公园游客管理概念的演变

要保护公园的生态、社会、经济和文化价值 ,游客管理具有根本的重要性 . 政府要求公园进一 步在财政上自给自足 . 正在制定一个更加完善的管理方法代替单纯地限制游客的数量 . 这种 方法鼓励公众参与公园的目标设定和游客满意度评价 ,并奖励胜任的财务管理 .     

Influence of water circulation rate on in situ measurements of benthic community respiration

The relationship between water circulation rate and benthic community respiration was investigated using in situ chambers fitted with variable speed pumps. A strong, positive relationship was exhibited for three estuarine study sites which represented a broad spectrum of sediment characteristics. Both aerobic respiration (65–90% of the total sediment oxygen demand, SOD) and chemical oxygen demand, COD (10–35%) increased with stirring of the overlying waters at velocities up to 20 cm s^-1. Contrary to the notion that COD accounts for any increase in SOD at velocities which initiate sediment resuspension, we observed that aerobic respiration was also stimulated by high velocities. We conclude that measurements of SOD in estuarine environments should be made using water circulation rates which attempt to mimic the natural environment, and that COD cannot be assumed unimportant and should be measured directly.Supported by National Science Foundation Grant SMI 78-03130, Md. Dept. of Natural Resources, MPPSP P2-72-02 (B)Contribution No. 1137, Center for Environmental and Estuarine Studies of the University of Maryland     

A hydromechanical principle for particle retention in Mytilus edulis and other ciliary suspension feeders

It is generally thought that the laterofrontal cirri of the bivalve gill act as filters that retain suspended particles in the through current and transfer the particles onto the frontal surface of the gill filaments. In Mytilus edulis calculations indicated that if water passed between the branching cilia of the cirri that are assumed to constitute the filter the pressure drop needed would amount to about 10 times the actual pressure drop across the whole gill. Thus, instead of acting as filters the laterofrontal cirri seem to move water. Presumably, the cirri together with the frontal cilia produce the water currents along the frontal surface of the gill filaments. Particle retention in the bivalve gill implies the transfer of suspended particles from the current of water about to enter an interfilamentar space into a neighbouring frontal surface current. The complex three-dimensional pattern of flow that arises where the 2 systems of current meet is characterized by steep velocity gradients. Particles that enter such steep, steady velocity gradients become exposed to transverse forces that cause the particles to migrate perpendicularly to the direction of flow. Whether particles enter the surface current, i.e. are retained, or they stay within the through current andescape, depends primarily upon particle size, and upon the steepness and height of the gradients within the boundary zone between the surface current and through current. Further studies are needed to evaluate the capacities and relative importance of this hydromechanical particle-trapping mechanism in suspension feeding bivalves. It is suggested that in downstream particle-retaining systems, e.g. on the tentacles of polychaetes and entoprocts, velocity gradients between through currents and surface currents also act as the particle-collecting mechanism.     

Re-appraisal of age composition,growth and survivorship of the deep-sea brittle star Ophiura ljungmani from size structure in a sample time series from the Rockall Trough

Samples were taken from a 2 900 m deep permanent station (centred on 54°40N; 12°16W) in the southern Rockall Trough, from November 1975 to September 1980, inclusive. Revision of juvenile size frequencies was necessary after removal of postlarvae of an annual non-viable settlement of Ophiocten gracilis (G. O. Sars) that were mistakenly included in a previous analysis. The present study of the revised data shows that settlement of Ophiura ljungmani (Lyman) occurs in summer when disk-size frequencies are dominated by the newly metamorphosed postlarvae. The likely age composition in larger sizes was suggested from the progression of modes along the size axis in juvenile size classes in consecutive were developed from Gaussian mixtures fitted by constrained computer search using, as starting values, component parameter values suggested from the frequency histograms. Choice between competing solutions was made on the basis both of goodness-of-fit and biological plausibility. However, identification of year-class structure amongst sizes >3 to 4 mm disk diameter remained conjectural owing to the low frequencies of adults in the samples. Comparison of the fitted component-means in the time series suggested a marked seasonal growth pattern, with maximal growth in spring. Probable age composition amongst adult sizes was extrapolated from von Bertalanffy growth parameters estimated from the means of juvenile year classes.Communicated by J. Mauchline, Oban     

Dispersion of Tellina tenuis from Kames Bay,Millport, Scotland

The dispersion of Tellina tenuis da Costa in the laboratory was analysed by the Clark and Evans nearest-neighbour test and by the Kolmogorov-Smirnov one-sample test. The dispersion was random, with a slight tendency toward aggregation that was independent of density. In the field, the dispersion was analysed by the Clark and Evans nearest-neighbour test and by the X² approximation to Fisher's coefficient of dispersion. The dispersion was again random, this time with a slight tendency toward spacing out that was independent of density. The tendency toward aggregation displayed in the laboratory was independent of the dispersion pattern shown at the start of the experiment, and also unaffected by the edge of the container. The apparent randomness suggests that T. tenuis is primarily a suspension feeder, but may be a deposit feeder under certain environmental conditions.     

Effects of pressure,temperature and oxygen on the oxygen consumption rate of the Midwater copepod Gaussia princeps

In this study we assessed the amount of lead accumulated in the body of a grazing mollusc by transfer from its algal food in laboratory experiments, and compared these results with the amounts found in naturally occurring molluscs and seaweed. Near La Jolla, California (USA), where the concentration of lead in seawater is probably less than 0.08 g l^-1, most of the naturally occurring Egregia laevigata contains less than 0.4 g Pb g^-1 wet weight. The total body masses, without shells, of juvenile Haliotis rufescens fed on this seaweed for 3 to 6 months showed similar concentrations. When, however, E. laevigata is placed for 1 to 6 days in seawater to which lead has been added (0.1 or 1.0 mg l^-1) both the seaweed and the abalone subsequently fed with it accumulate proportionally larger amounts of lead. After 6 months, young abalone fed on E. laevigata pretreated with 1.0 mg Pb l^-1 accumulated up to 21 g Pb g^-1 wet weight. This amount of lead had no apparent consequences on the growth or activity of the molluscs. Analyses of 6 different organs from adult abalone showed that the lead was selectively concentrated in the digestive gland. In the foot (muscle tissue), which is the part normally consumed by humans, only negligible amounts were found.     

Allelic esterase isozymes,their variation with season,position on the shore and stage of development in the cirripede Balanus balanoides

Samples of Balanus balanoides (L.) in the Menai Straits were taken from their upper limit of distribution on the shore, from mean low water (MLW) and at three different times of the year, January, May and August. Individual prosomae were homogenised, electrophoresed on polyacrylamide gels and esterase isozymes determined. Group BbEI esterase isozymes fitted the Hardy-Weinberg predicted values for 4 co-dominant alleles in all samples. A comparison of BbEI phenotype frequency distribution of the upper shore and MLW samples showed no significant difference at the 5% level. The phenotype frequency of samples taken at different times of the year were significantly different at the 5% level, due to an excess of allele A in winter and an excess of allele C in summer. It is argued that the seasonal variation of phenotype frequency is probably not due to selection operating on a balanced polymorphism, but that the expression of the alleles through the synthesis of esterase isozymes is dependent on some environmental agent, postibly temperature or day length.     

Production organique primaire dans un milieu saumâtre eutrophe (Etang de Berre). Effets d'une forte dilution (dérivation des eaux de la Durance)

¹⁴C primary production measurements were made over a period of 5 years (1965–1969, inclusive) in the brackish lake Etang de Berre, near Marseilles (France). The diversion of the River Durance into the Etang de Berre took place during this period (March 1966) and introduced an important modification into the organic production ecosystem, mainly through increased and variable freshening, accompanied by substantial nutrient input. The seasonal distribution of production rates displayed 3 bloom periods: the first (short and slight) in spring, the second (the most important as regards intensity and duration) in summer, and the third in autumn (October). Before the diversion of the river in 1965, the carbon-uptake rates in the lake ranged between 25 mg/m²/day in winter and 800 mg/m²/day in summer-autumn, the mean value for the year being 150 g C/m², which represents 2.5×10⁴ tons of photosynthesized carbon for the whole lake. After the diversion, more than 3000 mg C/m² day were measured; for 1968, the inclusive uptake rate was 384 g C/m², representing 6×10⁴ tons of synthesized carbon for the whole lake. Nevertheless, noticeable variations occurred from one year to another. From the annual nutrient input of phosphate to the Etang de Berre through the inflow of Durance waters, the quantity of potentially synthesizable elements has been calculated, in terms of carbon, according to the normal P:C ratio of organic substances; this quantity is called R. The difference between measured production, P, and R gives a measure of the regenerated production. This portion of production represented about 80% of the total production before 1968 but only 16% in 1969, a year of maximum fresh-water inflow. This phenomenon could be due to modifications of the ecophysiology of the phytoplankton resulting from the considerable freshening. With increasing nutrient load, eutrophication first occurs, then still greater dilution results in inhibition of production.