The goals of the NUTOX project are: (1) to clarify if the present dominance of non-siliceous harmful algal species is due to the high NP to Si- ratios found in European coastal waters (2) to understand how the ratios between N and P affect toxin production in some of the most harmful phytoplankton species found in European waters.
Occurrence of toxic blooms in coastal waters is related to abiotic and biotic factors that controls the structure and the growth of the phytoplankton community. One of the major abiotic factors controlling phytoplankton growth is nutrient availability with respect to concentrations and ratios. Thus, to assess the capability of potentially toxic species to bloom in coastal waters, attention will be focused on factors leading to (i) their dominance in the phytoplankton communities, and (ii) to their toxin production. Nutrient ratios influence not only algal succession in natural communities but also the production of toxin by certain phytoplankton species. However, the influence depends on which type of nutrient is limitant or deficient relative to others for the algal need. In most European marine waters the ratios between nitrogen (N) and phosphorus (P) in relation to silica (Si) have increased dùe to the high input from N and P from human activities. At the same time toxic algal blooms of non-silica requiring species, such as prymnesiophytes, dinoflagellates and blue-green algae have increased.
We will investigate if there is a connection between high NP:Si-ratios and selection towards toxic species by exposing the natural phytoplankton communities contained in mesocosms to a gradient of N:P:Si ratios (in the inflowing medium). In this way we will be able to see if a specific toxic species will outcompete the diatoms. In these experiments we will use a combination of new standardized and advanced methods. In an attempt to couple the nutrient cell status to toxicity, the cell toxin content will be determined by HPLC after cell-sorting a few thousands of the desired cells with the help of a flow cytometer. This will be the first time that the nuclear microprobe will be used for the study of the elemental composition of a single phytoplankton cell growing among thousands of other species in nature. These 2 experimental approaches have never been applied yet in phytoplankton ecology in order to get information on the connection between intracellullar nutrient composition and toxin production in toxic phytoplankton species occurring in nature.
The regulation of toxin production is not only due to genetical inheritance but also due to the cellular chemical composition (the latter being regulated by the medium the algae is growing in). The effect of N:P ratios on the cellular chemical composition and toxin production will be compared in different toxic species.
These species will be exposed to different N:P-ratios in semi-continuous cultures and a detailed measuring programme will be conducted using new advanced (as above) and standardized methods. The toxic species to be used will be isolated from northern (Skagerrak and Baltic) and southern (Atlantic) European waters .
In this way, NUTOX will bring clarification if the same species occurring in such different habitats have the same physiological behaviour. The targeted species will be chosen from dinoflagellates, prymnesiophytes and blue-green algae (cyanobacteria) groups. To check genetical inheritance vs N/P effect on toxin production, studies will be done with the PSP-toxin producer A tamasense isolated from different sites in the Skagerrak
and the southern Atlantic coast. Using the same approach (different N:P-ratios in semicontinuous cultures) our studies will focus on inducible genes expression related to toxin production.
A series of culture experiments in order to study the possibility of recovery from a high toxin production to a low one will be performed. This will be done by switching from toxin stimulating to an inhibiting medium. (switching of the N/P ratios).
The results obtained in NUTOX will allow identification of some key mechanisms leading to a toxic phytoplankton bloom and a high level of toxin production. On this basis a guideline for the European Community management policy in order to minimize toxin production and toxic blooms in sensitive areas can be suggested.
Funding SchemeCSC - Cost-sharing contracts