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 187 毫秒
1.
The present work analysed the main changes in subtidal algal assemblages in the last decade in an oceanic archipelago (Canary Islands – eastern Atlantic Ocean). Changes result from increases in cover of ephemeral benthic algae, such as the non-native chlorophyte Pseudotetraspora marina and the native cyanophytes Blennothrix lyngbyacea, Schizothrix calcicola and Schizothrix mexicana. Ephemeral algae overgrow subtidal assemblages which are extensively dominated by Lobophora variegata, but competitively do not exclude other species. Increases in the abundance of species coincided with a warming of about 2 °C in surface seawater temperature (SST) linked to the weakening of the Cold Canary Current and the Northwestern African upwelling. Shifts in the distribution and cover of ephemeral species follow the SST gradient from warmer waters in the western islands to colder waters in the eastern ones. While in the warmest western islands, species have spread quickly colonizing all type of substrates in just a few years (2005–2008), the occurrence of ephemerals towards the coldest eastern islands is yet inconspicuous.  相似文献   

2.
A study of the mesoscale distribution of phytoplankton communities observed along the Portuguese upwelling coast in 1985–1986 made it possible to identify an assemblage composed by the coccolithophores Helicosphaera carteri, Syracosphaera pulchra and Coronosphaera mediterranea. The assemblage was consistently present in the coast in the following years (1991, 1992, 1994, 2003 and 2005) and from 1992 onwards, Rhabdosphaera clavigera was recognised as being part of it, although in low concentrations During late summer, this group of species showed higher affinities with upwelling waters of subtropical origin (ENACWst) on the SW coast. At the end of the upwelling season, in autumn, the assemblage was advected to the NW shelf due to the intensification of the poleward surface circulation or meridional seasonal changes of environmental conditions. The species maximum abundances were not coincident in space: H. carteri developed at the central part of the western coast while blooms of S. pulchra and C. mediterranea generally occurred further south, such as at the upwelling centre of cape S. Vicente. Syracosphaera pulchra blooms were characterised by lower concentrations of C. mediterranea and vice-versa. The above patterns were recurrent along the years but the relative abundance of each species appeared related to the interannual variability of physical conditions as the upwelling.  相似文献   

3.
The larvae of two carangid fishes, silver trevally (Pseudocaranx dentex) and yellowtail scad (Trachurus novaezelandiae), were compared among coastal water masses and the East Australian Current (EAC). Samples followed a north to south gradient including a southern region of upwelling, generated as the EAC separated from the coast. Mean larval carangid densities were greater in the mixed layer (10-30 m) than the surface, but there was no difference between inshore and offshore stations or along latitudinal gradients. Overall, P. dentex recent larval growth over two days pre-capture was faster than T. novaezelandiae, and faster at inshore, coastal stations than in the EAC. Integrated larval growth rate (mm d−1) was usually faster at inshore stations for both species. T. novaezelandiae were enriched in both nitrogen (??15N) and carbon (??13C) stable isotopes relative to P. dentex. Larvae of both species captured within the upwelling region were enriched in ??15N and depleted in ??13C relative to other sites. Recent larval growth had a significant positive relationship with fluorescence (as a proxy of chlorophyll a biomass), and integrated larval growth rate had a significant positive relationship with fluorescence and larval isotope (??15N) composition. Recent and integrated growth of larval T. novaezelandiae and P. dentex was enhanced by EAC separation and upwelling, and also in coastal water; stimulated by food availability, and potentially through exploitation of a different trophic niche.  相似文献   

4.
基于个体模型的东海鲐鱼渔场形成机制研究   总被引：4，自引：2，他引：2  
鲐鱼Scomber japonicus资源丰富,在我国近海渔业中占有重要地位。其渔场的形成受海洋环境的制约,本文确定鲐鱼运动和物理环境之间的响应关系,建立起了基于个体的东海鲐鱼生长洄游模型。结果显示,鲐鱼集群分布与捕捞生产渔场基本吻合,鲐鱼聚集主要受台湾暖流、大陆沿岸水、黑潮影响,往往集群在一定温度范围内并在冷暖交汇区温盐梯度大偏暖水一侧。在台湾暖流和沿岸水交汇的锋面附近、台湾暖流暖水舌前端、黑潮与中国大陆沿岸水形成的潮境区域均有大量的鲐鱼聚集,并形成渔场。产卵位置的变动使偏西产卵位置的鲐鱼由于受台湾暖流影响较大,鲐鱼会呈长带状大量聚集在台湾暖流和沿岸水的锋面附近,并使在台湾暖流暖水舌前端的聚集数量增多,而偏东的产卵的鲐鱼受黑潮影响较大,聚集分布范围较大,会使黑潮形成的锋面附近聚集数量增多,而使台湾暖水舌的前端的聚集量减少。正常产卵位置在生存率方面是最佳产卵位置。研究表明鲐鱼所处空间位置不同,会影响其集群的位置,用数值模型验证了物理环境会对鲐鱼的洄游和渔场的形成产生影响。  相似文献   

5.
At regional scales, the distribution of species and the structure of assemblages vary with latitude within many marine and terrestrial systems. The oligotrophic coastal waters of Western Australia (WA) support highly speciose and endemic assemblages, yet spatial patterns in benthic structure are currently poorly known. We examined benthic assemblage composition along a latitudinal gradient of 28.5–33.5°S and a depth gradient of 14–62 m, on subtidal reefs in warm-temperate WA. We surveyed benthos using a remotely triggered digital stills camera. In total, we sampled macroalgae and sessile invertebrates at 201 sites spread across four locations. Percent cover of coarse taxonomic groups and dominant species was estimated from over 2000 photoquadrat samples. We recorded significant differences in benthic assemblage composition between locations, and along depth gradients within each location. However, the magnitude of change with depth was not consistent between locations, and shifts in assemblage composition along the depth gradients were not as pronounced as expected. The percent cover of all dominant benthic groupings differed between locations, and several key taxa, such as the kelp Scytothalia dorycarpa, brown foliose macroalgae, hard corals and sponges, changed predictably along the latitudinal gradient. Our study adopted a coarse taxonomic, but assemblage-wide, approach to describing macrobenthic assemblages, and clear differences between locations and depths were detected. The surveys have provided baseline data on broad scale ecosystem structure against which to detect future ecological change.  相似文献   

6.
南海东北部春季海表pCO_2分布及海-气CO_2通量   总被引：1，自引：1，他引：0  
2013年南海东北部春季共享航次采用走航观测方式,现场测定了表层海水和大气的二氧化碳分压(pCO2)及相应参数。结合水文、化学等同步观测要素资料,对该海域pCO2的分布变化进行了探讨。结果表明,陆架区受珠江冲淡水、沿岸上升流及生物活动的影响,呈现CO2的强汇特征;吕宋海峡附近及吕宋岛西北附近海域受海表高温、黑潮分支"西伸"、吕宋岛西北海域上升流等因素影响,呈现强源特征。根据Wanninkhof的通量模式,春季整个南海东北部海域共向大气释放约4.25×104 t碳。  相似文献   

7.
Mesoscale oceanographic features, such as upwellings, are known to play an important role in regulating the structure and productivity of nearshore marine communities. Stable isotope (δ13C and δ15N) and fatty acid analyses were employed to assess the influence of an upwelling cell along the south-eastern coastline of southern Africa on the diet of the mussel, Perna perna. Eight sites were sampled: two upstream, three in the vicinity and three downstream of the upwelling cell. Stable isotope and fatty acid signatures indicated that the mussels consumed a diet of detritus derived mainly from macroalgae, diatoms and dinoflagellates. One-way ANOVA on the δ13C and δ15N signatures and the principal component analysis of the fatty acid profiles of the mussels identified distinct groups corresponding to the above mentioned regions. The proportion of diatom biomarkers in the fatty acid profiles decreased downstream of the upwelling region while the proportion of dinoflagellate biomarkers increased. Upwelling regions are typically associated with elevated levels of productivity; however, these systems usually become silicon depleted and result in the replacement of diatoms with dinoflagellates. The highest proportions of the dinoflagellate markers were recorded in the two furthest sites downstream of the upwelling cell. The spatial variation in the diet of the mussels, therefore, appears to reflect the presence of the upwelling cell in the nearshore biology of the region.  相似文献   

8.
The demand for sensitive biological tools to assess the environmental quality of coastal waters at broad spatial scales is increasing. Many of the tools used are based on the taxonomic composition of biotic assemblages. They usually require a valuable taxonomic expertise while are unique reflecting the overall ecosystem integrity. Here, we evaluate the potential indicator value of several features of the epiphytic community (overall assemblage composition, species richness, and proportion of the main taxonomic groups) growing on the seagrass Posidonia oceanica leaves. We do so by empirically examining their changes along a disturbance gradient where multiple human activities have interactive and cumulative impacts, sampling at different spatial scales and at two different depths (5 and 15 m). Our results show that the specific composition of the epiphytic assemblages (i.e. species composition) closely reflects, in the deep meadows, the combined effects of different anthropogenic stressors along the gradient, showing an integrative and non-specific response. Similarly, an increase in the proportion of hydrozoans, and a decrease in the proportion of rhodophytes and chlorophytes are observed in deep meadows along the gradient. In shallow meadows, grazing and biotic features of the seagrass seem the main forcing factors determining species composition, and therefore masking the response of epiphytes to the deterioration gradient. After address the effect of natural sources of variability (water depth, within- and between-meadow heterogeneity), changes in epiphyte assemblages and in the proportion of hydrozoans, rhodophytes and chlorophytes in relatively deep meadows seem promising monitoring tools for detecting coastal environmental deterioration.  相似文献   

9.
The potential role of generalist herbivores to serve as a source of biotic resistance against algal invasion in marine ecosystems has been poorly examined. The present study investigates the capacity of Mediterranean herbivorous fishes to consume three of the most invasive seaweeds of the Western Mediterranean (Caulerpa racemosa, Lophocladia lallemandii and Womersleyella setacea) and examines vertical and temporal variations of such consumption. Our results show that although fish feed throughout the depth gradient examined (5–35 m), they concentrate in shallow waters, and can consume high amounts of C. racemosa. Such high ingestion of C. racemosa does not appear to be random, since this alga is consistently chosen when offered in pairs with several native species. Conversely, L. lallemandii and W. setacea are barely eaten by fish even though they can be very abundant in the field throughout the year. Our results suggest that fish could be an important controlling agent that has been overlooked in temperate marine invasions, and they may be able to provide certain resistance to C. racemosa invasion. In contrast, they are unlikely to exert any important control effects on L. lallemandii or W. setacea.  相似文献   

10.
Macrofaunal assemblages inhabiting the intertidal zone surrounding an input of secondary treated effluent were sampled in order to determine how the pollution impact varied temporally and spatially. Assemblages varied along the pollution gradient formed by the Bolivar Wastewater Treatment Plant outfall in Gulf St Vincent, South Australia. While the abundance of some species did not vary, the abundance of juvenile western king prawns (Melicertus latisulcatus) and blue crabs (Portunus pelagicus) progressively decreased with proximity to the outfall. Species richness and diversity also decreased towards the outfall. An increase in nutrient content in the water adjacent to the outfall is likely to explain these changes. At distances of 4 and 5 km away, species diversity increased and the abundance of M. latisulcatus decreased, possibly due to a change in habitat from sand to seagrass. The occurrence of a storm prior to sampling on one occasion masked the effects of pollution and habitat changes. The results of this study suggest that the disposal of treated effluent into Gulf St Vincent is having a localised effect on the faunal assemblages surrounding the discharge point.  相似文献   

11.
Spatial size variations of labial palps, gills and the adductor muscle of the invasive feral oyster, Crassostrea gigas, were studied along two gradients of suspended particulate matter (SPM) concentrations in the temperate macrotidal Bourgneuf Bay, (annual mean SPM concentration gradient of 21.0–154.0 mg l−1) and the adjacent Loire Estuary (annual mean SPM concentration gradient of 24.1–630.4 mg l−1) on the French Atlantic Coast. The gill-to-palp (G:P) ratios decreased with increasing turbidity, both in the bay and the estuary. Changes in G:P ratios were chiefly related to palp area variations, increasing gradually from low turbidity to very high-turbidity sites, while gill area showed no clear relationship with turbidity conditions. The G:P ratio, showing a significant relationship (r2 = 0.97) with SPM concentrations, is proposed as a pallial organ index of oyster acclimation to turbidity conditions. The area of the striated part of the adductor muscle was always greater than that of the smooth one, and adductor muscle area tended to decrease when SPM concentration increased. These observations show the morphological capacity of the oyster C. gigas to tolerate SPM concentrations above the feeding cessation thresholds previously determined experimentally. They also suggest that pallial organ size variations could help explain the success of recent feral oyster invasions in temperate turbid ecosystems.  相似文献   

12.
Considerable evidence exists, showing an accelerated warming trend on earth during the past 40–50 years, attributed mainly to anthropogenic factors. Much of this excess heat is stored in the world's oceans, likely resulting in increased environmental variability felt by marine ecosystems. The long-term effects of this phenomenon on oceanic tropical ecosystems are largely unknown, and our understanding of its effects could be facilitated by long-term studies of how species compositions change with time. Ichthyoplankton, in particular, can integrate physical, environmental and ecological factors making them excellent model taxa to address this question. While on eight (1987–1990, 1992 and 1998–2000) NOAA Fisheries cruises to the eastern Pacific warm pool, we characterized the thermal and phytoplankton pigment structure of the water column, as well as the neustonic ichthyoplankton community using CTD casts and Manta (surface) net tows. Over the 13-year period, 852 CTD and Manta tow stations were completed. We divided the study area into three regions based on regional oceanography, thermocline depth and productivity, as well as a longitudinal gradient in species composition among stations. We then analyzed temporal trends of ichthyoplankton species composition within each region by pooling stations by region and year and making pairwise comparisons of community similarity between all combinations of the eight cruises within each region. We also identified environment-specific species assemblages and station groupings using hierarchical clustering and non-metric multi-dimensional scaling (MDS). Our analyses revealed a longitudinal gradient in community structure and temporal stability of ichthyoplankton species composition. Over the 13 years ichthyoplankton assemblages in the two westernmost regions varied less than in the eastern region. MDS and cluster analyses identified five ichthyoplankton assemblages that corresponded to oceanographic habitats and a gradient in community composition. We hypothesize that the changes in thermocline depth during the El Niños of 1987–1988, 1997–1998 and the extended period of warmth during 1990–1994 altered productivity sufficiently to cause a shift in the abundances of foundation species of the upwelling systems of the eastern Pacific warm pool. Our study suggests that ichthyoplankton assemblages in oligotrophic waters are more resilient to changes in the thermocline than assemblages in upwelling regions; or that oligotrophic regions simply have less physical variation compared to upwelling regions.  相似文献   

13.
Previous research has suggested that competitive bottlenecks may exist for the Mediterranean grey mullets (Osteichthyes, Mugilidae) at the fry stage with the exotic Cyprinus carpio (Osteichthyes, Cyprinidae) playing a central role. As a consequence, the structure of grey mullet assemblages at later stages is thought to reflect previous competition as well as differences in osmoregulatory skills. This paper tests that hypothesis by examining four predictions about the relative abundance of five grey mullet species in 42 Western Mediterranean estuary sites from three areas (Aiguamolls de l'Empordà, Ebro Delta and Minorca) differing in the salinity level and occurrence of C. carpio. Field data confirmed the predictions as: (1) Liza aurata and Mugil cephalus were scarce everywhere and never dominated the assemblage; (2) Liza saliens dominated the assemblage where the salinity level was higher than 13; (3) Liza ramado always dominated the assemblage where the salinity level was lower than 13 and C. carpio was present; and (4) Chelon labrosus dominated the assemblage only where the salinity level was lower than 13 and C. carpio was absent. The catch per unit effort of C. labrosus of any size was smaller in the presence of C. carpio than where it had not been introduced, which is in agreement with the juvenile competitive bottleneck hypothesis. Discriminant analysis confirmed that the assemblage structure was linked to the salinity level and the occurrence of C. carpio for both early juveniles and late juveniles as well as adults. The data reported here reveal that the structure of grey mullet assemblages inhabiting Mediterranean estuaries is determined by salinity and competitive interactions at the fry stage.  相似文献   

14.
The seasonal trait of Nitzschia population was studied between May 2004 and February 2005 in Zhelin Bay. Twenty-five Nitzschia taxa were identified from samples. Among them, Nitzschia delicatissima, Nitzschia hybrida, Nitzschia longissima, Nitzschia panduriformis, Nitzschia paradoxa and Nitzschia pungens appeared all year round. The average population density of Nitzschia was 20.29 × 103 cells/dm3, contributing 16.59% to total phytoplankton. Comparing with other regions, Nitzschia population of Zhelin Bay have high species richness and intermediate population density. Nitzschia species richness of May and August was apparently lower than that of November and February, and this may be caused by water temperature and interspecific competition; Nitzschia population density was high in warm seasons (May and August) and low in cold seasons (November and February), and this may be caused by water temperature and zooplankton community structure; and underwater light intensity was important factor influencing spatial distribution of Nitzschia density.  相似文献   

15.
The spread of the invasive alga Caulerpa racemosa var. cylindracea in shallow-water habitats can present different faunal assemblage composition. We compared the amphipod assemblages associated with C. racemosa and natural habitats found on shallow-water Mediterranean soft substrata. Four vegetated habitats were compared: C. racemosa, Caulerpa prolifera, Cymodocea nodosa and Posidonia oceanica with unvegetated substrata. Samples were collected during two sampling periods (September 2004 and March 2005). A total of 63 amphipod species were recorded. The results showed that the vegetated habitats sampled, including C. racemosa stands, supported a higher abundance and species richness of amphipods. Furthermore, the assemblage structure differed between the different habitats, while the abundance of some species was significantly different, depending on habitat. For example, Microdeutopus obtusatus was favoured by C. racemosa habitat; Ampelisca diadema was associated with C. prolifera beds; and Hyale schmidti was more abundant in P. oceanica meadows. Habitat invasion by C. racemosa can exert an important influence on biotic assemblages, modifying habitat structure and associated fauna.  相似文献   

16.
In October 2005 spatial distribution of live and dead Acartia clausi and Acartia tonsa was studied in the Black and Marmara Seas and near the Marmara Sea inlet of the Bosphorus, in order to understand their fate upon transportation between two seas. The morphometric characteristics in both species from all studied areas, and the decreased abundance of A. clausi and A. tonsa from the Black Sea towards the Marmara Sea indicate that the Marmara Sea Acartia populations are formed by recruitment from the Black Sea. We observed mass mortality of A. clausi in the Marmara Sea near the Prince Islands. The majority of carcasses (66% of total A. clausi numbers in the Marmara Sea) were found in the salinity gradient layer.  相似文献   

17.
Long-term interannual changes in abundance, biomass, diversity and structure of littoral fish assemblages were examined between 1993 and 2009 by experimental trammel net fishing up to six times per year, within the warm period - May to September, at multiple areas along the eastern Adriatic coast with the aim of testing for the consistency of patterns of change across a large spatial scale (∼600 km). The results revealed spatially consistent increasing trends of total fish abundance and biomass growing at an average rate of 15 and 14% per year, respectively. Of the diversity indices analysed, the same pattern of variability was observed for Shannon diversity, while Pielou evenness and average taxonomic distinctness measures Δ∗ and Δ+ showed spatial variability with no obvious temporal trends. Multivariate fish assemblage structure underwent a directional change displaying a similar pattern through time for all the areas. The structural change in fish assemblages generally involved most of the species present in trammel net catches. A large pool of fish species responsible for producing the temporal pattern of assemblage change was relatively different in each of the areas reflecting a large geographic range covered by the study. An analysis of 4 fish species (Symphodus tinca, Pagellus erythrinus, Mullus surmuletus, Scorpaena porcus) common to each of the study areas as the ones driving the temporal change indicated that there were clear increasing trends of their mean catches across the years at all the study areas. A common pattern among time trajectories across the spatial scale studied implies that the factor affecting the littoral fish assemblages is not localised but regional in nature. As an underlying factor having the potential to induce such widespread and consistent improvements in littoral fish assemblages, a more restrictive artisanal fishery management that has progressively been put in place during the study period, is suggested and discussed.  相似文献   

18.
The decomposition rates of Phragmites australis and Fucus vesiculosus were experimentally determined in an estuarine system using the leaf-bag technique. The study was conducted in fifteen sites arranged in five areas, extending from freshwater, outside the tidal range, to the marine environment, near the mouth of the estuary. The leaf-bags (5 mm mesh), were set up with 3.0 g of dried substrate, submerged in the experimental sites at day 0 and collected at days 3, 7, 15, 30 and 60, to follow biomass loss. The biomass loss through the leaching phase (day 3) was about 16% for Phragmites australis and 33% for Fucus vesiculosus and was independent of salinity for both substrates. The difference in the remaining biomass between the two species increased with time and the decomposition rates differed along the salinity gradient. For F. vesiculosus, the decomposition rate was highest near the mouth of the estuary, corresponding to the preferential distribution area of the algae, and decreased towards freshwater. For Phragmites australis, the fastest decay was observed in the mid estuary, where Phragmites australis occurs naturally, confirming previous studies. The decomposition rates measured at different time intervals (0–15, 0–30 and 0–60 days) were always higher for the algae and decreased with time for both species. These results indicate that the use of decomposition rates as a measure of ecosystem integrity or quality status in transitional waters will not be straightforward and must take into account, among others, the test species, the study area positioning along the estuarine gradient, and the time interval for the calculation of the decomposition rate.  相似文献   

19.
Populations dominated by Cystoseira zosteroides, an endemic and threatened Mediterranean seaweed, colonize deep-water rocky habitats down to more than 50 m depth. Assemblages dominated by this species display high algal and invertebrate species richness. Algal biomass averages 1134 g dw m−2. Erect and turf algae account for only 25% of total algal dry weight, while encrusting corallines are responsible for the remaining 75%. Sponges, bryozoans and ascidians constitute the dominant sessile macrofauna. Cystoseira zosteroides is the dominant erect algae, with a mean biomass of 60.6 g dw m−2, and densities ranging from 4 to 7 plants m−2. The alien turf alga Womersleyella setacea has a biomass of 104.2 g dw m−2 and covers most of the understory substrate. The size-frequency distribution of C. zosteroides populations shows differences over time. Mean annual growth of the main axis is around 0.5 cm and mean annual mortality rate is lower than 2%. Recruitment was almost nil during the studied period of time (10 years). Processes structuring these deep-water Cystoseira stands must be driven by episodic disturbances, after-disturbance recruitment pulses, and long periods of steady growth that last at least 10 years. However, it is also possible that recruitment is irreversibly inhibited by the alien alga W. setacea in which case these old-growth stands are faced with extinction. The highly diversified assemblages and the low growth and low mortality rates of C. zosteroides indicate high vulnerability to natural and anthropogenic disturbances, and call for effective measures to ensure their conservation.  相似文献   

20.
Mysid shrimps are an important component of estuarine food webs because they play a key role in energy transfer as intermediate prey. We investigated the seasonal, tidal and depth specific variation in the diet of the estuarine mysids Neomysis integer and Rhopalophthalmus tartessicus and explored its implications for the planktonic community structure of a temperate estuary (Guadalquivir Estuary, SW Spain). Neomysis integer is an opportunistic omnivore feeding mainly on mesozooplankton and on members of the detrital–microbial loop, shifting prey seasonally according to availability. In contrast, R. tartessicus showed a more carnivorous diet and shifted its target prey during seasons of low resource availability. Despite statistically significant differences in diet composition, both species shared prey of similar size, particularly juvenile Mesopodopsis slabberi, the most abundant mysid species in this estuary, and copepods. Although these similarities imply inter-specific resource competition, their co-existence is achieved by niche partitioning and spatial segregation: the higher osmoregulatory capacity and foraging plasticity of N. integer confers a broader niche breadth for this species allowing N. integer to inhabit the more stressful oligohaline region of the estuary where R. tartessicus cannot survive. We propose that this mechanism relaxes the potential for competition between N. integer and R. tartessicus.  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