Modelling the effect of food availability on recruitment success of Cape anchovy ichthyoplankton in the southern Benguela upwelling system

Cape anchovy Engraulis encrasicolus adapted its reproductive strategies to the southern Benguela system by spawning over the Agulhas Bank, an area of low productivity that is located upstream of the predominant upwelling system. Frontal jet currents transport eggs and larvae toward the west coast of South Africa, where recruitment takes place. To characterise the recruitment dynamics of Cape anchovy ichthyoplankton, we used an individual-based model forced by a coupled hydrodynamic–biogeochemical model. The results show the importance of food (especially diatoms and copepods) dynamics on the spatial and temporal patterns of recruitment success, and also confirm the importance of the spawning area, timing and water depth on the recruitment success of Cape anchovy larvae.     

Confounding response of macrofauna from a confluence of impacts: brine and sewage pollution

Throughout the shores of the world,a confluence of different sources of pollution is common,e.g.,through outlets releasing brine,industrial,and domestic sewage.In this study,we assessed whether a combined disposal of domestic sewage and brine altered the patterns of abundance and assemblage structure of subtidal macrofauna inhabiting sandy seabeds on the south coast of Gran Canaria(Canary Islands,NE Atlantic Ocean).Samples were collected in two surveys(May 2008 and January 2009)at three distances(0,15,and30 m)away from the discharge point.Macrofaunal abundances showed different patterns with varying proximity from the disposal point in the two surveys.In May 2008,lower abundances were observed at0 m(53.89±46.82 ind.)than at 15 m(120±91.7 ind.)and 30 m(283.89±189.33 ind.)away from the disposal point.In January 2009,however,higher abundances were observed at 0 m(131.33±58.69 ind.)than at 30 m(100±24.44 ind.)and 15 m(84.78±58.39 ind.)away from the disposal point.Significant differences in macrofaunal assemblage structure were found with varying proximity from the discharge point in both surveys.The effect of proximity from the disposal point was confounded by changes in sedimentary composition between surveys,which contributed to explain differences in macrofaunal abundances and assemblage structure with varying proximity from the discharge point.As a result,confounding drivers of macrofaunal assemblage structure,here,changes in sediment composition,accounted for changes in macrofaunal abundances and assemblage structure with varying proximity from a combined disposal point of brine and sewage.     

Variability of Coulter Counter Data and their Relationship with Other Oceano-graphical Parameters

Abstract. Coulter counter data (from the upper 100 m of water) gathered during a cruise in October, 1976 in the Spanish waters of the Western Mediterranean are analysed in this paper. The ANOVA shows that the main sources of variability are the geographical situation and the depth level, while the sampling method especially affects the results for the larger particles. Repeating the counting in the same sample also introduces some changes which have less importance in the overall sense. Correlations of the particle counts with chlorophyll a, total POC and PON, POC and PON above 200u.m, estimated POC based on the particle size spectra, and SECCHI disc visibility were calculated and are discussed in order to assess the kind of information given by seston counts obtained from two different sampling methods and expressed both in absolute values (ppm by volume) and as a percentage of volume for the different channels.
Some striking results arise which suggest that the use of a Coulter counter together with some kind of sample treatment might give an insight into the qualitative and quantitative characterization of the pelagic ecosystem.     

中国多金属结核开辟区的深海环境

阐述了中国多金属结核开辟区深海环境的水文、生物和化学特征。开辟区海域水柱由表层混合层、温跃层、海底温跃层和海底边界层等不同水层构成，整个海域水动力条件总体上较为缓慢，但也存在着周期性的水流速度大于15cm/s的海底风暴；区内海底生态系统的显著特点是极低的生产力和生物过程速率，但生物多样性极高；整个区域内表层沉积物分布较均一，以低有机含量的硅质粘土、深海软泥为主，其化学组成上受沉积环境和早期成岩作用的影响和控制。     

Beta diversity of pelagic assemblages at fish aggregating devices in the open ocean

Owing to difficulties in accessing the vast open ocean, the beta (β) diversity of pelagic fish assemblages remains poorly studied. We investigated the relationship between assemblage similarity and geographical distance between anchored fish aggregating devices (FADs), sampled by standardised underwater visual censuses in three anchored FAD arrays in the Indian Ocean—at the Maldives, the Seychelles and Mauritius. The use of two complementary indices of β-diversity, based on presence/absence data (Jaccard similarity coefficient) and abundance data (Bray–Curtis index), revealed that geographical distance between sampling sites (from 4 to 257 km) appeared to have no effect on the similarity of fish assemblages associated with FADs within each array. The results of this preliminary study question the generalisation of the paradigm of an increase in β-diversity with geographic distance to the open-ocean fish community. Large-scale studies using a variety of datasets should be conducted to further investigate patterns of β-diversity in the open ocean.     

Carbon stable isotopes ratios of pelagic and littoral communities in Alchichica crater-lake, Mexico

Carbon stable isotope ratios were determined in dominant biotic components of pelagic and littoral systems in Alchichica crater-lake. Results showed that carbon signatures were significantly different between both systems. The pelagic environment was more depleted (−26.15 to −15.14 per mille) than the littoral zone (−21.03 to −17.91 per mille). The potential source end-point in the simplified pelagic community was established to be diatomaceous phytoplankton; its predicted value was −21.7 per mille. There is a clear evidence thatNodularia does not sustain the pelagic food chain. In contrast, the highly diverse littoral community was sustained by epiphytes. No allochthonous sources seemed to influence this food web.¹³C enrichment was observed along the components of both systems with fractionations of 0.8 to 1.4 per mille. The contribution of the seagrassRuppia maritima is probably associated with the detritus pathway. Carbon source partitioning between both systems was not recorded. The δ¹³C in Alchichica crater-lake was more enriched than in other saline lakes and could be attributed to different salinity and CO₂ concentrations among lakes.