Benthic Macroinvertebrates as Indicators of Environmental Degradation in the Southern Nearshore Zone of the Central Basin of Lake Erie

J. Great Lakes Res. 10(2): 197- 209 Internat. Assoc. Great Lakes Res., 1984

BENTHIC MACROINVERTEBRATES AS INDICATORS OF ENVIRONMENTAL DEGRADATION IN THE SOUTHERN NEARSHORE ZONE OF THE CENTRAL BASIN OF LAKE ERIE

Kenneth A. Krieger Water Quality Laboratory Heidelberg College Tiffin, Ohio 44883

ABSTRACT. The benthic macroinvertebrates of the central basin ofLake Erie were sampled with a Ponar grab in the summers of 1978 and 1979 along a 155-km reach of the nearshore zone (:s 12 km offshore) in Ohio, U.S.A., at depths of less than 20 m. The major groups and their most abundant species were, in order of overall abundance, Oligochaeta (Limnodrilus hoffmeisteri, L. cervix-L. claparedeianus group, L. maumeensis), Sphaeriidae (Pisidium caseTtanum, Po hens}owanum, Sphaerium corneum, Musculium transversum), and Chironomidae (procladius sp., Chironomus spp.). The average abundance of oligochaetes in the harbors was 21,000 individuals m-2 in 1978 and 12,700 m-2 in 1979, compared with 1,500 m-2 and 1,200 m-2, respectively, in the areas outside of harbors. Comparison of the macrobenthic assemblages with those in other regions of the Great Lakes, using several numerical indices as well as indicator species distributions, indicated that the general area of the nearshore zone outside of harbors possesses a moderate degree of Qrganic enrichment, with a gradient ofdecreasing pollution in an offshore direction. The harbors appeared to be severely degraded, as reflected by the high densities of oligochaetes and the almost complete absence ofall but the most pollution-tolerant species. The documentation ofspecies distributions will enable future assessments of changes in the nearshore benthic communities. ADDITIONAL INDEX WORDS: Pollution, organic matter, oligochaetes, chironomids.

INTRODUCTION The environmental degradation of Lake Erie, which has been a focus of research for decades, is reflected in changes observed in all major groups of its biota (Brinkhurst 1969, Dambach 1969, Cap and Frederick 1981). Most of the benthic macroinvertebrate studies have been conducted in the shallow western basin (summarized by Britt et af. 1973; Cones 1976), augmented by a few investigations in the offshore areas of all three basins (e.g., Brinkhurst et al. 1968). Veal and Osmond (1968) characterized the macroinvertebrate assemblages of the western basin and the Canadian nearshore zone « 8 km offshore) of the central and eastern basins, and Barton and Hynes (1978a, 1978b) described the community composition and dynamics in the wave zone « 2 m deep) of the Canadian shores of all three basins. Almost no historical information regarding the macrobenthic fauna of the southern nearshore zone of the central basin is available, the exception

being the pollution survey of Brown (1953) at the mouths of 10 southern tributaries. It is within the nearshore zone, however, that the most severe chemical pollution and organic enrichment have occurred as the result of heavy industrialization and dense urbanization. The region is used extensively for commercial and sport fishing, recreational boating, and water supplies. Through the Great Lakes International Surveillance Plan developed under the Great Lakes Water Quality Agreement of 1972, the Canadian and United States governments sponsored the Lake Erie Intensive Study of the physical, chemical, and biological limnology of the lake. Field sampling was conducted in 1978 and 1979 by approximately 25 organizations at over 500 stations within offshore and nearshore compartments. The objectives of the 2-year intensive study, stated specifically elsewhere (Winklhofer 1978), were to provide a detailed assessment of pollutant inputs to the lake and of the current condition of the lake, to identify

197

198

K. A. KRIEGER

emerging problem areas, and to detect changes in water quality on a broad geographic and historical basis. The purpose of this report is to document the macroinvertebrate communities and species distributions in the nearshore zone of the central basin in 1978 and 1979 in order to permit future assessments of changes in the community, and to evaluate the extent of environmental degradation in this area by comparing its benthic species associations with those in severely degraded regions of the other Laurentian Great Lakes. STUDY AREA The macroinvertebrates were sampled along a 155km reach of the nearshore zone in Ohio which parLAKE

-

57- -

alleled the shoreline of most of the southern central basin (Fig. 1). Station depths at the time of sampling ranged from <2 m close to shore to > 15 m at the most offshore stations (12 km). Bottom substrates varied throughout the study area (Fig. 2). On the basis of grab samples, the substrates were described as predominantly soft clay, fine to coarse sand, or a mixture of these, often with a layer of silt at the surface. Stations with impenetrable substrates, which included shale, hard clay, coarse sand, and pebbles, were not successfully sampled or yielded only small qualitative samples. Duplicate samples, and samples obtained the second year at some stations, occasionally yielded somewhat different substrates. Of 18 areas within the Great Lakes basin exhibit-

ERIE

~-..-s6"'"

10

N

I

- Sampled both years ... Sampled in 1978 only • Sampled in 1979 only 0

I

10 I

5 I

15 km

I

I

I

I

0

5

lomi

FIG. 1. The study area, showing station numbers referred to in the text and the approximate 5-, 10-, and 15-m depth contours at the time ofsampling in 1978. Harbor breakwalls also are shown. Stations at which no grab sample could be obtained are omitted. The heavy vertical bars separate the Vermilion-Lorain, Cleveland, and Fairport Harbor-Ashtabula areas. Dashed lines through the map of Lake Erie indicate the approximate boundaries of the western, central, and eastern basins.

MACROINVERTEBRATE INDICATORS OF POLLUTION IN LAKE ERIE

ing the most severe environmental degradation, three (the Black, Cuyahoga, and Ashtabula rivers and their harbors) were within the study area. Pollutants included volatile solids, oil and grease, heavy metals, nutrients, polychlorinated compounds, cyanide, and fecal coliforms (International Joint Commission 1981). METHODS Quantitative samples were obtained with a Ponar grab (0.053 m2 area) between 16-28 June 1978 (46 stations), 1-9 September 1978 (stations 75, 94,117, 121), and 12-23 July 1979 (35 stations) (Fig. 1). Most of the stations were sampled both years. Additional stations were sampled qualitatively where only a partial grab could be obtained, and at several stations a hard substrate prevented taking any grab samples (Fig. 2). Duplicate samples were collected at only six stations each year (stations 56, 63, 76, 93, 99, and 113 in 1978; 57, 73, 102, 111, 125, and 130 in 1979). At the remaining stations only a single grab was taken each year. The fresh samples were sieved in a stainless steel wash frame with 0.52-mm mesh openings by spraying with a strong stream of lake water. The sieved samples were preserved in an aqueous solution of 85% ethanol and 5070 glycerin and were stained with Phloxine B prior to sorting. All individuals in the samples were identified except where large numbers of oligochaetes were present. In these instances, one or more subsamples were randomly chosen until at least 100 anterior ends (immature or adult) were obtained. Unidentifiable immatures with and without hair setae were assigned to those species which can be keyed only as adults in the same proportions as the identified adults in each

199

sample, a practice similar to that adopted by others (Howmiller and Scott 1977). Quantitatively sampled stations outside of harbors were grouped into three alongshore areas (Vermilion-Lorain, Cleveland, Fairport HarborAshtabula) for comparison with each other and with the harbor stations (Fig. 1). Stations at harbor entrances (except Station 66) were grouped with the harbor stations as was a station just outside the northwest corner of Cleveland Harbor. RESULTS The coefficients of variation for total numbers of organisms in duplicate samples ranged from 24.9% to 99.9% in 1978 and from 12.0% to 96.3070 in 1979. Downing (1979) found that the variance of benthic data in general was less than the mean in only 2.5% of 1,500 sets of replicated samples. The macrobenthic fauna were dominated by the Oligochaeta, Sphaeriidae, Chironomidae, and Crustacea, in order of their overall abundance. Together these groups contributed from 85.5% to 100% of the total organisms in each of the four areas studied (Table 1). The Sphaeriidae and Chironomidae were more abundant in all areas in 1979 than in 1978, whereas the Oligochaeta were less numerous everywhere except in the Fairport Harbor-Ashtabula area, where they showed an increase. The Crustacea, which consisted almost entirely of the isopod Asellus racovitzai racovitzai Williams and the amphipod Gammarus fasciatus Say, were only occasionally major contributors to the fauna and were much less abundant in three of the four areas in 1979 than in 1978.

Rocky R

FIG. 2. The distributions ofpredominant substrate types, classified upon sampling in 1978 as soft clay, sand, a hard substrate, or a combination of these.

200

K. A. KRIEGER

TABLE 1. Mean number m-2 and contribution (%) ofmajor macroinvertebrate groups in 1978 and 1979 in four areas of the southern nearshore zone of Lake Erie. The first three areas combined form the Open area. Where replicated samples were taken at a station, the values were averaged. Significant differences were determined using the Mann- Whitney U test. VermilionLorain Number of Stations

Cleveland

Fairport HarborAshtabula

Open

Harbors

1978

1979

1978

1979

1978

1979

1978

1979

1978

1979

10

4

18

11

11

10

11

10

39

25

1,498*** 57.9

1,228*** 34.7

Oligochaeta Mean 070

1,597*** 64.8

226** 9.5

1,753*** 60.7

1,059** 27.8

989*** 44.9

1,815*** 50.2

21,090 97.4

12,676 87.1

54+ + 2.2

1,238 51.9

778+ + 26.9

1,884 49.4

436 19.8

565 15.6

454 2.1

581 4.0

496 19.2

1,253 35.4

Sphaeriidae Mean 070 Chironomidae 259* 10.5

906 38.0

294** 10.2

528 13.8

351** 15.9

587 16.2

61 0.3

1,061 7.3

301** 11.6

612 17.3

Mean 070

196 8.0

3* 0.1

36 1.2

19* 0.5

232 10.5

346 9.6

45 0.2

18* 0.1

132 5.1

147* 4.1

Cumulative 070

85.5

99.5

99.0

91.1

91.6

100.0

98.5

93.8

91.5

Mean 070 Crustacea

*Significantly different **Significantly different ***Significantly different + +Significantly different *Significantly different

from from from from from

91.5

Harbors at p<0.05. Harbors at p
Oligochaetes were significantly more abundant in the harbors than in the open areas (Table 1), with mean numbers in the harbors of 21,000 individuals m- 2 in 1978 and 12,700 m-2 in 1979. The Sphaeriidae and Chironomidae did not show a consistent pattern of abundance. The Crustacea were generally less abundant in the harbors than elsewhere and were significantly more abundant toward the eastern end of the study area in 1979 (Table 1). The oligochaetes, sphaeriid clams, and midges separately or together constituted a large majority of the individuals in all but three samples, where hydras (station 61, 1978), isopods and snails (station 134, 1978), or leeches and isopods (station 125, 1979) were the major contributors. Amphipods, nematodes, snails, hydras, isopods, and leeches each comprised >5010 of the macroinvertebrates in several samples. Other taxa (Table 2) were collected infrequently and in low numbers. The abundance and species richness of the turbellarians, nematodes, polychaetes, naidids, water mites, and ostracods were undoubtedly greater than the samples indicated. In general, soft sandclay or clay sediments yielded greater numbers of

macroinvertebrates than did sand and other, less penetrable substrates. Because of their importance throughout the study area and in other areas of the Great Lakes, the oligochaetes, sphaeriid clams, and midges are treated in detail below. Oligochaeta The oligochaete nomenclature accepted by Brinkhurst and Jamieson (1971) with recent revision of the genus Peloscolex (Brinkhurst 1979, 1981) is followed herein. Most specimens of Limnodrilus c1aparedeianus and L. cervix, which originally were identified separately in my samples, appeared to be intermediate between the two species (see Brinkhurst and Jamieson 1971). Because of the uncertainty of these identifications, I have grouped all individuals of the two species together as L. cervix-L. c1aparedeianus. Tubificids were represented by 17 species, of which 12 were found at > 10% of the stations (Table 3). Less frequently encountered were Aulodrilus Iimnobius Bretscher, A. pigueti Kowalewski, Isochaetides freyi (Brinkhurst) , Limnodrilus

MACROINVERTEBRATE INDICATORS OF POLLUTION IN LAKE ERIE

201

TABLE 2. Macroinvertebrate taxa other than Tubificidae, Sphaeriidae, and Chironomidae collected in the study area.

CNIDARIA, Hydridae PLATYHELMINTHES, Turbellaria NEMATODA ANNELIDA Polychaeta Manayunkia speciosa (Leidy) Oligochaeta Naididae ?Amphichaeta sp. Arcteonais /omondi (Martin) Nais elinguis Muller Ophidonais serpentina (Muller) Hirudinea ?Erpobdella sp. He/obdella stagnalis (Linnaeus) ARTHROPODA ACARINA Lebertiidae CRUSTACEA Amphipoda Gammarus fasciatus Say Isopoda Asellus racovitzai racovitzai Williams Ostracoda, Candonidae INSECTA Coleoptera ?Hydrochus sp. Stene/mis sp.·

Diptera Ephydridae ?Stratiomyidae Ephemeroptera Caenis sp. Stenonema sp.· Odonata Ischnura sp.· Plecoptera• Trichoptera Oecetis sp. Po/ycentropus sp. MOLLUSCA BIVALVIA Unionidae Lampsi/is sp. Proptera a/ata (Say)· GASTROPODA Hydrobiidae Amnico/a limosa (Say) Bithynia tentacu/ata (Linnaeus) Physidae Physella sp. Planorbidae Helisoma sp. Pleuroceridae Goniobasis livescens (Menke) P/eurocera acuta Rafinesque Valvatidae Va/vata /ewisi Currier Va/vata piscinalis (Muller) Va/vata tricarinata (Say)

·Collected only at stream mouth.

angustipenis Brinkhurst & Cook, and Tubijex tubifex (Muller). Limnodrilus hoffmeisteri was much more abundant than any other species throughout the study area (Table 3), contributing from 33 to 68070 of all individuals. The L. cervixL. claparedeianus group was the second largest contributor (8 to 31070). The distributions of several species followed distinct patterns, discussed later. Sphaeriidae The sphaeriid nomenclature agrees with that used by Mackie et al. (1980). Sphaeriid clams, represented by 13 species, were collected at 79070 of the stations in 1978 and 60070 in 1979. Except in the Fairport Harbor-Ashtabula area, they contributed substantially more to the macrobenthos in 1979 than in 1978. The sphaeriids were, overall, 2.5X more abundant in 1979 than in 1978 in the open

lake, but the data suggest only a slight increase in the harbors (Table 1). Pisidium casertanum (Poli) was by far the most widely distributed species, occurring in samples from over half of the stations in each area. Its average abundance was highly variable among the alongshore areas, but overall it tended to be only half as abundant in the harbors as in the open lake (Table 4). Most of the apparent differences in abundances between areas of this and the other macroinvertebrate species were not statistically validated because of the large variances among individual samples, as indicated by the coefficients of variation. Pisidium henslowanum (Sheppard) was approximately as abundant as P. casertanum in the two western areas but was much sparser in the Fairport Harbor-Ashtabula area and in the harbors (Table 4). It was collected at proportionally fewer stations

202

K. A. KRIEGER

TABLE 3. Percent contributions to total oligochaetes of those species encountered at > 10% of all stations. Area VermilionLorain Year Number of Stations

Aulodrilus americanus Brinkhurst & Cook A. pluriseta (Piguet) Branchiura sowerbyi Beddard Limnodrilus cervix BrinkhurstL. c1aparedeianus Ratzel L. hoffmeisteri Claparede L. maumeensis Brinkhurst & Cook L. udekemianus Claparede Potamothrix moldaviensis Vejdovsky & Mrazek P. vejdovskyi (Hrabe) Quistadrilus multisetosus (Smith) Spirosperma ferox (Eisen) Cumulative Percent Mean worms m-2

1978 10

Fairport HarborAshtabula

Cleveland 1978 18

1979 4

1979 11

1979 10

1978 11

Open

Harbors 1978 11

1979 10

1978 38

1979 24

0 4.4 1.1

0 0 13.2

0 0.7 0

2.7 5.6 0.2

2.3 3.0 0

2.6 3.1 0

0 0.3 0

0 0.5 0

0.4 2.1 0.3

2.6 4.0 0.4

30.5 32.6 12.6 0.5

15.6 35.0 30.0 0

18.1 56.1 4.8 1.1

12.0 47.9 12.8 0

11.0 67.8 6.1 2.8

7.9 62.1 8.4 4.3

25.0 40.0 5.0 4.0

15.9 51.2 3.1 3.4

20.1 51.8 7.2 1.3

9.7 55.9 10.7 2.5

10.2 5.2 0 0

0 0 0 0

6.2 1.1 2.3 0.1

2.7 4.4 1.1 0.8

2.5 0.2 1.6 0.2

0.5 1.4 0.7 4.2

0.6 0.4 2.2 0

0 0 5.4 0

6.6 2.0 1.5 0.1

1.3 2.5 0.8 2.8

97.1 1,598

93.8 226

90.5 1,753

90.2 1,059

97.5 1,088

95.2 2,016

79.5 12,675

93.4 1,537

93.2 1,279

77.5 21,090

TABLE 4. Mean number m-3 and coefficient of variation (C. V,) of the five most frequently encountered sphaeriid species in 1978 and 1979 in each area. The first three areas combined form the Open area. Where replicate samples were taken at a station, the values were averaged. Significant differences were determined using the Mann- Whitney U test. VermilionLorain 1978 Number of Stations

P. casertanum

10 25+

Cleveland

1979 4

Fairport Harbor Ashtabula

Harbors

Open

1978

1979

1978

1979

1978

1979

1978

1979

18

11

11

10

11

10

39

25

541 t 97

175 146

99 114

119 266

167 162

237 161

328 131

Mean C.V.(OJo)

131

317 135

392'+ 123

P. henslowanum

Mean C.V.(OJo)

11 173

273 112

328 202

745'1 153

3 333

4+ 315

19 232

37 180

155 305

373 + 220

S. corneum

Mean C.V.(OJo)

5 200

4t 246

40 217

91 147

353" 227

69 332

2 316

28 289

160' 325

M. partumeium

Mean C.V.(OJo)

3 200

21 274

9 267

7 331

12 179

7 255

4 315

12 340

9 226

M. transversum

Mean C.V.(OJo)

0

11 303

2t 332

46 243

32 115

80 186

31 139

18 358

13 201

*Significantly different **Significantly different ***Significantly different tSignificantly different tSignificantly different +Significantly different

from from from from from from

ot 2 316 0'

Harbors at p<0.05. Harbors at p
at the eastern end of the study area but in similar proportions in the harbors and the two western alongshore areas. Of the remaining species collected at > 10% of all stations, all were encountered less frequently or were totally absent from the samples collected west of Lakewood, Ohio.

Pisidium nitidum f. paupercu/um Sterki was present mostly in the vicinity of harbors but not in them (except for two individuals in the western end of Cleveland Harbor in 1978), and Sphaerium corneum (L.), though more widespread, was also absent from the harbors except Cleveland Harbor

MACROINVERTEBRATE INDICATORS OF POLLUTION IN LAKE ERIE

(38 specimens at station 87 in 1978, one at station 86 in 1979; Fig. 1). Conversely, Musculium transversum (Say) was found in each of the harbors except at Lorain, and the harbor samples yielded, on average, 3-4X as many individuals as the open lake samples (Table 4). Other species, for which distributional patterns were not discernible, were M. partumeium (Say), P. amnicum (Muller), P. compressum Prime, P. ?li//jeborgi Esmark & Hoyer, P. subtruncatum MaIm, P. ventricosum f. ventricosum Prime, S. simile (Say), and S. striatinum f. emarginatum (Prime).

Chironomidae The midges, represented by 19 genera (Table 5), comprised the entire dipteran fauna except for two larvae collected in 1978 (Table 2), and were collected at about 85% of the stations both years. As was true of the Sphaeriidae, the Chironomidae appeared to be more abundant and to contribute a greater percentage to the total number of organisms in 1979 than in 1978 (Table 1). Although they were significantly less abundant in the harbors in 1978 than in the open lake, in 1979 the reverse appeared to be true. Of four genera found in the harbors (Chironomus, Cryptochironomus, Polypedilum, and Procladius), only Chironomus and Procladius were present in more than incidental numbers. The density of Procladius larvae was similar statistically in all areas (Table 6), although its abundance followed the same general patterns noted for the Chironomidae as a whole. Chironomus spp. were much less abundant in the harbors both years, and were completely absent in the samples from the Lorain and Cleveland harbors. Of the

remaining genera, only Cryptochironomus was widely collected, with at most three individuals in anyone sample.

Distributions in Relation to Depth The offshore data were compiled into three depth intervals (0-8 m, >8-15 m, >15 m), using only those stations which had soft clay or sand-clay sediments and could be sampled adequately. The results (Table 7) should be interpreted with caution because of the few stations in two of the categories and the absence of information on seasonal changes in distribution patterns in the study area. Most of the major species in this study appeared to be important numerically at depths of < 8 m, with the notable exceptions of the Sphaeriidae and Procladius sp. Limnodrilus hoffmeisteri was important at all depths, while L. maumeensis and Q. multisetosus seemed to be less abundant in the > 8-15 m interval. The proportion of oligochaetes to total macroinvertebrates decreased from 81 % at 0-8 m to around 43 % at greater depths, which may indicate less organic enrichment at greater depths (further from shore). Sphaeriids increased greatly in abundance and frequency at >8 m. Chironomus spp. were important at all depths, while Proc1adius sp. increased in importance at greater depths. DISCUSSION

Sampling Biases The numerical estimates for most of the invertebrate groups in this and other benthic studies are conservative because of the sample device used (Resh 1979), sieving with a strong spray from a

TABLE 5. Chironomid larvae collected in the study area. Chironominae

Chironomus ?anthracinus Zetterstedt C. ?plumosus (Linnaeus) C. ?plumosus f. semireductus Cryptochironomus spp. Demicryptochironomus sp. Dicrotendipes sp. Endochironomus sp. Glyptotendipes sp. Harnischia ?curtilamellatus (Malloch) Microtendipes caelum Townes Parachironomus sp. Phaenopsectra sp. Polypedilum ?scalaenum (Schrank)

203

Chironominae (continued)

Pseudochironomus fulviventris (Johannsen) Saetheria tylus (Townes) Stictochironomus sp. Tanytarsus sp. Orthocladiinae Cricotopus sp. Tanypodinae Coelotanypus sp. Djalmabatista sp. Procladius sp.

K. A. KRIEGER

204

TABLE 6. Mean number m-2 and coefficient of variation (C. V,) of ProcIadius sp. and Chironomus spp. larvae in 1978 and 1979 in each area. The first three areas combined form the Open area. Where replicate samples were taken at a station, the values were averaged. Significant differences (see Table 4, footnotes) were determined using the MannWhitney U Test. VermilionLorain

Number of Stations Proc/adius sp.

Mean C.V.(OJo)

Chironomus spp.

Mean C.V.(OJo)

Fairport Harbor Ashtabula

Cleveland

Open

Harbors

1978

1979

1978

1979

1978

1979

1978

1979

1978

1979

10 117 107 128* 116

4 152 44 746***+ 57

18 127 144 146* 153

11 185 134 330**t 163

11

10 544 201 38 205

11

10 1053 106 2 300

39 141 138 142* 153

25 323 221 280**+ 163

186 142 150* 181

39 105 12 175

TABLE 7. Frequency (% ofstations), mean number m-2, and coefficients of variation (C. V,) ofmajor macroinvertebrate taxa at three depth intervals in 1978 at stations having clay or sand-clay sediments. N = number of stations in each interval.

0-8 m (N =6) L. hoffmeisteri L. cervix-L.clapar. L. maumeensis Q. multisetosus P. moldaviensis P. vejdovskyi A. pluriseta % oligochaetes P. casertanum P. henslowanum Procladius sp. Chironomus spp.

>8-15 m (N = 15)

070

Mean

C.V.

%

Mean

100 67 50 33 67 33 67

1,298 813 108 130 370 44 54 81 2 0 10 213

68 132 114 198 115 175 163 42 245

80 53 7 27 20 27 47

694 150 5 6 48 37 39 42 296 61 216 89

17 0 50 50

109 170

hose (Heuschele 1982), and the mesh size employed (Brinkhurst 1974, Resh 1979, Heuschele 1982), although the procedures are consistent with most Great Lakes ·work (Johnson and Brinkhurst 1971, Mozley and Garcia 1972, Mozley and Winnell 1975). Furthermore, early summer data are not necessarily representative of the mean annual standing crop (Brinkhurst 1974, Resh 1979). For example, the later sampling dates in 1979 than in 1978 permitted a new cohort of sphaeriid clams to contribute to total clam abundance in 1979, especially offshore. Factors Influencing Macroinvertebrate Distributions Johnson and Brinkhurst (1971) noted that temperature strongly influences species diversity in the Great Lakes, where both cold oligotrophic waters

73 40 87 80

>15m(N=5)

C.V.

%

Mean

C.V.

165 143 394 197 263 287 198 62 137 225 114 118

100

972 101 251 91 0 19 8 44 688 1,006 91 382

84 111 123 87

60

60 80 0 80 40 100 80 60 100

71 137 50 87 100 95 75

and warm eutrophic waters have low species diversities. They noted that chironomids have minimal informative value in the transition from oligotrophy to eutrophy in deep cold (3-4°C) basins because of their scarcity. At higher temperatures (5-6°C) Procladius denticulatus increases in response to the increased production of its prey, the oligochaetes, except where other, adverse factors exclude this midge. The Great Lakes are at the northern limit of the range of the genus Coelotanypus, and it is apparently for this reason that these larvae seem to be restricted to the western and southern parts of Lake Erie, where the water averages several degrees warmer than elsewhere in the lake. In contrast, several other taxa commonly regarded as indicative of more oligotrophic conditions, including Tanytarsus sp., are found primarily in the cooler northern and eastern parts of the lake (Brinkhurst et al. 1968).

MACROINVERTEBRATE INDICATORS OF POLLUTION IN LAKE ERIE

Species living near their temperature limits may serve as indicators of thermal pollution. Populations of the Asiatic clam, Corbicula fluminea, which is intolerant of prolonged temperatures below 2°C, have been found in thermal plumes in western Lake Erie (Scott-Wasilk et al. 1983). The oligochaete Branchiura sowerbyi also may indicate thermal pollution (Brinkhurst and Jamieson 1971), although its known range now does not strongly support this possibility (Mozley and Howmiller 1977). Temperature may influence the productivity of this species, as several experiments have indicated, and may partly account for its absence from Lake Michigan (Mozley and Howmiller 1977) but its presence as a dominant species in western Lake Erie (Keeler 1981) and Sandusky Bay (Wolfert and Hiltunen 1968). Depth may interact with temperature to restrict the distribution of Branchiura, as in this study it was found eastward to the Rocky River but always at depths of < 15 m. For several species, the distributional patterns associated with different depths contrast sharply with patterns in southeastern Lake Michigan. Whereas P. moldaviensis was important between 8-20 m in Lake Michigan (Mozley and Garcia 1972), this species decreased in its frequency and abundance with depth in Lake Erie and was absent at depths over 15 m. At depths over 8 m, the cold stenotherm P. conventus, not P. casertanum or P. henslowanum, was numerically dominant in Lake Michigan (Mozley and Howmiller 1977). Different bottom sediments in the two areas may account for some of the disparity. All of the Lake Michigan stations at depths of < 8 m had sandy or gravelly sediments (Mozley and Alley 1973) which, as in Lake Erie, typically possess fewer macroinvertebrates. Mozley and Howmiller (1977) noted that areas without accumulated fine sediments will lack high worm counts even in the presence of heavy organic pollution. The two areas in comparison also differ markedly in their temperature regimes and the shallower depths at which predominantly finer sediments are found in Lake Erie. Evidence of Environmental Degradation The documented changes in the benthos of organically enriched areas of the Great Lakes (Britt 1955, Carr and Hiltunen 1965, Veal and Osmond 1968, Howmiller and Beeton 1971, Cook and Johnson 1974) provide valuable clues to the present conditions in the central basin nearshore zone, for which historical evidence is lacking. Oligochaetes,

205

because they comprise a major faunal group consisting of various species assemblages in habitats with all ranges of organic enrichment, have provided the basis for several indices of pollution which have been applied to the Laurentian Great Lakes. Four of these indices were applied to the present data (Table 8) to permit a comparison with earlier studies. The values of these indices were computed for each station over the 2 years of sampling, the mean values were computed for each area, and the median values and distributions of the values for each area were compared using the nonparametric Mann-Whitney U test (Sokal and Rohlf 1969, Ryan et al. 1981). The number of oligochaetes m- 2 was first applied by Wright et al. (1955) to the western basin of Lake Erie. They classified as "clean" those benthic habitats possessing fewer than 100 tubificids m-2 and more than 100 Hexagenia naiads m- 2 • The presence of < 100 mayflies and from 100-1,000 tubificids m- 2 indicated "light" pollution, 1,001-5,000 tubificids m-2 indicated "moderate" pollution, and >5,000 tubificids m-2 was evidence of "heavy" pollution. In the present study, the three open-water areas possessed similar mean numbers of oligochaetes (including the few naidids collected), which were significantly lower (p< .001) than the mean number m-2 in the harbors. Mozley and Alley (1973) found for the south end of Lake Michigan that a system defining pollution on the basis of total numbers of oligochaetes is inadequate unless they exceed 10,000 m- 2 because at lower densities a large proportion of the worms is contributed by the pollution-sensitive Stylodrilus heringianus. This approach seems to work well in Lake Erie, however, where the worms in many areas consist entirely of pollution-tolerant species. Goodnight and Whitley (1961) used the relative abundance of oligochaetes as a measure of the extent of organic enrichment, with fewer than 60010 oligochaetes indicating "good" conditions, between 60% and 80% "doubtful" conditions, and more than 80% indicating" ... a high degree of either organic enrichment or industrial pollution" (Goodnight 1973). In the present study each of the open-water areas possessed a mean percentage of oligochaetes below 60%, which was significantly smaller (p< .001) than the percentage in the harbors (91 %) (Table 8). The indices based on absolute and relative abundances of oligochaetes suffer from their inability to detect subtle changes in pollution which may not

K. A. KRIEGER

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TABLE 8. Mean values of four indices of pollution for four areas of the southern nearshore zone of Lake Erie, derived from individual station averages for 1978 and 1979. The first three areas combined form the Open area. Significant differences (see Table 4, footnotes) were determined using the Mann- Whitney U test.

Number of Stations Oligochaetes. m- 2 Oligochaetes, 0,10 L. hoffmeisteri, % Trophic Condition

VermilionLorain

Cleveland

Fairport HarborAshtabula

Harbors

Open

10

19

12

12

41

1,545*** 47*** 44+ 1.85***

1,764*** 52*** 50 1.84*

1,463*** 46*** 62+ 1.86***

15,628 91 49 1.97

1,623*** 49*** 52 1.86*

affect overall oligochaete abundances but which may cause changes in species composition brought about by the different physiological responses of the individual species. Thus, single- or multiplespecies indices may be more sensitive than indices based on higher taxonomic categories (Howmiller and Scott 1977). Brinkhurst (1967) discovered that the relative contribution of L. hoffmeisteri in Saginaw Bay, Lake Huron, correlated well with the known flow of polluted Saginaw River water out of the bay, which led him to suggest that the percentage contribution of this species to total oligochaete abundance may be a useful indicator of organic pollution. In the southern nearshore zone of the central basin of Lake Erie, however, L. hoffmeisteri contributed similarly in both the harbors and open water, and the only statistical difference in percentages was between the VermilionLorain and Fairport Harbor-Ashtabula areas (Table 8), indicating a gradual increase in the contribution of L. hoffmeisteri from west to east. Howmiller and Scott (1977) proposed a trophic condition index (TCI) derived from the abundances of certain naidid and tubificid species of known tolerances to the ranges of trophic conditions or organic enrichment: Trophic Condition =

En, + 2En2 Eno + En, + En2

where EI10 is the total number of individuals of oligochaete species known to be intolerant of organic enrichment, En, is the total number in species characteristic of only slightly enriched areas, and En2 is the number belonging to species which are tolerant of more severely organically polluted areas. In Group 0 they placed Stylodrilus herin-

gianus, Spirosperma nikolskyi, Tubifex supe-

riorensis, Limnodrilus profundicola, T. kessleri, Rhyacodrilus coccineus, and R. montana. None of these species was observed in the samples collected in 1978 and 1979 from the study area, although Brinkhurst et al. (1968) found S. heringianus in the eastern basin and at their shallowest stations at the eastern end of the central basin. Group 1 included

Spirosperma ferox, Isochaetides freyi, Ilyodrilus templetoni, Potamothrix moldaviensis, P. vejdovskyi, Aulodrilus spp., Arcteonais lomondi, Dero digitata, Nais elinguis, Siavina appendiculata, and Uncinais uncinata. Group 2 was further subdivided by Mozley and Howmiller (1977) into L. angustipenis, L. hoffmeisteri, L. udekemianus, and Tubifex tubifex, which tolerate extreme organic enrichment, and into L. cervix, L. claparedeianus, L. maumeensis, and Quistadrilus multisetosus, which they indicated are restricted to areas of gross organic pollution. This last subdivision is of questionable value in Lake Erie, where three of the four species are widely distributed throughout the nearshore zone (Table 3). The samples contained five of the six tubificid species but none of the five naidid species in Group 1, and all eight species in Group 2. Other species will undoubtedly be added to this index as their physiological ecologies are sufficiently defined. In three areas of differing water quality in Green Bay, Lake Michigan, Howmiller and Scott (1977) obtained index values of 1.92, 1.84, and 1.53 in order of the decreasing effect of the highly polluted Fox River. In this study, the index was computed for each station based on all samples collected in 1978 and 1979. The index was then averaged for each area (Table 8). The index value for the harbors (1.97) was significantly higher than the values for the three open areas (1.84 to 1.86). The TCI values reflect the difference in the oligochaete species assemblages between the harbors

MACROINVERTEBRATE INDICATORS OF POLLUTION IN LAKE ERIE and the open lake. Several species in Groups 1 and 2 occurred commonly both within and outside of the harbors: A. pluriseta, L. cervix-L. clapare-

deianus, L. hoffmeisteri, L. maumeensis, L. udekemianus, Q. multisetosus, and P. vejdovskyi. Potamothrix moldaviensis was more commonly encountered outside of the harbors. Four other species in Group 1 were found only in the open waters: A. americanus and A. pigueti (except that both were present at the eastern, open end of Fairport Harbor); I. freyi (except for the mouth of Ashtabula Harbor), which was found only east of the Rocky River; and S. ferox, which was encountered only at stations over 10 m deep. Brinkhurst et al. (1968), whose samples were mostly from further offshore than in the present study, reported that S. ferox was the most abundant worm in the central basin. The absence of this relatively intolerant species (Mozley and Howmiller 1977) closer to shore may indicate more polluted conditions there, although the influence of depth must also be considered. Chironomid species associations are also important in interpreting the trophic condition of lakes (Saether 1979), and Brinkhurst et al. (1968) first developed the TCI from associations of larval midges in the Laurentian Great Lakes. Taxa which they grouped as intolerant (110) were represented in this study only by Tanytarsus sp. The taxa categorized as moderately tolerant (nt) were represented by Stictochironomus sp. and perhaps by Demicryptochironomus sp., and all 5 genera contributing tolerant (n2) species (Chironomus, Cryptochironomus, Microtendipes, Procladius, and Coelotanypus) were collected. The index cannot be strictly applied to the data in this study because it requires a knowledge of several individual species which may have been present but which were not identified beyond the generic level. Nevertheless, taxa assigned to group (n2) made up the vast majority of the chironomids in the quantitative samples, and only three samples possessed a TCI value below 2.00. The index value calculated for all areas of the western basin using Carr and Hiltunen's (1965) data also was 2.00. Values calculated by Brinkhurst et al. (1968) at mostly offshore stations were: western basin, 2.00; central basin, 1.91; eastern basin, 1.67; Lake Ontario, 1.07; Georgian Bay, 0.13. These index values should be interpreted with caution, as some of the most polluted areas in the Great Lakes are also the warmest. Because of temperature effects on species distributions (e.g., Coelotanypus), the index has a eutrophic bias in

207

southern areas and an oligotrophic bias in northern and deep areas (Mozley and Howmiller 1977). With the present data, in which Procladius and Chironomus were the only two common taxa, this bias appears to be minimal. One specimen of Chironomus (station 118) and two of Procladius (stations 64, 87) possessed deformed labial plates or ligulae. Hamilton and Saether (1971) described severe deformities of Chironomus collected in 1963 in western Lake Erie, first noted by Brinkhust et al. (1968), which included thickened body walls and deformed mouthparts. Because all three of their deformed Chironomus specimens were obtained at those locations, they inferred that an industrial waste substance from the Toledo area or agricultural chemicals from the upstream drainage may have been the causative agents. In the present study, however, the three specimens were widely dispersed, and one was taken near the Lorain municipal water intake. Further investigation of the incidence and nature of these deformities is needed before ascribing them to anthropogenic causes. The indicator value of sphaeriid clams in the Great Lakes is less well known than for the oligochaetes and midges (Clarke 1979). Several species of sphaeriids have been observed to increase in the early stages of organic enrichment but later to decline when deposit-feeders, e.g., oligochaetes, predominate (Mozley and Howmiller 1977). Musculium transversum especially appears to respond positively to organic enrichment (Carr and Hiltunen 1965, Fuller 1974). Carr and Hiltunen (1965) found that this species made a much larger contribution at stations in the western basin of Lake Erie where worm counts exceeded 5,000 m-2. The present data (Table 4) support their finding, with the greatest densities of M. transversum usually in the harbors. Mackie et al. (1980) stated that S. corneum, which was widespread in the study area, is usually found in fairly quiet water with little or no wave action and has been associated with organic enrichment. Thus, one would expect to find it in greatest numbers in the harbors; yet the present data do not support these generalizations. Contrarily, the almost total exclusion of S. corneum (as well as P. nitidum and M. partumeium) from the four harbors indicates that this species cannot tolerate conditions there, where the sediments possess a variety of toxins as well as organic wastes. Carr and Hiltunen (1965) similarly found that S. corneum was considerably less tolerant than M. transversum.

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K. A. KRIEGER CONCLUSIONS

Comparison of the macroinvertebrate species assemblages of the southern nearshore zone of the central basin of Lake Erie with those in other areas of the Great Lakes indicates moderate organic enrichment in the general area outside of harbors. There was evidence of a gradient of decreasing pollution in an offshore direction. The harbors are severely degraded, as reflected by the almost complete absence of all but the most pollution-tolerant species. The abundance and relative contribution of oligochaetes as well as the oligochaete trophic condition index showed significant differences between the harbors and the rest of the nearshore zone. The relative contribution of L. hoffmeisteri and the trophic condition index when applied to midge species failed to demonstrate a difference in the extent of pollution between the harbors and open areas. However, the distributions of individual midge species within the most tolerant group revealed strong differences. Conditions outside of the harbors generally appear to be an extension of those prevailing in the western basin in the 1960s and reflect somewhat greater organic enrichment than was apparent in the 1960s in the deeper, more offshore areas of the central basin. ACKNOWLEDGMENTS

I am grateful to many collegues who contributed toward this report. Taxonomic assistance was provided by R. O. Brinkhurst and K. R. Smith (Oligochaeta), J. B. Burch (Sphaeriidae), B. A. Foote (Diptera), S. C. Mozley (Chironomidae), and C. B. Stein (Gastropoda). P. J. Crerar identified and enumerated the oligochaetes. The crew of the R/V Roger R. Simons assisted in sample collection, and members of the Water Quality Laboratory assisted in sample processing, data management, and manuscript preparation. I am especially indebted to S. C. Mozley, R. O. Brinkhurst, and D. S. White for their invaluable suggestions regarding the manuscript. This study was funded in part by USEPA grant No. R005350012 and USEPA contract No. 68-01-5857. REFERENCES

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