MUSSELS:THE FORGOTTEN FAUNA OF REGULATED RIVERS. James B. Layzer and
<br />Mark E. Gordon, Tennessee Cooperative Fishery Research Unit, Tennessee
<br />Technological University, Box 5114, Cookeville, TN 38505.
<br />During the past century, freshwater mussel populations have declined precipitously
<br />throughout North America. Much of this Loss resulted from [he construction of dams.
<br />In the Cumberland River system, 23% (22 species) of the historic mussel fauna is
<br />extinct or listed as endangered. Several additional species have either been
<br />extirpated from the Cumberland River or exist only in small, nonreproducing
<br />populations. Mussels of headwater streams have been severely impacted by coal mining
<br />and poor land-use practices. For instance, nearly all mussels have been eliminated
<br />from the Lower 17 km of the Little South Fork Cumberland River due to coal mining.
<br />The eleven major dams constructed on the 1,105-km-long Cumberland River and its major
<br />tributaries have had devastating effects on species typical of larger rivers. For
<br />example, construction and operation of Center Hill Dam inundated about 150 km of
<br />riverine habitat, altered the temperature regime of the tailwater, blocked movements
<br />of host fishes, and alternately scours and exposes much of the streambed during
<br />hydroelectric peaking operations. These perturbations have eliminated more than 40
<br />species of mussels (including several endangered or extinct species) from the first
<br />15 km of tailwater; less than 50% of the historic fauna remains in the lower reach of
<br />tailwater. Recognition of mussel life history requirements during preconstruction
<br />could have reduced many of these impacts.
<br />STAB]LTTY W HYDROPSYCHE GUILDS ALONG A REGULATED STREAM: THE ROLE
<br />OF COMPETITIVE INTERACTIONS VERSUS ENVIRONMENTAL PERTURBATIONS.
<br />Julio A. Camazgo, C1T-INIA, Valdeolmos, Madrid, Spain and (present address) Department of
<br />Biology, Colorado State University, Fort Collins, CO 80523, USA
<br />Temporal alterations in the structure of Hydropsyche guilds were studied at three sampling stations along a
<br />regulated stream to examine the role of competitive interactions and environmental perturbations in determining
<br />species persistence. S-1 was placed upstream from adeep-release hydropower impoundment located in the middle
<br />Rio Duraton (northern Spain). S-2 and S-3 were respectively placed 2.5 and 7.6 km below the dam. Dischazge
<br />fluctuations of hypolimnial waters with a significant oxygen deficit were produced daily by the dam. Under
<br />unregulated conditions, I assume that the coexistence of competing species is a function of the species dominance
<br />(d') and the resource limitation (R), as major causes of interaction strength between competitors, and the niche
<br />overlap (O) as a major cause of connectance between competitors. The species dominance tends to increase with
<br />the number of subordinate species (d' = S2/S). S is the number of competing species and S2 represents the absolute
<br />difference between competing species with regazd to their relative abundances. Thus, and according to May's
<br />model of stability, a Hydropsyche guild would tend to be unstable if d'2 RZ O S >1 or 822 R2 O >S. In this work,
<br />I consider that the values of R and O are each 1. Therefore, a Hydropsyche guild would tend to be unstable when
<br />822 >S. Riffle macrobenthic surveys were undertaken in June and December of 1987, and in June of 1988. At
<br />S-1, values of S were 6, 6 and 5 and values of 822 were 3.8, 12.7 and 4.1. At S-2, values of S were 4, 3 and 3
<br />and values of 822 were 1.$, 0.2 and 1.6. At S-3, values of S were 4, 4 and 3 and values of f22 were 2.5, 2.3 and
<br />1.3. Values of total density and total biomass for Hydropsyche guilds were significantly (P<0.05) higher
<br />downstream than upstream from the dam. It is concluded that competitive interactions upstream and environmental
<br />perturbations downstream determined species persistence in Hydropsyche guilds. The perturbation tolerance
<br />appeazs to be a primary biotic factor affecting competitive abilities of Hydropsyche species.
<br />Ecological Responses to River Regulation: Macroinvertebrates and
<br />Fish
<br />THE EFFECTS OF RIVER-BED RESTRUCTURING ON FISH AND BENTHIC
<br />COMMUNITIES OF A 4th-ORDER STREAM (NECK, AUSTRIA).
<br />Mathias Jungwirth, Otto Moog & Susanne Muhar, Dept.
<br />Hydrobiol., State Univ. Agric., A-1180 Vienna, AUSTRIA
<br />Fifteen sections of seven different epipotamal streams have been studied between 1981 and 1984. These
<br />studies proved the impact of river bed structures on fish communities. Reduced spatial heterogeneity due to
<br />river straightening results in decreasing numbers of fish species, stock density and biomass. The variance of
<br />maxima] depths (VMD) is a practical and sensitive measure of habitat structure which significantly correlates
<br />with the fish species diversity (FSD).
<br />1987 these model was used for the evaluation of a planed restructuring project on a channelized section of
<br />the River Melk. After its realization in 1988, the reaction of the fish and benthic fauna was studied over
<br />three years. The results verified the VMD/FSD model. Number of fish species changed from 10 to 19, fish
<br />density and biomass as well as annual production of 0+ fish increased threefold.
<br />Tl~e number of benthic invertebrate taxa changed from 202 in the channelized section to 273 in the
<br />restructured area (in total 347 taxa have been recorded). Increased habitat variability - on the bank as well as
<br />on the channel bottom - is the explanation. A more diversified benthic community developed, favouring
<br />epipotamalic elements. In the restored stretch the drift of aquatic specimens and terrestric organisms
<br />decreased significantly in comparison with the ehannelized section. Channel structures and their impact on
<br />drift are discussed. _
<br />
|