Beaching and Natural Removal Dynamics of Pelagic Sargassum in a Fringing-Reef Lagoon

Beaching and Natural Removal Dynamics of Pelagic Sargassum in a Fringing-Reef Lagoon

Rutten, J. (TU Delft Environmental Fluid Mechanics; Universidad Nacional Autónoma de México)
Arriaga, Jaime (Universidad Nacional Autónoma de México)
Montoya, Leonardo D. (Universidad Nacional Autónoma de México)
Mariño-Tapia, Ismael J. (Universidad Nacional Autónoma de México)
Escalante-Mancera, Edgar (Universidad Nacional Autónoma de México)
Mendoza, E. Tonatiuh (Université de Rouen)
van Tussenbroek, Brigitta I. (Universidad Nacional Autónoma de México)
Appendini, Christian M. (Universidad Nacional Autónoma de México)

2021

Massive quantities of the pelagic brown macroalgae Sargassum spp. (sargassum) have been invading the Caribbean and West African shores since 2011, causing devastating effects on the coastal ecosystem and local economy. Little is known about sargassum beaching dynamics and the capacity of the coastal system to naturally remove beached sargassum. Here, we characterize the temporal variation in arriving and beached sargassum in a reef lagoon using a 5.2-year data set of hourly optical imagery, and identify the governing hydrometeorological conditions. Image classification reveals interannual variability in the start, duration, and intensity of the sargassum arrival season. Arrivals are associated with relatively low energy onshore directed winds and waves, and offshore abundance of sargassum. Furthermore, nearshore sargassum mat size is found to decrease with decreasing wave/wind energy. Once sargassum beaches, a berm of wrack is formed. Natural wrack removal was observed under elevated water levels and increased wave action. Three types of wrack removal were distinguished, depending on the water level (Formula presented.) with respect to the berm crest height (Formula presented.) and berm crest toe (Formula presented.) : gradual berm destruction with gaps developing in the seaward berm edge that grow larger with time (Type I; (Formula presented.)) and abrupt berm destruction with part of the wrack depositing on the upper beach (Type II; (Formula presented.)) or in the dunes (Type III; (Formula presented.)). Higher energy waves activate the reef circulation, which is suspected to flush part of the wrack out of the reef lagoon. We propose a conceptual model of nearshore sargassum dynamics in a reef lagoon system.

conceptual modeling
image analysis
reef lagoon
Sargassum spp.
swash
wrack berm

http://resolver.tudelft.nl/uuid:5894691b-c28f-49a8-879f-39bd3c15c03c

https://doi.org/10.1029/2021JC017636

2169-9275

Journal Of Geophysical Research-Oceans, 126 (11)

Institutional Repository

journal article

© 2021 J. Rutten, Jaime Arriaga, Leonardo D. Montoya, Ismael J. Mariño-Tapia, Edgar Escalante-Mancera, E. Tonatiuh Mendoza, Brigitta I. van Tussenbroek, Christian M. Appendini