Algal Effects on Littorella uniflora (L.) Ascherson in Scottish Lochs

Marrs, Susan J (1994) Algal Effects on Littorella uniflora (L.) Ascherson in Scottish Lochs. PhD thesis, University of Glasgow.

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Abstract

In order to investigate algal effects on submerged macrophytes, four lochs experiencing a range of algal loadings were studied over a two year period. Algal loading ranged from virtually no algal growth to extensive formation of filamentous algal mats and phytoplankton blooms During 1990 and 1991 SCUBA techniques were employed to regularly monitor the standing crop of aquatic macrophytes along the 1m isobath. In 1990 phytoplankton density was estimated by measuring phytoplankton chlorophyll a. In 1991 measurements of filamentous algal biomass and cover estimates of epiphytes on the leaves of Littorella uniflora (L.) Ascherson were also carried out. Detrended Correspondence Analysis (DCA) of the macrophyte communities in the four lochs showed the lochs were examples of one community type. A total of 15 species were recorded, of these, the following were present in each of the four lochs: Isoetes lacustris L.: Myriophyllum alterniflorum DC: Lobelia dortmanna L.: Littorella uniflora. Conditions in the four lochs ranged from acidic Loch Dee, to the oligotrophic mid-basin of Loch Lomond, through to mesotrophic/eutrophic Lake of Menteith and eutrophic Loch of Lowes. Morphological and some physiological attributes of Littorella field populations, measured over the two year period, were related to algal loading and measured abiotic parameters using stepwise linear multiple regression. Variation in morphology of Littorella, explained by the selected variables was generally low: this was attributed to a lack of morphological plasticity in this species. In contrast, physiological attributes, such as chlorophyll content and shoot nitrogen, had a far higher percentage variation that could be explained by the selected variables. The abiotic variables most commonly selected, to explain variations in Littorella attributes, were sediment organic content and exposure rating. Sites that were more exposed to wind/wave action tended to have fewer, smaller Littorella plants. Sites with a high sediment organic content tended to have a greater total macrophyte and Littorella biomass. Filamentous algal biomass was the most important variable that explained the variation in Littorella field measurements. Littorella plants under filamentous algal mats had a higher total leaf chlorophyll and nitrogen content and a lower chlorophyll a:b, indicating a possible shade response. In the presence of filamentous algal mats, Littorella also tended to have fewer leaves and a greater number of stolons per plant. In the absence of filamentous algal biomass data, phytoplankton chlorophyll a was more commonly selected to explain variation in Littorella field measurements. It is suggested that in situations where filamentous algae are present, but not quantified, the effects of phytoplankton on aquatic macrophytes may be overestimated. Epiphyte percentage cover was not selected to explain any of the variation in measured field attributes of Littorella. In a greenhouse experiment, Littorella showed a quadratic response to sediment organic content with maximal biomass accrual occurring at a sediment organic matter concentration of 75%. After six weeks under shade conditions in the greenhouse, Littorella plants were significantly smaller than unshaded controls. After the removal of shading Littorella plants grew rapidly, until 17 weeks after the removal of shading there was no significant difference in the biomass of previously shaded plants when compared with unshaded controls. In comparison with unshaded controls, plants that had been previously subjected to shading, tended to produce fewer shorter leaves and a greater number of new plants. Significant increases in the total chlorophyll concentration of leaves were observed 9 days after the application of shading. A decrease in chlorophyll a:b was only observed in experiments where shading was applied for between 3 and 6 weeks. Photosynthetic light response curves, measured using a gas phase oxygen electrode were determined in further greenhouse experiments. These data showed shade adapted Littorella to have a lower maximum photosynthetic rate and higher photosynthetic efficiency at low irradiances, when compared with unshaded controls. There were no differences between the dark respiration rates of shaded and unshaded Littorella. Shaded Littorella plants showed a higher A13C in comparison with unshaded controls, indicating a reduction in CAM at low irradiance. A model of population maintenance of Littorella in Scottish lochs is proposed. It is suggested that Littorella can withstand periods of algal shading by adapting physiologically with little or no loss in biomass, and the population is maintained by winter and spring growth. Loss of a population could occur under one of two sets of conditions: 1: Due to the seasonal presence of filamentous algal mats, the population becomes weakened by successive shading experiences and gradually declines. 2: The population may be able to be maintained under conditions of algal loading; however in the event of a catastrophic destruction of part or all of the population, recolonisation is not possible.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Kevin Murphy
Keywords: Ecology, Limnology, Microbiology
Date of Award: 1994
Depositing User: Enlighten Team
Unique ID: glathesis:1994-75808
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 18:08
Last Modified: 19 Nov 2019 18:08
URI: http://theses.gla.ac.uk/id/eprint/75808

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