Figure 1. Sampling locations, showing beach sampling in yellow and in-water sampling in blue.
Figure 2. Sargassum inundation events observed at sampling locations in Florida during the reporting period. Top Left: Pepper Park in Fort Pierce. Top Center: Boca Chica Beach near Key West. Top Right: Jetty Park in Fort Pierce. Bottom Left: Southernmost Point in Key West. Bottom Right: Harry Harris Park in Tavernier.
Water quality parameters and dissolved nutrient samples were collected at all sites. This project resulted in the collection of 241 Sargassum samples for stable isotope and heavy metal analysis. By morphotype, 129 S. fluitans and 109 S. natans VIII samples were collected. These morphotypes were collected at almost every site. Only three samples of S. natans III were collected from one site offshore of West Palm Beach on 04/02/2024. No S. natans VIII was collected offshore of West Palm Beach but was found at most sites in other locations. Fauna was collected from 51 sites and Sargassum-associated plankton was collected from 48 sites. Over 600 faunal tissue stable isotope samples were obtained from these collections, which will be used to help understand energy flow through the Sargassum food web. Video surveys are under review to identify species encountered using Sargassum.
Fauna associated with Sargassum mats was assessed using a ROV at 10 sites and floating camera systems at 21 sites, with a total of 62 videos recorded. The review of this video footage is still in process and, so far, has resulted in the detection of eight additional species not collected in dipnet samples. Further review of these videos will provide insight on how the use of Sargassum mats by larger, mobile fauna changes with location and environmental parameters.
Dipnet samples were taken at distances ranging from 0 – 15.7 miles from shore with an average distance of 5.37 miles. The number of organisms in each dipnet sample ranged from 0 – 3,481 with an average of 755. The number of species found in each dipnet sample ranged from 0 – 16 with an average of 7.58. No relationships were observed between the number of species and distance from shore.
Preliminary analysis has begun on faunal dipnet samples to determine occupation of Sargassum mats. Thus far, 19,637 organisms representing 34 different species have been found in 26 surveyed mats, Some of which are shown in figure 5 below. Common, almost ubiquitously occurring organisms, found in Sargassum mats included Portunus sayi, Latreutes fucorum, Leander tenuicornis, and Histrio histrio. Other less common organisms observed at multiple sites include Stephanolepis setifer, Caranx ruber, Platynereis dumerilii, Litiopia melanostoma, and Scyllaea pelagica.
Sampling was conducted at eleven sites pre-Sargassum inundation and ten sites post-inundation (Figures 6) to assess the ecological and chemical impacts of harvesting Sargassum from beaches. At each beach site, three transects were sampled for wrack cover and composition, beach slope, morphodynamics, chemistry of the water, wrack, and soil, and sediment grain size. Invertebrates were collected from wrack, sediment core samples, or hand netting and enumerated (Figure 7). Tissue samples were retained and processed for stable isotope and heavy metal analyses.
The Harmful Algal Bloom Lab partnered with the Florida Department of Emergency Management (FDEM) to harvest Sargassum from coastal waters around Florida during the expected 2024 bloom. The project ran from January to July 2024 and encompassed near-shore and offshore surveys, as well as beach surveys, from Southeastern Florida (Figure 1). These are the highlights from that project.
Over the project period, only light Sargassum inundation events were observed throughout Florida (Figure 2), with sparse aggregations observed offshore. Thus, most of the sampling represents baseline conditions that can be compared to heavier inundation events in future studies of this issue.
During sampling events, environmental parameters of seawater, such as temperature and pH were measured, water samples were collected to determine concentrations of chlorophyll and dissolved nutrients, Sargassum biomass was collected, and visual surveys were conducted when sea conditions allowed, using GoPro floating camera traps and Deep Trekker remotely operated vehicles (ROVs; Figure 3). At all sites, Sargassum was removed with dipnets (Figure 4), and the fauna within the collected biomass was extracted, identified, and enumerated. Some of the collected Sargassum was distributed to industry partners for biomass reuse. Sargassum and fauna collected are being processed in the FAU laboratory for stable isotope and heavy metal analyses.
Figure 3. Images from remotely operated vehicle surveys of Sargassum mats. The fauna in these surveys are being quantified to help identify the changepoint of when and where Sargassum ceases to function as a habitat and starts functioning as a harmful algal bloom.
Figure 4. Dipnet collections of Sargassum biomass. Left: From the Southernmost Point beach in Key West. Middle: Offshore collections from a FAU vessel. Right: Pouring the biomass into a bucket for processing.
Figure 5. Fauna collected from Sargassum mats in offshore collections. Top row, left to right: Kyphosus vaigiensis, Brassy chub; Coryphaena hippurus, Mahi mahi/Dolphinfish (juvenile); Stephanolepis setifer, Pygmy filefish. Bottom row, left to right: Seriola dumerili, Greater amberjack; Caranx ruber, Bar jack; Histrio histrio, Sargassum frogfish.
Figure 6. Beach sampling - (a) Subsurface wrack sampling at Bahia Honda State Park. (b) Water quality sampling at Smathers Beach in Key West. (c) Ghost crab collection at Bowman’s Beach in Sanibel. (d) Beach surveys being conducted at Bill Baggs State Park on Key Biscayne. (e) Beach sampling being set up at Bahia Honda State Park near Big Pine Key. (f) Swash coring and water quality sampling at Bowman’s Beach in Sanibel