Gulf of Maine ECOHAB - Ecology of Harmful Algal Blooms

Introduction:
Harmful algal blooms (HABs), are a serious economic and public health problem throughout the world. In the U.S., the most serious manifestation is paralytic shellfish poisoning (PSP), a syndrome caused by human ingestion of shellfish that accumulate toxins from dinoflagellates of the genus Alexandrium. These toxins cause human illnesses and death, shellfish quarantines, the mortality of birds, larval and adult fish, and even marine mammals (White et al. 1989; Geraci et al. 1989). Thousands of miles of U.S. coastline are affected. This reflects the persistence of the problem in some areas and its emergence in other areas historically free from outbreaks.
The economic impacts from PSP are significant. Shellfish quarantines, adverse health effects, and frightened consumers are direct impacts, but constrained development or investment decisions in aquaculture are examples of indirect, hidden costs. No national total is available, but estimates from individual events indicate the scale of the problem. For example, a single PSP outbreak cost Maine an estimated $6 million in 1980 (Shumway et al., 1988); such outbreaks occur annually in many states, and several have been more severe than the 1980 event. PSP on Georges Bank in 1988 closed the surf clam fishery which remains closed to this day - an estimated annual loss of $3 million (ECOHAB 1995). The expense of state-run PSP monitoring programs (typically $100-200,000 per year) should also be considered in an assessment of the total economic impact from PSP.

A key objective of ECOHAB-GOM is to understand the effects of physical processes on Alexandrium distributions at several scales, including the Gulf-wide scale, the regional scale, and the smallest scales in which localized blooms of cells develop or aggregate. Our (collective) observations and modeling will employ a nested approach, with overlapping grids of varying resolution and spatial coverage, in order to resolve at the same time the small-scale physical-biological interactions responsible for the initiation and cessation of blooms, the transport processes linking source regions with the major current systems, and the large-scale physical coupling between the different populations of Alexandrium within the GOM. The range of scales is so large that models are required for analysis and hypothesis testing, but they only provide meaningful information in the context of a well-designed observational effort.

The Satellite Oceanography Data Laboratory's Role:
Remote sensing is an essential tool for studying HAB ecology over time and space scales not amenable to ship sampling. Satellite data allow synoptic characterizations of hydrographic and biological variability, allowing an examination of linkages between regions, providing essential model input, fields for evaluation of model output, support for field programs and direct quantification of water mass movements. Key processes controlling phytoplankton and HAB ecology and distribution are directly linked to hydrographic processes evident in NOAA AVHRR sea surface temperature (SST) imagery (e.g. Tester et al.1991, Keafer and Anderson, 1993). In the Western Maine Coastal Current (WMCC), the relatively warm Alexandrium-containing coastal plume is evident in AVHRR data (Franks and Anderson 1992a) and key wind-driven processes influencing Alexandrium distributions can be detected (Keafer and Anderson 1993). AVHRR data also indicate Eastern Maine Coastal Current (EMCC) features (e.g. Brooks and Townsend, 1989). Furthermore, our remote sensing capabilities will be significantly enhanced during ECOHAB by data from three ocean color space missions. Color data will not provide a direct investigative tool, as Alexandrium rarely dominates the phytoplankton community and co-occurs with similarly pigmented dinoflagellates. However, in addition to improved temporal coverage, these data add multi-spectral and biological capability, allowing direct quantitative measurement of chlorophyll and turbidity and a significantly improved ability to track water masses.

Approach:
Two primary satellite data sets will be employed, NOAA AVHRR data to provide SST fields, and NASA SeaWiFS data to provide surface color. SeaWiFS is scheduled to be operational when this study begins. These data will be supplemented with OCTS (color data, presently orbiting) and MODIS data (color and SST data, Summer 2000 launch) as available. AVHRR and SeaWiFS data are/will be received and processed to geophysical products using SeaSpace Terascan and NASA SeaDAS software. These data will be supplemented with products acquired from the NOAA Coastwatch program. Level 2 OCTS and MODIS data will be acquired from national distribution sites. Algorithm development and determination of regionally specific coefficients for color data is beyond the scope of this project. For all satellite data, community-standard algorithms and methodologies will be used to calculate geophysical fields (SST, total pigments, chl a, and diffuse attenuation coefficient (K490); e.g. Kidwell 1995, McClain et al. 1995, Aiken et al. 1995). All image data will be subset and registered to a common grid for analysis and delivery to the study team.

The focus of our satellite data analysis is to locate and track specific water masses linked to Alexandrium distributions. Efforts include a) direct comparisons of satellite measured variables with in situ biological, chemical and physical measurements, b) analysis of image time series from the study period to determine location and variability of features and/or events (e.g. frontal zones, water masses, chlorophyll, regions of differing turbidity) identified as important in Alexandrium ecology c) analysis of time series data to determine differences in seasonality and phasing between GOM regions and d) generation of spatial and temporal fields/statistics for comparison with model output. Parallel use of both SST and color imagery reduces the limitations of SST imagery alone. Color is sometimes a better tracer of upper water column circulation than temperature as visible wavelengths emanate from deeper in the water column than infrared wavelengths. Surface heating can reduce or eliminate surface thermal signatures of hydrographic processes which might remain evident as color patterns. Furthermore, image products derived from mathematical combinations of color and SST and innovative use of available multi-spectral channels might prove optimal in defining/monitoring oceanographic features important in Alexandrium ecology (e.g. turbidity of freshwater plumes).