Gerardo Umaña-Villalobos | Universidad de Costa Rica (original) (raw)

Papers by Gerardo Umaña-Villalobos

Revista De Biologia Tropical, 2006

Yearly cycle of stratification and circulation at the Arenal Reservoir, Costa Rica. The behavior ... more Yearly cycle of stratification and circulation at the Arenal Reservoir, Costa Rica. The behavior of the water column of Arenal Reservoir, a tropical reservoir in Costa Rica, is analyzed based on temperature and dissolved oxygen data gathered on a monthly to bimonthly basis between 1986 and 1992. The depth profiles of temperature at Arenal Reservoir show the typical asymmetry of reservoirs, with a greater stratification in its deeper part near the dam, even though the main outflow is located at its head at the northwest end instead of the dam. A comparison of sampling stations at both ends show a deeper circulation pattern at the northern end. This coincides with other reports of a tilted structure of the thermal isopleth pattern in front of the water outlet. The dissolved oxygen showed some degree of anoxia at the bottom during part of the year, mainly from May until October. This was caused by the decomposition of the organic matter accumulated at the bottom at the time, mainly as remains of the vegetation from the former lagoon that was not removed before flooding. The stratification is clearly seasonal, occurring during the rainy season (April to October), specially in the deeper zones of the reservoir.

Revista De Biologia Tropical, Jul 20, 2016

The detailed response of tropical lake phytoplankton to weather variations has been little studie... more The detailed response of tropical lake phytoplankton to weather variations has been little studied, but it seems that composition varies in response to rain and wind variability over the course of the year. In order to gather more evidence on this variation, the weekly variability of phytoplankton composition was studied in Lake Bonilla, a low land (380 masl) 30 m deep tropical lake, from April 2010 to May 2011. Temperature variation at several depths was recorded automatically, and measurements of dissolved oxygen, water transparency, and nutrients were performed several times during the study period. The lake showed a warm monomictic pattern, with deep mixing occurring during the hemispherical winter, especially after a heavy rain period in December 2010. Phytoplankton was dominated by a few species: a colonial Cyanobacteria (Aphanocapsa sp., functional group F) and two colonial Chlorococcaceae (Botryococcus braunii and Eutetramorus tetrasporus, both in the functional group K). Their relative dominance shifted throughout the year, following changes in water column conditions in response to weather variations. Although changes in main functional groups indicate a shift in resource availability rather than energy, it was clear that attention should also be given to particular species adaptations beyond those used for establishing functional groups.

The literature on species diversity of phytoplankton of tropical lakes is scarce, and for the mai... more The literature on species diversity of phytoplankton of tropical lakes is scarce, and for the main part comes from studies of the big lakes in Africa, or deep lakes in South America, leaving a gap in the information about small shallow tropical lakes. In the present work the phytoplankton species composition and diversity of 27 shallow lakes and ponds in Costa Rica (Central America) was studied. The species composition was found to agree with other studies of tropical lakes, with a dominance of Chlorophyta, Cyanophyta, or in some cases Bacillariophyta or Euglenophyta; and a general paucity of Chrysophyta and Cryptophyta.

Verhandlungen, Oct 1, 2002

Revista De Biologia Tropical, Jul 18, 2010

Revista De Biologia Tropical, Apr 1, 2014

Despite the fact that little is known about the consequences of hydropower production in tropical... more Despite the fact that little is known about the consequences of hydropower production in tropical areas, many large dams (>15m high) are currently under construction or consideration in the tropics. We researched the effects of large hydroelectric dams on aquatic macroinvertebrate assemblages in two Costa Rican rivers. We measured physicochemical characteristics and sampled aquatic macroinvertebrates from March 2003 to March 2004 in two dammed rivers, Peñas Blancas and San Lorenzo, as well as in the undammed Chachagua River. Sites above and below the dam had differences in their physicochemical variables, with wide variation and extreme values in variables measured below the dam in the San Lorenzo River. Sites below the dams had reduced water discharges, velocities, and depths when compared with sites above the dams, as well as higher temperatures and conductivity. Sites above dams were dominated by collector-gatherer-scrapers and habitat groups dominated by swimmer-clingers, while sites below dams had a more even representation of groups. In contrast, a comparison between two sites at different elevation in the undammed river maintained a similar assemblage composition. Tributaries might facilitate macroinvertebrate recovery above the turbine house, but the assemblage below the turbine house resembled the one below the dam. A massive sediment release event from the dam decreased the abundance per sample and macroinvertebrate taxa below the dam in the Peñas Blancas River. Our study illustrates the effects of hydropower production on neotropical rivers, highlighting the importance of using multiple measures of macroinvertebrate assemblage structure for assessing this type of environmental impact.

Revista De Biologia Tropical, 2008

El Embalse Angostura fue terminado de inundar en el 2000, construido mediante una represa de conc... more El Embalse Angostura fue terminado de inundar en el 2000, construido mediante una represa de concreto en el río Reventazón, como parte de un sistema en cascada de represas para la generación de energía hidroeléctrica. Con el objetivo de estudiar sus características limnológicas se realizó una serie de mediciones básicas en el 2001. Se observó que el embalse se encuentra estratificado hacia su parte más profunda, y la termoclina inclinada, haciéndose más profunda cerca de la represa. Aunque hubo una disminución del oxígeno disuelto con la profundidad, el hipolimnion no estuvo anóxico en el momento de la visita (Febrero 2001). La conductividad mostró una capa de valores más altos que se inicia cerca de la entrada del agua del río Tuis y se hunde hacia la represa; esta capa también mostró una mayor turbidez que las aguas superficiales enfrente a la represa pero con menor clorofila. Esto indica que el flujo principal se mueve hacia la toma de aguas para la planta hidroeléctrica. Un segundo afluente proveniente del río Turrialba estaba temporalmente cerrado, el cual puede hacer variar este patrón de circulación encontrado.

Revista De Biologia Tropical, 2008

Benthic invertebrates of Cote Lake, Costa Rica. The benthic community of Lake Cote, a natural lak... more Benthic invertebrates of Cote Lake, Costa Rica. The benthic community of Lake Cote, a natural lake in Northwestern Costa Rica, was surveyed in two occasions (1/June and 28/August/2003) in order to determine possible gradients in community composition with depth, following a shore-center transect. In each opportunity, sediment samples were collected with an Ekman dredge at 10 stations ranging in depth from 1 to 12m. Two subsamples (500µm mesh screen), one to study macrofauna and the other to analize sediment characteristics, were collected from each dredge. Meiofauna (between 500 and 63µm mesh screen) was collected with a core (area: 5.3 cm 2 , depth: 4cm) in the dredge sediment (only in the second visit). Benthic fauna subsamples were preserved in 5% buffered formalin in freshwater stained with Rose Bengal. There was a decrease in temperature with depth, and oxygen levels dropped below 1mg/l below 8m depth. The percent of silt and clay increased with depth, with some exceptions and the center of the lake. A total species richness of 13 taxa was found, including macrofauna (8 taxa) and meiofauna (7 taxa). Lake Cote resembles other tropical lakes in the presence of oligochaete worms and the dipterans Procladius (Chironomidae), Tanytarsus (Chironomidae) and Chaoborus (Chaoboridae). The meiofauna also included some Coleoptera and Acari. Benthic composition was associated with habitat parameters such as substrate granulometry, dissolved oxygen and depth. The low abundance of chironomids may reflect a poor nutrient accumulation on the bottom, caused by the continuous mixing of the water body. Chironomids of the macrofauna were found from the shore to 9m depth. On the other hand, meiofaunal stages were found at less that 9m of depth. Chaoborus larvae were found between 8 and 11m depth, caused by diurnal migration to the deeper zone in the lake. Chaoborus and fish species probably predate on oligochaetes and maintain the low abundance of these worms. The total abundance of the macrofauna reached a maximum at a mid depth, with diversity being greater at shallower depths. The mean density of the macrofauna was 326 individuals per m 2 , and the mean density of the meiofauna was lower, with two organisms per 10cm 2. The distribution of the fauna was clumped, following a gradient with depth.

Lago Bonilla, located 370 m above sea level on the Eastem slopes of Volean Turrialba, Costa Rica,... more Lago Bonilla, located 370 m above sea level on the Eastem slopes of Volean Turrialba, Costa Rica, was vis ited four times during 1990-1991. Basic Iimonologica1 data were recorded in each visit. lt is oligomietic, mixing dur ing the coldest and windiest months sometime between Nov. and Feb, and eutrophic, with low Secchi transparencies, Cyanobacteria dominance and almost permanent anoxic conditions in the deepest portion. A shift in N to P ratio was observed, indicating a variation in the limiting factor during the year; N beco mes Iimiting during the driest months probably as a result of a lower input from the catchment due to lower runoff, coupled with a higher P input from the sediments during deep mixing periods. However, Iimitation by P was probably stronger than N when it occurred, according lo the N/P ralios. Phytoplankton in epilimnetic waters comprised 58 algal species, and was dominated by Cyanobacteria and Chlorophyta. Only a few species dominated Ihe community, mainly Cylindrospermum mínímum. and Tetraedron mínimum, rendering low diversity values. Zooplankton was also poor: only seven species were found. There were some indications of vertical migrations of sorne zooplankters.

La Laguna del Barva se visito una vez durante la epoca seca de 1988 y se estudio su morfometria y... more La Laguna del Barva se visito una vez durante la epoca seca de 1988 y se estudio su morfometria y limnologia basica. El area superficial es de 9x 103 m2, y la profundidadmaxima es de 7.7 m. La temperatura mostro una disminucion hacia el fondo, variando de 17°C en la superficie a 14°C enel fondo. El oxigeno disuelto mostro tambien una ligera curva de tipo clinogrado. Solamente 19 especies de algas fitoplanctonicas fueron observadas, con una densidad total que vario entre 1.25xl04 y 1.93xl04 celulas por mI. El alto grado de similitud taxonomica entre las diferentes profundidades y la distribucion vertical casi' uniforme delfitoplancton indican que en la laguna ocurren comunmente periodos de mezcla que alcanzan capas profundas. Sin embargo, aun estando localizada a bastante altura, la laguna no reune las caracteristicas de una laguna de paramo tipicamentepolimictica. La debil estratificacion encontrada no se puede explicar si se supone la existencia de periodos decirculacion total cada noche debido a la baja concentracion de oxigeno en el fondo.

Revista de Biologia Tropical, 1990

... Abstract. The Laguna del Barva was visited once during the 1988 dryseason. ... Basic limnolog... more ... Abstract. The Laguna del Barva was visited once during the 1988 dryseason. ... Basic limnology of fifty-one lakes in Costa Rica. Kurt A Haberyan, Sally P Horn, Gerardo Umaña in Revista de Biologia Tropical (2003). Save reference to library · Related research 5 readers. ...

Revista de Biología Tropical.

Universidad de Costa Rica, CIMAR y Escuela de Biología, Ciudad Universitaria, CR E-mail: gumana@c... more Universidad de Costa Rica, CIMAR y Escuela de Biología, Ciudad Universitaria, CR E-mail: gumana@cariari.ucr.ac.cr. ... The planktonic community of Laguna Hule, Costa Rica. La comunidad planctónica de la Laguna Hule, Costa Rica. ... MICROORGANISMS; PLANTS; ...

Revista de Biología …

Universidad Nacional Autónoma de Nicaragua, Centro para la Investigación en Recursos Acuáticos de... more Universidad Nacional Autónoma de Nicaragua, Centro para la Investigación en Recursos Acuáticos de Nicaragua, Departamento de Hidrología, Managua, NI E-mail: gumana@biologia.ucr.ac.cr E-mail: hchavarr@cariari.ucr.ac.cr. ... Comparación del fitoplancton en dos bahías del ...

Hydrobiologia, Sep 8, 2020

Long-term plankton studies in neotropical lakes are scarce. Here we studied plankton composition ... more Long-term plankton studies in neotropical lakes are scarce. Here we studied plankton composition in Lake Cote, Costa Rica, twice per year from 2002 to 2018, to monitor changes after it was modified as a reservoir for hydroelectricity in 2003. Plankton variation was examined for a long-term trend and its relationship with basic limnological characteristics of the lake. Phytoplankton was sampled from the surface and with a depth-integrating sampler. Zooplankton was caught with vertical hauls, at the same station at the middle of the lake. A total of 138 taxa of microalgae occurred, most from Chlorophyta and Cyanobacteria, to which dominant species belonged; Aulacoseira granulata was also ubiquitous. A shift in dominance occurred, from Cosmarium asphaerosporum to Aphanothece cf. microscopica, and Aphanocapsa cf. delicatissima. Zooplankton included 23 species of Cladocera, Copepoda, Rotifera, and Chaoborus. Most abundant were Keratella americana, Eubosmina tubicen, and Cyclopoida; Daphnia laevis became abundant after 2007 while E. tubicen declined. There was little correspondence between both planktonic components. Plankton composition was typical of a mesotrophic to eutrophic shallow lake, but changes indicated an increase in stratification, and can be attributed to combined effects of recent warming and outflow management for hydropower production.

Revista De Biologia Tropical, Nov 6, 2019

In tropical lakes, seasonal changes in plankton dynamics are minimal and irregular, since climati... more In tropical lakes, seasonal changes in plankton dynamics are minimal and irregular, since climatic conditions are fairly stable throughout the year, in most cases only long-term studies allow observing patterns in the dynamics of the plankton. Lake Río Cuarto is a maar-type meromic lake located in the plains of Northern Costa Rica, in the past there have been no limnological studies more than a year of sampling, in this work we present data on the composition of phytoplankton and zooplankton over four years, from 2013 to 2017, with the aim of analyzing changes in the plankton community in a longer period, associated with environmental variables. Phytoplankton was studied from subsurface samples, preserved in Lugol's solution and zooplankton from 20 m vertical hawls of a 64 µm mesh net, and preserved with formaline and later transferred to 95 % ethanol. Phytoplankton composition included 54 taxa, most of them were Chlorophyta, followed by Cyanobacteria and Bacillariophyta. The most abundant were: Synechococcus spp., Aphanocapsa sp. Coenochloris fotii, Chlorella sp. and Discostella stelligera. Total phytoplankton decreased from 2013 to 2017, mainly due to a decrease in Cyanobacteria. Zooplankton comprised 14 taxa, 5 cladocerans, 4 copepods, 1 diptera and 4 rotifers. The most abundant were: Keratella americana, Brachionus falcatus, Eubosmina tubicen and Arctodiaptomus dorsalis. There was a substitution of dominant species through time, at first (2013-2014) K. americana and E. tubicen alternated in dominance, and later (2015-2016), A. dorsalis, Diaphanosoma sp. and Ceridaphnia sp. became dominant, with a return of K. americana by 2017. The changes that occurred during the time of the study seem to be related to changes in the conditions of the lake, since its thermocline deepened with time and became more transparent. The abundance, of rotifers and Eubosmina tubicen, decreased associated to a decrease of Cyanobacteria. Those changes were not cyclical on an annual basis, but seemed to occur more on a long-term basis, as has been recognized earlier in the literature about tropical lakes.

Revista De Biologia Tropical, 2016

Se estudio el fitoplancton de tres lagunas de Costa Rica localizadas a diferente altitud y clima:... more Se estudio el fitoplancton de tres lagunas de Costa Rica localizadas a diferente altitud y clima: San Joaquin (10 m), Fraijanes (1660 m) y Barba (1840 m). Estas tres lagunas se semejan en canto a su area y morfologia. En total se encontraron 132 taxa. Se observo una disminucion del numero de taxa al aumentar la altitud de la laguna. En San Joaquin se observaron 71 taxa, en Fraijanes 63 y en Barba 31. Chlorophyta fue el grupo mas abundante en las tres lagunas, pero se detectaron diferencias apreciables en la composicion del plancton. La similitud global al nivel inferior de separacion de los taxa fue de 41.7%, siendo las dos lagunas mas similares San Joaquin y Fraijanes, con un 17% de similitud de Jaccard.

FIG. 1. Map showing the sampled localities during this work (numbers) and collections events with... more FIG. 1. Map showing the sampled localities during this work (numbers) and collections events with material deposited at the UCR (letters) in the Coto River basin, Pacific coast, Costa Rica; associate data is provided in Tables 1 and 2, respectively.

Frontiers in Microbiology

Prokaryotic diversity in lakes has been studied for many years mainly focusing on community struc... more Prokaryotic diversity in lakes has been studied for many years mainly focusing on community structure and how the bacterial assemblages are driven by physicochemical conditions such as temperature, oxygen, and nutrients. However, little is known about how the composition and function of the prokaryotic community changes upon lake stratification. To elucidate this, we studied Lake Cote in Costa Rica determining prokaryotic diversity and community structure in conjunction with physicochemistry along vertical gradients during stratification and mixing periods. Of the parameters measured, ammonium, oxygen, and temperature, in that order, were the main determinants driving the variability in the prokaryotic community structure of the lake. Distinct stratification of Lake Cote occurred (March 2018) and the community diversity was compared to a period of complete mixing (March 2019). The microbial community analysis indicated that stratification significantly altered the bacterial composit...

Zootaxa

In this paper we report the rediscovery of the endangered cichlid fish Amphilophus lyonsi (Gosse ... more In this paper we report the rediscovery of the endangered cichlid fish Amphilophus lyonsi (Gosse 1966) in the southern Pacific region of Costa Rica. Additionally, we provide new and updated information on the morphology, growth, habitat use and distribution of the species based on data and specimens recently collected as well as on museum material. This information will be relevant for future taxonomic and conservation studies/purposes, contributing to a better understanding on the biology of the species.

Revista De Biologia Tropical, 2006

Yearly cycle of stratification and circulation at the Arenal Reservoir, Costa Rica. The behavior ... more Yearly cycle of stratification and circulation at the Arenal Reservoir, Costa Rica. The behavior of the water column of Arenal Reservoir, a tropical reservoir in Costa Rica, is analyzed based on temperature and dissolved oxygen data gathered on a monthly to bimonthly basis between 1986 and 1992. The depth profiles of temperature at Arenal Reservoir show the typical asymmetry of reservoirs, with a greater stratification in its deeper part near the dam, even though the main outflow is located at its head at the northwest end instead of the dam. A comparison of sampling stations at both ends show a deeper circulation pattern at the northern end. This coincides with other reports of a tilted structure of the thermal isopleth pattern in front of the water outlet. The dissolved oxygen showed some degree of anoxia at the bottom during part of the year, mainly from May until October. This was caused by the decomposition of the organic matter accumulated at the bottom at the time, mainly as remains of the vegetation from the former lagoon that was not removed before flooding. The stratification is clearly seasonal, occurring during the rainy season (April to October), specially in the deeper zones of the reservoir.

Revista De Biologia Tropical, Jul 20, 2016

The detailed response of tropical lake phytoplankton to weather variations has been little studie... more The detailed response of tropical lake phytoplankton to weather variations has been little studied, but it seems that composition varies in response to rain and wind variability over the course of the year. In order to gather more evidence on this variation, the weekly variability of phytoplankton composition was studied in Lake Bonilla, a low land (380 masl) 30 m deep tropical lake, from April 2010 to May 2011. Temperature variation at several depths was recorded automatically, and measurements of dissolved oxygen, water transparency, and nutrients were performed several times during the study period. The lake showed a warm monomictic pattern, with deep mixing occurring during the hemispherical winter, especially after a heavy rain period in December 2010. Phytoplankton was dominated by a few species: a colonial Cyanobacteria (Aphanocapsa sp., functional group F) and two colonial Chlorococcaceae (Botryococcus braunii and Eutetramorus tetrasporus, both in the functional group K). Their relative dominance shifted throughout the year, following changes in water column conditions in response to weather variations. Although changes in main functional groups indicate a shift in resource availability rather than energy, it was clear that attention should also be given to particular species adaptations beyond those used for establishing functional groups.

The literature on species diversity of phytoplankton of tropical lakes is scarce, and for the mai... more The literature on species diversity of phytoplankton of tropical lakes is scarce, and for the main part comes from studies of the big lakes in Africa, or deep lakes in South America, leaving a gap in the information about small shallow tropical lakes. In the present work the phytoplankton species composition and diversity of 27 shallow lakes and ponds in Costa Rica (Central America) was studied. The species composition was found to agree with other studies of tropical lakes, with a dominance of Chlorophyta, Cyanophyta, or in some cases Bacillariophyta or Euglenophyta; and a general paucity of Chrysophyta and Cryptophyta.

Verhandlungen, Oct 1, 2002

Revista De Biologia Tropical, Jul 18, 2010

Revista De Biologia Tropical, Apr 1, 2014

Despite the fact that little is known about the consequences of hydropower production in tropical... more Despite the fact that little is known about the consequences of hydropower production in tropical areas, many large dams (>15m high) are currently under construction or consideration in the tropics. We researched the effects of large hydroelectric dams on aquatic macroinvertebrate assemblages in two Costa Rican rivers. We measured physicochemical characteristics and sampled aquatic macroinvertebrates from March 2003 to March 2004 in two dammed rivers, Peñas Blancas and San Lorenzo, as well as in the undammed Chachagua River. Sites above and below the dam had differences in their physicochemical variables, with wide variation and extreme values in variables measured below the dam in the San Lorenzo River. Sites below the dams had reduced water discharges, velocities, and depths when compared with sites above the dams, as well as higher temperatures and conductivity. Sites above dams were dominated by collector-gatherer-scrapers and habitat groups dominated by swimmer-clingers, while sites below dams had a more even representation of groups. In contrast, a comparison between two sites at different elevation in the undammed river maintained a similar assemblage composition. Tributaries might facilitate macroinvertebrate recovery above the turbine house, but the assemblage below the turbine house resembled the one below the dam. A massive sediment release event from the dam decreased the abundance per sample and macroinvertebrate taxa below the dam in the Peñas Blancas River. Our study illustrates the effects of hydropower production on neotropical rivers, highlighting the importance of using multiple measures of macroinvertebrate assemblage structure for assessing this type of environmental impact.

Revista De Biologia Tropical, 2008

El Embalse Angostura fue terminado de inundar en el 2000, construido mediante una represa de conc... more El Embalse Angostura fue terminado de inundar en el 2000, construido mediante una represa de concreto en el río Reventazón, como parte de un sistema en cascada de represas para la generación de energía hidroeléctrica. Con el objetivo de estudiar sus características limnológicas se realizó una serie de mediciones básicas en el 2001. Se observó que el embalse se encuentra estratificado hacia su parte más profunda, y la termoclina inclinada, haciéndose más profunda cerca de la represa. Aunque hubo una disminución del oxígeno disuelto con la profundidad, el hipolimnion no estuvo anóxico en el momento de la visita (Febrero 2001). La conductividad mostró una capa de valores más altos que se inicia cerca de la entrada del agua del río Tuis y se hunde hacia la represa; esta capa también mostró una mayor turbidez que las aguas superficiales enfrente a la represa pero con menor clorofila. Esto indica que el flujo principal se mueve hacia la toma de aguas para la planta hidroeléctrica. Un segundo afluente proveniente del río Turrialba estaba temporalmente cerrado, el cual puede hacer variar este patrón de circulación encontrado.

Revista De Biologia Tropical, 2008

Benthic invertebrates of Cote Lake, Costa Rica. The benthic community of Lake Cote, a natural lak... more Benthic invertebrates of Cote Lake, Costa Rica. The benthic community of Lake Cote, a natural lake in Northwestern Costa Rica, was surveyed in two occasions (1/June and 28/August/2003) in order to determine possible gradients in community composition with depth, following a shore-center transect. In each opportunity, sediment samples were collected with an Ekman dredge at 10 stations ranging in depth from 1 to 12m. Two subsamples (500µm mesh screen), one to study macrofauna and the other to analize sediment characteristics, were collected from each dredge. Meiofauna (between 500 and 63µm mesh screen) was collected with a core (area: 5.3 cm 2 , depth: 4cm) in the dredge sediment (only in the second visit). Benthic fauna subsamples were preserved in 5% buffered formalin in freshwater stained with Rose Bengal. There was a decrease in temperature with depth, and oxygen levels dropped below 1mg/l below 8m depth. The percent of silt and clay increased with depth, with some exceptions and the center of the lake. A total species richness of 13 taxa was found, including macrofauna (8 taxa) and meiofauna (7 taxa). Lake Cote resembles other tropical lakes in the presence of oligochaete worms and the dipterans Procladius (Chironomidae), Tanytarsus (Chironomidae) and Chaoborus (Chaoboridae). The meiofauna also included some Coleoptera and Acari. Benthic composition was associated with habitat parameters such as substrate granulometry, dissolved oxygen and depth. The low abundance of chironomids may reflect a poor nutrient accumulation on the bottom, caused by the continuous mixing of the water body. Chironomids of the macrofauna were found from the shore to 9m depth. On the other hand, meiofaunal stages were found at less that 9m of depth. Chaoborus larvae were found between 8 and 11m depth, caused by diurnal migration to the deeper zone in the lake. Chaoborus and fish species probably predate on oligochaetes and maintain the low abundance of these worms. The total abundance of the macrofauna reached a maximum at a mid depth, with diversity being greater at shallower depths. The mean density of the macrofauna was 326 individuals per m 2 , and the mean density of the meiofauna was lower, with two organisms per 10cm 2. The distribution of the fauna was clumped, following a gradient with depth.

Lago Bonilla, located 370 m above sea level on the Eastem slopes of Volean Turrialba, Costa Rica,... more Lago Bonilla, located 370 m above sea level on the Eastem slopes of Volean Turrialba, Costa Rica, was vis ited four times during 1990-1991. Basic Iimonologica1 data were recorded in each visit. lt is oligomietic, mixing dur ing the coldest and windiest months sometime between Nov. and Feb, and eutrophic, with low Secchi transparencies, Cyanobacteria dominance and almost permanent anoxic conditions in the deepest portion. A shift in N to P ratio was observed, indicating a variation in the limiting factor during the year; N beco mes Iimiting during the driest months probably as a result of a lower input from the catchment due to lower runoff, coupled with a higher P input from the sediments during deep mixing periods. However, Iimitation by P was probably stronger than N when it occurred, according lo the N/P ralios. Phytoplankton in epilimnetic waters comprised 58 algal species, and was dominated by Cyanobacteria and Chlorophyta. Only a few species dominated Ihe community, mainly Cylindrospermum mínímum. and Tetraedron mínimum, rendering low diversity values. Zooplankton was also poor: only seven species were found. There were some indications of vertical migrations of sorne zooplankters.

La Laguna del Barva se visito una vez durante la epoca seca de 1988 y se estudio su morfometria y... more La Laguna del Barva se visito una vez durante la epoca seca de 1988 y se estudio su morfometria y limnologia basica. El area superficial es de 9x 103 m2, y la profundidadmaxima es de 7.7 m. La temperatura mostro una disminucion hacia el fondo, variando de 17°C en la superficie a 14°C enel fondo. El oxigeno disuelto mostro tambien una ligera curva de tipo clinogrado. Solamente 19 especies de algas fitoplanctonicas fueron observadas, con una densidad total que vario entre 1.25xl04 y 1.93xl04 celulas por mI. El alto grado de similitud taxonomica entre las diferentes profundidades y la distribucion vertical casi' uniforme delfitoplancton indican que en la laguna ocurren comunmente periodos de mezcla que alcanzan capas profundas. Sin embargo, aun estando localizada a bastante altura, la laguna no reune las caracteristicas de una laguna de paramo tipicamentepolimictica. La debil estratificacion encontrada no se puede explicar si se supone la existencia de periodos decirculacion total cada noche debido a la baja concentracion de oxigeno en el fondo.

Revista de Biologia Tropical, 1990

... Abstract. The Laguna del Barva was visited once during the 1988 dryseason. ... Basic limnolog... more ... Abstract. The Laguna del Barva was visited once during the 1988 dryseason. ... Basic limnology of fifty-one lakes in Costa Rica. Kurt A Haberyan, Sally P Horn, Gerardo Umaña in Revista de Biologia Tropical (2003). Save reference to library · Related research 5 readers. ...

Revista de Biología Tropical.

Universidad de Costa Rica, CIMAR y Escuela de Biología, Ciudad Universitaria, CR E-mail: gumana@c... more Universidad de Costa Rica, CIMAR y Escuela de Biología, Ciudad Universitaria, CR E-mail: gumana@cariari.ucr.ac.cr. ... The planktonic community of Laguna Hule, Costa Rica. La comunidad planctónica de la Laguna Hule, Costa Rica. ... MICROORGANISMS; PLANTS; ...

Revista de Biología …

Universidad Nacional Autónoma de Nicaragua, Centro para la Investigación en Recursos Acuáticos de... more Universidad Nacional Autónoma de Nicaragua, Centro para la Investigación en Recursos Acuáticos de Nicaragua, Departamento de Hidrología, Managua, NI E-mail: gumana@biologia.ucr.ac.cr E-mail: hchavarr@cariari.ucr.ac.cr. ... Comparación del fitoplancton en dos bahías del ...

Hydrobiologia, Sep 8, 2020

Long-term plankton studies in neotropical lakes are scarce. Here we studied plankton composition ... more Long-term plankton studies in neotropical lakes are scarce. Here we studied plankton composition in Lake Cote, Costa Rica, twice per year from 2002 to 2018, to monitor changes after it was modified as a reservoir for hydroelectricity in 2003. Plankton variation was examined for a long-term trend and its relationship with basic limnological characteristics of the lake. Phytoplankton was sampled from the surface and with a depth-integrating sampler. Zooplankton was caught with vertical hauls, at the same station at the middle of the lake. A total of 138 taxa of microalgae occurred, most from Chlorophyta and Cyanobacteria, to which dominant species belonged; Aulacoseira granulata was also ubiquitous. A shift in dominance occurred, from Cosmarium asphaerosporum to Aphanothece cf. microscopica, and Aphanocapsa cf. delicatissima. Zooplankton included 23 species of Cladocera, Copepoda, Rotifera, and Chaoborus. Most abundant were Keratella americana, Eubosmina tubicen, and Cyclopoida; Daphnia laevis became abundant after 2007 while E. tubicen declined. There was little correspondence between both planktonic components. Plankton composition was typical of a mesotrophic to eutrophic shallow lake, but changes indicated an increase in stratification, and can be attributed to combined effects of recent warming and outflow management for hydropower production.

Revista De Biologia Tropical, Nov 6, 2019

In tropical lakes, seasonal changes in plankton dynamics are minimal and irregular, since climati... more In tropical lakes, seasonal changes in plankton dynamics are minimal and irregular, since climatic conditions are fairly stable throughout the year, in most cases only long-term studies allow observing patterns in the dynamics of the plankton. Lake Río Cuarto is a maar-type meromic lake located in the plains of Northern Costa Rica, in the past there have been no limnological studies more than a year of sampling, in this work we present data on the composition of phytoplankton and zooplankton over four years, from 2013 to 2017, with the aim of analyzing changes in the plankton community in a longer period, associated with environmental variables. Phytoplankton was studied from subsurface samples, preserved in Lugol's solution and zooplankton from 20 m vertical hawls of a 64 µm mesh net, and preserved with formaline and later transferred to 95 % ethanol. Phytoplankton composition included 54 taxa, most of them were Chlorophyta, followed by Cyanobacteria and Bacillariophyta. The most abundant were: Synechococcus spp., Aphanocapsa sp. Coenochloris fotii, Chlorella sp. and Discostella stelligera. Total phytoplankton decreased from 2013 to 2017, mainly due to a decrease in Cyanobacteria. Zooplankton comprised 14 taxa, 5 cladocerans, 4 copepods, 1 diptera and 4 rotifers. The most abundant were: Keratella americana, Brachionus falcatus, Eubosmina tubicen and Arctodiaptomus dorsalis. There was a substitution of dominant species through time, at first (2013-2014) K. americana and E. tubicen alternated in dominance, and later (2015-2016), A. dorsalis, Diaphanosoma sp. and Ceridaphnia sp. became dominant, with a return of K. americana by 2017. The changes that occurred during the time of the study seem to be related to changes in the conditions of the lake, since its thermocline deepened with time and became more transparent. The abundance, of rotifers and Eubosmina tubicen, decreased associated to a decrease of Cyanobacteria. Those changes were not cyclical on an annual basis, but seemed to occur more on a long-term basis, as has been recognized earlier in the literature about tropical lakes.

Revista De Biologia Tropical, 2016

Se estudio el fitoplancton de tres lagunas de Costa Rica localizadas a diferente altitud y clima:... more Se estudio el fitoplancton de tres lagunas de Costa Rica localizadas a diferente altitud y clima: San Joaquin (10 m), Fraijanes (1660 m) y Barba (1840 m). Estas tres lagunas se semejan en canto a su area y morfologia. En total se encontraron 132 taxa. Se observo una disminucion del numero de taxa al aumentar la altitud de la laguna. En San Joaquin se observaron 71 taxa, en Fraijanes 63 y en Barba 31. Chlorophyta fue el grupo mas abundante en las tres lagunas, pero se detectaron diferencias apreciables en la composicion del plancton. La similitud global al nivel inferior de separacion de los taxa fue de 41.7%, siendo las dos lagunas mas similares San Joaquin y Fraijanes, con un 17% de similitud de Jaccard.

FIG. 1. Map showing the sampled localities during this work (numbers) and collections events with... more FIG. 1. Map showing the sampled localities during this work (numbers) and collections events with material deposited at the UCR (letters) in the Coto River basin, Pacific coast, Costa Rica; associate data is provided in Tables 1 and 2, respectively.

Frontiers in Microbiology

Prokaryotic diversity in lakes has been studied for many years mainly focusing on community struc... more Prokaryotic diversity in lakes has been studied for many years mainly focusing on community structure and how the bacterial assemblages are driven by physicochemical conditions such as temperature, oxygen, and nutrients. However, little is known about how the composition and function of the prokaryotic community changes upon lake stratification. To elucidate this, we studied Lake Cote in Costa Rica determining prokaryotic diversity and community structure in conjunction with physicochemistry along vertical gradients during stratification and mixing periods. Of the parameters measured, ammonium, oxygen, and temperature, in that order, were the main determinants driving the variability in the prokaryotic community structure of the lake. Distinct stratification of Lake Cote occurred (March 2018) and the community diversity was compared to a period of complete mixing (March 2019). The microbial community analysis indicated that stratification significantly altered the bacterial composit...

Zootaxa

In this paper we report the rediscovery of the endangered cichlid fish Amphilophus lyonsi (Gosse ... more In this paper we report the rediscovery of the endangered cichlid fish Amphilophus lyonsi (Gosse 1966) in the southern Pacific region of Costa Rica. Additionally, we provide new and updated information on the morphology, growth, habitat use and distribution of the species based on data and specimens recently collected as well as on museum material. This information will be relevant for future taxonomic and conservation studies/purposes, contributing to a better understanding on the biology of the species.