Isolation and culture of the marine rotifer, Colurella dicentra (Gosse, 1887), from a Mississippi Gulf Coast estuary

Few marine rotifer species (e.g. Encentrum linheii and Synchaeta cecilia) have been cultured successfully besides Brachionus plicatilis and B. rotundiformis, commonly used to rear larvae of many marine fish species. The development of culture techniques for marine rotifers smaller in size than the Brachionus species may be useful for rearing fish species for which the currently used prey are too large. We evaluated the possibility of culturing Colurella dicentra isolated from a Mississippi Gulf Coast estuary. An experiment was conducted to determine the effects of salinity (10–35 g L^?1) on its population growth rate. Rotifers were fed Nannochloropsis oculata at a density of 100 000 cells mL^?1 for 15 days. Colurella dicentra survived in water with a salinity of 10–47 g L^?1. Densities of up to 300 rotifers mL^?1 were sometimes attained in cultures. Salinity influenced C. dicentra production (P<0.001). The mean rotifer numbers at 10 g L^?1 (22 840±2604 SD), 15 g L^?1 (25 980±7071 SD) and 20 g L^?1 (19 780±1029 SD) at the end of the experiment were similar (P>0.05), but were higher (P=0.05) than numbers at 25 g L^?1 (4240±1783), 30 g L^?1 (1300±264 SD) and 35 g L^?1 (100±101 SD). The population growth rate (r) of the rotifers was the highest at 15 g L^?1 (0.37–0.42 day^?1), and the lowest at 35 g L^?1 (?0.33–0.06 day^?1). This is the first report of C. dicentra in the estuarine waters of the Gulf of Mexico, and also the first time it has been cultured successfully.     

Ecology of larval blue sucker (Cycleptus elongatus) in the Mississippi River

Abstract –  Ecology of larval blue sucker, Cycleptus elongatus , a North American catostomid that has declined throughout its range, is poorly known because larvae have rarely been sampled. A total of 316 young blue suckers (16.0–39.0 mm total length) was captured over 3 years at 14 off-channel sites in Pool 25, Mississippi River. Blue suckers demonstrated distinct temporal and spatial abundance patterns. Blue suckers were only captured in late May/early June, and were more abundant during a year of little flooding. Abundance was correlated with the distance a site was from the main channel, being highest in island borders and island sloughs in proximity to the channel. Fish guts contained a relatively high biomass of chironomids and zooplankton, suggesting islands were providing suitable feeding opportunities. Because of their proximity to flows, slack waters provided by islands were accessible to blue sucker larvae dispersing from channel spawning areas and facilitated their development into rheophilic juveniles.     

Variation in prey selection and foraging success associated with early‐life ontogeny and habitat use of American paddlefish (Polyodon spathula)

Many fishes are planktivorous during early life and switch to piscivory or consume larger food items as ontogeny progresses. In contrast, paddlefish start as particulate feeders and later become filter feeders. Few studies have identified food items essential for paddlefish growth, survival and recruitment surrounding this ontogenetic diet shift. The objectives of this study were to investigate (i) prey types consumed by paddlefish, (ii) variability in prey selection surrounding an ontogenetic diet shift and (iii) whether habitat affected paddlefish prey selection or foraging success. We analysed gut contents of 189 wild age‐0 paddlefish from the middle Mississippi River (MMR) and also conducted a laboratory experiment to address these objectives. We found that paddlefish primarily foraged on benthic macroinvertebrates in the MMR, which differed from previous studies in lentic systems, suggesting young paddlefish prey selection may be labile depending on habitat (i.e., lotic versus lentic). Dominant prey of wild‐caught and experimental age‐0 paddlefish were caddisfly larvae (Trichoptera), followed by hemipterans and amphipods. We found little evidence that habitat attributes affected foraging success, but the most common prey items consumed were associated with wing dike habitat and the upstream and downstream tips of alluvial islands. Our experimental study revealed that if provided a mixture of organisms, age‐0 paddlefish will primarily consume macroinvertebrates while age‐1 paddlefish will mainly filter zooplankton. Overall results suggest young paddlefish prey selection can be highly variable, but also heavily reliant on a narrow group of prey resources.     

Identification of two haplotypes of cytochrome oxidase subunit II (COII) gene of the Formosan subterranean termite,Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), in southern Mississippi

BACKGROUND: Coptotermes formosanus Shiraki was accidentally introduced into the United States from Asia. The introduction of the pest has brought significant economic consequences. During the past decade, Mississippi has become a significantly infested state, partly due to the proximity to coastal port cities such as New Orleans. This study was initiated to investigate the origin and infestation route of C. formosanus in southern Mississippi. RESULTS: Twenty‐eight colonies (21 colonies from Mississippi, six from Louisiana, one from China) were collected. Sequencing and analysis of 112 sequences revealed 15 haplotypes of cytochrome oxidase subunit II (COII) gene in the world. Two haplotypes of COII were identified in Mississippi. In addition, specific primers were designed and tested differentially to amplify characteristic fragments for verifying and surveying different genotypes of C. formosanus in the future. CONCLUSION: Of the two haplotypes identified in Mississippi, the GA group was identical to those reported previously in Georgia, Louisiana, Alabama and other infested states. The second haplotype, the AT group, was identified for the first time in southeastern United States. Sequence identity of the AT‐group C. formosanus with those reported mainly in southeastern Asian countries provided evidence of at least two introductions of C. formosanus into the United States. Copyright © 2010 Society of Chemical Industry     

Simulated long-term nitrogen losses for a midwestern agricultural watershed in the United States

Adequate knowledge on the movement of nutrients under various agricultural practices is essential for developing remedial measures to reduce nonpoint source pollution. Mathematical models, after extensive calibration and validation, are useful to derive such knowledge and to identify site-specific alternative agricultural management practices. A spatial-process model that uses GIS and ADAPT, a field scale daily time-step continuous water table management model, was calibrated and validated for flow and nitrate-N discharges from a 365 ha agricultural watershed in central Iowa, in the Midwestern United States. This watershed was monitored for nitrate-N losses from 1991 to 1997. Spatial patterns in crops, topography, fertilizer applications and climate were used as input to drive the model. The first half of the monitored data was used for calibration and the other half was used in validation of the model. For the calibration period, the observed and predicted flow and nitrate-N discharges were in excellent agreement with r² values of 0.88 and 0.74, respectively. During the validation period, the observed and predicted flow and nitrate-N discharges were in good agreement with r² values of 0.71 and 0.50, respectively. For all 6 years of data, the observed annual nitrate-N losses of 26 kg ha⁻¹ for the entire simulation were in excellent agreement with predicted nitrate-N losses of 24.2 kg ha⁻¹. The calibrated model was used to investigate the long-term impacts of nitrate-N losses to changes in the rate and timing of fertilizer application. Results indicate that nitrate-N losses were sensitive to rate and timing of fertilizer application. Modeled annual nitrate-N losses showed a 17% reduction in nitrate-N losses by reducing the fertilizer application rate by 20% and switching the application timing from fall to spring. Further reductions in nitrate-N losses require conversion of row cropland to pasture and/or replacement of continuous corn or corn–soybean rotation systems with alternative crops.     

Influence of oceanographic conditions on abundance and distribution of post‐larval and juvenile carangid fishes in the northern Gulf of Mexico

Relationships between abundance of post‐larval and juvenile carangid (jacks) fishes and physical oceanographic conditions were examined in the northern Gulf of Mexico (GoM) in 2011 with high freshwater input from the Mississippi River. Generalized additive models (GAMs) were used to explore complex relationships between carangid abundance and physical oceanographic data of sea surface temperature (SST), sea surface height anomaly (SSHA) and salinity. The five most abundant carangid species collected were: Selene setapinnis (34%); Caranx crysos (30%); Caranx hippos (10%); Chloroscombrus chrysurus (9%) and Trachurus lathami (8%). Post‐larval carangids (median standard length [SL] = 10 mm) were less abundant during the spring and early summer, but more abundant during the late summer and fall, suggesting summer to fall spawning for most species. Juvenile carangid (median SL = 23 mm) abundance also increased between the mid‐summer and early fall. Most species showed increased abundance at lower salinities and higher temperatures, suggesting entrainment of post‐larval fishes or feeding aggregations of juveniles at frontal convergence zones between the expansive river plume and dynamic mesoscale eddy water masses. However, responses were species‐ and life‐stage specific, which may indicate fine‐scale habitat partitioning between species. Ordination methods also revealed higher carangid abundances at lower salinities for both post‐larval and juvenile life stages, with species‐ and life‐stage specific responses to SST and SSHA, further suggesting habitat separation between species. Results indicate strong links between physical oceanographic features and carangid distributions in the dynamic northern GoM.     

Predicting vertical accretion rates at an archaeological site on the Mississippi River floodplain: Effigy Mounds National Monument,Iowa

The Sny Magill Unit of Effigy Mounds National Monument, Iowa, contains the largest cluster of prehistoric effigy mounds on public land in North America. The mounds are situated atop a low terrace of the Upper Mississippi River, where they are slowly being buried by overbank deposition during floods. The terrace surface includes forest soils with argillic (Bt) or cambic (Bw) horizons developed in up to 1 m of loamy overbank deposits on top of Pleistocene sand and gravel. Radiocarbon evidence suggests that overbank deposits have accumulated since the end of the mound-building period (about 700 years BP), yielding a vertical accretion rate of about 0.6 mm yr^− 1. On the basis of ¹³⁷Cs analysis, accretion rates over the past 40–50 years average 1.25–2.07 mm yr^− 1, with some evidence for a decreasing rate since 1964. If these accretion rates are projected forward, several of the effigy mounds could be buried by flood deposits within 150–300 years. This ¹³⁷Cs-derived estimate agrees closely with an estimate of burial times based on flood frequency and observed flood deposit thickness during recent floods. However, the floodplain and backwater environments of the Upper Mississippi River are aggrading much more rapidly than the Sny Magill terrace surface, suggesting that burial of the entire terrace could occur within 80–400 years and the entire mound group could be buried within 150–850 years. The projected accretion rates and time to burial are subject to large uncertainties because of environmental change in the watershed, including recent trends toward increasing flood stages and decreasing suspended sediment loads.     

Assessing large-scale movement of an endangered fish: Dispersal of stocked age-0 pallid sturgeon in the lower Missouri River

1. Large-scale movement of fishes is a challenge for conservation and management in rivers, especially when individuals can cross jurisdictional boundaries.
2. Assessing large-scale movement is particularly difficult during early life stages, especially when endangered species are involved. After hatching, free embryos of the federally endangered pallid sturgeon (Scaphirhynchus albus) drift long distances during development. Following the transition to exogenous feeding, individuals may continue to move downstream, resulting in a potential two-step migration.
3. Tagged age-0 pallid sturgeon were stocked into the lower Missouri River, which provided an opportunity to assess pallid sturgeon dispersal as well as the hypothesized two-step migration. From July 2018 to April 2021, 79 individuals were captured, with most dispersing 200–800 km downstream from the stocking location.
4. The observed dispersal of pallid sturgeon supports the two-step downstream migration hypothesis. This migration may lead to dispersal into the Mississippi River, which highlights the need for expanded monitoring into the Mississippi River for an effective evaluation of pallid sturgeon recovery actions. This study also reinforces the importance of inter-jurisdictional management and collaboration to better account for the large-scale movement of river fishes.

     

Harvest of crayfish as an ecosystem service of wetlands compared to production systems with planted forage

ABSTRACT

Crayfish harvest as an ecosystem service of moist-soil wetlands in the Mississippi Alluvial Valley (MAV) was evaluated using estimates of crayfish yield and operational costs to create enterprise budgets. The average daily yield of crayfish was 2.13 lb/acre (95% CI = 1.19–3.00) and yield did not differ between wetlands dominated with Red Swamp Crayfish or White River Crayfish. Four hypothetical scenarios of harvest operations revealed annual costs associated with harvesting crayfish to be $163.89–370.75/acre. Although these costs were lower than estimated costs currently associated with harvesting crayfish from fields with planted forage in Louisiana ($749.96/acre), a three-fold reduction in crayfish yield (lb/trap/day) from moist-soil wetlands resulted in an increase in the break-even selling price from $1.25/lb in Louisiana to $1.70–$3.86/lb in the MAV. Although this enterprise will likely not compete with the Louisiana rice-crayfish industry, harvesting crayfish from moist-soil wetlands may contribute to ecosystem services provided by wetlands and aid in the reduction of the quantity of crayfish products imported into the U.S. market.     

Modeling landowner participation in a proposed reforestation loan program

The absence of available credit to finance reforestation investments among NIPF landowners has been one of the contributing reasons why landowners do not reforest after harvest. Financial assistance programs are therefore a solution to initiating reforestation investments. However, previous studies indicate many landowners are not actively participating in existing government assistance programs. This paper examines reforestation loans as an alternative financial assistance program. Landowner participation in a proposed reforestation loan program is modeled using logistic regression. Results indicate that landowner participation in the program is influenced by ownership size, socio-demographic characteristics, and availability of other forestry incentive and assistance programs.