Unravelling the trophic interaction between a parasitic barnacle (Anelasma squalicola) and its host Southern lanternshark (Etmopterus granulosus) using stable isotopes

The parasitic barnacle, Anelasma squalicola, is a rare and evolutionary fascinating organism. Unlike most other filter-feeding barnacles, A. squalicola has evolved the capability to uptake nutrient from its host, exclusively parasitizing deepwater sharks of the families Etmopteridae and Pentanchidae. The physiological mechanisms involved in the uptake of nutrients from its host are not yet known. Using stable isotopes and elemental compositions, we followed the fate of nitrogen, carbon and sulphur through various tissues of A. squalicola and its host, the Southern lanternshark Etmopterus granulosus, to better understand the trophic relationship between parasite and host. Like most marine parasites, A. squalicola is lipid-rich and clear differences were found in the stable isotope ratios between barnacle organs. It is evident that the deployment of a system of ‘rootlets’, which merge with host tissues, allows A. squalicola to draw nutrients from its host. Through this system, proteins are then rerouted to the exterior structural tissues of A. squalicola while lipids are used for maintenance and egg synthesis. The nutrient requirement of A. squalicola was found to change from protein-rich to lipid-rich between its early development stage and its definitive size

Determination of picomolar dissolved free amino acids along a South Atlantic transect using reversed-phase high-performance liquid chromatography

Dissolved free amino acids (DFAA) in seawater are a form of nitrogen (N) available for marine microbes. In oligotrophic environments where N-containing nutrients are the limiting factor for microbial growth, N nutrition from DFAA could be crucial, but as yet it is poorly resolved. Measurements of individual DFAA are challenging as concentrations are typically in the low nmol L− 1 range. Here we report modifications to methodology using o-phthaldialdehyde (OPA) derivatization and reversed phase high performance liquid chromatography (HPLC) that provide a 30-fold improvement in sensitivity enabling the detection of 15 amino acids in seawater with a limit of detection as low as 10 pmol L− 1 with accuracy and precision of better than 10%. This analytical methodology is now suitable for the challenging quantitation of DFAA in oligotrophic seawaters. The method was successfully applied to a suite of seawater samples collected on a cruise crossing the South Atlantic Ocean, where concentrations of DFAAs were generally low (sub nmol L− 1), revealing basin-scale features in the oceanographic distributions of DFAA. This unique dataset implies that DFAAs are an important component of the N cycle in both near-coastal and open oceans. Further calculations suggest that the proportions of organic N originating from DFAA sources were significant, contributing between 0.2 and 200% that of NH4 + and up to 77% that of total inorganic nitrogen in the upper 400 m in some regions of the transect

Southern Ocean humpback whale trophic ecology. I. Combining multiple stable isotope methods elucidates diet, trophic position and foraging areas

Southern Ocean humpback whales Megaptera novaeangliae are capital breeders, breeding in the warm tropics/subtropics in the winter and migrating to nutrient-rich Antarctic feeding grounds in the summer. The classic feeding model is for the species to fast while migrating and breeding, surviving on blubber energy stores. Whilst northern hemisphere humpback whales are generalists, southern hemisphere counterparts are perceived as krill specialists, but for many populations, uncertainties remain regarding their diet and preferred feeding locations. This study used bulk and compound-specific stable isotope analyses and isoscape-based feeding location assignments to assess the diet, trophic ecology and likely feeding areas of humpback whales sampled in the Ross Sea region and around the Balleny Islands. Sampled whales had a mixed diet of plankton, krill and fish, similar to the diet of northern hemisphere humpback whales. Proportions of fish consumed varied but were often high (2-60%), thus challenging the widely held paradigm of Southern Ocean humpback whales being exclusive krill feeders. These whales had lower 15N values and trophic position estimates than their northern hemisphere counterparts, likely due to lower Southern Ocean baseline 15N surface water values and a lower percentage consumption of fish, respectively. Most whales fed in the Ross Sea shelf/slope and Balleny Islands high-productivity regions, but some isotopically distinct whales (mostly males) fed at higher trophic levels either around the Balleny Islands and frontal upwelling areas to the north, or en route to Antarctica in temperate waters off southern Australia and New Zealand. These results support other observations of humpback whales feeding during migration, highlighting the species' dietary plasticity, which may increase their foraging and breeding success and provide them with greater resilience to anthropogenically mediated ecological change. This study highlights the importance of combining in situ field data with regional-scale isoscapes to reliably assess trophic structure and animal feeding locations, and to better inform ecosystem conservation and management of marine protected areas

Optical properties of tellurite glasses elaborated within the TeO2-Tl2O-Ag2O and TeO2-ZnO-Ag2O ternary systems

The optical properties of glasses elaborated within the TeO2-Tl2O-Ag2O and TeO2-ZnO-Ag2O ternary systems are presented. The paper is articulated in two parts. The first part concerns the TeO2-Tl2O-Ag2O system, where the linear refractive index, the absorption coefficient and the optical band gap are measured as a function of the Ag2O content. From ellipsometry measurements, it is noticed that the linear refractive index n0 remains constant up to 5 mol% in AgO0.5 and then slightly increases at higher concentrations (10 mol%). Such evolution of the refractive index was related to the higher electronic polarizability of Ag+ cations compared to that of Te4+ cations, assuming that the electronic polarizability of O2 anions remains constant. The reduction in the optical band gap value is attributed for some part to the higher quantity of non-bridging oxygen atoms induced by the depolymerization of the glass. The third order non-linear optical properties (c and Re(v(3)) values) of these TeO2-Tl2O-Ag2O glasses are then extracted from Z-scan measurements. For glass compositions ranging from 0 to 10 mol% in AgO0.5, the Re(v(3)) value shifts from roughly 60 to more than 80 times that of silica, which testify to the excellent non-linear optical properties of such TeO2-Tl2O glasses containing silver (tellurite glasses possess intrinsic high optical non-linearity). The addition of Tl2O induces the depolymerization of the glass framework but, on the other hand, helps to maintain the amplitude of the optical non-linearity, through the presence of highly polarizable Tl-based entities. Here, below 5 mol% in AgO0.5, it is believed that the activity of the electronic lone pair of Tl+ ions is inhibited. Over this limit, such lone pair would become active, explaining the clear increase of the Re(v(3)) value. Finally, the second part of the paper is devoted to the study of photoluminescence properties of new TeO2-ZnO-Ag2O glasses. Indeed, probably due to the creation of Ag+-Tl+ pairs, there is absolutely no photoluminescence detected for glasses elaborated in the TeO2-Tl2O-Ag2O system. At the opposite, the temperature dependent photoluminescence properties of TeO2-ZnO-Ag2O glasses are reported. Under UV-visible excitation at 385 nm, the samples emit orange light, with a broad emission wavelength peaking around 580-585 nm. The nature of the light emitting centers is discussed and two main hypotheses are debated: the creation of Ag+-Ag+ or Ag+-Zn2+ pairs, with stronger arguments more in favor of the last one