Photosynthetic characteristics of Dinophysis norvegica Claparede & Lachmann, a red-tide dinoflagellate

Abstract

The relationships between photosynthesis and photosynthetic photon flux densities (PPFD, P-f) were studied during a red-tide of Dinophysis norvegica (July-August 1990) in Bedford Basin. Dinophysis norvegica, together with other dinoflagellates such as Conyaulax digitate, Ceratium tripos, contributed ~50% of the phytoplankton biomass that attained a maximum of 16.7 jig Chla 1' and 11.93 x 10* total cells I1. The atomic ratios of carbon to nitrogen for D.norvegica ranged from 8.7 to 10.0. The photosynthetic characteristics of fractionated phyto- plankton (>30 jim) dominated by D.norvegica were similar to natural bloom assemblages: o (the initial slope of the P-l curves) ranged between 0.013 and 0.047 |ig C (u,g Chla)1 h1 (p.mol m'2 s~')~'; the maximum photosynthetic rate, />Bm, between 0.66 and 1.85 jig C (ngChla)1 h1; /k (the photoadaptation index) from 14 to 69 u,mol m'2 s~'. Carbon uptake rates of the isolated cells of D.norvegica (at 780 pimol m~2 s') ranged from 16 to 25 pg C celP1 h1 and were lower than those for C.tripos, G.digitate and some other dinoflagellates. The variation in carbon uptake rates of isolated cells of D.norvegica corresponded with PBm of the red-tide phytoplankton assemblages in the P-l experiments. Our study showed that D.norvegica, a toxigenic dinoflagellate, was the main contributor to the primary production in the bloom.