David C. Beckett

CONTRASTS IN DENSITY OF BENTHIC INVERTEBRATES BETWEEN MACROPHYTE BEDS AND OPEN LITTORAL PATCHES IN EAU-GALLE LAKE, WISCONSIN

-Small areas that are barren of plants commonly occur amidst dense littoral zone vegetation of lakes. This study compared the benthic invertebrate communities of nonvegetated patches to those in the surrounding vegetated sediments in a Wisconsin lake. Mean benthic invertebrate densities in the sediments of Ceratophyllum demersum and Potamogeton nodosus beds were 13 and seven times, respectively, those of nearby nonvegetated areas within the littoral zone. The contrast in densities was especially striking for the gastropods Amnicola limosa and Gyraulus parvus, which were collected below Ceratophyllum at 162 times and 48 times, respectively, their densities in open areas. The conjecture that these density differences were due to a lack of a detrital food base in the nonvegetated areas was not supported by our investigation. The most likely explanations for such a contrast in invertebrate densities are: (1) disturbance effects in areas lacking plants, and (2) increased predator efficiencies in the open zones. Removal of macrophytes by herbicides, drawdown or mechanical means creates large expanses of open areas; our data indicate that macrophyte removal would result in a less diverse and much less abundant invertebrate fauna in littoral zone sediments. More than 90% of the invertebrates in 0-1 5 cm cores were found within the top 5 cm in nonvegetated areas as well as in sediments below a rooted macrophyte (Potomageton nodosus) and a nonrooted macrophyte (C. demersum). Despite the presence of its root system, which might oxidize the sediments, proportional abundances of invertebrates deeper in the sediments below Potamogeton were not greater than those below Ceratophyllum or in the open zones.

Benthic Macroinvertebrates of Selected Aquatic Habitats of the Lower Mississippi River.

ABSTRACT We investigated the distribution of benthic macroinvertebrates in four aquatic habitat types in the lower Mississippi River: dike fields, a natural bank, a secondary channel, and an abandoned channel over a high flow (flood stage), two moderate, and two low flow periods. The biotas present in the natural bank, the secondary channel, and the abandoned channel showed only minor changes in composition over the various flow regimes. The natural bank was consistently dominated by the burrowing mayflies Tortopus incertus and Pentagenia vittigera and hydropsychid caddisflies; the consistently most common taxa in the secondary channel were the sand-dwelling chironomids Robackia claviger and Chernovskiia orbicus; phantom midges, tubificid oligochaetes, and fingernail clams were always the most abundant macroinvertebrates in the abandoned channel. The dike fields, however, showed large changes in biotic composition over the different flow regimes. These compositional changes correlated with changes in rive...

Epizoic invertebrate communities on upper Mississippi River unionid bivalves

-Based on the Great Lakes experience with Dreissena polymorpha, it is clear that the native freshwater mussel (family Unionidae) fauna will be one of the riverine communities most severely impacted if high zebra mussel densities occur. Negative impacts on unionids will also affect the epizoic invertebrate communities that live on the shells of the unionids. In 1991 and 1992 (prezebra mussel infestation) we determined the composition and density of epizoic invertebrates on individual unionids from the upper Mississippi River. The 1991 samples were from a location with a strong current; the numerically dominant epizoic invertebrates at this location were three species of hydropsychid caddisflies and the chironomid larvae: Polypedilum convictum, P scalaenum group, Rheotanytarsus sp., Microtendipes pedellus group and Thienemannimyia group. Strong correlations existed between effective surface area (ESA) (amount of shell surface area above the sediment-water interface) of the individual unionids and: (1) number of epizoic chironomid larvae (r = 0.81); (2) number of hydropsychid caddisflies (r = 0.73), and (3) total number of epizoic invertebrates (r 0.78). Sampling in a slower current area in 1992 revealed an epizoic composition dissimilar from that observed in 1991. Glyptotendipes nr. lobiferus was the most abundant epizoic larval chironomid, and, although caddisfly larvae were common, they mostly belonged to families other than the Hydropsychidae. Again, strong correlations existed between ESA of the unionids and: (1) total number of epizoic invertebrates (r = 0.64) and (2) number of epizoic chironomid larvae (r = 0.57). A strong correlation also existed between the size of the unionids and the number of epizoic taxa present (1991: r = 0.78; 1992: r = 0.77). Fiftythree invertebrate taxa were collected from the unionids; mean epizoic densities were ca. 9600 and 6400 invertebrates/M2 of ESA in 1991 and 1992, respectively. These results indicate that unionids are important substrates for epibenthic invertebrates, especially in rivers in which other large clean substrates are in short supply.

Characteristics of Tree Roosts of Rafinesque's Big-eared Bat (Corynorhinus rafinesquii) in Southeastern Mississippi

Abstract Cavity-roosting species of bats generally require patches of forest containing older timber, but such habitats have been reduced in the southeastern United States. Rafinesques big-eared bat, Corynorhinus rafinesquii, is a rare species for which data on natural roosts in the Gulf Coastal Plain (where caves are largely absent) are scant. We used radiotelemetry to locate tree roosts of C. rafinesquii in southeastern Mississippi from August 2001 until August 2004. We captured and radiotagged 25 bats that led us to 14 trees. Corynorhinus rafinesquii used hollow Nyssa spp. and Magnolia grandiflora. Most of these trees were still alive, relatively large (mean DBH = 79.4 cm, mean height = 18.5 m), possessed cavities with openings not located at their bases and were located adjacent to streams or other bodies of water. When bats shifted roosts among different trees, these sites were usually located nearby (mean distance ≅ 360 m). Tree roosts were apparently rare within the study area, and C. rafinesquii showed roost fidelity to particular areas of forest. Six tree roosts were used by multiple individuals and several trees were reused within tracking sessions and among years.

Short-term Roost Fidelity of Rafinesque's Big-eared Bat (Corynorhinus rafinesquii) Varies with Habitat

Abstract Conservation of cavity-roosting bats must take into account their frequent movements among multiple roosts within a forest. One such species, Rafinesques big-eared bat (Corynorhinus rafinesquii) is apparently rare or declining or both over its range. From 2001 through 2004 we captured C. rafinesquii at roosts located under bridges and used radiotelemetry to monitor movements of bats among roosts in southeastern Mississippi. We calculated an index of roost fidelity for individuals and compared indices based on sex, age-class, and location of capture (2 different sites). Of 25 different roost structures that we located, 14 were hollow trees and 11 were human-made (bridges, abandoned houses, and an oil tank). Overall, bats switched roosts every 2.1 days, changed roosts 2.6 ± 2.0 times (mean ± SD) per tracking period, and used 2.5 ± 1.2 roosts per tracking period. Bats that were captured together sometimes reunited at subsequent roosts. Dissimilarity in roosting opportunities between the 2 localities could have explained differences in roost fidelity among bats in the 2 areas. Roosting behavior of C. rafinesquii was comparable to that of other bats that primarily roost within tree cavities. The roosting strategy of C. rafinesquii appeared flexible; bats showed low day-to-day fidelity to roosts that were relatively common but not exceptionally stable (trees) and, in the apparent absence of tree roosts, higher fidelity to human-made roosts that were of higher structural integrity. Because C. rafinesquii moves frequently among roosts and alters fidelity by roost type, researchers should design sampling protocols and/or interpret data from surveys accordingly.

Seasonal Change in Plant-Dwelling Chironomidae and Naididae in a Wisconsin Lake

ABSTRACT We investigated the degree of change in the larval chironomid and naidid communities colonizing the macrophyte Potamogeton nodosus over the plants growing season. Sampling of plant-dwelling invertebrates at three sites in Eau Galle Lake, Wisconsin near the beginning of the growing season of P. nodosus (June—1987) and at the peak of this macrophytes development (August—1986 and 1987) revealed dramatic seasonal changes in abundance among the chironomid and naidid species. Non-burrowing chironomid larvae (Paratanytarsus sp., Thienemanniella nr. fusca, and Corvnoneura taris) dominated the June collections, whereas burrowing chironomids such as Polypedilum illinoense, Glyptotendipes dreisbachi, and Endochironomus nigricans dominated the August collections in both years. Naidids also showed a marked change from June to August; e.g. Nais pardalis, the most abundant naidid on P. nodosus in June, was not present in the August collectiona. The striking similarities between the August 1986 and August 1987...

Selective predation by four darter (Percidae) species on larval chironomids (Diptera) from a Mississippi stream

We determined seasonal foraging modes of four sympatric darter species, Etheostoma lynceum, E. stigmaeum, E. swaini and Percina nigrofasciata, from Beaverdam Creek, Mississippi (USA) at two scales of taxonomic resolution: (1) chironomid prey identified to family and (2) chironomid prey identified to genus/species. When chironomids were identified to family, high proportional similarity (PS) and low niche breadth (NB) values suggested the darters fed opportunistically on a relatively small number of available prey taxa. In contrast, when chironomids were identified to genus/species, concordant low PS and NB values suggested the darters fed like classic specialists, selecting a small number of prey taxa relative to prey availability in the resource base. The darters selected just one to four chironomid taxa from 52 available taxa across seasons. Our study shows that the scale of taxonomic resolution used to identify darter prey may influence the characterization of darter foraging modes.

Seasonal use of bridges by Rafinesque's big-eared bat, Corynorhinus rafinesquii, in Southern Mississippi

Abstract We conducted surveys of concrete bridges in southern Mississippi from 2000–2002 to determine the phenological pattern of use by Rafinesques big-eared bat, Corynorhinus rafinesquii. The earliest dates on which we located maternity colonies were 9 March 2000, 20 April 2001, and 15 May 2002. Maternity colonies increased in size and abundance as spring progressed. Pups were born in mid- to late May (first observed 12 May 2000, 15 May 2001, 27 May 2002) and nursed through midsummer (lactating females last captured 14 July 2000, 25 July 2001, 16 July 2002). Colony size and percentage of bridges occupied by bats declined in late summer. Colonies were absent during fall and winter, although we occasionally found solitary individuals during these seasons. Number of bats present under an occupied bridge ranged from 1 to 25. The mean number of individuals per occupied bridge was 4.6 (SD = 5.8) in 2000, 3.9 (SD = 5.0) in 2001, and 3.0 (SD = 4.4) in 2002. The mean number of adult females per maternity colony was 5.6 (SD = 3.1). Although we found males throughout the study period, females were largely absent from bridges outside of the maternity season, suggesting that much of the population used alternate roosts during this time.

Where Have All the Crangonyx Gone? The Disappearance of the Amphipod Crangonyx pseudogracilis, and Subsequent Appearance of Gammarus nr. fasciatus, in the Ohio River

Abstract Sampling conducted by personnel of two separate laboratories of the U.S. Environmental Protection Agency showed a single amphipod species, Crangonyx pseudogracilis, present in the Ohio River before the early 1970s. Subsequent sampling by personnel of both laboratories, along with invertebrate collections made by the West Virginia Department of Natural Resources and the first author of this paper showed that this species disappeared from the river in approximately 1973. Another amphipod species, Gammarus nr. fasciatus, invaded the Ohio River in 1973. Gammarus nr. fasciatus spread rapidly throughout the Ohio River, and is now one of its most common macroinvertebrate species. Although the evidence is circumstantial, it seems likely that the elimination of C. pseudogracilis from the Ohio River was caused by the damming of the river, especially the use of high-lift dams, completed from 1936 through the present. Experimental evidence indicates that the existing amphipod, G. nr. fasciatus, has a proclivity for slow-water conditions, which have been favored by the installation of the high-lift dams.

Survey of Salamanders in Mississippi Limestone Caves

Abstract During 2000–2002 we surveyed for salamanders in the larger limestone caves of Mississippi, all within the Vicksburg Group rock unit. We found four species: Plethodon mississippi was the most abundant, followed by Eurycea guttolineata, Eurycea cirrigera, and Desmognathus conanti. We did not find Pseudotriton montanus in any of the caves, and question the validity of an investigators statement made nearly 45 years ago that, “it is one of the most numerous salamanders in Mississippi limestone caves.” The salamander fauna we found is similar to that of the only other comprehensive survey of salamanders in Mississippi caves, conducted almost thirty years ago.