Adaptations to barnacle fouling in the mangroves <Emphasis Type="Italic">Kandelia obovata</Emphasis> and <Emphasis Type="Italic">Aegiceras corniculatum</Emphasis>

Mangrove trees planted for restoration or rehabilitation often fail to show satisfactory survivals. Although it is generally assumed that barnacle fouling is a factor in mangrove mortality, the sub-lethal response of mangroves to this fouling is not known. In the present study, we compare the leaf morphology (stomata density, leaf thickness, percentage thickness of palisade layer and number of hypodermal layers), lenticel density and the plant fitness (number of flowers or droppers per tree) between mangroves fouled by the acorn barnacle Fistulobalanus albicostatus (the fouled group, number of barnacles ~ 120 individuals per tree) and non-fouled mangroves (the control group). We observed 55 Kandelia obovata from three locations, two in Hong Kong (n = 35, fouled 25 and control 10) and one location in Taiwan (n = 20, fouled 10 and control 10). Aegiceras corniculatum (n = 45) was observed from two sites in Hong Kong, one on the east coast (n = 20, 10/10) and one on the west coast (n = 25, 10/15). In seedlings (K. obovata n = 10, 5/5), fouling density did not affect leaf morphology. In mature trees, however, leaves from fouled trees had significantly higher density of stomata and stem lenticel, a lower percentage thickness of leaf palisade layer and more layers of lower hypodermis in the leaves, probably for compensating the impeded gaseous exchange functions of the lenticels. The number of droppers and flowers on fouled mangroves was significantly lower. It is possible that after compensating for respiratory stress, the plant had less energy available for reproduction. Although there was no obvious barnacle-induced mortality in this study, barnacles appear to be related to a reduction in plant fitness. This may induce sufficient stress that over time fouled mangroves cannot sustain viable populations.     

两种淹水模式下施用钝化材料对镉污染农田水稻安全生产的影响

为实现镉(Cd)污染农田稻米安全生产,以中度Cd污染农田为研究对象,通过连续2 a的大田试验,对比分析了间歇性淹水和全生育期淹水2种淹水模式下,玉石粉、生物炭和粉煤灰这3种钝化材料施用后对土壤pH,有效Cd和稻米Cd含量的影响.结果 表明:①单一淹水处理下,全生育期淹水和间歇性淹水处理均可提高土壤pH,土壤有效Cd降低...     

RANS simulation of neutral atmospheric boundary layer flows over complex terrain by proper imposition of boundary conditions and modification on the k-ε model

In this study, a modelling methodology is proposed for RANS simulations of neutral Atmospheric Boundary Layer (ABL) flows on the basis of the standard k-ε model, which allows the adoption of an arbitrary shear stress model. This modelling methodology is first examined in the context of an open flat terrain in an empty domain to ascertain there are no substantial changes in the prescribed profiles. The results show that relatively good homogeneity can be achieved with this modelling methodology for various sets of inflow boundary profiles. In addition, to extend the solutions derived from the standard k-ε model to RNG k-ε model, the RNG k-ε model is in detail assembly and tuned. Finally, the topographic effects on surface wind speeds over a complex terrain are assessed with the combined use of the proposed methodology and the modified RNG model. The numerical results are in good agreement with wind tunnel testing results and long-term field observations. A discussion of the effects of horizontal homogeneity and turbulence models on the simulated wind flows over a complex terrain is also given.     

Density dependence and density independence during the early life stages of four marine fish stocks

Recruitment variability caused by density-dependent and density-independent processes is an important area within the study of fish dynamics. These processes can exhibit nonlinearities and nonadditive properties that may have profound dynamic effects. We investigate the importance of population density (i.e., density dependence) and environmental forcing (i.e., density independence) on the age-0 and age-1 abundance of capelin (Mallotus villosus), northeast Arctic cod (Gadus morhua), northeast Arctic haddock (Melanogrammus aeglefinus), and Norwegian spring spawning herring (Clupea harengus) in the Barents Sea. We use statistical methods that explicitly account for nonlinearities and nonadditive interactions between internal and external variables in the abundance of these two pre-recruitment stages. Our results indicate that, during their first five months of life, cod, haddock, and herring experience higher density-dependent survival than capelin. The abundance of age-0 cod depends on the mean age and biomass of the spawning stock, a result which has implications for the management of the entire cod stock. Temperature is another important factor influencing the abundance at age-0 and age-1 of all four species, except herring at age-1. Between age-0 and age-1, there is an attenuation of density-dependent survival for cod and herring, while haddock and capelin experience density dependence at high and low temperatures, respectively. Predation by subadult cod is important for both capelin and cod at age-1. We found strong indications for interactions among the studied species, pointing to the importance of viewing the problem of species recruitment variability as a community, rather than as a population phenomenon.     

Decreased pH does not alter metamorphosis but compromises juvenile calcification of the tube worm Hydroides elegans

Using CO₂ perturbation experiments, we examined the pre- and post-settlement growth responses of a dominant biofouling tubeworm (Hydroides elegans) to a range of pH. In three different experiments, embryos were reared to, or past, metamorphosis in seawater equilibrated to CO₂ values of about 480 (control), 980, 1,480, and 2,300 μatm resulting in pH values of around 8.1 (control), 7.9, 7.7, and 7.5, respectively. These three decreased pH conditions did not affect either embryo or larval development, but both larval calcification at the time of metamorphosis and early juvenile growth were adversely affected. During the 24-h settlement assay experiment, half of the metamorphosed larvae were unable to calcify tubes at pH 7.9 while almost no tubes were calcified at pH 7.7. Decreased ability to calcify at decreased pH may indicate that these calcifying tubeworms may be one of the highly threatened species in the future ocean.