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1.
J.E. Cinner 《Ocean & Coastal Management》2009,52(8):411-416
Human migration is a considerable issue for many coastal societies, affecting the ways that people use and manage natural resources. This paper examines reasons for migration in 14 coastal communities in Papua New Guinea (PNG) and compares coastal resource use and socioeconomic conditions between migrants and non-migrants to test the hypothesis that migrants have different levels of coastal resource use than non-migrants. Migrants had lower participation in the fishery, ranked fishing as a less important livelihood strategy, and had lower involvement in village decision-making, but had higher levels of human development. Common property systems such as tenure rights may prevent migrants from accessing marine resources. However, migrants' marginalization in decision-making processes may become increasingly contested where resources are scarce and migrants desire an increasing say in how they are allocated. The current limited use of coastal resources by migrants may be a latent problem that needs to be considered by resource managers, particularly in areas where rapid socioeconomic change is occurring and tenure institutions are fragile. 相似文献
2.
Juvenile migrants of Geotria australis were caught from July to early August 1986 in plankton nets set in the lower Waikato River. Migration occurred only at night and mainly mid‐river at the surface. The mean lengths and weights (± 95%c.i.) were 107.75 ± 3.98 mm and 0.94 ± 0.08 g respectively. 相似文献
3.
We investigated seasonal changes in carbon demand and flux by mesozooplankton communities at subtropical (S1) and subarctic sites (K2) in the western North Pacific Ocean to compare the impact of mesozooplankton communities on the carbon budget in surface and mesopelagic layers. Fecal pellet fluxes were one order higher at K2 than at S1, and seemed to be enhanced by copepod and euphausiid egestion under high chlorophyll a concentrations. The decrease in pellet volume and the lack of any substantial change in shape composition during sink suggest a decline in fecal pellet flux due to coprorhexy and coprophagy. While respiratory and excretory carbon by diel migrants at depth (i.e., active carbon flux) was similar between the two sites, the actively transported carbon exceeded sinking fecal pellets at S1. Mesozooplankton carbon demand in surface and mesopelagic layers was higher at K2 than S1, and an excess of demand to primary production and sinking POC flux was found during some seasons at K2. We propose that this demand was met by supplementary carbon sources such as feeding on protozoans and fecal pellets at the surface and carnivory of migrants at mesopelagic depths. 相似文献
4.
5.
《Marine and Petroleum Geology》1987,4(2):112-118
Water-sensitivity in sandstones is commonly ascribed to mobilization, transport and recapture of clays in downstream pore throats. This is based mainly on knowledge of the clay mineral content and its electrochemistry. This paper describes a method for directly observing water-sensitivity mechanisms under the microscope using pore networks etched in glass, with clays introduced into the networks. This allows direct identification of colloidal and transport factors, which is not possible in sandstone cores. The migration behaviour has been investigated with variations in flow rate, acceleration forces and salinity. Migration was observed to occur in two distinct modes: (1) as flocs, especially in concentrated brines and at high flow rates, (2) as deflocculated individual particles, especially in distilled water. Recapture of clays occurs by the formation of ‘particle briges’. The upstream pressure indicates that particle recapture is related to decreasing permeability. 相似文献
6.
《Marine Policy》2016
Most of the fishers of coastal East Africa particularly among the Bajuni, Kojani, Macua and Vezo ethnic communities have historically practiced migration. This study explores the strategies used by migrant fishers’ of Pemba in the Western Indian Ocean region. By adopting a modified sustainable livelihoods framework (SLF), the study uses in-depth interviews and questionnaires to explore the life histories of the fishers in migrant communities, their motivations to migrate, and their associated socioeconomic and ecological implications. Results point out to a complexity of factors contributing to migration including natural, to economic and social factors. Interaction of such factors is instrumental in shaping fisher migration as an activity into an important livelihood strategy. The study concludes that SLF provides holistic understanding of migration. However the incorporation of the ‘livelihood spaces’ extends this knowledge by integrating the spectrum of spatial aspects. This understanding is critical in the design of policies and interventions necessary to ensure resource sustainability and secure fishers livelihoods. This multi-method approach is critical in empirical study of fisher migration. 相似文献
7.
《African Journal of Marine Science》2013,35(1):395-400
Long-distance migration patterns of deep-water rock lobster Palinurus delagoae were investigated using tagrecapture data obtained over a period of 6 years (1995–2000). Of 7 654 animals tagged, 363 (4.7%) were recovered from South African and seven (0.1%) from Moçambican waters. Lobsters remained at large for up to 3.2 years and migrated distances of up to 495 km. Some 48.3% of juvenile lobsters (carapace length <65 mm) but only 2.1% of larger lobsters migrated further than 20 km. Movements were mostly north-eastwards (91.7% of migrants), for both sexes, and the migration rate of the fastest 5% of migrants was 0.43 km day?1. P. delagoae seems to have evolved long-distance, counter-current migrations as a retention mechanism to maintain its populations off both South Africa and Moçambique. The resource needs to be managed jointly between the two countries. 相似文献
8.
Natural oil and gas seeps on the Black Sea floor 总被引：3，自引：0，他引：3
Migration of hydrocarbons to the seafloor in the Black Sea occurs via direct seepages, mud volcanoes, and development of fluidized sediment flows (e.g., diapers). Gas migration occurs on the shelf, continental slope, and abyssal plain. Gas hydrates are spatially related to gas accumulations and are present in shallow subsurface sediment layers. Their distribution is controlled by the activity of mud volcanoes. In regions of methane seepages, specific biogeochemical processes related to the activity of methane-oxidizing bacteria are evident. This activity results in the formation of diagenetic minerals (carbonates, sulfides, sulfates, phosphates and other minerals). 相似文献
9.
A case study: imaging OBS multiples of South China Sea 总被引：3，自引：0，他引：3
The subseafloor structure offshore South China Sea was imaged using first-order water-layer multiples from ocean-bottom seismometer
data and the results were compared to conventional imaging using primary reflections. The mirror-imaging method employs a
primaries-only reverse time pre-stack depth migration algorithm to image the receiver ghosts. The additional travel path of
the multiples through the water layer is accounted for by a simple manipulation of the velocity model and processing datum:
the receivers lie not on the sea floor but on a sea surface twice as high as the true water column. Migration results show
that the multiple-migrated image provides a much broader illumination of the subsurface than the conventional image using
the primaries, especially for the very shallow reflections. The resulting image from mirror imaging has illumination comparable
to the vertical incidence surface streamer (single-channel) reflection data. 相似文献
10.
Sediment-level oscillations with heights of about 6 cm and shore-normal lengths of order 10 m have been measured in the swash zone of a high-energy, coarse-sand beach. Crests of oscillations were shore parallel and continuous alongshore. The oscillations were of such low steepness (height-to-length ratio approximately 0.006) that they were difficult to detect visually. The period of oscillation ranged between 6 and 15 min and decreased landward across the swash zone. The sediment-level oscillations were progressive landward with an average migration rate in the middle to upper swash zone of 0.8 m min−1. Migration was caused mostly by erosion on the seaward flank of the crest of an oscillation during a period of net seaward sediment transport. Thus, the observed migration was a form migration landward rather than a migration involving net landward sediment transport. The observed sediment-level oscillations were different than sand waves or other swash-zone bedforms previously described. 相似文献
11.
中尺度涡旋的运动整体可分为两部分：平移及转动。平移指涡旋在整个生命周期内的水平移动,而转动除了包括内转 （海表地转流引起的涡旋自身水体转动） 外,还包括形转 （涡旋实际边界最佳拟合椭圆的转动）。本文基于 1993—2018 年共计 26 年间的卫星高度计涡旋识别与追踪数据,首次对南海中尺度涡旋的完整运动形式,即形转、内转、平移展开了系统的研究。其中,对内转及平移的分析,可通过涡旋的识别追踪数据集直接进行;为研究涡旋形转,提出了一种基于涡旋识别追踪数据自动提取涡旋形转信息的算法,以此得到涡旋形转方向、每天形转的角度以及形转圈数等信息,获得涡旋形转数据集。通过对涡旋识别追踪数据以及形转数据集的统计分析发现：南海涡旋的平移方向多为西向,且其速率呈偏态分布,主要以南海南部偏高。同样,涡旋的内转速率也呈偏态分布,高速率内转的涡旋主要分布在吕宋海峡附近。涡旋的形转主要以南海南部速率偏高,且与涡旋的寿命及长轴有一定的关系,倾向于随着涡旋寿命的增长、涡旋长轴的增大而变慢。同时南海涡旋的这三种不同运动形式之间也存在一定的相关性。 相似文献
12.
胶州湾湾口海底沙波地形地貌特征及其活动性研究 总被引：2，自引：0，他引：2
利用多波束、侧扫声纳以及单道地震资料对胶州湾湾口潮流作用下形成的典型海底沙波地貌的平面形态、剖面特征和分布特点进行了分析研究。根据实测的水文资料计算了不同潮流流速下沙波的瞬时移动速度,推测了直脊型沙波和新月型沙波的形成]化过程:区内新月型沙波在西向优势流的作用下大约以50m/a的速度向西迁移,直脊型沙波则在两端方向不一致的优势流长期作用下,发生逆时针旋转,同时在往复流的作用下以一个平衡位置左右摆动;就地貌形态而言,新月型沙波是不稳定的,直脊型沙波达到相对平衡状态。 相似文献
13.
Wu Qu Michael Vicent Shija Jie Wu Min Jin Jianxin Wang Runying Zeng Zhuhua Chan 《海洋学报(英文版)》2022,41(8):120-128
The prokaryotic microbial communities in the sediments play crucial roles in the ecological functions of mangrove ecosystems. Therefore, the environmental factors that affect the structures of these prokaryotic microbial communities could indirectly participate in the regulation of mangrove functions, which is of great value for mangrove studies. The particle size (PS) of soils is recently demonstrated as a key environmental factor for shaping the microbial communities; however, this hypothesis has rarely been tested for mangrove environments. A case study of three tropical mangroves from Sanya, China was performed in this work to assess the influence of PS on the prokaryotic microbial community structures of bacteria, archaea, diazotrophs, and denitrifiers in the sediments. Results showed the variability in the spatial scale and the stability in the temporal scale for the prokaryotic communities, indicating that the tropical mangrove sediments could be a versatile but stable environment. Among the collected environmental factors, PS, salinity, and humidity had the greatest impacts, and PS mostly affected the structures of these prokaryotic communities based on its highest R2 values of canonical correspondence analysis, Mental test, and linear fitting (p≤0.05). Furthermore, PS was positively correlated with the diversity and abundance of diazotrophic communities and negatively correlated with the abundances of methanogenic communities including Methanobacteriaceae, Methanospirillaceae, Methanoregulaceae, and Methanosaetaceae. Former studies show the increasing trend of PS caused by the rise of sea level and the intensification of human activities. Therefore, our findings indicate that PS could be a potential intermediate that links climate change and human activities with the possible ecological function migration of mangroves; meanwhile, the increase of PS could in turn release the stress of these environmental changes by increasing the abundance and diversity of the diazotrophic community and decreasing the abundances of methanogens. 相似文献
14.
Fish communities in New Zealand rivers and their relationship to environmental variables 总被引：1，自引：1，他引：0
Fish abundance data from selected electric‐fishing records in the New Zealand Freshwater Fish Database (NZFFD) were used to identify riverine fish communities and to examine their relationship to environmental variables included in the NZFFD. Only 21 fish species, 18 native species, and three introduced salmonids, were present at 1% or more of the sites. We defined 12 fish communities characterised by a dominant species: two salmonid communities, two non‐diadromous native communities, and eight communities characterised by diadromous native species. Altitude and distance inland were the two most significant variables, reflecting differences between communities dominated by diadromous and non‐diadromous species. The next most important variables were related to the geographic location of the site. Other environmental variables that were highly correlated with the fish community assignments were stream width and percentage of native forest or farming land use in the catchment upstream of the site. Of the local habitat variables, percentage of cascade habitat and percentage of sand substrate were the most important discriminators between communities. Despite having only a limited set of broad‐scale environmental variables, we achieved 47% success in the prediction of community membership using multiple discriminant analysis, with another 21% of sites being near misses. A greater knowledge of barriers to migration of diadromous species and fine‐scale variables describing in‐stream habitat would probably increase the predictive ability of the model, although collection of such data is time consuming and therefore impractical on a national scale. 相似文献
15.
N. Simboura A. Zenetos M. Thessalou-Legaki M.-A. Pancucci A. Nicolaidou 《Marine Ecology》1995,16(4):283-306
Abstract. The infralittoral benthos was studied on three islands of the Northern Sporades in the Aegean Sea. Thirteen stations were sampled on both hard and soft substrata and 408 taxa were identified, some of zoogeographical interest. Multivariate statistical methods such as classification, ordination and Similarilies Terms Analysis were combined with existing ecological information to delineate the various communities present and to point to the indicator species characterising them. The communities were then defined using the indicator species and their affinities to typical biocoenoses. The main factor responsible for the observed distribution proved to be the type of substratum (algal cover or sediment type), which reflects the light and hydrodynamic conditions. The observed bathynietric zonation was similar lo that of the Balearic Islands in the western Mediterranean. 相似文献
16.
James J. Bell 《Marine Ecology》2002,23(4):297-311
Abstract. The sponge communities inhabiting a temperate semi-submerged sea cave were investigated at Lough Hyne Marine Nature Reserve, Co. Cork, Ireland. Thirty-one species of sponge were reported, the majority of which exhibited either an encrusting or massive morphology. Sponge density (averaged over depth) increased with horizontal distance (5 m intervals) into the cave until approximately 30 m, corresponding to the maximum algal intrusion (algal information from Norton et al. , 1971) . Species diversity and richness (averaged over depth) were highest at 10 m horizontal distance from the cave entrance. Variability in sponge density, diversity and richness was observed with increasing vertical depth (0.5 m intervals) at most horizontal intervals sampled (5 m apart). These three variables increased initially with depth, but then decreased towards the seabed. Bray-Curtis Similarity Analysis and Multi-Dimensional Scaling (MDS) showed cave sponge community composition to have greater similarity (50 %) with local loose rock habitats than the nearby cliffs. Similar processes structuring cave and loose rock sponge communities may account for this situation. Information collected from this and previous studies on the biotic (algal communities, other fauna and competition) and abiotic factors (water flow rate, depth, aerial exposure, light, cave morphology, nutrient depletion and humidity) affecting this and other caves is discussed with respect to its influence on the sponges inhabiting different parts of the cave. Although horizontal zonation patterns have been considered analogous to vertical distribution patterns for algal communities (due to similar decreases in light), this was not the case for the studied sponge communities. 相似文献
17.
While natural marine habitats with motion capabilities, e.g., kelps and seaweeds, have been studied alongside their associated fouling communities, little is known of the effect of motion on the communities of floating artificial habitats such as buoys, rafts, and pontoons, particularly in tropical systems. Hydrodynamic features greatly differ between floating and fixed artificial substrata, which in turn affect the structure of their associated communities. This study tested the hypothesis that floating and fixed artificial installations in a tropical reef system (Eilat, Red Sea) would support different benthic communities throughout space and time. Specifically, we examined differences in communities recruited onto settlement plates between floating and fixed installations deployed at three different sites, along a two-year monitoring period. The three sites exhibited distinct differences in species assemblages between the monitoring dates (6, 12, 18 and 24 months post deployment), mainly between the first and the last two dates. The average level of dissimilarity between floating and fixed installations increased over time at all sites. Over 50% of the dissimilarity between the floating and fixed installations resulted from five taxonomic groups i.e., bryozoans, bivalves, barnacles, sponges, including the amount of bare space on the settlement plates. The contribution of these groups to the dissimilarity changed both temporally within each site, and spatially among sites. The observed differences were related to the hydrodynamic characteristics of floating and fixed habitats, interacting with biotic features such as predation, successional processes and seasonality; and abiotic features including small-scale spatial changes, light, and position in the water column. 相似文献
18.
Coastal areas, and their small-scale fisheries, are important targets for both internal and transboundary migration partly because high mobility is an inherent feature of many artisanal fisheries livelihoods. As climatic changes are forecast to occur, environmental changes may trigger increased flows of migrant fishers. Policies that seek to promote development in ways that do not extensively degrade natural resources will thus have to deal with likely increases in flows of people across administrative boundaries. However, to date little attention has been directed at this issue and little is known about how policies related to coastal resources and development address these issues. This paper addresses this knowledge gap by analyzing policies and legal documents related to coastal resource management and development to examine the extent to which they recognize and integrate fishers' migration in their provisions. Migrant well-being and vulnerabilities are also addressed by examining the extent to which existing policies dealing with socio-economic development and environmental management address migrants and their needs. The analysis shows that policies related to governance of marine resources and coastal development lack an acknowledgment of fishers' migration issues and suggests that this signals an important gap in policy. The implications of this are discussed. The paper also highlights the fact that the invisibility of the issue in policy means that institutions developed to deal with coastal management at the community level may not have sufficient support from legal and policy documents, and may not be developed or equipped to handle the possible conflicts and difficult trade-offs that need to be addressed as a result of current and potentially increasing fishers’ mobility. 相似文献
19.
The U.S. Geological Survey deep crustal studies reflection profile across the Gulf of Maine off southeastern New England was affected by three sources of noise: side-scattered noise, multiples, and 20-Hz whale sounds. The special processing most effective in minimizing this noise consisted of a combination of frequency-wavenumber (F-K) filtering, predictive deconvolution, and spectral whitening, each applied in the shot domain (prestack). Application of the F-K filter to remove side-scatter noise in the poststack domain resulted in a much poorer quality profile. The prestack noise suppression processing techniques resulted in a reflection profile with good signal-to-noise ratios and reliable strong reflections, especially at depths equivalent to the lower crust (24–34 km). Certain geologic features, such as a buried rift basin and a crustal fault are resolved much better within the upper crust after this processing. Finite difference migration of these data using realistic velocities produced excellent results. Migration was essential to distinguish between abundant dipping and subhorizontal reflections in the lower crust as well as to show an essentially transparent upper mantle. 相似文献
20.
马来盆地前I群(即J、K、L、M群,渐新统—下中新统)具有良好的油气成藏条件:①发育多期有利于成藏的构造运动:前中新世伸展断裂阶段,湖相烃源岩大量发育;早、中中新世构造沉降阶段,并伴随盆地反转,形成前I群油气系统的储盖系统;②烃源岩优越:烃源岩为湖相富含藻类的页岩,成熟度较高,有机质含量较高;③储集层丰富:K群储集层为辫状河砂岩,J群储集层为河口湾河道砂岩和潮间砂岩;④盖层良好:主要盖层为盆地海侵期沉积的前J群三角洲—浅海相泥岩,次要盖层为K、L和M群内的湖泊相泥岩;⑤油气运移通道畅通:上倾侧向运移为主;⑥有利的生储盖组合:自生自储和下生上储的组合方式有利于油气藏的形成。前I群油气系统位于马来盆地的东南部,以生油为主。分析认为盆地的油气分布主要受烃源岩的分布、质量和成熟度以及构造圈闭形成的相对时间和油气运移方式的控制。 相似文献