Harmful Algal Bloom Forecast Project

Application of Remote Sensing to Red Tide Forecasts in the Gulf of Mexico: Proceedings of a Workshop

Introduction

Response to National Plan Objectives

Leading scientists in the fields of marine biotoxins, harmful algae, seafood safety, and public health designed "Marine Biotoxins and Harmful Algae: A National Plan" (Anderson, Galloway and Joseph 1993), in response to concern that the incidence of harmful algal blooms (HAB) was increasing and affecting the quality of the U. S. seafood supply. The goal of the National Plan is "effective management of fisheries, public health, and ecosystem problems related to marine biotoxins and harmful algae." Five of the eight objectives that were identified as critical to the success of the Plan can be addressed using remote sensing techniques. These five objectives are listed below.

• Objective 1: Develop forecasting capabilities for the occurrence and impacts of harmful marine algal blooms.
• Objective 2: Develop management and mitigation strategies to minimize the impacts of marine biotoxins and harmful algae.
• Objective 3: Provide for rapid response to toxic and otherwise harmful marine algal outbreaks.
• Objective 4: Identify and improve access to databases for bloom incidence, toxin occurrence in shellfish, mass mortality events, and epidemiology.
• Objective 5: Develop communication programs that incorporate educational and public health materials, electronic communication and on-site training.

A remote sensing system designed to monitor and track the formation and demise of HAB would allow an eventual forecast capability (objective 1) that is necessary to the development of management and mitigation strategies (objective 2) for rapid response to algal blooms (objective 3). In addition, routine monitoring data required for a forecast system would provide a database containing information concerning the type, location, frequency, and duration of an HAB. These data would support studies on the impacts of HAB on the fisheries industry, on public health, and for basic algal and oceanographic research (objective 4). The plan for a forecasting system calls for information to be displayed through the World Wide Web which would allow the research community, educators, coastal managers, and the general public equal access to information (objective 5). An HAB forecasting project provides a platform for the integration of information from a variety of sources, such as the NOAA Coastal Ocean Program’s Ecology and Oceanography of Harmful Blooms (ECOHAB), with the common goals of mitigation and control of HAB effects.

The Coastal Remote Sensing (CRS) program of the National Oceanic and Atmospheric Administration (NOAA) Coastal Services Center (CSC) hosted a workshop in July 1997 entitled, "Application of Remote Sensing to Red Tide Forecasts in the Gulf of Mexico" (see Appendix A). G. breve blooms in the eastern Gulf of Mexico were chosen as the pilot project. A combination of characteristics in this region increases the likelihood of success for a remote sensing program designed to monitor the initiation and progress of harmful algal blooms. Experts in the region’s ocean circulation, in phytoplankton physiology, and in remote sensing techniques, were invited to participate (see Appendices B and C). The workshop had the following goals:

• Review the current state of knowledge on the history, prior management responses, ecology, biology and bloom dynamics of Gymnodinium breve red tides that initiate in the Gulf of Mexico,
• Assess the potential of remote sensing methods to predict, monitor, and track G. breve red tides.

Pilot project: Gymnodinium breve in the Eastern Gulf of Mexico

Figure 1. Gymnodium breve cell. Cell diameter is approximately 32 mm. Photo courtesy if Florida Department of Environmental Protection.

G. breve is a dinoflagellate (Figure 1) found throughout the Gulf of Mexico and in coastal waters of the Atlantic Ocean from Florida to North Carolina. Although harmful blooms of G. breve have occurred as far north as the barrier islands of North Carolina (Tester and others 1991), they routinely occur along the southwest coast of Florida in the late summer and early fall and can persist on the order of months (Steidinger 1983). These blooms impact fisheries and tourist industries by inducing Neurotoxic Shellfish Poisoning (NSP). Ingestion of G. breve toxin by fish paralyzes the respiratory system causing death. Increased mortality of shellfish, waterfowl, and manatees has been noted during G. breve blooms (Gunter and others 1948; Landsberg and Steidinger 1997). These species are affected either by the neurotoxin itself or by the reduced water quality that results from a bloom. Human health is compromised by the presence of dead and decaying fish in the waters and on the beach. In addition, the aerosols produced by wave action as G. breve is washed ashore affect respiratory systems and cause asthma-like symptoms.

G. breve cells are positively phototactic and negatively geotactic; therefore, they are often found in highest abundance near the surface of the water column, but sub-surface concentrations also have been noted (Geesey and Tester 1993). Low ( 10⁰ - 10³ cells l^-1) background numbers of G. breve cells are found in the Gulf of Mexico and South Atlantic Bight (Geesey and Tester 1993); concentrations of 5 x 10³ cells l^-1 are sufficient to warrant closure of shellfish harvesting areas. G. breve grows at optimal rates in warm waters with a temperature range of 22 to 28°C (Rounsefell and Nelson 1966). G. breve is capable of growing at maximal rates at low concentrations of nitrogen and phosphorous and can utilize a variety of inorganic and organic nutrients (Vargo and Shanley 1985; Steidinger and others in press).

Physical oceanographic features influence the accumulation of cells and the conditions for growth. One hypothesis is that the warm Loop Current waters carry an inoculum population of G. breve cells. When the Loop Current intrudes northward into the Gulf of Mexico and eastward onto the Florida Shelf, the anti-cyclonic circulation of the Loop Current augments upwelling off the west Florida shelf. Upwelling conditions form an oceanic front and provide an environment that concentrates cells and may favor dinoflagellate growth (Blasco 1975; Haddad and Carder 1979). Other physical mechanisms that create upwelling off the coast of Florida also may be involved in the initiation of bloom conditions. Blooms are thought to initiate offshore and then move inland (Steidinger 1975; Tester and Steidinger 1997). Movement of the water mass onshore and alongshore depends on current and wind patterns. The factors that determine the intensity of a bloom are unclear. The intensity and duration of the bloom is dependent largely on the longevity and stability of the physical oceanographic environment. Mechanisms that contribute to termination of a bloom include wind-induced vertical mixing of the water column; wind-induced horizontal movement of cells into habitats that are unfavorable for growth (Tester and others 1991), or a decrease in salinity to below 24 ppt due to freshwater input (Aldrich and Wilson 1960).

The Loop Current, upwelling zones near the shelf, and other large-scale physical oceanographic features are visible in satellite-derived sea surface temperature (SST) (Figure 2) and sea surface height imagery. Any change in ocean color, which results from varying concentrations of phytoplankton near the surface, that is associated with the water masses also is detectable by remote sensing methods.

Algorithms to predict G. breve cell concentrations from ocean color have not been developed; however, blooms of this species often are mono-specific (Steidinger and Vargo 1988), and remote sensing techniques have been used to estimate cell concentrations from chlorophyll a concentrations (Tester and Steidinger 1997; Tester, Stumpf, and Steidinger 1997). These detectable features increase the probability that a remote sensing program would be an effective forecasting method.