Field Work
We recently finished a project funded by Maryland Sea Grant to look at Pseudo-nitzschia abundance and toxicity in the Chesapeake Bay and its tributaries. So far I have identified six species of Pseudo-nitzschia in Maryland and Virginia waters using TEM.
Pseudo-nitzschia fraudulenta found in samples from the Choptank River, a tributary of the Chesapeake Bay. The scale bars in the top two photos are 1 micron while the scale bar in the bottom photo is 5 microns.
Pseudo-nitzschia calliantha found in samples from the mesohaline and lower Chesapeake Bay. The scale bars in the top two photos are 1 micron while the scale bar in the bottom photo is 5 microns.
Pseudo-nitzschia multiseries isolated from the Choptank River in 2002. The scale bars in the top two photos are 1 micron while the scale bar in the bottom photo is 5 microns.
I also found P. subpacifica, P. pungens and P. cuspidata.
Toxin samples were collected by filtering 300 mL of water through a Whatman GF/F. Both the filter and the filtrate were stored at -80C until analysis by either HPLC, ELISA, receptor binding assay or mass spectrometry. The particulate domoic acid represents toxin inside the cell and collected on the filter. The dissolved domoic acid represents toxin released from the cell and present in the filtrate. Note the April 2004 sample from the Pocomoke River. There is no domoic acid inside the cells, but toxin was detected in the water. This raises questions concerning how long domoic acid can linger in the water column after a bloom. Recent research shows that domoic acid is primarily degraded by light (Bouillon et al. 2006, Bates et al. 2004). How long could domoic acid remain in the water after a bloom in the turbid environment of the Chesapeake Bay?
Below are two maps showing the location of high Pseudo-nitzschia abundances (left) and maximum domoic acid concentrations (right) in samples collected from 2002 to 2007. Note that there are far more locations that have Pseudo-nitzschia present than there are detectable domoic acid. This suggests that not all Pseudo-nitzschia in the Chesapeake produced domoic acid. Abundances were highest from winter to spring with thousands of cells/mL. DA was detected in 42% of samles tested, but concentrations were generally low ranging from 0 to 1037 pg DA/mL (average 176 pg DA/mL).
To the right is a similar map showing the maximum cell quota of DA in field samples. This was calculated by dividing the total amount of DA found in a sample by the concentration of Pseudo-nitzschia cells in the same sample and is a measure of how much DA is present per cell. This value can be very important since not all species of Pseudo-nitzschia produce the same amount of toxin. The DA cell quota ranged from <0.1 to 49.4 pg DA/cell (average 1.4 pg DA/cell).
There is also a relationship between Pseudo-nitzschia abundances and the environmental factors of temperature and salinity. To the left is a table of statistical results called a Spearman's correlation coefficient or rho (looks like a lower case P). The rho value describes how two parameters are correlated by describing the direction of the correlation (a negative value indicates that as one parameter increases the other decreases while a positive value indicates that both parameters increase or decrease with each other) and the strength of the correlation (values closer to 1 indicate a stronger relationship). In this case the two parameters are Pseudo-nitzschia abundance and temperature (first columns) and Pseudo-nitzschia abundance and salinity (second columns). The p value indicates if the correlation is significant. A p value greater than 0.05 means that there is no correlation and the rho value is meaningless. For example, looking at the table above we see that in winter the p value for salinity is 0.0000. That means Pseudo-nitzschia abundance and salinity are correlated in winter. The rho value is 0.4108. The number is positive which means as salinity increases so does Pseudo-nitzschia abundance. The actual number 0.4108 is close to halfway between 0 and 1 which indicates a medium strength correlation. In contrast, the p value for temperature and abundance in winter is 0.9554, which is greater than 0.05 and indicates no correlation between these parameters during winter months.
Below is an animated map showing Pseudo-nitzschia abundances (cells/L) in the Chesapeake Bay by month and year. Data for the map was collected from the Maryland Department of Natural Resources phytoplankton monitoring program and can be accessed at www.chesapeakebay.net. If you would like to restart the animation, refresh the page.
