Primary production of macrophytes: Terminology, approaches and a comparison of methods

The results of the activities, discussions and experimental work, of the Working Group on the Primary Productivity of Macrophytes in the course of the second GAP Workshop held in Haifa during 29 April-4 May, 1984 are presented. Concepts concerning some aspects of the primary production process and terminology associated with it are discussed, as well as their bearings on the approaches and methods for determining production and for the translation of short-term rates to long-term yields. A suggestion is made for a uniform usage of the presently inconsistently employed terms: primary production and primary productivity, for the process and the quality of the production, respectively. Specific growth rates, calculated from weekly weight determinations of cultured Gracilaria and Ceratophyllum prior to the workshop, were compared with growth rates calculated from photosynthetic- and respiration rates that were estimated during the workshop. These were obtained using O₂, ¹⁴C and ¹²C techniques simultaneously on the same plant samples, incubated in the same environmental conditions under which the plants had been cultivated. Possible suitability and limitations of the techniques which were used for estimation of the photosynthetic rates of the plants studied, under the conditions experienced, to predict actual growth rates are discussed.