Habitat suitability of the Wadden Sea for restoration of Zostera marina beds

A conceptual model is proposed, describing potential Zostera marina habitats in the Wadden Sea, based on reported data from laboratory, mesocosm and field studies. Controlling factors in the model are dynamics, degree of desiccation, turbidity, nutrients and salinity. A distinction has been made between a higher and a lower zone of potential habitats, each suitable for different morphotypes of Z. marina. The model relates the decline of Z. marina in the Wadden Sea to increased sediment and water dynamics, turbidity, drainage of sediments (resulting in increased degree of desiccation) and total nutrient loads during the twentieth century. The upper and lower delineation of both the higher and the lower zone of potential Z. marina habitats appear to be determined by one or a combination of several of these factors. Environmental changes in one of these factors will therefore influence the borderlines of the zones. The lower zone of Z. marina will be mainly affected by increased turbidity, sediment dynamics, degree of desiccation during low tide and nutrient load. The higher zone will be affected by increases in water and sediment dynamics, desiccation rates and nutrient loads. Potential Z. marina habitats are located above approx. –0.80 m mean sea level (when turbidity remains at the same level as in the early 1990s) in sheltered, undisturbed locations, and preferably where some freshwater influence is present. At locations with a high, near-marine, salinity, the nutrient load has to be low to allow the growth of Z. marina. The sediment should retain enough water during low tide to keep the plants moist. Our results suggest that the return of Z. marina beds within a reasonable time-scale will require not only suitable habitat conditions, but also revegetation measures, as the changes in the environment resulting from the disappearance of Z. marina may impede its recovery, and the natural import of propagules will be unlikely. Furthermore, the lower zone of Z. marina may require a genotype that is no longer found in the Wadden Sea. Received: 26 April 1999 / Received in revised form: 15 October 1999 / Accepted: 16 October 1999     

Does re-creation of extensive pasture-forest mosaics provide an economically sustainable way of nature conservation in Sweden''s forest dominated regions?

There is a major risk that many of the remaining semi-natural pastures in Swedish forest dominated regions will lose their grazing in the near future with lost biodiversity as a result. The reason is the high costs of grazing small pastures with cattle from generally small herds. The approaching decoupling of the present EU income support per head of cattle will increase the risk. Calculations based on economies of scale in beef production and opportunity cost of forest and arable land suggest that re-creating extensive pasture-forest mosaics consisting of existing semi-natural pastures and adjacent arable fields and forests can secure economically sustainable grazing. The risk of local extinction of grassland species due to habitat isolation is also lower in large mosaics than in small, scattered pastures.     

Vertical and horizontal distribution patterns of the giant sea anemone Heteractis crispa with symbiotic anemonefish on a fringing coral reef

The distribution patterns of the leathery sea anemone, Heteractis crispa, which contains an algal endosymbiont (zooxanthellae) and anemonefish, were investigated in relation to size distribution on a shallow fringing reef (3.2 ha, 0–4 m depth) in Okinawa, Japan. Individual growth and movements were also examined. Large individuals (>1,000 cm²) inhabited reef edges up to a depth of 4 m, while small anemone (<500 cm²) inhabited shallow reefs including inner reef flats. Individuals rarely moved, and their sizes were significantly correlated with their water depths. Growth of small anemones was negatively correlated with their distance from the reef edge, suggesting that reef edges provide more prey and lower levels of physiological stress. This study suggested that deep reef edges are suitable habitats for H. crispa. Large anemones were inhabited by large Amphiprion perideraion or large Amphiprion clarkii, both of which are effective defenders against anemone predators. Anemones that settle in deep reef edges may enjoy a higher survival rate and attain a large size because of their symbiotic relationship with anemonefish. However, early settlers do not harbor anemonefish. Their mortality rate would be higher in the deep edges than in shallow edges, the complicated topography of which provides refuge.     

Essential oil of Ayapana triplinervis from Reunion Island: A good natural source of thymohydroquinone dimethyl ether

Three specimens of Ayapana triplinervis (Vahl) R.M. King & H. Rob from Reunion Island (Indian Ocean) collected at two distant locations (North of the island; samples 1 and 2, South of the island; sample 3), in different growth phases (flowering; samples 1 and 3, vegetative; sample 2) were investigated for their leaf essential oil composition. This study reports the chemical character of this species on the island and investigates the relationship between essential oil composition, developmental stage and geographic location. Analysis by GC–FID and GC–MS enabled us to identify and quantify a total of 39 constituents accounting for 97.1–98.0% of the oils. The three essential oil samples, all obtained by hydrodistillation, showed a high percentage of the aromatic compound thymohydroquinone dimethyl ether (89.9–92.8%). All other minor components remained more or less unchanged both qualitatively and quantitatively with respect to the stage of growth. On the contrary, variations were observed with geographic distribution. The geographical variation of the chemical composition of the volatile oil of A. triplinervis from several sites in the world is also briefly discussed.     

Detection of haplotypic variation and natural hybridization in halepensis-complex pine species using chloroplast simple sequence repeat (SSR) markers

In this investigation, nine chloroplast, paternally inherited simple-sequence repeat (cpSSR) markers were used to describe genetic variation of three closely related species belonging to the halepensis complex ( Pinus halepensis Ait., P. brutia Mill. and P. eldarica Medwed.). Both the infinite allele model (IAM) and stepwise-mutation model (SMM) have been applied to the analysis of the genetic structure of natural populations and the geographical distribution of haplotypic variation. SMM-based estimators performed better than IAM-based estimators for large values of within-population diversity and divergence between population pairs. Overall, large haplotypic variation and high genetic divergence were detected for both P. halepensis and P. brutia . The genetic structures of the three species are discussed with consideration to the evolutionary and ecological characteristics of these species. Three highly informative markers showing size variants distinguishing P. halepensis from the other two species were used to provide more information on the occurrence of natural hybridization in a Turkish sympatric population of P. halepensis and P. brutia . Strong evidence of introgression of ' halepensis ' chloroplast haplotypes into P. brutia seeds (but not vice versa) was detected. According to previous evidence from controlled crossings, matings between the above species seem to be successful only when P. halepensis is the pollen donor and P. brutia is the female parent (but not reciprocally). The existence of unidirectional gene flow in sympatric populations confirms previous evidence about partial reproductive barriers between P. halepensis and P. brutia . Implications of the above evidence for the evolutionary history of these species are discussed.     

Linkages between seagrass,mangrove and saltmarsh as fish habitat in the Botany Bay estuary,New South Wales

Shallow-water vegetated estuarine habitats, notably seagrass, mangrove and saltmarsh, are known to be important habitats for many species of small or juvenile fish in temperate Australia. However, the movement of fish between these habitats is poorly understood, and yet critical to the management of the estuarine fisheries resource. We installed a series of buoyant pop nets in adjacent stands of seagrass, mangrove and saltmarsh in order to determine how relative abundance of fishes varied through lunar cycles. Nets were released in all habitats at the peak of the monthly spring tide for 12 months, and in the seagrass habitat at the peak of the neap tide also. The assemblage of fish in each habitat differed during the spring tides. The seagrass assemblage differed between spring and neap tide, with the neap tide assemblage showing greater abundances of fish, particularly those species which visited the adjacent habitats when inundated during spring tides. The result supports the hypothesis that fish move from the seagrass to the adjacent mangrove and saltmarsh during spring tides, taking advantage of high abundances of zooplankton, and use seagrass as a refuge during lower tides. The restoration and preservation of mangrove and saltmarsh utility as fish habitat may in some situations be linked to the proximity of available seagrass.     

Gait stability,variability and complexity on inclined surfaces

This study evaluated the gait stability, variability, and complexity of healthy young adults on inclined surfaces. A total of 49 individuals walked on a treadmill at their preferred speed for 4 min at inclinations of 6%, 8%, and 10% in upward (UP) and downward (DOWN) conditions, and in horizontal (0%) condition. Gait variability was assessed using average standard deviation trunk acceleration between strides (VAR), gait stability was assessed using margin of stability (MoS) and maximum Lyapunov exponent (λs), and gait complexity was assessed using sample entropy (SEn). Trunk variability (VAR) increased in the medial-lateral (ML), anterior-posterior, and vertical directions for all inclined conditions. The SEn values indicated that movement complexity decreased almost linearly from DOWN to UP conditions, reflecting changes in gait pattern with longer and slower steps as inclination increased. The DOWN conditions were associated with the highest variability and lowest stability in the MoS ML, but not in λs. Stability was lower in UP conditions, which exhibited the largest λs values. The overall results support the hypothesis that inclined surfaces decrease gait stability and alter gait variability, particularly in UP conditions.     

Genetic diversity assessment and estimation of phylogenetic relationships among 26 Fagaceae species using ISSRs

The family Fagaceae includes several species and presents huge genetic variability. In the last two decades, several genetic studies about phylogenetics and genetic diversity of Fagaceae have emerged. ISSR markers were used to evaluate the genetic diversity of 26 species of Fagaceae belonging to the genera Castanea, Fagus and Quercus. Among several primers tested, 17 were selected for the evaluation of diversity and estimation of genetic relationships. A total of 371 ISSR markers were produced and each primer revealed high polymorphism. Specific ISSR markers for the Quercus infrageneric groups were amplified. ISSRs proved to be a reliable tool for the discrimination of the analyzed species per genus, infrageneric group and/or ecological origin.     

Effect of nutrient level on competition intensity in the field for three coexisting grass species

A field experiment encompassing both neighbour- and nutrient-manipulations was conducted in a nutrient-impoverished old-field habitat to investigate how the intensity of plant competition was affected by soil nutrient level. Three perennial grasses were used as target species: Agropyron repens, Poa pratensis and Phleum pratense. Neighbour manipulations involved the removal (through herbicide application) of all neighbouring vegetation within a 20 cm or 40 cm radius around target plants. Target performance was measured under five levels of added nutrients (N-P-K) in both the neighbour-removal plots and in non-removal (control) plots. Both neighbour and nutrient manipulations had a highly significant effect on both biomass and tiller production but the interaction between these treatments was generally insignificant. Below-ground/above-ground biomass quotient was affected only by neighbour manipulations and was greatest in the control plots (with no neighbours removed) for all three species. The suppressive effect of neighbours was not markedly affected by nutrient level. However, yield suppression showed a significant decreasing trend with increasing nutrient level for biomass production in Agropyron and an increasing trend for tiller production in Phleum. For Poa, there was no trend in the intensity of competition across nutrient level. The results suggest that the general intensity of competition within this community neither increases nor decreases with increasing nutrient level. Rather, coexisting species appear to respond individually in terms of the intensity of competition that they experience. These results conflict with predictions from the triangular C-S-R model of plant strategies. However, they are consistent with a recently modified ‘habitat templet’ model for vegetation.