George L. Harp

Spatio-temporal changes of benthic macroinvertebrates in a cold Arkansas tailwater

This paper investigates spatial, seasonal and long-term changes in benthic macroinvertebrates in riffles of a cold tailwater. Cold tailwaters initially disrupt previously existing macroinvertebrate assemblages, but little is known about the long-term biological effects of a stable cold thermal regime. Assemblages at an upstream and downstream site of the Little Red River, Arkansas were investigated almost 30 years apart (1971 and 1999). Based upon published literature demonstrating the stability of benthic assemblages within unaltered environments, we predicted that the assemblages would be similar for each variable investigated. The benthic macroinvertebrate assemblages can be characterized as low diversity, with a total of 17 taxa identified. Isopods and Diptera comprised ~80% of all individuals. Other than chironomids, insects and particularly EPT taxa were poorly represented. Recent macroinvertebrate densities were significantly greater compared to the historical study period for the downstream site. Assemblage comparisons revealed moderate differences between study periods. Macroinvertebrate density was significantly greater upstream than downstream in the 1971 study period, yet taxa richness was significantly greater downstream for both study periods. Faunal composition was significantly different for upstream and downstream sites. Seasonal differences in numerical standing crop were identified for the 1971 upstream and 1999 downstream data sets. Low to moderate levels of seasonal, spatial and historical variation among benthic macroinvertebrate assemblages were attributed to environmental (temperature and flow) stability. The lack of aquatic insects other than chironomids over a 30-year period is indicative of the extreme constraints placed upon insect development within this cold regulated river.

Freshwater Mussel (Bivalvia: Unionidae) Assemblages of the Lower Cache River, Arkansas

Abstract Freshwater mussel beds of the lower 68 km of the Cache River, AR, were delineated and sampled using diving and stratified random sampling methodology to determine species richness, density, size structure, and population and community numerical standing crop (CNSC). A total of 38 mussel beds were delineated, including 14 major beds (Mbeds) and 24 minor beds (mbeds). Twenty six species were collected, four of which were previously unknown from the Cache River. Amblema plicata, Megalonaias nervosa, and Plectomerus dombeyanus were the most abundant. Estimates of CNSC ranged from 3705 ± 1908 to 122,115 ± 24,194 individuals in Mbeds with mean densities ranging from 6.2 to 44.1 mussels/m2. Nine of 16 species with > 10 individuals had a unimodal size frequency distribution and the other seven had multi-modal distributions. This study found impressive mussel assemblages in the lower Cache River, previously thought to contain only refugial pockets of mussel assemblages. Further monitoring of some species is recommended based on lack of recruitment.

Population Structure of an Endemic Species of Yellowcheek Darter, Etheostoma moorei (Raney and Suttkus), of the Upper Little Red River, Arkansas

Abstract The yellowcheek darter, Etheostoma moorei (Raney and Suttkus), is an endemic species of the upper Little Red River, Arkansas. Population estimates over the past two decades have identified an 80% reduction in numbers. Seventeen presumptive loci and six meristic characters were analyzed for 85 individuals to determine the relatedness of populations from three headwater streams. Genetic distances, based on allozyme analysis ranged from 0.000 to 0.213, with each stream population partitioning into distinct subpopulations. Turkey Fork individuals had high genetic distance values from Middle and South Fork individuals. None of the six meristic features studied demonstrated significant differences between stream sites. These findings and previous ecological and life history studies all suggest that the Turkey Fork and Middle/South Fork populations be treated as unique management units.

Genetic Variation and Genetic Structuring of a Numerically Declining Species of Darter, Etheostoma moorei Raney & Suttkus, Endemic to the Upper Little Red River, Arkansas

Abstract Gene products of 17 putative loci were analyzed to determine the genetic diversity for 85 individuals of Etheostoma moorei Raney & Suttkus, a darter species endemic to Arkansas, that has been subjected to severe habitat and numerical decline. Number of alleles per locus (1.3), heterozygosity (0.048) and polymorphism (25.9%) values were high relative to those of other darter species. Geographic samples did not exhibit isolation-by-distance, which may be associated with repeated extirpation and recolonization events. Of concern is the high number of polyallelic loci in Hardy-Weinberg disequilibrium (26%), indicative of populations undergoing genetic change. Several causative explanations were investigated with founder effect and inbreeding being the most plausible hypotheses. As these populations continue to decline in numbers, loss of genetic diversity appears imminent.