The proliferation of holopelagic Sargassum in the Atlantic Ocean and Caribbean Sea has significant ecological, economic, and environmental impacts. This session aims to bring together researchers from the international community to share their latest research on the causes, origins, and predictability of Sargassum accumulation and stranding events. The session will focus on several key areas to increase our knowledge and understanding of Sargassum ecology: 1. Insights into the genetic diversity of Sargassum across the Atlantic, including microbiome and geographic distribution, 2. Examination of the role of nutrient inputs from diverse sources, such as Amazon river outflow, upwelling systems, and atmospheric deposition (e.g., Saharan dust), in stimulating Sargassum growth, 3. Exploration of changing ocean currents and temperature on the patterns of distribution and intensity of Sargassum accumulations. 4. Development of models and predictive tools to forecast bloom events, integrating data from satellite observations, oceanographic measurements, and climate models to improve the accuracy of bloom predictions. 5. Assessment of the ecological consequences of large-scale Sargassum events on marine ecosystems, including impacts on biodiversity, fisheries, and coastal environments.
Lead Organizer: Fabio Nauer, Royal Netherlands Institute for Sea Research (NIOZ) (fabio.nauer@nioz.nl)
Co-organizers:
Linda Amaral-Zettler, Royal Netherlands Institute for Sea Research (NIOZ) (linda.amaral-zettler@nioz.nl)
Pierre-Yves Pascal, Université des Antilles (pierreyves.pascal@gmail.com)
Presentations
04:30 PM
Improving Predictive Models of Sargassum Drift Using Objective Eulerian Coherent Structures (9102)
Primary Presenter: Christian Appendini, UNAM - LIPC Sisal (cappendinia@iingen.unam.mx)
Forecasting the drift of floating particles, such as plastics, oil spills, and sargassum, is often hindered by uncertainties in ocean surface current fields and the initial locations of these particles. Such uncertainties can lead to large discrepancies between predicted and actual trajectories, complicating both environmental management and mitigation efforts. In this study, we address these uncertainties by incorporating Objective Eulerian Coherent Structures (OECS) into Lagrangian particle-tracking models. The OECS allows us to identify stable, hyperbolic structures in ocean flows that act as transport barriers, providing insight into persistent flow features that strongly influence the drift of floating objects. By leveraging the OECS, we correct Lagrangian trajectories to align with the natural movement patterns governed by these coherent structures, thereby improving the accuracy of drift predictions. Our results demonstrate that using OECS in particle forecasting models provides better forecasts for drifters in most cases, with the potential to improve the forecasting of sargassum rafts and other hazards, such as oil spills and plastics. This approach has immediate applications for enhancing sargassum tracking in the Caribbean, where massive accumulation has caused significant ecological and economic disruptions.
04:45 PM
Predicting growth and survival of holopelagic Sargassum using a mechanistic model under different environmental scenarios (9144)
Primary Presenter: Maria José Lagunes, MARBEC, LEMAR, IRD (maria_jose.lagunes@ird.fr)
Drifting holopelagic Sargassum morphotypes experience fluctuation in temperature and nutrient availability as they spread across the tropical Atlantic. Current studies have largely focused on the dispersion of this macroalga. However, accurately forecasting Sargassum morphotypes biomass distribution and stranding requires a deeper understanding of the trade-offs between environmental variable and organism functions such as growth, nutrient storage, and survival. Based on current knowledge of Sargassum morphotypes, a multi reserves DEB (Dynamic Energy Budget) theory is developed to simulate nutrient uptake and temperature response under different environmental conditions. Growth and survival based on nutrient availability and temperature scenarios encountered by Sargassum along their drift is explicitly quantified by estimating species parameters, performing simulations, and comparing them with experimental studies. As a part of the BIOMAS project (BIOenergetic Modeling Approach for Sargassum dynamics), the SargaDEB model will help in the estimation of Sargassum biomass and dispersion by integrating this model into a drift model in order to simulate Sargassum morphotypes proliferation on seasonal scale and through multiple years. Through this approach, we will gain understanding of the interplay between biological and physical factors that drive the dispersal and biomass proliferation of Sargassum to improve bloom predictions.
05:00 PM
SARGASSUM SHAPE ATTRIBUTES FOR KNOWLEDGE AND SATELLITE DETECTION IMPROVEMENT (9700)
Primary Presenter: Abigail Uribe-Martinez, UABC-Mx (abigailum@gmail.com)
Sargassum has different shapes resulting from several conditions, from concentration or aggregation to currents and wind. On the other hand, detection has been mainly based on algal floating indexes that may have issues regarding false positives that confuse mainly clouds, cloud shadows, and sun glint. Here, we analyzed the shape and spatial configuration metrics of sargassum polygons to improve the confidence of sargassum detection, minimize false positives in final outputs, and generate knowledge about sargassum aggregation patterns. We implemented this approach by contrasting 38 metrics in sargassum polygons obtained with medium-resolution satellite sensor Landsat-OLI, and we evaluated the confusion with other elements in the images. We also valued the contribution of several metrics to improve pelagic sargassum satellite detection. Twelve spatial and shape metrics were statistically different for sargassum polygons regarding false positive polygons, and we proved that these metrics improve the final detection process. This approach could be used as inputs for spatiotemporal pattern analysis, forecasting models, and impact analysis, among others, due to better confidence in the sargassum detection, avoiding over-estimations that can drive false conclusions due to the extreme presence of false positives.
05:15 PM
Empowering Coastal Communities through Citizen Science to Monitor Sargassum in the Tropical Atlantic (9550)
Primary Presenter: Ma. Eugenia Allende-Arandia, National Autonomous University of Mexico (mallendea@iingen.unam.mx)
The persistent influxes of pelagic sargassum across the tropical Atlantic have significantly impacted coastal communities, livelihoods, local economies, and the environment. Our research engaged sargassum-affected communities in Quintana Roo, Mexico, to explore the potential of citizen science in enhancing local responses to this seaweed. We established seven permanent volunteer monitoring stations with schools and local communities. Our initiative involved: (i) training school teachers, students (ages 11-18), and community members to monitor sargassum using the CoastSnap method; (ii) integrating these activities into school lessons explaining sargassum blooms and local adaptation efforts; and (iii) creating a global online network to connect schools affected by sargassum across the Atlantic. Our findings highlight the potential of citizen science in generating important data on the seasonality and local impacts of sargassum, while fostering a deeper understanding among participants. Engaging students and communities raised awareness and motivated them to contribute to monitoring efforts and develop local strategies for managing sargassum influxes. This project aims to show that community-led monitoring can enhance the development of locally appropriate management policies and adaptation strategies. Also, this presentation aims at promoting the use of CoastSnap as a platform for monitoring sargassum beaching events.
05:30 PM
Reduced transfer of metals and metalloids from stranded Sargassum to adjacent organisms (8857)
Primary Presenter: Pierre-Yves Pascal, Université des Antilles (pierreyves.pascal@gmail.com)
Since 2011 unprecedented biomass of holopelagic brown macroalgae Sargassum has stranded along the Caribbean coasts, inducing damages for coastal ecosystems, economy and human health. By accumulating metals and metalloids,Sargassum spp. can play a role in contaminant transportation from offshore to the coast. In order to evaluate those potential transfers, organisms (phanerogam: Halophila stipulacea, gastropoda: Littoraria angulifera and bivalvia: Isognomon alatus) from mangroves and seagrass of Guadeloupe (French West Indies) were sampled in coats exposed (Petit Cul-de-Sac Marin) and not exposed (Grand Cul-de-Marin) to Sargassum stranding. Two campaigns were realized during periods of massive (July 2020) and reduced (January 2021) stranding of Sargassum. Studied species presented different compositions in their 28 metal(loid)s trace elements with higher concentration in the bivalves Isognomon alatusin particular for the total Arsenic (tAs). None of the studied species presented an increased MTE concentration according to i) geographical proximity with stranded Sargassum and ii) temporal period of higher Sargassum stranding. The study suggests that transfer of metal, including As, from Sargassum to marine organisms would be limited.
05:45 PM
HIGH OCCURANCE AND BIOMASS OF SARGASSUM FILIPENDULA IN BEACH WRACK ALONG CAPE COD, MA (9593)
Primary Presenter: Mirta Teichberg, Marine Biological Laboratory (mteichberg@mbl.edu)
Pelagic blooms of macroalgae of the genus Sargassum spp. have been increasing across the Atlantic and into the Caribbean and other coastal areas. Along the Northwest Atlantic coastline in Cape Cod, MA, we observed an increase in occurrence of Sargassum filipendula, an attached-benthic form of Sargassum, washing up on beaches. In a survey, S. filipendula was found in the beach wrack of 77% of sites visited, with a maximum wet weight biomass of up to 6.6 kg m-2. Comparing nitrogen and carbon isotopic signatures from historic samples to present day samples, we found an increase in δ15N from 4.7 to 7.5 ‰ and a decrease in δ13C from -18.0 to -21.1 ‰, suggesting a shift in N and C sources. Heavier δ15N signature reflect an increase in wastewater as a source of N, which may be driving an increase in bloom occurrences. Lighter δ13C signatures reflect possible changes in metabolism and uptake of DIC in the region. An experimental study of desiccation exposure of S. filipendula showed signs of short-term desiccation tolerance with less than 3 hours of exposure compared to another bloom forming macroalga of the genus Gracilaria. These results imply that Sargassum has the potential to survive and expand to new areas even after detachment if desiccation exposure remains short-term between low and high tides. However, with more than 6 hours of desiccation exposure over repetitive days, a decrease in photosynthetic yield (Fv/Fm) and tissue loss was observed, indicating that these species are not able to cope or recover under longer-term desiccation conditions.
SS31B - Sargassum Accumulations in the Atlantic: Ecological Drivers, Impacts, and Predictive Models
Description
Time: 4:30 PM
Date: 28/3/2025
Room: W206A