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1.
The Humboldt Current System (HCS) is dominated by two pelagic species; Peruvian anchovy or anchoveta (Engraulis ringens) and sardine (Sardinops sagax). Using data from 43 acoustic surveys conducted from 1983 through 2005 by the Peruvian Marine Institute (IMARPE), we examined the distribution of these two species relative to water masses. We tested the hypothesis that anchovy was found more frequently in upwelled cold coastal water (CCW) and mixed waters (MCW) than in other water types and that sardine was more associated with more offshore oceanic surface subtropical water (SSW). Surface temperature, salinity, latitude, season and distance to the coast data were used to define water masses. Results using generalized additive models (GAM), modelling sardine and anchovy presence–absence as a function of year, water body, bottom depth and latitude, showed that anchovy were primarily found in CCW and MCS, while sardine were more ubiquitous relative to water masses with some predilection for SSW. These results were supported by various indexes of anchovy and sardine distribution versus water mass as well as temporal and location variables.  相似文献   

2.
Peruvian anchovy (Engraulis ringens) stock abundance is tightly driven by the high and unpredictable variability of the Humboldt Current Ecosystem. Management of the fishery therefore cannot rely on mid- or long-term management policy alone but needs to be adaptive at relatively short time scales. Regular acoustic surveys are performed on the stock at intervals of 2 to 4 times a year, but there is a need for more time continuous monitoring indicators to ensure that management can respond at suitable time scales. Existing literature suggests that spatially explicit data on the location of fishing activities could be used as a proxy for target stock distribution. Spatially explicit commercial fishing data could therefore guide adaptive management decisions at shorter time scales than is possible through scientific stock surveys. In this study we therefore aim to (1) estimate the position of fishing operations for the entire fleet of Peruvian anchovy purse–seiners using the Peruvian satellite vessel monitoring system (VMS), and (2) quantify the extent to which the distribution of purse–seine sets describes anchovy distribution. To estimate fishing set positions from vessel tracks derived from VMS data we developed a methodology based on artificial neural networks (ANN) trained on a sample of fishing trips with known fishing set positions (exact fishing positions are known for approximately 1.5% of the fleet from an at-sea observer program). The ANN correctly identified 83% of the real fishing sets and largely outperformed comparative linear models. This network is then used to forecast fishing operations for those trips where no observers were onboard. To quantify the extent to which fishing set distribution was correlated to stock distribution we compared three metrics describing features of the distributions (the mean distance to the coast, the total area of distribution, and a clustering index) for concomitant acoustic survey observations and fishing set positions identified from VMS. For two of these metrics (mean distance to the coast and clustering index), fishing and survey data were significantly correlated. We conclude that the location of purse–seine fishing sets yields significant and valuable information on the distribution of the Peruvian anchovy stock and ultimately on its vulnerability to the fishery. For example, a high concentration of sets in the near coastal zone could potentially be used as a warning signal of high levels of stock vulnerability and trigger appropriate management measures aimed at reducing fishing effort.  相似文献   

3.
Detecting regime shifts in the ocean: Data considerations   总被引：1，自引：0，他引：1  
We review observational data sets that have been used to detect regime shifts in the ocean. Through exploration of data time series we develop a definition of a regime shift from a pragmatic perspective, in which a shift is considered as an abrupt change from a quantifiable ecosystem state. We conclude that such changes represent a restructuring of the ecosystem state in some substantial sense that persists for long enough that a new quasi-equilibrium state can be observed. The abruptness of the shift is relative to the life-scale or the reproductive time-scale of the higher predators that are influenced by the shift. In general, the event-forcing is external to the biological ecosystem, usually the physical climate system, but we also identify shifts that can be ascribed to anthropogenic forcing, in our examples fishing. This pragmatic definition allows for several different types of regime shift ranging from simple biogeographic shifts to non-linear state changes. In practice it is quite difficult to determine whether observed changes in an oceanic ecosystem are primarily spatial or temporally regulated. The determination of ecosystem state remains an unresolved, and imprecise, oceanographic problem.We review observations and interpretation from several different oceanic regions as examples to illustrate this pragmatic definition of a regime shift: the Northeast Pacific, the Northwest and Northeast Atlantic, and Eastern Boundary Currents. For each region, different types of data (biological and physical) are available for differing periods of time, and we conclude, with varying degrees of certainty, whether a regime shift is in fact detectable in the data.  相似文献   

4.
Regime shift and principal component analysis of a spatially disaggregated database capturing time-series of climatic, nutrient and plankton variables in the North Sea revealed considerable covariance between groups of ecosystem indicators. Plankton and climate time-series span the period 1958–2003, those of nutrients start in 1980. In both regions, the period from 1989 to 2001 identified in principal component 1 had warmer surface waters, higher Atlantic inflow and stronger winds, than the periods before or after. However, it was preceded by a regime shift in both open (PC2) and coastal (PC3) waters during 1977 towards more hours of sunlight and higher water temperature, which lasted until 1997. The relative influence of nutrient availability and climatic forcing differed between open and coastal North Sea regions. Inter-annual variability in phytoplankton dynamics of the open North Sea was primarily regulated by climatic forcing, specifically by sea surface temperature, Atlantic inflow and co-varying wind stress and NAO. Coastal phytoplankton variability, however, was regulated by insolation and sea surface temperature, as well as Si availability, but not by N or P. Regime shifts in principal components of hydrographic and climatic variables (explaining 55 and 61% of the variance in coastal and open water variables) were detected using Rodionov's sequential t-test. These shifts in hydroclimatic variables which occurred around 1977, 1989, 1997 and 2001, were synchronized in open and coastal waters, and were tracked by open water chlorophyll and copepods, but not by coastal plankton. North–central–south or open-coastal spatial breakdowns of the North Sea explained similar amounts of variability in most ecosystem indicators with the exception of diatom abundance and chlorophyll concentration, which were clearly better explained using the open-coastal configuration.  相似文献   

5.
辽宁省海洋机动渔船结构调整的研究   总被引：1，自引：0，他引：1  
根据辽宁省海洋机动渔船统计资料，分析了海洋机动渔船的变化情况，运用多目标线性规划法对辽宁省海洋机动渔船结构配置进行了优化。结果表明：辽宁省各功率级别海洋机动渔船的功率数均有增长，并且各功率级别海洋机动渔船的功率结构不合理；各分级海洋机动渔船功率的优化估算比例是，184KW以上、88—184KW、44—87KW、15—43KW与14KW以下的功率占总功率的百分比分别约为31．6％、10．5％、27．0％、25．6％与5．3％。最后对渔船结构调整进行了讨论。  相似文献   

6.
In this paper we present results from dynamic simulations of the Northern California Current ecosystem, based on historical estimates of fishing mortality, relative fishing effort, and climate forcing. Climate can affect ecosystem productivity and dynamics both from the bottom-up (through short- and long-term variability in primary and secondary production) as well as from the top-down (through variability in the abundance and spatial distribution of key predators). We have explored how the simplistic application of climate forcing through both bottom-up and top-down mechanisms improves the fit of the model dynamics to observed population trends and reported catches for exploited components of the ecosystem. We find that using climate as either a bottom-up or a top-down forcing mechanism results in substantial improvements in model performance, such that much of the variability observed in single species models and dynamics can be replicated in a multi-species approach. Using multiple climate variables (both bottom-up and top-down) simultaneously did not provide significant improvement over a model with only one forcing. In general, results suggest that there do not appear to be strong trophic interactions among many of the longer-lived, slower-growing rockfish, roundfish and flatfish in this ecosystem, although strong interactions were observed in shrimp, salmon and small flatfish populations where high turnover and predation rates have been coupled with substantial changes in many predator populations over the last 40 years.  相似文献   

7.
The Gulf of Gabes located in southern Tunisia is one of the most productive ecosystems in the Mediterranean Sea. Despite its ecological importance, it is subject to high fishing pressure affecting the different components of the ecosystem. Given the multispecies, multigear nature of the fishery, there is a need to manage trade-offs between environmental and economic objectives. In this study, an Ecospace model was developed based on the previously constructed Ecopath model of the Gulf of Gabes and calibrated for the period 1995–2008 to investigate the response of the ecosystem to a set of alternative spatial management scenarios. These scenarios were derived from the current fishery regulation owing the important interest expressed by local fishery managers to assess new management measures. The results showed for each management scenario how bottom trawling and coastal fishing impact the different trophic groups and the complexity of interaction between these two fishing activities. Furthermore, spatially explicit simulations were performed to identify regions where the management measures are effective. Results suggested that for some trophic groups, these regions are well-defined which would be interesting to propose more accurate spatial measures. Finally, several indicators were calculated to evaluate the proposed management plans and provide managers with a straightforward set of decision rules to describe the potential trade-offs and fulfill both fisheries and conservation management objectives in the context of an ecosystem approach. The decision rules were based on observed trends to reduce uncertainty relative to the model complexity and provide consistent advice to decision-makers.  相似文献   

8.
Long-term, continuous, and real-time ocean monitoring has been undertaken in order to evaluate various oceanographic phenomena and processes in the East/Japan Sea. Recent technical advances combined with our concerted efforts have allowed us to establish a real-time monitoring system and to accumulate considerable knowledge on what has been taking place in water properties, current systems, and circulation in the East Sea. We have obtained information on volume transport across the Korea Strait through cable voltage measurements and continuous temperature and salinity profile data from ARGO floats placed throughout entire East Sea since 1997. These ARGO float data have been utilized to estimate deep current, inertial kinetic energy, and changes in water mass, especially in the northern East Sea. We have also developed the East Sea Real-time Ocean Buoy (ESROB) in coastal regions and made continual improvements till it has evolved into the most up-to-date and effective monitoring system as a result of remarkable technical progress in data communication systems. Atmospheric and oceanic measurements by ESROB have contributed to the recognition of coastal wind variability, current fluctuations, and internal waves near and off the eastern coast of Korea. Long-term current meter moorings have been in operation since 1996 between Ulleungdo and Dokdo to monitor the interbasin deep water exchanges between the Japanese and Ulleung Basins. In addition, remotely sensed satellite data could facilitate the investigation of atmospheric and oceanic surface conditions such as sea surface temperature (SST), sea surface height, near-surface winds, oceanic color, surface roughness, and so on. These satellite data revealed surface frontal structures with a fairly good spatial resolution, seasonal cycle of SST, atmospheric wind forcing, geostrophic current anomalies, and biogeochemical processes associated with physical forcing and processes. Since the East Sea has been recognized as a natural laboratory for global oceanic changes and a clue to abrupt climate change, we aim at constructing a 4-D continuous real-time monitoring system, over a decade at least, using the most advanced techniques to understand a variety of oceanic processes in the East Sea.  相似文献   

9.
Regime shifts in the Humboldt Current ecosystem   总被引：4，自引：0，他引：4  
Of the four major eastern boundary currents, the Humboldt Current (HC) stands out because it is extremely productive, dominated by anchovy dynamics and subject to frequent direct environmental perturbations of the El Niño Southern Oscillation (ENSO). The long-term dynamics of the HC ecosystem are controlled by shifts between alternating anchovy and sardine regimes that restructure the entire ecosystem from phytoplankton to the top predators. These regime shifts are caused by lasting periods of warm or cold temperature anomalies related to the approach or retreat of warm subtropical oceanic waters to the coast of Peru and Chile. Phases with mainly negative temperature anomalies parallel anchovy regimes (1950–1970; 1985 to the present) and the rather warm period from 1970 to 1985 was characterized by sardine dominance. The transition periods (turning points) from one regime to the other were 1968–1970 and 1984–1986. Like an El Nino, the warm periods drastically change trophic relationships in the entire HC ecosystem, exposing the Peruvian anchovy to a multitude of adverse conditions. Positive temperature anomalies off Peru drive the anchovy population close to the coast as the coastal upwelling cells usually offer the coolest environment, thereby substantially decreasing the extent of the areas of anchovy distribution and spawning. This enhances the effects of negative density-dependent processes such as egg and larval cannibalism and dramatically increases its catchability. Increased spatial overlap between anchovies and the warmer water preferring sardines intensifies anchovy egg mortality further as sardines feed heavily on anchovy eggs.Food sources for juvenile and adult anchovies which prey on a mixed diet of phyto- and zooplankton are drastically reduced because of decreased plankton production due to restricted upwelling in warm years, as demonstrated by lower zooplankton and phytoplankton volumes and the diminution of the fraction of large copepods, their main food source.Horse mackerel and mackerel, the main predators of anchovy, increase predation pressure on juvenile and adult anchovies due to extended invasion into the anchovy habitat in warmer years. In contrast to these periods of warm and cold temperature anomalies on the decadal scale, ENSO events do not play an important role for long-term anchovy dynamics, as the anchovy can recover even from strong ENSO events within 1–2 years. Consequently, the strong 1972–1973 ENSO event (in combination with overfishing) was not the cause of the famous crash of the Peruvian anchovy fishery in the 1970s.  相似文献   

10.
The Peruvian anchovy or anchoveta (Engraulis ringens) forages on plankton and is a main prey for marine mammals, seabirds, fish, and fishers, and is therefore a key element of the food web in the Humboldt Current system (HCS). Here, we present results from the analysis of 21,203 anchoveta stomach contents sampled during 23 acoustic surveys over the period 1996–2003. Prey items were identified to the genus level, and the relative dietary importance of different prey was assessed by determination of their carbon content. Variability in stomach fullness was examined relative to the diel cycle, the distance from the coast, sea surface temperature, and latitude, using generalized additive models (GAMs). Whereas phytoplankton largely dominated anchoveta diets in terms of numerical abundance and comprised >99% of ingested prey items, the carbon content of prey items indicated that zooplankton was by far the most important dietary component, with euphausiids contributing 67.5% of dietary carbon followed by copepods (26.3%). Stomach fullness data showed that anchoveta feed mainly during daytime between 07h00 and 18h00, although night-time feeding also made a substantial contribution to total food consumption. Stomach fullness also varied with latitude, distance from the coast, and temperature, but with substantial variability indicating a high degree of plasticity in anchoveta feeding behaviour. The results suggest an ecological role for anchoveta that challenges current understanding of its position in the foodweb, the functioning of the HCS, and trophic models of the HCS.  相似文献   

11.
A set of multiply nested atmospheric (The Penn State/NCAR Mesoscale Modeling system—MM5) and oceanic (Regional Ocean Modeling System—ROMS) models has been developed to investigate ecosystem forcing as part of the US. GLOBEC program. This study focuses on the most finely nested oceanic model in the hierarchy, that of the coastal Gulf of Alaska (CGOA) during 2001–2002, and compares the model's results to data collected by GLOBEC investigators. The 3-km resolution model realistically generates two physical features needed to reproduce the CGOA ecosystem: the cross-shelf water mass structure on the Seward Shelf, and the seasonal cycle of vertical structure. In addition, the temporal variability of currents and tracer fields generated by the model is greatly improved compared to previous work, as is the resolution of the Alaska Coastal Current (ACC). However, the treatment of the line-source freshwater source along the coast of Alaska still presents difficulties, because the model cannot resolve the many inlets and fjords where mixing takes place initially. This issue is investigated by testing the model's sensitivity to various forcing mechanisms which could compensate for this weakness, such as the addition of tidal mixing, the use of finely resolved winds, and the use of brackish runoff rather than purely freshwater for the line-source.  相似文献   

12.
As catch and effort statistics including fishing time and location are essential for producing abundance indices for utilized fish stocks, fishing states are encouraged under the FAO Code of Conduct for Responsible Fisheries to collect and maintain such statistics. However, for coastal fisheries (including artisanal fisheries) that are mainly composed of small-sized vessels which are usually too numerous to monitor, fisheries statistics collection systems are often either lacking or of insufficient quality (e.g. incomplete or inaccurate). Vessel monitoring system (VMS) data are commonly used to construct or improve estimation of fishing effort and fishing location in large-scale fisheries. Most coastal fisheries lack VMS but their countries do have coastal surveillance radar systems (CSRS) for security and enforcement purposes. This study illustrates and recommends opportunistic use of CSRS data to provide similar scientific benefits to VMS data for coastal fisheries. CSRS in combination with market landings data can construct logbook-like catch and effort statistics. This study introduces a method and demonstrates its usefulness for scientific research and management purposes, including the potential to obtain a higher accuracy and precision, particularly for fishing location and catch amount. Limitations of the CSRS data and challenges to managers involved in its application are also discussed.  相似文献   

13.
This paper presents a multilayered ecosystem modelling approach that combines the simulation of the biogeochemistry of a coastal ecosystem with the simulation of the main forcing functions, such as catchment loading and aquaculture activities. This approach was developed as a tool for sustainable management of coastal ecosystems. A key feature is to simulate management scenarios that account for changes in multiple uses and enable assessment of cumulative impacts of coastal activities. The model was applied to a coastal zone in China with large aquaculture production and multiple catchment uses, and where management efforts to improve water quality are under way. Development scenarios designed in conjunction with local managers and aquaculture producers include the reduction of fish cages and treatment of wastewater. Despite the reduction in nutrient loading simulated in three different scenarios, inorganic nutrient concentrations in the bay were predicted to exceed the thresholds for poor quality defined by Chinese seawater quality legislation. For all scenarios there is still a Moderate High to High nutrient loading from the catchment, so further reductions might be enacted, together with additional decreases in fish cage culture. The model predicts that overall, shellfish production decreases by 10%–28% using any of these development scenarios, principally because shellfish growth is being sustained by the substances to be reduced for improvement of water quality. The model outcomes indicate that this may be counteracted by zoning of shellfish aquaculture at the ecosystem level in order to optimize trade-offs between productivity and environmental effects. The present case study exemplifies the value of multilayered ecosystem modelling as a tool for Integrated Coastal Zone Management and for the adoption of ecosystem approaches for marine resource management. This modelling approach can be applied worldwide, and may be particularly useful for the application of coastal management regulation, for instance in the implementation of the European Marine Strategy Framework Directive.  相似文献   

14.
Ecosystem-based management is one of the most important approaches that may lead to reducing the impacts of fishing on ecosystems. In this context, we have assessed the impact of Iranian coastal fishing (using landing data of 49 exploited species) on the ecosystem of the North Sea of Oman (Sistan and Baluchestan Province), during the last decade (2002–2011), with emphasis on testing the occurrence of the “fishing down? phenomenon. The Mean Trophic Level (MTL) and Fishing-in-Balance (FiB) index are two indicators that we used for analysis. The data indicated that the increased total landings in this region might be related to the exploitation of marine fishery resources especially with regard to large pelagic fish. Over the past decade, moderate decreasing trends in MTL and an increasing trend in the FiB-index were observed. In this regard, an upward trend in the spatial expansion factor and also a downward trend in the piscivory index and in Primary Production Required (PPR) in the time period could all indicate a spatial expansion toward deep waters, the catching of the large pelagic piscivorous species, such as tuna, and a sign of fishing pressures on the ecosystem. The results suggest a range of fishery exploitation patterns throughout the food web but it seems that these patterns are not a consequence of ?fishing down?. We suggest that the monitoring research be continued in this region and these indicators should be used to make fisheries management decisions and to prevent the continuance of this trend in future.  相似文献   

15.
Decadal-Scale Climate and Ecosystem Interactions in the North Pacific Ocean   总被引：7，自引：0，他引：7  
Decadal-scale climate variations in the Pacific Ocean wield a strong influence on the oceanic ecosystem. Two dominant patterns of large-scale SST variability and one dominant pattern of large-scale thermocline variability can be explained as a forced oceanic response to large-scale changes in the Aleutian Low. The physical mechanisms that generate this decadal variability are still unclear, but stochastic atmospheric forcing of the ocean combined with atmospheric teleconnections from the tropics to the midlatitudes and some weak ocean-atmosphere feedbacks processes are the most plausible explanation. These observed physical variations organize the oceanic ecosystem response through large-scale basin-wide forcings that exert distinct local influences through many different processes. The regional ecosystem impacts of these local processes are discussed for the Tropical Pacific, the Central North Pacific, the Kuroshio-Oyashio Extension, the Bering Sea, the Gulf of Alaska, and the California Current System regions in the context of the observed decadal climate variability. The physical ocean-atmosphere system and the oceanic ecosystem interact through many different processes. These include physical forcing of the ecosystem by changes in solar fluxes, ocean temperature, horizontal current advection, vertical mixing and upwelling, freshwater fluxes, and sea ice. These also include oceanic ecosystem forcing of the climate by attenuation of solar energy by phytoplankton absorption and atmospheric aerosol production by phytoplankton DMS fluxes. A more complete understanding of the complicated feedback processes controlling decadal variability, ocean ecosystems, and biogeochemical cycling requires a concerted and organized long-term observational and modeling effort. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

16.
In coastal areas, offshore wave propagation towards the shore is influenced by water depth variations, due to sea bed bathymetry, tides and surges. Considering implications of climate change both on atmospheric forcing and sea level rise, a simple methodology involving numerical modelling is implemented to compute inshore waves from 1960 to 2099. Simulations take into account five scenarios of linear sea level rise and one climatic scenario for storm surges and offshore waves. The methodology is applied to the East Anglia coast (UK). Extreme event analysis is performed to estimate climate change implication on inshore waves and the occurrence of extreme events. It is shown, for this coastal region, that wave statistics are sensitive to the trend in sea level rise, and that the climate change scenario leads to a significant increase of extreme wave heights in the northern part of the domain. For nearshore points, the increase of the mean sea level alters not only extreme wave heights but also the frequency of occurrence of extreme wave conditions.  相似文献   

17.
基于分类回归树算法的东南太平洋智利竹筴鱼渔场预报   总被引：4，自引：0，他引：4  
为了提高智利竹筴鱼渔场预报水平和满足渔业捕捞生产的需要,利用2002—2008年的东南太平洋公海海域捕捞的中国大型拖网渔船共计15艘的生产统计资料,以及海洋环境数据(包括海表温度、叶绿素a浓度、表温距平、叶绿素a浓度距平、海表温度梯度强度和海面高度异常等数据),基于CART的算法,构建了智利竹筴鱼渔场决策树预报模型。用含1 114条记录的数据集对模型进行训练,并采用ROC方法对该模型诊断中心渔场的准确性进行了分析。最后将该模型应用于2009年各月份的智利竹筴鱼中心渔场预报,并与实际渔场位置进行了对比,结果显示预报渔场与实际生产位置基本一致,表明利用CART决策树方法建立智利竹筴鱼渔场预报模型是可行的。  相似文献   

18.
东南太平洋秘鲁鳀资源量预报模型的构建   总被引：2，自引：0，他引：2  
秘鲁鳀（Engraulis ringens）是栖息于东南太平洋沿岸的一种小型中上层鱼类。有效地对秘鲁鳀资源量进行预报将有助于为我国鱼粉进口企业提供决策支撑。为此,本研究结合秘鲁鳀生物（上一个渔汛季度的资源量、渔获物中的幼鱼比例）和环境（渔场水温和nino1+2区的温度距平）因素及捕捞量为预报因子,利用主成分分析和多元线性回归的方法对17个渔汛季度（2006年至2014年第一渔汛季度）秘鲁鳀的资源量建立预报模型并利用主成分分析的结果对影响秘鲁鳀资源变动的因子进行初步评价。研究表明,随着时间的推移样本量的增加,模型拟合资源量与真实资源量的平均相对误差逐渐下降,拟合资源量序列与真实资源量序列的相关系数逐渐增加。最终模型5（建模数据为2006-2013年第二渔汛季度的数据,验证数据为2014年第一渔汛季度的数据）能够很好地拟合出秘鲁鳀资源量的大小及变动趋势拟合资源量序列与真实资源量序列的相关系数为0.861;拟合资源量序列与真实资源量序列的平均相对误差为12%;预报得到的2014年第一渔汛季度的数据与真实值相比,相对误差为1%。结合主成分分析的结果对影响秘鲁鳀资源变动的因素进行评价结果表明,第一主成分的方差贡献率为46%,其中环境因素占据了最大的载荷;第二主成分的方差贡献率为23%,同样环境因素占据了最大载荷,但是,排名第二和第三的因素分别是上一个渔汛季度的资源量和捕捞量,其载荷相当;第三和第四主成分的方差贡献率分别为9%和7%,其中幼鱼比例占的载荷最大。根据各主成分得分序列与资源量序列的相关系数结果,环境因子对秘鲁鳀资源变动有重要影响。  相似文献   

19.
通过对2010/2011年夏季南极长城湾叶绿素a浓度和海流等环境参数的传感器连续观测;研究其时空变化特征及海流对浮游植物生物量的影响。结果表明;12.9 m水层叶绿素a浓度从12月中旬开始增长;直至2月上旬开始维持相对稳定;期间出现两个高值点（2.74 μg/L和3.76 μg/L）。叶绿素a浓度表现出了24 h周期变化特征;每日叶绿素a浓度最高值出现在正午前后时段的概率要高于其他时段。表层海水受西北风影响;流速较大;约为60~100 cm/s;中层和底层水体流速较小;约为10 cm/s。表层的风海流使海水在长城湾发生辐散;下层海水向上涌升;驱动了水体的垂直交换。长城湾与麦克斯韦尔湾存在水体交换;水体主要从中层进入湾内;从表层输出。长城湾的叶绿素a浓度与流速呈显著负相关;表明低流速环境有利于长城湾浮游植物的生长。  相似文献   

20.
Exergy, as the sum of energy and information contained in a given system due to living organisms, can act as a quality indicator of ecosystems. Here, we investigated the exergy of Marsala Lagoon (Mediterranean Sea), along with microbial (prokaryotic and heterotrophic nanobenthos) biomass, prokaryotic heterotrophic production and extracellular enzymatic activities, and the biochemical composition of sediment organic matter. The aim of the study was to assess the role of auxiliary energy (e.g. hydrodynamic stress) in the ecosystem functioning and efficiency of a ‘detritus sink’ lagoon. Samples were collected at sites characterized by contrasting hydrodynamic and trophic conditions. Exergy transfer through the benthic microbial loop was influenced by two main factors: (1) organic matter bioavailability; and (2) hydrodynamic forcing. At both sites, the values of total exergy were higher in summer than in winter, and the specific exergy decreased from winter to autumn, along with increasing auxiliary energy. Our data indicate that in coastal ‘detritus sink’ systems, auxiliary energy sources can have a crucial role in exergy transfer and ecosystem functioning through modifying the efficiency of transfer to higher trophic levels of the refractory organic detritus, which is otherwise lost by burial in the sediment. As coastal lagoons are often intensively modified by human activities, we conclude that maintenance of the natural hydrodynamic regimes is a key factor in the preservation of the functioning of lagoon ecosystems and of their provision of goods and services to humans.  相似文献   

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