PRIMARY PRODUCTION AND PHOTOSYNTHETIC QUOTIENTS OF SEAWEEDS FROM SAO-PAULO STATE, BRAZIL

Primary production was measured under natural conditions for five comm on species of seaweeds from the coast of the State of Sao Paulo, Brazi l, using oxygen electrode and pH single-endpoint techniques. Productiv ity ranged from over 500 mu mol O-2 g dw(-1) h(-1) (about 6 mg C g dw( -1) h(-1)) for Ulva fasciata Delile (Chlorophyta), a sheet-like form, to 30 mu mol O-2 g dw(-1) h(-1) (about 0.36 mg C g dw(-1) h(-1)) in La urencia papillosa (C. Agardh) Greville (Rhodophyta), a coarsely-branch ed form. Intermediate productivities were measured in two other coarse ly-branched forms, Hypnea musciformis (Wulfen) Lamouroux (Rhodophyta) and Pterocladia capillacea (Gmelin) Bornet et Thuret (Rhodophyta) and in the thick-leathery species, Sargassum cymosum C. Agardh (Phaeophyta ). Specific growth rates measured in the field or in continuous-flow s eawater systems for commercially-valuable red algae range from 1% day( -1) in II capillacea to 14% day(-1) in H. musciformis. Primary product ion and growth rates are in agreement with the functional-form model o f Littler and Littler. Available biomass information showed that the m aximum standing stocks did not correspond to the growth potential dete rmined from measurements of primary productivity and growth rates, sug gesting that levels of standing stocks are determined more by physical factors (wave action) and biological interactions (grazing) than by i ntrinsic growth rate potentials. The measured ratios of net photosynth etic O-2 release to CO2 uptake (photosynthetic quotient, PQ), were con sistently less than the theoretically expected values of 1.0 to 1.3 (m ean measured values: 0.42 to 1.01). The PQ values did not vary accordi ng to taxonomic division or functional-form group and were unaffected by experimental nutrient (nitrate + phosphate) enrichment. The continu ed use of PQ = 1.00 is recommended to facilitate interconvertibility i n comparisons between studies of primary production by seaweeds.