Zum Gehalt an Seston und Plankton im tropischen Atlantik

Zusammenfassung 1. Die hier vorgelegte Ausarbeitung enthält nur einen sehr kleinen Teil der Daten, die während der internationalen Untersuchungen seit 1963 im tropischen Atlantik gewonnen wurden. Sie bringt erste Ergebnisse von zwei Reisen des Verfassers im Frühjahr und Sommer 1963.2. Die gefundenen Werte von Seston und Eiweiß (Albumin-Äquivalente) waren im einzelnen sehr unterschiedlich; eine Deutung mit Hilfe von hydrographischen Daten genügte nicht in allen Fällen. Die Mittelwerte sind deutlich niedriger als die entsprechenden Zahlen aus dem Nordatlantik. Die höchsten Werte fanden sich an der Oberfläche; eine zweite Anreicherung wurde häufig in der Dichte-Sprungschicht beobachtet. Der aus den Eiweißzahlen errechnete Planktongehalt des Sestons war im östlichen Teil des untersuchten Gebietes auch im offenen Ozean unerwartet gering.3. Die Biomasse des Netzplanktons übertraf in gut mit Nährstoffen versorgtem Wasser die Biomasse des Mikroplanktons. Nur durch eine hohe Primärproduktion, wie sie in diesen Gebieten auch vielfach gemessen wurde, können die beobachteten Planktonbestände erhalten werden.4. Die gefundenen Verhältnisse lassen umfassendere Beobachtungen in tropischen Gebieten und Versuche über Nahrungsbedarf und Vermehrung der Planktonorganismen wünschenswert erscheinen.

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On the content of seston and plankton in the tropical Atlantic

Some results of two cruises in 1963 during the International Cooperative Investigations of the Tropical Atlantic (ICITA) are reported and interpreted. The average vertical distribution gives seston (particulate matter) values from 20 to 250 mg/m³, and albumin equivalents from 2 to 28 mg/m³. These amounts are considerably less than those observed in the northern part of the Atlantic Ocean. A great variation was observed, which could not always be explained by the general circulation. Accumulation at the surface was more obvious than concentrations of seston and plankton near or in the discontinuity layer of density. A stimulating influence of the equatorial undercurrent on productivity could not be established. In most areas the standing stock of micro-plankton was found to be low when compared to the biomass of larger plankton organisms.

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Herrn Professor Dr.Adolf Bückmann zum 65. Geburtstag in Verehrung gewidmet.     

Plankton und Stoffhaushalt der Mosel bei der Stauhaltung Enkirch 1981

River plancton becomes an important factor in rivers affected by man, as a result of a permanent abundance of P and N, and of a lowering of current velocity transforming a river into a chain of storage basins. This process is demonstrated by means of data from the storage basin of Enkirch on the river Mosel, where in summer the growth of plancton leads to an oxygen deficiency. The mechanisms involved are shown. They are controlled by flow, global radiation, and temperature.

     

Polares Plankton

Polar plankton Climatic changes such as the rise in temperature and ocean acidification have already severely impacted the planktonic life of the Southern Ocean. Our studies demonstrate that Antarctic plankton is changing. Large diatoms contribute most to primary production in the current Southern Ocean, whereas in the future small flagellates could become more abundant. Also zooplankton is impacted. Recent studies reveal a shift from a krill- to a salp-dominated food web in the Southern Ocean and the replacement of polar cold-water species by warm-tolerant species of adjacent regions.     

Plankton communities of an acidic,polymictic, brown-water lake

The plankton of an acidic, polymictic, brown-water lake was investigated over a one-year period. The phytoplankton community was dominated by Chlamydomonas sp., Melosira varians and Peridinium pusillum during different times of the year. Densities were abnormally low, with a maximum of only 13,781 individuals per liter during the March bloom. The water column was nearly void of phytoplankton during the fall. These low densities were attributed to several of the physical and chemical characteristics of the water, including low pH, low levels of nutrients and light limitation. The latter factor was important because of low light transmission into the highly colored water, shading from macrophytes and the nearly continuous transport of the phytoplankton into the aphotic zone due to mixing of the water column by sea breezes.The zooplankton was dominated by Diaptomus floridanus, Polyarthra vulgaris, Keratella cochlearis and Daphnia ambigua. The observed densities were typical of southeastern oligotrophic lakes. The zooplankton community did not exhibit a decrease in density that corresponded with the observed low phytoplankton densities, suggesting the possibility that they relied heavily on bacterial and detrital food sources.     

The Adaptation of Plankton Algae

The various aspects of the adaptation of plankton algae lo light and temperature are discussed. The shape of a light intensity-photosynthesis curve is shown to be an important means of describing the physiological adjustment of an algal population. If the algae are not exposed to adverse influences such as poisons, pronounced nutrient deficiency or light shocks, the rate of real photosynthesis per mg chlorophyll a at 1 Klux (incandescent light) should be about 0.4–0.6 mg C/hour. Hence this rate presents an excellent means of judging the quality of experiments. Experiments are presented where Chlorella pyrenoidosa was adapted to light intensities between 0.32 klux and 21 Klux. This alga adapts to different light intensities by varying the amount of pigments per cell. Algae grown at 1 Klux have about 10 times more chlorophyll per cell than those grown at 21 klux. Other species of algae—but by no means all—are shown to behave in the same way. The problem of algal resistance to photo-oxidation at high light intensities is discussed. Adaplation is shown to he one of the mechanisms which make the algae resistent. “Chlorophyll inactivation” is another. Experiments with the diatom Skeletonema costatum concerning adaptation to different temperatures have been performed. The fact that the alga has essentially the same rate of photosynthesis per cell at all light intensities at 20°C and 7°C, may be attributed to an increase of all the enzymes at the low temperature. The amount of protein per cell was twice as high at 7°C as at 20°C.     

The Adaptation of Plankton Algae

A survey of the adaptation of plankton algae in Nature to different light intensities and temperatures is given. The adaptation is always important for the plankton populations at all depths. However, the shade adaptation of the algae in the lower part of the photic zone is often of relatively little importance for the integral primary production per unit of surface, except on the by no means rare occasions when the bulk of the algae is found in this lower part. It is shown that the I_k of surface plankton during summer in the Arctic is high despite the low temperatures present. This is due to an increase of the enzyme quantities per cell. Daily fluctuations in I_k are due partly to photooxidation, partly to the fact that the periods for the production of chlorophyll and photosynthetic enzymes are mutually displaced. Despite the daily fluctuations in I_k the difference between “sun” pbytoplankton and “shade” pbytoplankton is distinct.     

Simulations in a Plankton Model

A technique for analyzing the stability of a zooplankton, phytoplankton, nutrient interaction model is described. This is an extension of a two-dimensional predator-prey model, incorporating a nutrient food source. In this study difference equations, rather than differential equations, are used to simulate the system since the systems are more easily studied in this formulation. Using only a few reasonable constraints on the system, a remarkable stability is obtained.     

The Adaptation of Plankton Algae

The variation in Skeletonema cells grown at 3 klux continuous illumination and 20°C is reported. Four different types of lamps gave no difference in the photosynthetic characteristics. The average diameter of the cells decreased from 8–3.5 μ during their six months vegetative period. The ratio between the pigment content in the largest and the smallest cells was about 2:1. A good correlation between cell volume and chlorophyll a content was found for this species. The content of chlorophyll c generally varied between 4 and 17 per cent of the chlorophyll a content. — A distinct correlation between the chlorophyll a content and the rate of photosynthesis per unit of cells at low light intensity was found. The rate of photosynthesis, in mg C per mg chlorophyll a and hour at 1 klux, varied between 0.40 and 0.70 for all 60 experiments with an average value of 0.56. The corresponding value for cells deficient in phosophorus was 0.19 and for cells deficient in nitrogen 0.09. — The material also showed a good correlation between the rate of photosynthesis per cell at 1 klux and the light-saturated rate of photosynthesis. I_k varied between 7 and 13 klux.     

Stability in a Plankton Model

A technique for analyzing the stability of a phytoplankton-nutrient interaction model is described which may be applicable to a broader range of models. It is shown that periodicity of solutions in a differential equation does not imply the same for the corresponding difference equation model.     

Plankton motility patterns and encounter rates

Many planktonic organisms have motility patterns with correlation run lengths (distances traversed before direction changes) of the same order as their reaction distances regarding prey, mates and predators (distances at which these organisms are remotely detected). At these scales, the relative measure of run length to reaction distance determines whether the underlying encounter is ballistic or diffusive. Since ballistic interactions are intrinsically more efficient than diffusive, we predict that organisms will display motility with long correlation run lengths compared to their reaction distances to their prey, but short compared to the reaction distances of their predators. We show motility data for planktonic organisms ranging from bacteria to copepods that support this prediction. We also present simple ballistic and diffusive motility models for estimating encounter rates, which lead to radically different predictions, and we present a simple criterion to determine which model is the more appropriate in a given case.