Date of Award

8-1980

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

Supervisor

Dr. G. P. Harris

Abstract

Daily measurements were taken during the summer of 1979 in Hamilton Harbour; a eutrophic, physically variable bay situated at the western end of Lake Ontario, to determine the impact of environmental fluctuations on the rates of primary production and growth, species succession and community diversity in the resident phytoplankton community. Nutrient loadings (P, N and C) were high and did not limit algal productivity and growth during the study period. Spatial and temporal heterogeneity was evident in the thermal structure, dissolved oxygen and nutrient distributions. Zm, the mixing depth and N², the water column stability were subject to physically induced, short term (<24 h) fluctuations and strong periodic motions in the range of days or weeks. The underwater light field was subject to random, short term oscillations. Zeu and ЄPAR were stable over short temporal scales, following fluctuations in algal biomass. The phytoplankton were strongly self-shaded (average Єs = 0.0108 in units m² mg chlorophyll aˉ¹) and self-shading increased as Cp; the chlorophyll package size decreased. Fluctuations in Zm were thus, the key environmental factor exerting stress on the phytoplankton, as the algae themselves controlled their own light climate.

Daily variability in the Zue/Zm ratio, strongly influenced by fluctuations in Zm, and water column stability; M² (secˉ²) accounted for the low and variable rates of ΣP and max Pv. In situ Pmax, Pe and Ik values were also low and variable and accounted for the low rates of ΣP and max Pv. The phytoplankton responded to the temporal spectrum of environmental change via a hierarchy of response mechanisms, from physiological regulation to true adaptation. In vivo fluoresecence (IVF, F + DCMU, F ratios and R values) was variable and represented rapid regulation (<24 h) to short term fluctuations in the light field and water column stability. F ratios and R values were low under conditions of water column stability (high N² and Zeu/Zm) and high under conditions of vertical mixing (low N² and Zeu/Zm). The cellular generation time represented a fundamental period integrating cellular adaptation with environmental change. Pmax varied with depth and time and responded positively to increases in the value of the Zeu/Zm ratio with a 5.0 - 6.0 day lag period. Pe was positively correlated with Pmax, negatively correlated with Ik and high Pe values lagged low Zeu/Zm ratios by 6.0 - 7.0 days. Ik responded to fluctuations in ΣIo over the previous two days and its extreme daily variability obscured its temperature dependence during the study.

The eight dominant algal species responded to water column stability: N², with lag periods of one or more generation times (2.0 - 8.0 days). Coelastrum spp., Oocystis borgeii, Scenedesmus sp. and Chlamydomonas sp. responded positively to increasing thermal stability, while Rhodomonas sp, Cryptomonas spp., Stephanodiscus spp. and Cyclotella sp. responded negatively. Species exhibiting the same lag period and the same response in terms of changes in numerical abundance to fluctuations in N², avoided competition by utilizing different scaling strategies. The phytoplankton exploited the nature of environmental fluctuations as a resource permitting the coexistance of species and enhancing community diversity in a physically variable environment.

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