Benthic Community Structure and Composition Among Rocky Habitats in the Great Lakes and Keuka Lake, New York

J. Great Lakes Res. 13(1):3-17 Internat. Assoc. Great Lakes Res., 1987

BENTHIC COMMUNITY STRUCTURE AND COMPOSITION AMONG ROCKY HABITATS IN THE GREAT LAKES AND KEUKA LAKE, NEW YORK

Michael H. Winnell and David J. Jude Great Lakes Research Division University of Michigan Ann Arbor, Michigan 48109 ABSTRA CT. Benthic invertebrates were collected from 12 rocky sites in Lake Michigan, Lake Superior, and Keuka Lake, New York. Proportionate abundances of benthic components occurring in rock scrape (131 spp.) and pumped (167 spp.) samples (190 spp. total) were compared using coefficient of community (eC) and percent similarity of community (PSc). Pumped samples were judged better estimators of benthic community structure and composition than were rock scrape samples because they more thoroughly and instantaneously sampled the benthos. Rock scrape samples in particular were subject to loss of Amphipoda. Comparisons among sites using CC, PSC, and cluster analysis indicated two major clusters of sites, one dominated by Chironomidae and the other dominated for the most part by the amphipod Hyalella azteca. No water chemistry differences of biological importance were noted during the fall and no biological interactions, such as fish predation, could explain observed benthic community differences. The factor which best accounted for differences in the benthic community among sites was physical characteristics such as water temperature, shelter from excessive wave activity, and rock configuration. However, despite differences, the most remarkable feature among rock sites was their similarity since dominant taxa of Amphipoda, Chironomidae, Acarina, and to some extent Naididae, were quite predictable, although rank order of dominance changed from site to site. Similarity among sites was attributed to similar trophic conditions, while dissimilarity was attributed to physical characteristics acting within and upon each site. ADDITIONAL INDEX WORDS: Biomass, coastal waters, invertebrates, scuba diving, statistical methods.

those of Barton and Hynes (1978) and Barton and Griffiths (1984) from which some excellent generalizations were made pertaining to the occurrence of benthos inhabiting rocky substrates of large lakes. Lauritsen and White (1979) and Manny (1983) generated quantitative estimates to compare the benthos inhabiting specific rocky sites. It is the purpose of this paper to compare rock scrape and pumped samples to determine which is an appropriate estimator of benthic community structure and composition and to compare rocky sites for differences in their respective benthic components.

INTRODUCTION

The majority of Great Lakes benthic studies have examined invertebrates occurring in unconsolidated sandy and silty substrates which comprise much of the area of the lakes [Teter (1960) in Lake Huron; Cook (1975) in Lake Superior; Nalepa and Thomas (1976) and Kinney (1972) in Lake Ontario; Alley and Mozley (1975), and Winnell and Jude (1979,1980, 1981,1982)inLakeMichigan].Onlya few studies have investigated rocky substrates within the Great Lakes [Krecker and Lancaster (1933) and Shelford and Boesel (1942) in Lake Erie; Judd and Gemmel (1971) and Bocsor and Judd (1972) in Lake Ontario; Manny (1983) in Lake Huron; Mozley (1975) and Lauritsen and White (1979) in Lake Michigan; and Barton and Hynes (1976, 1978) and Barton and Griffiths (1984) from the exposed shorelines of the Great Lakes]. The most extensive investigations were

METHODS Sample Collection

At each rocky site, divers of the University of Michigan Great Lakes Research Division collected samples for water chemistry analysis, periphyton 3

4

WINNELL and JUDE

and benthos samples, and sediment samples for biochemical oxygen demand and carbonhydrogen-nitrogen analyses. Divers also provided a physical description of the substrate, currents, turbidity, and types and quantity of predators and macrophytes. At most locations, divers photographed the site using a 35-mm Nikonos or an underwater video TV system. All diving was conducted from a 6-m Boston Whaler or from the R/ V Mysis or R/V Laurentian, operated by the Great Lakes Research Division. Sample Processing Sampling was conducted from October through December 1983 at eight sites in Lake Michigan, three sites in Lake Superior, and one site in Keuka Lake, New York (Fig. 1). Although the physical characteristics of the sites varied, all sites chosen had the common characteristic of being rocky (Table 1). Benthic animals were sampled by scuba divers who hand-collected rocks and vacuumed the substrate using a modified hand-operated boat bailing pump (see Dorr and Flath 1984; unpublished data, Great Lakes Research Division, Univ. Mich., Ann Arbor, MI). For rock scrape samples, divers collected rocks ranging in size from 10 cm to 30 cm. At each site, rocks were collected from as few as one but mostly from three locations for a total of 33 rock samples (Table 1). Rocks were placed in individual 125-/'m-mesh bags for transport to the surface. Bags with rocks were stored submersed in buckets of water until the rocks could be transferred to plastic bags and preserved in 100/0 formaldehyde. Pumped samples were collected from a measured area which varied from 0.2 m2 to 8.4 m2 but averaged 1.8 m2 (Table 1). At most sites, two pumped samples were collected, but at three sites only a single sample was collected (Table 1). Twenty-one pumped samples were collected. Pumped contents at each location were filtered through a 125-/'m-mesh bag, placed in 0.5-L Mason jars, and preserved in 10% formaldehyde. Results obtained from the Campbell site in Lake Michigan are not representative of the riprap occurring in the area sampled. Divers reported poor visibility and had difficulty locating the riprap. A considerable amount of sand was found overlying riprap owing to recent storm activity. Although species identified from this site are included in the species list, comparisons of sites are limited to the remaining 11 sites where samples were representative of the predominant habitat.

All rocks were scrubbed with a nylon brush and rinsed in water to remove benthic invertebrates and associated residue. Invertebrates and residue were retained on a 125-/'m-mesh sieve and stored in 85% ethanol. Depending on the quantity of sample residue, benthos was either sorted and enumerated from the whole sample or from a subsample obtained from a Folsom plankton sample splitter. Subsample size ranged from 1/2 to 1/128 of a sample, with most subsamples ranging from 1/4 to 1/ 32 of a sample. For subsamples, the remaining, unsorted portion of the sample was passed through a 590-/'m-mesh sieve from which the usually rarer, large invertebrates such as Decapoda, Ephemeroptera, Trichoptera, Gastropoda, Pelecypoda, and in some instances, Amphipoda and Isopoda, were removed and enumerated and added proportionally to the subsampled portion. All specimens were identified to the lowest practical taxonomic level. Benthos from pumped samples was expressed as number per square meter and as percentages of total benthos, while those from rock scrapes were expressed as percentages of total benthos. Comparisons of the benthos among sites were made by pooling rock scrape or pumped samples, respectively, within each site and expressing benthic components as percentages of total benthos, or percentages for taxa comprising major groups, e.g., Chironomidae, Naididae, Ephemeroptera. Data Analyses Similarity among sites was examined by three techniques. Coefficient of community (CC, which we equate with benthic community composition), percent similarity of community (PSc, which we equate with benthic community structure) (Johnson and Brinkhurst 1971), and cluster analysis (Cooley and Lohnes 1971, Anderberg 1973) were used in conjunction to assess presence of similar benthic communities among sites. Coefficient of community determined the percentage of species shared by two sites using the equation CC = [c/(a + b - c)]IOO; where a is the number of species at site A, b is the number of species at site B, and c is the number of species common to both sites. The CC measure tends to overestimate the value of rarer species (Whittaker and Fairbanks 1958). Relative abundance of the species occurring between two sites is addressed by PSc: PSc = 100 - 0.5Ela - b I; where a and b are the percentages of total benthos at sites A and B, respectively. The PSc measure tends to overestimate the value of more

BENTHOS OF ROCKY HABITATS IN LARGE LAKES -:-- PARTRIDGE 3k""tyLAND /( REEF

LAKE

SUPERIOR

5

,

LA~E SUP~R~R

P13

D

Ikm

__.,,,"~_PI2 -~-PI1

.--eVl IRISHMAN'S GROUNDS

• CHARLEVOIX

GTl GT 6 _---I"--llr'7 GT4 ~~\. GT5

TRAVERSE CITY BRANCHPORT

YAN KEUKA LAKE OUTLET

PENN

FIG. 1. Map of the study areas showing the Lake Michigan, Lake Superior, and Keuka Lake, New York sites. PI = Presque Isle, Lake Superior; GT = Grand Traverse Bay, CV = Charlevoix, CM = J.H. Campbell Plant, Lake Michigan; and KL = Keuka Lake, New York.

abundant species (Whittaker and Fairbanks 1958). When used in conjunction, CC and PSc determine whether a high affinity value between two sites results from similarly shared species, or species occurring in similar percentages of total benthos, or both. Johnson and Brinkhurst (1971) noted that there

are no predetermined ranges for CC and PSc values from which to assess high, moderate, and low affinity among samples. Rather, they stated that affinity ranges are study-specific, and in their study were determined from within-site values which were taken as the standard when assessing affinities among sites. Because we expected great-

WINNELL and JUDE

6

TABLE 1. Number of rock scrape and pumped samples collected and areas sampled at each site (see Fig. 1 for listing ofabbreviations). List ofphysical characteristics describing each site. Reliefis defined as deviation from a flat surface such that minimal relief would imply a flat surface and maximal, a rough terrain. Shelter is defined as protection from wave action. Area Water Clast pumped depth size (m 2) (m) (cm) Sites Rock Pump 3

PI2

3

PI3

3

2

2.8, 8.4

GT!

3

2

GT2

3

2

2.2, 3.4 1.7

Gn

3

2

GT4

2

2

GT5

3

GT6

CVl

KLi

CM

2

0.6, 2.8 1.1

PII

5-7

7-35

1-2.4 10-100

12

100

2-4.6 10-200

Interstices depth (cm)

Detrital floc

Periphyton length (mm) Vegetation

;5; 15-20

much

<2

none

;5; 100

much

<2

none

10

very much

10

none

;5; 100

moderate

;5;25

none

maximal moderate fine sand, pebbles maximal maximal fine to medium sand moderate minimal fine sand, gravel, pebbles maximal maximal fine sand

Relief

Shelter

3

1-30

;5;3

minimal

;5;3

none

minimal maximal

3.0

7

sandi bedrock

;5;3

minimal

;5;3

none

minimal minimal

9.6

5-30

100-200

none

maximal minimal

4

10-20

;5;3

very minimal moderate

<2

2

0.2, 1.2 1.7

<2

Chara, Elodea

minimal minimal

3

2

1.7

2.4

2-30

3-10

very minimal

<2

none

minimal maximal

3

2

1.7, 1.1

10.7

;5;30

<10

moderate

<2

none

minimal minimal

1.7

3-4.5

2-100

;5;25

much

<2

none

maximal minimal

3.4

7.6

3

est affinity within each site, CC and PSc values were determined among all sample replicates at each site for rock scrape and pumped samples, respectively. From these estimates an average within-site CC and PSc value for rock scrape and pumped samples was computed. These averages were generally greater than 30% for CC and 40070 for PSc measures. Based on these within-site values as our standard, high affinity was inferred for among-site CC and PSc values when they were ~ 30% and ~ 40%, respectively. Moderate affinity was inferred for CC and PSc values within the ranges 15-29% and 20-39%, respectively. Low affinity was inferred for CC and PSc values when they were < 15% and <20%, respectively. Cluster analysis was employed to group sites having similar percent distributions of the benthos. Because we were most interested in determining

Substrate type

Rock type angular, broken limestone cobble and boulder granite cobble and boulder granite

very angular limestone coarse to cobble, fine sand, limestone? gravel coarse to flat shale, clay, fine sand, bedrock gravel fine sand angular limestone fine sand, cobble pebbles limestone fine sand, cobble and gravel boulder limestone honey-combed, coarse to cobble fine sand, limestone gravel fine sand angular shale, sandstone

clusters of sites with similar proportions of benthos, cluster analysis was performed with all species expressed as a percentage of the total number of benthos. This technique clusters units (in this case, rocky sites) having certain attributes (in this case, proportionate species abundances). The procedure initially links the most similar sites, then sequentially joins clusters of sites to other clusters of sites until all have been linked together. A site (or cluster of sites) is considered more similar to another site (or cluster of sites) when the mathematical distance separating them is smaller than the distance separating them from any other site (or cluster of sites) (Statistical Research Laboratory 1980). Via this process, a dendrogram is constructed based on these distances which provides a condensed, visual representation of the similarity among the sites.

BENTHOS OF ROCKY HABITATS IN LARGE LAKES

Clusters were formed using the minimum variance algorithm. Using this method of uniting sites, cluster variance is the sum of the squared distances of the data points to the cluster centroid. Clusters are united when the merging of two clusters gives a minimum increase in the total within-group sum of squares. Distance between clusters was estimated using the Minkowski distance measure (Statistical Research Laboratory 1980). To assess the quality of the clustering technique, a cophenetic correlation was calculated. This measure is the correlation between the original data matrix and the final, derived data matrix (Statistical Research Laboratory 1980). Higher cophenetic correlation values connote better clustering, although there is no defined cut-off value determining good from bad cluster analyses. RESULTS AND DISCUSSION General Trends

A total of 190 benthic invertebrate species was identified from combined rock scrape and pumped samples (Table 2). Greatest numbers of species were collected for Chironomidae (50), Trichoptera (29), Naididae (21), and Acarina (20). Most notable among species collected were the pelecypod, Corbicula fluminea, and the naidid, Ripistes parasita (Schmidt). Although reported from Lake Erie (Scott-Wasilk et al. 1983), Corbicula has never been reported from any of the other Great Lakes (see White et al. 1984). The specimens collected in the pumped sample at the Campbell Plant site represent its first documented occurrence in Lake Michigan. All specimens were collected at a depth of 7.6 m in a gravelly, coarse-sand habitat amid the riprap at the J. H. Campbell Power Plant. The naidid, Ripistes parasita, was collected at a depth of 6-7 m in both pumped (11 m- 2 , 8070 of total benthos) and rock scrape (11 % of total benthos) (limestone) samples amid riprap near the intake and discharge structures of the Upper Peninsula Generating Company power plant located in Marquette, Michigan (Presque Isle site 1- Fig. 1). Ripistes parasita, previously thought to be a palaearctic species (Brinkhurst and Jamieson 1971, Chekanovskaya 1981), was first identified in North America from several New York rivers (Stimpson and Abele 1984), and since then, along the western-most extent of the North Channel in Lake Huron and in Thunder Bay, Lake Superior (Barton and Griffiths 1984). Its occurrence in the

7

present study from Marquette Bay, Lake Superior, further documents the presence of R. parasita in the Great Lakes and extends its distribution to the central portion of the southern shoreline of Lake Superior. Occurrence in or near areas frequented by ocean-going ships supports the claim R. parasita may have been introduced to the Great Lakes by these ships. Comparison of Rock Scrape and Pumped Samples

Fewer macroinvertebrate species were collected from rock scrape (131) than from pumped (167) samples (Table 2). Of 190 species collected, 106 were collected from both types of samples, 25 were collected only from rock scrape samples, and 61 occurred only in pumped samples. None of the species collected only by one technique was a numerically dominant form. Benthic community structure (PSc = 51 %) and composition (CC = 55%) for rock scrape and pumped samples were highly similar when all samples of each type were pooled, respectively. Rock scrape samples were dominated by Chironomidae [44% of total benthic density (TBD)], Acarina (26%), Naididae (8%), Enchytraeidae (8%), and Amphipoda (7%) (Table 3). Among the Chironomidae, the most common genera were Tanytarsus sp. (22% of total chironomid density) and Pseudosmittia sp. (14%). The most abundant acarinid was the oribatid, Hydrozetes sp. (83% of total acarinid abundance). The amphipod, Hyalella azteca, was the most abundant amphipod species (99%) collected from rock scrapes. The dominant benthic forms among pumped samples were the Chironomidae (39% TBD), Amphipoda (24%), Naididae (13%), Acarina (7%), and Ephemeroptera (6%) (Table 3). Tanytarsus sp. (22% of total chironomid density) and Cladotanytarsus sp. (17%) were the most abundant chironomid genera. The amphipod, H. azteca, represented 92% of all amphipods collected. Among the 21 species of naidids, Chaetogaster diastrophus was the most common (80% of total naidid abundance). The Hydracarina comprised a considerably greater percentage of total acarinid density in pumped samples (57%) than in rock scrape samples (12%), with Hygrobates the dominant hydracarinid genus in each (25% and 3%, respectively). The oribatid, Hydrozetes sp., was the most common acarinid in pumped (41 %) and rock scrape (83%) samples.

8

WINNELL and JUDE

TABLE 2. List of species identified from rock scrape and pumped samples collected at rocky sites located in Lake Superior (three sites), Lake Michigan (eight sites), and Keuka Lake, New York (one site), October through December 1983. For occurrence, a = rock scrape only, b = pump only, c = both. Taxon

Occurrence

Amphipoda Crangonyx pseudogracilis C. sp. Gammarus fasciatus G. /acustris G. pseudo/imnaeus Hya/ella azteca

c c b b c c

Isopoda Lirceus sp. Asellus sp.

c c

Decapoda Orconectes propinquus O. virilis

c c

Hirudinea He/obdella stagnalis Dina parva G/ossiphonia comp/anata Hirudinea sp. 1

b a c b

Naididae Chaetogaster cristallinus C. diastrophus C. setosus Nais barbata N. behningi N. bretscheri N. communis N. parda/is N. simp/ex N. variabilis Piquetiella michiganensis Pristina foreli P.osborni P. sima Ripistes parasita S/avina appendicu/ata Specaria josinae Sty/aria /acustris Uncinais uncinata Vejdovskyella comata V. intermedia

c c b c c c c c c c b b c c c b b b b b b

Aeolosomatidae Ae%soma /eidyi A. tenebrarum

c a

Tubificidae Au/odrilus piqueti Spirosperma ferox Immature with hair chaetae Immature without hair chaetae

b b c c

Taxon Chironomidae Corynoneura cf. /acustris C. cf. /obata Cricotopus sp. 1 C. sp. 2 Heterotrissocladius sp. Hydrobaenus sp. Nanocladius sp. Orthocladius (0.) sp. Parakiefferiella sp. Psectrocladius sp. Pseudosmittia sp. Synorthocladius cf. semivirens Thienemanniella sp. Chironomus sp. Cryptochironomus cf. digitatus Cryptochironomus sp. 3 C/adope/ma sp. Demicryptochironomus sp. Dierotendipes sp. Endochironomus sp. G/yptotendipes sp. Microtendipes sp. Parachironomus cf. abortivus Parachironomus sp. Paracladope/ma campto/abis-gr. Para/auterborniella sp. Paratendipes sp. Phaenopsectra sp. Po/ypedilum cf. sca/aenum P. cf. tuberculum Pseudochironomus cf. articaudus Saetheria ty/us Xenochironomus (X.) sp. C/adotanytarsus sp. Micropsectra sp. 1 Mieropsectra sp. 2 Paratanytarsus sp. Stempellina cf. bausei Stempellinella sp. Tanytarsus sp. Diamesa sp. Potthastia /ongimanus Ab/abesmyia sp. 1 Ab/abesmyia sp. 2 Conchape/opia sp. Labrundinia sp. Larsia sp. Procladius sp. Thienemannimyia sp. Zavrelimyia sp.

Occurrence c c c c c c a c c c c c c a b b c b c b a c c c b b b a c a c c c c c c c b c c a a c c c a a b c b

BENTHOS OF ROCKY HABITATS IN LARGE LAKES

9

TABLE 2. Continued Taxon Other Diptera Culicoides sp. Probezzia sp. Antocha sp. Hemerodromia sp. Ephemeroptera Ameletus sp. Caenis sp. Callibaetis sp. Ephemera sp. Ephemerel/a sp. Hexagenia sp. Paraleptophlebia sp. Stenacron sp. Stenonema ?femoratum Trichoptera Agrypnia sp. Ceraclea ancylus C. ? annulicornis C. resurgens C. submacula C. sp. 1 C. sp. 2 C. sp. 3 Helicopsyche borealis Hydroptila sp. 1 H. sp. 2 H. sp. 3 Lepidostoma sp. Leptoceridae ?gen. Mystacides sepulcharis M. sp. 2 M. sp. 3 Nectopsyche sp. Neureclipsis sp. Nyctiophylax sp. Oecetis sp. 1 O. sp. 2 O. sp. 3 Polycentropus centralis P. cinereus P. ?interruptus P. ?remotus Symphitopsyche sp. Triaenodes sp. Other Insecta Climacia areolaris Collembola sp. Isoperla sp. Parargyractis sp. Gastropoda Amnicola limosa A. walkeri Ferrissia paral/ela

Occurrence c b c c b c b c c c c c c b c c c b c a a c c c c c b c c a c a c c b c c c b c b a a b b a c b c

Taxon Fossaria humilis Gyraulus parvus Helisoma anceps H. trivolvis Pysel/a gyrina sayi Physel/a sp. Pleurocera acuta Stagnicola catascopium catascopium Valvata lewisi V. sincera V. tricarinata Undetermined Pulmonata Pelecypoda Corbicula fluminea Lampsilis radiata radiata Musculium transversum Pisidium casertanum P. fal/ax P. ferrugineum P. henslowanum P. lilljeborgi Sphaerium simile S. striatinum Acarina Hydrozetes sp. Hygrobates sp. Lebertia sp. Limnesia sp. Porohalacarus sp. Sperchonopsis verrucosa Torrenticola sp. Unionicola sp. Hydracarina sp. 1 Hydracarina sp. 2 Hydracarina sp. 3 Hydracarina sp. 4 Hydracarina sp. 5 Hydracarina sp. 6 Hydracarina sp. 7 Hydracarina sp. 8 Hydracarina sp. 9 Hydracarina sp. 10 Hydracarina sp. 11 Hydracarina sp. 12 Undetermined Hydracarina

Occurrence b c b b c b c b b b b c b a b c c b b b b b c c c c c a c b c

b b b b c c b a c a a a

Miscellaneous others Enchytraeidae Hydra sp. Manayunkia speciosa Pisicola geometra Stylodrilus heringianus Turbellaria spp.

c c c b b c

Branchiobdellidae

c

WINNELL and JUDE

10

TABLE 3. Mean density (X, no. m-1) and percentage of total benthos in pumped samples (% TB-P) for major taxonomic groups at each site. Also included is percentage of total benthos in rock scrape samples (% TB-R). Presque Isle 1

Presque Isle 2

Presque Isle 3

X

OJoTB-P

%TB-R

X

%TB-P

%TB-R

Amphipoda Naididae Chironomidae Ephemeroptera Trichoptera Gastropoda Oribatei Hydracarina Other

10.0 20.7 71.5 6.4 3.2 0.0 0.7 9.4 21.0

7.0 14.5 50.0 4.5 2.2 0.0 0.5 6.6 14.7

1.0 25.0 61.2 0.5 3.8 1.3 0.5 2.5 4.2

24.8 24.8 148.7 3.5 38.9 2.7 0.0 7.1 18.6

9.2 9.2 55.3 1.3 14.5 1.0 0.0 2.6 6.9

1.2 5.8 57.5 2.3 9.2 0.5 2.3 16.3 4.9

Total benthos

143.0

Taxon

269.0

Grand Traverse Bay 1 Taxon Amphipoda Naididae Chironomidae Ephemeroptera Trichoptera Gastropoda Oribatei Hydracarina Other Total benthos

%TB-P

%TB-R

X

838.9 82.9 168.2 1.5 1.6 1.3 68.7 30.8 135.5

63.1 6.2 12.7 0.1 0.1 0.1 5.2 2.3 10.2

17.5 7.3 19.0 0.1 0.6 0.0 31.4 1.4 22.7

37.9 56.8 324.3 4.1 3.6 76.0 191.7 45.0 67.7

1,328.6

805.9

Average similarity values among rock scrape samples (CC = 30%, PSc = 30%) were significantly greater than among pumped samples (CC = 26070, PSc = 24%) (ex = 0.10, Scheffe multiple comparison) (Figs. 2, 3). This result suggested benthic community structure and composition based on rock scrapes were more similar among sites than were those based on pumped samples. We suspect this difference is related to the number of microhabitats sampled by the two techniques. Rock scrapes sampled a more limited number of microhabitats (surface, sides, bottom, crevices, associated plant or mineral cover) than did pumped samples (all the previous microhabitats plus interstices among rocks, various substrates, and associated detrital floc and periphytic and macrophytic growth). In addition, the area sampled by the pumping technique in nearly all cases probably exceeded that of the rocks. A smaller number of microhabitats and area samples might be expected to support fewer benthic species and a different community structure.

222.0 1,617.1 1,375.9 3.7 3.4 4.7 22.8 10.0 163.9

%TB-P

%TB-R

6.5 47.4 40.3 0.1 0.1 0.1 0.7 0.0 4.8

1.6 13.9 70.5 0.6 6.0 0.0 4.7 0.0 2.7

3,414.3

Grand Traverse Bay 2

X

X

%TB-P 4.7 7.0 40.2 0.5 0.4 9.4 23.8 5.6 8.4

Grand Traverse Bay 3

%TB-R

X

%TB-P

%TB-R

0.9 3.7 29.5 0.1 0.2 0.1 58.0 0.8 6.7

26.7 149.3 176.0 0.2 2.0 16.3 10.7 98.7 56.9

5.0 27.8 32.8 <0.1 0.4 3.0 2.0 18.4 10.6

0.1 27.2 47.2 0.0 0.4 1.5 3.6 3.6 16.4

537.0

The degree of similarity among sites based on rock scrapes was surprising given the physical variability among sites (Table 1). Rock type included granite, limestone shale-like rock (clayey), and sandstone. Surface texture varied from smooth, to rough, to honeycomb, with coatings of travertine, periphyton, or only a thin layer of diatoms. At all sites, the underlying substrates were composed of a variety of pebbles, gravel, and sands. The similarity of benthic communities among widely disparate geographic locations likely arises from the fact that most benthic organisms encountered were collectors, grazers, and gathering forms or predators (Coffman 1978, Pennak 1978). This being the case, we conclude that microhabitat diversity as expressed by rock type, texture, and plant or mineral cover had minimal effect on benthic community structure and composition among rocky sites. It is possible that the single most important factor influencing site similarity based on rock scrapes may be a similarly exploitable food source (algae and diatoms). A similar result was

11

BENTHOS OF ROCKY HABITATS IN LARGE LAKES TABLE 3. Continued Grand Traverse Bay 4

Grand Traverse Bay 5

X

OJoTB-P

%TB-R

X

%TB-P

%TB-R

Amphipoda Naididae Chironomidae Ephemeroptera Trichoptera Gastropoda Oribatei Hydracarina Other

461.2 29.6 47.5 2.6 1.3 6.5 27.9 25.1 190.9

57.0 3.7 5.9 0.3 0.2 0.8 3.4 5.1 23.6

2.5 11.9 22.2 0.0 0.1 0.0 32.0 0.5 30.8

636.7 9.5 285.5 743.2 146.8 52.4 2.4 262.7 50.5

29.0 0.4 13.0 33.9 6.7 2.4 0.3 12.0 2.3

7.0 11.5 63.3 2.3 1.4 0.1 4.0 7.8 2.6

Total benthos

809.0

Taxon

2,194.4 Charlevoix

X

1,181.4 28.4 3,294.7 224.0 17.5 247.9 123.1 75.7 250.6

X

%TB-P

Amphipoda Naididae Chironomidae Ephemeroptera Trichoptera Gastropoda Oribatei Hydracarina Other

70.4 9.5 104.5 4.3 6.1 11.2 5.0 14.6 72.8

23.6 3.2 35.0 1.4 2.0 3.8 1.7 4.9 24.4

1.8 9.2 64.3 0.2 1.1 1.0 12.8 3.1 6.5

Total benthos

298.3

%TB-P

%TB-R

21.7 0.5 60.5 4.1 0.3 4.6 2.3 1.4 4.6

4.5 3.4 57.4 0.5 1.0 <0.1 12.9 2.7 17.6

5,447.6 Keuka Lake

%TB-R

Taxon

Grand Traverse Bay 6

All Sites Combined

X

%TB-P

%TB-R

X

%TB-P

%TB-R

487.6 0.0 331.4 18.3 0.0 114.2 14.2 66.3 24.3

46.2 0.0 31.4 1.7 0.0 10.8 1.3 6.3 2.3

9.4 2.4 65.1 5.4 0.6 0.8 12.9 0.8 2.6

358.1 194.1 593.9 95.3 19.5 45.3 43.8 57.7 104.3

23.7 12.8 39.3 6.3 1.3 3.0 2.9 3.8 6.9

7.2 7.9 43.5 0.8 1.2 0.2 22.7 3.1 13.4

1,055.6

found by Barton (1986) who concluded, using depth and substratum ordination analyses, that the Ontario shore of Lake Ontario had no unique assemblages of benthic species. Trophic status or water quality differences had the most impact on species composition. Differences between rock scrape and pumped sample estimates of community structure and composition were exacerbated by sampling error inherent in the two collection methods. Pumped samples offered a more instantaneous and thorough estimate of the benthos, except those forms tightly adhering to rock surfaces, inhabiting undersurfaces, or lodged in crevices. Rock scrapes, though theoretically collecting those potentially missed by pumped samples, underestimated forms capable of escape (Amphipoda). The inevitable disturbance to the benthic community due to movement through the water column and handling by divers in all likelihood altered existing community structure and composition occurring on rocks. Another factor which undoubtedly affected

1,512.3

comparisons between the two techniques was area sampled. Whereas pumped samples averaged 1.8 m2 , the area from rock scrapes, though not known, was likely less than that of pumped samples. Sampling larger areas is expected to yield greater numbers of species. These methodological differences probably skewed comparisons. However, the likelihood of a more thorough, instantaneous sample of a wider variety of microhabitats and the assurance of a measurement of area sampled led us to conclude that pumped samples are superior estimators of benthic community structure and composition. Thus, inter-site comparisons we make hereafter will use pumped samples only. Inter-site Comparisons Based on Pumped Samples

Cluster analysis of pumped samples grouped sites into two major clusters (Cluster I and 2) each of which was comprised of two sub-clusters of sites (Cluster lA, IB, and Cluster 2A, 2B) (see Fig. 4)

12

WINNELL and JUDE

PERCENT SIMILARITY OF COMMUNITY

FIG. 2. Percent similarity of community and coefficient of community values for the benthos of pooled rock scrape samples at 12 rocky sites (see Fig. 1) during autumn 1983. Dark shading indicates high affinity, cross-hatching indicates moderate affinity, and unshaded areas indicate low affinity. Numbers within each box are values for the two indices.

(cophenetic coefficient = 0.72). Cluster 1 sites were dominated by Chironomidae and Naididae, while Cluster 2 sites were dominated by Chironomidae and Amphipoda (Table 4). Chironomidae was the dominant major group in both clusters, making up 40010 TBD in Cluster 1 sites and 38% TBD in Cluster 2 sites. Although having similar percentages in the two clusters of sites, chironomid occurrence was less variable among Cluster 1 sites (33-55% TBD) than among Cluster 2 sites (3-91 % TBD). Naididae generally comprised a more substantial portion of the benthos (37% TBD, ranging 7-47% TBD) in Cluster 1 sites than in Cluster 2 sites (2% TBD, ranging 0-6% TBD). Amphipoda, largely Hyalella azteca, was notably more domi-

nant (32% TBD, ranging 22-63% TBD) among Cluster 2 sites than among Cluster 1 sites (6% TBD, ranging 5-9% TBD). Acarina, largely Hydrozetes sp., occurred frequently at all sites. However, Acarina comprised a more consistent, though not always greater proportion of the benthos in the second cluster sites (6% TBD, ranging 4-12%) than in the first cluster sites (8% TBD, ranging < 1-29% TBD). The wide range of Acarina values among Cluster 1 sites allowed the subdivision of these sites into those of Lake Superior (l % TBD, ranging < 1-7% TBD) and Grand Traverse Bay sites 2 and 3 (26% TBD, ranging 20-29% TBD) (Fig. 4, Table 4). Sites in the second cluster were subdivided based

BENTHOS OF ROCKY HABITATS IN LARGE LAKES

13

PERCENT SIMILARITY OF COMMUNITY

FIG. 3. Percent similarity of community and coefficient of community values for the benthos of pooled pumped samples at 12 rocky sites (see Fig. 1) during autumn 1983. Dark shading indicates high affinity, cross-hatching indicates moderate affinity, and unshaded areas indicate low affinity. Numbers within each box are values for the two indices.

on differences in amphipod and chironomid dominance. Among Cluster 2A sites (Grand Traverse Bay sites 1 and 4 and Keuka Lake, New York) Amphipoda made up 58010 TBD (ranging 46-63010 TBD) and Chironomidae made up 14010 TBD (ranging 6-31010 TBD). However, among Cluster 2B sites (Grand Traverse Bay sites 5 and 6 and Charlevoix site) the trend was opposite. Amphipod dominance was reduced to 24010 TBD (ranging 22-29010 TBD) and chironomid dominance increased to 46010 TBD (ranging 13-61010 TBD) (Table 4). Despite differences among sites as evidenced by pumped samples, and while PSc and CC values indicated low to moderate site communalities for

community structure and composition, the dominant forms within each major benthic group (Amphipoda, tribes of Chironomidae, Naididae, etc.) were remarkably similar. The same forms regularly constituted the dominant three to five taxa within each major group. The variety of rare individuals and the percent variability among the benthic components at each site resulted in moderate to low CC and PSc values that obscured the underlying similarity among sites where associations of dominant taxa appeared frequently, regardless of site. From these analyses, two opposing conclusions can be drawn. First, differences among sites were consistently attributable to minor variations in the population of H. azteca. Second, despite

14

WINNELL and JUDE

Cluster No. resque Isle I

~

I A Presque Isle 2 [ resque Isle 3

f--

Grand Traverse Boy 2

IB

~

L

Grand Traverse Boy 3

Campbell Grand Traverse Boy I

~

2 A Keuka Lake [ Grand Traverse Boy 4

2 Grand Traverse Boy 5

r--

2B Grand Traverse Boy 6

~

[ Charlevoix I

1.0

i

0.8

i

06

•

i

0.4

0.2

Similarity

FIG. 4. Cluster dendrogram for pooled pumped samples based on benthic invertebrates expressed as a percentage of total benthos. Cophenetic correlation = 0.72.

these differences the benthic fauna of both rock scrape and pumped samples was very similar among sites. The majority of benthic invertebrates collected were pollution intolerant and facultative forms (Mason et al. 1971, Lewis 1974, Hilsenhoff 1982). As was observed by Barton and Hynes (1978), many benthic forms of the rocky habitats are well represented in lotic environments (Hynes 1970), suggesting a confluence of the lentic and lotic systems. The similarity among communities regardless of site and the presence of similar trophic forms leads us to conclude that trophic conditions among sites were fairly similar. In support of this claim are results from water chemistry comparisons which showed no differences among sites of biological importance (unpublished data, Great Lakes Research Division, Univ. Mich., Ann Arbor, MI). Ranges (mg/L) for five parameters were: silica 0.8 (Lake Michigan) to 3.9 (Lake Superior); nitrate 0.15 (Lake Keuka) to 0.31 (Lake Superior); soluble reactive phosphorus 0.001 (Lake Michigan) to 0.009 (Keuka Lake); chloride 1.7

(Lake Superior) to 11.9 (Keuka Lake); ammonia 0.002 (Lake Superior) to 0.037 (Lake Michigan); and dissolved oxygen 9.8 to 13.3. We suspect that the variables which best accounted for observed biological differences among sites, especially site-specific proportional differences of Hyalella, were the physical variables of water temperature, shelter from severe wave activity, interstitial depth among rocks, topographical relief of each site, and amount of periphyton, macrophytes, and detrital floc. Possibly the factors most affecting occurrence of Hyalella at each site were topographical relief, rock type, and degree of shelter from severe weather; all of those in part or together afford protection against wave action. Barton and Hynes (1976) commonly observed Hyalella on most of the exposed rocky shorelines of the Great Lakes. However, they found them most often in areas sheltered from direct wave action. Krecker and Lancaster (1933) and Barton and Hynes (1978) reported greatest diversity of benthos in rocky areas characterized by flat or angular "rubble," postulating that this rock configuration allowed the greatest degree of protection of the substrate at sites exposed to wave action. At all sites where Hyalella composed < 40010 of the benthos [Grand Traverse Bay sites 1 (62% Hyalella» and 4 (41 % Hyalella) and Keuka Lake (45% Hyalella)] , the rock type was characterized by angular to very angular rocks (Table 1). At these sites, maximal interstitial depth and relief were recorded, although shelter from wave action varied. Among the three sites where Hyalella comprised 20-30% of the benthos, Grand Traverse Bay site 6 (22% Hyalella) offered maximal shelter, though minimal interstitial depth and relief, and Grand Traverse Bay site 5 (25% Hyalella) offered beds of Chara, which are often associated with occurrence of Hyalella (Cooper 1965). The Charlevoix site (23 % Hyalella) is exposed to severe wave action and is seemingly the most inhospitable and physically controlled of the three sites. The poor shelter afforded by this site is reflected not only by reduced numbers of Hyalella (68 m- 2), but also in reduced total benthic abundance. Consequently, the elevated percentage attributable to Hyalella is associated with overall low benthic density. Grand Traverse Bay sites 2 and 3, where Hyalella comprised only a small percentage of the benthos (5% and 4%, respectively), had minimal interstitial depth and topographical relief. The exposure of Grand Traverse Bay site 2 to wave action was minimal, while for site 3, it was maxi-

BENTHOS OF ROCKY HABITATS IN LARGE LAKES

15

TABLE 4. Mean density (X, no. m-1) and percentage of total benthos (% TB-P) for major taxonomic groups at each cluster of sites as determined from cluster analysis (see Fig. 4). Cluster 1 Taxon Amphipoda Naididae Chironomidae Ephemeroptera Trichoptera Gastropoda Oribatei Hydracarina Other Total benthos

OJoTB

X

OJoTB

X

OJoTB

68.7 412.5 449.3 3.6 7.0 21.9 50.2 34.8 70.5

6.1 36.9 40.2 0.3 0.6 2.0 4.5 3.1 6.3

97.8 660.1 608.7 4.8 10.4 2.4 9.4 5.2 78.3

6.6 44.7 41.2 0.3 0.7 0.2 0.6 0.4 5.3

32.3 103.1 250.1 2.2 2.8 46.2 101.2 71.8 61.1

4.8 15.4 37.3 0.3 0.4 6.9 15.1 10.7 9.1

1,118.8

1,476.7

Cluster 2 Taxon Amphipoda Naididae Chironomidae Ephemeroptera Trichoptera Gastropoda Oribatei Hydracarina Other Total benthos

Cluster 1B

Cluster 1A

X

671.5 Cluster 2B

Cluster 2A

X

OJoTB

X

OJoTB

624.1 29.1 739.3 179.0 31.5 68.4 42.6 80.4 135.0

32.4 1.5 38.3 9.3 1.6 3.5 2.2 4.2 7.0

617.6 45.0 152.6 5.3 1.1 25.9 41.5 35.6 142.9

57.9 4.2 14.3 0.5 0.1 2.4 3.9 3.3 13.4

1,928.3

mal. The low proportion of Hyalella at Grand Traverse Bay site 3 was expected given the high degree of exposure to wave action coincident with minimal shelter, but this was not expected at Grand Traverse Bay site 2. Little explanation can be offered as to why Hyalella occurred in such low proportions at Grand Traverse Bay site 2, except that the largely flat area covered by rounded cobble, gravel, and sand did not provide suitable shelter or habitat for Hyalella. While it is incongruous that the benthos at the Charlevoix site with a similar rocky substrate but considerably increased exposure to severe wave action would be dominated by Hyalella to a greater extent than would Grand Traverse Bay site 2, the benthic standing stock was considerably less. Given that Hyalella comprised 16070 of the benthos in one replicate but < 1% in another at Grand Traverse Bay site 2, considerable variability or sampling error is suggested. While Presque Isle sites 1 (angular rocks) and 2

1,066.2

X

629.5 15.8 1,228.2 323.8 56.8 103.9 43.5 117.7 132.3

OJoTB 23.8 0.6 46.4 12.2 2.1 3.9 1.6 4.4 5.0

2,646.8

(boulders and cobble) had rocky habitats similar to those in Lake Michigan that supported Hyalella in large percentages, the benthos at Lake Superior sites had minimal proportions of Hyalella. The colder water temperatures at Lake Superior sites may have limited the Hyalella population. Cooper (1965) determined that growth was negligible at lOoC, minimal at 15°C, and greatest at 20-25°C. We speculate that decreased densities and relative proportions of Hyalella at the three Lake Superior sites may be due in part to lower average summer temperatures and temperature maxima that are of shorter duration than at other sites, thereby lowering productivity. There was clearly a very complicated and interactive relationship among the physical factors characterizing the rocky habitats and the relative dominance of Hyalella azteca. However, a factor not yet considered is the role of fish predation in altering benthic community structure, particularly among forms like Hyalella which could be easily

16

WINNELL and JUDE

seen by fish. While we have no evidence to suggest this may have affected our results, this factor was not measured and therefore cannot be overlooked as a factor which could strongly influence observed benthic community structure. However, regardless of biological and physical differences noted among sites and possible causes for their differences, there remained a remarkable similarity of benthic components occurring in rocky habitats from widely separated geographic locations. Occurrence of dominant genera and species was surprisingly consistent. Consequently, even though dominance of particular benthic forms varied, similarities among rocky habitats were more striking than were differences. We conclude that similarities in benthic diversity among rocky sites suggested uniform trophic conditions and that dissimilarities were a function of changes in physical characteristics either acting within or upon the sites. ACKNOWLEDGMENTS

Our stalwart scuba divers, Mary Sweeney, Pam Mansfield, Janet Huhn, Laura and George Noguchi, Nancy Thurber, Tom Rutecki, Jim Wojcik, and Dan Hendrix are gratefully acknowledged for bravely plying cold Great Lakes waters in quest of benthos. We thank Cliff Tetzloff and the crew of the R/V Laurentian for their assistance on the Campbell Plant trip. We based some of our study design on earlier, similar work on Lake Huron by Bruce Manny, Great Lakes Fishery Laboratory, Ann Arbor, Michigan. Bev McClellan helped prepare text. This research was sponsored by Michigan Sea Grant Program with a grant, NOAA 80-D-000n, from the Office of Sea Grant, National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce, and funds from the State of Michigan. The U.S. Government is authorized to produce and distribute reprints for governmental purposes notwithstanding any copyright notation appearing herein. Contribution No. 450 of the Great Lakes Research Division, University of Michigan. REFERENCES Alley, W. P., and Mozley, S. C. 1975. Seasonal abun-

dance and spatial distributions of Lake Michigan macrobenthos, 1964-67. Great Lakes Res. Div. Spec. Rep. No. 54, Univ. Mich., Ann Arbor, Mich. Anderberg, M. R. 1973. Cluster Analysis for Applications. Academic Press, New York.

_ _ _ _ , and Griffiths M. 1984. Benthic invertebrates of the nearshore zone of eastern Lake Huron, Georgian Bay, and North Channel. J. Great Lakes Res. 10:407-416. Barton, D. R. 1986. Nearshore benthic invertebrates of the Ontario waters of Lake Ontario. J. Great Lakes Res. 12:270-280. _ _ _ _ , and Hynes, H. B. N. 1976. The distribution of Amphipoda and Isopoda on the exposed shores of the Great Lakes. J. Great Lakes Res. 2:207-214. _ _ _ _ , and Hynes, H. B. N. 1978. Wave-zone macrobenthos of the exposed Canadian shores of the St. Lawrence Great Lakes. J. Great Lakes Res. 4:27-45. Bocsor, J. G., and Judd, J. H. 1972. Effect of paper plant pollution and subsequent abatement on a littoral macroinvertebrate community in Lake Ontario: preliminary survey. In Proc. 15th Con! Great Lakes Res., pp. 21-34. Internat. Assoc. Great Lakes Res. Brinkhurst, R. 0., and Jamieson, B. G. 1971. Aquatic Oligochaeta of the World. Oliver and Boyd, Edinburgh. Chekanovskaya, O. V. 1981. Aquatic Oligochaeta of the USSR. Translated from Russian for the U.S. Dept. Int. and Nat. Sci. Foundation. Amerind Publ. Co. Pvt. Ltd., New Delhi, India. Coffman, W. P. 1978. Chironomidae. In An introduction to the aquatic insects of North America. ed. R. W. Merritt and K. W. Cummins, pp. 345-376. Kendall/Hunt Pub. Co. Dubuque, Iowa. Cook, D. G. 1975. A preliminary report on the benthic macroinvertebrates of Lake Superior. Fish. Res. Board Canada Tech. Rep. 572. Cooley, W. W., and Lohnes, P. R. 1971. Multivariate Data Analysis. Wiley and Sons Publ., New York. Cooper, W. E. 1965. Dynamics and production of a natural population of a fresh-water amphipod, Hyalella azteca. Ecol. Monogr. 35:377-394. Dorr III, J. A., and Flath, L. E. 1984. A portable, diver-operated, underwater pumping device. Prog. Fish-Cult. 46:219-220. Hilsenhoff, W. L. 1982. Using a biotic index to evaluate water quality in streams. Tech. Bull. No. 132. Dept. Nat. Res., Madison, Wise. Hynes, H. B. N. 1970. The Ecology of Running Waters. Univ. Toronto Press, Toronto. Johnson, M. G., and Brinkhurst, R. O. 1971. Associations and species diversity in benthic macroinvertebrates of Bay of Quinte and Lake Ontario. J. Fish Res. Board Can. 28:1683-1697. Judd, J. H., and Gemmel, D. T. 1971. Distribution of

benthic macrofauna in the littoral zone of southeastern Lake Ontario. Lake Ontario Environ. Lab., State Univ. Oswego, N.Y.

BENTHOS OF ROCKY HABITATS IN LARGE LAKES Kinney, W. L. 1972. The macrobenthos of Lake Ontario. In Proc. 15th Conf. Great Lakes Res., pp. 53-79. Internat. Assoc. Great Lakes Res. Krecker, F. H., and Lancaster, L. Y. 1933. Bottom shore fauna of western Lake Erie: a population study to a depth of six feet. Ecology 14:79-93. Lauritsen, D. D, and White, D. S. 1979. Comparative studies of the zoobenthos ofa natural and man-made rocky habitat on the eastern shore ofLake Michigan. Great Lakes Res. Div. Spec. Rep. No. 74. Univ. Mich., Ann Arbor, MI. Lewis, P. A. 1974. Taxonomy and ecology of Stenonema mayflies (Heptageniidae: Ephemeroptera). USEPA. Cincinnati, Ohio. Manny, B. 1983. Effect of increased nutrient loading on fish spawning and nursery habitat in Great Lakes nearshore waters. Great Lakes Fishery Lab. Quart. Rep. (July-Sept.). Mason, W. T.,Lewis,P. A.,andAnderson,J. B.1971. Macroinvertebrate collections and water quality monitoring in the Ohio River Basin 1963-1967. USEPA, Cincinnati, Ohio. Mozley, S. C. 1975. Preoperational investigations of zoobenthos in southeastern Lake Michigan near the Cook Nuclear Plant. Great Lakes Res. Div. Spec. Rep. No. 56. Univ. Mich., Ann Arbor, MI. Nalepa, T. E, and Thomas, N. A. 1976. Distribution of macrobenthic species in Lake Ontario in relation to sources of pollution and sediment parameters. J. Great Lakes Res. 2:150-163. Pennak, R. W. 1978. Fresh-water Invertebrates of the United States. Wiley and Sons Publ., New York. Scott-Wasilk, J., Downing, G. G., and Leitzow, J. S. 1983. Occurrence of the Asiatic clam Corbicula fuminea in the Maumee River and western Lake Erie. J. Great Lakes Res. 9:9-13. Shelford, V. E., and Boesel, M. W. 1942. Bottom animal communities of the island area of western Lake Erie in the summer of 1937. Ohio J. Sci. 42:179-190.

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Statistical Research Laboratory. 1980. Cluster analysis in MIDAS. Univ. Mich. Stimpson, K. W., and Abele, L. E. 1984. Ripistes parasita (Oligochaeta: Naididae), a distinctive oligochaete new to North America. Freshwat. Invertebr. Bioi. 3:36-41. Teter, H. E. 1960. The bottom fauna of Lake Huron. Trans. Am. Fish. Soc. 89:193-197. White, D. S., Winnell, M. H., and Jude, D. J. 1984. Discovery of the Asiatic clam, Corbicula fluminea, in Lake Michigan. J. Great Lakes Res. 10:329-331. Whittaker, R. H., and Fairbanks, C. W. 1958. A study of plankton and copepod communities in the Columbia Basin, southeastern Washington. Ecology 39:46-65. Winnell, M. H., and Jude, D. J. 1979. Spatial and temporal distribution of benthic macroinvertebrates and sediments collected in the vicinity of the J. H. Campbell Plant, eastern Lake Michigan, 1978. Great Lakes Res. Div. Spec. Rep. No. 75. Univ. Mich., Ann Arbor, MI. _ _ _ _ , and Jude, D. J. 1980. Spatial and temporal distribution of benthic macroinvertebrates and sediments collected in the vicinity of the J. H. Campbell Plant, eastern Lake Michigan, 1979. Great Lakes Res. Div. Spec. Rep. No. 77. Univ. Mich., Ann Arbor, MI. ____ , and Jude, D. J. 1981. Spatial and temporal distribution of benthic macroinvertebrates and sediments collected in the vicinity of the J. H. Campbell Plant, eastern Lake Michigan, 1980. Great Lakes Res. Div. Spec. Rep. No. 87. Univ. Mich., Ann Arbor, MI. ____ , and Jude, D. J. 1982. Effects ofheated discharge and entrainment on benthos in the vicinity of the J. H. Campbell Plant, eastern Lake Michigan, 1978-1981. Great Lakes Res. Div. Spec. Rep. No. 94. Univ. Mich., Ann Arbor, MI.