Estimation of algal standing stock and growth parameters usin in vivo fluorescence

Abstract

This paper is addressed to the following questions: 'How accurately does in vivo chlorophyll fluorescence of samples treated with Diuron (DCMU), notated F_M estimate autotrophic standing stock?' and 'How accurately does the Diuron response, ΔF (= F_M - F_V), estimate primary production?'. Data are drawn from several cruises in the western Tasman Sea, ranging between latitudes 25ºS. and 53ºS. The prediction of chlorophyll (µg chl u I^-1) from F_M (standard chl a fluorescence units) is given by Chl= 2 × 10^-3 F_M. The standard error is about 6 × 10^-4 F_M so the 'true' value will usually be within ±60% of the estimated mean value. The production parameter, PA(µg Cl^-1), as measured by ¹⁴C uptake under saturating light conditions, may be predicted for the euphotic zone other than the surface layer by P_A = 3 × 10^-2ΔF. If mean ΔF values are used the 'true' value will usually lie within ±25% of the estimate. A strong diel effect was found in the parameter Φ( =ΔFF_M^-1), the 'photochemical quantum efficiency', an estimator of relative growth rate. The diel cycle has the form of a major midday minimum, a minor midnight minimum, and pre-dawn and post-sunset maxima. This cycle must be removed before comparisons of Φ of samples taken at different times can be made.