Effects of Benthic Cyanobacteria on SE Florida Coral Reef Gorgonian Populations

In 2002, the presence of benthic cyanobacteria (genus Lyngbya ) was observed within annual coral reef monitoring sites off Broward County, southeast Florida. Thick filamentous mats were observed entangled and growing upon gorgonians (sea whips, fans, plumes and rods) and substratum within the permanent monitoring transects. The observed effects of Lyngbya on gorgonians included smothering of tissues causing bleaching and/or necrosis, which appeared to lead to partial mortality or complete mortality in severe instances when the entire colony was covered. The annual coral reef monitoring protocol includes taking images along permanent 30 m ² belt transects. From 2000 to 2007 images from 20 monitoring sites were analyzed to determine the percent of gorgonians present with Lyngbya , and NCRl developed CPCe software was used to estimate Lyngbya percent cover. Gorgonian densities within the belt transects were recorded in situ. From 2002-2007, Lyngbya was present in a least 6 monitoring sites. The height of the Lyngbya bloom occurred in 2003, which had the highest yearly percent cover (15%) and greatest occurrence within the monitoring sites (present at 16 of 20 sites). Two sites that exhibited the highest percent cover of Lyngbya in 2003 (87% and 71%) experienced a decrease in gorgonian density the following year. Most other sites with moderate Lyngbya percent cover followed this trend as well. The ability to capture these types of events is an important part of coral reef monitoring projects. This information will aid resource managers in making policy decisions on issues such as water quality which affect the health of coral reef resources.