Palaeogeographic reconstruction of the 1.55 Ma synchronous isolation of the Ryukyu Islands,Japan, and Taiwan and inflow of the Kuroshio warm current

In the Quaternary, the Ryukyu Islands evolved from a continental margin arc to an island arc by backarc spreading of the Okinawa Trough, accompanied by subsidence and isolation of the islands, a process that has continued to the present. Trough-parallel half grabens were filled with marine siltstone. Similar sediments filling orthogonal fault-controlled and west-draining non-tectonic valleys record island separation. New Quaternary nannofossil biostratigraphic data date the deposition of the marine siltstone at 1.552 ± 0.154 Ma. At that time, the entire 1000 km-long island chain comprising the Ryukyu Islands separated from the Asian continent by rifting extending from the Okinawa Trough to the Tsushima Strait. The Tokara, Kerama, and Yonaguni gaps, branched or transverse rifts of the Okinawa Trough, separate the island chain into subgroups of the Osumi, Amami, Okinawa, and Yaeyama islands, and Taiwan. The shallow Taiwan Strait separated Taiwan from the Chinese mainland. The Kuroshio warm current that previously ran offshore of the continental margin arc began to enter the opening backarc basin through the Yonaguni gap and to exit through the Tokara gap, flowing along the axis of the Okinawa Trough. Under influence of the warm current and because of entrapment of continentally sourced detrital sediments by the Okinawa Trough, coral reefs formed around each island. These reefs make up a unit called the Ryukyu limestone. Subsidence continued through the deposition of this limestone, resulting in further isolation of each island. Some islands did not separate from the mainland but emerged above sea level later as a result of volcanic edifice construction or forearc uplift. Following initial isolation, the Japanese islands and Taiwan may have been connected to the mainland by land bridges during some sea level low stands related to glacial periods, whereas the other islands remained isolated. Based on ages of isolation of each island, a Quaternary palaeogeographic map and ‘phylogenetic tree’ of the islands can be drawn showing the separation time of each island from the mainland and from each other. This information should be useful for phylogenetic molecular biologists studying evolution of Ryukyu endemic species and vicariant speciation and could facilitate analysis of the DNA substitution rate.     

A one‐year study of the Rostherne Mere ecosystem: seasonal dynamics of water chemistry,plankton, internal nutrient release,and implications for long‐term trophic status and overall functioning of the lake

A study of Rostherne Mere (Cheshire, UK) was undertaken to reveal relationships among various ecosystem components and assess the progress in lake recovery following sewage diversion. An intensive monitoring programme included measurements of dissolved oxygen, T, pH, electric conductivity, K, Mg, Ca, Si, N and P species, Secchi depth, suspended solids, chlorophyll‐a, phyto‐ and zooplankton counts. Recorded changes and the results of correlation analysis broadly confirmed to the classic limnoecological theory and allowed detailed interpretation of the dynamics observed. The Si level was used to estimate the amount of diatom detritus produced in spring. Chemical profiles were used to estimate the amount of nutrients accumulated in the hypolimnion during the stratified period. These estimates were compared with simulations made using the model of exponential decay, which showed a good performance in the case of Si but considerable underestimation in the case of P. The differences between the values simulated by the model and estimates based on field observations resulted from the additional P release from the sediments. This release could have been stimulated by a combination of factors, including the development of anoxic layers on the sediment–water interface and Si‐induced desorption from Fe, Al and Mn oxides. Internal P loading during the stratified period was thus estimated at about 4–9 g/m², suggesting that rapid changes in the lake's trophic status are at present unlikely. Certain aspects of this work (including interpretation of interrelationships between ecosystem components, estimation of the decomposition constant, analysis of factors controlling nutrient accumulation in the hypolimnion, and a low‐cost method to estimate internal P release) may be useful for studies of other aquatic systems and have, therefore, general limnological applicability. Copyright © 2001 John Wiley & Sons, Ltd.     

Oligocene to Middle Miocene basin development in the Vélez Rubio Corridor – Espuña (Internal-External Zone Boundary; Eastern Betic Cordilleras,SE Spain)

The Vélez Rubio Corridor and the area northwest of the Sierra Espuña are located on the Internal-External Zone Boundary. The External Zone is represented by the Southern Subbetic, the most basinward part of the former passive margin of Iberia, the Internal Zone by its unmetamorphosed highest unit, the Malaguide Complex, tectonically underlain by the metamorphosed Alpujarride Complex. During the Oligocene and Aquitanian, the Southern Subbetic was the locus of slope deposition with northeastern provenance of detritus. In the Malaguides of the Espuña, the detritus of Lower Oligocene transgressive conglomerates and Middle Oligocene fan deltas indicates Sardinian proximity. The Upper Oligocene to lower Aquitanian Ciudad Granada and Pliego formations of the Malaguide Complex, carrying exclusively Malaguide detritus, were deposited in grabens within the Malaguide realm during an extensional rifting phase. The Malaguides, still far removed from the Subbetic, underwent major thrusting during the Aquitanian. Of the sedimentary units found between the Internal and External Zones, the oldest unit (the allochthonous Aquitanian Solana formation) was deposited in submarine fans outside the Subbetic or Malaguide realms proper, but in close connection with the latter. The Internal Zone collided with the External Zone in the early Burdigalian with concomitant disruption of the Southern Subbetic slope. On the suture, a deep basin was formed and filled in by the Burdigalian Espejos formation carrying detritus from the Subbetic and from the Malaguide and Alpujarride Complexes. In the late Burdigalian, the Subbetic was thrust southward over the Espejos formation, thus double-sealing the collisional contact. During the latest Burdigalian to Langhian, new basins were formed along the Internal-External Zone Boundary and within the Southern Subbetic. The onset of strike-slip faulting caused shoaling and uplift of these basins. Onset of a new pattern of strike-slip faulting induced the formation of a new suite of basins during the Tortonian, e.g. the Lorca Basin.     

Enzymatic Approach to Fungal Association with Arthropod Guts: A Case Study for the Crustacean Host, Nihonotrypaea harmandi, and Its Foregut Fungus, Enteromyces callianassae

Abstract. In the callianassid shrimp Nihonotrypaea harmandi (Bouvier 1901), the trichomycete fungus Enteromyces callianassae Lichtwardt 1961 occurs exclusively on the foregut lining. The enzymes from both the shrimp and the fungus apparently hydrolyze certain nitrogen and carbon compounds in detritus. The activities of various proteases and carbohydrases contained in the foregut juice were compared between fungus-infected shrimps collected from a sandflat in Kyushu, Japan (51 % infection rate) and uninfected shrimps from a nearby sandflat. The concentration of enzymatically hydrolyzable amino acids (EHAA) in sediment liberated by the foregut juice with fungi was slightly lower than that by 0.1 mg·ml^-1 proteinase-K and significantly higher than that by the foregut juice without fungi. In both foregut juices, substantial enzyme activities were recorded for proteinase(s), peptidases, amylase, cellulase and β-1,3-glucanase, and minimal ones for maltase and cellobiase. Of the commercial substrates examined, only in the case of the mixture of 16 kinds of dipeptides was a significantly higher enzyme activity in the foregut juice with fungi observed. In the process of EHAA liberation from sediment, peptidases secreted by the fungus most probably act as a supplement to the endogenous secretion by the shrimp. This may explain the higher shrimp growth rate recorded for the population with fungi. However, the significantly higher sediment EHAA concentration of the sandflat inhabited by this population versus the population without fungi could be another crucial factor explaining the site difference in shrimp growth rate.     

Environmental factors influencing macrodetritus flux in North Inlet estuary

Floating macrodetritus transport was determined on 72 tidal cycles over 18 months. Floating macrodetritus was exported from the marsh-estuarine ecosystem to the Atlantic Ocean, but export was low (less than 1% of Spartina net aerial primary production). Season and processes within the system seem to determine ebb flux, while flood flux is best explained by a semi-lunar cycle or high water. The extensive observations reported here indicate macrodetritus probably should not be considered a major source of organic carbon export from marsh-estuarine systems.     

Organic nitrogen and caloric content of detritus III. Effect on growth of a deposit-feeding polychaete, Capitella capitata

Laboratory experiments showed that individual growth rate of the deposit-feeding polychaete, Capitella capitata (type 1) can be predicted by rate of organic nitrogen supply (ration) of detritus to the animals. The rate at which detritus is available to a deposit-feeder, whether by sedimentation to the bottom, or decomposition of otherwise undigestable components via microbial activity, or production rate of microbes themselves, is important and not just the concentrations of limiting substrate of different detritus sources. Even so, the portion of total caloric content of the detritus that can be utilized by a deposit-feeder—approximated by the ‘available’ caloric content—also contributes to limiting growth. However, available caloric content usually is low when nitrogen content is low, as in the case of vascular plant detritus. Trophic transfer efficiency (net production/food supplied) is a measurement of food chain transfer that is usually calculated in carbon or caloric units. If one is interested in comparing energy or carbon flow in food chains, then use of these parameters is appropriate; if one is interested in comparing the efficiencies of different species, then calculations must be made using nutritional factors limiting growth.     

A growth model of the cockle (Cerastoderma edule L.) tested in the Oosterschelde estuary (The Netherlands)

We present an ecophysiological model of the bivalve Cerastoderma edule that simulates individual growth and reproduction under ambient conditions in temperature and food availability in the Oosterschelde estuary, SW Netherlands. The model contains feedback loops in the uptake and metabolism of food and in the partitioning of carbon to the internal state variables: somatic tissue, storage, organic shell matrix and gametes.The model was calibrated for 24 parameters, based on random distributions of parameter values. This procedure includes an estimate of confidence intervals of the output variables. The simulated growth of shell length and animal wet and dry weight reflected the observed values of growth in the field for the period 1993 – 1997. The model is a tool for the integration of ecophysiological knowledge of this species and also for carrying-capacity studies of shellfish culture and for environmental management of populations in estuarine and coastal areas.