Showing papers on "Pelagic zone published in 1970"

Differential Isotopic Fractionation in Benthic Foraminifera and Paleotemperatures Reassessed

Abstract: Different species of benthic Foraminifera taken at the same level in an Atlantic core yielded different oxygen isotopic values. It was therefore impossible to deduce paleotemperature values. In addition, pelagic and benthic species showed the same isotopic variations, an indication that pelagic and benthic species reflect only the variation of oxygen-18 composition of the ocean.

Faunal variation on pelagic Sargassum

Abstract: Pelagic Sargassum was collected in late summer, late winter, and early and late spring from inshore waters, the Gulf Stream and the Sargasso Sea of the Western North Atlantic Ocean. The noncolonial macrofauna was picked from the weed samples. The 34 samples contained 67 species and 11,234 individuals. The Shannon-Wiener index of diversity had a mean value of 2.419±0.177 (t.05s x − ) and a statistical range between 1.401 and 3.437 (t.05 s). Mean diversity values were not significantly different among the various sampling series, and diversity did not vary with raft volume. High diversity values were related to an equitable distribution of species resulting from a stable environment and an area low in productivity. Species composition of the Sargassum organisms varied seasonally and geographically. Animals were more abundant in the spring than in the fall samples. Samples collected on a transect in the Gulf Stream and Sargasso Sea maintained a similar faunal composition.

Levels of Production in the Pelagic Environment of the Strait of Georgia, British Columbia: A Review

Abstract: Data have been accumulated on seasonal levels of nutrients, primary production, and zooplankton. The occurrence and abundance of larval fish in the surface layers have been reported together with an approximate estimate of the standing stock of commercially exploited fish. The results indicate that beyond local effects, the Strait of Georgia is comparable in productivity to other nearshore waters at the same latitude. The total primary productivity of the waters was found to be approximately 120 g C/m2 per year, but a high degree of areal patchiness in all production data emphasizes the necessity of basing predictions about particular subareas on knowledge specific to the subareas in question.

Population changes within a group of fish species in Lake Tanganyika following their exploitation

Abstract: Pelagic fish populations in Lake Tanganyika consist mainly of two small clupeid species and four centroponiid species which prey on them. Exploitation with purse-seines began in the southeast arm in 1962 and catches were sampled up to early 1969. Inshore clupeid populations were also sampled with a scoop-net (lusenga of the kind used in the traditional inshore fishery. Clupeid biomass reached annual maxima around September. One clupeid species, Stolothrissa tanganicae Regan, dominated pelagic catches except in 2 years when about equal quantities of the other clupeid, Limnothrissa miodon Blgr. were caught. Numbers of each predator (three species of Lates and Luciolates stappersii Blgr.) decreased from 1963 to 1966 and remained low thereafter. The clupeid catch rose from 1964 to 1967 and remained high in 1968. The average nightly catch weight per year of all species together altered relatively little. Changes in population size distributions occurred. Sampling methods were concluded to be valid for clupeid populations, but probably indi-cated only general changes in predator populations. Clupeid life-cycles are mostly accomplished within a year, and appear closely related to the periodic and spatial variations in plankton production. The two species are competitive and can replace one another in the pelagic zone. Certain distribution patterns of the clupeids and of the predator young are believed to be adaptations to severe predation. Low replacement rates under fishing pressure account for the decline of predator species, and the clupeid increase resulted from reduction in predation. A fairly stable exploited phase has apparently been reached in which clupeid biomass is much greater and predator biomass much less than in the natural state. The data encourage certain predictions. Similar major trends occurred in the much larger fishery in the Burundi sector of the lake.

Seasonal and daily dynamics in pelagic larvae of marine shelf bottom invertebrates in nearshore waters of Kandalaksha Bay (White Sea)

Abstract: Seasonal and daily population dynamics have been studied in pelagic larvae of littoral and upper-sublittoral bottom invertebrates in the plankton of the shallow, narrow Velikaya Salma Sound, which connects the inner and outer areas of the Kandalaksha Bay in the western part of the White Sea. Hydrologically, this Sound is characterised by a clearly defined cycle of great seasonal variations in water temperature coupled with more or less stable salinities and regular, pronounced semi-diurnal tides corresponding to daily and lunar monthly tidal cycles. The seasonal dynamics of larvae in the Sound reflect differences in occurrence of spawning periods in local waters of various species and systematic groups of bottom invertebrates. These differences are caused by the correlation of spawning periods of local species of different zoogeographical origin with the different water temperatures. They reflect, also, lunar periodicities of spawning and larval hatchings. The daily dynamics of larval abundancies are related to the daily spawning rhythms of many species with pelagic development affected by the daily tidal cycles of the Velikaya Salma Sound. A daily invasion of the Sound by pelagic larvae of bottom invertebrates from the inner and the outer parts of the Kandalaksha Bay occurs at ebb tide, and also at flood tide; the rhythms of the invasions coincide with the daily spawning rhythms of the Sound's invertebrates. From literature data summarized by Mileikovsky (1958a, b, 1960a, b, c, 1961, 1965, 1968, 1970), it is concluded that seasonal, lunar and daily (tidal) reproductive periodicities for the marine shallowshelf bottom invertebrates concerned, follow world-wide ecological patterns. It is evident that the effects of these rhythms upon the population dynamics of pelagic invertebrate larvae, as demonstrated by the present data on the Velikaya Salma Sound (White Sea), must also follow world-wide regularities.

The uranium content and the activity ratio 234 U/ 238 U in marine organisms and sea water in the western North Pacific

Abstract: The uranium content and activity ratio A234U/A238U were determined in open ocean water, marine plankton, marine algae and sea water in the environment in which plankton and algae live. The average uranium content of 3.34±0.28×10−6 g/l and the average activity ratio of 1.13±0.04 were obtained in open ocean water. The uranium contents in plankton and algae were respectively from 1.7 to 7.8×10−7 g/g and 0.4 to 23.5×10−7 g/g on dry basis with the respective concentration factors of 48 to 260 and 10 to 733. The activity ratio in plankton and algae ranged from 1.07 to 1.18 which coincided well with those in the environmental sea water.

The vertical structure of a pelagic community in the tropical ocean

Abstract: The vertical structure of the ecosystem in the euphotic zone of the western Equatorial Pacific has been studied. The studies were based on a continuous sounding of the bioluminescence field, with simultaneous, vertically aimed sampling made with the aid of a 5l water bottle and plankton nets. The bioluminescence field has a two-maxima structure with a more pronounced and permanent lower maximum found in the oligotrophic regions as deep as 60 to 100 m. In the narrow (10 m) layer of maximum bioluminescence, the concentration of zooplankton, as well as the concentration, activity and production of bacteria and phytoplankton, are several times higher than those in immediately adjacent waters at greater or lesser depth. At the same time, the concentration of nutrient salts in that layer diminishes sharply and approaches zero in the overlying water. Analysis of the data obtained shows that the production processes above the lower maximum layer are dependent not only on the turbulent influx of nutrient salts from the underlying layers, but also on the horizontal supply from the zone of upwelling. A pelagic community, in its different time aspects from the moment of water ascending until its sinking in the convergence zone, is suggested as a common system for modelling.

Biology of the small pelagic fishes in the new Volta Lake in Ghana: Part I: The lake and the fish: Feeding habits

Abstract: SummaryA number of small pelagic fish species were found in the new Volta Lake in Ghana. Three, the clupeids Cynothrissa mento and Pellonula afzeliusi, and the schilbeid Physailia pellucida, rapidly became dominant, and these together with another schilbeid Siluranodon auritus and the clupeid-like cyprinid Barilius niloticus are here considered. Pellonula and Physailia eat chiefly invertebrates; the former especially at the surface, the latter in mid-depths or at the bottom. Zooplankton is important to all sizes of Physailia, but only to juveniles of Pellonula. Barilius feeds almost entirely on adventitous forms taken at the surface and Siluranodon on algae and rotifers. Cynothrissa, the largest fish studied, feeds mainly on fish. The food range taken is thus wide, and differences in diet are discussed in terms of the probable future of each species in the new lake as it matures.

Complete cycle of development of a pelagic chaetognath in culture.

Abstract: THE complete cycle of development from egg to egg for a pelagic species of chaetognath has not been achieved previously1 in the laboratory. Dallot2 maintained Sagitta setosa and Murikami3,4 S. crassa long enough to observe cyclic reproductive changes. Murikami reared larvae for several days as I did5 with S. hispida. Otherwise, the life span of most chaetognaths brought into the laboratory has been measured in hours6. Extended studies of live chaetognaths would be useful because these are among the commonest marine macroplanktonic carnivores and, as such, must play a major part in the trophodynamics of the sea. They have also frequently been used as “indicator species” for water masses7.

The influence of pollution on pelagic larvae of bottom invertebrates in marine nearshore and estuarine waters

Abstract: At present, human activities on marine shores, nearshore waters and estuaries, as well as in rivers which discharge into the seas, are influencing nearshore and estuarine waters so strongly that the resultant changes affect the breeding and spawning of bottom invertebrates which inhabit these waters. The majority of bottom invertebrate species from the shallow shelf of all seas and oceans, and from all except the highest latitudes, pass through a pelagic larval phase during development. Thus, survival and maintenance of such species are determined by survival and distribution of larvae during their planktonic phase and their settling on the substrate. Consequently, an attempt to summarize all available data on the influence of pollution in marine and estuarine waters, not only on adult bottom invertebrates, but also on their pelagic larvae, will be of practical interest from both scientific and economic points of view. This paper represents a first step towards that goal. Despite the fact that all aspects of pollution-industrial wastes (including heated effluents producing “thermal pollution”), domestic sewage, oil and oil products, oil-spill removers and oil-emulsifiers, various pesticides, synthetic surfactants, etc.—exert harmful effects on pelagic larvae of bottom invertebrates under experimental conditions, in natural environments, free-swimming larvae are influenced only slightly by these pollutants. Pollution becomes a grave danger for larvae when they are settling on the substrate, as much higher concentrations of different pollutants may be present on the substrate than in the water mass above it (the pollution of every nearshore water mass usually varies greatly from place to place). Pelagic larvae of bottom invertebrates inhabiting comparatively clean parts of polluted regions are dispersed throughout all such regions by local currents, tidal oscillations, eddies and other small-scale water movements. They represent, therefore, the potential source for re-establishment of the normal composition of the bottom communities in these regions, after the abatement of pollution by means of natural causes or by man's own improvements.

The biology of false bay, south africa

Abstract: Summary The water in False Bay is derived from both the Agulhas and the Benguela currents and this is reflected in the nature and composition of the benthic fauna. Hydrological conditions within the bay are summarized and it is shown that the distribution of the warm and cold water species is related to the pattern of water temperatures in summer. The vertical distribution of the fauna on the shores and submerged banks is also briefly described. A great variety of demersal fishes feed along the rocky shores and submerged reefs. Pelagic fish such as albacore and tunny also migrate into the bay in summer, so that False Bay has become famous as an angling resort. This tourist attraction is of greater economic importance than commercial fishing in the bay.

Potential bioassay of natural seawaters and influence of certain trace elements on the growth of phytoplankton organisms

Abstract: 1. Natural sea water collected at different months from the English Channel at Plymouth and from the Celtic Sea were enriched with N, P, Fe and bioassayed with unialgal cultures of the pelagic diatomChaetoceros didymus, a reddish flagellate “A” andPhaeodactylum tricornutum. 2. The first two organisms together with the green algaStichococcus sp. (cf.S. cylindricus Butcher) were isolated from the Plymouth plankton and subcultured in artificial sea water, and thePhaeodactylum cornutum was supplied from the strain culture of the Plymouth Laboratory. The relative growth constant ofChaetoceros didymus was taken as an index to classify the different waters according to their suitability for the growth of this diatom. These waters could then be classified in the following order: (a) Celtic sea water of March, (b) Plymouth water of February, (c) Celtic sea water of May, (d) Plymouth water of July, (e) Celtic sea water of July and (f) Plymouth water of March. 3. Mixing of “good” and “bad” waters improved the qualities of the bad water, but growth again declined after 10–15 days. 4. Artificial sea water with soil extract approximates the qualities of “good” natural sea water. 5. Properties of the “bad” or “sterile” waters could be improved by additions of Cu, particularly when this metal in the natural water was impoverished. 6. Celtic Sea waters of May, July and (to a lesser extent) of March, induced auxospore formation inChaetoceros didymus. This capacity was inhibited by additions of traces of Cu. 7. Li causes elongation of cells in bothChaetoceros didymus andStichococcus sp. The morphological effects of this element on phytoplankton cells require further studies. 8.Phaeodactylum tricornutum and flagellate “A” gave similar results to those ofChaetoceros didymus with regard to the bioassayed waters employed. 9.Phaeodactylum tricornutum andStichococcus sp. appear to be sensitive to traces of Cu, while the latter species, together with flagellate “A”, can tolerate high concentrations of Li. 10. Evidence has also been obtained that the ageing of sea water could improve its qualities.

The Seasonal Distribution of Some Seabirds off Washington and Oregon, with Notes on Their Ecology and Behavior

Abstract: Knowledge of seabirds in pelagic waters off the Washington and Oregon coasts is quite fragmentary. Although there are papers on a few species in or near this general region (e.g., Martin 1942; Yocom 1947a, b; Kenyon 1950; Guiguet 1953; Sanger 1965; Poole 1966), the observations were usually qualitative and made from scattered locations or during only one season. An exception is McHugh's (1955) analysis of Black-footed Albatross distribution off North America in 1949-1950. Gabrielson and Jewett (1940) and Jewett et al. (1953) summarized knowledge of seabirds within a relatively few kilometers of shore, but only speculated on distribution and abundance of species in pelagic areas. Moreover, measurement of the oceanic environment concurrent with systematic seabird observations has been virtually nonexistent. Clearly, uniform observations repeated over several seasons have been needed for a better understanding of seabird distribution in the area.

Little Tuna Euthynnus affinis in the Hong Kong area

Abstract: This is the first description of the biology of Euthynnus affinis in the Hong Kong area and is based on examination of samples of fish and on other data collected during 1967-69. A population of E. affinis inhabits the south coast of Kwangtung, China where it is the commonest tuna species. Adult fish concentrated inshore to spawn each year during June-August in water of surface temperature 25-29°C and salinity 26-29‰. Two distinct size-groups of fish made up the spawning schools; many fish of mean size 62cm long (weight 4.5kg) and lesser numbers of fish of mean size 44cm long (weight 1.9kg). These size-groups were probably 2 and 1 years-old respectively. The tuna lived dispersed over the continental shelf during other months of the year. Food eaten consisted chiefly of pelagic fish and cephalopods. The behaviour, length-weight relation and growth rate of the fish are described. Commercially useful catches could probably be taken from the summer spawning concentrations if purse seining methods were used.

Records of pelagic copepods off Kaikoura, New Zealand

Abstract: Summary Additions to the pelagic copepod fauna of Kaikoura, New Zealand, include 20 species previously unrecorded and the males of 8 species for which females only had been recorded; further information concerning 2 other species is added.