Euphausia pacifica lives for a period of approximately one year, disappearing from the catches at a size of about 22-24 mm. Spawning, which occurs mainly inshore, extends from June through December but generally is most prominent in the autumn months. Average growth is calculated to be approximately 2.0 mm per month or 0.06 mm per day, with growth appearing to be faster during adolescent stages and somewhat slower during the older stages. These growth rates are several times greater than previous estimates for E. pacifica. These studies were based on length measurements obtained from monthly vertical meter net collections from stations off Newport, Oregon over a four year period. / Graduation date: 1969

Graduation date: 1978

During 1960-61 the abundance and distributions of four species of euphausiids (Euphausia pacifica Hansen, Thysanoessa spinifera Holmes, Thysanoessa longipes Brandt and Thysanoessa raschii M. Sars) and the developmental stages of one species, E. pacifica were studied each month in relation to temperature and salinity in Indian Arm, British Columbia, using the method of T-S-P diagrams. Euphausia pacifica probably is a resident species and as such was the most tolerant towards environmental conditions and their fluctuations in Indian Arm, followed in order of decreasing tolerance by the expatriate species T. spinifera, T. longipes and T. raschii. All species, (whether resident or expatriates), were useful biological indicators of oceanographic changes in Indian Arm, particularly with reference to the detection of outside waters entering the inlet. Field data indicated that temperature and salinity may have been contributory "regulatory factors" with regard to the vertical distribution of euphausiids in Indian Arm, particularly in the region of maximum temperature and salinity change in the thermocline and halocline, between about 10 m and the surface. In contrast, the occurrences and distribution of euphausiids in intermediate-depth and deeper waters and the general absence of adult specimens of E. pacifica, T. spinifera and T. longipes from the deep waters, below 120 m, and of T. raschii from waters below 60 m have suggested that regulatory factors other than temperature and salinity were also operative. Nauplii and metanauplii of E. pacifica were markedly restricted in their distribution to deeper water when compared with the broad vertical distribution of eggs, later developmental stages (calyptopii, furcilia) and the adults of this species, a feature which may be similarly caused. In the laboratory, experiments were conducted in attempts to determine if the variations in euphausiid distributions found in the field resulted from different reactions of species to temperature, salinity and/or combinations of temperature-salinity, or to some other property or properties acting within particular temperature-salinity ranges. In the laboratory specimens were induced to migrate vertically in temperature which increased and salinity which decreased towards the surface. The numbers migrating decreased progressively with increase in the temperature and with decrease in the salinity. The strongest effects occurred when the rate of change of either property was the maximum obtainable and when temperature and salinity gradients were combined. These experiments indicated, also, that specimens would migrate into higher temperatures and lower salinities than usually obtained in the field (and this, despite the much steeper gradients employed in the laboratory). In a second series of experiments temperature and salinity conditions were kept constant, or nearly so, and specimens (of E. pacifica) were induced to migrate from water originating in one area ("home') into water from another area ("foreign"). In general, specimens showed a preference towards the properties of "home" water and would "avoid" the "foreign" waters. In survival experiments specimens survived in larger numbers and for longer periods in "home" waters than in "foreign" waters or in mixtures of the two. There were indications of a seasonal fluctuation in survival of specimens. On the basis of the findings from the field and laboratory investigations, it is postulated that properties unique to different waters, and the reaction of euphausiids towards these "unique properties", were important in the occurrences and distribution of euphausiids in Indian Arm and their migration and survival in the laboratory. / Science, Faculty of / Zoology, Department of / Graduate

The feeding biology of three euphausiid species, Euphausia vallentini (adults and juveniles), E. longirostris and Nematoscelis megalops was investigated during austral autumn (April/May) of 1998 and 1999, in the vicinity of the Prince Edward Islands (Southern Ocean). Data on the abundance and biomass of these species, estimated from bongo net tows, were investigated. Trophic position was assessed using gut contents and stable nitrogen isotope measurements. Feeding rate and daily carbon ration were estimated using the gut fluorescence and the gut fullness techniques. Vertical migrations into the surface waters at night were found to be strong for Euphausia vallentini adults and juveniles. Associated with these migrations were clear diel feeding patterns. Insufficient data during daylight hours for E. longirostris made it impossible to determine diel feeding patterns, but high feeding activity did occur during dark hours. Nematoscelis megalops did not show any distinct diel feeding pattern, but slightly higher gut fullness indices in the late afternoon suggested that feeding activity may have been highest during this period. For both Euphausia spp. high gut pigment levels were recorded in 1999, which corresponded to higher ambient chlorophyll a concentrations for that year. Highest initial gut pigment levels and highest ingestion rates were found for Euphausia longirostris in both years and lowest values were observed for N. megalops. High phytoplankton and low metazoan contributions to the diet of Euphausia vallentini juveniles, as shown in the gut content analysis, and low stable nitrogen isotope ratios (ð¹⁵N = 1.39±0.31), both indicated that this group was principally herbivorous. The results of gut content analysis of the adults of E. vallentini were similar to those of the juveniles, however, stable nitrogen isotope results showed that there was a higher degree of omnivory (ð¹⁵N = 3.81±0.66). Daily ration estimates from the gut fluorescence and fullness techniques showed that between 3.3 and 25.7 % of E. vallentini adults total daily carbon ration was derived from autotrophic sources. Although the contribution of carnivory to the diet was difficult to determine, the adults of this species may be considered omnivorous. Irrespective of the degree of carnivory, a dietry shift with an increase in size was evident for this species. Gut content analysis for Euphausia longirostris showed that this species consumed large amounts of both phytoplankton and metazoan prey and this was reflected in the stable nitrogen isotope results (ð¹⁵N = 6.88±0.60). These findings were supported by the results of the daily carbon ration estimates which showed that autotrophic carbon contributed between 6.9 and 20.3 % of the daily carbon consumption. The gut content analysis suggested that N. megalops was omnivorous, and the stable nitrogen isotope results place it in a trophic position equivalent to that of E. longirostris (ð¹⁵N = 6.83±0.78). Calculations from daily ration estimates suggested that only 3.1 % in 1998, and 3.2 % in 1999, of the carbon ingested was of autotrophic origin. This species may therefore be considered carnivorous. Implications of the findings of this study are discussed in terms of carbon cycling in the Southern Ocean.

Thesis (Ph. D.)--Oregon State University, 1966. / Typescript. Includes bibliographical references (leaves 82-85). Also available online.

The degree of biochemical variability is, in many cases, thought to be related to environmental stability. Intraspecific protein variation was examined in Euphausia pacifica using starch gel electrophoresis. Specimens were collected from eight oceanic and three neritic stations over a wide geographic area. The interspecific aspect of this study examined the general protein patterns of five species of North Pacific euphausiids. Temperature, salinity and oxygen were monitored, at the time of biological collections, in order to distinguish between water types. Two major protein patterns characterize E. pacifica from the different regions. The pattern possessing the greatest number of bands occurs in highest frequency in areas of greatest environmental instability (as characterized by temperature, salinity, and oxygen); the highest frequency occurrence of the pattern with the lowest number of bands is in environmentally stable regions. The expression of each pattern appears related to the degree of fluctuation of the physical parameters monitored, but these parameters are not suggested as the direct cause of which pattern is expressed. The physical parameters serve only as a tool for characterizing the stability of a region. Analysis of the electrophoretic protein patterns from five species of euphausiids, Euphausia pacifica, E. gibboides, Thysanoessa spinifera, T. inspinata and Nematoscelis difficilis, revealed that each species possesses a unique protein pattern. The interspecific and intergeneric similarities of protein patterns parallel the existing morphological taxonomy. / Science, Faculty of / Zoology, Department of / Graduate

The trophodynamics of the numerically dominant euphausiid species within a region of high mesoscale oceanographic variability in the southwest Indian sector of the Antarctic Polar Frontal Zone (PFZ) were investigated during the austral autumns April/May) of 2004 and 2005. During the 2004 survey, sub-surface (200 m) temperature profiles indicated that an intense frontal feature, formed by the convergence of the Sub-Antarctic Front (SAF) and the Antarctic Polar Front (APF) bisected the survey area into two distinct zones, the Sub- Antarctic Zone (SAZ) and the Antarctic Zone (AAZ). Total integrated chlorophyll-a (chl-a) biomass was typical for the region (< 25 mg chl-a m⁻²), and was dominated by picophytoplankton. Total euphausiid abundance and biomass ranged from 0.1 to 3.1 ind m⁻³ and 0.1 to 8.1 mg dwt m⁻³, respectively, and did not differ significantly between the stations occupied in the SAZ and AAZ (p > 0.05). The multivariate analysis identified two interacting mechanisms controlling the distribution patterns, abundance and biomass of the various euphausiid species, namely (1) diel changes in abundance and biomass, (2) and restricted distribution patterns associated with the different water masses. Ingestion rates were determined for five euphausiid species. E. triacantha was found to have the highest daily ingestion rate ranging from 1 226.1 to 6 029.1 ng pigm ind⁻¹d⁻¹, while the lowest daily ingestion rates were observed in the juvenile Thysanoessa species (6.4 to 943.0 ng pigm ind⁻¹ d⁻¹). The total grazing impact of the selected euphausiids ranged from < 0.1 to 20.1 μg pigm m⁻²d⁻¹, corresponding to < 0.15 % of the areal chl-a biomass. The daily ration estimates of autotrophic carbon for the euphausiids suggested that phytoplankton represented a minor component in their diets, with only the sub-adult E. vallentini consuming sufficient phytoplankton to meet their daily carbon requirements. A cyclonic cold-core eddy spawned from the region of the APF located in the southwest Indian sector of the PFZ was the dominant feature during the 2005 survey. The total areal chl-a biomass throughout the region was low, ranging between 5.6 and 11.4 mg chl-a m⁻², and was significantly higher within the core of the eddy compared to the surrounding waters (p < 0.05). RMT-8 and WP-2 total euphausiid abundance and biomass estimates were high, and ranged from 0.004 to 0.36 ind m⁻³ and 0.065 to 1.21 mg dwt m⁻³, and from 0.01 to 18.2 ind m⁻³ and 0.01 to 15.7 mg dwt m⁻³, respectively. A distinct spatial pattern in the euphausiid community was evident with the Antarctic species, Euphausia frigida, E. triacantha and E. superba predominating within the core of the eddy, while the PFZ waters were characterized by the sub-Antarctic species, E. longirostris, Stylocheiron maximum, Nematoscelis megalops and Thysanoessa gregaria. The eddy edge acted as a transition zone where species from both regions co-occurred. Within the survey area the combined ingestion rate of the six numerically dominant euphausiid species ranged between 0.02 and 5.31 μg pigm m⁻²d¹, which corresponded to a loss of between < 0.001 and 0.11 % of the available chl-a biomass. E. triacantha and juvenile T. macura were identified as the dominant grazers. There was no apparent spatial pattern in the grazing activity of the euphausiids within the region of investigation. The average daily rations of the euphausiids examined were < 2 % of their body carbon. The low daily ration of the euphausiids could be ascribed to the predominance of small picophytoplankton in the region of investigation, which are too small to be grazed efficiently by larger zooplankton. The marked spatial patterns in species composition and the elevated abundance and biomass of euphausiids, suggest that the mesoscale eddies contribute to the spatial and temporal heterogeneity of the planktonic community of the PFZ and may represent important foraging regions for many of the apex predators within the region.

Graduation date: 1969

Thesis (Ph.D.) - University of St Andrews, June 2007.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Biológicas, Programa de Pós-Graduação em Ecologia, Florianópolis, 2012 / Made available in DSpace on 2012-10-26T10:48:09Z (GMT). No. of bitstreams: 1 302488.pdf: 4210895 bytes, checksum: 728b1bedc7603ae02f4550f94e42d36b (MD5) / Eufausiáceos podem ter sua distribuição afetada por diversos fatores, como a temperatura, massas d'água e a presença de uma topografia abrupta, como quebras de plataformas continentais e cordilheiras submarinas. O Arquipélago de São Pedro e São Paulo (ASPSP) (0°55'00"N e 29°20'45"W) constitui os picos emersos de uma cadeia de montanha submarina com direção Leste-Oeste pertencente à Cordilheira Meso Atlântica. Este trabalho tem como objetivo descrever a composição e abundância de eufausiáceos do ASPSP, verificando se há variação nictemeral, temporal e em locais com diferentes distâncias e profundidades ao redor do arquipélago. Amostras de plâncton foram coletadas entre abril de 2003 e julho de 2005 em duas diferentes distâncias ao redor do ASPSP, dia e noite, totalizando 96 amostras. Arrastos horizontais superficiais foram realizados utilizando rede cônico-cilíndrica de 50 cm de diâmetro de boca e 200 ?m de malha, com fluxômetro acoplado. Foram identificados 11 espécies e 4 táxons, com destaque para Euphausia spp., Euphausia americana, Stylocheiron carinatum, Thysanopoda spp., T. aequalis e T. tricuspidata. A curva de acumulação de espécies estabilizou com 69 amostras, indicando que todas as espécies presentes em águas superficiais próximas ao ASPSP foram capturadas. Obteve-se média (± EP) da abundância total de 245,38 ± 50,66 ind. o 100 m-3, variando de 4,19 ± 2,09 ind. o 100 m-3 em janeiro de 2005 a 1.918,48 ± 993,78 ind. o 100 m-3 em novembro de 2004. Os resultados mostraram que a interação da migração vertical com a profundidade e a distância em relação ao ASPSP afeta a distribuição dos eufausiáceos e que a temperatura é o fator responsável pela variação temporal.