Michael M. Gangloff

The influence of low-head dams on fish assemblages in streams across Alabama

Abstract We quantified fish assemblages in 20 streams containing mill dams in various physical conditions (dams intact, partially breached, or relict with normal flows) in Alabama, USA, during the period from 2006 to 2008. We used a backpack electroshocker to sample three 150-m reaches per stream: 500 to 1000 m downstream of the dam, 0 to 100 m downstream of the dam, and 100 m upstream of the impoundment. Species- and trait-based analyses revealed slightly different, but often complementary, information about fish assemblages. Fish species richness and benthic conditions differed longitudinally among reaches in streams with dams. In streams with breached dams, species richness, but not trait richness, was lower in upstream reaches than in downstream reaches. Overall, species and trait richness were correlated with benthic-habitat variables in streams with relict dams and were significantly correlated with water physicochemical variables in streams with intact and breached dams. Nonmetric multidimensional scaling ordination failed to resolve any discernable site groupings based on species abundance data, and indicator species analysis revealed 1 indicator species, Esox americanus, upstream of relict dams. Fourth-corner trait analysis revealed more trait associations in reaches in streams with breached dams than in those with intact or relict dams. Generalist spawners (nest-guarding polyphils) increased and taxa with a preference for cobble substrates decreased upstream of breached dams. Few longitudinal differences were observed in streams with relict and intact dams. Taken together, dams, particularly those that are breached, appear to exert a strong upstream influence on fish species richness and functional composition and could alter the trophic structure of the entire stream through habitat modifications or limitation of fish movements.

Associations between small dams and mollusk assemblages in Alabama streams

Abstract Small dams are ubiquitous yet poorly understood features in many streams. Dam removal is being used increasingly in stream restoration projects as a means to enhance habitat connectivity and ecosystem function. However, habitat- and assemblage-level effects of small dams on stream mollusk assemblages are poorly documented. We examined associations between stream physicochemical habitat variables and mollusk assemblages at 22 small (<10 m) dams in 3rd–5th order Alabama streams. We sampled 66 reaches (3 reaches/dam) associated with intact, breached, and relict small dams. For each dam, we designated 3 study reaches: 1) immediately downstream from the dam, 2) 500 to 5000 m downstream, and 3) 500 to 5000 m upstream from the impounded or formerly impounded zone. We used principal components analysis (PCA) to examine variation in physical-habitat conditions across all sites. Four principal components accounted for ∼72% of the variation in physical-habitat conditions across sites. One PC score (PC1, corresponding to increased substrate size) was negatively associated with several mollusk metrics including total mussel abundance, taxon richness, catch-per-unit-effort (CPUE), and density. We observed few significant differences between simple habitat variables at sites up- and downstream of dams. However, streams with intact dams had significantly higher mussel catch rates (CPUE) and taxon richness than did streams with breached or relict dams. We used forward-stepwise multiple regression to model the effects of habitat variables (as standardized PC scores) on mollusk assemblage metrics. PCs representing substrate composition were the strongest predictors of total mussel abundance and richness. Abundance of other mollusks including deposit-feeding snails, the exotic bivalve Corbicula fluminea, and fingernail clams was correlated with PC scores describing variability in substrate organic matter composition or stream gradient. We think these data indicate that some intact dams enhance mollusk habitat in downstream reaches. Streams with intact dams appear to be more geomorphically stable than streams with breached or relict dams and conditions in the mill reach may reflect preconstruction stream conditions. Breached dams warrant higher prioritization for removal than intact structures because habitat degradation may persist for decades and impede re-establishment of native mollusk populations.

Functional diversification within a predatory species flock.

Ecological speciation is well-known from adaptive radiations in cichlid fishes inhabiting lentic ecosystems throughout the African rift valley and Central America. Here, we investigate the ecological and morphological diversification of a recently discovered lotic predatory Neotropical cichlid species flock in subtropical South America. We document morphological and functional diversification using geometric morphometrics, stable C and N isotopes, stomach contents and character evolution. This species flock displays species-specific diets and skull and pharyngeal jaw morphology. Moreover, this lineage appears to have independently evolved away from piscivory multiple times and derived forms are highly specialized morphologically and functionally relative to ancestral states. Ecological speciation played a fundamental role in this radiation and our data reveal novel conditions of ecological speciation including a species flock that evolved: 1) in a piscivorous lineage, 2) under lotic conditions and 3) with pronounced morphological novelties, including hypertrophied lips that appear to have evolved rapidly.

Species-specific ontogenetic diet shifts among Neotropical Crenicichla: using stable isotopes and tissue stoichiometry

Ontogenetic diet shifts were compared among five sympatric pike cichlids Crenicichla in a subtropical South American stream using stable C and N isotopes and tissue stoichiometry (C:N). Within species, stable N isotopes were positively related to body size while C:N showed negative relationships. Stable C isotopes, however, were not related to body size in any species. By modelling the switch to piscivory using gut content-isotope-body size relationships, diet shifts were shown to be species-specific with regard to both rate and degree of piscivory. Compared to other piscivorous lineages, Crenicichla appear to be unusually small-bodied (based on maximum body size). Because of their diversity, abundance and dynamic size-structured functional roles, Crenicichla may exert broad and complex predation pressures on the aquatic community.

Influence of urban tributaries on freshwater mussel populations in a biologically diverse piedmont (USA) stream

The Southeastern USA is currently experiencing a period of rapid growth of human populations that is likely having profound effects on the region’s unique aquatic biota. Using both survey data and experimental protocols, we assessed the influences of water and habitat quality on freshwater mussel populations in a small Piedmont stream. Chewacla Creek is a high-quality stream located near the rapidly growing towns of Auburn and Opelika in east-central Alabama. From 1999 to 2007 we monitored freshwater mussel populations and measured substrate and water chemistry variables in Chewacla Creek. Surveys revealed that mussel abundance decreased substantially concomitant with degraded habitat and water quality downstream of three highly urbanized tributaries. We conducted sentinel trials using adult mussels (Villosa lienosa) in Chewacla Creek and a tributary (Parkerson Mill Creek) that receives wastewater discharge. Sentinel mussels were placed in cages at three locations downstream of the effluent discharge point and at one upstream site (control). Sentinel mussels exposed to wastewater discharge exhibited lower survival rates compared to control animals. Together, survey and experimental data suggest that degraded tributary sub-catchments may fragment mussel populations in high-quality streams. Moreover, our data indicate that protection of sensitive aquatic taxa necessitates effective management of water quality across large spatial scales.

Effects of Small Dams on Sunfish Assemblages in North Carolina Piedmont and Coastal Plain Streams

AbstractOver the past century dams have played a major role in restructuring North American stream communities. Effects of large dams on fish assemblages are well studied; however, effects of small dams are relatively unstudied. Sunfishes (family Centrarchidae) include many meso- and apex predators that are key components of North American lotic and lentic ecosystems. Additionally, centrarchids are widely introduced into impoundments well beyond their native ranges. Here, we examine sunfish assemblages at 75 sites associated with small dams in the Neuse, Tar, and Roanoke drainages in North Carolina. We predicted that streams with intact dams would have more introduced centrarchids than streams with breached or relict dams in response to dam-induced shifts in assemblage structure. Contrary to our predictions, streams with breached dams had significantly higher numbers of introduced centrarchids, but total and native centrarchid richness were not significantly different from streams with intact dams. Stream...

Land-use and local physical and chemical habitat parameters predict site occupancy by hellbender salamanders

Anthropogenic landscapes negatively impact stream habitats by altering hydrologic, sediment, and nutrient cycling regimes, thereby reducing or displacing populations of sensitive biota. The hellbender (Cryptobranchus alleganiensis) is an imperiled salamander endemic to eastern and central North American streams. Although once widespread, hellbender distributions have contracted and populations have declined in the past several decades. Hellbenders are considered indicators of stream quality; however, few studies have empirically linked hellbender presence to stream habitat or water-quality. We examined the ability of catchment-scale land-use and local physical and chemical habitat parameters to predict hellbender occurrence in an Appalachian headwater river drainage. Generalized linear models revealed that water-quality, local habitat, and catchment land-use are informative predictors of hellbender site occupancy. Because broad-scale land-use changes likely affect hellbender populations at multiple levels, management and conservation should focus on protecting streams at the catchment scale. In this system, ex-urban development appears to be the primary threat to hellbenders. However, threats to hellbender populations may be mitigated by management regulations targeting economically important outdoor recreational activities including trout fishing as well as existing streamside development guidelines.

A Previously Undocumented Locality of Eastern Hellbenders (Cryptobranchus alleganiensis alleganiensis) in the Elk River, Carter County, TN

Abstract Cryptobranchus alleganiensis alleganiensis (Eastern Hellbender) is a large, imperiled aquatic salamander found in rocky upland streams from New York to Alabama. Although widespread, many Hellbender populations are now highly fragmented by impoundments and degraded habitats. Hellbenders likely require specific stream habitats with relatively low anthropogenic impacts in order to maintain population viability. The Elk River is a small (5th order), high-gradient tributary of the Watauga River drainage that originates in Avery County, NC and flows northwest to Watauga Reservoir in northeastern Tennessee. Although the Elk Rivers headwaters are heavily impacted by development in the resort towns of Banner Elk and Sugar Mountain; its lower reaches flow through portions of the Pisgah and Cherokee National Forests and over several large waterfalls before reaching the reservoir. Hellbender presence was undocumented in the Elk River prior to 2010. We learned that Hellbenders were likely present in the lower Elk River from anecdotal reports of sightings in Tennessee. In 2010 and 2011, we surveyed for Hellbenders at 10 sites in the Elk River drainage. We observed multiple size classes, including larvae and juveniles, present in the lower Elk River. Development in headwater regions of the Elk River in North Carolina may have caused habitat degradation in the upper Elk River causing the extirpation of Hellbenders in the upper reaches.

Molecular systematics of the critically-endangered North American spinymussels (Unionidae: Elliptio and Pleurobema ) and description of Parvaspina gen. nov.

Despite being common in numerous marine bivalve lineages, lateral spines are extremely rare among freshwater bivalves (Bivalvia: Unionidae), with only three known species characterized by the presence of spines: Elliptio spinosa, Elliptio steinstansana, and Pleurobema collina. All three taxa are endemic to the Atlantic Slope of southeastern North America, critically endangered, and protected by the US Endangered Species Act. Currently, these species are recognized in two genera and remain a source of considerable taxonomic confusion. Because spines are rare in freshwater mussels and restricted to a small region of North America, we hypothesized that spinymussels represent a monophyletic group. We sequenced two mtDNA gene fragments (COI and ND1) and a fragment of the nuclear ITS-1 locus from >70 specimens. Bayesian and maximum-likelihood phylogenetic reconstructions suggest that the spinymussels do not comprise a monophyletic group. Elliptio steinstansana is sister to P. collina, forming a monophyletic clade that was estimated to have diverged from its most recent ancestor in the late Miocene and is distinct from both Elliptio and Pleurobema; we describe a new genus (Parvaspina gen. nov.) to reflect this relationship. Additionally, E. spinosa forms a monophyletic clade that diverged from members of the core Elliptio lineage in the mid-Pliocene. Furthermore, E. spinosa is genetically divergent from the other spinymussel species, suggesting that spines, while extremely rare in freshwater mussels worldwide, may have evolved independently in two bivalve lineages. Recognizing the genetic distinctiveness and inter-generic relationships of the spinymussels is an important first step towards effectively managing these imperiled species and lays the groundwork for future conservation genetics studies.

Seven Populations of the Southern Kidneyshell (Ptychobranchus jonesi) Discovered in the Choctawhatchee River Basin, Alabama

Abstract Ptychobranchus jonesi (Southern Kidneyshell) is one of the most imperiled freshwater mussels in North America. It is endemic to eastern Gulf of Mexico drainages from the Escambia to the Choctawhatchee River basins. Numerous recent surveys considered it restricted to a single population in the West Fork Choctawhatchee River in southeastern Alabama. We conducted comprehensive (9–15 hr per site) mussel searches in three high-quality reaches of the Pea River, a Choctawhatchee River tributary, to assess microhabitat associations for the Southern Kidneyshell. Habitat features were later used to identify subsequent search localities. We found undetected Southern Kidneyshell populations at a total of seven localities in the Choctawhatchee River Basin, AL. Although widely-distributed, the Southern Kidneyshell is extremely rare (n = 13) and comprised <0.3% of all mussels encountered. Prior surveys may have underestimated the distribution of the Southern Kidneyshell because they were broadly focused and thus did not expend the necessary effort to detect this rare mussel. Targeted searches in preferred microhabitats greatly increased Southern Kidneyshell catch rates and were used to detect four of the seven new populations. These results suggest that extensive searches within high-quality habitats are critical to detecting rare mussels in patchy habitats.