Seasonal and Mesoscale Variability in the Distribution of Antarctic Krill, \u3ci\u3eEuphausia superba\u3c/i\u3e, West of the Antarctic Peninsula

Observations collected between November 1991 and September 1993 during four multidisciplinary cruises were analyzed to provide a description of seasonal and mesoscale variability in the distribution and abundance of Antarctic krill, Euphausia superba, within continental shelf waters west of the Antarctic Peninsula and to investigate possible relationships between variability in krill distributions and variability in selected environmental parameters. Acoustic measurements of krill were made each season at designated locations to estimate the abundance of krill, in terms of vertically-integrated krill biomass and the number of aggregations, characterize the depth distribution of krill, and provide a quantitative description of the size, shape, and biomass of individual krill aggregations. The acoustic observations were coupled in time and space to environmental conditions defined by measurements of weather and sea ice parameters, hydrographic structure, concentrations of algal pigments, and net-based density estimates of krill and other zooplankton

Modeling the Growth Dynamics of Antarctic Krill Euphausia Superba

A time-dependent, size-structured, bioenergetically based model was developed to examine the growth dynamics of Antarctic krill Euphausia superba 2 to 60 mm in size. The metabolic processes included in the model are ingestion, a baseline respiration, respiratory losses due to feeding and digestion, and an activity-based respiration factor. The total of these processes, net production, was used as the basis for determining the growth or shrinkage of individuals. Size-dependent parameterizations for the metabolic processes were constructed from field and laboratory measurements. Environmental effects were included through time series of pelagic phytoplankton concentration that were derived from data sets collected west of the Antarctic Peninsula. Simulated growth rates during the spring and summer for all brill size classes were consistent with published growth rates; however, initial results indicated that winter shrinkage rates were too large. Although the use of a seasonally varying respiration activity factor (reduced winter respiration rates) resulted in winter shrinkage rates of adults that were consistent with observations of experimentally starved individuals, the annual change in length of specific size classes was still inconsistent with observations. Subsequent simulations examined the effect of ingestion of sea ice algae by krill in the late winter and early spring. The annual growth cycle best matched observations, particularly those for larval and subadult krill (\u3c35 mm), when reduced winter respiration rates and ingestion of sea ice algae were both included. These results suggest that the ability of krill to exploit a range of food sources and reduced winter metabolism rates are the mechanisms that allow krill to successfully overwinter. The need for additional observations of krill physiological processes, especially during winter, is clearly indicated

Analysis of Financial Accounting Techniques and Applications

This thesis sets to examine the core accounting principles in financial accounting and apply those principles to companies’ financial statements and 10-K’s. Starting from simple transactions and adjusting entries, each topic moves through the financial statements and applies them to different companies. The second half examines more advanced accounting topics such as pensions and the buying and selling of securities. Among each section is also a thorough set of figures that highlight specific journal entries, data, or calculations to enhance the understanding of these topics. Each topic was researched through various case examinations relating to a particular area of financial accounting

Can an Optical Plankton Counter Produce Reasonable Estimates of Zooplankton Abundance and Biovolume in Water With High Detritus?

The Optical Plankton Counter (OPC) has been used in oceanic and fresh waters to estimate zooplankton abundance and biovolume. However, it is not clear whether the OPC can produce accurate estimates of zooplankton abundance and biovolume in waters with high detritus. In order to test the capability of the OPC to estimate zooplankton abundance and biovolume in Chesapeake Bay, two sets of laboratory experiments were conducted using water with high detritus concentrations collected from the upper Choptank estuary of Chesapeake Bay and laboratory cultured Artemia. Our results suggest that the OPC is able to produce accurate estimates of zooplankton biovolume after correcting for the influence of background detritus in all the detritus concentrations used, but accurate estimates of zooplankton abundance only in water with background detritus \u3c100 particles l-1. The relationship between light attenuation and OPC background particle concentrations provides a useful way to estimate OPC background particle concentrations when direct OPC background particle measurements are not available. Light attenuation corrected OPC particle abundance and particle volume gave accurate estimates of zooplankton abundance and biovolume. However, the accuracy of the corrected OPC measurements by the estimated background particle concentrations was not as high as the corrected OPC measurements by the direct background particle measurements

Lagrangian Modelling Studies of Antarctic Krill (Euphausia superba) Swarm Formation

A two-dimensional Lagrangian particle model was developed to examine the spatial distribution of Antarctic krill (Euphausia superba). The time-dependent location of particles, which represent krill individuals, is determined by random diffusion, foraging activity, and movement induced by the presence of neighbours. Foraging activity is based on prescribed food conditions and is such that krill swim slower and turn more frequently in areas of high food concentration. The presence or absence of neighbours either disperses krill, if the local concentrations become too dense, or coalesces krill, if concentrations become too dilute, respectively. Predation on krill is included and affects swarm characteristics by removing individuals. Sensitivity studies indicate that the rate of krill swarm formation and the total number of swarms formed are determined primarily by foraging response and nearest neighbour sensing distance. Simulations using food distributions that are representative of those encountered at boundaries, such as fronts, mesoscale eddies, or the sea ice edge, show that foraging activity can produce rapid swarm formation. Results from other krill swarm models show that attraction between individuals is the primary mechanism producing krill swarms. However, the parameterizations for krill interactions used in those models and that used in this model differ, thereby implying different biological dynamics. Thus, parameterization of the basic interactions it) krill swarm models remains to be defined. (C) 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved

Super-Aggregations of Krill and Humpback Whales in Wilhelmina Bay, Antarctic Peninsula

Ecological relationships of krill and whales have not been explored in the Western Antarctic Peninsula (WAP), and have only rarely been studied elsewhere in the Southern Ocean. In the austral autumn we observed an extremely high density (5.1 whales per km2) of humpback whales (Megaptera novaeangliae) feeding on a super-aggregation of Antarctic krill (Euphausia superba) in Wilhelmina Bay. The krill biomass was approximately 2 million tons, distributed over an area of 100 km2 at densities of up to 2000 individuals m−3; reports of such ‘super-aggregations’ of krill have been absent in the scientific literature for >20 years. Retentive circulation patterns in the Bay entrained phytoplankton and meso-zooplankton that were grazed by the krill. Tagged whales rested during daylight hours and fed intensively throughout the night as krill migrated toward the surface. We infer that the previously unstudied WAP embayments are important foraging areas for whales during autumn and, furthermore, that meso-scale variation in the distribution of whales and their prey are important features of this system. Recent decreases in the abundance of Antarctic krill around the WAP have been linked to reductions in sea ice, mediated by rapid climate change in this area. At the same time, baleen whale populations in the Southern Ocean, which feed primarily on krill, are recovering from past exploitation. Consideration of these features and the effects of climate change on krill dynamics are critical to managing both krill harvests and the recovery of baleen whales in the Southern Ocean

The importance of Antarctic krill in biogeochemical cycles

Antarctic krill (Euphausia superba) are swarming, oceanic crustaceans, up to two inches long, and best known as prey for whales and penguins – but they have another important role. With their large size, high biomass and daily vertical migrations they transport and transform essential nutrients, stimulate primary productivity and influence the carbon sink. Antarctic krill are also fished by the Southern Ocean’s largest fishery. Yet how krill fishing impacts nutrient fertilisation and the carbon sink in the Southern Ocean is poorly understood. Our synthesis shows fishery management should consider the influential biogeochemical role of both adult and larval Antarctic krill

Estimating the density of Antarctic krill (<em>Euphausia superba</em>) from multi-beam echo-sounder observations using distance sampling methods

Antarctic krill is a key species in the Antarctic food web, an important prey item for marine predators and a commercial fishery resource. Although single-beam echo-sounders are commonly used to survey the species, multi-beam echo-sounders may be more efficient because they sample a larger volume of water. However, multi-beam echo-sounders may miss animals because they involve lower energy densities. We adapt distance sampling theory to deal with this and to estimate krill density and biomass from a multi-beam echo-sounder survey. The method provides a general means for estimating density and biomass from multi-beam echo-sounder data.</p

Old Dominion University

This “Late Breaking Hot Topic Paper ” introduces and tracks the progress of OceanDIVER, a project to develop a tele-immersive collaboratory that integrates archived oceanographic data with simulation and real-time data gathered from autonomous underwater vehicles. Specifically this paper describes the work in building CAVE6D, a tool for collaboratively visualizing environmental data in CAVEs, ImmersaDesks and desktop workstations