The purposes of this research have been to determine a) the basic physical causes of acoustic scattering from zooplanktonic organisms and b) necessary criteria for future acoustic studies involving these animals. In situ measurements at 102 kHz have been made of the scattering of sound from a volumetric distribution of a zooplanktonic organism, the euphausiid. Quantitative information was recorded on analog magnetic tape and subsequently converted to digital form for analysis. Based on simultaneous measurements of side and back scattering from euphausiids and on a mathematical model, four-fifths of the scattered sound is considered to be caused by the compressibility contrast between the animals and the sea water. The remaining one-fifth is attributed to density contrast. Acoustic energy distribution curves are characteristic of the number and size of the animals contained in the small volume of the ocean that was studied. Acoustic counting of the animals gave results that compared favourably with simultaneous controlled net sampling. The back scattering cross-section of a typical euphausiid at 102 kHz has been found to be 1.4 x 10⁻⁴ cm² . Based on this value it is possible to predict the optimum frequency and intensity of incident sound for future acoustic studies involving these animals. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The concentration of RNA (Schneider procedure, 1945) and the dry weight of the developing stages of the brine shrimp Artemia salina were measured during the first 63 days of growth of the organism in the laboratory; RNA and the dry weight of starved stage V Calanus plumchrus were followed for 20 days. The same techniques were applied to the developmental stages of several species of zooplankton obtained during the course of one year from Saanich Inlet, Vancouver Island, B.C. The data collected from the laboratory and the field were used to test the validity of the RNA/Growth relationship proposed by Sutcliffe (1965) as a means to predict the rate of increase in dry weight (growth rate) of such organisms. Errors in the estimation of RNA occured. These resulted from chromogenic materials other than the pentose sugars ribose and desoxyribose being present in the hot PCA extracts of zooplanktonic organisms. Detection of the interfering chromogens was possible by examining the absorption spectra of the hot PCA extracts treated with orcinol between the wave-lengths 550 to 700 mμ. An attempt has been made to minimize such errors by calculating the amount of RNA from the difference in absorbance recorded at 670 mμ minus that at 615 mμ. Correlation of growth predicted from RNA values and the observed increase in dry weight of the organisms was greatest during their most rapid period of development. During other periods of development, RNA values were generally in excess of requirements for the observed increase in dry weight and may represent metabolic processes other than those associated with this increase. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Quantitative volume-scattering measurements were compared to the distribution of euphausiids in Saanich Inlet, British Columbia. Scattering was recorded at 42, 107, and 200 kHz from the depths of high euphausiid concentrations, and volume-scattering coefficients were determined. No scattering from euphausiids was recorded by a 11 kHz echo-sounder. Daily variations in the volume-scattering coefficients, m(Δz), generally compared well with variations in the concentration of euphausiids. The daily behaviour of the high-frequency scattering layer., and therefore m(Δz) and the concentration of euphausiids, was influenced by moonlight and weather conditions as well as the presence or absence of an oxycline in the inlet. In the absence of an oxycline conditions would have been closer to conditions in the open ocean. Under these circumstances euphausiid concentrations and m(Δz) were low in the mornings and gradually increased throughout the day; the high-frequency scattering layer consolidated. During the evening migration, the layer became more diffuse, and the number of euphausiids per cubic metre decreased. The scattering cross-section, σ (cm²), of a euphausiid was found to increase with the average dry weight and length, and with increased frequency. For each cruise σ was approximately one order of magnitude apart at the three frequencies. The values of σ (in cm²) ranged from 4.81 x 10⁻⁵ to 5.21 x 10⁻³(200 kHz), 5.49 x 10⁻⁶ to 3.99 x 10⁻⁴ (107 kHz), and 2.30 x 10⁻⁷ to 3.67 x 10⁻⁵ (42 kHz). / Science, Faculty of / Zoology, Department of / Graduate

In 1971, changes were observed in the overwintering population sizes of Calanus plumchrus Marukawa, Galanus marshallae Frost and Calanus pacificus californicus Brodsky in the Strait of Georgia, British Columbia. Calanus plumchrus and C. pacificus were less common than in previous years, while C. marshallae was more common. Based on scattered data taken since the turn of the century, these changes appeared to be abnormal. Because Calanus plumchrus constituted a significant proportion of the biomass of the zooplankton community, it was possible that the observed fluctuations were indicative of changes in the structure of the zooplankton community within the Strait. Thus a unique opportunity was presented to study a zooplankton community and Its relationship to environmental parameters. Multiple correlation analysis, cluster analysis, multiple regression analysis, factor analysis and principal components analysis were used to analyse zooplankton concentrations and hydrographic data taken in overwintering periods from I969 to 1974. Additional hydrographic data were used to examine relationships between physical and biological data three and six months out of phase. The multivariate techniques allowed an efficient analysis of the relationships within and between the biological and physical data banks. More than one multivariate method was used as each method gives a slightly different viewpoint on the data. A combination of methods thus produces a more complete picture of the system being analysed, while points of overlap between the techniques act as internal checks on the consistency of the analysis. The analysis indicates a recent shift in the hydrographic regime of the Strait of Georgia. The shift is most obvious in the salinity, but can also be seen in the temperature, and in both cases is strongest in Strait of Georgia deep water. It involves subtle changes in salinity and temperature structure. These changes axe of uncertain biological significance but indicate fluctuations in the process of deep water formation. Deep water is formed in the Southern Passages by the mixing of incoming Strait of Juan de Fuca intermediate and deep water with outflowing near surface fresher water. Changes in either of these components, or in the degree of mixing, may produce some changes in the quality of the deep water, which intrudes into the Strait of Georgia in late summer. These changes in quality appear to affect the zooplankton community. Individual zooplankton species are strongly influenced by temperature and stability characteristics or related factors. Temperature and stability during the fall intrusion are particularly important to the overwintering zooplankton community three months later. The same two factors in spring also affect zooplankton in the following winter. The concentrations of Calanus plumchrus and C. marshallae have significant (p<O.05) linear regressions with concurrent temperature at 350 m. The regression lines have opposite slopes and intersect in the region of normal ambient temperature at 350 m. This result suggests that deep water temperature, or a temperature associated, factor, strongly affects the relative fluctuations in the numbers of both species. Principal components and factor analysis of the hydrographic data both suggest that the most important factor in the structure of the water column is its subdivision into near surface, intermediate and deep water. However, in both temperature and salinity components a portion of the variance is associated with a temporal trend within the deep water. Principal components of the zooplankton similarly associate 15% of the zooplankton variance with a temporal trend. No species is strongly weighted on these components, and the association appears to be a function of the whole community, rather than of individual species. As an adjunct to this investigation, ecological separation between Calanus plumchrus and C. marshallae was investigated. Both species have similar distributions and life histories. Feeding competition between them is minimized by a separation in their ability to filter small particles from the water. Calanus plumchrus can feed readily on particles above 3>5 ym in diameter, while C. marshallae can not efficiently filter particles below about 10.5 ym in diameter. Thus, Calanus plumchrus can exploit a potentially rich food source with no competition from Calanus marshallae. This advantage may maintain Calanus plumchrus within the Strait of Georgia despite the detrimental effect of a shift in deep water temperature or related factors. It also suggests that, given a more "normal" physical climate, Calanus plumchrus could revert to its traditional dominance. If Calanus plumchrus continues to drop, or remains at suppressed levels, the economically important fish species that utilize it as food will have to shift prey species, probably to Calanus marshallae. Feeding on C. marshallae will involve a greater energy expenditure to obtain the same ration, and may be detrimental to some predators. / Science, Faculty of / Zoology, Department of / Graduate

The Knysna estuary system, on the south coast of South Africa, was sampled for zooplankton over period of one year. All species were recorded and an attempt was made at relating the distribution of populations to physical factors within the estuary. Over 50 species were identified. Pseudodiaptomus hessei, Acartia(Paracartia) longipatella and A.(Acartiella) natalensis were the dominant copepods in the upper estuary. Paracalanus spp. were dominant near the mouth. Zooplankton distribution was found to be related to tidal exchange. The zooplankton displayed a seasonal cycle of abundance, with maximum numbers occuring during summer. P. hessei displayed no pronounced seasonal cycle in abundance. Its abundance was strongly related to freshwater inflow. Seasonal succession was evident between A. natalensis, the summer dominant, and A. longipatella, the winter dominant. The controlling factors for this cyclical dominance were not clear. Diel vertical migration behaviour was shown to various degrees by virtually all zooplankton populations. The stimulus for this behaviour could not be definitely identified.

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