Associations of benthic macroinvertebrates typical of various biotopes in Otsego Lake have been recognized and classifie d according to the types of substrates on which they occur. The distributions of many of these animals correlate closely with the bottom substrate patterns in aquatic environments (Harman, 1972; Hutchinson, 1993). Mollusca are used as representative taxa because they are ecologically important and are a relatively restricted and sedentary taxocene (Harman, 1974c; Harman et al., 1980).
Five major associations have been recognized: (1) clean cobble (water-washed gravel, channery, or be drock); (2) eulittoral silt and detritus; (3) littoral silt and detritus; (4) profundal silt and detritus; and (5) autochthonous organic material (living and decaying aquatic vegetation).
The "clean cobble" association occurs along all exposed shores that have rocks or other hard objects large enough to afford protection from waves. The mollusk most indicative of these biotopes is Physa heterostropha. Other mollusks in this association are Spirodon carinata (rare in Otsego), and infrequently, Lymnaea humilis. Other organisms commonly associated are the Bryozoa Fredricella sp.; the leeches Erpobdella punctata and Helobdella stagnalis; the Plecoptera Atoperla ephyre and Neoperla clymene (no longer present); the Zygoptera Enallagma sp. and Ischnura sp.; the Ephemeroptera Stenonema frontale, S. tripunctatum and Heptagenia lucidipennis, and several baetids; the Trichoptera Pycnopsyche sp.; and the isopod Asellus militaris.
The "eulittoral silt and detritus" association occurs along the protected shores where mud banks with high organic content occur. The mollusks indicating this assemblage are: Viviparus georgianus (no longer present); Lymnaea humilis; L. columella; and Succinea ovalis. Other organisms found in these very shallow environments are the Oligochaeta Tubifex sp., Aeolosoma sp., and Haplotaxis sp.; the Anisoptera T etragoneuria sp. and Epicordulia sp.; the Diptera Chironomidae and Palpomya sp.; the Hemiptera Gerris comatus, Notonecta undulata and Saldula interstitialis; the Coleoptera Dineutus assimilis, Gyrinus confinus, and G. marginellus; and the decapod Orconectes propinquus.
The "littoral silt and detritus" association is indicated by the snails, Lymnaea emarginata (uncommon in Otsego), Helisoma anceps and H. campanulata (no longer present). Bivalves indicative of this assemblage are Anodonta cataracta and other members of its subfamily on soft bottoms, and Lampsilis radiata and Elliptio complanata on harder substrates. In many cases, their distributions overlap. Other organisms found in this association are most of the oligochaetes; the burrowing Ephemeroptera, Ephemera simulans and Hexagenia rigida; the Diptera, Chironomidae, in comparatively low numbers, and Palpomyia sp p., Bezzia spp., and Probezzia spp.
The "profundal silt and detritus" association is represented by the fingernail clam Pisidium compressum, a preponderance of chironomids (Diptera), and most species of oligochaetes. Pisidium compressum is replaced on deep clay bottoms by P. subtruncatum (Figure 118).
The "autochthonous organic material" association is indicated by the snails Amnicola limosa, A. integra, A. lustrica, Valvata sincera (in one restricted location), Lymnaea palustris (no longer present) and L. emarginata, Gyraulus parvus and Promenetus exacuous. Other organisms in this large assemblage are the sponges Spongilla spp.; the Odonata Libellula sp. and Sympetrum sp.; the Megaloptera Sialis mohri; the Lepidoptera Nymphula sp.; the Hemiptera Plea striola, Palmacorixa buenoi, and Rhopalosiphym nymphaea; the Coleoptera Haliplus immaculi collis, H. cribarius, Peltodytes edentulus, Tropisternus natator, Laccophilus maculosus, Hydroporus pulcher, H. undulatus, Hygrotus sayi, H. inaequalis and Bidessus flavicollis, the Trichoptera Oecetis cinerascens, Arthripsodes sp., Mystacides sepulchralis, M. longicornis, Leptocella albida, L. exquisita, Phryganea cinera, Polycentropus sp., Pycnopsyche sp., and Cheumat opsyche sp.; the Hydracarina Limnochares spp., Limnesia spp., Piona spp. and Eylais spp.; and the Amphipoda Crangonyx gracilis and Hyalella aztecta.
Benthic macroinvertebrates have long been considered important indicators of water quality in lakes and streams (Baker, 1916; Berg, 1938; Berg, 1963; Hutchinson, 1993; Loeb and Spacie, 1994). Recently, the concepts of biodiversity, ecological integrity and biological sustainability have been de fined relative to the benthic community (Woodley et al., 1993) utilizing species richness as a basis for quantitative analysis.
Briefly, species richness can be considered equivalent to the number of taxa in a particular habitat. Ecological integrity is a function of the species richness in a contemporary community compared to a "pristine" community with identical limiting characteristics or, if available, historical records from the same community. The more a contemporary community i s like its "pristine" model, the more viable it is assumed to be. Biological sustainability is a measure of ecological integrity, considering the presence or absence of, or the dominance of, exotic species in a community. Sustainability relates to the ability of a community to maintain its ecological function while resisting successful invasion by exotic species.
Calculations relevant to the above concepts have been made for selected biotope types (based on substrate character) representing the entire shoreline of Otsego Lake. Information was derived from Nevin's (1936) 1935 work on Otsego Lake and Field Station data from 1968 to present (Badgley, 1990; Berry, 1989; Ehlers, 1989; LaBarre, 1990; Harman, 1970a; 1971a; b; 1972a; 1977; 1994c; Harman and Sohacki, 1975; Harman et al., 1980; Fagnani and Harman, 1987; Montione, 1989). In addition, unpublished data collected during formal courses and field trips have been also incorporated.
Between 1969 and 1993, 153 taxa of bent hic macroinvertebrates were represented. Hydracarina (watermites) collected in 1980 by Simmons (1982) add 18 taxa (Table 44), and Chironomidae (Diptera) studied by Fagnani (1979-82) add 121 species (Table 45) (Fagnani and Harman, 1987) for a total of 292 taxa. For purposes of the above analyses, only taxa appearing in Table 41 are utilized because of the specialized nature of the data presented in Tables 44 and 45.
In 1935, Nevin (1936) collected benthic invertebrates and tabulated data conc erning littoral macrobenthic biomass (wet weight in grams) from various depths in Otsego Lake. In 1968, Harman (Harman et al., 1980) collected benthos at 53 eulittoral stations, from deep water stations, and sites along six transects at various depths from the surface to the deepest portion of the lake (Figure 115). Other citations mentioned above include collections from specific locations (such as Goodyear Swamp or Rat Cove) or various sites along the 1968 transects (Figure 98, TR- ). In 19 93, Hayes (1994) repeated the transect studies and Wheat (1994) repeated the eulittoral studies. The 53 shore stations studied in 1968 were grouped into areas of similar substrate character and location along the lake shore (Figure 115).
The resultant collection areas were: 1) Rat Cove, a protected embayment with substrates rich in silt and decaying organic matter (DOM) in the southwest; 2) the exposed west shore, unstable cobble and channery substrates; 3) Goodyear Swamp Sanctuary, simila r to Rat Cove; 4) the north end, sandy exposed shoreline; 5) Clarke Point, a stable boulder and cobble substrate on the most exposed area of the lakeshore; 6) Hyde Bay, a site which in its pristine state was similar to Rat Cove and Goodyear Swamp, but which has been altered greatly by backfilling and the construction of a sand beach and swimming area; 7) the east shore, similar to the west shore but having more exposure to the prevailing westerly winds; and 8) the south end, similar to the north end b ut more diverse with areas of silt and DOM, and heavily impacted by Village waterfront activities.
Species richness at the eulittoral sites was calculated by combining the records of taxa available from 1968 through 1988 and comparing them to collections made from 1989 through 1993. Comparing current species richness with that of an earlier, and presumably more pristine, situation allows for a review of the ecological integrity of these communities. Long term studies comparing macrobenthic i nvertebrate communities often suffer because of lack of continuity, since various investigators possess different levels of training. The above dates were chosen to include collections by individuals with similar expertise. Hundreds of samples, quantitative and qualitative, as well ongoing observations resulting in additions to the lists of taxa by students and faculty (verified by WNH) make up this database.
The data are presented in Table 41. Tables 42a-c are derived from the lists in Ta ble 41. Table 42a illustrates the species richness at each site from 1968-88 and from 1989-93. Table 42b shows the richness of Ephemeroptera (mayflies), Plecoptera (stoneflies), and the Trichoptera (caddisflies). (The EPTs are a group of generally pollution intolerant taxa). EPTs have been used widely for stream water quality characterization (e.g. Bode et al., 1993). Streams exhibiting low numbers of EPTs are considered highly impacted, while those with comparat ively high numbers are viewed as being relatively unstressed. Table 42c is a similar comparison, using a taxocene with which WNH is more familiar regarding habitat requirements, the Mollusca (Doremus and Harman, 1977; Harman, 1970b; 1972b; 1974c; 1978a; b; Harman and Berg, 1970; Herrman and Harman, 1975; Hutchinson, 1993; Katsigianis and Harman, 1973; MacNamara and Harman, 1974; 1975; Weir, 1977).
Of the taxa collected between 1968-88 (109), 24 were not present in the 1989-93 samples. Ei ght of those were Trichoptera (caddisflies), a pollution sensitive taxocene. Both genera of Plecoptera (stoneflies) have disappeared. Possibly more instructive, taxa encountered from 1968-88 occurred in 347 locations. Those same taxa were found at only 200 sites between 1989-93. Between 1989-93, 51 taxa were collected that were not observed in 1968-88. These data result in the information presented in Tables 42a, b and c. Lakewide average species richness has decreased 27.5% between 1968-88 and 1 989-93. The pollution intolerant EPTs species richness has decreased by 56.1%. Mollusca species have decreased by 52.9%.
Sites along the lakeshore have been impacted to varying degrees, Hyde Bay having suffered the greatest because of the development of a sand beach and filling of about 50 acres of adjacent wetlands. It is assumed that the number of taxa present before the construction, approximated the situation found in Rat Cove and Goodyear Swamp (wetlands associated with protected emb ayments), ca. 74 taxa. Using that figure (rather than the 31 that is, as expected, more indicative of sandy beaches with silty areas), this site has experienced a loss of 56 taxa or 75.7% since the 1960s. Aquatic macrophytes dominant in that area are the introduced exotics Potomogeton crispus and Myriophyllum spicatum, indicating a decreased sustainability. Therefore, Hyde Bay is expected to have a diminished ability to resist further exotic introductions.
Numbers of pollution intolerant taxa dropped even in areas where total numbers of taxa remained stable. Goodyear Swamp Sanctuary maintained the same number of taxa, yet EPTs were reduced by 40% and mollusks by 75%. These calculations are an indication of serious lakewide problems regarding environmental quality. As illustrated by the leeches (Annelida; Hirudinea), some eurytopic taxa have become more abundant in eulittoral regions.
The observed reduction in eulittoral macrobenthic invertebrate species richness between 1968 and 1993, especially stenotopic taxocenes and the Mollusca, has undoubtedly been affected by the alteration of water levels associated with the dam in Cooperstown. The surface of Otsego Lake was raised about 0.4 m (18") in the early 1950s.
Photographs from the 1930-50 period show a eulittoral zone along much of the shoreline of compacted gravel and cobbles well colonized by emergent vegetation, on all but the most exposed shorelines. Above that, a berm of unconsolidated gravel and channery, apparently heaved upward by the ice each late winter and spring, is evident. Since the water level was raised, that unconsolidated material is constantly exposed to wave action. The emergent plants are gone along the majority of the shores. About 20% of the shoreline has been "protected" by lakeside property owners with boulders or breakwaters in an attempt to stabilize their eroding waterfronts.
Many of the arthropods and mollusks normally occupying stable cobble substrates were already uncommon in the 1968 survey, probably due to molar action of loose gravel. Mollusks in that category, as well as those dependent on emergent vegetation for food and cover, are now missing from the species lists.
Table 43 presents biomass in g/m2, represented by macrobenthos collections in 1935, 1969 and 1993. Data are presented relative to littoral and profundal species distribution. Figures 116 and 117 use the same information to illustrate percent biomass of major invertebrate taxa at various depths in 1968 and 1993. Biomass remained stable between 1935 and 1969, but a trend towards increasing standing crop is evident in 1993.
In deeper waters, the distribution of larger taxa (Figures 116 and 117) and the biomass of benthic organisms (Table 43) have changed over the period of study. Figure 116, from data collected in 1968 (Harman et al., 1980), shows a preponderance of biomass attributed to mollusks in the eulittoral environment, arthropods from 4-30 m in depth, and oligochaete annelids in the deepest waters (40 m+). These distributions reflect shallow water diversity of substrates and the organisms living on them, the homogeneous substrates of the middle depths and the corresponding dominance of chironomid flies and oligochaetes in the deepest water where they experience periodic low oxygen concentrations.
The litoral benthic community, from 4-20 m in depth, has changed from a biomass dominated by arthropoda [burrowing mayflies and midges (Harman et al., 1980)] (Figure 116) to mollusks (Figure 117). It is assumed that this change in taxa is associated with the introduction of Eurasian milfoil (Myriophyllum spicatum) in the 1980s and the resultant domination of the littoral plant community by this species, greatly reducing plant diversity (see "Phytobenthos" section). Biomass of invertebrates has increased throughout these depths indicating the concurrent increase in standing crop, and, apparently, productivity.
In deep waters (30-48 m) biomass has also increased. The Oligochaete annelids have become dominant over a greater depth distribution at the expense of the fingernail clams (Mollusca: Sphaeriidae) and the Chironomidae (Insecta: Diptera). These annelids are generally more tolerant to low oxygen concentrations than those groups which have dominated in the deepest regions since at least the 1960s. It is assumed the general trend towards lower oxygen concentrations in recent years is the causat ive factor in this change.