Amy N.S. Siuda

Between 1993 and 2023, 5,587 neuston net tows were conducted onboard Sea Education Association’s (www.sea.edu) SSVs Westward and Corwith Cramer during oceanographic research cruises across the North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Cruise tracks varied seasonally and annually. The neuston net (1.0m × 0.5m frame, 33​3​ um mesh) was deployed from a boom extended 5 m off the ship’s port side while sailing on a port tack. Any wind​r​ows of Sargassum were thus crossed perpendicularly and any bow wake effect was minimized. Tows were conducted at two knots for 30 minutes for a typical distance of ~1.0 nm; tow distance (m) was calculated as the difference between start/end GPS locations (1993–2003) and from minute-by-minute GPS locations (2004–2023). Standard net processing included identifying pelagic Sargassum specimens to morphotype, patting dry, and weighing using a spring scale to yield mass (g) for each morphotype. Three common holopelagic morphotypes are reported: Sargassum natans var. natans (Sn_n), S. natans var. wingei (Sn_w), and S. fluitans (Sf). Weighted arithmetic mean Sargassum density (g/km2) was calculated from the sum of Sargassum mass divided by the sum of tow area for all tows in a given year (season, time frame) for a given region. Morphotypes reported as percentage of total collected biomass in a given year (season, time frame) for a given region. The date and GPS position were captured with each sample. All net tows were assigned to one of five regions defined on the basis of physical oceanographic boundaries. Analysis of data was organized by ecological year (March–February, corresponding with the start of the annual spring bloom period in the Sargasso Sea) and season (spring/summer March-August, fall/winter September-February). In most years, neuston tows occurred during both the spring/summer and fall/winter seasons in a region; sporadic changes in cruise track may have caused occasional missed seasons. Examined time frames (pre-MODIS 1993-1999, pre-GASB 2000-2010, early GASB 2011-2014, and recent GASB 2015-2023) were selected for comparison with satellite data and Great Atlantic Sargassum Belt (GASB) dynamics. Quality control confirmed accurate, consistent data entry and GPS positions, and filtered out incomplete records. Blank cell = no data.

Microplastics have been recognized as an emerging contaminant. Copepods are abundant primary consumers in marine food webs. Interactions between copepods and microplastics can lead to negative health effects to the individual and may have implications for populations and ecosystems through biomagnification. Laboratory and field studies have observed various species of zooplankton ingesting microplastics, however, this is the first study to observe microplastic-copepod interactions in Tampa Bay. Over 2 years (November 2017-January 2020), 14 sampling cruises were conducted with seven stations throughout Tampa Bay. At each station copepods were collected by towing a 200 μm mesh ring net (0.5 m diameter) for 3 min. 1,000 individual Acartia tonsa copepods were picked from each sample and digested to release gut contents. Gut contents were stained in a Nile Red solution and then visualized using epifluorescent microscopy, quantified, photographed and sized using image analysis. In Tampa Bay, A. tonsa consumed fragments over fibers, ranging from 0.018 to 0.642 mm, with an average particle size of 0.076 mm. An overall average of 15.38 particles were ingested per 1,000 copepods, or 6.48 particles m–3 when normalized for environmental copepod concentrations. While significant differences were detected between stations and months, no clear spatial (from head to mouth of estuary) or temporal (between wet and dry seasons) trends in ingestion rate or ingested particle size were evident. These results show that A. tonsa ingested microplastics throughout Tampa Bay. These robust baseline data, for a copepod species that dominates estuarine zooplankton communities around the world, set the stage for valuable comparisons between estuaries with different physical mechanisms and levels of anthropogenic impact, allowing for exploration of how the environmental conditions impact ecological interactions.

Although there is growing concern about ingestion of microplastics by marine organisms, little research has been conducted on marine herbivores. This is the first study to document microplastic ingestion within the family Sirenia. Subsamples were collected from five locations in the gastrointestinal tracts (GI) of 26 dead manatees (Trichechus manatus latirostris) from Tampa Bay, Florida. During gross necropsies, macroplastic pieces were found in seven individuals (26.9%). Careful visual examination of the subsampled portions of the GI contents indicated that 19 individuals (73.1%) contained plastic particles. As five individuals had both macro and microplastic pieces, the overall frequency of occurrence of plastic ingestion was 76.9%. Due to the large volume of cellulose-rich ingested material, it was not feasible to analyze the entire gut contents, nor was it feasible to conduct chemical or enzymatic digestion; therefore, it is very likely that many microplastic pieces were not detected. Despite these technical challenges, it is clear that manatees in Tampa Bay are routinely consuming microplastics in addition to larger plastic pieces. Currently, nothing is known about the physiological effects of microplastic ingestion in sirenians, however environmental plastics could be concentrated by manatees through ingestion and the subsequent production of microplastics-laden feces.

The recent recurring blooms of pelagic Sargassum spp. (sargasso) in the tropical Atlantic forming the Great Atlantic Sargasso Belt, are composed of distinct algal species and morphological forms, for which little understanding of basic development exists. Growth rate measurements across a range of environmental conditions in semi-controlled settings may aid in understanding the blooms. However, measuring the growth of this pelagic seaweed has proved to be challenging, as it tends to lose vigor in standard culturing systems. This work describes in-situ and ex-situ culture systems, that mimicked the pelagic condition by keeping the algae in motion. Growth rates measured in both systems were comparable, and in the same order of magnitude as those measured for sargasso in the Sargasso Sea. The morphotype VIII of the species S. natans, which became abundant with the blooms, had a higher in-situ growth rate (doubling time 17.9 – 26.3 d) than S. fluitans III (doubling time 25.6 – 83.3 d) under the studied conditions and temperatures (27–29 °C). Fertilizer addition to the in-situ trials did not result in higher growth rates, even though tissue content analysis showed that both N and P were taken up by the algae. In the ex-situ trials, S. natans VIII responded unfavorably to higher temperature (31 °C), whereas S. fluitans III did not. This preliminary study showed that both in-situ and ex-situ culture are feasible to determine growth rates of sargasso, paving the way for future (semi-) controlled studies on bloom dynamics in relation to abiotic and biotic conditions.

Single-use plastics are a well-documented source of plastic debris and consequently a marine debris prevention policy priority. From August 2018 through May 2020, the Reduce Single-Use Project at Eckerd College (RSU) set out to raise the campus awareness of plastic marine debris, with the goal of reducing the community's single-use plastic consumption. To accomplish this, RSU facilitated a series of education and outreach events incentivizing vohmtary plastic reduction, including academic courses, community workshops, and coastal cleanups. Knowledge gains by the community were quantified through campus-wide surveys. Reduction of single-use plastic consumption was encouraged by providing reusable alternatives, inviting the community to participate in plastic reduction challenges, and ultimately working with the College administration to implement a campus-wide Break Free From Plastic Pledge barring the use of campus funds to purchase unnecessary single-use plastics. Behavioral changes were quantified via self-reported survey responses and observations of heavy plastic consumption areas on campus. Through this research, institutional policy changes that resulted in the direct removal of single-use plastics from campus locations (i.e., vendors offering wooden cutlery instead of plastic in the dining hall; swapping out plastic bags for paper at the campus bookstore) were i'ound to be the most effective method for reducing the consumption of single-use plastics. These policy changes were embraced by vendors and the College administration due to a demand for change from the campus community. Thus, individual behavior change fueled institutional policy change, which perpetuated further single-use plastic reduction.

Single-use plastic has devastating impacts on the natural environment and scalable theory-based interventions are urgently needed to curb plastic consumption. The purpose of this study is to test the impact of two brief plastic reduction interventions on consumption on college campuses and whether these effects will be mediated by changes in the extended Theory of Planned Behavior (TPB) model consisting of attitudes, subjective norms, perceived behavioral control, moral norms, descriptive norms, and self-identity. 375 undergraduate students (77% female) from two colleges in the southeastern US completed baseline measures of plastic consumption beliefs and behavior in line with the extended TPB model. Participants were then randomized into one of three groups - control group (n = 152), app intervention group (who tracked plastic behavior on a mobile phone app for a week and received TPB-based daily messages via push notifications; n = 89), or pledge intervention group (who made a pledge to reduce plastic for a week and received TPB-based daily messages via email; n = 134). All participants completed the survey again after the intervention week. Results showed that the extended TPB model along with the intervention condition significantly predicted changes in plastic behavior over the week, (R2 = 0.24, p < .001). Additionally, mediation analysis revealed that the pledge group (compared to the control group) reported a significant decrease in plastic consumption over the week-long intervention, with indirect effects via changes in attitudes, perceived behavioral control, and descriptive norms. The app group (compared to the control group) decreased plastic consumption less and showed no change to the extended TPB constructs. Results suggest that plastic reduction interventions that influence the extended TPB constructs can be expected to have corresponding changes in plastic consumption behavior.

Between 2011 and 2020, 6,790 visual observations of holopelagic were recorded across the North Atlantic Ocean to describe regional distribution, presence, and aggregation state at hourly and 10 km scales. Influences of oceanographic region and wind/sea conditions as well as temporal trends were considered; marine megafauna associates documented the ecological value of aggregations. Holopelagic was present in 64% of observations from the western North Atlantic. Dispersed holopelagic fragments and clumps were found in 97% of positive observations whereas aggregated windrows (37%) and mats (1%) were less common. Most field observations noted holopelagic in quantities below the AFAI algorithm detection limit for the MODIS sensor. Aggregation state patterns were similar across regions; windrow proportion increased with higher wind speeds. In 8 of 10 years in the Sargasso Sea holopelagic was found in over 65% of observations. In contrast, the Tropical Atlantic and Caribbean Sea exhibited greater inter-annual variability (1-88% and 11-78% presence, respectively) that did not align with extremes in central Atlantic holopelagic areal coverage determined from satellite observations. Megafauna association patterns varied by taxonomic group. While some study regions were impacted by holopelagic dynamics in the equatorial Atlantic, the Sargasso Sea had consistently high presence and operated independently. Field observations capture important dynamics occurring at fine spatiotemporal scales, including transient aggregation processes and ecological value for megafauna associates, and therefore remain essential to future studies of holopelagic .

Sargassum (class: Phaeophyceae, order: Fucales) is a complex group of marine brown macroalgae. There are 361 accepted species, mostly benthic, distributed globally in temperate and tropical waters (Guiry & Guiry, 2021). Among these, however, the world's only holopelagic macroalgae are as follows: Sargassum fluitans and S. natans. These drifters are suspected to reproduce asexually, maintain buoyancy via gas-filled floats, and establish a surface ocean habitat in the subtropical North Atlantic, equatorial Atlantic, Caribbean Sea, and Gulf of Mexico that is unparalleled in the open ocean. Individual, radial branching clumps are dispersed across the sea surface, aggregated by helical Langmuir circulation into parallel windrows, or concentrated into dense mats measuring 10s of meters across

Pelagic Sargassum macroalgal rafts in the North Atlantic support sessile and motile epifauna that attract ecologically and economically important migratory organisms. Three prevalent pelagic Sargassum morphotypes vary in their degree of branching and foliation, and thus have different structural complexities that can influence their respective value as motile epifauna habitat. Sargassum fluitans III and S. natans I have denser foliation, creating a complex habitat; in contrast, S. natans VIII is more open and architecturally simple. In 2015/2016, 373 dip net samples of algae were collected from the Tropical Atlantic, Greater Caribbean, Gulf of Mexico, Gulf Stream, and Sargasso Sea. 20,975 individual motile epifauna from 32 taxa were recorded. Sargassum fluitans III supported higher densities of individuals and greater numbers of taxa than S. natans VIII or S. natans I , a pattern attributed to its more complex architecture and consistent with communities on benthic and floating macroalgae. Most assemblages comprised a few dominant and many rare motile epifauna; when compared to historical studies, dominant motile epifauna had shifted. These findings suggest important differences in ecological value between pelagic Sargassum morphotypes with implications for coastal and pelagic conservation strategies, which warrant consideration given recent shifts in morphotype distribution and recurring pelagic Sargassum inundation events.

The pelagic brown macroalga Sargassum supports rich biological communities in the tropical and subtropical Atlantic region, including a variety of epiphytic invertebrates that grow on the Sargassum itself. The thecate hydroid Aglaophenia latecarinata is commonly found growing on some, but not all, Sargassum forms. In this study, we examined the relationship between A. latecarinata and its pelagic Sargassum substrate across a broad geographic area over the course of 4 years (2015–2018). The distribution of the most common Sargassum forms that we observed ( Sargassum fluitans III and S. natans VIII ) was consistent with the existence of distinct source regions for each. We found that A. latecarinata hydroids were abundant on both S. natans VIII and S. fluitans III , and also noted a rare observation of A. latecarinata on S. natans I . For the hydroids on S. natans VIII and S. fluitans III , hydroid mitochondrial genotype was strongly correlated with the Sargassum substrate form. We found significant population genetic structure in the hydroids, which was also consistent with the distributional patterns of the Sargassum forms. These results suggest that hydroid settlement on the Sargassum occurs in type-specific Sargassum source regions. Hydroid species identification is challenging and cryptic speciation is common in the Aglaopheniidae. Therefore, to confirm our identification of A. latecarinata , we conducted a phylogenetic analysis that showed that while the genus Aglaophenia was not monophyletic, all A. latecarinata haplotypes associated with pelagic Sargassum belonged to the same clade and were likely the same species as previously published sequences from Florida, Central America, and one location in Brazil (São Sebastião). A nominal A. latecarinata sequence from a second Brazilian location (Alagoas) likely belongs to a different species.