首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The present study reports on population structure analysis of the marbled crabPachygrapsus marmoratus (Fabricius, 1787) from the Tunisian coast, an appropriate location to study biogeographical process...  相似文献   

2.
The fishery for the edible sea urchin Paracentrotus lividus is of great importance to many European regions, although in some of them this species has shown a wide scale decline in recent years. This paper reports on direct (on P. lividus) and indirect (on the co-occurring but not fished echinoid, Arbacia lixula) effects of sea urchin harvesting in shallow rocky reefs in North-western Sardinia (Italy, central-western Mediterranean Sea), where this activity is intensively practised. Density, size (test diameter), and biomass of both species were assessed in autumn 2004 at two locations impacted by P. lividus fishery, and at two controls within an adjacent Marine Protected Area. Density of P. lividus and A. lixula was significantly greater at the controls than at the exploited locations. The average test diameter of P. lividus was also significantly larger at the controls, where large-sized specimens (i.e. >5 cm) were notably more abundant. The average size of A. lixula did not significantly differ between the impacted locations and the controls. The average biomass of P. lividus was significantly greater at the controls than at the exploited locations, whereas no differences were detected for A. lixula. These results reveal the existence of a heavy fishing impact on P. lividus in North-western Sardinia and the need for regulation of its harvesting to prevent severe direct effects on its populations. Since no indirect effects on A. lixula have been detected, it could be hypothesized that this species did not benefit from P. lividus fishery due to an only moderate competition for habitat and resources between these two echinoids. Implications for management of edible sea urchin fishery are also discussed.  相似文献   

3.
Numerous studies of interactions between urchins and algae in temperate areas have shown an important structuring effect of sea urchin populations. These studies focused almost wholly on the effect of high urchin densities on laminarian forests. In contrast, algal communities below 5–6 m depth in the northwestern Mediterranean are characterised by low sea urchin densities (<5 ind m−2) and the absence of laminarian forests. No previous research has addressed sea urchin/algal interactions in this type of community. To determine the effect of the most abundant echinoid species, Paracentrotus lividus, on well-established algal communities in this area, we performed a removal–reintroduction experiment in rocky patches located between 13 and 16 m depth in the northwestern Mediterranean, where sea urchin densities ranged between 0.9 and 3.4 ind m−2. After 6 months, the cover of non-crustose algae was significantly higher in the plots from which sea urchins had been removed than in control plots (84 vs 67% cover). These removal plots reverted to their original state upon reintroduction of sea urchins. The non-crustose algae consisted of turfing and frondose forms, with the former representing some 70% of the non-crustose algal cover. Change in the cover of turfing algae was responsible for the significant increase in algal development in the sea urchin removal plots. The response of frondose algae to the treatment varied between algal species. It is concluded that grazing by P. lividus exerts a significant effect on habitat structure, even in communities with low sea urchin densities, such as those found in vast areas of the Mediterranean sublittoral.  相似文献   

4.
This study investigates the effect of different Mediterranean habitats on spine and gonad colouring and gonadal index in the purple sea urchin Paracentrotus lividus (Echinodermata: Echinoidea). Specimens were collected in winter 2012 in Posidonia oceanica meadows and rocky bottom areas at two sites in Southern Sardinia (Italy, Tyrrhenian Sea). Colorimetric analyses of spines and gonads were conducted with a digital colorimeter using CIELAB colour spaces, which defines the colour in terms of three coordinate values: lightness (L*), redness (a*) and yellowness (b*). Lightness and redness of the spines differed significantly between habitats, whereas colour spaces of the gonads did not. A careful analysis of the gonad index showed it to be significantly affected by habitat, registering higher values in rocky bottom locations. In conclusion, it seems that habitat does affect spine colour but not gonad colour. Spine colour seems to be site‐dependent, whereas the gonad index depends solely on the habitat.  相似文献   

5.
Sea urchins can alter the composition and dynamics of algal communities by grazing. Changes in their displacement capability can influence their grazing and thus their effect on algal communities. The daily and monthly movement of Paracentrotus lividus inside and outside a marine reserve in the NW Mediterranean Sea was studied in order to determine the role of predation in sea urchin movements and its potential grazing impacts. During the 3‐month study, the total distance travelled by sea urchins ranged from 71.8 to 673.6 cm (mean = 379.2 cm, SD = 221.3). Home ranges (distances from the initial position) were between 50 and 302 cm (mean = 150.7 cm, SD = 99.4). Movements were not directional but random, with a mean of 150 cm around the initial position. The activity of Paracentrotus lividus was significantly higher at night than during daylight. Total displacement at the end of the experiment was significantly higher in the unprotected area than in the reserve, as was the home range. The linear distance travelled in a 24‐h period ranged between 6 and 220 cm with a mean home range of 51 cm. These results agree with those of other authors, and allow us to rule out major migratory processes of sea urchin populations in this area. Nevertheless, these results underline the role of predatory fishes in reducing herbivory pressure by trophic cascades, reinforcing the evidence that sea urchin escape behaviour may be an important factor in structuring algal communities.  相似文献   

6.
The taxonomy of oysters has been traditionally based on characteristics of the shell. More recently, the analysis of protein and DNA polymorphism has provided a means to overcome difficulties in distinguishing the different species of oysters based solely on shell morphology. In order to identify oysters of the Tunisian north-east coast, we sequenced a 16S rRNA mitochondrial fragment from 68 oysters sampled from the Bizert Lagoon and the Gulf of Hammamet in northern Tunisia. Comparison of oyster 16S rRNA sequences available in GenBank showed the presence of both Ostreola stentina and Crassostrea gigas in our samples, which could not be detected on the basis of shell morphology only. These data confirmed that C. gigas, a non-native species, is now naturalised in the Bizert Lagoon. Furthermore, significant levels of genetic divergence among the 16S rRNA haplotypes from O. stentina populations have been observed. Specifically, the haplotypes found in the Bizert Lagoon are closer to those previously detected from Morocco and Portugal, whereas those in the Gulf of Hammamet are closer to the haplotypes from the south of Tunisia, with a divergence ranging from 2.1% to 2.7% between the northern and eastern Tunisian haplotypes. The possible impact of the Siculo-Tunisian Strait on the phylogeography of O. stentina is discussed.  相似文献   

7.
Molecular data have shown that jellyfishes are more geographically restricted and evolutionarily divergent than previously thought. We examined genetic variation and divergence within the meroplanktonic barrel jellyfish Rhizostoma pulmo in the Mediterranean Sea; specific sampling areas were the northern Adriatic, western Mediterranean and Tunisian coast. A total of 19 sampling sites and 68 sequences of the mtDNA cytochrome c oxidase subunit I (COI) gene were used. Of the 68 COI sequences, 45 were newly collected specimens which originated from nine sampling sites along the Tunisian coast. A total of 24 haplotypes were obtained and the specimens sampled were characterised by relatively high levels of haplotype diversity (h = 0.866) and low levels of nucleotide diversity (π = 0.004). Haplotype network analysis showed the presence of three distinct phylogenetic lineages (populations), with separate geographic ranges in the northern Adriatic, western Mediterranean and Tunisian coast. The observed genetic differentiation between these three lineages was supported by the presence of significant genetic differentiation between the 19 populations (FST = 0.757, p < 0.001). The high level of genetic differentiation detected in the barrel jellyfish investigated could be attributed to either intrinsic and/or extrinsic barriers to genetic exchange between different populations that may have adapted to different environmental conditions.  相似文献   

8.
A new population of vestimentiferan tubeworms was discovered during a recent expedition to a mud volcano field in the Alboran Sea, western Mediterranean Sea. Morphological data and mitochondrial cytochrome-c-oxidase subunit 1 (COI) sequences show that the Alboran tubeworm is essentially identical to Lamellibrachia sp. found in the eastern Mediterranean. This is the first record of a vestimentiferan species in the western basin of the Mediterranean, an area with direct connection to the Atlantic via the Strait of Gibraltar and therefore of great importance to the study of distributional patterns and evolution of Mediterranean species. We examine the current hypotheses on the biogeographic distribution of vestimentiferan species in the eastern Atlantic and Mediterranean Sea and conclude that independently of when Lamellibrachia colonized the Mediterranean, neither the present hydrological settings of both Mediterranean Sea and Atlantic Ocean, nor vestimentiferans reproductive biology are impeditive to the presence of the Mediterranean species of Lamellibrachia in the NE Atlantic. The West African and Lusitanian margins are the most likely places to find living populations of this species in the NE Atlantic.  相似文献   

9.
The gizzard shad, Konosirus punctatus, is one of the most important fish species in Korea, China, Japan and Taiwan, and therefore the implementation of an appropriate population structure analysis is both necessary and fitting. In order to clarify the current distribution range for the two lineages of the Korean gizzard shad (Myoung and Kim 2014), we conducted a multivariate morphometric analysis by locality and lineage. We analyzed 17 morphometric and 5 meristic characters of 173 individuals, which were sampled from eight localities in the East Sea, the Yellow Sea and the Korean Strait. Unlike population genetics studies, the canonical discriminant analysis (CDA) results showed that the two morphotypes were clearly segregated by the center value “0” of CAN1, of which morphotype A occurred from the Yellow Sea to the western Korean Strait with negative values, and morphotype B occurred from the East Sea to the eastern Korean Strait with positive values even though there exists an admixture zone in the eastern Korean Strait. Further studies using more sensitive markers such as microsatellite DNA are required in order to define the true relationship between the two lineages.  相似文献   

10.
为比较分析雷州半岛东、西两岸湖栖鳍虾虎鱼(Gobiopterus lacustris)遗传差异,以COI基因和D-loop区部分序列为分子标记,获取雷州半岛湖栖鳍虾虎鱼群体COI序列44条(九龙山群体21条,高桥群体23条)、D-loop序列53条(九龙山群体25条,高桥群体28条)。基于COI基因部分序列分析结果显示:619 bp的44条序列中,统计的变异位点29个;T、C、A、G碱基组成分别为:27.8%、31.0%、23.7%、17.5%,且A+T(51.5%)高于C+G(48.5%);单倍型多样性比较,九龙山群体(0.695)高桥群体(0.324);遗传分化分析表明东、西群体分化显著(Snn=0.0.591,0.01P0.05),基因流(Nm)为5.37,遗传分化系数(Gst)为0.147,固定指数(Fst)为0.042(0.001P0.01),核苷酸差异数(Kxy)为2.547,核苷酸歧义度(Dxy)为0.004。而基于D-loop区部分序列分析结果表明:563 bp的53条序列中,变异位点133个;T、C、A、G碱基组成分别为:32.3%、14.8%、35.5%、17.4%,A+T(67.8%)明显高于C+G(32.2%);单倍型多样性与COI分析结果类似,九龙山群体(0.797)高桥群体(0.661);遗传分化分析表明东、西群体分化极显著(Snn=0.970,P0.001),Fst为0.315(P0.001),Nm值为0.55,Gst、Kxy、Dxy分别为:0.157、3.506、0.006;AMOVA分析揭示群体内变异程度高于群体间;聚类分析表明,基于COI基因与D-loop区部分序列构建的邻位链接法聚类树(NJ树)均存在按照采样点聚类的现象,但D-loop更为明显。综上,雷州半岛东、西两岸湖栖鳍虾虎鱼群体出现较为明显的分化现象。  相似文献   

11.
Three ecological and geographical forms of Luciogobius guttatus from the western and eastern coasts of the Korean Peninsula as well as the coasts of, Jeju Island which is located to the south of the peninsula are described and compared based on morphological characteristics. The environments of these three coastal areas are different, and the morphometrics show a clear pattern of differentiation and reveal the discreteness of the western, eastern and Jeju groups. In addition, a discriminant analysis (DA), a principal component analysis (PCA) of morphometric characteristics, and a t-test for meristic characteristics all show that the three populations of L. guttatus differ from each other. Three divergent lineages of L. guttatus are described with the possibility of niche differentiation between the western, eastern and Jeju coastal habitats. The standard length of eastern populations was greater than that of western and Jeju populations, and those with morphometric characteristics had a longer body. In addition, eastern populations had a higher number of vertebrae. We speculate that the characteristics of eastern populations evolved through the difference in tide level and gravel density, whereas the difference between western and Jeju populations is due to geographical distance.  相似文献   

12.
The invasive green alga Caulerpa racemosa var. cylindracea represents an important threat to the diversity of Mediterranean benthic coastal ecosystems by interfering with native species and modifying benthic assemblages. The present study deals, for the first time, with the temporal and spatial variability of the biomass and phenology of C. racemosa considering both deep- and shallow-water populations. Two sampling depths (30 and 10 m) were sampled at three different rocky bottom sites every 3 months in the Archipelago of Cabrera National Park (Western Mediterranean). All morphometric variables analysed showed a spatial variation and temporal patterns depending on depth. Between depths, C. racemosa biomass, stolon length, number of fronds and frond length were usually significantly higher at deep-water populations, suggesting that C. racemosa grows better in deep-waters. Deep- and shallow-water populations displayed a high temporal variation although no evidence of seasonal patterns was found, in contrast with what has been reported by other authors. The sources of this variability are still unknown but probably both physical factors and differential herbivory pressures display a key role.  相似文献   

13.
Abstract. Nine allozyme and two minisatellite loci were used to investigate potential genetic differentiation among three samples of Mediterranean poor cod, Trisopterus minutus capelanus, from the Gulf of Lion, the Tuscan Archipelago and the Aegean Sea. Both types of markers showed consistent results, with FST values of 0.0262 and 0.0296 (P < 0.0015, after Bonferroni correction for multiple tests) for allozymes and minisatellites, respectively. Allele frequency heterogeneity tests between pairs of samples showed a clear separation between the two western Mediterranean samples (Gulf of Lion, Tuscan Archipelago) and the eastern one (Aegean Sea). The results indicate that at least two reproductively isolated populations of poor cod occur in the Mediterranean.  相似文献   

14.
《Marine Geology》1999,153(1-4):29-39
During Ocean Drilling Program (ODP) Legs 160 and 161, sapropels were recovered both in the western and eastern Mediterranean. This obliges to a reassessment of the previous studies focused on sapropels from only the eastern Mediterranean, and to consider the changes which occurred in the Mediterranean climate but also in the water characteristics both in the Atlantic and in the western Mediterranean. In the North Atlantic, the position of the polar front which migrated southwards during glacial times and the melting of northern ice caps during interglacial periods, together with the convection in the Labrador and Norwegian Seas, appear essential to control the salinities of the waters facing the Strait of Gibraltar. The salinities of the surface and intermediate layers constitute the first driving force of the Mediterranean dynamics, the second driving force being the Mediterranean climate. The stagnation of deep waters leading to sapropel deposition in the western Mediterranean may be explained by a drastic weakening of the density difference between Mediterranean outflow and Atlantic intermediate waters facing the Strait of Gibraltar. This weakening was induced primarily by the salinity decrease of Atlantic surface water and secondly by a rather high salinity in the Atlantic intermediate layer, rather than by a drastic deterioration of the Mediterranean climate. This scenario probably concerns most of the sapropel events and it may be used for the knowledge of Atlantic and Mediterranean functioning over climatic changes.  相似文献   

15.
The deep-sea habitat, from 200 to 2000 m depth, has long been thought as an ecosystem where biotic and abiotic factors vary very little and consequently species are not disturbed by processes and phenomena which could promote fast evolutionary mechanisms. Unfortunately, biological information relating to deep water is limited, especially regarding the population genetics of species inhabiting the Mediterranean Sea, and general patterns cannot be inferred. In this study we report data on the population genetic structure of Aristeus antennatus , a deep-sea decapod crustacean species which has been widely studied due to its important economic value. We surveyed and examined the variation in a 369-bp fragment of the mtDNA control region from individuals caught by Spanish and Italian trawlers in eight localities. High levels of mitochondrial control region haplotypic diversity (ranging from 0.884 to 0.989) were observed. AMOVA showed a high level of genetic variation, more within than between populations, and a low but significant ΦST value was recovered. Minimum spanning network did not separate any haplotype group and haplotype distribution does not mirror the geographic origin of the samples. The absence of population substructuring was also observed with a principal coordinates analysis, which uses an individual-by-individual comparison. These results revealed extensive gene flow among populations. Information on demographic history based on mismatch analysis revealed an unstable population, showing an alternate pattern of growth and decline. Our results indicated that in the western and central Mediterranean basins A. antennatus is a large panmictic population with a fluctuating abundance. The absence of deep-sea barriers and adult migration may prevent the structuring of the species into genetically differentiated populations.  相似文献   

16.
Despite the large body of work published in the last two decades on the reproduction of the sea urchin Paracentrotus lividus, the reproductive aspects linked to hydrodynamic conditions and their influence on gonad production remain poorly understood. The present paper aims to evaluate the effect of hydrodynamism on the reproductive cycle of P. lividus. Variability in the gonadosomatic index (GSI) of P. lividus was estimated seasonally from 2007 to 2008 at two shallow sub-littoral flat basaltic areas at Ustica Island (Western Mediterranean). GSI was higher in the sites characterized by low hydrodynamism than in those with high hydrodynamism. Results also suggest a possible role for hydrodynamism in triggering processes of resource limitation (food shortage), probably by interfering with P. lividus feeding activity.  相似文献   

17.
The sea urchin Paracentrotus lividus is common in the Mediterranean in shallow subtidal rocky habitats and in Posidonia oceanica beds. The aim of this study is to investigate whether protection has the same effect on the population structure of P. lividus occurring in rocky reef habitats and in P. oceanica beds. These results are important to generate hypotheses about the influence of human harvesting, predatory pressure and migration processes on P. lividus in the two habitats.  相似文献   

18.
The variability of the water transport through three major straits of the Mediterranean Sea (Gibraltar, Sicily and Corsica) was investigated using a high-resolution model. This model of the Mediterranean circulation was developed in the context of the Mercator project.The region of interest is the western Mediterranean between the Strait of Gibraltar and the Strait of Sicily. The major water masses and the winter convection in the Gulf of Lions were simulated. The model reproduced the meso-scale and large-scale patterns of the circulation in very good agreement with recent observations. The western and the eastern gyres of the Alboran Sea were observed but high interannual variability was noticed. The Algerian Current splits into several branches at the longitude of the Strait of Sicily level, forming the Tyrrhenian branch, and, the Atlantic Ionian Stream and the Atlantic Tunisian Current in the eastern Mediterranean. The North Current retroflexed north of the Balearic Islands and a dome structure was observed in the Gulf of Lions. The cyclonic barotropic Algerian gyre, which was recently observed during the MATER and ELISA experiment, was evidenced in the simulation.From time-series of 10-day mean transport, the three straits presented a high variability at short time-scales. The transport was generally maximum, in April for the Strait of Gibraltar, in November for the Strait of Sicily, and in January for the Strait of Corsica. The amplitudes of the transport through the Straits of Gibraltar (0.11 Sv) and Sicily (0.30 Sv) presented a weaker seasonal variability than that of the Strait of Corsica (0.70 Sv).The study of the relation between transport and wind forcing showed that the transport through the Strait of Gibraltar is dependent on local zonal wind over short time-scales (70%), which was not the case for the other straits (less than 30%). The maximum (minimum) of the transport occurred for an eastward (westward) wind stress in the strait. An interannual event was noticed in November–December 2001, which corresponded to a very low transport (0.3 Sv), which was characterised by a cyclonic circulation in the western Alboran Sea. That circulation was also reproduced by the model for other periods than winter during the interannual simulation.The transport through the Strait of Sicily is not influenced by local wind.The wind stress curl of the northwestern Mediterranean influenced the transport through the Strait of Corsica.  相似文献   

19.
Abstract. A number of recent field‐based studies have investigated the possible functions of covering behaviour in a range of echinoid species. Some of these have found important relationships between covering behaviour and environmental factors, such as light (in particular, ultra‐violet light) and covering item availability. However, these studies have often shown considerable within‐species variation, thus making covering functionality both within and between species difficult to interpret. The present study experimentally investigates individual variability in covering behaviour characteristics of the sea urchin Paracentrotus lividus (Lamarck). Data were collected bimonthly over a 1‐year period at Lough Hyne, Ireland, by observing P. lividus in outdoor aquaria. Significant variations in covering behaviour characteristics were observed as a function of individual size and mobility but not as a function of sex. A significant relationship between water temperature, mobility and covering behaviour was also found and is hypothesized to have implications for grazing activity in P. lividus. In contrast to previous field studies of P. lividus at Lough Hyne, no summer ‘peak’ in the proportion of individuals covering was observed. However, there was a significant relationship between local solar radiation and ‘time to first cover’. Overall, these data highlight (i) the ecological significance of individual variation in P. lividus covering behaviour and (ii) the importance of investigating multiple factors as potential determinants of echinoid covering behaviour.  相似文献   

20.
Interannual salinity variations in the Tsushima Strait are investigated on the basis of historical hydrographic data. The EOF analysis revealed that the most dominant mode is the in-phase salinity variation between the eastern and western channels. The time coefficients of the EOF first mode in summer show a negative correlation with the Changjiang discharge, which indicates that salinity in the Tsushima Strait tends to decrease over summer, related to a large discharge of the Changjiang. The eigenvectors of the first mode are larger in the eastern channel than those in the western channel, though the low salinity water mainly flows through the western channel. This is because the low salinity water spreads into the eastern channel as well as the western channel over summers with a large discharge of the Changjiang. The out-of-phase salinity variation between the channels is extracted as the EOF second mode; this is the predominant variation in the western channel. The time coefficients of the second mode in summer show no significant correlations to the volume transports through the western channel and the transport differences between channels. A relationship between the EOF second mode and variations in the wind stress over the East China Sea is suggested.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号