Response of copepods to elevated pCO2 and environmental copper as co-stressors--a multigenerational study.

We examined the impacts of ocean acidification and copper as co-stressors on the reproduction and population level responses of the benthic copepod Tisbe battagliai across two generations. Naupliar production, growth, and cuticle elemental composition were determined for four pH values: 8.06 (control); 7.95; 7.82; 7.67, with copper addition to concentrations equivalent to those in benthic pore waters. An additive synergistic effect was observed; the decline in naupliar production was greater with added copper at decreasing pH than for decreasing pH alone. Naupliar production modelled for the two generations revealed a negative synergistic impact between ocean acidification and environmentally relevant copper concentrations. Conversely, copper addition enhanced copepod growth, with larger copepods produced at each pH compared to the impact of pH alone. Copepod digests revealed significantly reduced cuticle concentrations of sulphur, phosphorus and calcium under decreasing pH; further, copper uptake increased to toxic levels that lead to reduced naupliar production. These data suggest that ocean acidification will enhance copper bioavailability, resulting in larger, but less fecund individuals that may have an overall detrimental outcome for copepod populations

Visualisation of the copepod female reproductive system using confocal laser scanning microscopy and two-photon microscopy

We examined mating behaviour in the harpacticoid copepod Tube battagliai Volkmann-Rocco, 1972, in particular the process of delivering spermatophore seminal contents to the female urosome. Labelling using 4′6′ diamidino-2-phenylindole (DAPI) coupled with two-photon confocal laser scanning microscopy successfully visualised the spermatophore and female internal reproductive system. Sections of the female urosome were imaged to examine seminal fluid stores. The female tissues were found to auto-fluoresce as red emission under green excitation, requiring no additional tissue labelling. DAPI-labelled seminal fluid stores were identified within the female reproductive system. The details observed agreed with previous descriptions of copepod reproductive anatomy and of spermatophores. Specimens cultured under pH 8.10 and a simulated ocean acidification scenario (pH 7.67) were compared for changes in reproductive anatomy and spermatophore size and site attachment. No differences were observed in spermatophore attachment or the female reproductive system but spermatophore size was reduced significantly at pH 7.67 compared with pH 8.10. This size reduction was, however, in proportion to an overall reduction in female body size at reduced pH. Confocal microscopy is shown here to be a valuable tool to investigate detailed reproductive processes in copepods

Oxidation behavior of molybdenum silicides and their composites

A key materials issue associated with the future of high-temperature structural silicides is the resistance of these materials to oxidation at low temperatures. Oxidation tests were conducted on Mo-based silicides over a wide temperature range to evaluate the effects of alloy composition and temperature on the protective scaling characteristics and testing regime for the materials. The study included Mo{sub 5}Si{sub 3} alloys that contained several concentrations of B. In addition, oxidation characteristics of MoSi{sub 2}-Si{sub 3}N{sub 4} composites that contained 20--80 vol.% Si{sub 3}N{sub 4} were evaluated at 500--1,400 C