Looking at the Florida Red Tide Historical Database

Florida's historical red tide sampling effort was directed toward event response. Today, the sampling effort has changed and increased substantially.

Florida has one of the largest and longest continually recorded electronic harmful algal bloom (HAB) databases in the United States. Florida red tide data have been collected since 1954 by numerous agencies and organizations. This historical database is principally an event response database. The intent of the program was to either determine the geographic extent of a Karenia brevis red tide or to monitor inshore waters for red tide abundance and, if necessary, close shellfish harvesting areas to protect public health. When K. brevis reached cell counts of 5,000 cells per liter of seawater at barrier island passes which open into estuaries or inland waters, shellfish beds in the area would be closed until it was safe to harvest again. Sometimes, shellfish beds were closed for months at a time.

Although the database consists mainly of event response data, there were long-term projects (2 to 5 years) as well. For these projects, samples were collected routinely from fixed stations, sometimes along transects (sample areas) from shore to locations more than 70 kilometers (km) offshore. These data are useful for looking at the offshore origin of red tide and its movement across the west Florida shelf. The transects went far enough offshore to document red tide presence. The transects were typically sampled monthly from surface to bottom. Cruise data also have more corollary environmental information, or information on naturally evolving environmental circumstances, such as temperature, salinity, dissolved oxygen, and light penetration. Data from cruises also have metadata with a contact name for obtaining more data if available. Metadata is information about the stored data, such as what method was used to count the cells or what method was used to determine salinity - the "what," "where," and "how" of the database.

Since 1998, federal and state funded monthly red tide cruises at permanent and temporary sampling stations have increased the value of the database because of the repetitive nature of the data collection. The collection and measurements of additional variables, such as nutrients, chlorophyll, and dissolved oxygen have also improved the database value. The five-year, federal funded Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) Florida program (FWC, University of South Florida, Mote Marine Laboratory, and 10 other institutions) was a comprehensive and productive research effort. It involved more than 70 monthly inshore and offshore stations as well as 1- to 3-week cruises during red tide blooms to study specific aspects of these blooms on the west Florida shelf. Much of the ECOHAB: Florida data, such as nutrients, is retained by the individual researchers, who are analyzing and publishing their data.

The historical sampling effort was directed toward event response and was not designed for statistical analyses, such as stratified random sampling. Today, the sampling effort has changed and increased substantially, with three times as many samples collected than in early years. Thus, the historical red tide event data cannot be compared accurately with today's event and research cruise data for inshore and offshore red tide samples. However, the basic data can be used to determine geographical areas affected, movement of red tide from offshore to inshore, and movement alongshore. In some cases, the red tide database can be combined with other data sets such as salinity, temperature, winds, currents, and hurricane paths to look at patterns. Such analyses are being pursued with geographic information system (GIS) technology. In future months we will post new imagery that will show hurricane paths in relation to red tides and determine whether red tides were terminated by passage of these storms, investigate the transport of red tides into estuaries in relation to prevailing salinity patterns in the estuary (red tide does not thrive below 2.4 percent salt or 24 parts per thousand salinity), and investigate other aspects of red tide monitoring and research. GIS tools allow us to visualize relationships from large datasets. As further mathematical analyses are done on specific data sets, graphics will also be posted.

Figure 1 below represents one way of presenting summary data from the entire Florida red tide historical database. Figure 2 represents one way of presenting geographic summary data from the database. Figures 3a through 3h and 4a through 4d represent graphic images that portray movement of red tide from offshore to inshore.

Figure 1. Decadal representation of red tide samples with Karenia brevis counts greater than100,000 cells per liter by month. Blue diamonds represent 1954 through 1964, pink squares represent 1965 through 1974, yellow triangles represent 1975 through 1984, turquoise Xs represent 1985 through 1994, and purple barred Xs represent 1995 through 2004. If you were to compare only the two decades with the most samples collected, you would miss all the variation in the interim decades and would misidentify a shift in "seasonality." Counts above 100,000 cells per liter (fish-killing concentrations) were least common in the winter and early spring. This window is important to manatee populations along the southwest coast of Florida. If a red tide occurs between March and May and salinities are high in the bays, red tide can move in and threaten manatees, which are an endangered species (Landsberg and Steidinger 1998). Karenia brevis along the west coast of Florida does not do well in less than 2.4 percent salt or greater than 24 parts per thousand salinity.

Graph of red tide samples with Karenia brevis counts greater than 100,000 cells per liter by month

Figure 2a-2b. Number of samples with greater than 100,000 cells per liter by year. This graph shows percent of the number of samples where the Karenia brevis count was above 100,000 cells per liter. In this graphic, as well as in any percentage graphic, the percent is influenced by sampling effort. Each year has the number of samples (effort) near its corresponding peak. In this case, it is important to understand sampling effort (total number of samples) and why the samples were collected. Were the red tide samples collected as part of a directed event response; or as part of an established, routine cruise sampling; or as part of a statistically designed sampling program?

Number of samples off Tampa Bay with greater than 100,000 cells per liter by year

Number of samples off Charlotte Harbor with greater than 100,000 cells per liter by year

Figure 3a-3h. 1976 daily red tide data in the form of Karenia brevis abundance and location. These daily images of red tide abundance are coded by circles for counts up to 100,000 cells per liter and squares for counts greater than 100,000 cells per liter. The color code is to indicate age of the sample. A new record is light in color and older records, up to 60 days, are dark in color. The images progress from September 16, 1976, when the Fish and Wildlife Research Institute (as the Department of Natural Resources Marine Research Laboratory) and Mote Marine Laboratory, on contract to the National Aeronautics and Space Administration (NASA), were sampling two transects up to 73 km offshore. This first image shows the sampling stations as small circles with no K. brevis counts. The next image for September 22, 1976, shows K. brevis above background concentrations at 20 km offshore on the Sarasota transect. The next sequence of images shows the red tide onshore, its southerly movement, and how it increased in abundance. The image from November 31, 1976, shows the older samples with more recent, high-abundance samples inshore. The remaining images show the aging of the bloom. The initiation of this red tide was confirmed to be more than 18 km offshore. The only data that can be used to look at offshore initiation of red tides is repetitive cruise data out to greater than 70 km because then it can be determined when K. brevis occurs offshore before coming inshore.

To view the 1976 daily red tide data graphics, Download an Automated PowerPoint File (695KB) or Download a PDF File (469KB)

Figure 4a-4d. 1979 daily red tide data in the form of Karenia brevis abundance and location. The event was first identified in the Big Bend area of Florida. There had been K. brevis sampling off Tampa Bay and Sarasota with below background abundances of K. brevis. Above background levels were found 80 km offshore (November 27, 1979). The next image, for December 10, 1979, shows the inshore and southerly movement of red tide. It also shows most of the higher concentrations of K. brevis beyond the 18 km line. The last two images, for December 21, 1979, and December 28, 1979, show the movement of the red tide southward toward the Florida Keys. The movement of this red tide and its concentration at a current boundary or front was documented (Haddad, 1982). There are more images, but these four capture the movement well. In addition to these two separate years of samples, there are several other years that include cruise data that can be used to show origin and transport of red tides on the west Florida shelf.

To view the 1979 daily red tide data graphics, Download an Automated PowerPoint File (458KB) or Download a PDF File (297KB)

Visit the following pages for more complete daily accounts of the 1976 and 1979 red tides as well as the 1985 red tide.

Legend: Understanding the Temporal Animation HTML |PDF

Daily Account of 1976 Red Tide
Daily Account of 1979 Red Tide
Daily Account of 1985 Red Tide

Throughout this discussion of the historical red tide database, we have used a Karenia brevis count of greater than 100,000 cells per liter of seawater as the indicator for bloom concentrations because this is the level of abundance at which fish kills first occur (100,000 to 250,000 cells). This is also the abundance at which satellites can detect blooms.

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