ABSTRACT
Se estudió la variación espacial y temporal del fitoplancton en la Laguna de Unare desde noviembre 1988 hasta julio 1989. Las muestras de agua superficial se fijaron con formalina (10 por ciento) neutralizada con carbonato de sodio, para determinar la abundancia microalgal según el método de Utermõhl. Se encontró un aumento progresivo de la abundancia fitoplanctónica durante el período de estudio. Los valores promedios mensuales mínimos y máximos (8,63 x 102 y 4,53 x 105 cel. ml-1) se registraron en noviembre 1988 y junio 1989, respectivamente. Las diatomeas dominaron hacia el este de la Laguna (>50 por ciento del total de individuos) favorecidas por la penetración de agua marina y continental en esta zona. El resto de la laguna estuvo dominado por cianobacterias (>80 por ciento). Se encontraron diferencias altamente significativas (Fs = 28,736, p<0,001) con relación a la distribución temporal de los principales grupos de microalgas (cianobacterias, diatomeas, euglenofitas, dinoflagelados). Al inicio del estudio se observó la mayor variabilidad con relación a los grupos fitoplanctónicos, predominando las diatomeas. Estas fueron sustituidas por las cianobacterias que dominaron el fitoplancton hasta el final del período de estudio. Es importante mantener la conexión de la laguna con las aguas adyacentes para favorecer el desarrollo del fitoplancton y por ende la productividad primaria de este cuerpo de agua, la cual sustenta el resto de las comunidades del sistema.
Spatial and temporal changes in phytoplankton from Unare Lagoon were studied from November 1988 until July 1989. Water samples were fixed with neutral formaldehyde (10 percent) to determine microalgal abundance following Utermõhl´s method. Abundance increased continuously throughout the study period. The minimum and maximum average values (8.63 X 102 and 4.53 X 105 cell. ml-1) were measured in November 1988 and June 1989, respectively. Diatoms were the dominant group on the eastern side of the lagoon (>50 percent of the total number of organisms) and were favored by continental and marine water exchange. The rest of the lagoon was dominated by cyanobacteria (>80 percent of the total number of organisms). Highly significant temporal differences (Fs = 28.736, p<0.001) with respect to the distribution of the microalgal groups (cyanobacteria, diatoms, euglenophytas and dinoflagellates) were registered. High group variability occurred at the beginning of the study period when diatoms were dominant. It is important to maintain the connection between the lagoon and the adjacent waters in order to maintain phytoplankton growth and primary productivity which sustains the rest of the communities in this water body.
Subject(s)
Cyanobacteria/chemistry , Diatoms/chemistry , Eukaryota , Coastal Lagoon/analysis , Venezuela , Marine BiologyABSTRACT
Se describen 9 especies de diatomeas (Bacillariophyta) pertenecientes a las Subclase Thalassiosirophycidae y Coscinodiscophycidae. Las muestras de agua de las lagunas de Unare y Píritu (Venezuela) fueron colectadas entre Noviembre 1988 y Julio 1989. Los especimenes fijados con formol neutralizado y montados con Bálsamo de Canadá, se examinaron mediante microscopia de contraste de fase. Las especies estudiadas fueron: Thalassiosira eccentrica (Ehrenberg) Lange et al., T. leptopus (Grun) Hasle & Fryxell, Cyclotella menenghianiana (Kützing) Wood, C. striata (Kützing) Grunow in Cleve et Grunow, Coscinodiscus asteromphallus (Ehrenberg) Makarova, C. janischi (Schmidt) Wood, C. marginatus (Ehrenberg) Navarro, C. subtilis (Ehrenberg) var. normanii (Gregory) Van Heurck, Actinocyclus octonarius (Ehrenberg) Navarro.
Subject(s)
Coasts/analysis , Diatoms/classification , Ecology , Ecosystem , Coastal Lagoon/analysisABSTRACT
Biovolume variation of twelve centric diatom species from eight natural habitats of the northeastem continental shelf of Venezuela were analyzed. Also, the morphometric variable that exerts the greatest influence on the biovolume was determined. Samples were collected with a net (mesh 36 microns), or with a Niskin bottle (5 l) and fixed with neutralized formaldehyde (4 per cent). Water temperature and salinity were measured. The species studied were: Detonula sp., Skeletonema costatum, Lauderia annulata, Pseudoguinardia recta, Cerataulina pelagica, Helicotheca tamesis, Rhizosolenia styliformis, Proboscia alata, Guinardia flaccida, G. striata, Dactyliosolen fragilissimus y Leptocylindrus danicus. Forty individuals of each species from each locality were isolated and measured with a Leitz Wetzlar binocular microscope with an ocular micrometer, magnified 400X. A one-way ANOVA showed the existence of highly significant differences (p < 0.001) in the biovolume of the species regarded with its locality. These differences could be due to: (a) temporal differences in sample collection: (b) the existence of populations in different phases of their vital cycles; (c) genetic differences; (d) and differences in the physical-chemical environment at each locality. The diameter was the morphometric variable exhibiting the largest positive correlation (r > or = 0.77, p < 0.001) with biovolume for all species, except for H. tamesis. In the latter, the apical axis (or side) exhibited the best correlation with biovolume (r = 0.94, p < 0.001). The high correlation between the diameter and/or the apical axis with the biovolumen suggests that the latter could be predicted from these morphometric variables with great reliability in these species.
Subject(s)
Biometry , Diatoms , Sodium Chloride , Temperature , Genetic Variation , Population Density , Seasons , VenezuelaABSTRACT
RESUMEN: La flora diatomológica de las Lagunas de Unare y Píritu, Venezuela, comprende organismos dulceacuícolas, estuarinos y marinos. En este trabajo se describen quince (15) especies de diatomeas (Bacillariophyta) pertenecientes a la subclase Bacillariophycidae. Las muestras de agua de las lagunas de Unare y Píritu (Venezuela), fueron colectadas entre noviembre 1988 y julio 1989. Estas fueron fijadas con formol neutro (10 %) y se examinaron mediante microscopía de contraste de fase. Las especies estudiadas fueron: Dictyoneis marginata (Lewis) Cleve, Cymbella affinis (Kützing) Cleve, Cymbella sp., Achnanthes brevipes var. intermedia (Kützing) Cleve, Lyrella irroratoides (Hustedt) Mann, Navicula carinifera (Grunow) Peragallo, Navicula liber (W. Smith) Peragallo, Navicula vacillans (Schmidt) Peragallo, Navicula sp., Amphora crassa var. campechiana Grunow, Amphora decussata Grunow, Caloneis powelli (Lewis) Cholnoky, Tryblionella acuta (Cleve) Mann in Round et al., Tryblionella apiculata Gregory, Surirella febigerii Lewis.