Soler Figueroa, Brenda M.

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    Deciphering bahía fosforescente: New approaches towards the understanding of this unique ecosystem
    (2015) Soler Figueroa, Brenda M.; Otero Morales, Ernesto; College of Arts and Sciences - Sciences; González Lagoa, Juan G.; Sastre Wirshing, Miguel P.; Armstrong, Roy; Corredor, Jorge; Department of Marine Sciences; Valdés Pizzini, Manuel
    For decades, bioluminescent bays and lagoons have intrigued and puzzled researchers due to the accumulation of high cell densities of the bioluminescent dinoflagellate Pyrodinium bahamense var. bahamense. In recent years the general community have been concerned due to the perceived decrease in the abundance of this species and consequently the bioluminescence in one of the most important bioluminescent bay in Puerto Rico, Bahía Fosforescente. Additionally, temporal fluctuations with a non-bioluminescent dinoflagellate, Ceratium furca var. hircus, have been reported through the years. The lack of extensive and systematic monitoring studies over the past fifty years has been one of the major barriers in deciphering what mechanisms drives the fluctuations of species in this bay. The main goal of this research was to identify the links between the environmental and meteorological conditions, and the patterns of variability of P. bahamense and C. furca and the bioluminescence levels (BL) at Bahía Fosforescente. The specific objectives of this study were to: 1) determine the daily, spatial and seasonal variability of P. bahamense and C. furca, 2) identify the environmental factors that may drive the spatial and temporal (short-term and seasonal) fluctuations of these species, 3) determine the BL in the bay and to help evaluate the putative declining bioluminescence trend, and 4) identify the role of different environmental conditions on the BL. To achieve this, studies were conducted with a high temporal and spatial resolution and various environmental variables were measured (e.g. nutrients, dissolved organic matter fluorescence-DOMFl, chlorophyll, turbidity, pH, dissolved oxygen, salinity, temperature, wind speed and direction, rainfall). Furthermore, BL were recorded in situ with an Underwater Bioluminescence Assessment Tool (UBAT) and historical P. bahamense records were used to estimate BL and determine trends in bioluminescence over the years. Results from each of the studies conducted in this dissertation underscore the importance of seasonal patterns as a significant factor modulating the abundance of P. bahamense and C. furca, and the BL at Bahía Fosforescente. Overall, seasonal changes in rainfall promoted variations in several environmental conditions, resulting in seasonal shifts in the abundance of each dinoflagellate in the system. Pyrodinium bahamense was the numerically dominant dinoflagellate during the wet season (average 2010: 7.8 x 104 ±1.4 x 104 cells L-1 standard error; average 2012: 6.8 x 103 ±6.5 x 102 cells L-1), reaching in some occasions a bloom condition (i.e. 105 cells L-1). In contrast, a shift towards high cell densities of C. furca was observed during the dry season (average 2011: 1.2 x 104 ±2.8 103 cells L-1; average 2013: 2.3 x 104 ±2.2 x 103 cells L-1). The high cell densities of P. bahamense during the wet season appeared to be related to nutrient inputs (November 2010 - PO4: 0.09-1.92 μmol L−1; N+N: 0.34-7.67 μmol L−1; NH4+: 2.9-29.4 μmol L−1) and probably other land/watershed derived materials after rainfall events, which are important for the growth and bloom formation of this species. In contrast, the capacity of C. furca to prey over other planktonic organisms was suggested to be important to maintain their populations during periods of low nutrients concentrations (March 2011 - PO4: 0.17– 0.5 μmol L−1; N+N: 0.2–1.23 μmol L−1; NH4+: 0.2-7.8 μmol L−1) and a minor runoff influence. A multivariate analysis (i.e. Distance based redundancy analysis-dbRDA) further confirmed that the seasonal variability in the dinoflagellates composition was better explained by salinity, DOMFl, pH and silicates, environmental variables that are strongly modulate by pluviosity. Even though changes in the daily and spatial distribution of these organisms were also observed, each dinoflagellate maintained their seasonal dominance. Winds and wind-derived currents were suggested to be important in the short-term spatial fluctuations of both dinoflagellates, with the highest concentrations mainly observed in the north, northeast and southeast regions of the bay. The seasonal shifts in the dinoflagellates composition were accompanied by changes in the BL. Maximum BL (average: 4.3 x 1011 ±4.9 x 1010 photons sec-1 L-1) characterized the wet season and were related to high concentrations of P. bahamense (average: 2.5 x 104 ±6.3 x 103 cells L-1). A two-fold reduction in BL relative to the wet season was observed during the dry season (average: 1.8 x 1011 ±3.1 x 1010 photons sec-1 L-1), but peaks in bioluminescence during this period were associated to the presence of heterotrophic bioluminescent dinoflagellates such as Protoperidinium spp. (average: 1.4 x 103 ±6.4 x 102 cells L-1). An evaluation of BL based on publications over the past fifty years showed variations, but not a declining trend, thus opposing the notion of dwindling BL at the bay and supporting the idea that as during past decades, the present conditions remain favorable for the accumulation of abundant populations of bioluminescent dinoflagellates. Summarizing, results from these studies provide substantial evidence to support that weather and the resultant environmental conditions are the principal factor controlling the alternating abundances of P. bahamense and C. furca at Bahía Fosforescente. This represents a scientific advance in understanding the population dynamics of two potentially harmful dinoflagellates species in Bahía Fosforescente. Results show the importance of high-frequency monitoring to understand better the role of environmental forcing on the populations densities of these fast fluctuating organisms, especially in the present times of global climate change. Thus, a well-established long-term monitoring program will provide the best science based management approach to guarantee the role of this environment as an important habitat for protected species and for tourism.