Simultaneous optimization of dynamic bioprocesses

It is known that the optimal control may introduce significant economical benefits into production processes, thus being an important and challenging research area with practical relevance. The modeling and optimization of biotechnological processes has been object of research and their related results have generated improvements in operating conditions and strategies, however, the inherent features of dynamical bioprocesses prevent the application of conventional optimization algorithms, hence making necessary the development of tailored methods and strategies. The objective of this work is to develop mathematical programming strategies for simultaneous optimization of dynamic systems and evaluate their computational performance. Simultaneous optimization with orthogonal collocation is applied to a simplified model for biosynthesis of penicillin from glucose, which was studied by Cuthrell and Biegler (1989). The results show that discretization of differential equations systems (DAE) by orthogonal collocation in finite elements efficiently transforms dynamic optimization problems into nonlinear programming (NLP) problems, enabling to solve complex problems with several control variables and minimizing the approximation error

Cryptic life stages in scyphozoan jellyfish: Larval settlement preferences of the South American sea nettle Chrysaora plocamia

Bloom forming jellyfish have received considerable attention over the past years. And while the eye-catching medusa is well studied, little is known about its small, inconspicuous and hard to find polyp-counterpart. In fact, so hard to find that polyps of most scyphozoan species have not been detected in their natural habitat. Considering the important roles polyps may play in jellyfish bloom formation, identifying the criteria for planulae to select suitable microhabitats that warrant the well-being and survival of polyps is a key issue. In order to find clues on the characteristics of natural habitats of Chrysaora plocamia polyps, settlement preferences of planulae were determined in a laboratory study. The settlement density, geotaxis and colour preferences were assessed, using a three-dimensional substrate that provided settlement areas of different orientation, levels of shelter and colours. Planulae exclusively colonized horizontal surfaces in an upside down position, tended to settle in sheltered areas and showed significant preferences for green and red substrates. If planulae of the jellyfish C. plocamia display similar preferences in the field, polyps should be found on protected substrates that provide overhangs, small caves, crevices or roof-surfaces, and green or red substrates, like stipes and blades of macroalgae, or crustose coralline algae

Recurrent, thermally-induced shifts of species distribution range in the Humboldt Current Upwelling System

El Niño-Southern Oscillation (ENSO) is a global climate variablility, which fundamentally influences environmental patterns of the Humboldt Current System (HCS) off Chile and Peru. The surf clams Donax obesulus and Mesodesma donacium are dominant and highly productive bivalves of exposed sandy beaches of the HCS. Existing knowledge indicates that El Niño (EN, warm phase of ENSO) and La Niña (LN, cold phase of ENSO) affect populations of both species in a different way, although understanding of the mechanisms underlying these effects is still lacking. The aim of this study was to test hypotheses attempting to explain field observations on the effect of strong EN or LN events by using controlled experimental conditions. Growth and mortality rates of both species were registered during a four-week experiment under EN temperature conditions, normal temperature conditions and LN temperature conditions. While D. obesulus exhibited reduced growth and higher mortality under LN conditions, M. donacium showed reduced growth and higher mortality under EN conditions. The results clearly indicate different temperature tolerance windows for each species, possibly reflecting the evolutionary origins of the Donacidae and Mesodesmatidae in regions with contrasting temperature regimes. These results provide experimental support for previous hypotheses suggesting that thermal tolerance is the driving factor behind observed changes in the species distributions of D. obesulus and M. donacium during the extreme phases of ENSO. 2010 Elsevier Ltd. All rights reserved

The elusive life cycle of scyphozoan jellyfish – metagenesis revisited

Massive proliferations of scyphozoan jellyfish considerably affect human industries and irreversibly change food webs. Efforts to understand the role of jellyfish in marine ecosystems are based on a life cycle model described 200 years ago. According to this paradigm the pelagic medusae is considered seasonal and alternates with the benthic polyp stage from which it derives. However, we provide evidence that a) the occurrence of several species of medusae is not restricted to a season in the year, they overwinter, b) polyp- and medusa generations are neither temporally nor spatially separated, and c) "metagenesis" which is defined as the alternation between sexual and asexual generations does not always occur. Hence we recommend additions to the current model and argue that the scyphozoan life cycle should be considered multi-modal, rather than metagenetic. The implications of these findings for jellyfish proliferations, including possible consequences and associated environmental drivers, are discussed

A comparison of the suitability of different stains for inducing a non-lethally, detectable mark in Concholepas concholepas and Mesodesma donacium

Different stains are used to internally mark calcified structures of mollusc shells in growth experiments. Because of interspecific variations in marking success, an assessment of suitability for each species is necessary. The potential of calcein, alizarin red, and strontium chloride hexahydrate (strontium chloride) was investigated for the Chilean abalone Concholepas concholepas and the surf clam Mesodesma donacium, two molluscs of commercial importance in Chile. Wild specimens from Northern Chile were marked using different concentrations and immersion periods of the three stains. Animals were reared for 20 days to allow growth, mortality, body condition index (BCI), and growth rate was measured to assess the effects of the treatments. To detect marks, individuals were culled and shell sections analyzed using scanning electron microscopy for strontium chloride and fluorescence microscopy for calcein and alizarin red, respectively. Strontium chloride produced narrow bright bands only at concentrations of 2,880 [mg x [l.sup.-1] and 24 h exposure. Calcein markings produced fluorescent bands detectable in all treatments (50 and 100 mg x [l.sup.-1], 3 and 6 h) whereas alizarin red only yielded irregular bands with 50-100 mg x [l.sup.-1] and 6 h exposure. Our results show that growth rates of C. concholepas are significantly affected by the stains factor: Strontium chloride showed the lowest growth rates whereas that of alizarin red and calcein was similar to the control group. High concentrations of strontium chloride negatively affected (P < 0.05) the body condition of the gastropod. Although no statistical differences were found, BCI of M. donacium followed the same trend as observed for C. concholepas. In conclusion, calcein was the best growth marker for both species because it produced bright, long-lasting bands even at low concentrations and immersion times without detectable lethal or sublethal effects