Planktono bendrijos tyrimai teikia esminę informaciją vertinant ežerų ekologinę būklę ir jų raidos tendencijas, nes planktono dumbliai yra pagrindiniai, o dažnai ir vieninteliai pirminės organinės medžiagos producentai, o zooplanktonas yra grandis tarp pirminių producentų ir aukštesnių mitybos lygmenų pelaginėje mitybos grandinėje. Vertingiausi ekologiniu pažiūriu yra mezotrofiniai Lietuvos ežerai. Juos pagal zooplanktono bendrijas galima suskirstyti į 3 (charakteringas) grupes: ežerus, kuriuose gyvena irklakojis vėžiagyvis Limnocalanus macrurus, ežerus apgyvendintus kito relikto Eurytemora lacustris ir ežerus be ledynmečio reliktinių planktono vėžiagyvių. Informacija apie šių ežerų grupėse vykstančius procesus teikia galimybę vertinti Lietuvos mezotrofinių ežerų raidos tendencijas. Darbo tikslas – nustatyti charakteringų mezotrofinių Lietuvos ežerų planktono dumblių ir vėžiagyvių bendrijų struktūrą ir kaitą, palyginti ežerų grupių planktono bendrijas ir įvertinti Lietuvos mezotrofinių ežerų kitimo tendencijas. Darbe atlikti kompleksiniai mezotrofinių ežerų fitoplanktono ir zooplanktono struktūros tyrimai. Šie duomenys įvertina dabartinę Lietuvos mezotrofinių ežerų būklę ir jos raidos tendencijas, bei papildo informaciją apie mezotrofinių ežerų fitoplanktoną ir zooplanktoną. Pirmą kartą Lietuvoje atlikti dumblių ramybės stadijų aktyvacijos veiksnių tyrimai. Tirtuose ežeruose apibūdintos 32 anksčiau Lietuvoje neregistruotos dumblių ir melsvabakterių rūšys. / Studies of plankton community provide vital information in assessing the ecological status of lakes and their evolution. Phytoplankton is essential, and often the only primary producer of organic matter. Zooplankton takes an important place in the pelagic food chain because of the link between the primary producers and higher trophic levels. The most valuable are Lithuanian mesotrophic lakes. Depending on zooplankton communities, those lakes can be divided in 3 (characteristic) groups: lakes with glacial relict calanoids Limnocalanus macrurus, lakes with another calanoids Eurytemora lacustris and lakes without relict crustaceans. The information obtained after examination of several lakes from different groups, is useful for evaluating the status of Lithuanian mesotrophic lakes. The aim of the present study was to identify defining characteristics of phytoplankton and zooplankton community structure and change in Lithuanian mesotrophic lakes, compare plankton communities and to assess change trends of Lithuanian mesotrophic lakes. In this study complex analyses of phytoplankton and zooplankton structure were performing in mesotrophic lakes. Our data assess the current state of Lithuanian mesotrophic lakes and complement the information about phytoplankton and zooplankton in mesotrophic lakes. The obtained results are important for evaluation of the ecological status of the lakes and providing the environmental control tools to ensure good ecological status of the lakes. For... [to full text]

Studies of plankton community provide vital information in assessing the ecological status of lakes and their evolution. Phytoplankton is essential, and often the only primary producer of organic matter. Zooplankton takes an important place in the pelagic food chain because of the link between the primary producers and higher trophic levels. The most valuable are Lithuanian mesotrophic lakes. Depending on zooplankton communities, those lakes can be divided in 3 (characteristic) groups: lakes with glacial relict calanoids Limnocalanus macrurus, lakes with another calanoids Eurytemora lacustris and lakes without relict crustaceans. The information obtained after examination of several lakes from different groups, is useful for evaluating the status of Lithuanian mesotrophic lakes. The aim of the present study was to identify defining characteristics of phytoplankton and zooplankton community structure and change in Lithuanian mesotrophic lakes, compare plankton communities and to assess change trends of Lithuanian mesotrophic lakes. In this study complex analyses of phytoplankton and zooplankton structure were performing in mesotrophic lakes. Our data assess the current state of Lithuanian mesotrophic lakes and complement the information about phytoplankton and zooplankton in mesotrophic lakes. The obtained results are important for evaluation of the ecological status of the lakes and providing the environmental control tools to ensure good ecological status of the lakes. For... [to full text] / Planktono bendrijos tyrimai teikia esminę informaciją vertinant ežerų ekologinę būklę ir jų raidos tendencijas, nes planktono dumbliai yra pagrindiniai, o dažnai ir vieninteliai pirminės organinės medžiagos producentai, o zooplanktonas yra grandis tarp pirminių producentų ir aukštesnių mitybos lygmenų pelaginėje mitybos grandinėje. Vertingiausi ekologiniu pažiūriu yra mezotrofiniai Lietuvos ežerai. Juos pagal zooplanktono bendrijas galima suskirstyti į 3 (charakteringas) grupes: ežerus, kuriuose gyvena irklakojis vėžiagyvis Limnocalanus macrurus, ežerus apgyvendintus kito relikto Eurytemora lacustris ir ežerus be ledynmečio reliktinių planktono vėžiagyvių. Informacija apie šių ežerų grupėse vykstančius procesus teikia galimybę vertinti Lietuvos mezotrofinių ežerų raidos tendencijas. Darbo tikslas – nustatyti charakteringų mezotrofinių Lietuvos ežerų planktono dumblių ir vėžiagyvių bendrijų struktūrą ir kaitą, palyginti ežerų grupių planktono bendrijas ir įvertinti Lietuvos mezotrofinių ežerų kitimo tendencijas. Darbe atlikti kompleksiniai mezotrofinių ežerų fitoplanktono ir zooplanktono struktūros tyrimai. Šie duomenys įvertina dabartinę Lietuvos mezotrofinių ežerų būklę ir jos raidos tendencijas, bei papildo informaciją apie mezotrofinių ežerų fitoplanktoną ir zooplanktoną. Pirmą kartą Lietuvoje atlikti dumblių ramybės stadijų aktyvacijos veiksnių tyrimai. Tirtuose ežeruose apibūdintos 32 anksčiau Lietuvoje neregistruotos dumblių ir melsvabakterių rūšys.

We deployed depth-specific drifters in the western and eastern parts of the South Arm basin of Lake Opeongo and collected zooplankton samples at west and east fixed stations and at additional up- and downwind locations at three depths of the epilimnion under a range of wind conditions. Water currents had highest association with the immediate wind direction and the direction they travelled was dependent on wind strength. Along the main west-east fetch large zooplankton resided high in the epilimnion and were transported eastwards by strong surface currents where they accumulated. Small zooplankton were more uniformly distributed with depth and their accumulation patterns and transport mechanisms are less clear. Along shorter fetches oriented off-angle with the main one accumulations of zooplankton occurred at all downwind locations under heavy winds although the patterns are more variable and complex. These downwind accumulations likely create high quality habitat for warm water fish.

Microstructure and acoustic data were collected in Saanich Inlet, British Columbia, and at Ocean Station P in the eastern subarctic North Pacific Ocean with the objective of observing krill-generated turbulence. At Ocean Station P, although a number of species composing the zooplankton community are large enough to generate turbulent flow (Re > 10e3), no turbulence events could be correlated with presence of swimming marine organisms and measurements indicated turbulence generated by shear. Zooplankton densities were likely too low to produce turbulence at the scale of an aggregation and the O(10e-2 m) scattered turbulent signals generated by individuals are difficult to detect in the natural environment. In Saanich Inlet, higher dissipation rates were observed in regions of high acoustic backscattering, suggesting that zooplankton-generated turbulence was occurring. Although presence of zooplankton was often correlated with high dissipation rates, high dissipation rates were frequently observed in the absence of zooplankton, suggesting multiple sources of turbulence. High dissipation rates were observed in the presence of non-migrating zooplankton as much as in the migrating layer. These turbulence events occurred at a scale of more than 1 m as they were positively detected by our dissipation rate estimation technique. This suggests that marine organisms can act together to generate turbulence at scales that can produce diapycnal mixing. Over all time-series collected, dissipation rates in the presence of zooplankton averaged 1.4 x 10e-8 W/kg whereas the average in the absence of zooplankton was 0.7 x 10e-8 W/kg.

A biological front at the mouth of Saanich Inlet results in higher rates of primary productivity at the inlet mouth relative to the head creating a gradient that could influence zooplankton distribution. A shallow sill (75m) at the inlet mouth restricts circulation below sill depth, isolating the deep basin for much of the year. Anoxia develops in the isolated basin and the depth of the anoxic layer changes during the year. During the day, pelagic zooplankton form a deep scattering layer. Between April 2005 and March 2006. I conducted monthly 200kHz acoustic surveys between the mouth and head of Saanich Inlet to test the hypothesis that zooplankton density was greater near the mouth relative to the head. I was also interested in how changing anoxic layer depth affected the distribution of the deep scattering layer. I found that zooplankton density followed a headward gradient in the spring and summer. with the highest densities near the mouth. Zooplankton density was higher near the mouth or the mid-inlet relative to the head in 75% of transects. I did not observe a zooplankton density gradient during the winter. Zooplankton distribution was affected by dissolved oxygen concentration. Deep scattering layer depth was significantly correlated with the depth of the anoxic layer and vertical compression of the deep scattering layer increased as the anoxic layer moved upwards. When the depth of the anoxic layer was less than 90 meters. zooplankton were nearly absent. Vertical migration of the deep scattering layer to surface waters at night has been well documented. but zooplankton migration patterns in the shallow waters of Saanich Inlet have not been described. I used 200kHz acoustic data collected by the VENUS observatory (96m) and an autonomous acoustic system deployed at a shallow site (62m) in Patricia Bay to study zooplankton migration patterns. Horizontal movement of the deep scattering layer over shallow depths following vertical migration was infrequent. Over 41 days of observation at the shallow site. I only observed deep scattering layer zooplankton on 12 days. At the shallow site. night-time volume backscatter was dominated by the emergence of benthic zooplankton. The movement of these scatterers into the water column at night resulted in a 14-fold increase in volume backscatter over daytime values. I observed this emergence pattern at both sites. which represents an important component of benthic-pelagic coupling in Saanich Inlet. In contrast to the deer scattering layer. which migrated to the surface each night, emergent zooplankton remained within 30-40 meters of the seafloor and did not ascend into surface waters.

Climate change has a wide range of effects with the potential to cause broad changes in marine ecosystems. The Arctic is predicted to be one of the most highly impacted areas, with average temperatures increasing by as much as 3-5°C. As temperatures rise, Arctic sea ice is disappearing earlier each year, leading to changes in the ocean environment. Thick-billed murres (Uria lomvia) (TBMU) and northern fulmars (Fulmarus glacialis) were collected at colonies in the eastern Canadian Arctic to examine potential changes in Arctic marine food webs over the past three decades. Otoliths and invertebrates were examined in the murre stomachs, and the results compared to data collected from the same colonies in the 1970s and 1980s. Few changes were observed in the diets of the high Arctic thick-billed murres where the ice-associated Arctic cod continue to dominant the prey items found in the thick-billed murres. Significant changes were found in birds sampled from the low and mid-Arctic. In the low Arctic, Arctic cod has declined across all of the colonies sampled, while the capelin, which is a sub-Arctic species, has become dominant in the diets of the birds in the low Arctic and a common prey species mid-Arctic where it was not observed in the diet of TBMUs previously, indicating a northward expansion of this species. The proportion of invertebrate species has changed in some zones and mysids now constitute a large proportion of the murre diet in the low and mid Arctic where hyperid and gammarid amphipods used to be the main invertebrate consumed. The birds can be used as samplers of the marine environment, and as integrators of the environmental changes that are occurring, but prey were not the only items found in the stomachs on birds sampled. Marine plastic debris was also found in the stomach contents of both murres and fulmars from every colony sampled indicating plastic ingestion is becoming a widespread problem for Arctic seabirds. Plastics found in northern fulmars indicate that marine plastic debris is increasing in the Arctic Archipelago, and monitoring of this recognized indicator species of plastic debris will allow long term monitoring of man-made debris in Canada’s north. Plastic debris was also found in thick-billed murres from all of the colonies sampled. Although murres are not useful indicators of general marine plastic debris the presence of plastics at all the colonies sampled indicate that plastics are not just a problem for surface feeding seabirds, but a threat to a number of species found in Canadian waters.

Graduation date: 1992

Thesis (Ph. D.)--Dept. of Botany, University of Adelaide, 1991. / Typescript (Photocopy). Includes bibliographical references (leaves 166-189).

Thesis (Ph.D.)--University of Western Australia, 2006.

Food webs are structured by intricate nodes of species interactions which govern the flow of organic matter in natural systems. Despite being long recognized as a key component in ecology, estimation of food web functioning is still challenging due to the difficulty in accurately measuring species interactions within a food web. Novel tracing methods that estimate species diet uptake and trophic position are therefore needed for assessing food web dynamics. The focus of this thesis is the use of compound specific nitrogen and carbon stable isotopes and molecular techniques for assessing predator-prey interactions and energy flow in natural aquatic ecosystems, with a particular focus on the species links between phytoplankton and zooplankton. The use of δ15N amino acid values to predict organism trophic position are evaluated through a meta-analysis of available literature which included measurements from 359 marine species (article I). Through a controlled feeding study isotope incorporation in aquatic organisms, across both plant-animal and animal-animal species linkages is further assessed (article II). These studies showed that δ15N amino acid values are useful tools for categorizing animal trophic position. Organism feeding ecology influenced nitrogen trophic discrimination (difference in isotope ratio between consumer and diet), with higher discrimination in herbivores compared to omnivores and carnivores (article I). Nitrogen isotope trophic discrimination also varied among feeding treatments in the laboratory study (article II). The combined findings from articles I &amp; II suggest that researchers should consider using group specific nitrogen trophic discrimination values to improve accuracy in species trophic position predictions.  Another key finding in the controlled laboratory study (article II) was consistently low carbon isotope discrimination in essential amino acids across all species linkages, confirming that these compounds are reliable dietary tracers. The δ13C ratios of essential amino acids were applied to study seasonal dynamics in zooplankton resource use in the Baltic Sea (article III). Data from this study indicated that zooplankton assimilate variable resources throughout the growing season. Molecular diet analysis (article IV) showed that marine copepod and cladoceran species ingested both autotrophic and heterotrophic resources. Evidence from both articles III &amp; IV also revealed that zooplankton feed on a relatively broad range of diet items but not opportunistically on all available food sources. Mesozooplankton feeding patterns suggested that energy and nutritional flows were channelled through an omnivorous zooplankton food web including microzooplankton prey items. Overall the results of this thesis highlight that stable isotope ratios in specific compounds and molecular techniques are useful tracing approaches that improve our understanding of food web functioning. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript.</p><p> </p>