Differences in herbivore preferences, phlorotannin production, and nutritional quality between juvenile and adult tissues from marine brown algae

 Juvenile and adult marine organisms differ in their morphology, chemistry, physiology, behavior, and ecology. Because juvenile algae are thinner, smaller, and have more delicate tissues than adults, they are often assumed to be more susceptible to grazers. We examined within-species food preferences of four common generalist herbivores for juvenile and adult tissues of eight common brown algae in two-choice laboratory food-preference experiments. Our results showed that juvenile algae did not tend to be a preferred food of herbivores. Juvenile tissues were significantly preferred over adult tissues in only four of the 32 combinations of algae and herbivores tested. In 12 experiments, adult tissues were preferred over juvenile tissues, and no choice occurred in the remaining 16 experiments. When sea urchins exhibited a preference, it was always for adult tissues. The other three herbivores, an isopod and two snails, were more variable in their choices, sometimes preferring juveniles, sometimes adults, and sometimes having no preference. We measured nitrogen and phlorotannin concentrations in adult and juvenile seaweeds to see whether these parameters were correlated with herbivore food preferences. Nitrogen levels were similar in juveniles and adults of three algal species and were higher in juveniles of two. Phlorotannin levels were higher in juveniles of four species and lower in juveniles of one. The other three species showed no differences in phlorotannin levels. Phlorotannin concentrations decreased with increasing juvenile size in three species and increased with increasing size in one species. Neither nitrogen nor phlorotannin concentrations explained overall herbivore food preferences for algae of different stages. Our results suggest that preferences of certain grazers for juvenile algae are not as strong as previously assumed and are dependent on herbivore species. Preferences between juveniles and adults are likely to be determined by a combination of morphological and chemical features of the tissues and the unique responses of herbivore species to those features. Received: 10 April 2000 / Accepted: 19 November 2000     

Dimethylsulfoniopropionate and dimethylsulfide in the marine flatworm Convoluta roscoffensis and its algal symbiont

 A distinct smell of dimethylsulfide (DMS) was noted at the edge of the intertidal mudflat of Marennes-Oléron Bay, at the French Atlantic coast, where dense populations of the marine flatworm Convoluta roscoffensis Graff (Platyhelminthes: Turbellaria) were present. DMS is the cleavage product of dimethylsulfoniopropionate (DMSP). DMSP was shown to be present in high amounts in sediment containing the flatworm as well as in axenic cultures of the symbiotic alga Tetraselmis sp. that was isolated from the flatworm. In untreated sediment samples containing C. roscoffensis the concentration of DMS was as high as ∼55 μmol l⁻¹ sediment, and in samples that were fixed with glutaraldehyde the concentration of DMS was even three orders of magnitude higher (∼66 mmol l⁻¹ sediment). This rapid cleavage of DMSP to DMS in fixed samples was unexpected. Pure DMSP was stable in glutaraldehyde, and it was therefore concluded that a DMSP-lyase was responsible for cleavage in the field samples. The isolated symbiotic alga, Tetraselmis sp., did not show DMSP-lyase activity, indicating that DMSP-lyase may have been present in the flatworm, although the role of bacteria could not be excluded. The Chl a-specific DMSP content of C. roscoffensis (∼200 mmol g⁻¹) was much higher than that of Tetraselmis sp. (∼30 mmol g⁻¹). Possibly, DMSP was not only present in the symbiotic alga, but was also incorporated in the body tissue of the flatworm. It remains unclear what the function of DMSP is in C. roscoffensis. In Tetraselmis sp., but not in C. roscoffensis, DMSP increased with increasing salinity. It was concluded that salinity probably does not play an important role in the dynamics of DMSP and DMS in sediment containing C. roscoffensis. Received: 21 January 2000 / Accepted: 29 August 2000     

Statistical modeling of seasonal and environmental influences on the population dynamics of an estuarine fish community

A statistical modeling study was performed on the population fluctuations of the 15 commonest fish species frequenting the tidal Scheldt estuary in Belgium. These included marine juvenile and seasonal visitors, estuarine residents and diadromous fish species that were recorded on the filter screens of a power plant cooling-water intake between September 1991 and April 2001. The species population abundance was regressed against a candidate set of 6 environmental variables and 13 instrumental variables, accounting for seasonality and long-term trends present in the data. Population abundances of the different species were, in general, best described by seasonal variables. Seasonal components contributed, on average, up to 63.8% of the variance explained by the models. Ten species were found to show a slightly negative, though significant, trend over the period of the survey. Most models also included at least one environmental variable, and 25.4% of the explained variance could be attributed to environmental fluctuations. Of all physico-chemical variables, dissolved oxygen was the most important predictor of fish abundance, suggesting that the estuary suffered from poor water quality during the survey. Temperature, salinity, freshwater flow, suspended solids and chlorophyll a concentrations were minor determinants of fish abundance.Communicated by O. Kinne, Oldendorf/Luhe     

Arsenic in groundwaters of the Lower Mekong

Increasing incidence and awareness of arsenic in many alluvial aquifers of South-east Asia has raised concern over possible arsenic in the Lower Mekong Basin. Here, we have undertaken new research and reviewed many previous small-scale studies to provide a comprehensive overview of the status of arsenic in aquifers of Cambodia and the Cuu Long Delta of Vietnam. In general natural arsenic originates from the Upper Mekong basin, rather than from the local geology, and is widespread in soils at typical concentrations of between 8 and 16 ppm; (dry weight). Industrial and agricultural arsenic is localised and relatively unimportant compared to the natural alluvial arsenic. Aquifers most typically contain groundwaters of no more than 10 μg L⁻¹, although scattered anomalous areas of 10 to 30 μg L⁻¹ are also quite common. The most serious, but possibly ephemeral arsenic anomalies, of up to 600 μg L⁻¹, are associated with iron and organic-rich flood-plain sediments subject to very large flood-related fluctuations in water level, resulting in transient arsenopyrite dissolution under oxidizing conditions. In general, however, high-arsenic groundwaters result from the competing interaction between sorption and dissolution processes, in which arsenic is only released under reducing and slightly alkaline conditions. High arsenic groundwaters are found both in shallow water-tables, and in deeper aquifers of between 100 and 120 m depth. There is no evidence of widespread arsenicosis, but there are serious localised health-hazards, and some risk of low-level arsenic ingestion through indirect pathways, such as through contaminated rice and aquaculture. An almost ubiquitous presence of arsenic in soils, together with the likelihood of greatly increased groundwater extraction in the future, will require continuing caution in water resources development throughout the region.     

Measurement of the leaching behaviour of granular solid wastes

Leaching of granular solids can be described in terms of specific mass transfer functions of a simple mathematical form.

The parameters can be determined by column leaching experiments under well known flow conditions.

Initially available concentrations are obtained from batch experiments at high dilution. Total concentrations in the solids are determined independently to calculate the available fractions.

The determination of the flow pattern is done by radiotracer measurements. Leachates are analyzed by various analytical methods including AAS and INAA. Total concentrations in the solids are determined by INAA preferably.     

Exposure and Health Effects of Cadmium

The results of a study of photocatalytic degradation of phenol using aqueous oxygenated TiO₂ (anatase) suspensions in a batch Pyrex photoreactor are reported. The influence on the photodegradation rate of various parameters as pH, phenol and TiO₂ content, oxygen partial pressure, anions present in the dispersions was investigated. A complete oxidation of phenol was observed. Intermediate compounds, catechol and quinone, were detected. It was observed that the photodegradation also proceeded with sunlight radiation. A mechanistic and kinetic model, which accounts for the results obtained, is given. Likely reasons for inactivity of the rutile modification for this reaction are also given.     

Assessing Landscape Condition Relative to Water Resources in the Western United States: A Strategic Approach

The Environmental Monitoring and Assessment Program (EMAP) is proposing an ambitious agenda to assess the status of streams and estuaries in a 12-State area of the western United States by the end of 2003. Additionally, EMAP is proposing to access landscape conditions as they relate to stream and estuary conditions across the west. The goal of this landscape project is to develop a landscape model that can be used to identify the relative risks of streams and estuaries to potential declines due to watershed-scale, landscape conditions across the west. To do so, requires an understanding of quantitative relationships between landscape composition and pattern metrics and parameters of stream and estuary conditions. This paper describes a strategic approach for evaluating the degree to which landscape composition and pattern influence stream and estuary condition, and the development and implementation of a spatially-distributed, landscape analysis approach.     

Characterization of humic-rich hydrocolloids and their metal species by means of competing ligand and metal exchange--an on-site approach

An improved on-site characterization of humic-rich hydrocolloids and their metal species in aquatic environments was the goal of the present approach. Both ligand exchange with extreme chelators (diethylenetetraaminepentaacetic acid (DTPA), ethylendiaminetetraacetic acid (EDTA)) and metal exchange with strongly competitive cations (Cu(II) were used on-site to characterize the conditional stability and availability of colloidal metal species in a humic-rich German bogwater lake (Venner Moor, Münsterland). A mobile time-controlled tangential-flow ultrafiltration technique (cut-off: 1 kDa) was applied to differentiate operationally between colloidal metal species and free metal ions, respectively. DOC (dissolved organic carbon) and metal determinations were carried out off-site using a home-built carbon analyzer and conventional ICP-OES (inductively-coupled plasma-optical emission spectrometry), respectively. From the metal exchange equilibria obtained on-site the kinetic and thermodynamic stability of the original metal species (Fe, Mn, Zn) could be characterized. Conditional exchange constants Kex obtained from aquatic metal species and competitive Cu(II) ions follow the order Mn > Zn > > Fe. Obviously, Mn and Zn bound to humic-rich hydrocolloids are very strongly competed by Cu(II) ions, in contrast to Fe which is scarcely exchangeable. The exchange of aquatic metal species (e.g. Fe) by DTPA/EDTA exhibited relatively slow kinetics but rather high metal availabilities, in contrast to their Cu(II) exchange.     

Field scale variability of cadmium and zinc in soil and barley

CaCl₂-extractable soil Cd and Zn contents have been suggested as a measure of bioavailability. To investigate the ability of this measure to reflect spatial patterns of Cd and Zn concentrations in barley (Hordeum vulgare L.) in an arable field, plant and soil samples were taken from a 0.5 ha area sandy soil contaminated with Cd and Zn. Cd and Zn contents in barley and yield were spatially variable. Yield was low, which may have been caused by Zn toxicity or atrazine turnover. For Cd, CaCl₂-extractable soil contents explained only 17% of the variation in Cd contents in grain, and for Zn no significant correlation was observed. Nevertheless, surface plots of CaCl₂-extractable soil contents and contents of barley grain illustrated their corresponding spatial patterns. Despite the poor linear correlation between CaCl₂-extractable soil-Cd and grain-Cd, a stochastic model for long term behaviour of Cd in field soils predicted observed variability in Cd contents of barley grain well from spatial variability of soil pH and organic matter content. The probabilistic model predicted behaviour of Cd in terms of probability, and was more appropriate than the deterministic approach.     

Economic Science, Endangered Species, and Biodiversity Loss

Abstract: Although economic analysis can be used to argue for preservation of species and habitats, many natural assets represent inferior investments in society's asset portfolio. We demonstrate this for the case of ancient temperate rainforests and minke whales (  Balaenoptera acutorostrata ). For both rainforests and whales, we determined their value for harvest and balanced this against society's valuation of the preserved stock. For the market and nonmarket data available, we then determined how much rainforest and how many minke whales global society should keep in its asset portfolio. Although ecologists increasingly attempt to justify preservation of biological assets on economic grounds, we argue that this might be a dangerous approach to take. Ultimately, it may be necessary to reexamine the ethical foundations for conservation of nature and biodiversity, including the economist's use of utilitarianism. We suggest that the safe minimum standard approach may prove useful in practice.