Estuaries exhibit a wide array of human impacts that can compromise their ecological integrity, because of rapid population growth and uncontrolled development in many coastal regions worldwide. Long-term environmental problems plaguing estuaries require remedial actions to improve the viability and health of these valuable coastal systems. Detailed examination of the effects of pollution inputs, the loss and alteration of estuarine habitat, and the role of other anthropogenic stress indicates that water quality in estuaries, particularly urbanized systems, is often compromised by the overloading of nutrients and organic matter, the influx of pathogens, and the accumulation of chemical contaminants. In addition, the destruction of fringing wetlands and the loss and alteration of estuarine habitats usually degrade biotic communities. Estuaries are characterized by high population densities of microbes, plankton, benthic flora and fauna, and nekton; however, these organisms tend to be highly vulnerable to human activities in coastal watersheds and adjoining embayments. Trends suggest that by 2025 estuaries will be most significantly impacted by habitat loss and alteration associated with a burgeoning coastal population, which is expected to approach six billion people. Habitat destruction has far reaching ecological consequences, modifying the structure, function, and controls of estuarine ecosystems and contributing to the decline of biodiversity. Other anticipated high priority problems are excessive nutrient and sewage inputs to estuaries, principally from land-based sources. These inputs will lead to the greater incidence of eutrophication as well as hypoxia and anoxia. During the next 25 years, overfishing is expected to become a more pervasive and significant anthropogenic factor, also capable of mediating global-scale change to estuaries. Chemical contaminants, notably synthetic organic compounds, will remain a serious problem, especially in heavily industrialized areas. Freshwater diversions appear to be an emerging global problem as the expanding coastal population places greater demands on limited freshwater supplies for agricultural, domestic, and industrial needs. Altered freshwater flows could significantly affect nutrient loads, biotic community structure, and the trophodynamics of estuarine systems. Ecological impacts that will be less threatening, but still damaging, are those caused by introduced species, sea level rise, coastal subsidence, and debris/litter. Although all of these disturbances can alter habitats and contribute to shifts in the composition of estuarine biotic communities, the overall effect will be partial changes to these ecosystem components. Several strategies may mitigate future impacts.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0376892902000061

Environmental threats and environmental future of estuaries

Indirect effects of contaminants in aquatic ecosystems.

A new microscopic method for simultaneously determining in situ the identities, activities, and specific substrate uptake profiles of individual bacterial cells within complex microbial communities was developed by combining fluorescent in situ hybridization (FISH) performed with rRNA-targeted oligonucleotide probes and microautoradiography. This method was evaluated by using defined artificial mixtures of Escherichia coli and Herpetosiphon aurantiacus under aerobic incubation conditions with added [H-3]glucose. Subsequently, we were able to demonstrate the potential of this method by visualizing the uptake of organic and inorganic radiolabeled substrates ([C-14]acetate, [C-14]butyrate, [C-14]bicarbonate, and P-33(i)) in probe-defined populations from complex activated sludge microbial communities by using aerobic incubation conditions and anaerobic incubation conditions (with and without nitrate). For both defined cell mixtures and activated sludge, the method proved to be useful for simultaneous identification and analysis of the uptake of labeled substrates under the different experimental conditions used. Optimal results were obtained when fluorescently labeled oligonucleotides were applied prior to the microautoradiographic developing procedure. For single-cell resolution of FISH and microautoradiographic signals within activated sludge flocs, cryosectioned sample material was examined with a confocal laser scanning microscope. The combination of in situ rRNA hybridization techniques, cryosectioning, microautoradiography, and confocal laser scanning microscopy provides a unique opportunity for obtaining cultivation-independent insights into the structure and function of bacterial communities.

https://aem.asm.org/content/aem/65/3/1289.full.pdf

Combination of fluorescent in situ hybridization and microautoradiography-a new tool for structure-function analyses in microbial ecology

Complete optical absorption and fluorescence spectra were collected for a diverse suite of 0.2-μm-filtered marine, riverine, and estuarine waters, as well as for colored dissolved organic matter (CDOM) isolated from several of these waters by solid-phase C 18 extraction. Absorption and fluorescence parameters for these samples are reported. For surface waters, variations in the fluorescence quantum yields obtained with 355- and 337-nm excitation fell within a narrow window (< 2.5-fold variation about the mean values), demonstrating that fluorescence measurements can be used to determine absorption coefficients of CDOM in the ultraviolet region with reasonably good accuracy. Methods for predicting absorption coefficients and line shapes from the fluorescence data are introduced and tested. The absorption and fluorescence spectra of CDOM extracted from some seawaters differed significantly from those of the original waters, demonstrating that material isolated by hydrophobic adsorption is not necessarily representative of the suite of colored organic matter present in aquatic systems. These results clearly illustrate that great care must be taken when extracted material is used to infer the optical properties of natural waters

Optical absorption and fluorescence properties of chromophoric dissolved organic matter in natural waters

During the past 50 years, the human population has more than doubled and global agricultural production has similarly risen. However, the productive arable area has increased by just 10%; thus the increased use of pesticides has been a consequence of the demands of human population growth, and its impact has reached global significance. Although we often know a pesticide′s mode of action in the target species, we still largely do not understand the full impact of unintended side effects on wildlife, particularly at higher levels of biological organization: populations, communities, and ecosystems. In these times of regional and global species declines, we are challenged with the task of causally linking knowledge about the molecular actions of pesticides to their possible interference with biological processes, in order to develop reliable predictions about the consequences of pesticide use, and misuse, in a rapidly changing world.

/pdf/wildlife-ecotoxicology-of-pesticides-can-we-track-effects-to-mk63282yqz.pdf

Wildlife Ecotoxicology of Pesticides: Can We Track Effects to the Population Level and Beyond?

On 20 April 2010, the Deepwater Horizon explosion, which released a US government—estimated 4.9 million barrels of crude oil into the Gulf of Mexico, was responsible for the death of 11 oil workers and, possibly, for an environmental disaster unparalleled in US history. For 87 consecutive days, the Macondo well continuously released crude oil into the Gulf of Mexico. Many kilometers of shoreline in the northern Gulf of Mexico were affected, including the fragile and ecologically important wetlands of Louisiana's Mississippi River Delta ecosystem. These wetlands are responsible for a third of the nation's fish production and, ironically, help to protect an energy infrastructure that provides a third of the nations oil and gas supply. Here, we provide a basic overview of the chemistry and biology of oil spills in coastal wetlands and an assessment of the potential and realized effects on the ecological condition of the Mississippi River Delta and its associated flora and fauna.

https://bioone.org/journals/bioscience/volume-62/issue-6/bio.2012.62.6.7/Oil-Impacts-on-Coastal-Wetlands--Implications-for-the-Mississippi/10.1525/bio.2012.62.6.7.pdf

Oil Impacts on Coastal Wetlands: Implications for the Mississippi River Delta Ecosystem after the Deepwater Horizon Oil Spill

Although the occurrence of microbial (algal, protozoan, bacterial, and fungal) epibionts on marine crustaceans and other invertebrates has been documented repeatedly, the ecological context and significance of these relationships generally are not well understood. Recently, several studies have examined the population and community ecology of algal and protozoan epibionts on freshwater crustaceans. Even so, the study of microbial epibionts in aquatic environments is still in its infancy. In this review, we summarize associations of microalgae, protozoans, and bacteria with marine crustaceans, especially copepods. We note differences and commonalities across epibiont taxa, consider host-epibiont cycling of nutrients, generate hypotheses relevant to the ecology of the host and the epibiont, and suggest future research opportunities. Microsc. Res. Tech. 37:116–135, 1997. © 1997 Wiley-Liss, Inc.

Epibiotic microorganisms on copepods and other marine crustaceans

Direct and indirect effects of diesel-contaminated sediment on microalgae, meiofauna, and meiofauna-microalgae trophic interactions were examined in a microcosm study of the sediment community from a Spartina aZterniJora salt marsh. Microcosms of natural sediment were given small daily doses of contaminated sediment over a 28-d period, creating low-, medium-, and high-diesel treatment concentrations of -0.5, 5.5, and 55 ppm PAH, respectively. Diesel caused initial (within 7 h) reductions in microalgal grazing by meiobenthic harpacticoid copepods. Over longer periods of exposure (7-28 d), grazing on microalgae by copepods as a group was reduced in highdiesel treatments, primarily because of high copepod mortality. In contrast, grazing by and abundance of Cletocamptus deitersi (a copepod) was significantly enhanced in high-diesel treatments. Concurrent with reduced grazing by copepods, nematode grazing rates increased significantly in high-diesel treatments, indicating possible competition for microalgae between copepods and nematodes. In spite of transiently enhanced grazing by nematodes and C. deitersi, total meiofaunal grazing on microalgae was reduced in high-diesel treatments. Increased Chl a: pheopigment ratios in contaminated sediments were also indicative of reduced grazing pressure. A large (10X) increase in microalgal biomass was observed in high-diesel treatments and was likely a consequence of reduced meiofaunal grazing. The general responses observed in microcosms were also observed in a field study of polycyclic aromatic hydrocarbon contamination. Collectively, our data indicate that benthic microalgal biomass is controlled by meiofaunal grazing and that meiofauna may compete for limited algal resources. Furthermore, consideration of multiple trophic levels and their interactions allows a more complete and ecologically meaningful understanding of the mechanisms by which contaminants induce changes in natural communities.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1997.42.3.0561

Response of a benthic food web to hydrocarbon contamination

14 C-labeled algae) and benthic microalgal abundance and composition (HPLC analysis of photopigments) were measured every 6 h over a 48-h period. Midday feeding peaks were detected in Coullana sp. juveniles and adult females (but not males), Microarthridion littorale, Pseudostenhelia wellsi , and ostracods and were coincident with peaks in microalgal biomass. This pattern of midday feeding peaks by meiofauna differs from classical models of zooplankton feeding, which typically peak at night. Midday feeding peaks were apparently influenced by functional responses to food availability (ostracods and Coullana sp. females and juveniles), entrained diel rhythms (M. littorale), influence of light—positive ( M. littorale) or negative (Coullana sp.), and possibly by vertical migration of diatoms within sediment. The negative influence of light on grazing by Coullana sp. may have implications for its feeding activity during midday low tides. Diatoms dominated the benthic microalgae, but cyanobacteria and chlorophytes contributed significantly to the planktonic community. Coullana sp. gut pigments indicate that at least part of its diet is planktonic, but it selectively avoids planktonic cyanobacteria. Diel variation of microalgal biomass appears to be influenced by meiofaunal grazing, which implies that meiofauna represent an important link between microalgal primary production and higher trophic levels.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2000.45.2.0381

Kevin R. Carman

Papers

Indirect effects of contaminants in aquatic ecosystems.

Oil Impacts on Coastal Wetlands: Implications for the Mississippi River Delta Ecosystem after the Deepwater Horizon Oil Spill

Epibiotic microorganisms on copepods and other marine crustaceans

Response of a benthic food web to hydrocarbon contamination

Diel feeding behavior of meiofauna and their relationships with microalgal resources