Effects of crab–halophytic plant interactions on creek growth in a S.W. Atlantic salt marsh: A Cellular Automata model

The Bahía Blanca Estuary (38° 50′ S, and 62° 30′ W) presents salt marshes where interactions between the local flora (Sarcocornia perennis) and fauna (Chasmagnathus granulatus) generate some kind of salt pans that alter the normal water circulation and condition its flow and course towards tidal creeks. The crab–vegetation dynamics in the salt marsh presents variations that cannot be quantified in a reasonable period of time. The interaction between S. perennis plant and C. granulatus crab is based on simple laws, but its result is a complex biological mechanism that causes an erosive process on the salt marsh and favors the formation of tidal creeks. To study it, a Cellular Automata model is proposed, based on the laws deduced from the observation of these phenomena in the field, and then verified with measurable data within macroscale time units. Therefore, the objective of this article is to model how the interaction between C. granulatus and S. perennis modifies the landscape of the salt marsh and influences the path of tidal creeks. The model copies the basic laws that rule the problem based on purely biological factors.The Cellular Automata model proved capable of reproducing the effects of the interaction between plants and crabs in the salt marsh. A study of the water drainage of the basins showed that this interaction does indeed modify the development of tidal creeks. Model dynamics would likewise follow different laws, which would provide a different formula for the probability of patch dilation. The patch shape can be obtained changing the pattern that dilates.     

Relative microbial activity and mineralization associated with water masses in the lower Cook Inlet,Alaska

A study of the microbial uptake and respiration (mineralization) of radioactive glutamic acid was made in 141 surface water samples in the Cook Inlet, Alaska during three sampling periods (October, 1976; April, 1977; and November, 1977). The rate at which the test substrate was incorporated into cell material plus that respired as CO₂ was used to calculate the relative microbial activity. A northern water mass with salinities less than 31 showed high rates of relative microbial activity but low mineralization rates as indicated by respiration of¹⁴CO₂. The reverse pattern was seen in the water mass (salinity higher than 31) to the south which was more typical of coastal water. These data suggest that the organic nutrients in these two water masses are quite different either qualitatively or quantitatively. This study illustrates how the observed measurement of relative microbial activity might be helpful in defining specific water masses.(The publication of this article was unintentionally delayed owing to a fault in secretarial routine.)Published as Technical Paper No. 6009, Oregon Agricultural Experiment Station.     

A model of ocean current flow and drifter motion

A minor generalization of the theory of random walk is used as a basis for a model of ocean current flow. The model is then applied in a computer simulation of drifter motion. The results of simulation indicate that the geometry of a coastline can have significant impact on the distribution of drifter landings.     

Geochemical variation in ferromanganese nodules and associated sediments from the Pacific Ocean

The major and minor element compositions of a suite of abyssal sea-floor ferromanganese nodules and associated sediments from the eastern central Pacific have been used to examine inter-element relationships and the mineralogy of the nodules, the relationship between the composition of nodules and their associated sediments and regional variations in composition with respect to likely modes of formation of such deposits. Apart from Mn and Fe, significant proportions of the total Ti, Ca, Mg, K, Ba, Sr, Th and Y and almost all the P, As, Ce, Co, Cu, Mo, Ni, Pb, Zn and Zr are present in the oxide fractions of the nodules. The Mg, Ba, Cu, Mo, Ni and Zn contents are significantly correlated with the Mn content, while Ti, P, As, Pb, Sr, Y and Zr are similarly correlated with the total Fe content.Nodules from the northeastern tropical Pacific have Mn/Fe ratios higher than those in the oxide fractions of their associated sediments, todorokite as the principal Mn phase and relatively high concentrations of minor elements associated with Mn. Nodules from the south central Pacific have Mn/Fe ratios similar to those in the oxide fractions of the associated sediments, δ-MnO₂ as the only Mn-phase, and relatively high concentrations of minor elements associated with Fe. There appears to be a smooth gradation in composition in the tropical Pacific between these two end members.The regional compositional variation is interpreted as a reflection of different sources of metals for, and different growth mechanisms of, sea-floor nodules. The oxide precipitate from sea water consists of δ-MnO₂, has a relatively low Mn/Fe ratio and minor element contents related to the total Fe and Mn(δ-MnO₂) content. The oxide precipitate forming in areas of very low sedimentation as a result of diagenetic remobilisation in the surface sediment consists of todorokite, and has a high Mn/Fe ratio and enhanced metal content in the Mn-(todorokite)phase. Available information on the morphology and compositional variation of individual nodules from the tropical Pacific corroborates these contrasting metal sources and suggests that they can be resolved on the scale of an individual oxide concretion.     

The mysid Siriella armata as a test organism in toxicology: Effects of cadmium

A shrimp-like crustacean of the coastal Zooplankton in the north-western Mediterranean Sea, the mysid Siriella armata, offers a test organism whose life cycle is entirely controllable under laboratory conditions. The effects of the heavy metal cadmium were studied on adults and juveniles cultured in the laboratory including acute toxicity, bioaccumulation and effects on growth, ingestion and moult cycle.     

User participation and fishery management performance within the pacific fishery management council

Fish populations have the potential to contribute to the long-term economic and social benefit of humans, but to do so they must be managed in ways which maintain ecological health. There are many ways that management performance can be assessed, but four measures are particularly pertinent to sustainability: equity, stewardship, regulatory resilience, and efficiency. A key factor in management performance is the process by which management tools are developed and implemented. One approach that has been recommended to improve performance is to structure the management process around user participation. The paper analyzes three case studies of user participation in ad hoc processes of Pacific groundfish management: the development of a license limitation program; an inter-gear sablefish allocation; and the development of a sablefish individual quota (IQ) program. The case studies illustrate the role played by participation in contributing to the equity, stewardship, resilience, and efficiency of the management process. The effect of user participation was mixed in the three cases, depending on the history of participation, the structure and process of participation, on resource conditions and on the characteristics of the program under consideration. Participation can contribute positively to fishery management performance when there is a history of collective decision-making, the time line is slow enough to allow a full consideration of the issues, educational possibilities are pursued and the condition of the resource allows equitable compromises.     

A Late Pleistocene submarine slide on the Bear Island Trough Mouth Fan

A large submarine slide on the southern flank of the Bear Island Trough Mouth Fan, southwestern Barents Sea continental slope, has a run-out distance of about 400 km, a total volume of about 1100 km³, and is younger than 330 ka. Three seismic units, comprising mainly hemipelagic sediments has partly filled the slide scar. An increased sedimentation rate on the Bear Island Trough Mouth Fan from Late Pliocene time, probably in combination with abundant earthquakes, is the most likely cause of the slide. Based on these and previous studies, we suggest that large-scale slides were important sediment transport processes during Plio-Pleistocene.     

The University of Durham Southern Hemisphere VHE gamma ray telescope

The design of very high energy (VHE) gamma ray telescopes is discussed and it is shown that a triple-mirror telescope operating in threefold fast coincidence provides an effective instrument. The design, construction and operation of a large VHE gamma ray telescope with an energy threshold of 300 GeV (at the zenith) and incorporating several novel features is described. The use of a coincidence guard ring technique is shown to result in the rejection of about 50% of the off-source (proton) events which form a high background and limit the sensitivity of such telescopes.