Cedeño-Maldonado, Deborah J.

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    Spectral properties and population dynamics of the harmful dinoflagellate Cochlodinium polykrikoides (Margalef) in southwestern Puerto Rico
    (2008) Cedeño-Maldonado, Deborah J.; Armstrong, Roy A.; College of Arts and Sciences - Sciences; García Sais, Jorge R.; Gilbes Santaella, Fernando; Tomas, Carmelo R.; Aponte, Nilda E.; Department of Marine Sciences; Cortés Figueroa, José
    Recurrent blooms of the potentially ichthyotoxic dinoflagellate Cochlodinium polykrikoides were observed since 1958 at Bahía Fosforescente, a bioluminescent bay in southwestern Puerto Rico. Despite its potential deleterious effects, no previous efforts have been conducted to understand the population dynamics of this organism within this bay. This pioneer study assessed the role of climatological and physical-chemical parameters on the bloom dynamics of C. polykrikoides in Bahía Fosforescente. Monthly samplings took place at six stations from May 2002 to July 2003. Sea surface temperature, salinity, dissolved oxygen concentration and vertical attenuation coefficients of downwelling irradiance [Kd (PAR)] were determined at each station. Surface water samples were simultaneously collected for determinations of C. polykrikoides abundance, nutrients and chlorophyll a concentrations. Cochlodinium polykrikoides showed a strongly aggregational spatial distribution towards the northwest margin of the bay, where cell abundance ranged from 0 (undetectable) to 1.34 x 106 cells L-1. The temporal distribution of C. polykrikoides blooms at this site followed a similar tendency to that observed for the rainfall regime. Statistical analyses showed that both the spatial and temporal distributions of C. polykrikoides blooms in these waters are associated with high concentrations of nutrients, particularly phosphates. A combination of factors including the semi-isolated nature of the area, prevailing southeast winds, low tidal amplitude, processes promoting enhanced nutrient availability (i.e. precipitation, nutrient cycling and turbulent mixing), as well as adaptative strategies and specific life-form characteristics of C. polykrikoides, contribute to the recurrence of blooms of this species in the northwestern margin of the bay. Given the potential noxious effects of Cochlodinium polykrikoides, effective strategies to monitor the blooms of this species in Bahía Fosforescente are needed. The strong bio-optical signatures (striking brownish-red water discolorations) usually associated with these blooms make them suitable for optical detection. This work reports the first comprehensive characterization of the optical properties of C. polykrikoides, aimed to facilitate the accurate interpretation of the variations in ocean color observed during blooms of this species in natural waters. The feasibility of in situ hyperspectral remote sensing reflectance [Rrs ( )] data to discriminate and quantify C. polykrikoides blooms in Bahía Fosforescente was also evaluated. The pigment composition, and the apparent (Rrs) and inherent (absorption, scattering, backscattering and attenuation) optical properties of C. polykrikoides were characterized based on pure cultures. Field data, including measurements for determinations of Rrs ( ) and inherent optical properties, as well as water samples for determinations of C. polykrikoides abundance, chlorophyll a concentration and other biogeochemical parameters, were collected in Bahía Fosforescente during May 2002 to July 2003, and/or during May 2007. Cochlodinium polykrikoides showed the typical pigment profile and absorption properties of most dinoflagellates with strong backscattering signals at 589 and 620 nm, accounting for the characteristic brownish-red discoloration of its blooms. Results suggested the potential application of in situ hyperspectral Rrs data to differentiate the blooms of C. polykrikoides from that of some other bloom-forming species present in Bahía Fosforescente. This data also proved suitable for quantitative estimations of C. polykrikoides abundance under bloom conditions, through the application of chlorophyll-based semi-empirical algorithms.