22 resultados para Historical interpretation

em Plymouth Marine Science Electronic Archive (PlyMSEA)


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This document provides details of the transfer of the Norman Holme archive data held in the National Marine Biological Library onto a modern database, specifically Marine Recorder. A key part in the creation of the database was the retrieval of a large amount of information recorded in field notebooks and on loosely-bound sheets of paper. As this work involved amending, interpreting and updating the available information, it was felt that an accurate record of this process should exist to allow scientists of the future to be able to clearly link the modern database to the archive material. This document also provides details of external information sources that were used to enhance and qualify the historical interpretation, such as estimating volumes and species abundances.

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The Continuous Plankton Recorder (CPR) survey has collected plankton samples from regular tracks across the world's oceans for almost 70 y. Over 299,000 spatially extensive CPR samples are archived and stored in buffered formalin. This CPR archive offers huge potential to study changes in marine communities using molecular data from a period when marine pollution, exploitation and global anthropogenic impact were much less pronounced. However, to harness the amount of data available within the CPR archive fully, it is necessary to improve techniques of larval identification, to genus and species preferably, and to obtain genetic information for historical studies of population ecology. To increase the potential of the CPR database this paper describes the first extraction, amplification by the polymerase chain reaction and utilization of a DNA sequence (mitochondrial 16S rDNA) from a CPR sample, a formalin fixed larval sandeel.

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Monitoring of Phaeocystis since 1948 during the Continuous Plankton Recorder survey indicates that over the last 5.5 decades the distribution of its colonies in the North Atlantic Ocean was not restricted to neritic waters: occurrence was also recorded in the open Atlantic regions sampled, most frequently in the spring. Apparently, environmental conditions in open ocean waters, also those far oVshore, are suitable for complete lifecycle development of colonies (the only stage recorded in the survey). In the North Sea the frequency of occurrence was also highest in spring. Its southeastern part was the Phaeocystis abundance hotspot of the whole area covered by the survey. Frequency was especially high before the 1960s and after the 1980s, i.e., in the periods when anthropogenic nutrient enrichment was relatively low. Changes in eutrophication have obviously not been a major cause of long-term Phaeocystis variation in the southeastern North Sea, where total phytoplankton biomass was related signiWcantly to river discharge. Evidence is presented for the suggestion that Phaeocystis abundance in the southern North Sea is to a large extent determined by the amount of Atlantic Ocean water Xushed in through the Dover Strait. Since Phaeocystis plays a key role in element Xuxes relevant to climate the results presented here have implications for biogeochemical models of cycling of carbon and sulphur. Sea-to-air exchange of CO2 and dimethyl sulphide (DMS) has been calculated on the basis of measurements during single-year cruises. The considerable annual variation in phytoplankton and in its Phaeocystis component reported here does not warrant extrapolation of such figures.

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An historical data set, collected in 1958 by Southward and Crisp, was used as a baseline for detecting change in the abundances of species in the rocky intertidal of Ireland. In 2003, the abundances of each of 27 species was assessed using the same methodologies (ACFOR [which stands for the categories: abundant, common, frequent, occasional and rare] abundance scales) at 63 shores examined in the historical study. Comparison of the ACFOR data over a 45-year period, between the historical survey and re-survey, showed statistically significant changes in the abundances of 12 of the 27 species examined. Two species (one classed as northern and one introduced) increased significantly in abundance while ten species (five classed as northern, one classed as southern and four broadly distributed) decreased in abundance. The possible reasons for the changes in species abundances were assessed not only in the context of anthropogenic effects, such as climate change and commercial exploitation, but also of operator error. The error or differences recorded among operators (i.e. research scientists) when assessing species abundance using ACFOR categories was quantified on four shores. Significant change detected in three of the 12 species fell within the margin of operator error. This effect of operator may have also contributed to the results of no change in the other 15 species between the two census periods. It was not possible to determine the effect of operator on our results, which can increase the occurrence of a false positive (Type 1) or of a false negative (Type 2) outcome

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Anthropogenically released CO2 is dissolving in the ocean, causing a decrease in bulk-seawater pH (ocean acidification). Projections indicate that the pH will drop 0.3 units from its present value by 2100 (ref. 1). However, it is unclear how the growth of plankton is likely to respond. Using simulations we demonstrate how pH and carbonate chemistry at the exterior surface of marine organisms deviates increasingly from those of the bulk sea water as organism metabolic activity and size increases. These deviations will increase in the future as the buffering capacity of sea water decreases with decreased pH and as metabolic activity increases with raised seawater temperatures. We show that many marine plankton will experience pH conditions completely outside their recent historical range. However, ocean acidification is likely to have differing impacts on plankton physiology as taxon-specific differences in organism size, metabolic activity and growth rates during blooms result in very different microenvironments around the organism. This is an important consideration for future studies in ocean acidification as the carbonate chemistry experienced by most planktonic organisms will probably be considerably different from that measured in bulk-seawater samples. An understanding of these deviations will assist interpretation of the impacts of ocean acidification on plankton of different size and metabolic activity.