Phyto-and Zooplankton Research Articles

Elevated cadmium accumulation in marine organisms from Terra Nova Bay (Antarctica)

As a contribution towards identification of the principal environmental factors involved in cadmium accumulation in Antarctic marine organisms and the establishment of a baseline near the Italian Antarctic Station “Baia Terra Nova”, surface sediments, plankton and benthic organisms were studied in coastal waters of Terra Nova Bay (Ross Sea). The cadmium content of sediments was similar to that regarded as background in most marine coastal areas, whereas in surface water, phytoand Zooplankton it was similar to values measured in areas of enhanced upwelling. Algal and animal taxa dominating benthic associations had a higher cadmium content than related species from other seas. Very high concentrations of the metal were found in sponges (10–80 μg/g dw) and in the digestive gland of molluscs (up to 345 μg/g inNeobuccinum eatoni). The rapid regeneration of cadmium and its natural occurrence and bioavailability in highly productive coastal waters seem to be responsible for cadmium accumulation in the tissues of marine organisms near the “Baia Terra Nova” station.

Factors affecting the respiration/ETS ratio in marine zooplankton

Factors affecting the respiration/ETS ratio in marine zooplankton

Convergent succession of phytoplankton in microcosms with different inoculum species composition

Different initial mixtures of phyto-and zooplankton from different lakes were grown under identical chemical and physical conditions in medium size (8-and 12-1) laboratory microcosm cultures until convergence of phytoplankton species composition was attained. Five such experiments with four (four experiments) or three (one experiment) microcosm cultures were run. Three experiments were performed with weak stirring which permitted sedimentary elimination of the diatoms. Two experiments were conducted with stronger stirring to prevent sedimentation. In the three "sedimentation intensive" experiments, the final phytoplankton community was composed of the filamentous chlorophyte Mougeotia thylespora together with a smaller biomass of nanoplanktic algae. In the two "sedimentation free" experiments the final phytoplankton community consisted of pennate diatoms. Both dissolved nutrient concentrations and the chemical composition of biomass suggested strong nutrient limitation of algal growth rates in the final phase of the experiments. The zooplankton communities at the end of the experiments were composed of species that were apparently unable to ingest the large, dominant algae and that presumably fed on the nanoplanktic "undergrowth" and the bacteria. There was a distinct sequence of events in all experiments: first, the large zooplankton species (Daphnia and Copepoda) were replaced by smaller ones (Chydorus, Bosmina, rotifers); second, all cultures within one experiment developed the same nutritional status (limitation by the same nutrient); and third, the taxonomic composition of phytoplankton of the different cultures within one experiment converged. The last took 7-9 weeks, with is about 2-3 times as long as the time needed in a phytoplankton competition experiment to reach the final outcome.

Succession of the plankton community during coastal reclamation with the solid wastes.

The plankton community was investigated in the pond constructed on the coast line of Kitakyushu City, Northern Kyushu, Japan, where various kinds of solid wastes such as soil from land source, domestic wastes, and industrial wastes, had been dumped from 1980 to 1987. The cell density of phytoplankton continued to increase gradually and red tides were observed from 1983. The plankton community was predominated by several species of diatoms, dinoflagellates, Cryptophyceae, green algae, filamentous bacterium, ciliates, and rotifers. Some of them occurred continuously or cyclically during certain periods. Closing to the end of reclamation, a phototrophic red sulfur bacterium Thiocapsa roseopersicina predominated twice and discolored the water to purple-brown. At the first time, phytoplankton almost disappeared from the pond but retrieved after a few months, and at the second time phytoplankton occurred abundantly with the phototrophic bacterium. Thus, in the case of this pond, the specific phyto-and zooplankton adapting to the water quality seem to have appeared one after another during almost whole time of this investigation. A large amount of plankton was suggested to play an important role in the self-purification of the water quality in the pond, and the pond acts as an oxidation pond for the polluted water caused by the solid wastes dumped.

Moult cycle and seasonal activities of chitinolytic enzymes in the integument and digestive tract of the Antarctic krill, Euphausia superba

Chitinolytic activity was quantified in euphausiid integuments in relation to moulting. In Euphausia superba, shortly before moult the activity increased in chitinase and N-acetyl-β-D-glucosaminidase to pronounced maxima indicating the onset of massive resorption of cuticular material. Enzymatic activity of E. superba corresponded to values in Meganyctiphanes norvegica, a boreal euphausiid which was investigated for comparison, as well as in insecta. Antarctic krill from winter catches displayed activities comparable to summer material suggesting physiological preparation for moulting. Accordingly, moulting did not cease during winter. Both enzymes were also active in the digestive tract in summer as well as in winter krill: chitin containing food of phyto-and zooplankton origin is digestable. Seasonally stable activities did not point to changes in nutritional preference. In contrast to other crustacea, digestive enzyme activity was not reduced around moult, suggesting a high capacity to continuously utilize food sources including chitin. This property can be linked directly to the high energy need caused by the necessity of constant active swimming in both krill species.

Seasonal variations in the trophic structure of phyto-and zooplankton communities in lakes in different trophic states

A number of environmental factors are important in regulating the trophic structure of plankton. Increased nutrient supply results in an explosive development of small algae and herbivorous zooplankton. In the eutrophic lakes (Greifensee, Hallwilersee) several algal community collapses occur each year as a consequence of the grazing habit of the zooplankton, although only the grazing phase in May/June results in a ‘clear water period’. Vertical mixing influences the zooplankton community by reactivating the resting stages of predatory copepods. Predation phases can only be observed in lake Lucerne, where the hypolimnion ist deep and aerobic. Well balanced relationships between the different trophic levels are restricted to the phases with growth limiting conditions.

Phytoplankton, Zooplankton and Bacteria: Standing Crop and Production Relationships in a Eutrophic Lake

Standing crop and production of bacteria, phytoand zooplankton, and chemical and physical parameters were studied during 1975 in the small eutrophic Lake Bysjon, Sweden. Phytoplankton specific growth and loss rates were calculated over a two-month period during spring circulation. Phytoplankton developed a springStephanodiscus and a late-summer Aphanizomenon bloom. Physical and chemical parameters, including organic and inorganic nutrient fractions, varied rapidly during bloom development and decline. Peaks in bacterial numbers developed immediately following collapse of both algal blooms, indicating algal autolysis and decomposition products as important substrates for bacterial growth. Net phytoplankton excretion was under 1% of 14C annual production. Due to low over-all predation, large filter feeders dominated the zooplankton. The zooplankton seasonal succession was probably due to selective predation by fish, food availability and physiological differences among species. Calculation of phytoplankton growth rate constants, grazing losses, and other losses during the spring Stephanodiscus bloom showed that nongrazing losses (sedimentation, death and decomposition) predominated.

Notes on the Simulation of Natural Aquatic Conditions in Fresh‐Water by the Use of Small Non‐Circulating Balanced Aquaria

The methods developed for handling small non-circulating balanced aquaria supplied with river water were a gradual development during the five year period mentioned, and were given their first trials after I had faced complete failure with small jars supplied with the variously fouled water drawn from the taps connected with the large overhead tank located near the ceiling in the dark in the floating station's laboratory.1 The water supply used in the more successful experiments was dipped up in buckets, from the boat deck, as it lay in Cook's Slough, a small arm of the Illinois River. The Slough, except at flood stages, is reasonably clear, though never completely so, and during the growing season is always well supplied with a rich phytoand zoo-plankton, and usually with considerable coarse vegetation and a great variety of insect larvae, snails, worms, crustacea, and other small invertebrates. EQUIPMENT