Assessment Of The Freshwater Mussel Community Of The Upper Mahoning River Watershed And Factors Influencing Diversity And Abundance In Small Streams

Author : Bryce Edward Daniels
Publisher :
ISBN 13 :
Total Pages : 114 pages
Book Rating : 4.:/5 (486 download)

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Download or read book Assessment of a Freshwater Mussel (mollusca: Bivalvia) Community in the Licking River, at Butler, Pendleton County, Kentucky written by Bryce Edward Daniels and published by . This book was released on 2000 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study was undertaken to assess the current condition of the freshwater mussel (also called unionid) (Bivalvia: Unionidae) community in the Licking River at the State Route 177 bridge crossing in Butler, Pendleton County, Kentucky. A recent study indicated a drastic decline in the reproduction occurring in this historically diverse assemblage, evident through findings of few glochidia in stream drift and the absence of glochidial encystment on any of the fishes collected. An intensive community analysis provided information on the current size demography of the resident populations, and monitored the presence of species historically known from this site. It also provided evidence of juvenile recruitment and reproduction, through presence/absence of juveniles at the site and glochidia (mussel larvae) in drift net samples or encysted upon fishes. Results from this survey would be useful for future monitoring of this community, and would provide important information that can be used in comparison with other mussel assemblages for which various have been quantified. Land use practices that had been or are currently being employed upstream of the proposed study site were considered to better understand the point and nonpoint source pollution factors that might be influencing community changes. It was hypothesized that upstream land use practices were contributing to a previously documented decline of reproduction at this locality. Qualitative and quantitative searches yielded 27 extant unionid species within the area, and resulted in the discovery of juveniles of eight species, including two juveniles of the state and federally endangered fanshell, Cyprogenia stegaria. Quantitative sampling, consisting of substrate excavation of randomly selected 0.25 m2 plots yielded 130 individual unionids, representing 17 species, at a total density of approximately 4.3 unionids / m2. Calculations showed the most abundant species, the spike, Elliptio dilatata, to have had the highest importance value in the quantitavely sampled areas. Analysis of drift net samples yielded 159 unionid glochidia and 434 juvenile Corbicula fluminea, the exotic Asian clam, out of approximately 730 m3 of stream drift. Examination of 545 fishes collected from the site yielded 241 glochidia encysted on either gills or fins of 47 individual fish hosts, for an average of 5.13 glochidia per infected fish. Eight species of fish were represented by hosts bearing encysted glochidia. These eight species comprised 71.74% of all fishes collected. The emerald shiner, Notropis atherinoides, was the most abundant fish from the three collections, bore the most glochidia, and had the highest prevalence of encystment. Twenty-seven emerald shiners were encysted with 195 unionid larvae; one individual was found bearing 105 glochidia encysted upon its gills. The dominant human influence in the lower Licking River drainage is agriculture, which has lead to a decrease of riparian buffer along a large proportion of the banks within the watershed, and has also allowed livestock access to the streams. The decrease of a riparian buffer and cattle access allows for more direct introduction of chemicals (i.e., pesticides and fertilizers), as well as decreases bank stability, which, in turn, leads to excessive sediment introduction. Such anthropogenic factors and large numbers of C. fluminea, have likely impacted the resident mussel fauna. Although this mussel community remains diverse, the lack of juvenile representation for all but eight species indicated a breakdown in a very important stage in the life history for the rest of the community. Recent reproduction was evident through the presence of glochidia encysted on host fishes and being broadcast into the water column; however, accurate recruitment patterns for resident populations could not be obtained without identification of the glochidia. The only definitive sign of a particular species having recently recruited new members was through the presence of juveniles in the quantitative and/or qualitative samples. These analyses provided baseline population data for each species which can be used in future monitoring of this biologically and historically significant site. There is a great need for future monitoring of such communities, so dynamics of the community can be more definitively recorded, and fluctuations in population structures can be analyzed. Compilations of long-term monitoring efforts on such diverse mussel communities should allow more accurate speculation, in comparison to watersheds with similar land uses, on the effects of such anthropogenic factors as point and nonpoint source pollutants on unionids. Better understanding of the impacts of these factors to natural communities should lead to better management strategies to ameliorate these impacts, conserving existing communities.