Ej. Carpenter et al., THE DINOFLAGELLATE DINOPHYSIS-NORVEGICA - BIOLOGICAL AND ECOLOGICAL OBSERVATIONS IN THE BALTIC SEA, European journal of phycology, 30(1), 1995, pp. 1-9
Observations of the dinoflagellate Dinophysis norvegica in the Baltic
Sea during the summers of 1991-1993 indicate that maximal abundances (
c.40-150 x 10(3) cells l-1) were found at the thermocline, typically a
t 12-degrees-C. Maximum densities were usually between 12 and 15 m whe
re 2.9% and 1.5% of surface photon irradiances, respectively, were mea
sured. No diel vertical migration was observed, and cell densities in
the mixed layer were always low. Photosynthesis versus irradiance meas
urements with an oxygen electrode indicated that these populations had
a P(max) of 2.47 [coefficient of variation (CV) 7.3%] and 3.4 (CV 4.7
%) mg O2 mg Chl a-1 h-1, and compensation values of photon irradiance
were 16.5 and 83 mumol m-2 s-1 in 1992 and 1993, respectively. Both ox
ygen electrode and C-14 light/dark bottle measurements indicated that
D. norvegica had very little net photosynthesis at the depths where it
was most abundant; it would have had about 2.5-fold greater capacity
at photon irradiances present closer to the surface. Calculated carbon
doubling times via photosynthesis averaged 4-11 months. There was no
observable diel rhythm of DNA synthesis, suggesting that either D. nor
vegica was not dividing synchronously (asynchronous division is common
in heterotrophs) or not dividing at all. Electron microscopy did not
reveal the presence of food vacuoles, but feeding and digestion could
have been extracellular. The data suggest that this species is a mixot
roph which received its primary nutrition via heterotrophic means duri
ng our observation periods in the summers of 1991-1993.