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Adrian Marchetti - Ph.D. Candidate

Physiological aspects of Fe nutrition and toxin production by oceanic and coastal diatoms of the genus Pseudo-nitzschia

Outline of Proposed Research

    Iron concentrations within vast regions of our world’s oceans have been proven to limit the growth of primary producers.  Recent evidence has shown that iron fertilization in these areas has resulted in increased productivity and algal blooms (Martin et al. 1994 Nature 371; Coale et al. 1996 Nature 379; Boyd et al. 2000 Nature 407).  As phytoplankton transport a large amount of carbon to the ocean depths it has been suggested that large scale open ocean Fe fertilization could be a possible solution in combating a recent increase in atmospheric carbon dioxide.  Given the dramatic success of mesoscale Fe enrichment experiments in the Equatorial Pacific and the Southern Ocean, further Fe fertilization experiments are planned.  Alleviation of Fe stress in these Fe-limited communities results in a phytoplankton species composition shift where larger diatoms become dominant.  In particular, in the Northeast Pacific, the pennate diatom Pseudo-nitzschia spp. becomes the dominant group, comprising more than 80% of primary producer biomass (Boyd et al. 1996 MEPS 136).

Over the last decade, toxin monitoring programs have been established along the coasts of Canada and the United States. One toxin, domoic acid, produced by certain Pseudo-nitzschia spp. has been well studied since outbreaks have occurred both on the east and west coasts of North America.  A domoic acid monitoring program coordinated by Dr. Vera Trainer of the National Marine Fisheries Service (Seattle, Washington) has identified a potential “hotspot” for consistent and relatively high concentrations of domoic acid within the Tully Eddy off the mouth of the Juan de Fuca Strait.  In this respect, the Tully Eddy may produce a seed population of Pseudo-nitzschia spp. that may fuel blooms of this diatom and domoic acid production along the west coast of Vancouver Island and Washington State (Vera Trainer, pers. comm.).   By studying coastal areas prone to high concentrations of domoic acid, we may ascertain the conditions that promote the production of this toxin.


Objectives: The aims of my research are to: 

a)      gain an understanding of oceanic Pseudo-nitzschia spp. physiology and ecology given the implications of shifting the phytoplankton community to these pennate diatoms during large-scale iron fertilization experiments in the North Pacific

b)      determine adaptations made by oceanic Pseudo-nitzschia species dealing with Fe limitation by comparing them with their coastal counterparts

c)      provide information for a model to forecast coastal bloom events of Pseudo-nitzschia spp. and verify conditions that facilitate the production of domoic acid in the field, as well as determine possible roles that this toxin may serve.


Methods:  My research is divided into field and laboratory studies.  At the present time I have participated on four cruises to Ocean Station Papa (OSP), a well-studied iron limited region of the subarctic NE Pacific.  I have conducted experiments examining the effects of iron addition on these phytoplankton communities and I am investigating the possible production of toxins by these oceanic Pseudo-nitzschia variants as well a role that domoic acid may serve.  I have also begun a coastal time series transect of an area prone to high domoic acid concentrations located in the Tully Eddy.  Laboratory studies include the culturing of Pseudo-nitzschia spp. from Ocean Station Papa and the Tully Eddy.  Biochemical parameters, physiological characteristics and production of domoic acid will be determined and compared between coastal and oceanic isolates for both Fe replete and Fe limited conditions.


Significance:  In July of 2002, a large-scale Fe fertilization experiment (part of the Canadian SOLAS project) will take place at OSP.  The intent of my research is to assist in the understanding and possible ramifications of these large-scale Fe fertilization projects by focusing on the ecophysiology of the induced dominant member of the phytoplankton community, Pseudo-nitzschia spp. 

Outbreaks of domoic acid have resulted in millions of dollars in marine harvest losses (eg. Razor clams) as well as mortalities of marine mammals, birds and even humans.  By studying physical and biological parameters of regions associated with high levels of this toxin, a better understanding of what conditions facilitate domoic acid production may be achieved.