Parallel implementation of the SHYFEM (System of HydrodYnamic Finite Element Modules) model

This paper presents the message passing interface (MPI)-based parallelization of the three-dimensional hydrodynamic model SHYFEM (System of HydrodYnamic Finite Element Modules). The original sequential version of the code was parallelized in order to reduce the execution time of high-resolution configurations using state-of-the-art high-performance computing (HPC) systems. A distributed memory approach was used, based on the MPI. Optimized numerical libraries were used to partition the unstructured grid (with a focus on load balancing) and to solve the sparse linear system of equations in parallel in the case of semi-to-fully implicit time stepping. The parallel implementation of the model was validated by comparing the outputs with those obtained from the sequential version. The performance assessment demonstrates a good level of scalability with a realistic configuration used as benchmark

Population structure and reproductive biology of Laetmonice producta Grube (Polychaeta, Aphroditidae) in Antarctic waters, and relationships with an endosymbiont polychaete.

The large scale-worm Laetmonice producta Grube 1877 is the most abundant aphroditid polychaete in Antarctic coastal waters. We investigated the demographic structure and some reproductive features of different L. producta populations from high-Antarctic (Weddell Sea) and Antarctic Peninsula (King George Island) shelf bottoms, collected in summer 1996 (ANT-XIII/3, EASIZ I cruise) and autumn 2000 (ANT-XVII/3, EASIZ III cruise). L. producta in the studied geographic areas showed a wide bathymetric range (200-850 m depth), and a different size distribution pattern with depth, characterised by a reduction of large specimens in the deepest stations. The species is gonochoric, with females more abundant in specimens of larger sizes. Eggs at different stages of maturation (ranging from 40 to 320 μm in diameter) were examined in 270 individuals from different stations and size classes. Egg size showed a slightly bimodal trend, with largely overlapping egg cohorts, suggesting a continuous reproduction, and a long-lasting gametogenesis. Significant differences (Kolmogorov-Smirnov test, P<0.05) in egg-size frequency distribution were detected only when data of the two geographic areas were compared (Weddell Sea vs King George Island), and not according to stations within each area, and females' size. The two sets of geographic samples were collected in different seasons and therefore it was not possible to assess if differences observed are due to sampling time or to geographic factors. Mature spermatozoa were recognisable only in autumn male specimens from King George Island, and showed a rounded nucleus and a short conical acrosome. Occurrence of an endosymbiont polychaete, Veneriserva pygoclava meridionalis (new sub-species of Dorvilleidae), was recorded in the coelomic cavity of 163 specimens of L. producta, 125 of which were from the deepest station of the Weddell Sea (stn. 14, 850 m depth). L. producta females with and without the endosymbiont did not show differences in egg-size distribution. The reproductive features of L. producta, together with its large size and slow growth, seem typical of a long-living predator species, and uncoupled from the typical summer environmental conditions and the pulsating system of coastal Antarctic waters

Diversity of reproductive features in some Antarctic polynoid and sabellid polychaetes, with a description of Demonax polarsterni sp. n. (Polychaeta, Sabellidae)

The Polynoidae and Sabellidae represent two polychaete families with contrasting life habits and different phylogenetic constraints. Species of both families studied in this work were collected on the shelf of the Eastern Weddell Sea (Antarctica) during the EASIZ-I (1996) and EASIZ-II (1998) expeditions. Among the Polynoidae, three different species of the genus Harmothoe were observed to brood eggs under the dorsal elytra, which is an uncommon feature in this family. The egg size of all brooding taxa ranged between 120 and 216 μm. Three Sabellidae species were studied: Myxicola cf sulcata is gonochoric with eggs among the largest (up to 1000 μm) recorded for the sabellids. Eggs, as well as larvae, are incubated within the branchial crown, a feature newly discovered for the genus Myxicola. Demonax polarsterni n. sp. (a newly discovered taxon) and Euchone pallida are gonochoric and possess relatively large eggs (350 μm and 270 μm, respectively). In comparison with cogeneric species of temperate areas, the Antarctic Sabellidae have larger egg dimensions and egg brooding that seems unconstrained by adult size