C.5.2.5 Nutrient physiology (PIs: Cullen, Anderson)

Rationale: Our efforts to model and understand Alexandrium distributions in a layered coastal ecosystem require that we parameterize migration behavior and physiology as a function of nutrient availability, yet this can only be determined from laboratory experiments. Research will thus be conducted to characterize the interactions of nutrition and behavior in determining the growth and biochemical characteristics of Alexandrium (cf. Cullen 1985; MacIntyre et al 1997). Such data will be invaluable for the process studies where a number of species-specific diagnostic measurements are planned. Specific objectives include: a) Development and evaluation of diagnostics of nutrient limitation and growth rate, suitable for application in the field; and b) Elucidation of the effects of nutrition on migration behavior in GOM Alexandrium .

Approach: Isolates will be grown in batch and semi-continuous culture to characterize the effects of nutrition on physiological state and biochemical composition. The same analyses will be conducted on laboratory water columns (tanks) under a range of conditions (nutrient replete, N-stratified, N-depleted; see MacIntyre et al. 1997). Analyses will include measures of chemical composition (particulate C and N, carbohydrate, protein, lipid, photosynthetic pigments), photosynthesis (see Cullen et al 1992), chlorophyll fluorescence yield (Kroon et al 1993), and optical characteristics (scatter and absorption). Other "physiological indicators" of nutrient stress in Alexandrium may also be examined, but these are only under development in the Anderson laboratory at this time. These include markers for P and Fe limitation, and an indicator of the activity of cell surface phosphatases and amine oxidases involved in utilization of DOM.

Complementary research will explore the effects of cyst formation on nutrient dynamics. The work described above will be repeated, but with two compatible mating types. A single clone under nutrient-limiting conditions may have very different physiology than that same isolate grown in the presence of a compatible mating type. The results will allow the physiological markers of gamete formation and encystment to be identified. These experiments will use mixed cultures grown under the regimes described above (including tanks).

These laboratory studies will be conducted at Dalhousie University by Cullen, in collaboration with Anderson. Four years of experimental work are planned, though the research outlined above can be completed in three. The evaluation of new diagnostics (which will dramatically increase the level of physiological information we can extract from the field and process studies) justify another year of work. Some of the costs for this work will be borne by Cullen's NSERC-funded research program.