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The General Annual Cycle of Chlorophyll Standing Crop in Loch Creran

Paul Tett and Andrew Wallis
Journal of Ecology
Vol. 66, No. 1 (Mar., 1978), pp. 227-239
DOI: 10.2307/2259190
Stable URL: http://www.jstor.org/stable/2259190
Page Count: 13
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The General Annual Cycle of Chlorophyll Standing Crop in Loch Creran
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Abstract

(1) This paper introduces an investigation of the factors controlling phytoplankton growth in Creran, a typical sea-loch on the west coast of Scotland. (2) The hydrography of the loch is summarized. Salinity, irradiance and photosynthesis profiles suggest that the lower limits of the reduced-salinity surface layer and of the euphotic zone can conveniently be taken to coincide at a depth of 8 m. (3) The general annual cycle of phytoplankton standing crop in the loch is shown by a combined plot of 908 chlorophyll a measurements made between 1970 and 1976 in the 1-8 m depth zone. Limits that theoretically include 95% of the data are superimposed on this plot, and show that a number of features recur regularly from year to year. (4) These recurring features are: a winter low (< 0.5 mg chl. m-3); a spring increase, with chlorophyll reaching 1 mg m-3 at some time between 17 February and 12 March, and attaining 12-37 mg chl. m-3 between 13 March and 11 April; a biomass of 1-7 mg chl. m-3 from June until mid-September; no definite autumn bloom; and a reduction of chlorophyll levels to below 1 mg m-3 by 26 November. (5) The importance of salinity layering in the control of the phytoplankton cycle is briefly discussed. The spring increase in Creran starts at about the same time as in other sea-lochs and fjords, and thus 1 or 2 months earlier than in similar seas where the stability of the water column is controlled by temperature. (6) The theoretical basis of the 95% limits superimposed on the data plot is discussed in an Appendix. It is suggested that these limits can be used predictively.

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