Swimming and feeding by the scyphomedusa Chrysaora quinquecirrha

The semaeostome scyphomedusa, Chrysaora quinquecirrha (Desor, 1848), is an abundant and important planktonic predator in estuaries and coastal waters of the eastern USA during the summer. We videotaped free-swimming medusae in the laboratory and in the field in order to determine the relationship between swimming motions and prey encounter with capture surfaces. Medusae were collected from the Choptank River (Chesapeake Bay) in September 1992 and in the Niantic River, Connecticut, USA in July 1994. We used newly hatched Artemia sp. nauplii and fluorescein dye to trace water motions around swimming medusae. Swimming results in a pulsed series of toroids which travel along the medusan oral arms and tentacles. Prey are entrained in this flow and the location of naupliar encounter was influenced by the phase of the pulsation cycle during which entrainment occurred. Flow-field velocities, measured by tracking particles adjacent to the bell margin during contraction, increased with bell diameter. Received: 29 March 1997 / Accepted: 11 April 1997     

Challenge of materials substitution

The impacts of materials substitution in the automobile industry were examined in a symposium at the 99th Winter Annual Meeting of the American Society of Mechanical Engineers. Papers were contributed by W.D. Compton of the Ford Motor Company, R.B. Gavert of the Office of Technology Assessment, US Congress, J.T. Herridge and R.W. Hale of Battelle Columbus Laboratories, A.H. Purcell of Technical Information Project Incorporated, and M.B. Bever of the Massachusetts Institute of Technology. Symposium on Measurements of the Impacts of Material Substitution – A Case Study in the Automobile Industry, San Francisco, 10–15 December 1978.     

Escape of the ctenophore Mnemiopsis leidyi from the scyphomedusa predator Chrysaora quinquecirrha

The ctenophore Mnemiopsis leidyi A. Agassiz, 1865 is known to be eaten by the scyphomedusan Chrysaora quinquecirrha (Desor, 1948), which can control populations of ctenophores in the tributaries of Chesapeake Bay. In the summer of 1995, we videotaped interactions in large aquaria in order to determine whether M. leidyi was always captured after contact with medusae. Surprisingly, M. leidyi escaped in 97.2% of 143 contacts. The ctenophores increased swimming speed by an average of 300% immediately after contact with tentacles and 600% by mid-escape. When caught in the tentacles of C. quinquecirrha, the ctenophores frequently lost a portion of their body, which allowed them to escape. Lost parts regenerated within a few days. The striking ability of M. leidyi to escape from C. quinquecirrha may be critically important in maintaining ctenophore populations in situ. Received: 14 November 1996 / Accepted: 4 December 1996     

Selective predation and caloric consumption by the siphonophore Rosacea cymbiformis in nature

Individuals of the siphonophore Rosacea cymbiformis (Chiaje, 1822) were collected in surface waters of the Gulf of California during July/August 1978, off Southern California during May 1980, and in the Sargasso Sea during July 1979. Specimens were preserved within 30 min after capture, and the ingested prey in the gastrozooids were examined microscopically and identified to the closest practical taxon. Most gastrozooids (50 to 84%) contained recognizable prey organisms. The prey were primarily copepods, but crab zoeae, pelagic molluscs, juvenile shrimps and mysids were also commonly eaten. There were significant differences between the sizes and types of prey organisms that had been ingested and that were available in the environment of the siphonophores. Electivity indices for the prey demonstrated that the large and/or active prey were selected. The feeding selectivity exhibited by the siphonophores probably depends upon speed and diameter of the prey, which affect the frequency of contact with the siphonopore tentacles. Behavioral observations suggest that R. cymbiformis feeds primarily in the light. Digestion experiments indicate that most prey remain in the gastrozooids for 8 h or more before egestion. The caloric values of common prey types were derived from their length to dry weight regressions. The caloric consumption of R. cymbiformis during the 4 to 6 h feeding period following sunrise was estimated to be from 0.109 to 0.365 cal per gastrozooid; the daily caloric consumption was projected to be at least 2.4 to 8.2 times that required to balance metabolism.     

CO2 recycling by reaction with renewably-generated hydrogen

A laboratory-scale reactor system was built and operated to demonstrate the feasibility of catalytically reacting carbon dioxide (CO₂) with renewably-generated hydrogen (H₂) to produce methane (CH₄) according to the Sabatier reaction: CO₂ + 4H₂ → CH₄ + 2H₂O. A cylindrical reaction vessel packed with a commercial methanation catalyst (Haldor Topsøe PK-7R) was used. Renewable H₂ produced by electrolysis of water (from solar- and wind-generated electricity) was fed into the reactor along with a custom blend of 2% CO₂ in N₂, meant to represent a synthetic exhaust mixture. Reaction conditions of temperature, flow rates, and gas mixing ratios were varied to determine optimum performance. The extent of reaction was monitored by real-time measurement of CO₂ and CH₄. Maximum conversion of CO₂ occurred at 300–350 °C. Approximately 60% conversion of CO₂ was realized at a space velocity of about 10,000 h^?1 with a molar ratio of H₂/CO₂ of 4/1. Somewhat higher total CO₂ conversion was possible by increasing the H₂/CO₂ ratio, but the most efficient use of available H₂ occurs at a lower H₂/CO₂ ratio.     

Throwaways to go?

The Senior Advisory Group of the US government's Resource Conservation Committee is holding public hearing on two prominent materials conservation policy options - a national mandatory deposit system on beverage containers to eliminate ‘throwaways’, and a national system of ‘product charges’ on goods produced from virgin materials. A national hearing was held on 19 October 1977 to hear views on the controversial mandatory deposit issues, and is reported below.