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Spatio-temporal variability of small copepods (especially Oithona plumifera) in shallow nearshore waters off the south coast of South Africa 总被引：1，自引：0，他引：1
Francesca Porri Christopher D. McQuaid William P. Froneman 《Estuarine, Coastal and Shelf Science》2007,72(4):711-720
Although small copepods are one of the main dietary sources for many commercially important fish, their role in the pelagic trophic dynamics has traditionally been underestimated due to the methodology commonly used in plankton sampling. Temporal variation in abundance of adults and nauplii of small copepods (particularly Oithona plumifera) in nearshore waters on the south coast of South Africa was investigated fortnightly over 14 months at site (km) and location (100 m) scales. Sampling was within <500 m of the shore, where depth was ca. 10 m, using vertical hauls of an 80-μm mesh plankton net from 1 m above the seabed to the surface. Twenty-seven adult copepod taxa were recorded, but Oithona spp. was consistently the most abundant. Taxon richness was 7–19 on each sampling occasion. There was strong temporal variation (Oithona varied between 0 and 2300 m−3), but much of this was short-term variability (e.g. between consecutive sampling sessions), with no seasonality or other long-term discernable patterns. There were periods of consistently low numbers, but very high numbers often followed samples with low abundances. Nor was there spatial structure at the location scale, though numbers differed between sites. Despite considerable variability at the location scale within sites, Kenton consistently showed higher densities than High Rocks. Separate analyses, with Bonferroni adjustment, showed that this difference was significant on eight out of 21 occasions for Oithona, six for other pelagic copepods and three for nauplii. This suggests that hydrodynamics favour aggregation of plankton at Kenton. A high degree of short-term variability, with a tendency for aggregation of small zooplankton at certain sites has implications for both pelagic processes and food-web links between the benthic and pelagic environments. 相似文献
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Katja Fennel 《Ocean Dynamics》2001,52(2):58-70
Elken et al. (1994) suggested that phytoplankton patchiness can be generated by mesoscale eddies in light-limited, nutrient-replete
environments. This hypothesis is explored using two ecological models of different physical complexity. The model results
support the idea that the coupling of mesoscale eddy circulation and phytoplankton growth leads to differential growth rates
and thus generates variability in phytoplankton distributions. The specific circulation of a cyclonic eddy isolates a phytoplankton
population in its core. Due to the reduced vertical mixing, a higher growth rate is supported in the core, and phytoplankton
concentrations increase compared to the surrounding environment. A one-dimensional model is used to explore the hypothesis
in general and to perform sensitivity studies. A more realistic simulation uses a coupled three- dimensional model for the
western Baltic Sea. Starting from vertically and horizontally homogeneous distributions for nutrients and plankton, the models
generate patchiness due to the proposed mechanism. The described mechanism may apply for other mesoscale variable environments
during light-limited growth periods as well, e.g., the frontal region of the Southern Ocean.
Received: 31 March 2001 / Accepted: 31 August 2001 相似文献
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Total evaporation is of importance in assessing and managing long-term water use, especially in water-limited environments. Therefore, there is need to account for water utilisation by different land uses for well-informed water resources management and future planning. This study investigated the feasibility of using multispectral Landsat 8 and moderate resolution imaging spectroradiometer (MODIS) remote sensing data to estimate total evaporation within the uMngeni catchment in South Africa, using surface energy balance system. The results indicated that Landsat 8 at 30 m resolution has a better spatial representation of total evaporation, when compared to the 1000 m MODIS. Specifically, Landsat 8 yielded significantly different mean total evaporation estimates for all land cover types (one-way ANOVA; F4.964?=?87.011, p < 0.05), whereas MODIS failed to differentiate (one-way ANOVA; F2.853?=?0.125, p = 0.998) mean total evaporation estimates for the different land cover types across the catchment. The findings of this study underscore the utility of the Landsat 8 spatial resolution and land cover characteristics in deriving accurate and reliable spatial variations of total evaporation at a catchment scale. 相似文献
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We present a study on the emergence of spatial variability, or patchiness, in biophysical simulations of plankton ecosystems. Using a standard approach to modelling such ecosystems, we represent a distribution of plankton as a lattice of non-identical interacting oscillatory populations. Spatial variation is imposed in population parameters, such as maximum growth rate, leading to a spread in the natural (uncoupled) population properties. Using the methods of synchronisation theory, the emergent spatial structure of the coupled system is investigated as a function of the strength of interaction between populations. Surprisingly, a range of coupling strength is found to induce a tenfold increase in the spread in frequency of oscillation of populations in comparison with the uncoupled level of spatial variation. This apparent desynchronisation corresponds to the formation of temporally evolving clusters of local synchronisation: the interplay of grid-cell scale variability and dispersal between populations leads to patchiness at larger scales. However, the occurrence and length-scale of this patchiness is found to be sensitive to typical simulation parameters such as spatial resolution and strength of dispersal, with emergent spatial structure altering abruptly from patchy to homogeneous as these parameters are varied. These results indicate that whilst cluster synchronisation may be a genuine mechanism for the formation of spatial structure in plankton distributions, biophysical modellers should be aware of the possibility of artificial patchiness arising from the basic physical structure of their model. 相似文献
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J.R. Seymour L. Seuront M.J. Doubell J.G. Mitchell 《Estuarine, Coastal and Shelf Science》2008,80(4):589-597
Sampling was conducted within inshore and offshore sites, characterized by highly dissimilar hydrodynamic and hydrobiological conditions, in the Eastern English Channel. The eutrophic inshore site was dominated by the influence of a dense bloom of the Prymnesiophyceae phytoplankton species Phaeocystis globosa, while the offshore site was characterized by more oceanic conditions. Within each site the microscale distributions of chlorophyll a and several flow cytometrically-defined subpopulations of heterotrophic bacteria and viruses were measured at a spatial resolution of 5 cm. The inshore site was characterized by comparatively high levels of microscale spatial variability, with concentrations of chlorophyll a, heterotrophic bacteria, and viruses varying by 8, 11 and 3.5-fold respectively across distances of several centimeters. Within the offshore site, microscale distributions of chlorophyll a and bacteria were markedly less variable than within the inshore site, although viruses exhibited slightly higher levels of heterogeneity. Significant mesoscale variability was also observed when mean microbial parameters were compared between the inshore and offshore sites. However, when the extent of change (max/min and coefficient of variation) was compared between meso- and microscales, the variability observed at the microscale, particularly in the inshore site, was substantially greater. This pattern suggests that microscale processes associated with Phaeocystis globosa bloom dynamics can generate heterogeneity amongst microbial communities to a greater degree than large scale oceanographic discontinuities. 相似文献
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