Lack of Correlation in Two Bacteria Indicator Species in Near-Shore Marine Waters, Sarasota County, Florida

In the U.S., Federal guidelines and funding are provided to the states and tribes to monitor coastal recreational waters for pathogens or pathogen indicators to determine instances where pathogens may be present in amounts could be unhealthful for humans. The Florida Department of Health monitors beach waters, and for the period 2002–2011 collected weekly samples which were tested for two indicator species–enterococcus and fecal coliform–at all coastal counties. Beaches were posted with public health advisories when concentrations exceed 104 #CFU/100mL for enterococcus or 400#CFU/100mL for fecal coliform. The objective of this research was to determine whether presence of these two bacteria species in samples of near-shore marine waters is quantitatively associated. The research uses data from 16 Sarasota County beaches for the nine-year period August 2002–June 2011, the longest period for which weekly data are available for both enterococcus and fecal coliform. Results show poor correlation. Only 2 of the 16 beaches showed correlation coefficient R² of 0.70 or better when regressing one of these species against the other, with R² less than 0.35 for 4 of the 16. The 16 beaches showed variation in the number of occasions when the two different organisms were present in such high amounts as to trigger an advisory for bathers. Conclusions demonstrate that correlation of the two varies greatly among beaches, and that for many beaches the correlation between the two species is weak, with the implication that monitoring for either of the two may miss episodes when human-originating bacteria could be present in unhealthful amounts.