Survey of zooplankton in Brant Lake, Horicon, NY INTRODUCTION

Transcription

1 Survey of zooplankton in Brant Lake, Horicon, NY Sarah Newtown 1, Alejandro Reyes 2 INTRODUCTION Located in the middle of the aquatic food chain, zooplankton provide a critical energy pathway for higher trophic levels while also being able to exert grazing pressure on primary producers, limiting algae growth. Changes in population size and composition as a result of these factors make zooplankton a good indicator of the impact of invasive species (Havel and Shurin 2004). Invasion by dreissenid mussels (Dreissena spp.) can result in a decrease in small bodied rotifers due to predation and competition for niche space (Mihuc et al. 2012). It has also been shown that alewife (Alosa pseudoharengus) predate upon large bodied copepods and cladocerans, thereby resulting in an assemblage shift to small bodied crustaceans (Mihuc et al. 2012). The same effect can be seen with an invasion of spiny water flea (Bythotrephes longimanus) (Yan et al. 2011). A significant change in the community composition of native zooplankton, as a result of invasive species introduction, can unbalance the ecosystem by reducing filter feeding daphnia and removing the forage base for native fish (Walsh et al. 2016). The results are amplified both up and down the food chain, altering the ecology of the system (Harman et al. 2002). Brant Lake is a 584 ha lake located in Warren County, NY within the Adirondack Park. It is a public access lake which receives boaters from Lake George, Lake Champlain, and the Great Lakes, all of which contain populations of invasive species such as zebra mussels, spiny water flea, and alewife. As a consequence of Brant Lake s proximity to these water bodies, there is an increased risk of introduction. The goals of this study were to characterize zooplankton community assemblage and dynamics within Brant Lake and to detect any new invasive species. Because of the planktonic life stages of various invasive species (zebra/quagga mussels and spiny water flea), they have the potential to show up in routine zooplankton monitoring. The results of this study will provide the stakeholders with baseline information on the current community composition of zooplankton in the lake, better preparing them to respond to and quantify an early invasion. METHODS Zooplankton samples were collected from Site 1 in Brant Lake (Figure 1) in conjunction with standard limnological monitoring. This sample site was chosen because it is the deepest part of the lake at approximately 18m (Holdren et al. 2001). One vertical tow was conducted using a 153 micron mesh Wisconsin net starting from 2m off the bottom (16m). The net was retrieved at a rate of approximately 1m/s. Samples were collected from April 26, 2015 to 1 SUNY Oneonta Biology Department. 2 MS graduate candidate. SUNY Oneonta.

2 October 27, All samples were stored at room temperature in 125 ml plastic bottles and preserved with 70% ethanol containing a rose-bengal stain. Figure 1. Map showing the location of the sample site, Site 1. Site 2 was not used in this study. In the lab, 1 ml aliquots were taken using a Henson Stemple pipette and placed on a Sedgewick Rafter gridded cell to be enumerated. In order to maintain consistency when quantifying zooplankton in all the samples, at least 100 zooplankton were counted per sample; as many subsamples were taken as needed to reach a count of at least 100 organisms. All identifications were made using Carling et al. (2004). All identifications were verified by staff at the Lake Champlain Research Institute. RESULTS AND DISCUSSION Fifteen taxa representing seven families were observed during the study (Table 1). The zooplankton community is dominated by small rotifers, namely Keratella cochlearis, Kellicottia longiseta, and Polyarthra major. The rarest organisms were Asplanchna spp., Tropocyclops, Daphnia longiremis, and Bosmina coregoni, which were only present once in all eight samples.

3 Table 1. All species observed from Brant Lake, 2015, and their final counts. Two mixing events occurred during the sample period; the first was around 4/26/2015 and the second was around 10/27/2015 (Figure 2). Between these events, thermal stratification was present, with the thermocline forming between 6-8m. Figure 3. Temperature data for all date s samples were collected.

4 Early June had the highest abundance of organisms, with a second, smaller peak of organisms during September. Cladocera abundance peaked in June with Bosmina longispina being the most dominant organism. The larger Daphnia, galeata mendotae, showed a slight increase in abundance in late summer, but overall was in low abundance throughout the survey. Copepod abundance was generally low during the season, with Diacyclops thomasi being the dominant species observed. Interesting to note was the differential peaks of Leptodiaptomus and Skistodiaptomus oregonensis. There may be some temporal separation taking place between these taxa, however our sample sizes are too low to draw any definitive conclusions. Rotifer abundance peaked in June, with Keratella cochlearis being the dominant species. All other species do not show a major trend seasonally. Overall, the zooplankton community of Brant Lake is dominated by smaller bodied organisms such as rotifers and unknown juvenile stages (copepodites and nauplii). The small bodied nature of the community can be partially attributed to predation pressure. Predation pressure has been implicated in changes in zooplankton and abundance vertically (Iwasa 1982). On 27 October, the sample collected had a high number of Chaoborus present. Chaoborus (Chaoboridae) is a genus of aquatic midges that are voracious predators on zooplankton. It is known that Chaoborus instar IV primarily feed on cladocerans for most of the year (Moore et al. 1994). Predation by Chaoborus could explain why cladocerans are in such low abundance for the entire sampling period. Recently, a fisheries survey of Brant Lake found a large population of rainbow smelt (Osmerus mordax) (Reyes unpublished data). Rainbow smelt show a preference for feeding on large bodied copepods and cladocerans, resulting in a population of small bodied crustaceans (Sheppard et al. 2012). We believe that the combined predation pressure of both Chaoborus and rainbow smelt had has a significant impact on the zooplankton community assemblage. No larval stages of invasive species were found during the course of the survey. This result can mean one of two things. First, there are no invasive species present. Second, invasive species are at such a low abundance in the lake, that their larvae are not being detected in our sampling. For zebra mussels, they require a calcium level of around 20mg/L to successfully produce larvae (Hincks and Mackie 1997). Mean surface calcium levels in Brant Lake are 8.37mg/L (Reyes, unpublished data), making successful reproduction unlikely, implying they are not in the lake at this moment. Spiny water fleas in Lake Champlain show up during the fall of 2014 (Mihuc unpublished data) and they are known to inhabit the deeper portions of lakes (Yan et al. 2011). Since we have samples in the fall, and from the deep portion of the lake, we are confident that our sampling approach would have captured spiny water flea if present.

5 Figure 3. Monthly abundances of Cladocera, Copepoda and Rotifera, Brant Lake, Note change in x-axis values for each graph. CONCLUSIONS The goal of this study was to provide the stakeholders of Brant Lake with a list of zooplankton taxa and any new invasive species found during sampling. No new invasive species were observed in any of the samples collected. These baseline data can be used to start a monitoring program aimed at detecting new invasive species and changes within the

6 zooplankton community. This will enable the stakeholders to detect a new invasive species introduction before management becomes cost prohibitive. REFERENCES Carling, K.J., I.M. Ater, M R. Pellam, A.M. Bouchard, and T.B. Mihuc A guide to the zooplankton of Lake Champlain. Scientia Discipulorum 1(1):4. Havel, J.E., and J.B. Shurin Mechanisms, effects, and scales of dispersal in freshwater zooplankton. Limnology and Oceanography 49(4part2): Hincks, S.S., and G.L. Mackie Effects of ph, calcium, alkalinity, hardness, and chlorophyll on the survival, growth, and reproductive success of zebra mussel (Dreissena polymorpha) in Ontario lakes. Canadian Journal of Fisheries and Aquatic Sciences 54(9): Holdren, C., B. Jones, and J. Taggart Managing lakes and reservoirs. North American Lake Management Society; Terrene Insitute. Iwasa, Y Vertical migration of zooplankton: A game between predator and prey. The American Naturalist 120(2): Mihuc, T.B., F. Dunlap, C. Binggeli, L. Myers, C. Pershyn, A. Groves, and A. Waring Long-term patterns in Lake Champlain s zooplankton: Journal of Great Lakes Research 38: Moore, M.V., N.D. Yan, and T. Pawson Omnivory of the larval phantom midge (Chaoborus spp.) and its potential significance for freshwater planktonic food webs. Canadian Journal of Zoology 72(11): Sheppard, K.T., A.J. Olynyk, G.K. Davoren, and B.J. Hann Summer diet analysis of the invasive rainbow smelt (Osmerus mordax) in Lake Winnipeg, Manitoba. Journal of Great Lakes Research 38: Walsh, J.R., S.R. Carpenter, and M.J.V. Zanden Invasive species triggers a massive loss of ecosystem services through a trophic cascade. Proceedings of the National Academy of Sciences: