Pantoja-Agreda, Fernando
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Publication Autotrophic picoplankton in tropical reservoirs: A hydrobiological approximation of their abundance, dynamics and diversity(2016) Pantoja-Agreda, Fernando; Otero-Morales, Ernesto; College of Arts and Sciences - Sciences; Santos Flores, Carlos J.; Pérez Alegría, Luis R.; González Lagoa, Juan G.; Department of Marine Sciences; Beaver, Linda W.In the present study, the abundance, dynamics and diversity of photosynthetic picoplankton were studied, with emphasis on the picocyanobacteria community, in two tropical reservoirs of Puerto Rico (Cerrillos and Lucchetti). Evolutionary changes in autotropic picoplankton over the limnological cycle, as well as environmental factors that control its population were analyzed. Autotrophic picoplankton cells were identified and quantified using flow cytometry and epifluorescence microscopy. These techniques allowed the identification of two populations of picoplanktonic organisms in the Cerrillos Reservoir. The picocyanobacteria (phycoerythrin-rich Synechococcus type) were dominant throughout the study, with maximum abundance of 6.6 × 104 cells mL-1. Picoeukaryotes were two orders of magnitude less abundant. The biomass of autotrophic picoplankton averaged of 0.56 mg L-1 and the contribution to the total chlorophyll-a was 11%. Chlorophyll-a concentration reflected the annual variation of autotrophic picoplankton. Its concentration was highest during the period of maximum stratification when solar radiation and nutrients increased. The picoplanktonic community was structured in accordance to thermal stratification, nutrient and light availability. Limnological conditions and seasonal dynamics of the picocyanobacteria community in two tropical reservoirs of different trophic status were compared. Environmental parameters that control the trophic status, abundance and biomass of picocyanobacteria of the reservoirs were analyzed and compared. The application of Carlson trophic state index showed the Cerrillos Reservoir as oligomesotrophic and Lucchetti as eutrophic. Flow cytometry techniques allowed clear differentiation between the picocyanobacteria and other groups of picoplankton in both systems. The results suggest differences in productivity and abundance of picocyanobacteria between reservoirs. The picocyanobacteria were present throughout the year in the two reservoirs, however their abundance and biomass were significantly higher in the oligo-mesotrophic reservoir than in the eutrophic system. The temporal and vertical dynamics of picocyanobacteria were compatible with the period of stratification and mixing, showing a unimodal pattern with a maximum peak of abundance during the summer, an important difference from the lakes in temperate latitudes which have two fluctuations in the picoplankton density during the annual cycle. Finally, 16S DNA samples from the two reservoirs with different trophic status were compared to determine the composition and diversity of the picocyanobacteria community through the environmental metagenomics technique. Greater part of the sequences grouped at the phylum Cyanobacteria of Cerrillos reservoir were dominated by Synechococcus, representing 29% of the total genera found, and with a few sequences of Cyanobium (5%). In the Lucchetti reservoir, the picocyanobacteria group comprised two genera: Synechococcus representing 2%, and Cyanobium with 0.1% of all genera of the microbial community. The picocyanobacteria community in the ecosystems studied was diverse and variable, and the strains were dispersed in the tree of polyphyletic origin. Most lineages were unique to a single ecosystem, however certain strains were present in both environments and their closest relatives are in different geographic regions and with contrasting limnological characteristics. It appears that the trophic state of the reservoirs studied significantly influences the diversity, composition and abundance of picocyanbacteria community. Picocyanobacteria exhibited high plasticity and can easily adapt to eutrophic conditions, however their community was best developed in oligomesotrophic environments.Publication Dinámica fisicoquímica y fitoplanctónica del embalse Guajataca, Puerto Rico(2006) Pantoja-Agreda, Fernando; Santos-Flores, Carlos J.; College of Arts and Sciences - Sciences; Martínez, Gustavo A.; Alfaro, Mónica; Department of Biology; Garcia, Jorge R.Artificial reservoirs, as well as the natural lakes, are threatened by the contamination, fertilization (nutrients) or the gradual eutrophication of their waters, with the subsequent loss of water quality. Therefore, during an evaluation of water availability, it is not only necessary to know water quantity, but also its physical, chemical and biological characteristics, and determine an optimal use. The purpose of the following investigation was to evaluate the physicochemical and phytoplanktonic characteristics of the Guajataca reservoir, with the purpose of knowing the spatial, temporal, and vertical dynamics of the water quality, the phytoplankton community present in the photic zone, the chlorophyll-a concentrations, and the trophic state of the reservoir. Monthly samplings were conducted during the day (09:00), from March 2004 until February 2005, in two sampling stations: the inlet and near the dam. Water transparency was determined by means of the Secchi disk. For each station, punctual profiles were made, at each meter, from the surface until the maximum depth, measuring: temperature (ºC), dissolved oxygen (O2 mg/l), pH [H+] and conductivity (μS/cm/25ºC). Within the photic zone of the two stations, samples were collected in the water column with a horizontal-type Van Dorn bottle with capacity of 2 liters. A liter was used for chemical analyses (total nitrogen, total phosphorus, turbidity, suspended solids), while the other one was used to study the phytoplankton. Algal biomass was estimated by means of the chlorophyll-a acetone extraction method. Phytoplankton was fixed in 4% formalin, concentrated by centrifugation to 100 ml, and later counted with the aid of a 1 ml Sedgwick-Rafter sedimentation chamber. Low transparency values were registered, probably due to the high content of organic and inorganic matter in the water. A stable thermal stratification was observed during most of the year, what allowed us to classify the reservoir as warm monomictic. Dissolved oxygen dissolved in the surface was relatively high; however, anoxic conditions were present in the hypolimnion during the whole period of study. The reservoir presented a low salinity, reflected in its low conductivity values. The water pH was slightly alkaline. Moderate nutrient concentrations were detected, especially of available phosphorus; therefore, when applying the Carlson index the reservoir was classified as mesotrophic. The relationship NT:PT, was higher than 9, indicating that phosphorus was the limiting nutrient in the reservoir. The values for suspended solids and turbidity were very low, so these parameters probably do not interfere with the productivity of the reservoir. Chlorophyll-a concentration reflected the annual variation in phytoplankton, its concentration being higher during summer, when solar radiation was also higher. The diversity and abundance of the phytoplankton was relatively low, as a total of 22 taxa, belonging to 20 genera and 6 classes, were registered. Euglenophyta was the dominant group along the year, contributing 43.9% of the total biomass. The dinoflagellates (Pyrrophyta) were the second most important group with 34.9% of the biomass, and Chlorophyta was the group with 10.71%. The phytoplanktonic community was structured (distributed), basically, in accordance to nutrient and light availability. Their behavior closely followed the climatic variations, particularly of the pluvial regime.