Distribution of Macrobenthic Species in Lake Ontario in Relation to Sources of Pollution and Sediment Parameters

J. Great Lakes Res., July 1976. 2(1):150-163. Internat. Assoc. Great Lakes Res.

DISTRIBUTION OF MACROBENTHIC SPECIES IN LAKE ONTARIO IN RELATION TO SOURCES OF POLLUTION AND SEDIMENT PARAMETERS 1

T.F. Nalepa and N.A. Thomas U.S. Environmental Protection Agency~ National Field Investigations Center~ Cincinnati~ Ohio and Large Lakes Program~ Grosse Ile Laboratory~ Grosse Ile~ Michigan Accepted 22 March 1976

Abstract. Bottom samples were collected in Lake Ontario during the International Field Year for the Great Lakes (IFYGL) in November 1972. Samples were collected in tripl icate at 55 stations located throughout the lake. Sand prevailed at the shallow areas but silt dominated the intermediate and deep-water areas. Total carbon and total Kjeldahl nitrogen content of the sediment increased with increased depth, but no trend was evident in the total phosphorus content. Oligochaetes and the amphipod Pontoporeia affinis accounted for 92% of all organisms collected. The former group dominated the shallowareas while the latter dominated the intermediate and deep-water zones. Stylodrilus heringianus and Limnodrilus hoffmeisteri were the most widely distributed species, being collected at 51 of the 55 stations. Several approaches were used to evaluate trophic conditions in the lake - the indicator species approach, the 01 igochaete-density index, a modified "Goodnight-Whitleyl' index, and the Brinkhurst % L. hoffmeisteri index. The indicator species approach proved to be the most sensitive index because inconsistencies arose when the other indices were appl ied. The most obviously eutrophic areas were near the mouth of the Niagara River and off Toronto. These areas were characterized by high oligochaete densities dominated by either L. hoffmeisteri or T. tubifex. Mesotrophic conditions were evident along the southern shoreline from the mouth of the Niagara River to Rochester, New York. Stylodrilus heringianus~ L. hO.ffmeisteri~ T. tubifex~ and P. affinis were significantly related to some of the measured sediment parameters ih either the intermediate or deep-water areas.

INTRODUCTION

Lakes (IFYGL). The purposes of this particular survey were to 1) add to our knowledge of the species composition and relative abundance of benthic macroinvertebrates in the lake; 2) utilize the macroinvertebrate community to determi ne

This survey of benthic macroinvertebrates was part of an overall biological assessment of Lake Ontario during the International Field Year for the Great I

Present address: Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration, Ann Arbor, Michigan.

150

LAKE ONTARIO MACROBENTHOS areas of enrichment within the lake; 3) relate species distributions to physico-chemical parameters of the sediment. The changing nature of the Great Lakes in response to accelerated eutrophication necessitates the constant monitoring of the biological community to detect and evaluate any time-related changes. Recently, several lake-wide surveys have been conducted to characterize the macrobenthos of Lake Ontario (Brinkhurst et al. 1968; Hiltunen 1969; Kinney 1972). This survey not only provides additional information on the benthic community structure of Lake Ontario, but also adds a seasonal perspective to these earlierworks since it was conducted in November. The composition of the benthic community provides a sensitive tool to evaluate trophic conditions in a particular area. The indicator species approach (Hiltunen 1967, 1969; Brinkhurst et al. 1968) has been perhaps .the most common and widely applicable technique to evaluate trophic conditions in the Great Lakes but other techniques (Carr and Hiltunen 1965; Brinkhurst 1967; Howmiller and Beeton 1971) have also been used. To determine specific areas of environmental perturbation in Lake Ontario, the distribution of the benthic community is ~escribed in terms of the indicator-species approach, and the other community indices are compared and contrasted to it. The distribution of a particular benthic species is the culmination of a complex number of variables. Bes~des the trophic state of an area, other factors, such as depth, substrate type, and water and sediment chemistry, interact directly or indirectly to determine the species composition in a particular area. In the Great

151

Lakes, some authors have attempted to relate the distribution of species to sediment parameters in a limited area (Brinkhurst 1967; Johnson and Matheson 1968). This work is a similar attempt, but on a broader scale. METHODS Triplicate sediment samples were collected with a Ponar grab (.05m 2) at 55 stations located throughout the lake (Fig. 1). Sampling depth ranged from 7-223 m. Sediment from one of the three replicate grab samples taken at each station was mixed and a small portion removed to be analyzed for total carbon, total Kjeldahl nitrogen, total phosphorus and particle size distribution. The other two samples and the remainder of the third were washed through a U.S. Standard No. 30 mesh sieve and the res i due preserved in 10% forma 1in. All organisms were stained

FIG. 1. Lake Ontario sampling stations, November 1972.

with rose bengal (1 :10) to facilitate sorting and counting. When a sample contained an extremely large number of organisms, it was divided into quadrants in the sorting tray and the total number of organisms in a quadrant were picked, identified, and applied to the

152

NALEPA and THOMAS

entire sample. The oligochaetes were cleared in Amman's lactophenol before identification (Brinkhurst 1963). At least 100 oligochaetes were identified from each of the replicate samples. In determining the mean number/m 2 , no correction was made for the small portion taken for sediment .9nalysis from one of the replicates. Total carbon was measured using a Beckman carbonaceous analyzer. Total Kjeldahl nitrogen and total phosphorus were measured using procedures described in Standard Methods for the Examination of Water and Wastewater, 13th Edition,1971. Particle size distribution of the sediment was determined by washing each sample through a 63-micron screen and performing a pipette analysis (Krumbein and Pettijohn 1938) of the material passing. Sand, silt, and clay fractions were thus determined. The mean diameter of the sediment size grain distribution is expressed in phi units (phi = -1092 of the mean particle diameter in mm). The greater the phi unit (¢) the finer the sediment. Partial correlation and multiple regression analyses were employed to determine if any significant relationships (P < .05) existed between the distribution of major species and the measured physical-chemical sediment parameters. Each station was assigned to one of three depth categories: < 35m (22 Stations), 40-90m (13 stations), and> 90m (20 stations). In this way, the effects of depth in the analysis were reduced, The threQ depth categories were termed the shallow, intermediate, and deep zones respectively. The designation of a particular species as a trophic indicator (oligotrophic, mesotrophic, or eutrophic) follows the general

concepts outlined in previous macrobenthic surveys done in the Great Lakes (Hiltunen 1967, 1969; Brinkhurst 1967; Brinkhurst et al. 1968) . RESULTS Sediment Chemistry

The nitrogen content in the sediment generally increased with increased sampling depth. Mean content for the shallow, intermediate and deep zones were .07%, .14% and .20%. The sediments at Station 44, at a depth of 190m, had the highest nitrogen content (.36%) of any station. Trends in phosphorus content in relation to depth were not apparent. The mean content at the deeper depths, however, was sligr.tly greater and more unifor~ than the shallow and intermediate depth stations. The content ranged from .01% at Station 12 to .72% at Station 19. The mean total carbon in the sediment at the shallow, intermediate, and deep-water stations was 1.2%,1.5% and 3.0%. Concentrations at individual stations ranged from .2% (Station 50) to 10.0% (Station 44). Sediment ParticZe Size Distribution

Sand dominated the substrate at all the shallow water stations except at Stations 2 and 3, along the southwestern shoreline, at Station 60, near Rochester, New York, and at Station 96, in the northeastern end of the lake. At these stations the sediment was composed primarily of silt. At the intermediate depth stations, sand dominated the substrate at Stations 21 and 78 alona the northern shoreline, sand and

LAKE ONTARIO MACROBENTHOS TABLE I.

153

Total species list of benthic macroinvertebrates collected in Lake Ontario, November 1972.

ANNELI DA Oligochaeta Enchytraeidae Lumbricillus sp. Lumbr i cu I i dae Stylodrilus heringianus Tubificidae AulodY'ilus pigueti A. pluriseta LimnodY'ilus cervix L. hoffmeisteri L. profundicola L. udekemianus Peloscolex ferox P. muUisetosus Potamothrix moldaviensis P. vejdOvskyi Psammoryctides curvisetosus Rhyacodrilus sp. Tubifex ignotus T. kessleri americanus T. tubifex Undetermined immature forms with hair setae without hair setae Hirundinea Glossiphoniidae Helobdella stagnalis CRUSTACEA Amphipoda Gammarus fasciatus Pontoporeia affinis Isopoda AseUus sp. Mysidacea Mysis relicta

INSECTA Chironomidae Chironomus anthracinus - gr. C. plumosus - gr. Cryptochironomus cf. digitatus C. species 2 C. species 3 Heterotrissocladius cf. grimshawi H. cf. subpilosus Microspectra sp. Monodiamesa tuberculata Parachironomus sp. Potthastia cf. longimanus Procladius sp. Tanytarsus sp. MOLLUSCA Gastropoda Amnicola sp. Bulimus (=BythiniaJ tentaculatus Physa sp. VaZvata sincera V. tricarinata Pelecypoda Pisidium spp. Sphaerium corneum S. lacustre S. cf. nitidum S. striatinum S. transversum PLATYHELMINTHES

silt were in about equal proportions lake than in the southern. The mean particle size at Station 89, and silt dominated distribution in phi units for the at the remaining stations. shallow, intermediate, and deep At deep-water stations, water stations was 3.0¢ (sand), silt dominated the substrate atall 4.7¢ (sandy silt), and 6.2¢ (silt). stations except Stations 24, 38, Phi uni ts ranged from 1. 6¢ to 7. 5¢ and 64 in the northern half of the (Table 2). lake. Sand was most abundant at these stations, It was obvious that sand extended to a greater depth in the northern half of the

NALEPA and THOMAS

154 TABLE 2.

Station

Depth

2 Sediment type (phi units) and abundance (number/m ) of major groups and species in Lake Ontario, November 1972. The total number of 01 igochaetes is given in Fig. 2 and the number of amphipods is given in Fig. 4. Phi unit

1

Total Organ 1sms

SityZOdt'iLU8

hel'ingicmu8

Limnod1'ilu8 hoffmeisteri+

Tuhifex tubifex

immature w/o hai r setae

+immature w/o hal r

Potamothrix vejdovskyi

Other 01 i gochaetes

Total

Total

Total

Ch j ronom i dae

Pe 1ecypoda

Gastropoda

setae

Shallow-water stations

14 12 19 i, 59 41 42 60 3 66 103 I 79 ,', 98 31 30 97 48 2 7 96 35 50

7.2 14.0 14.0 14.4 16.0 19.8 20.0 21.0 21.0 22.0 22.0 22.0 23.4 26.0 27.0 27.0 28.8 30.0 30.0 30.0 35.0 35.0

2.2 3.0

3. I 1.8 4.7 4.0 2.2 3. I

3.3 1.6

3.3 2.6 2.2 4.9 1.8 5.5 1.7

61,699 12,345 6,207 574 8,600 4,687 4,576 4,460 8,193 4,609 11,340 1,966 4,533 6,705 13,707 1,187 1,166 6,712 6,813 1,239 8,527 5,047

o 2,500 453 30 5,213 1.000 100 1,770 5,613

o

9,740 552 480 4,887 9,280 340 1,153 2,120 367 220 8,267 4,533

31,617 5,716 3,427 350 520 67 3,800 1,193 1,580 3,866 853 280 1,700 500 480 467 13 2,540 1,186 860 180 427

16,380 2,420 947 127 400 20 80

10,193

773 900 20 80

o

80 874 67 13 307

3,513 946 480 47 2,387 3,600 516 207

413 800 667 973 120 320 593 1,920 80

o

240 350 1,840 300

o

o

413 1,867 93 80 40

833 47 193

o

47

o

133 63

o

1,013 1,793 420 183

o o

246 40 53

o o

567 287 40

5,461 3,232 384

1,120 47 93 27 13

894 13 61 294 86 40 20 93 27

o 7

186

34 7 20 13

o

o

1,407 193 1,660 647 667 113 1,113 140 290 657 2,373 33 333 407 5 587 1,253 467

267 34 1,767

o

74 27

o

113 100 26

13 20

o o

o o 7

o

I ntermed i ate-water stat ions

99 65 37 21 8 78 52 89 68 92 62 83 5

40. I 41.0 46.0 52.0 54.0 54.0 67.0 76.0 85.0 87.0 87.0 88.0 90.0

5.2 1.7 2.6 3.7 5.6 5.9 6.9 5.9

2,850 1.786 5,413 3,253 46,454 3,855 6,780 4,165 1,840 11,620 500 1,074 1.506

o

290

527

33

I, I 80

53 53 4,587

1,186

o

1,187 1,926 880 200 833 120 187 193

190

o o

41,307

o

167 453 140 1,740

40 13 27 2,713

53 46

o o

o

134

o

30

o o

o

o

o o o o o

33 214

o

7

o 13 27

o

267 167 67 63

o

74

o o 7

o o o

10

133

230 53 100 27 53

o

7 73

o

o

33

o o o o

33

o o o

o o o

o

60 80 653

o

60

o

Deep-water stat ions

*

34 38 64 15 10

77 46 17 54 24 26 69 j2 85 56 45 71 40 44 75

96.0 99.0 103.0 106.2 114.0 12.6 126.0 127.8 136.0 146.0 146.0 152.0 167.0 167.0 176.0 180.0 186.0 187.0 190.0 223.0

7.3

4.3 3.4 6.7 6.8 6.2

2.9 7.2 6.9 7.5 6.2 6.9 7.4 6.5

3,507 830 1,500 2,143 474 2,020 1,267 607 1,968 213 1,094 1,141 927 80 1,420 320 1,314 1,080 1,240 313

500 167 173 260 33 473 287 120 507

o

113 187 420 40 507 213 460 313 260

33

13 13 14 203 74 73 27 20 67

o 7

o 7 13 500 40 73 20

o

87

o o

27

13

30

10

7

20 67 53 67 13

o o

60 54 193 47

o o

o o 7 30

o o

o o

o o o

o o o o o

o o o o

o o o o o 7

o o o o 7

o 7

o o o 54

7

o 7

o o

o

40

o o

13

o o

27

o

o o o

10

o o o o

o

27

o

13 10

o

247

7

o o o 7

o

o o o o o

33

o

o

o o o o o o o o o o o

o o o

o o o o

o

o

o o

o o o

*Number of organisms may be underestimated due to partial loss of sample in sh-ipment.

1<4 ¢ '" sand; > 1+ ¢ = silt.

Macroinvertebrates

A total of 48 taxa were differentiated (Table 1). The greatest number of taxa was collected at Station 60, near Rochester. New York~ and at Station 14, near the mouth of the Niagara River. The

number of taxa clearly decreased as sampling depth increased. The mean estimated number of orqanisms/m 2 also decreased with increased depth (Table 2). Mean densities for the shallow, i ntermedi ate and deep-water stati ons were 11 ,800/m 2 , 7,000m/ 2 and 1,240/m 2.

LAKE ONTARIO MACROBENTHOS

155

increased depth - 41%, 63%, and 73% at each of the three depth zones (Fi 0. 3). Stylodrilus heringianus,

which is considered an oligotrophic indicator species in the Great Lakes, was not collected at Station 14, near the mouth of the Niagara River, Station 8, near Toronto, or at Stations 99 and 103 in the far FIG. 2. Distribution and relative eastern end of the lake. It was abundance (no/m 2 ) of total 01 igocollected in relatively low numbers chaetes at the sampl ing stations. at Stations 59 and 60, near Rochester. Sty lodri lus heringianus wa s respectively. The dominant inverte- collected in greatest numbers at brate groups were the oligochaetes Stations 1, 30, and 35. and the amph ipods (rna in1y P01itopo,Y'e1:a Mature Limnodrilus hoffaffinis) which accounted for 56% meisteri~ along with immature forms and 36% of all organisms collected. without hair setae, likely L. hoffOligochaetes dominated at the shal- meisteri, were also collected at 51 low stations while P. affinis domi- stations and comprised 21% of all nated in the intermediate and deep the oligochaetes obtained (Table 2). water zones. This species, while found in a wide vari ety of habitats, reaches maximum Distribution of Oligochaetes densities in organically enriched areas. It was collected in greatLake-wide oligochaete densi- est numbers near the mouth of the ties are given in Fig. 2. Mean Niagara River (Stations 12, 14), oligochaete densities at the shalnear Toronto (Station 8), near low, intermediate, and deep-water Rochester (Station 60), and at stations were 8,400/m 2 , 4,430/m 2 Station 103. At Station 14, immaand 361/m2 . Densities were greatture forms without hair setae est at Stations 12, 14, and 30, numbered 31,300/m2 , six times near the mouth of the Ni agara Ri ver greater that at any of the other and at Station 8, just off Toronto. stations. It is likely, however, If Station 8, with an oligochaete that some of these immature forms density of 46,200/m 2 , were excluded were Potamorthrix moldaviensis. from the intermediate depth staOther Limnodrilus species considertions, the mean for these stations ed part of the pollution-tolerant would decrease to 1,220/m2 . The Limnodrilus complex, L. cervix and oligochaete density at Station 14, L. udekemianus, attained maximum 61,600/m 2 , was the highest density densities of 240/m 2 at Station 14. ever reported from near the mouth The former species was collected of the Niagara River. only at this station while the latter was also taken at Stations Stylodrilus heringianus was 2, 12, and 98. one of the most widely distributed species,being collected at 51 of Tubifex tubifex and immature forms with hair setae, likely the 55 stations, and accounted for 57% of all the oliqochaetes colT. tubifex~ was the next most abunlected (Table 2). -It comprised a dant species, being collected at 40 greater proportion of the total stations and accounted for 9.9% of oligochaete abundance with all the oligochaetes obtained 841

100 1,412

OSWEGO

156

NALEPA and THOMAS

t

COBOURG

• • • • • .• : • ••• PORT HOPE

_____

OSWEGO

~

STYLODRIWS

HERINGIANUS

L1MNODRIWS HOFFMEISTER I .. IMMATURE WID HAIR SETAE

TUBlFEX TU8lFEX .. IMMATURE WI twR SETAE BUFI"ALO

FIG. 3.

OTHER

-

~

1",,;:;;:;,,;:;,1 [===:J

Percent composition of major oligochaete species and species groups at the various sampling stations.

(Table 2). Althouqh T. tubifex is considered a pollution-tolerant form, it is also found in oliqotrophic deep-water habitats. At the shallow-water stations, this species was collected in largest numbers at Station 14 and was also collected in comparatively large numbers along the southwestern shoreline (Stations 2 to 31) and near Toronto (Station 19). It did not dominate the oligochaete fauna at any of the shallow-water stations. At the intermediate and deep-water stations, it was most abundant at Station 8 near Toronto and at Stafion 92 near Oswego, New York. The density of T. tubifex at Station 8 was 4l,300/m 2 , four times greater than at any other station. This species dominated (>50%) the oliQochaete fauna at Stations 8, 92, and 15 (Fig. 3). Oligochaete species displaying littoral distributions were Aulodrilus spp., Peloscolex ferox, Peloscolex multisetosus, Potamothrix vejdovskyi and Potamothrix moldaviensis. Except for P. multisetosus , all of these species

are considered typical of mesotrophic conditions. Most of these species were consistently collected along the southern shoreline between the mouth of the Niagara River and Rochester. The composition of these species at Station 14 is noteworthy. The density of P. vejdovskyi at this station was l6,400/m 2 , eight times greater than at any other station and the density of P. moldaviensis was 1,990/m2 , 30 times greater. Peloscolex ferox and Aulodrilus spp. although generally distributed along the southern shoreline, were not collected at Station 14. Pelos.colex multisetosus, a pollution tolerant form, was collected along the southern shoreline at Stations 7 and 8 near Toronto and at Stations 79 and 92 in the eastern end of the lake. These shoreline species dominated the oligochaete fauna only at two stations, 42 and 79. Peloscolex ferox was the most abundant species at both stations. Distribution of Chironomids

The chi ronomi ds were genera lly

LAKE ONTARIO MACROBENTHOS restricted to the shallow-water stations. PY'ocladius sp., the most widespread species, was collected at 15' of the' 22 shallow-water stations. It attained a maximum density of 1,050/m2 at Station 14, ten times greater than that found at any of the other stations. It was collected at only one station over 36m, Station 15. The poll ution tolerant forms, Chironomus anthracinus-gr., Chironomus plumosus-gr., and Cryptochironomus, were common along the southern shoreline from the mouth of the Niagara River to Rochester, and at Station 103. The greatest density of these species occurred at Station 60, near Rochester. The most widely distributed pollution-intolerant form was Heterotrissocladius cf. subpilosus. It was generally collected at the deep-water stations but was also collected at Stations 1 and 48. Chironomid species considered to be pollution-intolerant co-occurred with pollution-tolerant forms at Stations 1,2, and 66. Distribution of Amphipods Pontoporeia affinis, considered to be an oligotrophic indicator species, was absent or occurred in relatively low numbers in the shallow waters along the southern shoreline from the mouth of the Niagara River east to Rochester and near Toronto (Fig. 4). This species was most abundant in the far western end of the lake (Stations 1,2), along the central northern shoreline (Stations 35,37, 50, 52), just off Oswego (Station 92), and at Station 97. A maximum of 11,200/m2 was collected at this last station. Pontoporeia affi~is accounted for 22%, 61%, and 58% of all organisms collected in the shallow, intermediate and deep water zones respectively.

157

FIG. 4. Distribution and relative abundance (no/m 2 ) of Pontoporeia affinis and Gammarus fasciatus at the various sampl ing stations. Uncircled numbers indicate the abundance of P. affinis and the circled numbers indicate the abundance of G. fasciatus. An asterisk (*) denotes neither species collected.

The other amphipod, Gammarus fasciatus, was collected along the

southern shoreline, near Toronto, and at a few scattered stations in the far eastern end of the lake (Fig. 4). A maximum of 993/m 2 was collected at Station 60, near Rochester. Gammarus fasciatus, generally considered to be a shallow water form, was collected at Station 8 at a depth of 54m. Distribution of Molluscs

Gastropods were restricted to the shallow-water stations (Table 2). Valvata sincera accounted for 63% of all gastropods collected and was the only gastropod collected in the far eastern end of the lake. The greatest number and species of gastropods occurred near the mouth of the Niagara River, near Rochester, and at Station 79. A maximum of 1,770/m 2 was collected at Station 60. The various species of Sphaenum were al so restricted to the shallow-water stations. Sphaerium cf. nitidum was the most common and widely distributed species, comprising 95% of all the sphaeriids

158

NALEPA and THOMAS

1,000/m2 and 5,000/m2 indicates mild pollution, and more than 5,000/m2indicates severe pollution. Using these criteria, the majority of the shallow-water stations (12 of 22) in Lake Ontario would be considered severely polluted and the remainder, excluding Station 59, would be considered moderately polluted. Of the 13 intermediate depth stations, Station 8 near Toronto and Stati on 92 near Oswego wou1d be cons i dered severely po11 uted , 5 other stations would be considered mildly polluted, and the remainder would be considered not polluted. ReZationship between Species Distri- All the deep-water stations had olibution and Sediment Parameters gochaete densities of less than 1,OOO/m 2 (Fig. 2). Only four of the major Mozley and Alley (1973) have species collected were significantly suggested that, as a criterion for related (P < .05) to any of the severe pollution, an area must have measured sediment parameters. Three an oligochaete density of greater of these species were oligochaetes - than 10,000/m2 over several repliS. heringianus was inversely recates. If thi s suggesti on were lated to percent nitrogen and followed, only Stations 14 and 30, particle size distribution at the near the mouth of the Niagara intermediate depth stations; L. River, and Station 8) near Toronto, hoffmeisteri was directly related would be considered severely polto percent nitrogen and percent car- luted. bon at the deep-water stations; and Goodnight and Whitley (1960), T. tubifex was directly related to working in a midwestern stream, percent nitrogen and percent phoshave suggested that the relative phorus also at the deep-water staabundance of oligochaetes to other tions. The only other significant benthic organisms can be used as relationship involved P. affinis an index to pollution. Areas with and the particle size distribution, greater than 80% oligochaetes are also at the deEp-water stations. considered "highly polluted," areas The two were inversely related. with between 60% and 80% are considered "doubtful," and areas with AppZication of Trophic Indices less than 60% are considered in "good condition." In the Great The total density of oligoLakes, Howmil1er and Beeton (1971) chaetes has been used often to have used this approach to assess assess pollutional effects in the water quality in Green Bay, Lake Great Lakes (Carr and Hiltunen Michigan. Since S. heringianus is 1965; International Joint Commisconsidered an oligotrophic indision Report 1969; Howmiller and cator species and is widely disBeeton 1971; Mozley and Alley1973). tributed in Lake Ontario, this The original index, as prooosed by index was modified to include only the percent Tubificidae present Wright and Tidd (1933), maintains that an oligochaete density of less in the total number of organisms than 1,000/m2 indicates neqligible collected. According to thismodified index, Stations 8, 14, 19, and pollution, a density of between collected. It attained a maximum density of 1,170/m2 near the mouth of the Niagara River. Sphaerium transversum~ considered to be a pollution-tolerant form, was collected only at the mouth of the Niagara River and near Rochester. pisidium spp. was collected from all the depth zones. Mean density at the shallow, intermediate, and deep-water st~tions were 754/m 2 , 105/m 2 , and 19/m2 respectively. These species attained a maximum density of 3,720/m 2 near the mouth of the Niagara River.

LAKE ONTARIO MACROBENTHOS 59 are considered "highly polluted," Stations 42 and 103 are "doubtful, and the remaining stations are considered in good condition. Brinkhurst (1967) has suggested that the percentage of L. hoffmeistepi to other oligochaetes may be used as an index to po11 ution. The greater the percentage, the more polluted the area. Generally, a percentage of at least 50% is indicative of perturbed conditions. The stations with the highest percentage of L. hoffmeistepi~ considering both mature and immature forms, were Stations 103 (84%), 60 (83%), 96 (69%) and 14 (51%), (Fig. 3). II

DISCUSSION TPophic Indices

The application of various "pollution-indices" to the species data provided little information that was not already obvious from using the indicator-species approach. These indices were generally in agreement in categorizing the extent of pollution at the various stations, but the fact that some discrepancies did arise illustrates that they must be applied cautiously. The most obviously enriched stations were Station 14 near the mouth of the Niagara River and Stati on 8 near Toronto. Both these stations were characterized by oligochaete densities that exceeded 10,000/m2 over several replicates (oligochaete-density index), and the Tubificidae comprised over 80% of all the organisms collected (modified Goodnight-Whitley index). However, although the Brinkhurst index (percent L. hoffmeistepi to other 01 igochaetes) indicated that Station 14 was somewhat enriched (51%), it indicated that Station 8,

159

where T. tubifex completely dominated the oligochaete fauna, was relatively unpolluted (9%). This difference in species dominance was likely related to the difference in depth between the two stations, 7m at Station 14 and 54m at Station 8. There is a general tendency for LimnodpiZus spp. to be replaced by greater numbers of T. Tubifex with increased sampling ~epth, particularly near sources of organic wastes (Zahner 1964; Johnson and Matheson 1968). Hiltunen (1969) sampled at a depth of 18.5m off Toronto and found a much higher percentage of L. hoffmeistepi and a lower percentage of T. tubifex than we did at our station at 54m. The oligochaete fauna was dominated by T. tubifex (including immature forms with hair setae) at only two other stations, Stations 15 and 92. Both of these stations were located in deeper waters near river inputs the Niagara River and the Oswego River respectively. Near the Niaqara River, then, the transition .. from a L. hoffmeistepi dominated oligochaete fauna (Station 14) to a T. tubifex dominated one (Station 15) with increased sampling depth was quite evident. A shallow-water station was not located off the Oswe.go River. Station 92 was the only station below 36m that displayed other evidence of enrichment besides an oligochaete fauna dominated by T. tubifex. The fauna at thi s stati on was characterized by a relatively high number of oligochaetes and, also, the mesotrophic indicator AuZodpiZus spp. and the eutrophic indicator P. muZtisetosus were found. However, both the Brinkhurst index and the modified Goodniqht-Whitley index considered this station in "good condition." Even though the oligochaete fauna at Stati on 60, near Rochester, was dominated by L. hoffmeistepi~

160

NALEPA and THOMAS

and thus was considered enriched according to the Brinkhurst index, the modified Goodnight-Whitley index indicated that this station was in "good condition." The high number of gastropods, sphaeriids, and pollution-tolerant chironomids collected there apparently biased the results derived from this latter index. Stations 19, 42, and 59were considered enriched by one indexor the other but not by both. The macrofauna of the three replicates at Station 19, off Toronto, was extremely variable. This station may be located in an area transitional in water quality. The oligochaete densities at this station were high but not exceedingly so. The samples from Station 59 may have been partially lost in shipment, making quantitative comparisons impossible. Indicator Species Sty lodri lus heringianus wa s collected in reduced numbers orwas totally absent at shallow-water stations nearest urban centers. These results confirm that it is an oligotrophic-indicator species, as had been suggested by other macrobenthic surveys done in Lake Ontario (Hiltunen 1969; Kinney 1972). Stylodrilus heringianus is generally not found shallower than 15m (Mozley and Garcia 1972) but, since all the shallow-water stations were deeper than 14m (excluding Station 14), its absence near urban centers cannot be attributed solely to a depth effect. Stylodrilus heringianus was collected in greatest numbers at Stations 1,30, and 35. The high total oligochaete density noted at each station suggested that enriched conditions existed, but this Great Lakes oligotrophic indicator, nevertheless, dominated the fauna. This was especially true at Station

30. The total oligochaete abundance at this station exceeded 10,000/m2 over several replicates, but S. heringianus composed 68% of the tota 1 fauna. Each of the three stations was located downcurrent from urban inputs - Station 1 from Toronto, Station 30 from the Niaqara River, and Station 35 from Port Hope and Cobourg, Ontario. It appears, then, that S. heringianus which cannot tolerate "grossly" enriched areas, can attain high densities in areas more "mildly" enriched. Its absence from Stations 96 and 103 is unexplainable. The other oligotrophic-indicator species, P. affinis was not collected near urban centers, but also was not collected or occurred in relatively low numbers along the southern shoreline from the mouth of the Niagara River to Rochester. The oligochaete mesotrophic-indicator species (P. vejdovskyi 3 P. ferox 3 Aul9dritu8 spp., P. multisetosus) and the pollution tolerant chironomid Chironomus anthracinus-gr., were most consistently collected along this shoreline. The other amphipod species, G. fasciatus is considered a shallow, warm-water form but little is known about its pollution tolerance in the Great Lakes. The fact that G. fasciatus was collected at stations where P. affinis was absent or collected only in reduced numbers would seem to indicate that G. fasciatus is a pollution-tolerant form (or cannot compete effectively with P. affinis). Hiltunen (1969) stated that the effects of environmental conditions on Gammarus sp. (likely G. fasciatus) were not apparent since it was abundant off Rochester but absent off Toronto. His sampling stations off Toronto were at 18.5m and 91.5m. Gammarus sp. was not collected at either depth while P. affinis was collected only at the deeper station. In 3

3

LAKE ONTARIO MACROBENTHOS the present study ~ G. fasciatus was collected at Station 8 at a depth of 54 meters off Toronto but P. affinis was not taken there. On the other hand, G. fasciatus was not collected, but P. affinis was taken, at a sampling depth of 77m off Toronto (IFYGL macrobenthic survey, June 1972, unpublished data). Thus, the impact of Toronto s effluents on Lake Ontario appear to extend to a depth of between 54 and 77 meters. Differences in oligochaete densities and composition tend to confirm this possibility. Tubifex tubifex dominated the former depth while S. heringianus dominated the latter.

161

finding that indicates its preference for coarser sediments. Pollution has affected the distribution of S. heringianus in this depth range in Lake Ontario (Kinney 1972) but, since most of the intermediate depth stations were located along this relatively unpolluted northern half of the lake, the effects of enrichment on the distribution of S. heringianus in this depth range were minimized. LimnodrUushoffmeisteri and T. tubifex, both pollution tolerant forms, were related to chemical factors in the sediment only at the deep-water stations, an area where the effects of enrichment were minimal. Johnson and Matheson (1968), working in Hamilton Bay and Species Distribution and Sediment Parameters adjacent Lake Ontario, related increased numbers of these species In attempting to relate the to greater richness of the sediment, as measured by percent carbon, perdistribution of any of the species to the measured sediment parameters, cent nitrogen, and percent phosphorus. They noted, however, that th is it must be noted that any species distribution is the end result of relationship is complex and dependent on numerous other factors. a complexity of factors, both direct and indirect. The effects Recent evidence indicates that an of depth, substrate type, sediment important factor in the distribution of these specie~ (as well as chemistry, and, especially, the other oligochaete species) is the degree of enrichment interact to fraction of sediment able to supmake any unifactoral analysis someport bacterial colonies and the what misleading. The effects of depth were somewhat reduced in this interrelationships of species in study by placing the stations into utilizing this food source (Brinkone of three depth categories. hurst 1972). This fraction depends However, the interrelationship of more on the quality of organic substrate type and the degree of material present than the total enrichment on species distributions quantity (Johnson and Brinkhurst were clearly evident. 1971). The oligochaete density and StyZodriZus heringianus is comoosition at the shallow-water commonly found in sand and gravel stations in Lake Ontario, on a along lakeshores (Brinkhurst 1965). broad scale, certainly emphasizes At the shallow-water stations in this point. For instance, the Lake Ontario, this relationship qreatest density of oligochaetes, was masked because this species is of which 68% were likely L. hoffsensitive to polluted conditions. meisteri and T. tubifex, was colIn the intermediate depth zone, S. lected at the mouth of the Niagara heringianus was inversely related River (Station 14) in a substrate to increases in the silt and clay that consisted of 85% sand and had fractions of the sediment, a a carbon conte~t of only 0.3%. I

162

NALEPA and THOMAS

On a smaller scale, the shallow-water macrofauna appeared to be related to some of the measured sediment parameters. Stations 96 and 97 were located near each other and were at about the same depth. The substrate at the former station consisted of 88% silt, and the latter of 85% sand. Although similar oligochaete densities were collected at both stations, the macrofauna at Station 96 consisted of twice as many L. hoffmeisteri and T. tubifex and nine times fewer s. heringianus than at Station 97. Station 96 also had five times fewer P. affinis than Station 97. Several authors have studied the distribution of P. affinis in relation to sediment type in the Great Lakes. Marzolf (1965), working in upper Lake Michigan, found that P. affinis was not related to the particle size distribution of the sediment but only to the number of bacteria present. Henson (1970) found that, on the average, P. affinis was most abundant in upper Lake Huron sediments that might be classified as silty sands but he did not measure bacterial abundance. In the present study the ~bundance o~ P. affini? ~a~ related to partlcle Slze dlstrlbutioh in the deep-water zone, indicating a preference for the coarser silts rather than the finer silts found in this area. There was no significant relationship.

between the distribution of P. affinis and sediment type in the shallow or intermediate depth zones. In the shallow zone, the distribution of P. affinis was obviously more influenced by the degree of enrichment than by sediment type at a given station, for it was not collected or was collected in reduced numbers at stations considered moderately enriched (Stations 30,31,41,19), although these stations had a substrate type which, according to Henson (1970), this species might prefer. Factors that might have influenced the distribution of P. affinis in the intermediate depth zone (excluding the polluted Station 8) were not apparent. ACKNOWLEDGEMENTS The authors wish to express their gratitude to Dr. Samuel Mozley, Great Lakes Research Division, University of Michigan, for identifying most of the chironomids and for his helpful review of the manuscript; to Mr. William T. Mason, Jr., Potomac River Basin Commission, for verifying the identificationof some chironomids; and to Mr~ Jarl K. Hiltunen, U.S. Fish and Wildlife Service, Great Lakes Fishery Laboratory, for verifying the identification of some oligochaetes.

REFERENCES Brinkhurst, R.O. 1963. Taxonomical studies on the Tubificidae (Anne 1ida, 01 igochaeta). Inter. Rev. ges. HydrobioZ. (Systematische Beihefte), 2:1-89. 1965. Observations on the recovery of a British river from gross organic pollution. HydrobioZogia, 24:9-51. 1967. The distribution of aquatic oligochaetes in Saginaw Bay, Lake Huron. LimnoZ. Oceanogr.~ 12:137-143.

LAKE ONTARIO MACROBENTHOS

163

1969. Changes in the benthos of Lakes Erie and Ontario. Bull. Buffalo Soc. Nat. Sci.~ 25:45-65. 1972. The role of sludge worms in eutrophication. Ecol. Res. Ser.~ EPA-R3-72-004, 69p. --------------., Hamilton, A.L. and Herrington, H.B. 1968. Components of the bottom fauna of the St. Lawrence Great Lakes. Great Lakes Inst., Univ. Toronto, Pub1. No. PR33, 50 p. Carr, J.F. and Hiltunen, J.K. 1965. Changes in the bottom fauna of western Lake Erie from 1930 to 1961. Limnol. Oceanogr.~ 10:559-569. Goodnight, C.J. and Whitley, L.S. 1960. Oligochaetes as indicators of pollution. Froc. l5th Annual Waste Conf.~ Purdue Univ. pp. 139-142. Henson, E.B. 1970. Pontoporeia affinis (Crustacea, Amphipoda) in the Straits of Mackinac region. Froc. l3th Conf. Great Lakes Res.~ Internat. Assoc. Great Lakes Res., pp. 601-610. Hiltunen, J.K. 1967. Some oligochaetes from Lake Michigan. Trans. Amer. Microsc. Soc.~ 86:433-454. 1969. Th~ benthic macrofauna of Lake Ontario. Great Lakes Fish Comm. Tech. Rpt., 14:39-50. Howmi11er, R.P. and Beeton, A.M. 1971. Biological evaluation of environmental quality, Green Bay, Lake Michigan. J. Water Poll. Control Fed.~

43:123-133.

International Lake Erie Water Pollution Board and International Lake Ontario - St. Lawrence River Water Pollution Board, 1969. Pollution of Lake Erie, Lake Ontario and the International Section of the St. Lawrence River. Vol. 3, Report to the International Joint Commission, 329 p. Johnson, M.G. and Brinkhurst, R.O. 1971. Benthic community metabolism in Bay of Quinte and Lake Ontario. J. Fish. Res. Bd. Canada~ 28: 1715-1725. - - - - - - - - . and Matheson, D.H. 1968. Macroinvertebrate communities of sediments of Hamilton Bay and adjacent Lake Ontario. Limnol. Oceanogr. ~ 13: 99-111. Kinney, W.L. 1972. The macrobenthos of Lake Ontario. Proc. l5th Conf. Great Lakes Res.~ Internat. Assoc. Great Lakes Res., pp. 53-79. Krumbein, W.C. and Pettijohn, F.J. 1938. Manual of sedimentary petrography. Appleton-Century - Crofts, Inc., New York. Marzolf, G.R. 1965. Substrate relations of the burrowing amphipod Pontoporeia affinis in Lake Michigan. Ecology~ 46:579-592. Mozley, S.C. and Garcia, L.C. 1972. Benthic macrofauna in the coastal zone of southern Lake Michigan. Proc. l5th Conf. Great Lakes Res.~ Internat. Assoc. Great Lakes Res., pp. 102-116. - - - - - - . and Alley, W.P. 1973. Distribution of benthic invertebrates in the south end of Lake Michigan. Proc. l6th Conf. rrreat Lakes Res.~ Internat. Assoc. Great Lakes Res., pp. 87-96. Wright, S. and Tidd, W.K. 1933. Summary of 1imnologica1 investigations in western Lake Erie in 1929 and 1930. Trans. Amer. Fish. Soc.~ 63:271-285. Zahner, R. 1964. Beziehungen zwischen dem Aufreten von Tubificiden und der Zufuhr organischer Stoffe im Bodensee. Intern. Rev. ges. Hydrobiol.~

49:417-454.