80 REPORTS: An inventory ofmeroplankton associated with Myriophyllum spicatum, focusing on Acentria ephemerella, in Otsego Lake, summer 1997 Mary Miner INTRODUCTION Myriophyllum spicatum, commonly known as Eurasion Watermilfoil, was first documented in Otsego Lake in 1986 (Dayton and Smith, 1986). It has since become a nuisance to lakeside residents, in places forming thick mats at the surface which potentially hinder boat travel and decrease property value. With a photosynthetic rate two to six times that of native plants (Anon, 1986), and an earlier annual period of growth (Hutchinson, 1975), M spicatum reduces native plants' chance to compete for light and space. The spread of M spicatum was closely monitored after its discovery. Subsequent growth and mapping of its distribution were recorded in 1987. At this time, clones of milfoil were found only in the northern part ofthe Lake (Merrifield and Harman, 1988). By 1988 it wasnoted that M spicatum had inhabited all substrates suitable for it's growth within the Lake, including the south end (Stalter, 1989). In the summer of 1990, the percent cover of M spicatum at four sites showed that it was a dominant species throughout the littoral zone (Sanders, 1990). It has been observed that M spicatum has not created as large a problem in Otsego as it has in many other lakes. It has been proposed that this is due to the presence ofacentria ephemerella, a lepidopteran which, in its larval stage, feeds on the meristematic region of milfoil (Harman, 1998). The larvae's feeding habits cause the plants to grow laterally rather than vertically. The result is shorter clones of M spicatum which do not reach the surface of the water. This years study focuses on the meroplankton found to inhabit M spicatum beds, with emphasis placed on evaluating the densities ofa. ephemerella. Meroplankton (defined as the macroinvertebrate community living in direct association with macrophyte beds) were surveyed at four sites on Otsego Lake. The selected sites were dominated by milfoil. Special attention was paid to Acentria to investigate whether or not it may be controlling the growth of M spicatum. F.H.V. Mecklenburg Conservation Fellow, summer 1997. Present affiliation: Cooperstown Central High School.
81 MATERIALS AND METHODS On July 11,24, and August 7, 1997, four sites, accessed by boat, were chosen for the purpose of finding representative areas from which to sample M spicatum. The sites were located at the north and south ends of the Lake, Rat Cove and Hyde Bay (Figure 1). At each location, M spicatum was collected by hand and placed in 5 gallon buckets. The milfoil was covered with water and allowed to sit for a period of 2 to 4 days so that the invertebrates would come loose from the plants. At the end of this period, each bucket was sorted through by hand and the meroplankton was extracted. The invertebrates were placed in 70% ethanol for later identification. The milfoil was saved to be dried and weighed in order to attempt to normalize animal densities. The meroplankton were identified (Merritt, 1996), (Pennak, 1989) and sorted according to site, date and taxon. Their numbers and weights were recorded in order to find the biomass per unit of milfoil (dry weight) at each site. RESULTS AND DISCUSSION Table 1 shows the taxa encountered during this study. Tables 2-13 show the biomass of species found per biomass of milfoil for each site on all three dates. Differing amounts of milfoil were collected at each site. Therefore, grams of species per kilogram of milfoil was determined in order to present the data semi-quantitatively. Information about Hyde Bay is synthesized in Tables 2-4; the north site in 5-7; Rat Cove in 8-10; and the south site in 11-13 (See Figure 1 for site locations). Milfoil was found to be dense at the site on the North end of the Lake, Hyde Bay, and in Rat Cove. Hyde bay was the only site having significant representatives of other macrophyte species. At the South end of the Lake, milfoil clones were significantly less dense than in the other three sampling sites. Several observations of milfoil were made upon each collecting date. The beds ofm spicatum were noticeably thicker later in the season. It was also observed that the clones of milfoil did not create large mats at the surface at any sites. In Hyde Bay, Rat Cove, and the south site, the milfoil did not reach the surface, and rarely did so at the north site. On July 11, Acentria was found only in Rat Cove and the north site. On July 24, it was found in the two previous sites as well as in the south site. During the second sampling, Acentria were discovered to be much more numerous. The third sampling found Acentria equally as numerous as in the second sampling. Rat Cove and the north site were the only sites in which Acentria was found on all three dates. The explanation for the low numbers ofacentria on the first collecting date was that the species were at the end oftheir first 1997 generation. The second and third collecting dates
82 Otsego Lake Rat Cove Site 1I11\1'KOHl/) RflY o 1 f<m L J South Site r.usouf.ii/\nn/\ nivr 1\ Figure 1: Sites of M. spicatum collection on July 11, July 24, and August 7, 1997. *-Site location
83 All Sites, Summer 1997 TAXA July 11 July 24 August 7 Platyhelminthes ~ Tricladida Planariidae...... Annelida Hirudinea Pharyngobdellida Erpobdellidae.... Rhynchobdellida Glossiphoniidae Helobdelfa stagnalis.... Oligochaeta Haplotaxida Naididae...... Basommatrophora Gyraulus parvus...... Physidae Physa integra...... Mesogastropoda Hydrobiidae Amnicola limosa...... Arachnida Acariformes...... Hyalelfa azteca...... Isopoda Asellidae Caecidota.. Ephemeroptera Caenidae Caenis...... TABLE 1: Taxa ofall sites, summer 1997
84 TAXA July 11 July 24 August 7 Odonata (Anisoptera) Libellulidae * Odonata ( Zygoptera) Coenagrionidae Coenagrion or Enallagma * * * Hemiptera Mesoveliidae Mesovelia Lepidoptera Nepticulidae * * * * Pyralidae Acentria * * * Trichoptera Leptoceridae Mystacides Oecetis Hydroptilidae Agraylea * * * * * * Orthotrichia * * * Coleoptera Curculionidae * * * * Ceratapogonidae * Chironomidae Empididae * * * * TABLE 1 (continued): Taxa of all sites, summer 1997
85 Otsego Lake Hyde Bay-July 11, 1997 TAXA Number In grams g/ko milfoil IPlatyhelmInthes Tricladlda Planariidae 7 0.0094 0.0001 Basommatrophora Gyraulus parvus 7 0.0237 0.0003 Mesogastropoda Hydrobiidae Amnicola limosa 4 0.0375 0.0005 Arachnida Acariformes 5 0.0020 0.00003 Hya/ella azteca 9 0.0056 0.0001 Ephemeroptera Caenidae Caenis 2 0.0028 0.00004 Chironomidae 7 0.0074 0.0001 TABLE 2: Taxa of Otsego Lake Hyde Bay, July 11, 1997
86 Otsego Lake Hyde Bay-July 24, 1997 TAXA Number In grams g\kg milfoil IPlatyhelminthes Tricladida Planariidae 176 0.1989 2.5235 Annelida. Oligochaeta Haplotaxida Naididae 7 0.0006 0.0076 Basommatrophora Gyraulus parvus 38 0.0653 0.8285 Physidae Physa integra 1 0.0024 0.0304 Mesogastropoda Hydrobiidae Amnicola limosa 18 0.1844 2.3395 Hyalella azteca 7 0.0019 0.0241 Ephemeroptera Caenidae Caenis 1 0.0017 0.0216 Trichoptera Leptoceridae Oecetis 1 0.0040 0.0507 Chironomidae 6 0.0010 0.0127 TABLE 3: Taxa of Otsego Lake Hyde Bay, July 24,1997
87 Otsego Lake Hyde Bay-August 7, 1997 TAXA Number In grams g/kg milfoil If-'Iatyhelmlnthes ~ Tricladida Planariidae 130 0.1026 0.0006 Annelida Oligochaeta Haplotaxida Naididae 2 <.0001 <.0001 Basommatrophora Gyraulus parvus 73 0.1330 0.0008 Mesogastropoda Hydrobiidae Amnicola limosa 13 0.0289 0.0002 Arachnida Acariformes 1 0.0008 0.000005 Hya/ella azteca 7 0.0024 0.00001 Lepidoptera Pyralidae Acentria 1 0.0159 0.0001 Chironomidae 12 0.013 0.0001 -- TABLE 4: Taxa of Otsego Lake Hyde Bay, August 7, 1997
88 Otsego Lake North-July 11, 1997 TAXA Number In grams klkg milfoil Platyhelminthes Tricladida Planariidae 17 0.0272 0.1967 Annelida Hirudinea Rhynchobdellida Glossiphoniidae Helobdella stagnalis 2 0.0135 0.0976 Oligochaeta Haplotaxida Naididae 3 <.0001 <.0001 Basommatrophora Gyraulus parvus 4 0.0079 0.0571 Mesogastropoda Hydrobiidae Amnicola limosa 1 0.0106 0.0767 Arachnida Acariformes 1 0.0004 0.0029 Hyalella azteca 11 0.0093 0.0673 Hemiptera Mesoveliidae Mesovelia 1 0.0007 0.0051 Lepidoptera Nepticulidae 4 0.0097 0.0702 Pyralidae Acentria 1 0.0003 0.0022 Trichoptera Leptoceridae Mystacides 1 0.0083 0.0600 Oecetis 1 0.0012 0.0087 Hydroptilidae Orthotrichia 8 0.0052 0.0376 Chironomidae 10 0.0024 0.0174 TABLE 5: Taxa of Otsego Lake North, July 11, 1997
89 Otsego Lake North-July 24, 1997 TAXA Number In grams g/kg milfoil _... PlalYflelminthes Tricladida Planariidae 223 0.2894 1.1870 Annelida Hirudinea Pharyngobdellida Erpobdellidae 1 0.0007 0.0029 Rhynchobdellida Glossiphoniidae He/obdella stagnalis 1 0.0195 0.0800 Oligochaeta Haplotaxida Naididae 4 0.0004 0.0016 Basommartrophora Gyraulus parvus 31 0.0691 0.2834 Physidae Physa integra 16 0.0490 0.2010 Mesogastropoda Hydrobiidae Amnico/a limosa 13 0.1783 0.7313 Arachnida Acariformes 6 0.0025 0.0103 Hyalel/a azteca 34 0.0178 0.0730 Ephemeroptera Caenidae Caenis 2 0.0102 0.0418 -- TABLE 6: Taxa of Otsego Lake North, July 24, 1997
90 TAXA Number In grams g/kg milfoil Odonata (ZygopferaJ Coenagrionidae Coenagrion or Enallagma 1 0.178 0.7301 Lepidoptera Nepticulidae 2 0.0012 0.0049 Pyralidae Acentria 9 0.0362 0.1485 Chironomidae 10 0.0045 0.0185 TABLE 6 (continued): Taxa of Otsego Lake North, July 24, 1997
91 Otsego Lake North-August 7, 1997 TAXA Number In grams g/kg milfoil II-'Iatyhelmlnthes Tricladlda Planariidae 181 0.1743 0.0006 Annelida Oligochaeta Haplotaxida Naididae 19 0.0012 0.000004 Basommatrophora Gyraulus parvus 101 0.1924 0.0007 Physidae Physa integra 2 0.0120 0.00004 Mesogastropoda Hydrobiidae Amnicola limosa 1 0.0013 0.000005 Arachnida Acariformes 4 0.0033 0.00001 Hyalella azteca 5 0.0035 0.00001 Ephemeroptera Caenidae Caenis 1 0.0029 0.00001 TABLE 7: Taxa of Otsego Lake North, August 7,1997
92 TAXA Number In grams g/kg milfoil Odonata ( Zygoptera) Coenagrionidae Coenagrion or Enallagma 1 0.0002 0.000001 Lepidoptera Nepticulidae 1 0.0002 0.000001 Pyralidae Acentria 4 0.0474 0.0002 Trichoptera Leptoceridae Oecetis 4 0.0094 0.00003 Hydroptilidae Orthotrichia 1 0.0001 0.0000003 Coleoptera Curculionidae 3 0.0044 0.00002 Chironomidae 18 0.0061 0.00002 TABLE 7 (continued): Taxa of Otsego Lake North, August 7,1997
93 Otsego Lake Rat Cove-July 11, 1997 TAXA II-'Iatyhelmlnthes Tricladida Pfanariidae Annelida Hirudinea Rhynchobdellida Glossiphoniidae Helobdella stagnalis Basommatophora Gyraulus parvus Physidae Physa integra Mesogastropoda Hydrobiidae Amnicola limosa Hyalella azteca Ephemeroptera Caenidae Caenis Odonata (Zygoptera) Coenagrionidae Coenagrion or Enallagma Lepidoptera Nepticulidae Pyralidae Acentria Trichoptera Hydroptilidae Orthotrichia Coleoptera Curculionidae Chironomidae Number In grams g/kg milfoil 13 0.0194 0.1820 1 0.0022 0.0206 2 0.0064 0.0601 1 0.0040 0.0375 4 0.0292 0.2740 2 0.0034 0.0319 4 0.0132 0.1239 1 0.0312 0.2928 6 0.0094 0.0882 1 0.0140 0.1314 12 0.0043 0.0403 1 0.0014 0.0131 6 0.0022 0.0206 TABLE 8: Taxa ofotsego Lake Rat Cove, July 11, 1997
94 Otsego Lake Rat Cove-July 24, 1997 TAXA Platyhelminthes Tricladida Planariidae Annelida Hirudinea Rhynchobdellida Glossiphoniidae Helobdella stagnalis Oligochaeta Haplotaxida Naididae Basommatrophora Gyraulus parvus Hyalella azteca Ephemeroptera Caenidae Caenis Odonata (Zygoptera) Coenagrionidae Coenagrion or Enallagma Lepidoptera Nepticulidae Pyralidae Acentria Trichoptera Leptoceridae Oecetis Hydroptilidae Orthotrichia Coleoptera Curculionidae Chironomidae I Number In grams g/kg milfoil 90 0.0725 0.4495 1 0.0029 0.0180 14 0.0016 0.0099 2 0.0102 0.0632 1 0.0005 0.0031 1 0.0004 0.0025 2 0.0316 0.1959 9 0.0107 0.0663 23 0.0773 0.4792 1 0.0171 0.1060 41 0.0224 0.1389 4 0.0052 0.0322 1 0.0005 0.0031 35 0.0122 0.0756 TABLE 9: Taxa of Otsego Lake Rat Cove, July 24, 1997
95 Otsego Lake Rat Cove-August 7, 1997 TAXA Number In grams g/kg milfoil Platyhelminthes Tricladlda Planariidae 220 0.1865 0.0010 Annelida Hirudinea Pharyngobdellida Erpobdellidae 2 0.0023 0.00001 Oligochaeta Haplotaxida Naididae 7 0.0009 0.000005 Basommatrophora Gyraulus parvus 6 0.0157 0.0001 Physidae Physa integra 1 0.0130 0.0001 Mesogastropoda I Hydrobiidae Amnicola limosa 5 0.0498 0.0003 Arachnida Acariformes 6 0.0013 0.00001 Hyalella azteca 4 0.0014 0.00001 Ephemeroptera Caenidae Caenis 1 0.0018 0.00001 TABLE 10: Taxa of Otsego Lake Rat Cove, August 7, 1997
96 TAXA Number In grams g/kg milfoil Odonata (Anisoptera) Libellulidae 1 0.0011 0.00001 Lepidoptera Nepticulidae 8 0.0089 0.00005 Pyralidae Acent,ia 15 0.0668 0.0003 Trichoptera Leptoceridae Oecetis 9 0.0108 0.0001 Hydroptilidae Agraylea 1 0.0011 0.00001 Orthotrichia 39 0.0305 0.0002 Coleoptera Curculionidae 2 0.0031 0.00002 Chironomidae 436 0.1801 0.0009 TABLE 10 (continued): Taxa of Otsego Lake Rat Cove, August 7, 1997
97 Otsego Lake South-July 11, 1997 TAXA Number In grams g/kg milfoil IPlatyhelminthes Tricladida Planariidae 5 0.0001 0.0022 Basommatrophora Gyraulus parvus 1 0.0014 0.0302 Arachnida Acariformes 2 0.0001 0.0022 Ephemeroptera Caenidae Caenis 10 0.0223 0.4804 Trichoptera Leptoceridae Oecetis 14 0.0399 0.8595 Hydroptilidae Orlhotnd7ia 134 0.6920 14.9074 Chironomidae 39 0.0152 0.3274 TABLE 11: Taxa of Otsego Lake South, July 11, 1997
98 Otsego Lake South-July 24, 1997 TAXA Number In grams g/kg mlifoll Platyhelminthes Tricladida Planariidae 36 0.0225 0.1749 Annelida Hirudinea Rhynchobdellida Glossiphoniidae Helobdella stagnalis 4 0.0772 0.6001 Oligochaeta 1 Haplotaxida Naididae I 15 0.0012 0.0093 Basommatrophora j Gyraulus parvus 3 0.0053 0.0412 I Hyalella azteca 0.0117 ~r015 Ephemeroptera I Caenidae Caenis 1 0.0046 0. 0358 1 Lepidoptera Pyralidae Acentria Trichoptera I 3 I 0.0144 ~~I Leptoceridae Oecetis 3 0.0227 0.1765 Hydroptilidae Orthotrichia 99 0.0770 0.5986 Chironomidae 80 0.0231 0.1796 TABLE 12: Taxa of Otsego Lake South, July 24, 1997
99 Otsego Lake South-August 7, 1997 TAXA Number In grams g/kg milfoil PlatyhelmInthes Tricladida Planariidae 131 0.1310 0.0010 Annelida Hirudinea Pharyngobdellida Erpobdellidae 1 0.0023 0.00002 Oligochaeta Haplotaxida Naididae 4 <.0001 <.0001 Basommatrophora Gyraulus parvus 1 0.0027 0.00002 Arachnida Acariformes 2 0.0003 0.000002 Hyalella azteca a 0.0051 0.00004 Isopoda Asellidae Caecidota 1 0.0007 0.00001 Ephemeroptera Caenidae Caenis 2 0.0071 0.0001 TABLE 13: Taxa of Otsego Lake South, August 7, 1997
100 TAXA Number In grams g/kg milfoil Odonata (Anisoptera) Libellulidae 2 0.0004 0.000003 Lepidoptera Pyralidae Acentria 11 0.0349 0.0003 Trichoptera Leptoceridae Oecetis 13 0.0652 0.0005 Hydroptilidae 1 0.0003 0.000002 Agraylea 19 0.0570 0.0004 Orthotrichia 27 0.0249 0.0002 Coleoptera Curculionidae 1 0.0008 0.00001 Ceratapogonidae 1 0.0005 0.000004 Chironomidae 146 0.0586 0.0004 Empididae 1 0.0015 0.00001 TABLE 13 (continued): Taxa of Otsego Lake South, August 7,1997
101 sampled members of the second generation (Harman, 1997). The greatest diversity in plant species was found in Hyde Bay. At other sites, M. spicatum grew in undiversified clumps, except for at the south site which was monospecific to milfoil, though in low density. The greatest diversity in meroplankton was found in Rat Cove and the north site. At each site, species from thirteen or fourteen different families were found (see Tables 5-10). Therefore, there was no correlation between meroplankton and macrophytic diversity. Members of the families Planariidae and Chironomidae were the dominant species at each of the sites. This study provides background information of the meroplankton found to inhabit Myriophyllum spicatum beds. The data collected seemed to indicate that Acentria, found in insignificant numbers, was probably not the cause for the lack of proliferation of M spicatum in Otsego Lake. This was a preliminary study ofacentria populations in Otsego lake and further research should be conducted. Surveys conducted later in the season may better coincide with highest larvae densities and therefore would better evaluate the local population of these animals. REFERENCES Anon. 1986. Draft environmental impact statement for treatment of Eurasion Watermilfoil in Lake George. Lake George Park Commissions, pp. 1-107 plus appendices and ancillary materials. Dayton, B. R. and D. R. Swift. 1987. Composition of aquatic macrophyte communities in Otsego Lake: A preliminary study, p. 68-78, In 19 th Ann. Rept. (1986). SUNY Oneonta Biological Field Station, SUNY Oneonta. Harman, W. N. 1997. Personal Communication. SUNY Oneonta Biological Field Station, SUNY Oneonta, Oneonta, NY. Hutchinson, G. E. 1970. The chemical ecology of three species of Myriophyllum (Angiospermae, Haloragaceae). Limnology and Oceanography, Vol. 15, No.1, pp. 1-5. Merrifield, M. 1. and W. N. Harman. 1988. The taxonomy, distribution and abundance of Myriophyllum (Myrtiflorae: Haloragaceae) in Otsego Lake, New York, In 20 th Aim. Rept. (1987), SUNY Oneonta Biological Field Station, SUNY Oneonta, pp. 103-116. Merritt, R. W., and K. W. Cummins (eds.) 1996. Aquatic insects of North America. Kendall/Hunt Publishing Company. Dubuque,IA. Pennak, R. W. 1989. Freshwater invertebrates of the United States, 3 rd Ed. John Wiley and Sons, Inc. New York.
102 Sanders, R. L. 1990. Recent studies in the distribution and abundance of Myriophyllum spicatum in Otsego Lake, New York. In 23 rd Ann. Rept. (1990), SUNY Oneonta Biological Field Station, SUNY Oneonta, pp. 160-164. Stalter, A. M. 1989. The distribution and abundance ofmyriophyllum spicatum in Otsego Lake, New Yark. In 21 st Ann. Rept. (1987), SUNY Oneonta Biological Field Station, SUNY Oneonta, pp. 34-38.