Studies on the nanophytoplankton of the Firth of Clyde

Hannah, Fiona Jackson (1979) Studies on the nanophytoplankton of the Firth of Clyde. PhD thesis, University of Glasgow.

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Abstract

The significance of the nanophytoplankton in the Firth of Clyde was assessed during the period January 1976 to May 1978 by estimating its contribution to the total chlorophyll and productivity of the area. Its significance both temporally and spatially were investigated. The nanophytoplankton in the Firth of Clyde is made up predominantly of small flagellates of maximum cell dimension less than 10 mum, many being in the size range 2-5 mum. It includes organisms from most algal classes with the exception that the Diatomaceae is poorly represented. One to two cell chains of Skeletonema costatum are included in this group and also small single cells of a Chaetoceros spp, which were occasionally observed. Weekly (followed by fortnightly) samples were collected from a midchannel station in the Fairlie Channel to assess the seasonal significance of the nanophytoplankton. Nutrient analyses, particle size distributions and microscopic examination of the samples were carried out as well as chlorophyll and productivity determinations. To assess how representative the chosen sampling station was of the Fairlie Channel as a whole, several grid surveys were carried out in which the chlorophyll levels from 16 stations covering an area of 0.75 km2 were compared. Although on three out of six occasions significant differences were observed between stations, these being mainly found when inshore stations were compared with those in midchannel, the main sampling station did not differ significantly from the other stations, and the results from this station reflected the seasonal changes which occurred in the Channel. The seasonal patterns of the total phytoplankton and nutrients in the Pairlie Chsinnel were similar to those observed in the past. In terms of total chlorophyll a and productivity, higher levels were recorded in 1976 than in 1977. The total chlorophyll a in 1976 reached values of above 10 mg m-3 during the spring diatom increase in April and also in July when the maximum fixation rate of 66.6 mg carbon m-3 h-1 was recorded. In 1977 maximum values of chlorophyll (7.8 mg m-3) and fixation (55.7 mg C m-3h-1) were observed during an autumnal bloom in September. While the contribution of the netplankton (predominantly diatoms) was high during bloom conditions in spring and summer, over an annual. cycle the nanophytoplankton in the upper 10 metres of the water column contributed at least 50% the activity. During 1976 and 1977 the average % contribution of the nanophytoplankton to the productivity was 50% and its contribution to the chlorophyll was 60%. Figures of up to 100% contribution of the nanophytoplankton to the biomass and productivity have been recorded. The nanophytoplankton formed a more stable component of the phytoplankton fluctuating in terms of chlorophyll and productivity less dramatically over the year than the netplankton. The relative importance of the two fractions of the phytoplankton showed a marked seasonality. The nanophytoplankton was highly significant during late autumn, winter and early spring forming the major part of the biomass at these times. Following the spring diatom increase, the phytoplankton was made up almost exclusively of nanophytoplankton in 1976, while in 1977 it was of slightly less significance. During summer the contribution of the nanophytoplankton to the biomass and productivity was approximately equal to that of the netplankton. Sampling was extended to other areas of the Firth to assess the spatial distribution of the nanophytoplankton and its significance. In the Inner Firth Area, the observed contribution of the nanophytoplankton to the total chlorophyll ranged from 20-98%. Higher netplankton values at stations situated near the estuary in comparison with those found lower down in the Firth were the main cause of variations in the total chlorophyll over the area since the nanophytoplankton varied- less dramatically. In Loch Long and the Gareloch, the nanophytoplankton contributed 11-62% of the chlorophyll and 13-77% of the productivity during a period of investigation in August 1976. In a separate study of two rockpools on Great Cumbrae Island, it was found that the nanophytoplankton was very productive in this type of extreme environment, producing high levels of fixation (maximum recorded rate of 189 mg C m-3h-1) in the early months of 1976 when production in the sea was at a minimum. In these pools, the average contribution of the nanophytoplankton was 83% to the total chlorophyll and 86% to the productivity. The significance of the nanophytoplankton in relation to the rest of the ecosystem in the Firth of Clyde is discussed.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: A D Boney
Keywords: Biological oceanography, Microbiology
Date of Award: 1979
Depositing User: Enlighten Team
Unique ID: glathesis:1979-73366
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56
URI: http://theses.gla.ac.uk/id/eprint/73366

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