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881.
The impact of motorcycle traffic on soil and vegetation of stabilized coastal dunes, Israel 总被引:1,自引:0,他引:1
This study aimed to assess the response of soil and annual plant vegetation of stabilized coastal dunes in Israel, to varying
intensities of off-road motorcycle (ORM) traffic, and to assess their resistance and resilience to such a disturbance. A standard
experimental procedure that included 0, 20, 50, 100 and 200 ORM straight passes and 150 ORM turn passes was used. Plant ground
cover, mean plant height, species richness, species diversity, soil penetrable depth, organic matter and moisture contents
were measured on several dates within a period of 372 days after the experiment. Results have shown that: (1) ORM passes had
a significant immediate impact on annual plants that increased with traffic intensity. The impact on the soil was detected
only as an increase of penetrable depth. (2) The maximum impact on annual plants was observed in the wheel ruts and turn areas.
The impact on the area between the wheel ruts and on the margins outside the wheel ruts was indirect and smaller. (3) Annual
plant ground cover and mean plant height were less sensitive parameters than species richness and species diversity for determining
the impact of ORM traffic on the area. (4) One year after the experiment, soil and annual plant vegetation in all passes were
very similar to their pre-experimental condition. This indicates high resilience and recovery potential of the Mediterranean
stabilized coastal dune ecosystem to ORM disturbance. 相似文献
882.
Composite sampling techniques for identifying the largest individual sample value seem to be cost effective when the composite samples are internally homogeneous. However, since it is not always possible to form homogeneous composite samples, these methods can lead to higher costs than expected. In this paper we propose a two-way composite sampling design as a way to improve on the cost effectiveness of the methods available to identify the largest individual sample value. 相似文献
883.
884.
P. Mumby J. Chisholm A. Edwards C. Clark E. Roark S. Andrefouet J. Jaubert 《Marine Biology》2001,139(1):183-189
In April-May 1998, mass coral bleaching was observed in the lagoon of Rangiroa Atoll, Tuamotu Archipelago, French Polynesia. Six months later, the extent of bleaching-induced coral mortality was assessed at three sites. Corals in the fast-growing genus Pocillopora had experienced >99% mortality. Many large colonies of the slow-growing genus Porites (mean horizontal cross-sectional area 5.8 m2) had also died - a phenomenon not previously observed in French Polynesia and virtually unprecedented world-wide. At one site, 25% of colonies, or 44% of the pre-bleaching cover of living Porites, experienced whole-colony mortality. At the two other sites, recently dead Porites accounted for 41% and 82% of the pre-bleaching live cover. Mortality in Porites was negatively correlated with depth between 1.5 and 5 m. Using a 50-year dataset of mean monthly sea surface temperature (SST), derived from ship- and satellite-borne instruments, we show that bleaching occurred during a period of exceptionally high summer SST. 1998 was the first year in which mean monthly SSTs exceeded the 1961-1990 upper 95% confidence limit (29.4°C) for a period of three consecutive months. We suggest that the sustained 3-month anomaly in local summer SST was a major cause of coral mortality, but do not discount the synergistic effect of solar radiation. Recovery of the size-frequency distribution of Porites colonies to pre-bleaching levels may take at least 100 years. 相似文献
885.
Spawned gametes were collected from colonies of Acropora longicyathus at One Tree Island and Goniastrea aspera at Magnetic Island, Great Barrier Reef, Australia, for use in fertilisation trials. Mean fertilisation rates were significantly reduced compared with controls (P<0.003), when gametes from the branching coral A. longicyathus were exposed to elevated ammonium concentrations at 1 µM and above in one cross (60-64% reduction), and at 100 µM in another cross (16% reduction). Mean fertilisation success of A. longicyathus gametes was also significantly reduced compared with controls in both crosses (P=0.000) at concentrations of 1 µM phosphate and above (35-75% reduction), and at 1 µM ammonium plus 1 µM phosphate and all higher concentrations (68-74% reduction). Similarly, the mean percentage of regular embryos that were developing normally was significantly reduced in most nutrient treatments compared with controls (P=0.000). Fertilisation trials using gametes from the brain coral G. aspera resulted in a significantly lower percentage of regular embryos (P=0.001) and a significantly higher percentage of deformed embryos (P=0.001) developing after exposure to elevated nutrient treatments compared with controls. Mean fertilisation rates for this species were only significantly reduced (P=0.034) in the 50 µM ammonium plus phosphate treatment in one cross (8% reduction), compared with the control. Therefore, ammonium and phosphate enrichment significantly impairs fertilisation success and embryo development in scleractinian reef corals. 相似文献
886.
Chromosomal and nuclear characteristics of deep-sea hydrothermal-vent organisms: correlates of increased growth rate 总被引:2,自引:0,他引:2
A range of tissue and cell types from adult and juvenile stages of vent- and non-vent-dwelling deep-sea and shallow-water organisms were compared for signs of cell division, in preparation for a cytogenetic study of the different groups. Virtually all the Mid-Atlantic Ridge (MAR) vent species (bresiliid shrimp, bathymodiolid mussel, branchipolynoid polychaete, and a range of small gastropods) showed an abundance of metaphase chromosome spreads, indicating a generally high intrinsic rate of cell division, irrespective of their phylogenetic group. In comparison, similar tissues and life-history stages (i.e. gonad, developing eggs and gill) from two deep-sea bathypelagic crustaceans, Hymenodora and Gnathophausia, failed to yield any convincing evidence of cell division. This indicated that rates of growth and reproduction in the rest of the deep sea are extremely low. While much has been written about the contrasting growth rates of vent versus non-vent organisms, this is the first direct evidence of differences in cell-division rate between vent and non-vent species, which undoubtedly reflects contrasting conditions relating to food availability and temporal stability in these two deep-sea environments. The cells of shallow-water marine invertebrates (Mytilus, Nucella, Littorina, Pomatoceros and Crangon), based on the results of previous cytogenetic investigations, occupy an intermediate position with respect to their cell-division kinetics. When chromosome numbers, DNA content and nuclear diameters were compared between vent and non-vent species, this showed that no change had occurred in these characters since the time of vent colonisation. Representative chromosome spreads from hydrothermal-vent organisms are shown here for the first time. 相似文献
887.
M. Zimmer J. P. Danko S. C. Pennings A. R. Danford A. Ziegler R. F. Uglow T. H. Carefoot 《Marine Biology》2001,138(5):955-963
Three isopod species (Crustacea: Isopoda), commonly found in the intertidal and supratidal zones of the North American Pacific
coast, were studied with respect to symbiotic microbiota in their midgut glands (hepatopancreas). Ligia pallasii (Oniscidea: Ligiidae) contained high numbers of microbial symbionts in its hepatopancreatic caeca. Numbers of endosymbionts
were strongly reduced by ingestion of antibiotics. By contrast, the hepatopancreas of Idotea wosnesenskii (Valvifera: Idoteidae) and Gnorimosphaeroma oregonense (Sphaeromatidea: Sphaeromatidae) did not contain any microbiota. Results of feeding experiments suggest that microbial endosymbionts
contribute to digestive processes in L. pallasii, the most terrestrial of the three isopods that we studied. The acquisition of digestion-enhancing endosymbionts may have
been an important evolutionary step allowing isopods to colonize terrestrial habitats where relatively indigestible leaf litter
is the primary food source. By contrast, the ability to digest phenolic compounds was most developed in one of the more marine
species, suggesting that this trait may have evolved independently in isopod species that consume a phenolic-rich diet, whether
in marine habitats or on land.
Received: 28 August 2000 / Accepted: 8 December 2000 相似文献
888.
Population structure of yellowfin tuna (Thunnus
albacares) in the western Pacific Ocean, inferred from microsatellite loci 总被引:1,自引:0,他引:1
Five polymorphic microsatellite loci were examined in 1391 yellowfin tuna (Thunnus albacares) from eight regions of the western (Coral Sea, eastern Australia, Fiji, Indonesia, Philippines and Solomon Islands) and eastern (California and Mexico ) Pacific Ocean. Across all samples, numbers of alleles per locus ranged from 7 to 30 (mean: 17.0), and observed heterozygosities per locus ranged from 0.223 to 0.955 (mean: 0.593). Temporal collections were available for three areas: no significant temporal heterogeneity was observed for the Coral Sea (1991/1992 and 1995/1996 collections) or eastern Australia (1994/1995, 1995/1996, 1996/1997 and 1997/1998), but there was slight but significant heterogeneity at one locus (cmrTa-161) between the two Philippines collections (1994/1995 and 1996/1997). Genotypes generally showed a good fit to Hardy-Weinberg expectations within populations; only cmrTa-208 in the pooled Coral Sea population gave a significant deviation after Bonferroni correction for 40 tests, with a small but significant excess of homozygotes. Four loci showed no evidence of population differentiation following contingency Chi-squared and FST analyses. The fifth locus, cmrTa-161, showed small but significant differentiation (FST=0.002, P<0.001). This heterogeneity was largely a result of the Philippines 1994/1995 and Fiji collections; there was no correlation with geographic distance. The average FST across all five loci was very low (FST=0.002), but it was significant (P<0.001). It is unclear whether this low but significant differentiation reflects noise in the dataset, perhaps arising from experimental error, or real population differentiation. The finding of very limited population heterogeneity accords with most of the earlier allozyme and mitochondrial DNA studies of yellowfin tuna in the Pacific Ocean. 相似文献
889.
The Fleet (southern England) is a stable (ca. 5,000 years) coastal saline lagoon that supports a population of Alcyonidium resembling the common coastal epiphyte, Alcyonidium gelatinosum (L.). A combination of morphological, reproductive, and ecological characters was used to compare lagoonal and non-lagoonal proximate populations. Comparisons revealed a difference in the timing of spawning, considered to be related to the temporally restricted availability of viable substrata within the lagoonal basin. Allochronous spawning and spatial separation together suggest that the lagoonal taxon is reproductively isolated. The two populations were further compared with seven other coastal populations of Alcyonidium using randomly amplified polymorphic DNA (RAPD) analysis. The results confirm the individuality of the lagoonal taxon but also a close relationship with three A. gelatinosum populations. We present and consider four hypotheses that may account for the presence of this genetically distinct taxon: (1) diversification within the Fleet; (2) colonisation from another lagoon; (3) non-indigenous species status; and (4) introduction by shipping or other anthropogenically mediated dispersal mechanism. Significant diversification on the time scale involved has been demonstrated for isolated freshwater environments and, therefore, is feasible within a saline lagoon. Hypothesis 1 and, to a lesser extent, hypothesis 2 are consistent with the recognition of individual lagoons as 'biogeographic' islands of importance for their unique or characteristic biodiversity. The study also represents the first example of concordant morphological, reproductive, and genetic diversification in a marine bryozoan. 相似文献
890.
E. Gornung C. Cordisco A. Rossi De S. Innocentiis D. Crosetti L. Sola 《Marine Biology》2001,139(1):55-60
This study continues a comparative cytogenetic analysis of the fish family Mugilidae, reporting the karyotype characterization of the leaping mullet, Liza saliens, by C-banding, Ag- and fluorochrome-staining, and completing the fluorescence in situ hybridization (FISH)-mapping of the 18S and 5S rRNA genes (rDNA) to the chromosomes of the six Mediterranean mullets, namely L. saliens, L. ramada, L. aurata, Mugil cephalus, Chelon labrosus and Oedalechilus labeo. In all species, except M. cephalus, the 5S rDNA sites were localized on a medium-sized acrocentric chromosome pair, which was considered homeologous in all of them. In L. saliens, an additional 5S rDNA site was detected in a location close to the one shown by major ribosomal genes in M. cephalus, i.e. the subtelomeric region of chromosome pair 1. The 5S rDNA site in M. cephalus is located on the smallest chromosome pair of the complement, which, on the other hand, though on a different position, bears 18S rDNA in all the species of Liza and Chelon examined. The heterochromatin composition and the major and minor ribosomal gene locations suggest that the karyotype of L. saliens (subgenus Protomugil) can be considered intermediate between the karyotype of the more primitive M. cephalus and those of the other Liza (subgenus Liza) species and of the representatives of the more derived genera Chelon and Oedalechilus. 相似文献