Thomas C Michot | University of Louisiana at Lafayette (original) (raw)
Papers by Thomas C Michot
Abstract. Whole body and liver analyses indicated that winter-ing redheads (Aythya americana; n =... more Abstract. Whole body and liver analyses indicated that winter-ing redheads (Aythya americana; n = 70) in coastal Louisiana (one site) and Texas (two sites) were relatively free of contam-ination with common trace elements, organochlorines, and hy-drocarbons. Most trace elements, including As, Cr, Hg, Mg, Mn, Ni, Pb, Se, Sr, and Zn, were within background concen-trations in livers; levels of B, Cd, Cu, and Fe were elevated in some specimens. Only one organochlorine, DDE, was detected in redhead carcasses, but its concentration was below reported toxic levels in waterfowl. Body burdens of aliphatic and aro-matic hydrocarbons were generally low, but levels of pristane, total hydrocarbons, and the ratios of phytane:n-octadecane and pristane:n-heptadecane were indicative of possible chronic ex-posure to petroleum. Based on brain cholinesterase assays, redheads were not recently exposed to organophosphorous or carbamate pesticides. Of 30 elements or compounds tested for seasonal differenc...
Fact Sheet, 1997
Communities of submerged aquatic vegetation (SAV) are important components of many freshwater, br... more Communities of submerged aquatic vegetation (SAV) are important components of many freshwater, brackish, and marine aquatic ecosystems. They prevent erosion by baffling the impacts of waves, especially from storms. These aquatic plant communities remove nutrients and other pollutants from river and runoff inputs to coastal areas, preventing their entry into surrounding waters. They provide nursery habitat for fish, shrimp, and other species, as well as forage for wintering waterfowl and endangered species such as sea turtles and manatees. Unfortunately, not only have the distribution and abundance of seagrasses in the northern Gulf of Mexico declined precipitously during the past 50 years, most notably from widespread deterioration of water quality, but submerged aquatic plant communities are also susceptible to long-term environmental changes that are predicted to accompany global climate change.
Le complexe des zones humides de la Louisiane, l'un des plus important des Etats-Unis pour le... more Le complexe des zones humides de la Louisiane, l'un des plus important des Etats-Unis pour les anatides, Anatidae, est en train de changer rapidement. Environ 2 310 km 2 de zones humides, essentiellement des marais a vegetation emergente, ont disparu (transformes en eaux libres) entre 1956 et 1990, et d'autres marais continuent a disparaitre a l'heure actuelle. Ce processus est entretenu par des facteurs tels que l'affaissement naturel, l'elevation globale du niveau de la mer, la penetration d'eau salee, la perte de depots de nutriments et de sediments par le Mississippi et les modifications provoquees par la construction de canaux et les berges en remblai en resultant. Les efforts d'amenagement du milieu ont eu des resultats mitiges. Tous les ans, cette zone sert d'aire d'hivernage a environ 3 millions de canards, Anatinae, et 400000 oies, Anser sp., et constitue ainsi pour les anatides l'une des plus importantes aires d'hivernage du continent. Elle accueille 19% de la population hivernante des Etats-Unis de 14 especes de canards et d'oies, dont plus de 60% des populations des Etats-Unis de trois especes (le canard brun, Anas fulvigula, le canard chipeau, Anas strepera, et la sarcelle soucrourou, Anas discors) et plus de 20% des populations de neuf autres especes. Les regressions des effectifs totaux de canards, de canards de surface et de canards plongeurs sur les annees n'ont montre aucune variation significative des effectifs entre 1969 et 1994 (P > 0,05). De plus, dans la region cotiere de la Louisiane, il n'a ete note ni diminution, ni augmentation, significative pour aucune espece particuliere de canard entre 1969 et 1994 (P > 0,05). Pendant les 26 annees d'etude, aucune des dix especes de canards pour lesquelles des donnees sur la reproduction etaient disponibles, n'a montre de correlation positive entre la population presente en Louisiane au milieu de l'hiver et la population nicheuse nord-americaine, et, pour aucune de ces especes, il n'a ete note de diminution significative du pourcentage de la population nicheuse nord-americaine qui hiverne dans la region cotiere de la Louisiane. Une diminution significative (r 2 = 0,52, p = 0,0001) a ete notee pour les effectifs d'oies des neiges, Anser caerulescens, dans la region cotiere de la Louisiane entre 1969 et 1994, alors qu'au cours de la meme periode les effectifs d'oies rieuses, Anser albifrons, ont augmente (r 2 = 0,66, p = 0,0001). Chez les oies, les variations des effectifs sont probablement liees aux variations des effectifs des populations continentales et a leurs deplacements vers les zones agricoles, plutot qu'a la disparition des marais. Le fait que les populations de canards n'ont pas reagi aux modifications de l'habitat (telle que la disparition des marais) est peut-etre due a une intensification des efforts d'amenagement de ces habitats pendant cette periode. Il se peut aussi que l'on n'ait pas encore atteint le seuil au dela duquel la disparition des marais diminuerait la nourriture pour les anatides dans ces zones desormais en eau libre.
This report is preliminary and has not been reviewed for conformity with U.S.
Scientific Investigations Report, 2011
Fact Sheet, 2002
is the largest natural freshwater lake in Louisiana, covering more than 46 square miles (120 km 2... more is the largest natural freshwater lake in Louisiana, covering more than 46 square miles (120 km 2) (fig. 1). The lake is a principal stopover and wintering site for hundreds of thousands of migratory waterfowl and shorebirds. Scientists from the USGS National Wetlands Research Center are applying some of the research facility=s specialtiesCwetland plant research, aerial and ground surveys, digital mapping, and computer modelingCto facilitate wetland management at Catahoula Lake. Lake Management Catahoula Lake is long and shallow with major seasonal fluctuations in water levels. The difference between annual low and high water levels can be 18 feet (6 m) or greater when flooding is extreme. Local rainfall and backwater flooding from the Red, Black, and Mississippi Rivers largely determine lake levels. In 1972, a gated diversion canal was constructed to control water levels. U.S. Fish and Wildlife Service personnel at Catahoula National Wildlife Refuge manipulate lake water levels under shared management responsibility with the Louisiana Department of Wildlife and Fisheries and the U.S. Army Corps of Engineers. The goal of the current lake management plan is to maintain seasonal trends of winter and spring high water and summer and fall drawdown primarily to provide optimal habitat for migratory birds. The drawdown periods are characterized by dramatically reduced water levels that are about 8 feet (2.4 m) lower than Figure 1. Catahoula Lake National Wildlife Refuge lies on the eastern shore of Catahoula Lake in central Louisiana.
Circular, 2007
It is not known whether en route fall migratory birds (August-October) are likely to suffer more ... more It is not known whether en route fall migratory birds (August-October) are likely to suffer more from direct or secondary effects of hurricanes. On September 24, 2005, Hurricane Rita wreaked havoc on Louisiana's coast by toppling trees over vast areas and by stripping away microhabitats that harbor the invertebrates and produce the fruits upon which migrant landbirds depend (e.g., canopy foliage, vine tangles, epiphytes, leaf litter, and thickets of perennial plant species). Such transient effects of a hurricane on wildlife food resources are poorly understood, but these effects may have longterm consequences for some wildlife species.
Circular, 2007
Hurricane Rita significantly impacted the chenier forests of southwestern Louisiana, an important... more Hurricane Rita significantly impacted the chenier forests of southwestern Louisiana, an important habitat for Neotropical migratory birds. Sediment deposition was measured along transects at Hackberry Beach chenier, and Rita's effects on chenier structure and morphology were determined.
Wetlands, 1994
We studied biomass and macronutrient content of Halodule wrightii (shoalgrass) throughout the win... more We studied biomass and macronutrient content of Halodule wrightii (shoalgrass) throughout the winter and of Thalassia testudinum (turtlegrass) and Syringodium fitiforme (manateegrass) in January in Chandeleur Sound, Louisiana. Halodule, the primary food of wintering redheads, had the lowest biomass of the three species on the study area in midwinter. Macronutrient content of Halodule did not change during the winter, but aboveground and belowground biomass showed a 90 and 49% (P < 0.0001) decrease from October to March. Macronutrient content seems not to be the basis for selection by redheads of Hatodule over the other two seagrass species or of selection of belowground over aboveground parts.
The American Naturalist, 2013
Migratory birds are often suggested to be important vectors for long-distance dispersal (LDD) of ... more Migratory birds are often suggested to be important vectors for long-distance dispersal (LDD) of plant and animal propagules. The scale of such dispersal events (hundreds to thousands of kilometers) can influence landscape-level biological processes and species distributions. However, the few vector species studied and the lack of proper integration of their migratory movement in models of LDD has precluded the study of their potential as long-distance biotic dispersers. By means of a mechanistic model parameterized with empirical data, we first investigated the properties of seed dispersal curves generated by migratory birds and then analyzed the effect of bird size on model parameters and consequent seed dispersal patterns. Seed dispersal curves showed in most cases large and heavy tails, resulting in relatively frequent LDD (up to 3.5% of dispersal distances longer than 100 km). Bird size mediated trade-offs between bird movement and seed retention time that, in turn, determined seed dispersal patterns and the potential of each bird species as an LDD vector. Our modeling framework builds on a mechanistic understanding of seed dispersal by migratory birds and may thus be a useful tool to estimate the scale and frequency of bird-mediated, large-scale transport of native, invasive, and pathogenic organisms.
The American Naturalist, 2005
Waterfowl often have been assumed to disperse freshwater aquatic organisms between isolated wetla... more Waterfowl often have been assumed to disperse freshwater aquatic organisms between isolated wetlands, but no one has analyzed the impact of this transport on the population structure of aquatic organisms. For three cladocerans (Daphnia ambigua, Daphnia laevis, and Sida crystallina) and one bryozoan (Cristatella mucedo), we estimated the genetic distances between populations across North America using sequences of several mitochondrial DNA genes and genotypic frequencies at allozyme and microsatellite loci. Waterfowl movements across North America (estimated from band recovery data) explained a significant proportion of the gene flow occurring between populations across the continent for three of the four species, even after controlling for geographic distances between localities. The fourth species, S. crystallina, has propagules less likely to survive desiccation or ingestion by birds. Differences in the capacity to exploit bird-mediated transport are likely to have important consequences for the ecology of aquatic communities and the spread of invasive species.
Environmental Management, 2014
Anthropogenic disturbances in wetland ecosystems can alter the composition and structure of plant... more Anthropogenic disturbances in wetland ecosystems can alter the composition and structure of plant assemblages and affect system functions. Extensive oil and gas extraction has occurred in wetland habitats along the northern Gulf of Mexico coast since the early 1900s. Activities involved with three-dimensional (3D) seismic exploration for these resources cause various disturbances to vegetation and soils. We documented the impact of a 3D seismic survey in coastal marshes in Louisiana, USA, along transects established before exploration began. Two semi-impounded marshes dominated by Spartina patens were in the area surveyed. Vegetation, soil, and water physicochemical data were collected before the survey, about 6 weeks following its completion, and every 3 months thereafter for 2 years. Soil cores for seed bank emergence experiments were also collected. Maximum vegetation height at impact sites was reduced in both marshes 6 weeks following the survey. In one marsh, total vegetation cover was also reduced, and dead vegetation cover increased, at impact sites 6 weeks after the survey. These effects, however, did not persist 3 months later. No effects on soil or water properties were identified. The total number of seeds that germinated during greenhouse studies increased at impact sites 5 months following the survey in both marshes. Although some seed bank effects persisted 1 year, these effects were not reflected in standing vegetation. The marshes studied were therefore resilient to the impacts resulting from 3D seismic exploration because vegetation responses were short term in that they could not be identified a few months following survey completion.
Abstract. Whole body and liver analyses indicated that winter-ing redheads (Aythya americana; n =... more Abstract. Whole body and liver analyses indicated that winter-ing redheads (Aythya americana; n = 70) in coastal Louisiana (one site) and Texas (two sites) were relatively free of contam-ination with common trace elements, organochlorines, and hy-drocarbons. Most trace elements, including As, Cr, Hg, Mg, Mn, Ni, Pb, Se, Sr, and Zn, were within background concen-trations in livers; levels of B, Cd, Cu, and Fe were elevated in some specimens. Only one organochlorine, DDE, was detected in redhead carcasses, but its concentration was below reported toxic levels in waterfowl. Body burdens of aliphatic and aro-matic hydrocarbons were generally low, but levels of pristane, total hydrocarbons, and the ratios of phytane:n-octadecane and pristane:n-heptadecane were indicative of possible chronic ex-posure to petroleum. Based on brain cholinesterase assays, redheads were not recently exposed to organophosphorous or carbamate pesticides. Of 30 elements or compounds tested for seasonal differenc...
Fact Sheet, 1997
Communities of submerged aquatic vegetation (SAV) are important components of many freshwater, br... more Communities of submerged aquatic vegetation (SAV) are important components of many freshwater, brackish, and marine aquatic ecosystems. They prevent erosion by baffling the impacts of waves, especially from storms. These aquatic plant communities remove nutrients and other pollutants from river and runoff inputs to coastal areas, preventing their entry into surrounding waters. They provide nursery habitat for fish, shrimp, and other species, as well as forage for wintering waterfowl and endangered species such as sea turtles and manatees. Unfortunately, not only have the distribution and abundance of seagrasses in the northern Gulf of Mexico declined precipitously during the past 50 years, most notably from widespread deterioration of water quality, but submerged aquatic plant communities are also susceptible to long-term environmental changes that are predicted to accompany global climate change.
Le complexe des zones humides de la Louisiane, l'un des plus important des Etats-Unis pour le... more Le complexe des zones humides de la Louisiane, l'un des plus important des Etats-Unis pour les anatides, Anatidae, est en train de changer rapidement. Environ 2 310 km 2 de zones humides, essentiellement des marais a vegetation emergente, ont disparu (transformes en eaux libres) entre 1956 et 1990, et d'autres marais continuent a disparaitre a l'heure actuelle. Ce processus est entretenu par des facteurs tels que l'affaissement naturel, l'elevation globale du niveau de la mer, la penetration d'eau salee, la perte de depots de nutriments et de sediments par le Mississippi et les modifications provoquees par la construction de canaux et les berges en remblai en resultant. Les efforts d'amenagement du milieu ont eu des resultats mitiges. Tous les ans, cette zone sert d'aire d'hivernage a environ 3 millions de canards, Anatinae, et 400000 oies, Anser sp., et constitue ainsi pour les anatides l'une des plus importantes aires d'hivernage du continent. Elle accueille 19% de la population hivernante des Etats-Unis de 14 especes de canards et d'oies, dont plus de 60% des populations des Etats-Unis de trois especes (le canard brun, Anas fulvigula, le canard chipeau, Anas strepera, et la sarcelle soucrourou, Anas discors) et plus de 20% des populations de neuf autres especes. Les regressions des effectifs totaux de canards, de canards de surface et de canards plongeurs sur les annees n'ont montre aucune variation significative des effectifs entre 1969 et 1994 (P > 0,05). De plus, dans la region cotiere de la Louisiane, il n'a ete note ni diminution, ni augmentation, significative pour aucune espece particuliere de canard entre 1969 et 1994 (P > 0,05). Pendant les 26 annees d'etude, aucune des dix especes de canards pour lesquelles des donnees sur la reproduction etaient disponibles, n'a montre de correlation positive entre la population presente en Louisiane au milieu de l'hiver et la population nicheuse nord-americaine, et, pour aucune de ces especes, il n'a ete note de diminution significative du pourcentage de la population nicheuse nord-americaine qui hiverne dans la region cotiere de la Louisiane. Une diminution significative (r 2 = 0,52, p = 0,0001) a ete notee pour les effectifs d'oies des neiges, Anser caerulescens, dans la region cotiere de la Louisiane entre 1969 et 1994, alors qu'au cours de la meme periode les effectifs d'oies rieuses, Anser albifrons, ont augmente (r 2 = 0,66, p = 0,0001). Chez les oies, les variations des effectifs sont probablement liees aux variations des effectifs des populations continentales et a leurs deplacements vers les zones agricoles, plutot qu'a la disparition des marais. Le fait que les populations de canards n'ont pas reagi aux modifications de l'habitat (telle que la disparition des marais) est peut-etre due a une intensification des efforts d'amenagement de ces habitats pendant cette periode. Il se peut aussi que l'on n'ait pas encore atteint le seuil au dela duquel la disparition des marais diminuerait la nourriture pour les anatides dans ces zones desormais en eau libre.
This report is preliminary and has not been reviewed for conformity with U.S.
Scientific Investigations Report, 2011
Fact Sheet, 2002
is the largest natural freshwater lake in Louisiana, covering more than 46 square miles (120 km 2... more is the largest natural freshwater lake in Louisiana, covering more than 46 square miles (120 km 2) (fig. 1). The lake is a principal stopover and wintering site for hundreds of thousands of migratory waterfowl and shorebirds. Scientists from the USGS National Wetlands Research Center are applying some of the research facility=s specialtiesCwetland plant research, aerial and ground surveys, digital mapping, and computer modelingCto facilitate wetland management at Catahoula Lake. Lake Management Catahoula Lake is long and shallow with major seasonal fluctuations in water levels. The difference between annual low and high water levels can be 18 feet (6 m) or greater when flooding is extreme. Local rainfall and backwater flooding from the Red, Black, and Mississippi Rivers largely determine lake levels. In 1972, a gated diversion canal was constructed to control water levels. U.S. Fish and Wildlife Service personnel at Catahoula National Wildlife Refuge manipulate lake water levels under shared management responsibility with the Louisiana Department of Wildlife and Fisheries and the U.S. Army Corps of Engineers. The goal of the current lake management plan is to maintain seasonal trends of winter and spring high water and summer and fall drawdown primarily to provide optimal habitat for migratory birds. The drawdown periods are characterized by dramatically reduced water levels that are about 8 feet (2.4 m) lower than Figure 1. Catahoula Lake National Wildlife Refuge lies on the eastern shore of Catahoula Lake in central Louisiana.
Circular, 2007
It is not known whether en route fall migratory birds (August-October) are likely to suffer more ... more It is not known whether en route fall migratory birds (August-October) are likely to suffer more from direct or secondary effects of hurricanes. On September 24, 2005, Hurricane Rita wreaked havoc on Louisiana's coast by toppling trees over vast areas and by stripping away microhabitats that harbor the invertebrates and produce the fruits upon which migrant landbirds depend (e.g., canopy foliage, vine tangles, epiphytes, leaf litter, and thickets of perennial plant species). Such transient effects of a hurricane on wildlife food resources are poorly understood, but these effects may have longterm consequences for some wildlife species.
Circular, 2007
Hurricane Rita significantly impacted the chenier forests of southwestern Louisiana, an important... more Hurricane Rita significantly impacted the chenier forests of southwestern Louisiana, an important habitat for Neotropical migratory birds. Sediment deposition was measured along transects at Hackberry Beach chenier, and Rita's effects on chenier structure and morphology were determined.
Wetlands, 1994
We studied biomass and macronutrient content of Halodule wrightii (shoalgrass) throughout the win... more We studied biomass and macronutrient content of Halodule wrightii (shoalgrass) throughout the winter and of Thalassia testudinum (turtlegrass) and Syringodium fitiforme (manateegrass) in January in Chandeleur Sound, Louisiana. Halodule, the primary food of wintering redheads, had the lowest biomass of the three species on the study area in midwinter. Macronutrient content of Halodule did not change during the winter, but aboveground and belowground biomass showed a 90 and 49% (P < 0.0001) decrease from October to March. Macronutrient content seems not to be the basis for selection by redheads of Hatodule over the other two seagrass species or of selection of belowground over aboveground parts.
The American Naturalist, 2013
Migratory birds are often suggested to be important vectors for long-distance dispersal (LDD) of ... more Migratory birds are often suggested to be important vectors for long-distance dispersal (LDD) of plant and animal propagules. The scale of such dispersal events (hundreds to thousands of kilometers) can influence landscape-level biological processes and species distributions. However, the few vector species studied and the lack of proper integration of their migratory movement in models of LDD has precluded the study of their potential as long-distance biotic dispersers. By means of a mechanistic model parameterized with empirical data, we first investigated the properties of seed dispersal curves generated by migratory birds and then analyzed the effect of bird size on model parameters and consequent seed dispersal patterns. Seed dispersal curves showed in most cases large and heavy tails, resulting in relatively frequent LDD (up to 3.5% of dispersal distances longer than 100 km). Bird size mediated trade-offs between bird movement and seed retention time that, in turn, determined seed dispersal patterns and the potential of each bird species as an LDD vector. Our modeling framework builds on a mechanistic understanding of seed dispersal by migratory birds and may thus be a useful tool to estimate the scale and frequency of bird-mediated, large-scale transport of native, invasive, and pathogenic organisms.
The American Naturalist, 2005
Waterfowl often have been assumed to disperse freshwater aquatic organisms between isolated wetla... more Waterfowl often have been assumed to disperse freshwater aquatic organisms between isolated wetlands, but no one has analyzed the impact of this transport on the population structure of aquatic organisms. For three cladocerans (Daphnia ambigua, Daphnia laevis, and Sida crystallina) and one bryozoan (Cristatella mucedo), we estimated the genetic distances between populations across North America using sequences of several mitochondrial DNA genes and genotypic frequencies at allozyme and microsatellite loci. Waterfowl movements across North America (estimated from band recovery data) explained a significant proportion of the gene flow occurring between populations across the continent for three of the four species, even after controlling for geographic distances between localities. The fourth species, S. crystallina, has propagules less likely to survive desiccation or ingestion by birds. Differences in the capacity to exploit bird-mediated transport are likely to have important consequences for the ecology of aquatic communities and the spread of invasive species.
Environmental Management, 2014
Anthropogenic disturbances in wetland ecosystems can alter the composition and structure of plant... more Anthropogenic disturbances in wetland ecosystems can alter the composition and structure of plant assemblages and affect system functions. Extensive oil and gas extraction has occurred in wetland habitats along the northern Gulf of Mexico coast since the early 1900s. Activities involved with three-dimensional (3D) seismic exploration for these resources cause various disturbances to vegetation and soils. We documented the impact of a 3D seismic survey in coastal marshes in Louisiana, USA, along transects established before exploration began. Two semi-impounded marshes dominated by Spartina patens were in the area surveyed. Vegetation, soil, and water physicochemical data were collected before the survey, about 6 weeks following its completion, and every 3 months thereafter for 2 years. Soil cores for seed bank emergence experiments were also collected. Maximum vegetation height at impact sites was reduced in both marshes 6 weeks following the survey. In one marsh, total vegetation cover was also reduced, and dead vegetation cover increased, at impact sites 6 weeks after the survey. These effects, however, did not persist 3 months later. No effects on soil or water properties were identified. The total number of seeds that germinated during greenhouse studies increased at impact sites 5 months following the survey in both marshes. Although some seed bank effects persisted 1 year, these effects were not reflected in standing vegetation. The marshes studied were therefore resilient to the impacts resulting from 3D seismic exploration because vegetation responses were short term in that they could not be identified a few months following survey completion.
