IO - Instituto de Oceanografia
URI permanente desta comunidadehttps://rihomolog.furg.br/handle/1/361
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Resultados da Pesquisa
- ItemThe effect of salinity on larval development of spider crab Libinia spinosa (Brachyura, Majidae) reared in the laboratory(1999) Hereu, Clara María; Calazans, Danilo Koetz deOvigerous females of Libinia spinosa were collected in the oceanic region adjacent to the Patos Lagoon and were maintained in the laboratory at 20° and 30 PSU until spawning. After hatching larvae were transferred to compartmented plastic boxes of approximately 25 ml with filtered sea water of different salinities (25, 30 and 35 PSU) and kept under photoperiod of 12 h light: 12 h dark. Water was changed every other day, and larvae were checked daily to assess molt and death rates. Larvae were fed Artemia sp. nauplii newly hatched. Survival to megalopa was higher at salinitiesof 30 and 35 than at salinity 25. Although larvae reached megalopal phases in all three salinities mortality was 100% during this phase. Salinity had no effect on duration of zoea stage I whereas development of zoea II was significantly delayed in the lowest salinity tested. The results obtained were compared to other species of the same genus which were maintained under similar conditions. Nevertheless, there is a difference between the larval development length reported in another study for this species, where the mean length of larval stages was longer.
- ItemRheological properties of marine organic aggregates: importance for vertical flux, turbulence and microzone(1991) Jenkinson, lan R.; Bidijanda, Bopi; Turley, Carol; Abreu, Paulo Cesar Oliveira Vergne de; Riebesell, Vif; Smetacek, VictorFor marine cnvironmcnlS whcrc aggrcgalcs arc composed of ~ 50 % organic matLer. various panunctcrs relevant to aggregation arc quanlified and compared with those in other aggregation regirnes. Sorne possible environrnental crfects o f the rheological propert ie s of rn<.lri ne organic aggregates <.Ire reviewed. T he interaction belwccn shear forces in the water and aggrcgate rheology is likely \() delermine: firstly, the sink ing spced of aggregates and hence vertical organic nux rates: secondly, the volume of microzones, with impl ications for equi libria and kinet ics of chemical reaet ions in the pelagie milieu: and th irdly. the dcgrec o f turbulence dantping between aggregates, due to absorption of energy through viscous dissipation inside viscoelastic aggregates during their deformati on. Whether organic sub-micrornelrc panicles incrc:tse the viscosity of bul k seawater at :t g iven 1cnglhseale (such as that of turbulence) wi ll depend on their shape and the degree to which Iheir rheologieal and surface-active propcrties allow adhesion or intertanglcment to fo rm matrices. Sonte preliminary resul ts are gi"cn o f the rheo]ogieaJ properties of somc laboralOry-produced marine org.mic aggregates.
- ItemEffect of Fish and Mesozooplankton Manipulation on the Phytoplankton Community in the Patos Lagoon Estuary, Southern Brazil(1994) Abreu, Paulo Cesar Oliveira Vergne de; Granéli, Edna; Odebrecht, Clarisse; Kitzmann, Dione Iara Silveira; Proença, Luís Antônio de Oliveira; Resgalla Junior, CharridAn enclosure experiment in the Patos Lagoon estuary, southern Brazil (32°S, 52°W) investigated the response of phytoplankton to the enhancement of mesozooplankton and fish abundance. Addition of nutrients (NO3 − and PO4 −) stimulated the growth of 3–20 μm diameter phytoplankton, especially the diatomCylindrotheca closterium, which, in turn, was heavily grazed by the dominant mesozooplankter, the copepodAcartia tonsa. Acartia did not consume small (2–3 μm) autotrophic flagellates and the cyanobacteriaAnabaena sp., despite their high cell number. Largest grazing ofC. closterium by the copepod occurred only after a decrease of ciliate abundance. The addition of mesozooplankton did not change the levels of primary production, but it significantly increased the phytoplankton assimilation number. Highest chlorophylla concentrations were measured in enclosures stocked with juveniles of the fishXenomelaniris brasiliensis. The large phytoplankton biomass and low mesozooplankton abundance found in this treatment indicates an, effective predator-mediated action on the phytoplankton community.
- ItemEfeito da temperatura sobre o desempenho da Rã-touro (Rana catesbeiana Shaw, 1802)(1999) Figueiredo, Mario Roberto Chim; Agostinho, Claudio Angelo; Baêta, Fernando da Costa; Lima, Samuel LopesEste estudo foi realizado para avaliar os efeitos do ambiente sobre a performance de rã-touro (Rana catesbeiana Shaw, 1802), criada em gaiolas de fibra de vidro instaladas no interior de estufas climatizadas. Após um período inicial de 15 dias de adaptação às instalações, à temperatura constante de 25,0ºC, os seguintes tratamentos foram aplicados: temperaturas de 23,0; 26,0; 29,0; 32,0; e 35,0oC, por 30 dias, para rãs com 100 g PV inicial; 24,5; 26,0; 27,5; 29,0; 30,5; e 32,0oC, também por 30 dias, para rãs com 20 g PV inicial; e a combinação das temperaturas de 26,0 e 29,0oC com os fotoperíodos de 8, 12 e 16 h de luz a cada 24 horas, para rãs com 100 g PV inicial. Derivando-se as equações de regressão que explicam os efeitos de temperatura sobre o desempenho das rãs, estimaram-se melhores ganhos de peso à temperatura de 27,6 e 30,1oC, para rãs com 100 e 20 g PV inicial, respectivamente, com melhor crescimento a 28,2oC, para as rãs de 100 g PV inicial, e a 29,7ºC, para as rãs de 20 g PV inicial. A temperatura interagiu com fotoperíodo nos seus efeitos sobre ganho de peso e crescimento corporal, peso e rendimento de carcaça, consumo de alimentos e conversão alimentar.
- ItemJuvenile Mullets (Pisces: Mugilidae) in the Estuary of Lagoa dos Patos, RS - Brazil(1991) Vieira Sobrinho, João PaesJuvenile mugilids collected during a 5 yr monthly beach seine survey in the shallow waters of the Lagoa dos Patos estuary, Brazil were examined in order to describe spatial and temporal patterns of species abundance. Species occurrence and abundance could be classified into two seasonal periods related to changes in water temperature and salinity. One period, associated with warmer and more saline waters and typified by a mixture of the three species (Mugil platanus, M. curema, and M. gaimardianus), occurred during the first 5-6 mo of each year. From mid-winter throught early summer M. curema and M. gaimardianus were scarce or absent, resulting in a second period associated with cold and less saline waters and typified by M. platanus. A life history model for M. platanus in southern Brazil is proposed.
- ItemKey to the larvae and decapodids of genera of the Infraorder Penaeidea from southern Brazilian coast(1993) Calazans, Danilo Koetz deAn ilustrated key with criteria for differentiating phases and stages of fifteen genera of penaied larvae and magalopa of the Southern Brazilian coast was constructed entirely from planktonic samples and published larval descriptions. The key identifies the genera Aristeomorpha; Gennadas; Pleoticus; Solenocera; Mesopenaeus; Sicyonia; Xiphopenaeus; Trachypenaeus; Artemesia; Parapenaeus; Penaeus; Sergestes; Acetes; Peisos; and Lucifer.
- ItemStructuring of a postspring phytoplankton community by manipulation of trophic interactions(1992) Olsson, Per; Granéli, Edna; Carlsson, Per; Abreu, Paulo Cesar Oliveira Vergne deTo study the effects of grazing on a natural post-spring phytoplankton community a land-based mesocosm experiment was performed during late spring 1988 (7-18 June). 300-1 polyethylene cylinders, immersed in a flexible pool for temperature regulation, were filled with a plankton community filtered through a 90-pm nylon net. In duplicate cylinders, the ambient copepod concentration (mainly an Acartia sp.), five times the ambient concentration, ambient concentration + medusae of the scyphozoan Aurelia aurita (L.) and ambient concentration + mussels (Mytilus edulis L.) were added. Nutrients were added throughout the experimental period to keep the concentrations at 5 pM nitrate, 0.5 pM phosphate and l0 #M silica. Chl a, nutrients and densities of phytoplankton, ciliates and copepods were measured throughout the experiment. We observed that the diatoms remaining from the sprimz bloom could, with small additions of nutrients, outgrow their grazers. Only a small reduction in copepod grazing pressure through medusae predation on copepods was required for an even stronger growth and domir:ance by diatoms. This pattern of development could be broken by an increase in Acartia sp. biomass. An initial addition of five times the natural concentration of Acartia sp. led to a rapid growth of monads, < 3 #m, which constituted almost 100°o of the biomass after 3 days. When Acartia sp. decreased in biomass, diatoms and cryptomonads became dominant. As the small naked ciliate Urotricha sp. had already been eliminated by the initially abundant copepods in the cylinders where the copepod concentration was five times the ambient concentration, there were few grazers left to make use of the ample food supply. Urotricha sp. could possibly control the < 3- #m monads if not or only moderately predated by Acartia sp., indicated by the lower increase in monad biomass in the cylinders where mussels or medusae were added. M. edulis was capable of grazing down all phytoplankton species to very low densities, except monads < 3 #m, in spite of nutrient additions, indicating a possible nonspecies-selective control ofphytoplankton abundance by benthic filter-feeders in eutrophicated areas.
- ItemInfluence of the hydrological cycle on the bacterioplankton of an impacted clear water amazonian lake(1997) Anésio, Alexandre Magno Barbosa; Abreu, Paulo Cesar Oliveira Vergne de; Esteves, Francisco de AssisFree-living and attached bacterial population sizes were determined fortnightly from December 1991 to December 1992 in natural and disturbed areas of an Amazonian clear water lake (Batata Lake, Para´, Brazil) impacted by bauxite tailings. The bacterioplankton showed distinct patterns during different phases of the hydrological cycle. Total bacterial population size and rates of thymidine incorporation (measured during high and low water phases) were high during low water, with values ranging from 3.3 3 105 to 1.1 3 106 cells ml21, and from 0.28 to 4.01 mg C l21 h21, respectively. The population size of free-living bacteria was larger at the natural station, while no differences were observed between attached bacterial populations at both stations. However, production and turnover rate of attached bacteria were high at the disturbed area. During low water, bacterial growth appeared to be driven mainly by the input of dissolved organic carbon (DOC) from phytoplankton origin. During high water, bacterial abundance was reduced, probably as the result of dilution and the input of less labile DOC from floodplains. The presence of bauxite tailings seems to influence bacterial dynamics in an indirect way, probably due to shading of phytoplankton cells and, hence, reducing the DOC supply for bacterial growth. This study, the first on the microbial ecology of an Amazonian clear water lake, demonstrated that water level variations exert a strong influence on the bacterioplankton dynamics.
- ItemThe stability of trophic mass-balance models of marine ecosystems: a comparative analysis(1997) Vasconcellos, Marcelo Cunha; Mackinson, Steven; Sloman, Katherine; Pauly, DanielDynamic simulations of 18 ECOPATH mass-balance marine trophic models are used to explore the stability of systems when briefly impacted by a fishery on the key ‘wasp–waist’ populations occurring at intermediate trophic levels. The results are related to different ecosystem goal functions previously identified as representative of three attributes of ecosystems development: community complexity, homeostasis and energetics. System recovery time, the time required for all functional groups to returns to baseline level, and here used as a measure of model stability, was inversely correlated to Finn’s Cycling Index, i.e. to the fraction of ecosystem throughput that is recycled, and to the mean length of trophic pathways in the systems. Systems with higher capacity to recycle detritus are systems with a higher ability to recover from perturbations. The results are in agreement with the E.P. Odum’s theory of ecosystem development, where recycling is interpreted as a chief positive feedback mechanism that contributes to stability in the mature systems by preventing overshoots and destructive oscillations due to external impacts.
- ItemDistribution patterns and feeding success of anchovy, Engraulis anchoita, larvae off southern Brazil(1998) Vasconcellos, Marcelo Cunha; Freire, Kátia de Meirelles Felizola; Castello, Jorge PabloFeeding success and changes in horizontal patchiness relative to size were studied for anchovy, Engraulis anchoita, larvae caught with a Bongo net off southern Brazil. Results show higher feeding success rates during winter, when the combined effect of enrichment, stability and retention mechanisms seems to create optimal conditions for larval feed-ing. Under optimal feeding conditions larvae of more than 10 mm have higher feeding success rates than smaller size class- es. With a simple body structure and low swimming capabilities, larvae of up to 10 mm show a low level of patchiness, low evasion rate of the sampling gear and feeding on small food particles only. Results corroborate the hypothesis of a critical period between two important ontogenic phases: the beginning of exogenous feeding and the onset of active swimming, gas gland buoyancy and school forming behavior.