The Seasonal Impact of the Island Mass Effect on Coastal Biogeochemistry and Phytoplankton Assemblage: The Case of the Tropical and Volcanic Island of Guadeloupe (French West Indies).
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| Title: | The Seasonal Impact of the Island Mass Effect on Coastal Biogeochemistry and Phytoplankton Assemblage: The Case of the Tropical and Volcanic Island of Guadeloupe (French West Indies). |
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| Authors: | Moreau, Emma1 (AUTHOR) emoreau@ipgp.fr, Boye, Marie1 (AUTHOR), Pascal, Pierre‐Yves2 (AUTHOR), Messié, Monique3 (AUTHOR) |
| Source: | Journal of Geophysical Research. Oceans. Apr2026, Vol. 131 Issue 4, p1-30. 30p. |
| Subject Terms: | *Phytoplankton, *Nutrient cycles, *Marine ecology, *Coastal zone management, *Islands, Seasons |
| Geographic Terms: | Guadeloupe, Atlantic Ocean, Caribbean, Caribbean Sea |
| Abstract: | The Island Mass Effect (IME) in tropical regions remains understudied, despite its potential to fertilize oligotrophic oceanic gyres and impact on higher trophic levels. Guadeloupe provides an ideal case study of IME due to its diverse nutrient sources, dual exposure to the Caribbean Sea on the western coast and Atlantic Ocean on the eastern coast, and seasonality. Two field campaigns (June 2023, early wet season; January 2024, dry season) assessed macro‐ and micro‐nutrient sources including dissolved iron (DFe) and nitrate (NO3−) and their effects on phytoplankton biomass and composition. Key Fe sources included river outflows influenced by hydrothermalism, weathering, sediment resuspension on the Atlantic shelf, and Saharan dust deposition, with contributions varying seasonally and spatially. Nitrate inputs were mainly linked to anthropogenic river influence, with additional Sargassum contributions in June. On the Atlantic coast, seasonal shifts in DFe and NO3− fluxes, associated with river inputs in the dry season and dust and Sargassum in the wet season, did not lead to major changes in phytoplankton assemblages. Diatoms dominated the continental shelf, where NO3− and DFe were higher. Marked seasonal changes in phytoplankton occurred only on the Caribbean coast, associated with increased DFe and localized diatom blooms near river outflows in June, although cyanobacteria generally remained the dominant group on this coast. Overall, two distinct IMEs were identified, shaped by contrasting nutrient regimes on each coast. However, offshore nutrient export was minimal and cyanobacteria predominated in offshore oligotrophic waters. These findings enhanced our understanding of IME variability and island‐driven nutrient cycling in tropical systems. Plain Language Summary: Tropical islands can fertilize surrounding marine waters through a process known as the Island Mass Effect (IME), creating biological oases in tropical ocean deserts. However, this effect remains poorly understood, especially in these oceanic regions where nutrients are scarce. This study focused on the Guadeloupe Island in the Caribbean, exposed to both the Atlantic Ocean and the Caribbean Sea, and influenced by natural and human‐related nutrient sources. We conducted two field campaigns, one during the dry season (January) and one at the start of the wet season (June), to measure nutrient inputs to coastal waters and their impact on microscopic marine plants called phytoplankton. We found that iron and nitrate, two essential nutrients, came from rivers, atmospheric dust, sediment, and stranded seaweed (Sargassum), but their inputs changed with location and season. Despite this variability, large phytoplankton called diatoms consistently dominated near the Atlantic coast, where nutrients were abundant, while smaller cyanobacteria thrived offshore, in nutrient‐poor waters. Overall, the IME was detected on both coasts of Guadeloupe but remained close to shore. This study shows how geography and seasonality together shape nutrient supply and marine life around tropical islands. Key Points: Sources and fluxes of Fe and macronutrients were different from the east and west coasts of southern Guadeloupe and varied seasonallyHigh nutrient inputs favored diatoms on the Atlantic coast, while low inputs on the Caribbean coast favored cyanobacteria and diazotrophsTwo distinct island mass effects were observed in the south of Basse‐Terre Island, but they were only limited to the coast [ABSTRACT FROM AUTHOR] |
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| Database: | GreenFILE |
| Abstract: | The Island Mass Effect (IME) in tropical regions remains understudied, despite its potential to fertilize oligotrophic oceanic gyres and impact on higher trophic levels. Guadeloupe provides an ideal case study of IME due to its diverse nutrient sources, dual exposure to the Caribbean Sea on the western coast and Atlantic Ocean on the eastern coast, and seasonality. Two field campaigns (June 2023, early wet season; January 2024, dry season) assessed macro‐ and micro‐nutrient sources including dissolved iron (DFe) and nitrate (NO3−) and their effects on phytoplankton biomass and composition. Key Fe sources included river outflows influenced by hydrothermalism, weathering, sediment resuspension on the Atlantic shelf, and Saharan dust deposition, with contributions varying seasonally and spatially. Nitrate inputs were mainly linked to anthropogenic river influence, with additional Sargassum contributions in June. On the Atlantic coast, seasonal shifts in DFe and NO3− fluxes, associated with river inputs in the dry season and dust and Sargassum in the wet season, did not lead to major changes in phytoplankton assemblages. Diatoms dominated the continental shelf, where NO3− and DFe were higher. Marked seasonal changes in phytoplankton occurred only on the Caribbean coast, associated with increased DFe and localized diatom blooms near river outflows in June, although cyanobacteria generally remained the dominant group on this coast. Overall, two distinct IMEs were identified, shaped by contrasting nutrient regimes on each coast. However, offshore nutrient export was minimal and cyanobacteria predominated in offshore oligotrophic waters. These findings enhanced our understanding of IME variability and island‐driven nutrient cycling in tropical systems. Plain Language Summary: Tropical islands can fertilize surrounding marine waters through a process known as the Island Mass Effect (IME), creating biological oases in tropical ocean deserts. However, this effect remains poorly understood, especially in these oceanic regions where nutrients are scarce. This study focused on the Guadeloupe Island in the Caribbean, exposed to both the Atlantic Ocean and the Caribbean Sea, and influenced by natural and human‐related nutrient sources. We conducted two field campaigns, one during the dry season (January) and one at the start of the wet season (June), to measure nutrient inputs to coastal waters and their impact on microscopic marine plants called phytoplankton. We found that iron and nitrate, two essential nutrients, came from rivers, atmospheric dust, sediment, and stranded seaweed (Sargassum), but their inputs changed with location and season. Despite this variability, large phytoplankton called diatoms consistently dominated near the Atlantic coast, where nutrients were abundant, while smaller cyanobacteria thrived offshore, in nutrient‐poor waters. Overall, the IME was detected on both coasts of Guadeloupe but remained close to shore. This study shows how geography and seasonality together shape nutrient supply and marine life around tropical islands. Key Points: Sources and fluxes of Fe and macronutrients were different from the east and west coasts of southern Guadeloupe and varied seasonallyHigh nutrient inputs favored diatoms on the Atlantic coast, while low inputs on the Caribbean coast favored cyanobacteria and diazotrophsTwo distinct island mass effects were observed in the south of Basse‐Terre Island, but they were only limited to the coast [ABSTRACT FROM AUTHOR] |
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| ISSN: | 21699275 |
| DOI: | 10.1029/2025JC023236 |
