Leachate effects of pelagic Sargassum spp. on larval swimming behavior of the coral Acropora palmata

Abstract

An emerging disturbance for Caribbean reefs is the massive arrival of pelagic Sargassum, which deteriorates water quality due to the production of leachates. The highest arrivals of Sargassum took place when broadcasting corals spawned. We experimentally determined the effect of Sargassum leachates on swimming behavior of Acropora palmata larvae through five treatments (control, stain (simulating 100% leachate color), and 25%, 50% and 100% Sargassum leachate concentrations) during 30 min (10 min of videos and 20 min of post-observations). In the videos, larvae with leachates reduced swimming speed, were positively geotactic, the percentage of individuals that swam in a spiral pattern increased, and most behavioral displacements occurred at lower frequencies than larvae without leachates. Moreover, symptomatic spiral behavior was higher in the presence of leachates, suggesting that this behavior may be an effect of pollution. During post-observations, most larvae with leachates were motionless. This is the first time that Sargassum leachates have been documented modifying larval swimming behavior, which may reduce larval dispersion and genetic diversity. We suggest that a future evaluation of the effects of leachates at lower concentrations and over longer periods of exposure is needed. The resilience of corals may be compromised if Sargassum arrivals become frequent events. Globally, coral reefs are being degraded by several stressors (e.g., climate change, bleaching, overfishing and emergent diseases 1-5), especially those in the Caribbean 6. An emerging stressor for Caribbean reefs is the massive arrival of two pelagic macroalgal species: Sargassum fluitans and S. natans. Pelagic Sargassum drifts on the surface of the sea, providing an important habitat for a great diversity of organisms 7,8. The presence of a high biomass of pelagic Sargassum spp. began in 2011 in the central Atlantic Ocean and the Caribbean Sea 9. However, Sargassum influx in the Mexican Caribbean has only occurred since 2014, with the highest peaks reported in September 2015 (~2360 m 3 algae km −1) and May 2018 (8793 m 3 algae km −1) 10. Unfortunately, the massive arrival of pelagic Sargassum is predicted to become a recurring disturbance 9. Decomposition of the accumulated biomass of pelagic Sargassum in the coastline produces leachates that reduce dissolved oxygen (DO) and pH, and increase turbidity and temperature, deteriorating water quality 10,11. These leachates create conditions similar to eutrophication and may contain heavy metals such as mercury (Hg) and methylmercury (MeHg) 12 , methane 13 , lactic acid 14 , and high concentrations of ammonium and phosphorus 10. In the Mexican Caribbean, many coral species inhabit lagoon reefs (i.e., near to the coastline) where leachates of pelagic Sargassum have been observed and dispersed from the coastline toward the reef crest. In this context, some coral species became stressed and presented partial or total mortality due to the presence and decomposition of Sargassum 11 (Fig. 1). Brooding a...

Opportunities for valorisation of pelagic Sargassum in the Dutch Caribbean

“…SBT can also affect trophic dynamics in coastal communities, as was recently shown for the sea urchin Diadema antillarum that changed diet when the source of available organic matter was modified due to large inputs of decaying Sargassum [42]. In addition, SBT can alter animal behaviour, as was shown by Antonio-Martínez [43], who found effects that the swimming behaviour of coral larvae was modified by pelagic Sargassum leachate, which may reduce larval dispersion and genetic diversity.…”

Aquatic ecosystems science using an imaging spectrometer

“…109,110 Massive Sargassum beachings are now considered HABs 111 due to significant and persistent light attenuation and habitat displacement of benthic ecosystems such as coral reefs and seagrass beds. 112,113 Impacts in coastal environments from Sargassum accumulation include fish mortality, altered coastal and wetland biochemistry, release of toxic products due to decomposition, and beach accumulations that impact sea turtles and other important species in coastal and marine reserves. 114 Satellite remote sensing data have been used to identify and monitor Sargassum distribution throughout the Greater Caribbean and Atlantic regions using a simple ocean color index, namely the Floating Algae Index (FAI).…”

The Impact of Sargassum Inundations on the Turks and Caicos Islands

“…It is likely these died due to hypoxia due to the deterioration in-water quality. Sargassum leachate has been found to reduce dispersal ability of elkhorn coral (Acropora palmata) larvae [46], an endangered coral species that is present on the coral reefs in front of East Bay Beach and Coast Guard.…”