maine.gif (9991 bytes)Component of ECOHAB-GOM

  PRELIMINARY RESEARCH RESULTS


This constitutes a preliminary scientific progress report for NOAA Grant No. NA66RG0495 to the University of Maine; Principal Investigators: D.W. Townsend, N.R. Pettigrew and A.C. Thomas  

Preliminary Report Prepared May 1999   

FOR RECENT PUBLICATION DESCRIBING 1998 RESULTS click here


Possible Factors Affecting Alexandrium Dynamics in the Northern Gulf of Maine
David W. Townsend, Neil R. Pettigrew and Andrew C. Thomas, University of Maine

Background
Our interest in studying Alexandrium in the offshore waters of the eastern and the western portions of the Gulf of Maine was stimulated by observations reported by Martin and White (1988) of consistently high abundances of Alexandrium within the Bay of Fundy. In one of the two years that they extended their sampling into the Gulf of Maine, Martin and White observed extremely high cell densities in a band of water roughly coincident with the location of the core of the well-mixed, cold and nutrient-rich Eastern Maine Coastal Current/Plume system (Townsend et al., 1987; Brooks and Townsend, 1989; Bisagni et al., 1995; Pettigrew et al., 1998; Figure 1 and Figure 2).

Another observation reported some time ago in this region of the Gulf lead us to suspect that the Eastern Maine Coastal Current/Plume system was intimately involved with the distribution of Alexandrium along the shoreline of Maine, New Hampshire and Massachusetts. This observation was the "sandwich" phenomenon, where it was noted that a stretch of the Maine coast between the western edge of Penobscot Bay and an area east of Mount Desert Island, Maine, seldom displayed Paralytic Shellfish Poisoning (Figure 3; Hurst and Yentsch, 1981; Yentsch et al., 1986; Shumway et al., 1988). If indeed, as suggested by Martin and White's (1989) results, Alexandrium distributions were highest in the offshore waters away from the immediate shoreline, then it would follow that the offshore-directed surface flow that is commonly observed in the "sandwich" region (Brooks and Townsend, 1989; Bisagni et al., 1995; Pettigrew et al., 1998) is likely tied in some way to processes that effectively exclude Alexandrium from affecting shellfish on these shores. As for why Alexandrium reaches such high cell densities offshore, we suspected nutrients were key, since these eastern Gulf of Maine waters have the highest surface concentrations of inorganic nutrients of any area of the Gulf of Maine region (Townsend et al., 1987).

Northern Gulf of Maine Component of ECOHAB-GOM
The specific objectives of the University of Maine component are to: (1) Investigate the physical oceanography, nutrient chemistry, and abundances and distributions of Alexandrium in the coastal and offshore waters of the northern Gulf of Maine and to identify the factors that regulate Alexandrium population dynamics. (2) Determine the linkages between the major Gulf-wide current systems, in particular the Eastern Maine Coastal Current (EMCC) and western Maine coastal waters, and between the Gulf of Maine and the Bay of Fundy with respect to freshwater, nutrients, and Alexandrium cells. (3) Identify environmental factors that result in the initiation of Alexandrium blooms in Gulf of Maine waters, and determine how those blooms are controlled with respect to their spatial and temporal distributions.

Data Collection
We conducted surveys of the coastal and offshore waters of the northern Gulf of Maine between New Hampshire and the outer Bay of Fundy during the summer 1998, collecting data from more than 200 stations on each of three cruises (June, July and August). CTD casts were made at all stations and water samples were collected for analyses of phytoplankton chlorophyll, inorganic nutrients and Alexandrium cell densities. An underwater PAR sensor was mounted on the CTD package. Quantitative counts of Alexandrium cells, based on epifluorescence microscopy and an immunological stain specific to Alexandrium, developed by Anderson's group at WHOI, are still underway as of this writing. Thus far we have completed our counts for near surface waters (2 m) for each of our three survey cruises (Figure 4, Figure 5 and Figure 6).

Discussion of Early Results
The distributions of Alexandrium on all three of our survey cruises displayed maximum cell densities in the offshore waters of the Gulf, and not immediately adjacent to the shoreline as one might initially expect, based on historical patterns of shellfish toxicity (see Maine Department of Marine Resources Shellfish Toxicity Reports). Highest cell densities were observed in two broad patches: one in the Bay of Fundy and another in the offshore waters south of Penobscot Bay. When examined against the satellite images of sea surface temperatures(Figures 7, Figure 8, Figure 9), we saw that highest cell densities were well correlated spatially with the cold surface waters that characterize the Eastern Maine Coastal Current/Plume system. We also noted that as the summer progressed the highest densities of Alexandrium appeared to receded toward the eastern portions of the Gulf and the Bay of Fundy; that is, highest cell densities were observed in August in the Bay of Fundy. Highest cell densities encountered thus far are on the order of 5,500 per liter in the near surface waters.

In addition to seeking a better understanding of the interconnectedness of the eastern and western Gulf of Maine waters with respect to transport pathways of Alexandrium, our group is most interested in understanding the possible environmental factors that allow bona fide blooms of Alexandrium to develop, especially blooms with cell densities as high as those reported by Martin and White (1988; >100,000 cells per liter). It has already been shown that species of Alexandrium, and most large dinoflagellates in general, have high light and high nutrient affinities (Epply and Thomas, 1969; Eppley et al., 1969). Thus we have begun to explore the possible relationships between Alexandrium cell densities and these two variables. One example of our initial analyses is given in Figure 10 for our June survey cruise (see data updates at:/ECOHAB/Data-Updates-Eastern-Maine.html). We computed a nondimensional parameter that presents the suitability of light and nutrient fields as they might relate to a phytoplankton population that requires high levels of each. Our approach was to take the ratio of the depth of the 10% surface illumination (based on our PAR profiles at daytime stations) to the depth of the 4 M nitrate concentration (based on a polynomial fit to each station profile). The result of this analysis for our June cruise, when we saw high abundances Alexandrium over broad areas of the offshore Gulf waters, is given as a surface contour plot (Figure 10). The dark areas in Figure 10 outside of the 0.5 contour line (e.g., with ratios <0.5) represent regions where the combined light and nutrient environments would be expected to be less than optimal for Alexandrium growth. The early light-nutrient model shows promise and generally explains the highest cell densities. The model will be developed further as we incorporate parameters for horizontal advection, and the seasonal changes in water column stratification and the ambient light levels.

We view these results as very encouraging but we do stress, however, that we have completed only the first of three field sampling seasons and that as such our results presented here are still somewhat preliminary. Nonetheless our confidence is growing that we are on the right track and that through continuing analyses of our extensive data sets and with two more field seasons before us we will begin to unravel some of the dynamics of Alexandrium populations in the Gulf of Maine.

Click here for data

Acknowledgements:
These data were collected with the assistance at sea by a number of people, many of whom are not listed here.  Laboratory analyses of nutrients, cell counts, and data reduction/plotting were, and continue to be, performed by Maura Thomas, Annette Brickley, Abby Deitz, Katherin Moffett and Keska Kemper.

Last Update: Tuesday, July 07, 2009

 

Bisagni, J. J., D. J. Gifford, and C. M. Ruhsam. 1995. The spatial and temporal distribution of the Maine Coastal Current during 1982. Cont. Shelf Res. 16:1-24.

Brooks, D. A., and D. W. Townsend. 1989. Variability of the coastal current and nutrient pathways in the eastem Gulf of Maine. J. Mar. Res. 47:303-321.

Eppley, R. W. and W. H. Thomas. 1969. Comparison of half-saturation constants for growth and nitrate uptake of marine phytoplankton. J. Phycol. 5:375-379.

Eppley, R. W., J. N. Rogers and J. J. McCarthy. 1969. Half-saturation constants for uptake of nitrate and ammonium by marine phytoplankton. Limnol. Oceanogr. 14:912-920.

Hurst, J. W. and C. M. Yentsch. 1981. Patterns of intoxication of shellfish in the Gulf of Maine coastal waters. Can. J. Fish. Aquat. Sci. 38:151-156.

MacIsaac, J. J., G. S. Grunseich, H. E. Glover and C. M. Yentsch. 1979. Light and nutrient limitation in Gonyaulax excavata: nitrogen and carbon trace results. In Toxic Dinoflagelate Blooms. Taylor and Seliger (eds), pgs. 107-110. Elsevier.

Martin, J.L. and A. White. 1988. Distribution and abundance of the toxic dinoflagellate Gonyaulax excavata in the Bay of Fundy. Can. J. Fish. Aquat. Sci. 45: 1968-1975.

Pettigrew, N. R., D. W. Townsend, H. Xue, J. P. Wallinga and P. Brickley. 1998. Observations of the Eastern Maine Coastal Current and its Offshore Extensions in 1994. J. Geophysical Res. 103 (C13):30,623-30,639.

Shumway, S. E., S. Sherman-Caswell and J. W. Hurst. 1988. Paralytic shellfish poisoning in Maine: montoring a monster. J. Shellfish Res. 7:643-652.

Townsend, D. W., J. P. Christensen, D. K. Stevenson, J. J. Graham, and S. B. Chenoweth. 1987. The importance of a plume of tidally-mixed water to the biological oceanography of the Gulf of Maine. J. Mar. Res. 45:515-529.

Yentsch, C.M., P.M. Holligan, W.M. Balch and A. Tvirbutas. 1986. Tidal stirring vs. stratification: Microalgal dynamics with special reference to cyst-forming, toxin-producing dinoflagellates. pp. 224-252. In: Bowman, M.J., C.M. Yentsch and W.T. Peterson (eds.) Tidal Mixing and Plankton Dynamics. Springer-Verlag, N.Y. 502 p.

(FIG_1)-Martin&White_Fig_with_legend.tif (148684 bytes)
Figure 1. Concentrations of Alexandrium in surface waters of the Bay of Fundy and eastern Maine. Note the highest concentrations (>106 L-1) in the outer Bay of Fundy and in a band roughly coincident with the core of the EMCC (from Martin and White, 1988).

(FIG-2)-Plume-Close-up.tif (40720 bytes)
Figure 2. AVHRR satellite image of sea surface temperature in eastern Maine in June 1999. Note the plume of cold water (darker shades) leaving the Maine coast between Mt. Desert Is. and Jonesport.

(FIG-3)Yentsch et al Fig.tif (227568 bytes)
Figure 3. From Yentsch et al., (1986). Plot of shellfish toxicity, in unts of g toxin per 100 grams tissue weight, for 1984. Notice the high toxicity levels in western Maine waters and in far eastern Maine and the void in toxin levels, the "sandwich" region, between Penobscot Bay and Mount Desert Island. Data from J. Hurst.

(FIG-4)June-Alex-B&W.gif (53932 bytes)
Figure 4. Cell densities (number of cells/liter) of Alexandrium sp. at 2m depth for the June 1998 survey cruise.

(FIG-5)July-Alex-B&W.gif (53295 bytes)
Figure 5. Cell densities (number of cells/liter) of Alexandrium sp. at 2m depth for the July 1998 survey cruise.

(FIG-6)August-Alex-B&W.gif (53167 bytes)
Figure 6.   Cell densities (number of cells/liter) of Alexandrium sp. at 2m depth for the August 1998 survey cruise.

FIG-7Junesat1.gif (182837 bytes)
Figure 7. AVHRR satellite image of sea surface temperature in the Gulf of Maine in June 1998 (Yearday 153).

FIG-8Julysat1.gif (176310 bytes)
Figure 8. AVHRR satellite image of sea surface temperature in the Gulf of Maine in July 1998 (Yearday 200).

FIG-9Aug-Satn12-98239-2237-2.gif (97990 bytes)
Figure 9. AVHRR satellite image of sea surface temperature in the Gulf of Maine in August 1998 (Yearday 239).


(FIG-10)Ratio-10%-June-B&W.gif (51800 bytes)
Figure 10. Areal contour plot of the ratio of the depth of the 10% light level to the depth of the 4 M nitrate concentration in the Gulf of Maine - Bay of Fundy region during June 1998.