Notes: Abstract Iron-stress-mediated effects on biochemical constituents of the red tide dinoflagellateGymnodinium sanguineum Hirasaka were examined in 1988 by comparing Fe-replete and Fe-deplete batch cultures. The influence of nitrogen source (NO3 or NH4) on characteristics of Fe-deplete cells was also studied [i.e., Fe-deplete/NO3-grown (= — Fe/NO3) vs Fe-deplete/NH4-grown (= — Fe/NH4)]. Common to both N sources were reductions of chlorophylla (chla) and Fe quotas (per cell volume) by 75% and ca. 1.5 orders of magnitude, respectively, under Fe depletion. The Fe requirement ofG. sanguineum exceeded those of certain neritic diatoms by one to two orders of magnitude. — Fe/NH4 cells exhibited 30 to 50% greater N quotas and free amino acid:protein ratios than did Fe-deplete cells grown on NO3. In vivo fluorescence:chla increased with Fe deficiency particularly in — Fe/NO3 cultures, surpassing — Fe/NH4 values by ca. two-fold. Effects of Fe depletion were consistent with this element's essential role in the biosynthesis of chla and components of the photosynthetic electron transport (PET) system, and also in NO3 utilization. Fe:N ratios were larger (1.5-fold) for iron-deficient NO3-grown than NH4-grown cells, likely reflecting the Fe content of NO3 assimilatory enzymes [nitrate (NR) and nitrite (NiR) reductase] and of electron transport components needed to provide reductant, coupled with a diminished capacity of — Fe/NO3 cells to acquire and assimilate nitrogen. Indicators of PET efficiency suggested that under iron stress, supply of Fe for NR and NiR is partly at the expense of iron-containing PET components. Utilization of nitrate by NO3-grown cells was inhibited sufficiently by Fe depletion to yield symptoms bordering on N deficiency. In an ecological context, the most important effect mediated by nitrogen source may be the determination of critical QFe (i.e., Fe required to just sustain maximal growth), thereby regulating the degree of growth limitation for a given subsaturating iron concentration.

Notes: Abstract Twenty-eight strains of toxic dinoflagellates in the genusAlexandrium from the northeastern United States and Canada were characterized on the basis of morphology, bioluminescence capacity, mating compatibility, and toxin composition. The distributions of these characters were evaluated in the context of regional patterns of paralytic shellfish poisoning (PSP) and coastal hydrography. Two morphospecies were identified-A. tamarense Lebour andA. fundyense Balech. The two are interspersed geographically though there are areas, such as the Gulf of Maine, where apparently onlyA. fundyense occurs. Southern waters (Cape Cod, Connecticut, and Long Island) have especially diverse populations. The two species are sexually compatible. Virtually all northern isolates are bioluminescent, whereas southern isolates include bioluminescent and non-bioluminescent strains. Cluster analyses, based on high performance liquid chromatography (HPLC) determinations of the suite of toxins produced by each isolate, revealed two and perhaps three distinct groups. One is comprised almost exclusively of northern strains, and the other of southern strains. A Cape Cod cluster may be separable from the southern group. These analyses explain a previously reported north-to-south trend of decreasing toxicity, as the northern isolates produce greater proportions of the more potent toxins than do southern forms. The overall perspective is that the biogeography of toxicAlexandrium spp. in the study region is not that of a single, widespread, homogeneous population, but rather is comprised of several sub-populations, each with its own physiological characteristics and history. Two scenarios are considered with respect to this regional biogeography. The first invokes recent and continuing dispersal of isolates to the south from a center of origin in the north, followed by recombination and strong selection. The second holds that the northern and southern populations diverged from a common ancestor (vicariance), but now represent localized populations with little mixing of genotypes. Neither hypothesis can be completely refuted by the data presented here, though the weight of the evidence favors the latter. The correct scenario may be a combination of both, with recent and continuous speading occuring within the Gulf of Maine and perphaps the Gulf of St. Laerence, but with endemic localized populations persisting without genetic exchange in most southern locations. These data also indicate that although morphological criteria separate toxicAlexandrim isolates from the study region into two morphospecies, these assignments do not coincide with clusterings based on toxin composition or allozyme electrophoresis, and they are further violated by mating results. A revision of taxon designations to the varietal level could be justified.

Notes: Abstract Iron and nitrogen (NO3 and NH4) uptake by the red tide dinoflagellateGymnodinium sanguineum Hirasaka were studied in 1988 in Fe-replete and Fe-deplete batch cultures. Saturated rates of Fe transport (ϱ, mol l−1 cell vol h−1) for cultures grown on NO3 or NH4 were measured following resuspension in either N source (i.e., NO3 or NH4). Enhanced Fe uptake capacity developed under Fe stress, and was manifested in all experiments except in that involving a transition from NH4 to NO3 nutrition. Suppression appears to have resulted from a reduced ability of NH4-grown cultures to utilize nitrogen in the form of NO3, thereby causing cells to remain nutritionally stressed (with respect to N rather than Fe, however). Supporting evidence was provided by the complete initial inhibition of NO3 uptake when Fe-deplete, NH4-grown cells were given saturating iron additions. When NH4 was supplied continuously (i.e., no N source transition), NH4-grown cells showed the greatest iron-stressmediated enhancement (i.e., Fe-replete vs Fe-deplete) of Fe transport (2.5-fold) accompanied immediately by NH4 uptake. Our findings are considered in relation to the potential consequences for this dinoflagellate of reduced iron bioavailability and available nitrogen source.

Notes: Abstract A comparative investigation of the chemical composition of Thalassiosira antarctica var. antarctica vegetative and resting stages revealed C:N and C:chl a ratios to be lower in vegetative cells. These trends primarily reflect vegetative levels of C/cell below, and N/cell and chl a/cell levels above those of spores. There was a change in chemical composition with the initial formation of resting spores, and spores continued to modify their composition while maintained in a cyclic light/dark regime for about one and one half weeks. Most notable was a net increase in carbon and chlorophyll a per cell. Spores then subjected to darkness for over one week appeared to retain most of the carbon and chlorophyll a previously synthesized. These findings support the idea that resting spores enhance the survival capabilities of a species under adverse conditions.