Nutrient-phytoplankton interrelationships in the Eastern Tropical Pacific Ocean

ENGLISH: Near surface nutrient distributions in the eastern tropical Pacific Ocean, using data from the EASTROPAC Expedition of 1967-68 and pre~EASTROPAC data, are described. Nutrient concentrations were maximal along the equator, in the Peru Current and its offshore extension, and in the Costa Rica Dome and westward tensions of this feature. Nutrient-poor water was found north of the equator well offshore. In this water nitrate was often undetectable (<0.1 µg-at/liter) at the surface, but phosphate and silicic acid concentrations were moderate. Enrichment experiments showed that nitrogen was the primary limiting nutrient in poor water even though large amounts of organic N were found. Half saturation constants (K s ) were determined for ammonium-supported phytoplankton growth. These data were used to calculate near-surface primary productivity values which compared favorably with 14C values. Assimilation ratio measurements indicated that algae were not extremely nitrogen-deficient. Laboratory-determined K, values for phosphate and silicic acid indicated that these nutrients were rarely limiting. In rich water, chlorophyll levels were less than expected from nutrient levels, and this anomaly may be related to limitation by nutrients other than nitrogen (N), phosphorus (P), or silicon (Si), or to grazing. SPANISH: Se describe la distribución subsuperficial de los nutrientes en el Océano Pacífico oriental tropical, empleando los datos de la Expedición EASTROPAC de 1967~68 y datos anteriores a éstos. La concentración de nutrientes fue máxima a lo largo del ecuador, en la Corriente del Perú, en su prolongación mar afuera, en el Domo de Costa Rica y en las prolongaciones occidentales de esta característica. Se encontraron aguas pobres en nutrientes al norte del ecuador y bastante mar adentro. En estas aguas el nitrato era casi imperceptible (<0.1 µg-at/litro) en la superficie, pero las concentraciones de fosfato y ácido silícico fueron moderadas. Los experimentos de enriquecimiento indicaron que el nitrógeno era el principal nutriente limitante en aguas pobres, aun cuando se encontraron grandes cantidades de nitrógeno orgánico. Se determinaron las constantes de saturación media (K s ) para el desarrollo del fitoplancton sostenido por el amonio. Estos datos se emplearon para calcular los valores de la productividad primaria cerca a la superficie que pueden compararse favorablemente con los valores del 14C. Las medidas de la proporción de asimilación indican que las algas no tenían una deficiencia extremada de nitrógeno. Los valores determinados en el laboratorio de K, para el fosfato y ácido silícico indicaron que estos nutrientes limitaron rara vez la producción. En aguas ricas, los niveles de clorofila fueron inferiores a lo esperado según los niveles nutritivos y esta anomalía puede relacionarse a la alimentación o a la escasez de otros nutrientes distintos al nitrógeno (N), fósforo (P) o silicio (Si).

Nutrient digestibility and growth response of rainbow trout (Salmo gairdneri ) fed different carbohydrate types

Seven groups of fingerling rainbow trout (S. gairdneri ) were fed for 10 weeks on 0%, 10%, 20% and 30% of cassava or rice in isonitrogenous diets. Optimum growth and food utilization was at 20% dietary cassava. High fiber content of the control diet did not suppress protein digestibility in this group. Rather, at all levels, protein digestibility was good and remained between 84.4% and 90.1%. However, in the control group, carbohydrate digestibility was very poor. The cassava diets which had the highest digestible energy as carbohydrate produced the best growth performance, food utilization and protein sparing. At the levels studied, the dietary carbohydrates produced no hyperglycamic effect on the fish

The influence of some environmental variables on the apparent abundance of skipjack tuna, Katsuwonus pelamis, in the Eastern Pacific Ocean

ENGLISH: The abundance of skipjack larvae in the central and western Pacific approximately doubled for every 1°C increase in sea-surface temperature (SST) from 23°C to a maximum of about 29°C, and then usually decreased with further increases in SST. Skipjack larvae are scarce in the eastern Pacific Ocean (EPO), so most skipjack recruits and adults in this area are believed to have originated in the central and, possibly, the western Pacific. The catch per unit of effort (CPUE), in short tons per day's fishing, and the catch rate, in number of fish per day's fishing, are estimates of apparent abundance in a fishery. The logarithm of the annual CPUE for skipjack for international baitboats in the EPO for the 1934-1960 period was positively correlated with SST in the spawning area in the central Pacific 18 months earlier (r2 0.31), during the July-June period when most of the recruits in each cohort were presumed to have been spawned. Adequate data for other environmental variables were not available for testing with the baitboat data. The other environmental variables available and selected for testing for correlation with estimates of skipjack abundance for purse seiners for the 1961-1984 period and the reasons for their selection are as follows. 1)Wind-mixing index (WMI). The degree of mixing in the upper layers of the ocean is proportional to the cube of the wind speed, called WMI. The degree of mixing in the spawning areas of the central and the western Pacific may affect the concentration of organisms that skipjack larvae feed upon, thereby influencing their survival, and ultimately determining cohort strength and the number of recruits to the eastern Pacific fishery. 2) SST in the fishing areas at the time of fishing (SST). The CPUE for yellowfin tuna has been shown to be inversely related to SST in the fishing areas, and there are indications that skipjack CPUE is lower during EI Nino events when SST is higher than normal. 3) North-south SST gradient across the thermal front off the Gulf of Guayaquil. This is a measure of the degree of upwelling and nutrient enrichment of the upper waters south of the front and ultimately of the production of food for tunas. 4) Speed of the North Equatorial Countercurrent (NECC). Young skipjack may migrate from the central Pacific to the EPO in the eastward flowing NECC; if so, the number of recruits might be affected by variations in the speed of the current. The logarithm of the annual catch rate of skipjack recruits by international purse seiners in the EPO for the 1961-1984 period was positively correlated with SST in the spawning area of the central Pacific 18 months earlier (r2 = 0.21),and inversely correlated with WMI in the spawning area 18 months earlier (r2 0.46). The logarithm of CPUE for purse seiners in the area off the Gulf of Guayaquil was not correlated with SST in the spawning area 18 months earlier, but was inversely correlated with WMI in the spawning area 18 months earlier (r2 = 0.19), and inversely correlated with the north-south SST gradient in the fishing area at the time of fishing (r2 0.32). Neither of these estimates of apparent abundance from purse seiners were correlated with SST in the fishing areas, or with the speed of the NECC at earlier times. SPANISH: La abundancia de larvas de barrilete en el Pacífico central y occidental se multiplicó por dos, aproximadamente, por cada aumento de 1°Cen la temperatura de la superficie del mar (TSM) entre 23°C y un máximo de unos 29°C, y luego generalmente disminuyó con más aumentos en la TSM. Las larvas de barrilete son escasas en el Océano Pacífico oriental (OPO), y por lo tanto se cree que la mayoría de los reclutas y adultos en esta zona surgieron del Pacífico central, y posiblemente también del Pacífico occidental. La captura por unidad de esfuerzo (CPUE), en toneladas cortas por día de pesca, y la tasa de captura, en número de peces por día de pesca, son estimaciones de la abundancia aparente en una pesquería. El logaritmo de la CPUE anual de barrilete lograda por barcos de carnada en el OPO en el período 1934-1960 se correlacionó positivamente con la TSM en la zona de desove en el Pacífico central de 18 meses antes (r2 = 0.31), durante el período de junio-julio en el cual se cree que nació la mayoría de los reclutas en cada cohorte. No se dispuso de datos suficientes sobre otras variables ambientales para comprobarlos con los datos de los barcos de carnada. Las demás variables ambientales disponibles y seleccionadas para someterlas a pruebas de correlación con las estimaciones de la abundancia del barrilete de barcos cerqueros en el período 1961-1984, y las razones por su selección, son las siguientes: 1) Indice de mezcla por el viento (IMV). El grado de mezcla en las capas superiores del océano es proporcional al cubo de la velocidad del viento, llamado IMV. Es posible que el grado de mezcla en las zonas de desove del Pacífico central y occidental afecte la concentración de los organismos que alimentan a las larvas del barrilete, afectando así la supervivencia de éstas, y finalmente determinando el tamaño de las cohortes y el número de reclutas a la pesquería del OPO. 2) TSM en la zona de pesca al realizarse la pesca (TSM). Se ha mostrado que la relación de la CPUE del atún aleta amarilla a la TSM en la zona de pesca es inversa, y existen indicaciones que la CPUE de barrilete es inferior durante eventos del Niño, cuando las TSM son superiores a lo normal. 3) Gradiente norte-sur de las TSM a través del frente térmico frente al Golfo de Guayaquil. Esto es una medida del grado de afloramiento y enriquecimiento nutritivo del nivel superior de las aguas al sur de dicho frente, y finalmente de la producción de alimento para los atunes. 4) La velocidad de la Contracorriente Ecuatorial del Norte (CCEN). Es posible que los bariletes juveniles migren del Pacífico central al Pacífico oriental en la CCEN, que fluye hacia el este; de ser así, es posible que la cantidad de reclutas se vea afectada por variaciones en la velocidad de la corriente. El logaritmo de la tasa anual de captura de reclutas de barrilete por cerqueros de varias banderas en el OPO en el período 1961-1964 estuvo correlacionado de forma positiva con las TSM en la zona de desove del Pacífico central de 18meses antes (r2 0.21),y de forma inversa con el IMV de la zona de desove de 18 meses antes (r2 0.46). El logaritmo de la CPUE de los cerqueros en la zona frente al Golfo de Guayaquil no estuvo correlacionado con las TSM en la zona de desove de 18 meses antes, pero sí estuvo correlacionado de forma inversa con el IMV en la zona de desove de 18 meses antes (r2 0.19),y con el gradiente norte-sur de las TSM en la zona de pesca al realizarse la pesca (r2 0.32). Ninguna de estas estimaciones de abundancia aparente provenientes de barcos cerqueros estuvo correlacionada con las TSM en las zonas de pesca o con la velocidad de la CCEN en épocas anteriores. (PDF contains 140 pages.)

Digestibility and nutrient utilization of soybean milk concentrate based diets in Oreochromis niloticus

The digestibility and utilisation of two fresh soybean milk concentrate based diets, two stale soybean milk concentrate based diets and two Fishman based diets serving as control, at optimal (30%) and suboptimal (20%) protein levels were evaluated in Oreochromis niloticus. The diets were as follows: Diet I (control) - fishmeal based diet at 30% crude protein, Diet II (control) Fishman based diet at 20% crude protein, Diet III - fresh soybean milk concentrate based diet at 30% crude protein, Diet IV - fresh soybean milk concentrate based diet at 20%, Diet V - stale soybean milk concentrate based diet at 30% crude protein, Diet VI-stale soybean milk concentrate based diet at 20%. Dry matter digestibility differed not significantly with variation in diets (P:0.05). A significant variation was recorded in the protein, lipid and ash digestibility. Proteins were more digestible at optimum than suboptimum level. Ash digestibility was lowest of all the nutrients. Variations in the utilisation of the diets in terms of weight gain, specific growth rate, food conversion ration, protein efficiency ration and apparent net protein utilization were insignificant (P: 0.05). All diets compared favourably with the standard control diet Diet I. This findings suggest the suitability of stale soybean milk concentrate utilisation as protein supplements in the diets of late fry Oreochromis niloticus

Digestibility and nutrient utilisation of soybean bran-based diets in Nile tilapia Oreochromis niloticus

The digestibility and utilisation of two soybean bran-based diets and two fishmeal-based diets serving as control, at optimal (30%) and suboptimal (20%) protein levels were evaluated in Oreochromis niloticus. These were Diet I (Control)-fishmeal based diet at 30% crude protein, Diet II (Control) - fishmeal based diet at 20% crude protein, Diet III - hydrolysed Soybean Bran based diet at 30% crude protein, Diet IV - hydrolysed Soybean Bran based diet at 20%. Dry matter digestibility differed insignificantly with variation in diets (P<0.05). There was significant variation in the protein (p 20.05), lipid and ash digestibility. Protein was more digestible at optimum level than sub-optimum level, while lipid and ash digestibility did not vary with their inclusion levels. Variation in the utilisation of the diets was significant (P<0.05) except for survival. It was observed that the best diet was Diet 1, closely followed by Diet II with highest values of mean final weight, specific growth rate, protein efficiency ratio and the apparent net protein utilisation. The high digestibility values of Diets III and IV suggests their inclusion in fish diet to spare protein for growth

Indication of pollution in a teaching and research farm reservoir

The production and productivity of a water body is largely dependent on its quality. One major source of water pollution is from the agrochemicals from nearby farmlands. The quality of water in the Obafemi Awolowo University Teaching and Research Farm Reservoir (Ile-Ife, Nigeria) was monitored between October, 1993 and March, 1994. Structured questionnaires were administered to obtain information on the types of agrochemicals in use on the farm. Water samples were collected fortnightly for analyses of the physico-chemical parameters and ionic content of the water. Investigation revealed that 21 agrochemicals had been in use on the farm. The physico-chemical parameters of the water showed that the water was very poor in nutrient. The high concentration of ammonium ion contents of the water shows an indication that the residues of certain agrochemicals got into the water to pollute it. Agrochemicals should be used with great caution on farmlands especially in areas close to water bodies from which man obtains fish and other proteinous foods. This paper also suggests a regular monitoring of water quality of reservoirs in order to pick the earliest signs of pollution

Water quality and nutrient dynamics - Lake Victoria, Kenya

Limnological studies in Lake Victoria (Kenyan portion) have been sporadic. Water quality and nutrient dynamics studies are being undertaken in fifteen sampling sites that have been divided into four ecological zones namely: Nyanza Gulf, Rusinga Channel, open waters inshore and open waters. The ongoing study will show how the physical and chemical paramenters affect fish distribution and abundance.

An evaluation of the pelagic primary productivity and potential fish yield of Kainji Lake, Nigeria

The environmental conditions of Kainji Lake from 1971/72 to date appear to have stabilized to a large extent, judging from the similarity of physico-chemical parameters investigated in this study over the period. Solar radiation (as reflected in variation in temperature) and pH have remained largely constant over the years, while conductivity (index of nutrient enrichment), though significantly higher in 1995/96, could be described as sporadic and needs further monitoring to ascertain its trend in the lake. While water transparency and dissolved oxygen were higher in 1971/72 compared to the other years, these increases cannot be said to be overwhelming. The lower transparency in 1995/96 was due to the exceptional flood of that year and may have also accounted for the poorer dissolved oxygen concentration compared to the other years due to its impact on photosynthesis. There is no evidence from this study to indicate that primary productivity has increased over the years. Consequently, the observed increase in fish yield by the KLFPP from CAS, which is corroborated by estimates from the MEI, cannot be supported on the basis of improved photosynthetic production. The phenomenal high levels of conductivity recorded during certain periods in 1995 (600 mu mhos cm super(-1)) are hitherto unknown in the lake and may indicate a trend towards nutrient enrichment. However, it is premature at this stage to conclude on its long-term impact on primary production and consequently, on fish yield. Secondly, the notion of overfishing in the 80s (Ita, 1993), may need to be further examined as low or dwindling catches could be due to a number of factors among which are the level of fishing effort, the type and efficiency of gears and the intensity of sampling. It would appear that with the intervention of KLFPP, the better management of the lake's fisheries would increase the current level of catch. It also needs to be examined how much of the clupeid fisheries, which is now known to account for a substantial proportion of the total fish yield in Kainji Lake, was included in the sampling of the 80s. (PDF contains 43 pages)

The impact of varying nutrient regimes in earthen freshwater ponds on the comparative ecology of diurnally occurring candidate live feeds

The daytime composition and relative abundance of zooplankton species were studied in three treatments of two replicate earthen ponds each with nutrient sources and water replenishment regimes. Treatment -A (200m super(2) surface area supplied 900kgha super(-1) pig manure only). Treatment -B (200m super(2) surface area supplied 70kgha super(-1) month super(-1) pig manure, 50kgha super(-1) month super(-1) N.P.K. [15:15:15] and 30kgha super(-1) month super(-1) Urea) and Treatment-C (1500m2 surface area supplied 1150kgha super(-1) month super(-1) commercial grade 40% crude protein compounded feed). Water replenishment for Treatment A was daily tidal deluge from the New Calabar River while that for treatment B and C was from column-well and occasional rains. No zooplankton species were recovered from the pig-manure only treatment (A) while only Diffugia constricta and Difflugia urceolata were the two protozoans that occurred together in treatments B (combined fertilization) and C (compounded feed only) in contrast, Difflugia acuminate and three rotifers, Collurella uncinata, Diurella stylata and Keratella quadrata occurred only treatment B. similarly, Arcella arenaria, Arcella costata, Centropyxis aculeate, Difflugia pyriformis, Branchionus calyciflorus, Lepadella patella, Polyarthra trigla and Onchocanmptus mohammedi were recovered from treatment C. Arcella costata was the most abundant zooplankton in the entire experiment, while Arcella arenaria was very abundant in treatment C, Collurella uncinata was very abundant in treatment B. The inference is that combined fertilization of earthen freshwater ponds tend to be more suitable for the culture of rotifers such as Brachionus calyciflorus, popular in fish larva nursery, while those supplied compounded feed could be used to produce protozoans where desirable

Plant nutrients and major ions in the Little Sea, Studland, Dorset

This short paper records some measurements made on the Little Sea, a shallow, coastal, acidic lake on Studland Heath, Dorset. The lake, formed about 100 years ago by dunes cutting off a sea inlet, has not received any input of agricultural fertilizers or other waste products for at least the last 30 years. It is a Site of Special Scientific Interest (SSSI). Samples of surface water were taken from the northern and southern ends of the lake at 3-monthly intervals, from July 1995 to April 1996. The first samples in July 1995 were taken during a period of drought; rain, sometimes very heavy, came in late September. With the exception of silicate, potassium and phosphate, there were no large changes in plant nutrient concentrations during the year. The concentration of nitrate-nitrogen was very low (close to the limits of analytical detection), but total phosphorus at ca. 30 mu g per litre was similar to concentrations found in some of the Cumbrian eutrophic lakes. The large number of algal species at low cell/colony concentrations suggested that the lake is mesotrophic. Sodium, chloride and magnesium in the lake water were close to the same proportions as those found in sea water. Dry and wet deposition of sea-salts on the lake surface and its catchment area probably is the major source of sodium, magnesium and chloride ions in the lake, and also accounts for about half of the mean potassium and sulphate concentrations.

Symposium on Llangrose Lake: the ecology and conservation of a large nutrient-rich lake in South Wales

This paper summarises a meeting which discussed the ecology and conservation of Llangorse Lake in South Wales. The meeting was organised by the British Ecological Society (Aquatic Ecology Group), in association with the Countryside Council for Wales (CCW), Brecon Beacon National Park Authority (BBNPA) and Environment Agency Wales. It took place on 22 October 1998.

Toxicidade e bioacumulação de cobre em micro-organismos fotoautotróficos

Microalgas e cianobactérias têm sido amplamente recomendadas para biomonitoração de metais pesados e outros poluentes, sendo considerados indicadores sensíveis às alterações ambientais e utilizados como organismos testes na regulamentação dos níveis de metal. Estes micro-organismos fotossintetizantes são produtores primários da base da cadeia alimentar aquática e são os primeiros a serem afetados pela poluição por metais pesados. O cobre é um metal normalmente considerado como nutriente essencial para a vida aquática mas pode ser tóxico para algumas espécies. Portanto, neste estudo foram avaliados o efeito tóxico e a bioacumulação de cobre (II) em quatro espécies de micro-organismos fotoautotróficos componentes do fitoplâncton dulcícola, duas cianobactérias filamentosas (Anabaena sp. e Oscillatoria sp) e duas microalgas da classe das clorofíceas (Monorraphidium sp. e Scenedesmus sp.). O meio de cultivo utilizado nos ensaios foi o ASM-1 com e sem a presença de cobre (0,6 mg/L a 12 mg Cu2+/L) onde, o efeito tóxico do metal foi monitorado por contagem celular para as microalgas e por peso seco para as cianobactérias. A bioacumulação do metal foi avaliada da mesma forma para todos os micro-organismos, através de coletas de amostras no decorrer do experimento e determinação da concentração de cobre em solução por espectrometria de absorção atômica com chama. Os resultados obtidos mostram que o efeito tóxico do metal é diretamente proporcional à concentração inicial para os micro-organismos estudados, mas que o cobre (II) foi mais tóxico para as cianobactérias que para as microalgas verdes. A bioacumulação teve uma relação direta com o efeito tóxico do metal sobre os micro-organismos. Os resultados obtidos permitem sugerir que cobre (II) tem efeito negativo no fitoplâncton, inibindo o crescimento e alterando parâmetros metabólicos como a fotossíntese. A bioacumulação do metal pode comprometer os níveis tróficos da cadeia alimentar, afetando seu transporte para seres superiores

The effect of oxygen concentration in water on the growth and nitrogen metabolism in the fry of rainbow trout [Translation from: Rybnoe Khoziaistvo,V.33, 74-75, 1957]

To ascertain the effect of various concentrations of oxygen in water on the fry of rainbow trout experiments were made with aquaria at various concentrations of oxygen. The food supplied was chironomid larvae (Chironomus plumosus). A surplus of food was supplied to the fry. Indices are given of the reaction of the fry to different temperatures.