A new matrix factorization program 'CHEMTAX was used to ~nterpret high-performance hquid chromatography (HPLC) pigment data from a transect between Prydz Bay Antarct~ca and Australla dunng March 1987 The program calculated the abundance of diatoms dinoflagellates haptophytes resembling Emiliania huxleyl haptophytes resembling P h a e o c j~s t~s antarctlca cyanobacteria prasinophytes, chlorophytes and cryptophytes along the transect The results were compared with those of microscopy and particle size analysis The transect was dominated by small cells particle size analysis showed that particles < 2 pm represented 27 to 44 Oh of the total by number while particles 2 to 20 pm represented 55 to 68% Particles >20 pm never represented more than 3 % by number but constituted 57 to 93 % of the total v o l u n~e Microscop~c analysis showed that small flagellates were the most abundant cells along the transect wlth a 5-fold increase In abundance at 47"s Numbers of dlatoms (most <20 pm in size) Increased markedly south of the Polar Front, correlating with the concentration of silica D~noflagellate numbers were relatively constant along the transect although somewhat higher north of 5 0 " s Those <20 pm in size were most numerous and accounted for most of the latltudinal vanation Interpretation of HPLC pigment data using the CHEM TAX program was consistent with microscopical analysis The computed abundances of diatoms and dinoflagellates correlated more strongly with the numbers of small (<20 pm) dlatoms and d~noflagellates, respectively than with large ones Computed cyanobactenal abundances correlated well wlth microscopical observations except for small errors where cyanobactena were absent probably d u e to m~sallocation of zeaxanthln from chlorophvtes and praslnophytes The program was able to distinguish 2 populations of haptophytes along the transect representing Phdeocystis antarctlca and coccol~thophonds even though their pigment compositions were qualitatively (though not quantitatively) Identical It also indicated the separate distributions of chlorophytes and prasinoxarithin-containing praslnophytes, and showed the presence of cryptophytes where none were observed by microscopy

Numerous investigators have demonstrated marked interspecific differences in tolerance of Antarctic marine phytoplankton to UVB exposure. Consequent changes in species composition have been proposed but as yet not demonstrated. We conducted competition experiments in which mixed cultures of Antarctic marine diatoms and colonial and flagellate stages in the life cycle of the haptophyte Phaeocystis antarctica were exposed to natural Antarctic solar irradiance. Results demonstrated UVB-induced changes in species cornposltion favouring the colonial stage of P. antarct~ca following 2 d exposure or less. These data indicate the potential for altered trophodynamlcs and carbon flux in Antarctic waters as a result of ozone depletion. Our results also show the limited predictive value of results obtained using UVB exposures above those likely to be experienced in the natural environment.

No abstract

In H. reticulatum, gametes differed from other zooids principally in that some of them bore an electron·dense apical cap between their flagella. Conjugation did not take place until the walls of the coenobia, in which the gametes developed, ruptured; and often did not occur even among the liberated gametes. Only in zooids collected from cultures in which conjugation was evident were these apical caps extended as fertilization tubules. Fertilization took place by the fusion of the tip of this tubule on one gamete with the membrane between the flagella of another which apparently lacked a fertilization tubule. Subsequent lateral fusion of the united zooids produced quadriflagellate zygotes which were active for only a short time before flagellar retrac· tion and cell wall deposition. Karyogamy usually preceded wall secretion. Gametes failing to conjugate often laid down a wall to form azygotes.

[Manusoript reoeived 18 August 1971] Ab8tractVegetative zooids of H. reticulatum, produoed by cleavage of parental ooenobial oytoplasm, linked together within their parental oell walls to form oylindrioal nets oharaoteristio of this alga. A oonspiouous feature of net-forming zooids were bands of miorotubules underlying the plasmalemma. An active role is proposed for these miorotubules in the ordered linking of the zooids. Amorphous material, presumably adhesive, was seen only in interoellular spaces between aggregating zooids. Following adhesion of the zooids, eaoh one usually linking with four others, their flagella were retraoted and both flagellar miorotubules and basal bodies disintegrated. Centrioles arose de novo on the nuolear envelope of eaoh cell at the time of deposition of a bilayered wall.