Seasonal changes in bioluminescence and dinoflagellate composition in a tropical bioluminescent bay, Bahía Fosforescente, La Parguera, Puerto Rico

• Bioluminescence levels were modulated by seasonal weather patterns.
• Shifts in the dinoflagellates composition were related to pluviosity.
• Blooms of Pyrodinium bahamense were influenced by terrestrial/watershed runoff.
• Ceratium furca was the numerically dominant dinoflagellate during the dry season.

Decreases in bioluminescence in Bahía Fosforescente have been associated with alternations between bioluminescent (Pyrodinium bahamense) and non-bioluminescent (Ceratium furca) dinoflagellates, two potentially harmful algal bloom species (HABs). Until now, these changes in bioluminescence have never been quantified, and their relationship with seasonality remains unclear. This study quantified the bioluminescence potential (BP) in the bay with a high spatiotemporal resolution to evaluate the status of this phenomenon and to determine the link between seasonality on the BP and dinoflagellate composition. Biweekly measurements, from August 2012 to July 2013, were conducted at six stations with an Underwater Bioluminescent Assessment Tool. The highest BP were observed during the wet season and were correlated (Spearman rank correlation: r = 0.89, n = 64, p < 0.001) with high cell densities of P. bahamense. Ceratium furca cell densities surpassed those of P. bahamense during the dry season, with concomitant reductions in the BP. The presence of other potentially bioluminescent dinoflagellates, such as Protoperidinium spp., during the latter season, with abundances higher than those of P. bahamense, suggests their contribution to the BP. It is suggested that environmental changes exerted by different meteorological conditions cause variations in the BP by modulating the dinoflagellate composition. Overall, a higher BP were observed in the northern area of the bay, suggesting that wind-driven currents promoted the accumulation of organisms in this region. This study underscores how weather, changes in the abundance of these two potentially HAB species, and the BP at Bahía Fosforescente are critically linked.