Growth and lipid class composition of the Arctic pelagic amphipod Themisto libellula

Carnivorous zooplankton is a key element to the energy transfer through the arctic food web, linking lipid rich herbivores to the top predators. We investigated the growth and lipid dynamic of the Arctic pelagic amphipod Themisto libellula in Kongsfjorden (Svalbard, 79°N) from May to October 2007. Additional samplings were performed in spring and summer 2006 and further north in Rijpfjorden (80°N), in September 2006 and 2007. In Kongsfjorden, the first free-swimming stages (3 mm) appeared early May and reached their adult length (25 mm), in October. During their first year, they grew according to a Von Bertalanffy model and most probably constituted a single cohort. Juveniles had the highest growth rate (0.19 mm day−1) and revealed relatively low total lipid (TL) content (about 2.5% wet weight (WW)) with phospholipids as the major lipid class. Sub-adults showed a distinct decrease of growth rates which coincided with the increase of neutral lipid storage, reflecting a switch in energy allocation, from somatic growth to lipid storage. Indeed wax esters (WE) increased up to 48.5% TL on average in adults in 2006 while triacylglycerols (TAG) remained almost constant below 25.2% TL. The absence of lipid accumulation (in disproportion of the weight) in 2007 could be explained by a higher metabolism of T. libellula or preys of lower quality. In Rijpfjorden, adults in their second year continued accumulating lipid (up to 10% WW) with high and similar proportions of both lipid classes, WE and TAG. We highlighted that T. libellula exhibited a variable lipid metabolism along its life cycle depending on its physiological needs and environmental conditions

The diet of the calanoid copepod, Pseudodiaptomus hessei, in a permanently open southern African estuary inferred from fatty acid analyses

The fatty acid (FA) composition of Pseudodiaptomus hessei, one of the most abundant copepod species in southern African estuaries and lakes, reveals potential food selectivity and the importance of flagellate prey in their diets. Differences in FA profiles between males and females were recorded; however, none of these patterns matched the reproductive activities of the copepod. Our findings stress the importance of improving our knowledge of FA biosynthesis pathways to employ fatty acids as trophic markers in feeding studies of zooplankton in temperate environments

Dedikasi Untuk S. Othman Kelantan

Tanggal 30 Julai lalu, dunia kesusasteraan Melayu kehilangan seorang lagi sasterawan Negara dan juga perjuang bahasa yang cukup disegani iaitu Dr. Syed Othman Syed Omar atau dikenali sebagai S. Othman Kelantan yang meninggal dunia pada usia 70 tahun

Mesozooplankton community distribution on the Agulhas Bank in autumn: Size structure and production

The Agulhas Bank on the tip of southern Africa, like other shelf seas, is a relatively productive environment which plays a crucial role in the biology and success of many commercially valuable fish species. Fish and their larvae depend on zooplankton to feed on but, despite their importance, little is known about zooplankton distribution and production on the Agulhas Bank. Here we present results from a survey conducted in March 2019 on the East and Central Agulhas Bank, investigating mesozooplankton abundance, biovolume, taxonomic composition, size distribution (normalised biovolume size spectrum (NBSS) approach) and secondary production. A clear cross-shore gradient was observed with the inner-shelf having higher abundance and biovolume of mesozooplankton dominated by small-size organisms, most likely mirroring higher overall productivity of the coastal waters, while the outer-shelf showed the opposite trend (i.e., low abundance and biovolume; shallow NBSS slopes). This general pattern on the outer-shelf was, however, disturbed in one location (between 24 and 25°E) with a distinguishable mesozooplankton community, most likely linked to the passage of a meander on the inshore side of the Agulhas Current. The Central Agulhas Bank was typified by high mesozooplankton biomass (∼4 g C m-2), comparable to upwelling areas and dominated by copepods and doliolids. High copepod biomass was observed in this region before and was linked to a feature called the “Cold Ridge”. However, during our survey, no such ridge was observed. The mixed layer depth was relatively deep (>20 m) and high Chlorophyll a concentration was measured at depth, despite low net primary production rates. We suggest that this region is prone to other mechanisms such as retention due to cyclonic circulation or processes injecting nutrients in the upper mixed layer that require further research. Secondary production on the Agulhas Bank was in the same range as other shelf seas (0.03–1.55 g C m-2 d-1) and was correlated with mesozooplankton biomass. The comparison of primary and secondary production, measured simultaneously, suggested that mesozooplankton exert a significant control on net primary production, and can, in some areas, be food-limited (e.g., Central Agulhas Bank and inshore waters)

Spatial and temporal variability of net primary production on the Agulhas Bank, 1998–2018

Despite the importance of Agulhas Bank (AB) marine productivity in supporting South African coastal fisheries and shelf ecosystems, there are relatively few regional-scale assessments of its spatial and temporal variability, and most productivity studies have been limited in scale. Here we use satellite-derived Net Primary Production (NPP) rates calculated using the Vertically Generalized Production Model (VGPM) to examine the spatial and temporal dynamics of NPP over the 21-year satellite record (1998–2018) on the AB. In calculating VGPM NPP we used the OCCI Chlorophyll-a product, SST from Operational-Sea-Surface-Temperature-and-Sea-Ice-Analysis (OSTIA) and PAR from GlobColour level-3 mapped products as these represent the longest datasets that fit our extended study period. We examine spatial trends between the eastern and central AB, as well as three areas of the bank (around Port Alfred, the Tsitsikamma coast, and the ‘cold ridge’) that have been previously identified as contributing significantly to the overall productivity of the AB. The AB shows only a moderate degree of seasonality in NPP calculated from the VGPM, with NPP being highest in austral summer (1.7–1.8 g C m−2 d−1) and lowest in winter (0.9–1.0 g C m−2 d−1), and remains relatively high (>1 g C m−2 d−1) throughout the year, contrasting sharply with other shelf systems. Considered annually, NPP on the bank was 516 g C m−2 yr−1 (38 Mt C yr−1 when scaled to the total shelf area) which is higher than many other shelf systems though lower than the neighbouring Benguela system and is indicative of a moderately productive shelf system fuelled by perennial NPP. Comparing different sections of the AB from east to central bank, and including the three upwelling areas, highlighted that spatial differences in NPP were relatively limited; that these three upwelling areas made similar contributions to their relative proportion of the total shelf area, and that average rates of NPP are spatially similar across the bank, though notable high rates occur in some coastal upwelling areas. Interannual variability in NPP was relatively modest, varying between years by only ∼15% over the two decades assessed. Over the 21-year data set, there was a slight (∼0.26% yr−1) statistically-significant decline in calculated NPP over time for the AB as a whole, which, when examined on a pixel-by-pixel basis, indicated that most of the decline was on the central bank between 100 m and 200 m isobaths. In summer, an increase in NPP occurred on the EAB (26.5–28°E). In conclusion, the AB is a significant site of perennial moderate levels of NPP, varying little interannually and with only a slight decline in NPP over time. These factors lead to a stable environment in terms of ecosystem productivity so that the AB makes a significant contribution to the productivity of South African regional fisheries

The small pelagic fishery of the Pemba Channel, Tanzania: what we know and what we need to know for management under climate change

Small pelagic fish, including anchovies, sardines and sardinellas, mackerels, capelin, hilsa, sprats and herrings, are distributed widely, from the tropics to the far north Atlantic Ocean and to the southern oceans off Chile and South Africa. They are most abundant in the highly productive major eastern boundary upwelling systems and are characterised by significant natural variations in biomass. Overall, small pelagic fisheries represent about one third of global fish landings although a large proportion of the catch is processed into animal feeds. Nonetheless, in some developing countries in addition to their economic value, small pelagic fisheries also make an important contribution to human diets and the food security of many low-income households. Such is the case for many communities in the Zanzibar Archipelago and on mainland Tanzania in the Western Indian Ocean. Of great concern in this region, as elsewhere, is the potential impact of climate change on marine and coastal ecosystems in general, and on small pelagic fisheries in particular. This paper describes data and information available on Tanzania's small pelagic fisheries, including catch and effort, management protocols and socio-economic significance

Nutrition et dynamique lipidique de l'hypérien Themisto libellula (importance en terme de stratégie)

Themisto libellula est un amphipode relativement peu étudié bien qu omniprésent et abondant dans le plancton arctique. De part son régime alimentaire carnivore et en tant que proie pour de nombreux prédateurs supérieurs, il pourrait constituer un maillon important de la chaîne alimentaire et contribuer de façon significative aux transferts énergétiques. Les principaux objectifs de cette thèse sont: i) de comprendre comment T. libellula est adapté aux conditions polaires, ii) de connaître son rôle trophodynamique. En 2006 et 2007, de mai à octobre, des prélèvements et des expériences ont été réalisés dans le Kongsfjorden, fjord situé sur la côte Ouest des Svalbard (79 N). Les résultats montrent que l énergie alimentaire est investie dans la croissance au cours des premiers mois de vie (printemps) puis stockée sous forme de lipides à forte valeur énergétique (été-automne). L analyse des acides gras comme marqueurs trophiques a mis en évidence un changement de régime alimentaire au cours du développement, les individus les plus jeunes adoptant un régime mixte phytoplancton - zooplancton et les plus âgés un régime composé principalement de copépodes du genre Calanus. Des expériences complémentaires de prédation ont permis de préciser les taux d ingestion journalier et la sélectivité de T. libellula. Dans leur ensemble, les résultats montrent une bonne synchronisation entre le cycle de vie de T. libellula et la dynamique des niveaux trophiques inférieurs. La surabondance de ressources alimentaires par rapport à leurs besoins et la faible pression de prédateurs potentiels dans la zone suggèrent que le Kongsfjorden constitue une aire de nourricerie idéale pour les juvéniles et les sub-adultes de T. libellula.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Nutrition et dynamique lipidique de l'hypérien Themisto libellula (importance en terme de stratégie)

Themisto libellula est un amphipode relativement peu étudié bien qu omniprésent et abondant dans le plancton arctique. De part son régime alimentaire carnivore et en tant que proie pour de nombreux prédateurs supérieurs, il pourrait constituer un maillon important de la chaîne alimentaire et contribuer de façon significative aux transferts énergétiques. Les principaux objectifs de cette thèse sont: i) de comprendre comment T. libellula est adapté aux conditions polaires, ii) de connaître son rôle trophodynamique. En 2006 et 2007, de mai à octobre, des prélèvements et des expériences ont été réalisés dans le Kongsfjorden, fjord situé sur la côte Ouest des Svalbard (79 N). Les résultats montrent que l énergie alimentaire est investie dans la croissance au cours des premiers mois de vie (printemps) puis stockée sous forme de lipides à forte valeur énergétique (été-automne). L analyse des acides gras comme marqueurs trophiques a mis en évidence un changement de régime alimentaire au cours du développement, les individus les plus jeunes adoptant un régime mixte phytoplancton - zooplancton et les plus âgés un régime composé principalement de copépodes du genre Calanus. Des expériences complémentaires de prédation ont permis de préciser les taux d ingestion journalier et la sélectivité de T. libellula. Dans leur ensemble, les résultats montrent une bonne synchronisation entre le cycle de vie de T. libellula et la dynamique des niveaux trophiques inférieurs. La surabondance de ressources alimentaires par rapport à leurs besoins et la faible pression de prédateurs potentiels dans la zone suggèrent que le Kongsfjorden constitue une aire de nourricerie idéale pour les juvéniles et les sub-adultes de T. libellula.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Picoplankton and nanoplankton composition on and around a seamount, affected by an eddy dipole south of Madagascar

Picoplankton and nanoplankton community abundances were sampled on and around a seamount located on the Madagascar Ridge, in November 2016. Prochlorococcus, Synechococcus, picoeukaryote and nanoplankton community abundances both on the seamount and in the immediate vicinity (approximately 100 km) surrounding it were analysed using flow cytometry. The original aim of the study was to estimate whether or not the seamount had an effect on the picoplankton and nanoplankton community distribution. However, coupled altimetry and in situ ship data indicated that a dipole eddy was also sampled during this time, which had a substantial effect on the results. Results reveal that picoeukaryotes contributed the most to carbon biomass within the anticyclone, showing higher abundances in the stations situated within the southern slopes of the seamount which also fell within the anticyclone. The southern slope of the seamount contained higher Synechococcus, Prochlorococcus and picoeukaryote abundances, whereas nanoplankton dominated in the cyclonic eddy. Species composition and abundance was significantly different on versus off the seamount, driven by nanoplankton biomass. These results indicate significantly high abundance above the slopes of the seamount, driven by picoeukaryotes, which seem to be amplified by the dipole presence. The resulting variability in microbial abundance both on the southern slopes of the seamount as well as within the dipole has far reaching implications with regard to larger organism proliferation and carbon export during such events in this region

Feeding of Themisto libellula (Amphipoda Crustacea) on natural copepods assemblages in an Arctic fjord (Kongsfjorden, Svalbard)

Ingestion rates and selectivity of the Arctic pelagic amphipod Themisto libellula were studied experimentally in Kongsfjorden (Svalbard, 78A degrees N) during the summer period. Feeding incubations were conducted on naturally occurring copepod communities at different concentrations ranging from 25 to 250 preys L-1. The ingestion rates increased with food availability from 1.3 to 17.7 preys ind(-1) day(-1), which corresponded to 0.3-11% of body carbon day(-1). Despite the high prey concentration used in the experiments the satiation level was not reached. We suggested that T. libellula is able to take the maximum benefit from dense patches of preys, which represent a good adaptation to the high variability in food supply characteristic of polar environment. Copepodids stage III of Calanus spp. appeared to be the preferred preys of T. libellula. Smaller copepods such as Oithona similis and Pseudocalanus spp., were also selected but only when their relative abundance exceeded 25% of the total prey available. The potential predation impact of T. libellula is discussed in relation to the mesozooplankton small-scale patchiness and predator abundance