A mathematical model of the assimilation process in the copepod Calanus finmarchicus (Gunnerus) : computer simulations discussed in relation to experimental results

Feeding, digestion and assimilation are usually treated as separate aspects in studying the physioecology of copepods. A general model predicting the assimilation rate from ingestion rate, phytoplankton species compositon and digestive or physiological state of the animal is presented. The assumption is made that digestion is accompanied by a subsequent decrease in cell volume, which is equal to the assimilated part of the cell. In addition, a time delay between ingestion and the onset of digestion is assumed to describe the digestion properties of the algal cells. The model predicts a decrease in assimilation efficiency with increasing ration. The minimum gut passage time and the digestion rate seem to be the most important parameters for the production of copepods. These and other characteristics of the model are discussed in relation to available information

Biovolume spectrum theories applied: spatial patterns of trophic levels within a mesozooplankton community at the polar front

Three-dimensional data on the mesoscale distribution of hydrography and mesozooplankton were collected at the Polar Front, northwestern Barents Sea, in spring 2008 (29 April–15 May) using a combination of multinet and towed instrument platform equipped with Laser Optical Plankton Counter, fluorometer and CTD. Trophic levels (TLs) within the zooplankton community (whole community and size-separated) were analysed for three consecutive periods using biovolume spectrum theory, which proved to be a powerful tool in the physically and biologically variable frontal system. Trophic structure was highly variable in time and across the Polar Front, but was mostly related to the phytoplankton bloom (as determined by fluorescence). High TLs of 5.5 within the zooplankton community were observed outside bloom situations (mostly in Atlantic Water) and were likely due to increased omnivory of Calanus spp., which dominated the large zooplankton size group that had a lower TL (2.2) during the bloom than outside blooms (max. TL 5.6). A strong input of herbivorous barnacle nauplii (Cirripedia) into the upper layer (35 000 ind. m−3 in net samples) substantially decreased mean TL in the marginal ice zone. Differences in TL estimates based on biovolume spectrum theory and other methods (stable isotopes, lipid markers, dietary analyses) are discussed

Comparative analysis of Calanus finmarchicus demography at locations around the Northeast Atlantic

Standardized time-series sampling was carried out throughout 1997 at seven locations around the Northeast Atlantic to investigate regional variations in the seasonal demography of Calanus finmarchicus. Sites ranged from an inshore location in the North Sea, where C. finmarchicus formed only a small component of the zooplankton (2000 mgC m-2 during spring and summer). The internal consistency of the demographic time-series from each site was investigated by three partial models of life-cycle processes. In general, the demography of late copepodites could be accounted for by a relatively simple forecast model of stage development and diapause. However, there was a large discrepancy between nowcast estimates of egg production based on female abundance, temperature, and chlorophyll, and hindcast simulations of the egg production required to account for the observed abundance of early copepodite stages. The results point to a gap in our understanding of seasonal variations in rates of egg production and/or survival of nauplii. Overall, the population sampled at Weathership M appeared to be reasonably self-contained, but all other sites were reliant on invasion of overwintered stock in spring. At least two generations were observed at all but one site, but the extent to which these were generated by discrete bursts of egg production varied between sites and seemed to be partly dependent on the proximity to an overwintering location

Three Dimensional Functional Cartography Of The Human Basal Ganglia By Registration Of Optical And Histological Serial Sections

In functional neurosurgery, there is a need for accurate locatisation of the functional targets. One example is given by Parkinson's disease. The surgical intervention is based on the introduction of electrodes in the subthalamic nucleus. This nucleus is targeted on pre-operative stereotactic MR acquisitions. But MR imaging of the basal ganglia is intrinsically limited, first by image resolution, and second by the relationship between the measured MR signal and the real anatomy, not clearly understood. On the other hand, detailed and accurate cartography of the basal ganglia can be performed on post mortem histological serial sections. Indeed, histology overcomes the limitations of MR imaging. Moreover, staining of histological sections allows to recover functional information. But histology is by nature two-dimensional. An histological data set consists in a series of disorganized serial sections, as three dimensional shape information was lost during sectioning. Therefore, the first step toward the integration of histological and MR information is to perform a reliable three dimensional reconstruction of the histological volume. Acquisition of photographs during sectioning, showing the histological sections before sectioning, as well as fiducial landmarks, allows to reconstruct a volume with three dimensional integrity, and is further used to register each histological section with its corresponding optical section

Microbial mediation of benthic biogenic silica dissolution

Pore water profiles from 24 stations in the South Atlantic (located in the Guinea, Angola, Cape, Guyana, and Argentine basins) show good correlations of oxygen and silicon, suggesting microbially mediated dissolution of biogenic silica. We used simple analytical transport and reaction models to show the tight coupling of the reconstructed process kinetics of aerobic respiration and silicon regeneration. A generic transport and reaction model successfully reproduced the majority of Si pore water profiles from aerobic respiration rates, confirming that the dissolution of biogenic silica (BSi) occurs proportionally to O 2 consumption. Possibly limited to well-oxygenated sediments poor in BSi, benthic Si fluxes can be inferred from O 2 uptake with satisfactory accuracy. Compared to aerobic respiration kinetics, the solubility of BSi emerged as a less influential parameter for silicon regeneration. Understanding the role of bacteria for silicon regeneration requires further investigations, some of which are outlined. The proposed aerobic respiration control of benthic silicon cycling is suitable for benthic–pelagic models. The empirical relation of BSi dissolution to aerobic respiration can be used for regionalization assessments and estimates of the silicon budget to increase the understanding of global primary and export production patterns