Journal of Environmental Management 252 (2019) 109650 Available online 7 October 2019 0301-4797/© 2019 Elsevier Ltd. All rights reserved. Research article Motile macrofauna associated with pelagic Sargassum in a Mexican reef lagoon Luz Ver� onica Monroy-Vel� azquez a , Rosa Elisa Rodríguez-Martínez b, * , Brigitta I. van Tussenbroek b , Teresa Aguiar a , Vivianne Solís-Weiss b , Patricia Briones-Fourz� an b a Trasatl� antico 8A, Manzana 27, Supermanzana 18. Villas Morelos I, Puerto Morelos, Quintana Roo, Mexico b Unidad Acad� emica de Sistemas Arrecifales, Instituto de Ciencias Del Mar y Limnología, Universidad Nacional Aut� onoma de M� exico, Puerto Morelos, Quintana Roo, Mexico A R T I C L E INFO Keywords: Pelagic Sargassum Motile macrofauna Diversity Abundance Mexico ABSTRACT Buildup of decaying pelagic Sargassum on the beaches and coasts of the Mexican Caribbean during the massive arrivals of 2015 and 2018 had detrimental impacts on the environment and tourist industry. To avoid ecological and economic impacts from massive beaching of Sargassum, it would be better to remove the pelagic algal masses while still at sea. However, out at sea, pelagic Sargassum rafts constitute an ecosystem with a diversifed asso- ciated fauna and their removal could impact this fauna. We conducted a survey on the motile macrofauna associated to pelagic Sargassum rafts in the Puerto Morelos reef lagoon, Mexican Caribbean. Pelagic Sargassum was sampled with nets at 2 m, 50 m and 500 m from shore, at four sites during the months of September, October and November 2018. The 108 samples contained 10,296 individuals belonging to 32 taxa distributed over eight Phyla. The main phyla were Arthropoda (48%), Annelida (41%) and Mollusca (15%). Fish abundance was low (10 individuals) with only fve species, of which three are typically associated with Sargassum rafts and two are common in seagrass meadows and coral reefs. Species composition and abundance of motile macrofauna varied with month and zone; the nearshore zone had the lowest abundance but there was no difference in the abun- dance of the fauna associated with rafts 50 or 500 m offshore. Three of the four most abundant species (together accounting for 89% of the individuals) were species typically associated with pelagic Sargassum, and the fourth was an amphipod that was only registered once near shore. Although more studies over larger time and spatial scales are required, these results suggest that the removal of pelagic Sargassum within the reef lagoon may not have a signifcant effect on local populations of motile macrofauna. 1. Introduction In 2014, pelagic Sargassum (Sargassum fuitans and S. natans) started to arrive in unusually large quantities to the Mexican Caribbean coast, reaching a peak in September 2015, when the Puerto Morelos Reef National Park (PMRNP) received ~2,360 m 3 algae km 1 coast (Rodrí- guez-Martínez et al., 2016). After a decrease during 2016 and 2017, the infux of Sargassum increased again in 2018, peaking in May at 8, 793 m 3 km 1 (CI: 8,848 m 3 km 1 ) (unpublished data). Leachates and particulate organic matter from the beached decaying algal masses colored the usually clear near-shore waters murky brown, causing Sar- gassum-brown-tides that provoked mortality of nearshore seagrasses and fauna, and deterioration of the water quality of coastal ecosystems (Van Tussenbroek et al., 2017). Since 2014, the management strategy of the government and hotel owners has been the removal of Sargassum from the beach, either manually or with machines. This strategy, however, was insuffcient to remove all beached Sargassum in a timely manner and, when employed inadequately, resulted in beach erosion, as sand was removed with the beached algal masses (Rodríguez-Martínez et al., 2016) or destruction of sea turtle nests and hatchlings (Maurer et al., 2015). In mid-2018, the Mexican government began placing interception barriers in coral reef lagoons to prevent the Sargassum for reaching the shore. This strategy, however, did not solve the ecological and economic problems because the algae were not removed from the barriers, so they were either transported to nearby areas by wind and currents, or died and sank in the coral reef lagoon. Currently, new techniques are being proposed to extract the Sargassum trapped on the interception barriers * Corresponding author. E-mail address: rosaer@cmarl.unam.mx (R.E. Rodríguez-Martínez). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: http://www.elsevier.com/locate/jenvman https://doi.org/10.1016/j.jenvman.2019.109650 Received 14 March 2019; Received in revised form 25 September 2019; Accepted 28 September 2019