An inventory ofmeroplankton associated with Myriophyllum spicatum, focusing on Acentria ephemerella, in Otsego Lake, summer 1997

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1 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 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 Present affiliation: Cooperstown Central High School.

2 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 (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

3 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, *-Site location

4 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

5 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

6 85 Otsego Lake Hyde Bay-July 11, 1997 TAXA Number In grams g/ko milfoil IPlatyhelmInthes Tricladlda Planariidae Basommatrophora Gyraulus parvus Mesogastropoda Hydrobiidae Amnicola limosa Arachnida Acariformes Hya/ella azteca Ephemeroptera Caenidae Caenis Chironomidae TABLE 2: Taxa of Otsego Lake Hyde Bay, July 11, 1997

7 86 Otsego Lake Hyde Bay-July 24, 1997 TAXA Number In grams g\kg milfoil IPlatyhelminthes Tricladida Planariidae Annelida. Oligochaeta Haplotaxida Naididae Basommatrophora Gyraulus parvus Physidae Physa integra Mesogastropoda Hydrobiidae Amnicola limosa Hyalella azteca Ephemeroptera Caenidae Caenis Trichoptera Leptoceridae Oecetis Chironomidae TABLE 3: Taxa of Otsego Lake Hyde Bay, July 24,1997

8 87 Otsego Lake Hyde Bay-August 7, 1997 TAXA Number In grams g/kg milfoil If-'Iatyhelmlnthes ~ Tricladida Planariidae Annelida Oligochaeta Haplotaxida Naididae 2 <.0001 <.0001 Basommatrophora Gyraulus parvus Mesogastropoda Hydrobiidae Amnicola limosa Arachnida Acariformes Hya/ella azteca Lepidoptera Pyralidae Acentria Chironomidae TABLE 4: Taxa of Otsego Lake Hyde Bay, August 7, 1997

9 88 Otsego Lake North-July 11, 1997 TAXA Number In grams klkg milfoil Platyhelminthes Tricladida Planariidae Annelida Hirudinea Rhynchobdellida Glossiphoniidae Helobdella stagnalis Oligochaeta Haplotaxida Naididae 3 <.0001 <.0001 Basommatrophora Gyraulus parvus Mesogastropoda Hydrobiidae Amnicola limosa Arachnida Acariformes Hyalella azteca Hemiptera Mesoveliidae Mesovelia Lepidoptera Nepticulidae Pyralidae Acentria Trichoptera Leptoceridae Mystacides Oecetis Hydroptilidae Orthotrichia Chironomidae TABLE 5: Taxa of Otsego Lake North, July 11, 1997

10 89 Otsego Lake North-July 24, 1997 TAXA Number In grams g/kg milfoil _... PlalYflelminthes Tricladida Planariidae Annelida Hirudinea Pharyngobdellida Erpobdellidae Rhynchobdellida Glossiphoniidae He/obdella stagnalis Oligochaeta Haplotaxida Naididae Basommartrophora Gyraulus parvus Physidae Physa integra Mesogastropoda Hydrobiidae Amnico/a limosa Arachnida Acariformes Hyalel/a azteca Ephemeroptera Caenidae Caenis TABLE 6: Taxa of Otsego Lake North, July 24, 1997

11 90 TAXA Number In grams g/kg milfoil Odonata (ZygopferaJ Coenagrionidae Coenagrion or Enallagma Lepidoptera Nepticulidae Pyralidae Acentria Chironomidae TABLE 6 (continued): Taxa of Otsego Lake North, July 24, 1997

12 91 Otsego Lake North-August 7, 1997 TAXA Number In grams g/kg milfoil II-'Iatyhelmlnthes Tricladlda Planariidae Annelida Oligochaeta Haplotaxida Naididae Basommatrophora Gyraulus parvus Physidae Physa integra Mesogastropoda Hydrobiidae Amnicola limosa Arachnida Acariformes Hyalella azteca Ephemeroptera Caenidae Caenis TABLE 7: Taxa of Otsego Lake North, August 7,1997

13 92 TAXA Number In grams g/kg milfoil Odonata ( Zygoptera) Coenagrionidae Coenagrion or Enallagma Lepidoptera Nepticulidae Pyralidae Acentria Trichoptera Leptoceridae Oecetis Hydroptilidae Orthotrichia Coleoptera Curculionidae Chironomidae TABLE 7 (continued): Taxa of Otsego Lake North, August 7,1997

14 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 TABLE 8: Taxa ofotsego Lake Rat Cove, July 11, 1997

15 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 TABLE 9: Taxa of Otsego Lake Rat Cove, July 24, 1997

16 95 Otsego Lake Rat Cove-August 7, 1997 TAXA Number In grams g/kg milfoil Platyhelminthes Tricladlda Planariidae Annelida Hirudinea Pharyngobdellida Erpobdellidae Oligochaeta Haplotaxida Naididae Basommatrophora Gyraulus parvus Physidae Physa integra Mesogastropoda I Hydrobiidae Amnicola limosa Arachnida Acariformes Hyalella azteca Ephemeroptera Caenidae Caenis TABLE 10: Taxa of Otsego Lake Rat Cove, August 7, 1997

17 96 TAXA Number In grams g/kg milfoil Odonata (Anisoptera) Libellulidae Lepidoptera Nepticulidae Pyralidae Acent,ia Trichoptera Leptoceridae Oecetis Hydroptilidae Agraylea Orthotrichia Coleoptera Curculionidae Chironomidae TABLE 10 (continued): Taxa of Otsego Lake Rat Cove, August 7, 1997

18 97 Otsego Lake South-July 11, 1997 TAXA Number In grams g/kg milfoil IPlatyhelminthes Tricladida Planariidae Basommatrophora Gyraulus parvus Arachnida Acariformes Ephemeroptera Caenidae Caenis Trichoptera Leptoceridae Oecetis Hydroptilidae Orlhotnd7ia Chironomidae TABLE 11: Taxa of Otsego Lake South, July 11, 1997

19 98 Otsego Lake South-July 24, 1997 TAXA Number In grams g/kg mlifoll Platyhelminthes Tricladida Planariidae Annelida Hirudinea Rhynchobdellida Glossiphoniidae Helobdella stagnalis Oligochaeta 1 Haplotaxida Naididae I Basommatrophora j Gyraulus parvus I Hyalella azteca ~r015 Ephemeroptera I Caenidae Caenis Lepidoptera Pyralidae Acentria Trichoptera I 3 I ~~I Leptoceridae Oecetis Hydroptilidae Orthotrichia Chironomidae TABLE 12: Taxa of Otsego Lake South, July 24, 1997

20 99 Otsego Lake South-August 7, 1997 TAXA Number In grams g/kg milfoil PlatyhelmInthes Tricladida Planariidae Annelida Hirudinea Pharyngobdellida Erpobdellidae Oligochaeta Haplotaxida Naididae 4 <.0001 <.0001 Basommatrophora Gyraulus parvus Arachnida Acariformes Hyalella azteca a Isopoda Asellidae Caecidota Ephemeroptera Caenidae Caenis TABLE 13: Taxa of Otsego Lake South, August 7, 1997

21 100 TAXA Number In grams g/kg milfoil Odonata (Anisoptera) Libellulidae Lepidoptera Pyralidae Acentria Trichoptera Leptoceridae Oecetis Hydroptilidae Agraylea Orthotrichia Coleoptera Curculionidae Ceratapogonidae Chironomidae Empididae TABLE 13 (continued): Taxa of Otsego Lake South, August 7,1997

22 101 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 Draft environmental impact statement for treatment of Eurasion Watermilfoil in Lake George. Lake George Park Commissions, pp plus appendices and ancillary materials. Dayton, B. R. and D. R. Swift Composition of aquatic macrophyte communities in Otsego Lake: A preliminary study, p , In 19 th Ann. Rept. (1986). SUNY Oneonta Biological Field Station, SUNY Oneonta. Harman, W. N Personal Communication. SUNY Oneonta Biological Field Station, SUNY Oneonta, Oneonta, NY. Hutchinson, G. E The chemical ecology of three species of Myriophyllum (Angiospermae, Haloragaceae). Limnology and Oceanography, Vol. 15, No.1, pp Merrifield, M. 1. and W. N. Harman 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 Merritt, R. W., and K. W. Cummins (eds.) Aquatic insects of North America. Kendall/Hunt Publishing Company. Dubuque,IA. Pennak, R. W Freshwater invertebrates of the United States, 3 rd Ed. John Wiley and Sons, Inc. New York.

23 102 Sanders, R. L 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 Stalter, A. M 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