6/07/2017  |   09:00 - 09:15   |  306C

MISMATCH BETWEEN BENTHIC MACROINVERTEBRATE DENSITIES AND STABLE ISOTOPES OF FISHES IN DYNAMIC HIGH-HEAD RESERVOIRS IN THE WILLAMETTE RIVER BASIN, OREGON. How do seasonally fluctuating reservoir water levels affect the availability of benthic invertebrates vs. zooplankton as prey for fishes? The Willamette River Basin, Oregon is impounded by high-head dams that undergo water level fluctuations, exposing much of the sediments. We examined the littoral benthic macroinvertebrate community, zooplankton, and fishes including juvenile Chinook Salmon, Bluegill, Largemouth Bass and crappie at three such reservoirs (Fall Creek, Hills Creek and Lookout Point). We found very low densities of benthic macroinvertebrates (generally < 25/m2), dominated by Chironomidae. Stable carbon isotope ratios of benthic macroinvertebrates were variable across families, but were enriched compared to those of zooplankton. Although observed macroinvertebrate densities were very low and gut contents of fishes suggested that Daphnia are their dominant food source, the relatively enriched carbon isotope ratios of fishes suggest a major macroinvertebrate contribution to their diets. We explore hypotheses to explain this mismatch of low observed macroinvertebrate densities with their apparent dietary importance to fishes, as suggested by isotopic ratios.

Christina A. Murphy (Primary Presenter/Author), U.S. Geological Survey, Maine Cooperative Fish and Wildlife Research Unit, Orono, ME, christina.murphy@maine.edu;
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Ivan Arismendi ( Co-Presenter/Co-Author), Oregon State University, Department of Fisheries & Wildlife, ivan.arismendi@oregonstate.edu;


Stephen K. Hamilton ( Co-Presenter/Co-Author), Michigan State University & Cary Institute of Ecosystem Studies, hamilton@kbs.msu.edu;


Sherri Johnson ( Co-Presenter/Co-Author), U.S. Forest Service, Pacific Northwest Research Station, sherrijohnson@fs.fed.us;


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6/07/2017  |   09:15 - 09:30   |  306C

CHIRONOMIDAE LARVAE AS ECOSYSTEM ENGINEERS IN A LENTIC ENVIRONMENT The abundance of chironomid larvae may reach the point where the larvae significantly affect the physical and chemical properties of lake sediment. In some years the larvae of Tanytarsus gracilentus occur in enormous densities in Lake Mývatn, N.E. Iceland. On those occasions the larvae modify the top 2 cm of the sediment, which is then packed with larval tubes and forms a crust on top of liquefied sediment. The larvae, therefore, may influence the chemical fluxes at the water-sediment interface. Also, by the tube building activities, the larvae alter the physical properties of the sediment. The shear strength and the erodibility of sediment change significantly by this activity. I will present results where the effect of larval densities was studied in relation to physical properties of soft sediment (i.e. its shear strength, erodibility and flow). The results are based on laboratory experiments as well as direct measurements in the field. Shear strength of the sediment was positively correlated with larval density. The erodibility of the sediment indicated that the erosion was highest in low to moderate larval densities.

Jón S. Ólafsson (Primary Presenter/Author), Marine and Freshwater Research Institute, Iceland, jon.s.olafsson@hafogvatn.is;


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6/07/2017  |   09:30 - 09:45   |  306C

THE FALL EMERGENCE OF THE MAYFLY, HEXAGENIA LIMBATA, FROM WESTERN LAKE ERIE The mass emergence of Hexagenia mayflies during June-July from western Lake Erie has been an annual event since the early 1990s, after an absence of over 30 years. Similarly, observations of “stray” adults along the shoreline well past (August and September) this peak emergence period have commonly been reported, although their specific origin remains unknown. In October of 2016, large numbers of Hexagenia limbata adults were observed at Cedar Island Marina along the north shore of Lake Erie equal to about 50% of that seen the previous July, although noticeably smaller than those in July. Nymphs with black-wing pads were collected off the west side of Pelee Island and exuvae were found on the lake’s surface. Size-frequency analysis indicated that eggs began hatching in early August 2016, and nymphs grew rapidly to the size that had black-wing pads in early October. Still many of the emerging adults may have been from eggs that had hatched in October 2015, a population at a very low density in the lake. No such fall emergence was noticed from Lake St. Clair.

Ronald Griffiths (Primary Presenter/Author), Oregon State University, Oregon Hatchery Research Center, Corvallis, OR 97331, ron.griffiths@oregonstate.edu;


Don W Schloesser ( Co-Presenter/Co-Author), U.S. Geological Survey, Great Lakes Science Center, dschloesser@usgs.gov;


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6/07/2017  |   09:45 - 10:00   |  306C

HEXAGENIA SPP. IN WESTERN LAKE ERIE OF THE GREAT LAKES-- COMEBACK AND REVIEW OF A SENTINEL TAXON? In the mid 1950s, mayfly nymphs disappeared from western Lake Erie and many areas of the Great Lakes. In 1993, after 40 years of absence, mayflies returned to western Lake Erie and there has been a sustained presence of mayflies for the past 25 years. However, densities fluctuated dramatically with a 'boom-and-bust' cycle ever 3-4 years. As a result, a hypothesis was developed that mayflies were exhibiting a density-dependent relationship. This possible relationship was contradictory to the explanation for the absence of mayflies between the mid-1950s and mid-1990s (i.e., eutrophication). Several studies examined the hypothesis of density dependency and found there is evidence the abundance of mayflies interacts with 'residual' pollution to create anoxic conditions determining densities of mayflies in western Lake Erie. As waters of Lake Erie are restored, the density-dependent hypothesis may become more important in interpretation of meaningful endpoints for this taxon used in management-restoration plans for western Lake Erie and, possibly, elsewhere in the Great Lakes.

Don W Schloesser (Primary Presenter/Author), U.S. Geological Survey, Great Lakes Science Center, dschloesser@usgs.gov;


Martin A. Stapanian ( Co-Presenter/Co-Author), Great Lakes Science Center, mstapanian@usgs.gov;


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6/07/2017  |   10:00 - 10:15   |  306C

EFFECTS OF WATERSHED AND IN-STREAM LIMING ON MACROINVERTEBRATE ASSEMBLAGES IN ACIDIFIED TRIBUTARIES TO AN ADIRONDACK LAKE Water quality and ecosystems in the Adirondack Mountain Region of New York are recovering slowly from decades of acid deposition. Liming techniques are being explored as tools to accelerate this recovery. In 2012, a program was initiated using in-stream and aerial (whole-watershed) liming to improve water quality and Brook Trout (Salvelinus fontinalis) recruitment in three chronically acidified tributaries of a high-elevation Adirondack lake. Macroinvertebrates were sampled annually between 2013 and 2016 at 3 treated and 3 untreated (control) sites to assess the effects of each liming technique on this community. Despite marked improvements in water chemistry in all three limed streams, preliminary analyses do not indicate a clear positive response by macroinvertebrate communities. Species richness exhibited no response to either liming technique, and total macroinvertebrate abundance responded negatively to all three lime applications. The proportion of acid-sensitive taxa was generally low at all treated and untreated sites, but increased gradually at one of the in-stream liming sites. These results are consistent with a body of literature suggesting that liming is generally ineffective at restoring macroinvertebrate communities to a pre-acidification condition.

Scott George (Primary Presenter/Author), U.S. Geological Survey, sgeorge@usgs.gov;


Barry Baldigo ( Co-Presenter/Co-Author), U.S. Geological Survey, bbaldigo@usgs.gov;


Greg Lawrence ( Co-Presenter/Co-Author), U.S. Geological Survey, glawrenc@usgs.gov;


Randy Fuller ( Co-Presenter/Co-Author), Colgate University, rfuller@colgate.edu;


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