Why is relating plankton community structure to pelagic production so problematic?

The conceptual framework for quantitative marine ecology is attributable to Victor Hensen (1887), who proposed that quantitative studies of plant and animal production in the sea would permit predictions of annual fishyields. Hensen was strongly influenced by concurrent conceptual developments in agriculture, in which crop production was being predicted from knowledge of physiology and its relationship to environmental variables. As fish were being “harvested” by man, it was argued that relationships similar to agriculture existed between primary production and fish yield. Thus was born the notion that pelagic ecosystems were structured from the “bottom-up”, or resource-limited. Subsequent refinements argued that, from basic knowledge of how verticalmixing regulates primary production, and assuming certain features of food-chain length and efficiency, one can estimate fish yields. Fundamental to these arguments are assumptions concerning resource limitation which appear to be uncertain as generic marine pelagic characteristics, primarily that trophic levels are nutrient/food limitedand respond to increased resource availability by elevated standing stocks. Whereas this conceptual model explains certain features of energy flow, it fails to describe how marine pelagic foodwebs are structured andwhy they function as they do. Rather, it appears that certain taxa are better than others at integrating their environments and regulating the flux of materials through the foodweb, and that predation is as important as resource limitation. There appears to be a distinct need in pelagic research to focus on predation, not as a rate process so much as a mechanism responsible for organism behaviour, morphology, life history and community structure

Intra-Firm and Inter-Firm Agglomeration: The Location Decisions of Multi-Unit Firms

abstract: Agglomeration research has investigated a key research question, i.e., why do firms in a specific industry co-locate geographically? In the agglomeration literature, it has been assumed that each firm has one business establishment in a cluster such that firms always co-locate with competitors. However, it is often observed that firms operate several business establishments in a cluster, so they co-locate not only with competitors (i.e., inter-firm agglomeration) but also with their own business establishments (i.e., intra-firm agglomeration). While inter-firm agglomeration is a counterpart to the traditional concept of agglomeration, intra-firm agglomeration is a new concept in agglomeration research. The separation between intra-firm and inter-firm agglomeration raises two research questions – 1) how does intra-firm agglomeration differ from inter-firm agglomeration? and 2) do firms decide their locations for intra-firm vs. inter-firm agglomeration differently? These questions actually extend the key question in agglomeration research into a new setting in which firms have several business establishments in a cluster. I proposed that firms can extract more benefits but neutralize more threats from agglomeration through intra-firm agglomeration than through inter-firm agglomeration. I further developed research hypotheses to test this argument in a research context in which multi-unit firms decide their new establishments’ distances to competitors and their other establishments at the same time. The hypotheses received empirical support in an empirical setting in which 10 large multi-unit hotel firms established new hotels in 20 U.S. cities, and several supplementary analyses show that these results are robust.Dissertation/ThesisDoctoral Dissertation Business Administration 201

Tools for crushing diatoms – opal teeth in copepods feature a rubber-like bearing composed of resilin

Diatoms are generally known for superior mechanical properties of their mineralised shells. Nevertheless, many copepod crustaceans are able to crush such shells using their mandibles. This ability very likely requires feeding tools with specific material compositions and properties. For mandibles of several copepod species silica-containing parts called opal teeth have been described. The present study reveals the existence of complex composite structures, which contain, in addition to silica, the soft and elastic protein resilin and form opal teeth with a rubber-like bearing in the mandibles of the copepod Centropages hamatus. These composite structures likely increase the efficiency of the opal teeth while simultaneously reducing the risk of mechanical damage. They are supposed to have coevolved with the diatom shells in the evolutionary arms race, and their development might have been the basis for the dominance of the copepods within today's marine zooplankton

Effects of rising temperature on pelagic biogeochemistry in mesocosm systems: a comparative analysis of the AQUASHIFT Kiel experiments

A comparative analysis of data, obtained during four indoor-mesocosm experiments with natural spring plankton communities from the Baltic Sea, was conducted to investigate whether biogeochemical cycling is affected by an increase in water temperature of up to 6 °C above present-day conditions. In all experiments, warming stimulated in particular heterotrophic bacterial processes and had an accelerating effect on the temporal development of phytoplankton blooms. This was also mirrored in the build-up and partitioning of organic matter between particulate and dissolved phases. Thus, warming increased both the magnitude and rate of dissolved organic carbon (DOC) build-up, whereas the accumulation of particulate organic carbon (POC) and phosphorus (POP) decreased with rising temperature. In concert, the observed temperature-mediated changes in biogeochemical components suggest strong shifts in the functioning of marine pelagic food webs and the ocean’s biological carbon pump, hence providing potential feedback mechanisms to Earth’s climate system

Taxonomic and Environmental Variability in the Elemental Composition and Stoichiometry of Individual Dinoflagellate and Diatom Cells from the NW Mediterranean Sea

Here we present, for the first time, the elemental concentration, including C, N and O, of single phytoplankton cells collected from the sea. Plankton elemental concentration and stoichiometry are key variables in phytoplankton ecophysiology and ocean biogeochemistry, and are used to link cells and ecosystems. However, most field studies rely on bulk techniques that overestimate carbon and nitrogen because the samples include organic matter other than plankton organisms. Here we used X-ray microanalysis (XRMA), a technique that, unlike bulk analyses, gives simultaneous quotas of C, N, O, Mg, Si, P, and S, in single-cell organisms that can be collected directly from the sea. We analysed the elemental composition of dinoflagellates and diatoms (largely Chaetoceros spp.) collected from different sites of the Catalan coast (NW Mediterranean Sea). As expected, a lower C content is found in our cells compared to historical values of cultured cells. Our results indicate that, except for Si and O in diatoms, the mass of all elements is not a constant fraction of cell volume but rather decreases with increasing cell volume. Also, diatoms are significantly less dense in all the measured elements, except Si, compared to dinoflagellates. The N:P ratio of both groups is higher than the Redfield ratio, as it is the N:P nutrient ratio in deep NW Mediterranean Sea waters (N:P = 20–23). The results suggest that the P requirement is highest for bacterioplankton, followed by dinoflagellates, and lowest for diatoms, giving them a clear ecological advantage in P-limited environments like the Mediterranean Sea. Finally, the P concentration of cells of the same genera but growing under different nutrient conditions was the same, suggesting that the P quota of these cells is at a critical level. Our results indicate that XRMA is an accurate technique to determine single cell elemental quotas and derived conversion factors used to understand and model ocean biogeochemical cycles

Interactive Effect of UVR and Phosphorus on the Coastal Phytoplankton Community of the Western Mediterranean Sea: Unravelling Eco- Physiological Mechanisms

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Accommodating Dynamic Oceanographic Processes and Pelagic Biodiversity in Marine Conservation Planning

Pelagic ecosystems support a significant and vital component of the ocean's productivity and biodiversity. They are also heavily exploited and, as a result, are the focus of numerous spatial planning initiatives. Over the past decade, there has been increasing enthusiasm for protected areas as a tool for pelagic conservation, however, few have been implemented. Here we demonstrate an approach to plan protected areas that address the physical and biological dynamics typical of the pelagic realm. Specifically, we provide an example of an approach to planning protected areas that integrates pelagic and benthic conservation in the southern Benguela and Agulhas Bank ecosystems off South Africa. Our aim was to represent species of importance to fisheries and species of conservation concern within protected areas. In addition to representation, we ensured that protected areas were designed to consider pelagic dynamics, characterized from time-series data on key oceanographic processes, together with data on the abundance of small pelagic fishes. We found that, to have the highest likelihood of reaching conservation targets, protected area selection should be based on time-specific data rather than data averaged across time. More generally, we argue that innovative methods are needed to conserve ephemeral and dynamic pelagic biodiversity