Hazard characterization and risk assessment are commonly used to prioritize vectors of nonindigenous species (NIS) for inspection or other prevention opportunities. Commercial shipping vessels are a ...target of such vector-based management since ballast water has been known to transport NIS between aquatic ecosystems globally. Here we used a risk-based screening protocol to prioritize vessels discharging ballast water to the lower Columbia River and Oregon coast. We began by adapting established methods of assessing risk factors that influence the initial stages of the invasion process (arrival and survival). We created relative risk scales for each factor using data collected from vessels that discharged ballast water in three unique zones within our study area. We then organized a decision tree based on the confidence level of the proxies used for each risk factor to create a tool that prioritizes vessels with high risk ballast water for attention from regulatory personnel. In order of consideration, decision tree factors included: intent to discharge ballast water, reported adherence to required management practices, environmental distance between source and discharge locations (habitat suitability), ballast water discharge volume (propagule pressure number and frequency), and ballast water age (organism viability). As a result, vessels were prioritized on a scale of low, medium, medium-high, or high. We applied the decision tree to a 2016 dataset of vessel arrivals and found that 173 of 1,592 arrivals were deemed high priority, with most occurring at ports in the freshwater zone of the Columbia River (158), followed by fewer in the estuarine zone of the Columbia River (4) and in Coos Bay (11). The decision tree is transferable to NIS prevention and regulatory efforts in other port systems. The vessel prioritizations are adaptable for managers using risk assessment strategies to allocate limited regulatory program resources for vector screening.
The productivity of aquatic ecosystems depends on the supply of limiting nutrients. The invasion of the Laurentian Great Lakes, the world's largest freshwater ecosystem, by dreissenid (zebra and ...quagga) mussels has dramatically altered the ecology of these lakes. A key open question is how dreissenids affect the cycling of phosphorus (P), the nutrient that limits productivity in the Great Lakes. We show that a single species, the quagga mussel, is now the primary regulator of P cycling in the lower four Great Lakes. By virtue of their enormous biomass, quagga mussels sequester large quantities of P in their tissues and dramatically intensify benthic P exchanges. Mass balance analysis reveals a previously unrecognized sensitivity of the Great Lakes ecosystem, where P availability is now regulated by the dynamics of mussel populations while the role of the external inputs of phosphorus is suppressed. Our results show that a single invasive species can have dramatic consequences for geochemical cycles even in the world's largest aquatic ecosystems. The ongoing spread of dreissenids across a multitude of lakes in North America and Europe is likely to affect carbon and nutrient cycling in these systems for many decades, with important implications for water quality management.
Animal excretion provides nutrients for primary productivity and can be a crucial component of ecosystem nutrient cycling. The concentrations of carbon (C), nitrogen (N), and phosphorus (P) in an ...animal’s excretion are strongly influenced by the C:N:P stoichiometry (molar ratios) of its body and of the food it eats. We measured the C:N:P ratios of quagga mussel (
Dreissena rostriformis bugensis
) tissues and excreta and of seston across wide environmental and spatial gradients in the upper Laurentian Great Lakes. We then investigated how mussel excretion rates were impacted by stoichiometric mismatch—the difference between the C:P ratios of mussel tissues and the C:P ratios their food. Quagga mussel internal C:N:P stoichiometry varied significantly across sites and seasons, driven primarily by changes in tissue P concentrations. When mussel tissues had substantially lower C:P ratios than seston (that is
,
strong stoichiometric mismatch), mussels excreted significantly less N and P relative to C. Excretion C:N ratios varied by nearly threefold, while C:P ratios varied by tenfold. The effect of the stoichiometric mismatch on excretion stoichiometry was more dramatic in the spring, when mussels had higher tissue P concentrations, than in the summer. This suggests seasonality in mussel P demand. Our results challenge the assumption of strict internal homeostasis in consumers and demonstrate that food and tissue stoichiometry need to be considered to predict consumer excretion stoichiometry. These findings help to better understand the impact of consumer-driven nutrient cycling in aquatic environments and quagga mussel contributions to the nutrient budgets of invaded ecosystems.
The invasive quagga mussel (Dreissena rostriformis bugensis) can significantly alter the biogeochemical cycling of ecologically important nutrients, such as P and N, in lacustrine ecosystems. While ...D. rostriformis bugensis has invaded large portions of the Great Lakes, its distribution within waterbodies has fluctuated over time. Anticipating the effects of D. rostriformis bugensis on invaded ecosystems requires lake-wide monitoring because the effects of D. rostriformis bugensis are dependent on the size and distribution of mussel populations throughout a waterbody. During the summer of 2018 and 2019, I conducted a benthic survey consisting of ponar grabs and benthic imaging technology (BIS) to assess the distribution, areal density, and areal biomass of D. rostriformis bugensis populations in Lakes Huron and Michigan. I compared the results of my survey to other contemporary surveys of both lakes and found that, recently, D. rostriformis bugensis populations have expanded into deeper regions of Lake Michigan and contracted into more shallow regions of Lake Huron. In addition, ongoing recruitment by juvenile D. rostriformis bugensis has occurred in portions of both lakes that are deeper than other recent reports, which indicates the biomass of these populations will grow in the future. To better understand the ability of quagga mussels to invade profundal habitats and their response to food availability, I investigated the effects of starvation on quagga mussels under laboratory conditions. In an 8-month trial, I compared survival, growth, tissue elemental composition as well as respiration and nutrient transformation rates of starved mussels to mussels fed a high-quality diet. My results indicate that quagga mussels are highly starvation tolerant at temperatures characteristic of the hypolimnia in the Great Lakes, with greater than 95% survival rates after 231 days under starvation conditions. Starved mussels had lower respiration and excretion rates of P and N compared to well-fed mussels. I show that quagga mussels are highly resilient to disruptions in food supply, which helps explain their invasion success in the cold and food-limited profundal zone of the Great Lakes.
The AFL-CIO generally supports the concept of short-time compensation as a tool in dealing with the many consequences of unemployment, but not as a no-cost or low-cost solution. The AFL-CIO has ...outlined the conditions critical for short-time compensation programs: 1. Short-time compensation must not be viewed as an alternative to active government programs to stimulate the economy and employment opportunities. 2. The needs of the totally unemployed must be given the highest priority. The AFL-CIO wants assurances that firms using the concept do not lay off the most recently hired and less-costly-to-recruit workers first. Few employers are using the short-time concept because other options, such as shutting down for a period, are less costly. Elective work sharing is more desirable than unilateral decisions by employers or even by a majority of workers in the local labor union.
ONE OF THE WAYS American workers have developed to cope with inflation is to have escalator or cost-of-living clauses negotiated into their contracts to increase their pay as prices go up.
The compressed work week, flexitime, and job sharing are discussed from the labor perspective. The author suggests that it is unlikely that unions will endorse flexible work arrangements that ...jeopardize the eight-hour-day concept. (LBH)
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