27 ± 6

b

0 ± 0 276 ± 172b

2012 67 ± 30

c

693 ± 88ac 93 ± 16bc 49 ± 13b0 ± 0 1,690 ± 678

c

P-value <0.01 <0.01 <0.01 <0.01 0.24 <0.01

> 90 m

2000 1,707 ± 232a627 ± 69 94 ± 32 58 ± 12 0 ± 0 0 ± 0

2003 924 ± 83ab404 ± 76 71 ± 38 17 ± 4 0 ± 0 2 ± 1

2007 427 ± 82

bc

559 ± 138 109 ± 50 21 ± 5 0 ± 0 135 ± 135

2012 252 ± 69c489 ± 154 92 ± 25 49 ± 15 0 ± 0 748 ± 612

P-value 0.05 0.30 0.24 0.15 - 0.22
35

Table 10. Mean (±SE) density (no./m2) of major taxa at sites in the 18-30 m, 31-50 m, and 51-90 m intervals in 

Georgian Bay and North Channel in 2002, 2007, and 2012. See Table 2 for the number of stations in each interval in 

each of the three sampling years. Differences between years were tested with ANOVA (P-value given). If the Pvalue was ≤ 0.05, Fisher’s LSD was used for pairwise comparisons. Results of such comparisons are provided by 

subscripts; values with the same subscript were not significantly different (P > 0.05ND = not determined. 

Interval/

Year

Taxa

Diporeia Oligochaeta Sphaeriidae Chironomidae D. polymor D. r. bugens

Georg. Bay

18-30 m

2002 1,687 ± 830 707 ± 344 1,814 ± 525

a

162 ± 34 19 ± 10 0 ± 0

2007 55 ± 55 1,388 ± 1,043 61 ± 21

b

555 ± 302 21 ± 21 278 ± 278

2012 3 ± 3 573 ± 145 0 ± 0

c

148 ± 121 0 ± 0 3 ± 3

 P-value 0.07 0.99 <0.01 0.61 0.48 0.68

31-50 m 

2002 1,457 ± 596a767 ± 293 853 ± 214 94 ± 26 24 ± 23 36 ± 34

2007 50 ± 48

ab 728 ± 332 195 ± 114 195 ± 155 5 ± 5 1,335 ± 1,330

2012 0 ± 0b2,499 ± 576 195 ± 81 63 ± 58 18 ± 18 382 ± 221

 P-value 0.02 0.18 0.14 0.18 0.89 0.59

51-90 m

2002 1,684 ± 306a413 ± 144 291 ± 110a44 ± 11 2 ± 2 0 ± 0a

2007 99 ± 56b150 ± 60 84 ± 14ab 56 ± 13 2 ± 2 1 ± 1

a

2012 0 ± 0c391 ± 107 55 ± 16b21 ± 8 0 ± 0 144 ± 130

b

 P-value < 0.01 0.11 0.05 0.07 0.65 0.05

N. Channel

18-30 m

2002 2,046 ± 705 653 ± 269 875 ± 280 99 ± 22 1 ± 1 0 ± 0

2007 1,022 ± 423 478 ± 230 232 ± 41 676 ± 384 0 ± 0 0 ± 0

2012 357 ± 171 1,245 ± 549 914 ± 319 275 ± 72 0 ± 0 0 ± 0

 P-value 0.25 0.32 0.11 0.42 ND ND

31-50 m 

2002 896 ± 401 322 ± 163 357 ± 163 198 ± 57 0 ± 0 0 ± 0

2007 660 ± 432 257 ± 119 338 ± 137 470 ± 243 0 ± 0 0 ± 0

2012 751 ± 320 239 ± 158 346 ± 146 170 ± 75 0 ± 0 0 ± 0

 P-value 0.64 0.72 0.59 0.89 ND ND

51-90

2002 3,349 ± 43 ,174 ± 232 635 ± 200 54 ± 25 0 ± 0 0 ± 0

2007 253 ± 253 307 ± 244 79 ± 21 29 ± 21 0 ± 0 0 ± 0

2012 121 ± 107 483 ± 311 224 ± 100 490 ± 345 0 ± 0 0 ± 0

 P-value ND ND ND ND ND ND
36

Table 11. Mean (±SE) biomass (gAFDW/m2) of major taxa at sites in the 18-30 m, 31-50 m, and 51-90 m intervals 

in the main basin, Georgian Bay and North Channel in 2012 See Table 2 for the number of stations in each interval 

in each of the three sampling years. 

Region/

Interval

Taxa

Diporeia Oligochaeta Sphaeriidae Chironomidae D. polymo D. r. bugen

Main basin

18-30 m 0 ± 0 1.48 ± 0.37 <0.01 ± <0.01 0.03 ± 0.01 0.02 ± 0.02 2.64 ± 1.76

31-50 m 0 ± 0 0.63 ± 0.09 0.01 ± <0.01 0.03 ± 0.01 0 ± 0 14.39 ± 4.56

51-90 m 0.01 ± <0.01 0.32 ± 0.05 0.01 ± <0.01 0.01 ± <0.01 0 ± 0 5.23 ± 2.36

>90 m 0.04 ± 0.01 0.23 ± 0.07 0.01 ± <0.01 0.01 ± <0.01 0 ± 0 4.32 ± 3.97

Georg. Bay 

18-30 m 0 ± 0 0.45 ± 0.29 0.01 ± 0.01 0.03 ± 0.03 0 ± 0 0.13 ± 0.13

31-50 m 0 ± 0 0.94 ± 0.39 0.01 ± <0.01 0.04 ± 0.04 0.77 ± 0.77 11.30 ± 4.95

51-90 m 0 ± 0 0.17 ± 0.06 0.01 ± <0.01 <0.01 ± <0.01 0 ± 0 2.97 ± 2.93

N. Channel

18-30 m 0.17 ± 0.07 0.38 ± 0.16 0.07 ± 0.02 0.08 ± 0.05 0 ± 0 0 ± 0

31-50 m 0.12 ± 0.05 0.15 ± 0.07 0.02 ± 0.01 0.10 ± 0.08 0 ± 0 0 ± 0

51-90 m <0.01 0.08 0.01 0.14 0 ± 0 0 ± 0
37

Figure 1. Location of sampling sites in Lake Huron, Georgian Bay, and North Channel, 2000, 2002, 2003, 2007, and 

2012. See Table 2 for those sites specifically sampled in 2007 and 2012.
38

Figure 2. Location of sampling sites in Saginaw Bay in 2006-2010. These were the same sites sampled in 1987-

1996. Dashed line separates the inner bay from the outer bay. Depth contours given in meters. An “x” indicates sites 

sampled with SCUBA divers and a circled black dot indicates sites sampled with a Ponar grab. 
39

Figure 3. Mean (± SE) density (no./m2) of major macroinvertebrate groups at stations in inner Saginaw Bay with 

water depths of > 6 m and with a substrate of silt (Stations 4, 7, and 10). Densities in 1987-1996 were taken from 

previous surveys (Nalepa et al. 2002). Note different scales of the Y-axis. 
40

Figure 4. Mean (± SE) density (no./m2) of major macroinvertebrate groups at stations in inner Saginaw Bay with 

water depths of < 6 m and with a substrate of sand/gravel (Stations 13, 14, and 16). Densities in 1987-1996 were 

taken from previous surveys (Nalepa et al. 2002). Note different scales of the Y-axis. 
41

Figure 5. Mean (± SE) density (no./m2) of major macroinvertebrate groups at a station in inner Saginaw Bay with a 

substrate of silty sand (Station 11). Densities in 1987-1996 were taken from previous surveys (Nalepa et al. 2002). 

Note different scales of the Y-axis. 
42

Figure 6. Mean (± SE) density (no./m2) of major macroinvertebrate groups at a station in outer Saginaw Bay with 

water depth of 12 m (Station 24). Densities in 1987-1996 were taken from previous surveys (Nalepa et al. 2002). 

Note different scales of the Y-axis. 
43

Figure 7. Mean (± SE) density (no./m2) of major macroinvertebrate groups at a station in outer Saginaw Bay with 

water depth of 16 m (Station 20). Densities in 1987-1996 were taken from previous surveys (Nalepa et al. 2002). 

Note different scales of the Y-axis. 
44

Figure 8. Mean (± SE) density (no./m2) of major macroinvertebrate groups at a station in outer Saginaw Bay with 

water depth of 28 m (Station 23). Densities in 1987-1996 were taken from previous surveys (Nalepa et al. 2002). 

Note different scales of the Y-axis. 
45

Figure 9. Yearly mean (± SE) biomass (g AFDW/m2) of non-dreissenid taxa for the various stations and station 

groups in the inner (upper panel) and outer (lower panel) portions of Saginaw Bay during the periods 1987-1996 

and 2001-2009. Inner Bay: silt = solid line, solid point; silty sand = dashed line, open point; sand/gravel = dashed 

line, solid point. Outer Bay: 12 m = solid line, solid point; 16 m = dashed line, solid point; 28 m = dashed line, 

open point. 
46

Figure 10. Mean density (no./m2) of D. r. bugensis in the main basin of Lake Huron in 2000, 2003, 2007, and 2012.
47

Figure 11. Mean density (no./m2) of D, polymorpha in the main basin of Lake Huron in 2000, 2003, 2007, and 

2012.
48

Figure 12. Mean density (no./m2) of Diporeia in the main basin of Lake Huron in 2000, 2003, 2007, and 2012. 
49

Figure 13. Mean density (no./m2) of Oligochaeta in the main basin of Lake Huron in 2000, 2003, 2007, and 2012. 
50