Ecohydrodynamics of Cold-Water Coral Reefs: A Case Study of the Mingulay Reef Complex (Western Scotland)

Ecohydrodynamics investigates the hydrodynamic constraints on ecosystems across different temporal and spatial scales. Ecohydrodynamics play a pivotal role in the structure and functioning of marine ecosystems, however the lack of integrated complex flow models for deep-water ecosystems beyond the coastal zone prevents further synthesis in these settings. We present a hydrodynamic model for one of Earth''s most biologically diverse deep-water ecosystems, cold-water coral reefs. The Mingulay Reef Complex (western Scotland) is an inshore seascape of cold-water coral reefs formed by the scleractinian coral Lophelia pertusa. We applied single-image edge detection and composite front maps using satellite remote sensing, to detect oceanographic fronts and peaks of chlorophyll a values that likely affect food supply to corals and other suspension-feeding fauna. We also present a high resolution 3D ocean model to incorporate salient aspects of the regional and local oceanography. Model validation using in situ current speed, direction and sea elevation data confirmed the model''s realistic representation of spatial and temporal aspects of circulation at the reef complex including a tidally driven current regime, eddies, and downwelling phenomena. This novel combination of 3D hydrodynamic modelling and remote sensing in deep-water ecosystems improves our understanding of the temporal and spatial scales of ecological processes occurring in marine systems. The modelled information has been integrated into a 3D GIS, providing a user interface for visualization and interrogation of results that allows wider ecological application of the model and that can provide valuable input for marine biodiversity and conservation applications.     

Reefs from space: Satellite imagery,marine ecology,and ethnography in the Dominican Republic

Coral reef bleaching is an obvious indication that coastal marine ecosystems are being stressed. However, bleached reefs alone are poor indicators because they reflect the final stages of stress. This research project used multidate satellite imagery to look for coral reef changes as indicators of stress. Findings suggest that (1) satellite imagery can be used to identify small-scale changes in coastal marine ecosystems, including coral reefs; (2) remote sensing, marine ecology, and ethnographic data can be integrated to suggest potential causes of coral reef stress; and (3) changes in reef, seagrass, and mangrove ecozones are more closely tied to fishing, tourism, and land use practices than to global warming.     

On the edge: The use of infrared thermography in monitoring responses of intertidal organisms to heat stress

Monitoring changes in the environment and the corresponding effects on biological systems still represents a major challenge in many marine and terrestrial ecological studies. Infrared thermography (IRT), and its application within the marine environment, represents an effective non-invasive tool for measuring the temperatures of organisms and their surrounding environment in situ. The use of IRT within the intertidal zone is particularly useful since habitat and organismal temperatures are highly variable across both fine spatial and temporal scales. We review the growing number of intertidal studies that utilise IRT to investigate the role of small-scale temperature variability in contributing to various demographic and ecological processes. In particular, we introduce two indicators of the thermal quality of intertidal habitats that can be readily used by ecologists but also management and conservation policy makers to assess the suitability of a given habitat for a range of species under actual and predicted climatic conditions. We also outline a range of potential applications involving IRT that have yet to be explored for monitoring coastal environments. These include combining photogrammetry, unmanned aerial vehicles and IRT to large-scale three-dimensional thermal maps of intertidal habitats. We also suggest ways in which this technology could facilitate environmental management objectives in a warming world, such as the identification and quantification of thermal refugia across various spatial and temporal scales. We affirm with previous studies that such thermal refugia are vital for the adaptation of intertidal communities to climate change and that IRT could facilitate more effective management and conservation of these areas. The IRT applications outlined in this review are by no means exhaustive or limited to rocky intertidal environments. We envision that IRT will become increasingly popular as environmental management agencies become increasingly concerned about global climate change and how to combat its negative consequences on ecosystems.     

宁德水产养殖区水质状况及驱动力分析

水产养殖对海岸带生态系统的水环境有显著影响,研究水产养殖地区的水质动态及其驱动力对海洋牧场建设和海岸带生态系统管理有着重要意义。以宁德为研究区域,基于2017年夏季和冬季水质监测和遥感影像等数据,通过地理信息系统技术和统计分析软件,分析了水产养殖区域的水质现状、水质变化和驱动力。结果表明,该海域水质处于重污染状态,富营养化水平较高。除了悬浮物和总磷之外,其他水质指标都呈现出显著的季节性差异,不同季节影响水质的因素也不相同。水质的季节性变化是初始水质状况、养殖活动和自然因素共同作用的结果。基于研究结果,笔者建议结合高分遥感技术对养殖区水面覆盖和利用进行监测,对养殖类型和行为(如饵料类型和投放方式)进行调控,开展水质长期监测和风险应急管理,保障海洋牧场社会经济效益的同时降低生态环境影响、防控生态和人体健康风险。     

IMOS National Reference Stations: A Continental-Wide Physical,Chemical and Biological Coastal Observing System

Sustained observations allow for the tracking of change in oceanography and ecosystems, however, these are rare, particularly for the Southern Hemisphere. To address this in part, the Australian Integrated Marine Observing System (IMOS) implemented a network of nine National Reference Stations (NRS). The network builds on one long-term location, where monthly water sampling has been sustained since the 1940s and two others that commenced in the 1950s. In-situ continuously moored sensors and an enhanced monthly water sampling regime now collect more than 50 data streams. Building on sampling for temperature, salinity and nutrients, the network now observes dissolved oxygen, carbon, turbidity, currents, chlorophyll a and both phytoplankton and zooplankton. Additional parameters for studies of ocean acidification and bio-optics are collected at a sub-set of sites and all data is made freely and publically available. Our preliminary results demonstrate increased utility to observe extreme events, such as marine heat waves and coastal flooding; rare events, such as plankton blooms; and have, for the first time, allowed for consistent continental scale sampling and analysis of coastal zooplankton and phytoplankton communities. Independent water sampling allows for cross validation of the deployed sensors for quality control of data that now continuously tracks daily, seasonal and annual variation. The NRS will provide multi-decadal time series, against which more spatially replicated short-term studies can be referenced, models and remote sensing products validated, and improvements made to our understanding of how large-scale, long-term change and variability in the global ocean are affecting Australia''s coastal seas and ecosystems. The NRS network provides an example of how a continental scaled observing systems can be developed to collect observations that integrate across physics, chemistry and biology.     

Dramatic Variability of the Carbonate System at a Temperate Coastal Ocean Site (Beaufort,North Carolina,USA) Is Regulated by Physical and Biogeochemical Processes on Multiple Timescales

Increasing atmospheric carbon dioxide (CO₂) from anthropogenic sources is acidifying marine environments resulting in potentially dramatic consequences for the physical, chemical and biological functioning of these ecosystems. If current trends continue, mean ocean pH is expected to decrease by ~0.2 units over the next ~50 years. Yet, there is also substantial temporal variability in pH and other carbon system parameters in the ocean resulting in regions that already experience change that exceeds long-term projected trends in pH. This points to short-term dynamics as an important layer of complexity on top of long-term trends. Thus, in order to predict future climate change impacts, there is a critical need to characterize the natural range and dynamics of the marine carbonate system and the mechanisms responsible for observed variability. Here, we present pH and dissolved inorganic carbon (DIC) at time intervals spanning 1 hour to >1 year from a dynamic, coastal, temperate marine system (Beaufort Inlet, Beaufort NC USA) to characterize the carbonate system at multiple time scales. Daily and seasonal variation of the carbonate system is largely driven by temperature, alkalinity and the balance between primary production and respiration, but high frequency change (hours to days) is further influenced by water mass movement (e.g. tides) and stochastic events (e.g. storms). Both annual (~0.3 units) and diurnal (~0.1 units) variability in coastal ocean acidity are similar in magnitude to 50 year projections of ocean acidity associated with increasing atmospheric CO₂. The environmental variables driving these changes highlight the importance of characterizing the complete carbonate system rather than just pH. Short-term dynamics of ocean carbon parameters may already exert significant pressure on some coastal marine ecosystems with implications for ecology, biogeochemistry and evolution and this shorter term variability layers additive effects and complexity, including extreme values, on top of long-term trends in ocean acidification.     

滨海湿地植被地上生物量遥感反演

盐沼植被生物量是滨海湿地生态系统碳循环研究的重要参数,是湿地生态系统健康评价、资源可持续利用的关键指标,开展盐沼植被地上生物量监测方法研究具有重要意义。目前,遥感技术在湿地生物量监测领域已经得到广泛应用,但反演方法仍以统计模型为主,模型构建需要实测数据支撑,时空拓展性不强。选择江苏盐城丹顶鹤保护区为研究区,基于冠层辐射(PROSAIL)传输模型,通过局部和全局敏感性分析,对模型参数本地化,构建了互花米草地上生物量半经验反演模型,应用于Landsat 8 OLI遥感影像,获得了互花米草地上生物量的时空分布。研究结果表明,利用PROSAIL模型模拟互花米草冠层反射率,叶面积指数(LAI)、叶片干物质含量(Cm)、叶倾角分布参数(LIDF)、等效水厚度(Cw)、叶绿素含量(Cab)、叶片结构参数(N)为高敏感性参数,类胡萝卜素含量(Car)、土壤参数(P_soil)为低敏感性参数;利用不同时刻的遥感影像反演了地上生物量,遥感反演结果与实测数据对比,拟合度R²为0.83,均方根误差(RMSE)为0.43kg/m²,平均相对误差(MRE)为15.7%,精度较高,模型具有较好的时空普适性。研究发展了盐沼植被地上生物量遥感反演方法,解决了以往过于依赖现场实测数据构建反演模型的局限性,该方法可以为研究滨海湿地生态系统碳循环以及准确估算其碳汇潜力提供技术支持。     

Influence of salinity on bacterioplankton communities from the Brazilian rain forest to the coastal Atlantic Ocean

Background

Planktonic bacteria are recognized as important drivers of biogeochemical processes in all aquatic ecosystems, however, the taxa that make up these communities are poorly known. The aim of this study was to investigate bacterial communities in aquatic ecosystems at Ilha Grande, Rio de Janeiro, Brazil, a preserved insular environment of the Atlantic rain forest and how they correlate with a salinity gradient going from terrestrial aquatic habitats to the coastal Atlantic Ocean.

Methodology/Principal Findings

We analyzed chemical and microbiological parameters of water samples and constructed 16S rRNA gene libraries of free living bacteria obtained at three marine (two coastal and one offshore) and three freshwater (water spring, river, and mangrove) environments. A total of 836 sequences were analyzed by MOTHUR, yielding 269 freshwater and 219 marine operational taxonomic units (OTUs) grouped at 97% stringency. Richness and diversity indexes indicated that freshwater environments were the most diverse, especially the water spring. The main bacterial group in freshwater environments was Betaproteobacteria (43.5%), whereas Cyanobacteria (30.5%), Alphaproteobacteria (25.5%), and Gammaproteobacteria (26.3%) dominated the marine ones. Venn diagram showed no overlap between marine and freshwater OTUs at 97% stringency. LIBSHUFF statistics and PCA analysis revealed marked differences between the freshwater and marine libraries suggesting the importance of salinity as a driver of community composition in this habitat. The phylogenetic analysis of marine and freshwater libraries showed that the differences in community composition are consistent.

Conclusions/Significance

Our data supports the notion that a divergent evolutionary scenario is driving community composition in the studied habitats. This work also improves the comprehension of microbial community dynamics in tropical waters and how they are structured in relation to physicochemical parameters. Furthermore, this paper reveals for the first time the pristine bacterioplankton communities in a tropical island at the South Atlantic Ocean.     

Spatial variability overwhelms seasonal patterns in bacterioplankton communities across a river to ocean gradient

Few studies of microbial biogeography address variability across both multiple habitats and multiple seasons. Here we examine the spatial and temporal variability of bacterioplankton community composition of the Columbia River coastal margin using 16S amplicon pyrosequencing of 300 water samples collected in 2007 and 2008. Communities separated into seven groups (ANOSIM, P<0.001): river, estuary, plume, epipelagic, mesopelagic, shelf bottom (depth<350 m) and slope bottom (depth>850 m). The ordination of these samples was correlated with salinity (ρ=−0.83) and depth (ρ=−0.62). Temporal patterns were obscured by spatial variability among the coastal environments, and could only be detected within individual groups. Thus, structuring environmental factors (for example, salinity, depth) dominate over seasonal changes in determining community composition. Seasonal variability was detected across an annual cycle in the river, estuary and plume where communities separated into two groups, early year (April–July) and late year (August–Nov), demonstrating annual reassembly of communities over time. Determining both the spatial and temporal variability of bacterioplankton communities provides a framework for modeling these communities across environmental gradients from river to deep ocean.     

Denitrification in coastal ecosystems: methods, environmental controls, and ecosystem level controls, a review

In this review of sediment denitrification in estuaries and coastal ecosystems, we examine current denitrification measurement methodologies and the dominant biogeochemical controls on denitrification rates in coastal sediments. Integrated estimates of denitrification in coastal ecosystems are confounded by methodological difficulties, a lack of systematic understanding of the effects of changing environmental conditions, and inadequate attention to spatial and temporal variability to provide both seasonal and annual rates. Recent improvements in measurement techniques involving ¹⁵ N techniques and direct N₂ concentration changes appear to provide realistic rates of sediment denitrification. Controlling factors in coastal systems include concentrations of water column NO ₃ ^– , overall rates of sediment carbon metabolism, overlying water oxygen concentrations, the depth of oxygen penetration, and the presence/absence of aquatic vegetation and macrofauna. In systems experiencing environmental change, either degradation or improvement, the importance of denitrification can change. With the eutrophication of the Chesapeake Bay, the overall rates of denitrification relative to N loading terms have decreased, with factors such as loss of benthic habitat via anoxia and loss of submerged aquatic vegetation driving such effects.     

Environmental science and management of coastal lagoons in the Southern Mediterranean Region: key issues revealed by the MELMARINA Project

Lagoons in the heavily populated, semi-arid coastal zone of the Southern Mediterranean Region exemplify the conflict between human utilisation of water and related resources and aquatic ecosystems. Having recognised the requirement to improve understanding of the functioning of the region’s coastal wetlands, the MELMARINA Project undertook integrated hydro-ecological monitoring and modelling within lagoons in Morocco, Tunisia and Egypt. This article highlights some key issues regarding environmental science and management of the region’s coastal lagoons revealed during the course of the project. It stresses the importance of hydrology as a key control upon lagoon functioning and ecosystem dynamics. Hydrological modifications due to water resource management schemes are the cause of many recent changes experienced within lagoons. Linkages between water quality, water availability, human activities and biological characteristics of coastal lagoons are discussed with particular reference to the controls upon vegetation within the MELMARINA lagoons. A series of methodological advances are reviewed which have potential for wider application within coastal lagoons. It is suggested that the use of lagoon sediment for environmental reconstruction can be invaluable, especially when monitoring data are lacking. Recent advances in instrumentation technologies make long-term continuous monitoring more feasible although these approaches can be combined with more traditional site surveys to provide wider spatial coverage at the expense of temporal resolution. Wider spatial coverage can also be achieved through the use of space-borne or aerial remote sensing imagery whilst longer-term trends in site characteristics can be assessed through historical map analyses. Geographical Information Systems, which facilitate the storage and interrogation of large and varied datasets, have enormous potential. Similarly, coupled hydro-ecological models can inform understanding of lagoon functioning and can assess scenarios associated with environmental change or alternative management approaches. The application of integrated, basin-wide approaches to the management of water resources and aquatic ecosystems in the Southern Mediterranean Region is advocated. This includes the application of principles from the EU’s Water Framework Directive. Finally, the need to place management in the context of climate change and associated sea level rise is stressed. Emphasis should be placed on the development of adaptation strategies designed to minimise the effects of these changes. Guest editors: J. R. Thompson & R. J. Flower Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons     

Lake trout otolith chronologies as multidecadal indicators of high-latitude freshwater ecosystems

High-latitude ecosystems are among the most vulnerable to long-term climate change, yet continuous, multidecadal indicators by which to gauge effects on biology are scarce, especially in freshwater environments. To address this issue, dendrochronology (tree-ring analysis) techniques were applied to growth-increment widths in otoliths from lake trout (Salvelinus namaycush) from the Chandler Lake system, Alaska (68.23°N, 152.70°W). All otoliths were collected in 1987 and exhibited highly synchronous patterns in growth-increment width. Increments were dated, the widths were measured, and age-related growth declines were removed using standard dendrochronology techniques. The detrended time series were averaged to generate an annually resolved chronology, which continuously spanned 1964–1984. The chronology positively and linearly correlated with August air temperature over the 22-year interval (p < 0.01), indicating that warmer summers were beneficial for growth, perhaps by increasing fish metabolic rate or lake productivity. Given the broad distribution of lake trout within North America, this study suggests that otolith chronologies could be used to examine responses between freshwater ecosystems and environmental variability across a range of temporal and spatial scales.     

Fecal Pollution in Coastal Marine Sediments from a Semi-Enclosed Deep Embayment Subjected to Anthropogenic Activities: An Issue to Be Considered in Environmental Quality Management Frameworks Development

Sewage discharge is a major source of pollution in marine environments. Urban wastewaters can directly enter marine environments carrying pathogen organisms, organic loads, and nutrients. Because marine sediments can act as the ultimate fate of a wide range of pollutants, environmental quality assessment in this compartment can help to identify pollution problems in coastal areas. In the present study, characterization of surficial marine sediments allowed assessment of fecal pollution in a semi-enclosed deep embayment that is subjected to anthropogenic activities. Physicochemical parameters and fecal indicators presented a great spatial heterogeneity. Fecal coliform and Clostridium perfringens showed accumulation in an extensive area, not only in proximity to sewage discharge points, but also in sediments at 100 meters depth. Results included herein demonstrated that, in coastal areas, urban wastewater discharge can affect the whole ecosystem through accumulation of fecal matter in bottom sediments. Application of multivariate techniques provided useful information with applicability for management of coastal areas in such complex systems. Environmental implications of wastewater discharge in coastal areas indicate the need to implement and include sediment quality control strategies in legislative frameworks.     

Seasonal variations of community structures phytoplankton in groundwater discharge areas along the Northern Yucatán Peninsula coast

The highly touristic Yucatán Peninsula is principally constituted with coastal marine environments. Like other coastal areas, this has been affected by the increase of waste water discharge, hydrological modifications and land use changes in the area. The phytoplankton community structure is one of the main components of coastal ecosystems and the most affected in hydrological processes. In order to follow the seasonal variations, the phytoplankton was characterized to follow the hydrological variability in two sites (Dzilam and Progreso) of the Northern Yucatán Peninsula. For this, cruises were carried out monthly during one year, from April 2004 to March 2005, with two samplings per season (dry, rainy and "nortes"). Hydrological variability was associated with seasonality and directly linked to groundwater discharges in the Dzilam area, and waste water discharges in the Progreso area. The highest nutrient concentrations occurred mainly during the rainy season. The phytoplankton community changes observed throughout the year suggested that the hydrological and chemical variability associated with seasonality and anthropogenic impacts have a strong influence. The substitution of diatoms by dinoflagellates as the dominant group in Progreso was the result of seasonal variability itself, but also could have been caused by eutrophic processes; while in Dzilam, the major presence of diatoms could have been favored by groundwater discharges. The results of this study can be used to understand the linkages between stressors from the anthropogenic activities and coastal water quality and changes.     

Can dispersions be used for discriminating water quality status in coastal ecosystems? A case study on biofilm-dwelling microbial eukaryotes

Multivariate dispersions are an effective ecological indicator to evaluate the environmental heterogeneity and human disturbance in global ecological research. To explore the feasibility of the dispersions for assessing water quality status, a dataset of the biofilm-dwelling microbial eukaryote communities was studied in coastal waters of the Yellow Sea, northern China at two numerical resolutions. The community dispersion patterns represented a significant variability in both community structure and species composition in response to environmental heterogeneity. Multivariate approaches revealed that the species composition was the primary contributor to the community dispersion. Mantel analysis showed that the spatial variations in both community structure and species composition were significantly correlated with the changes of the nutrients, pH, dissolved oxygen (DO) and chemical oxygen demand (COD). The dispersion measures at both numerical resolutions were found to be remarkably related to the nutrient ammonium nitrogen and DO. Thus, we suggest that multivariate dispersions of the microbial eukaryote communities may be used as a potential bioindicator of water quality status in marine ecosystems.     

Real-time remote monitoring of water quality: a review of current applications, and advancements in sensor, telemetry, and computing technologies

Recent advances in communication and sensor technology have catalyzed progress in remote monitoring capabilities for water quality. As a result, the ability to characterize dynamic hydrologic properties at adequate temporal and spatial scales has greatly improved. These advances have led to improved statistical and mechanistic modeling in monitoring of water quality trends at local, watershed and regional scales for freshwater, estuarine and marine ecosystems. In addition, they have greatly enhanced rapid (e.g., real-time) detection of hydrologic variability, recognized as a critical need for early warning systems and rapid response to harmful algal bloom events. Here, we present some of the landmark developments and technological achievements that led to the advent of real-time remote monitors for hydrologic properties. We conclude that increased use and continuing advancements of real-time remote monitoring (RTRM) and sensing technologies will become a progressively more important tool for evaluating water quality. Recent engineering and deployment of RTRM technologies by federal and state regulatory agencies, industries, and academic laboratories is now permitting rapid detection of, and responses to, environmental threats imposed by increased nutrient loadings, development of hypoxic and anoxic areas, toxicants, and harmful algal bloom outbreaks leading to fish kill events and potential human health impacts.     

An approach to analyzing environmental drivers to shape spatial variations in body-size structure of biofilm-dwelling protozoa during an annual cycle in marine ecosystems

As an inherent trait, body-size structure has been used to summarize functional features of a community instead of taxonomic resolutions due to the high redundancy for bioassessment. In this study, the multivariate approaches were used to determine the environmental drivers to the spatial variation in body-size structure based on an annual dataset of biofilm-dwelling protozoa. Samples were monthly collected at four stations within a gradient of pollution in coastal waters of the Yellow Sea, northern China during a 1-year cycle. The second-stage (2STAGE) clustering and ordination analyses demonstrated that the annual patterns were significantly different among four sampling stations. Mantel analysis showed the spatial variations in body-size structures of the protozoa were significantly correlated with the water quality status along the pollution gradient. Best matching analysis revealed that the potential environmental drivers to shape the spatial difference in body-size structure may be pH, chemical oxygen demand (COD) and nutrients (e.g., soluble phosphates, ammonia and nitrates). It is suggested that the multivariate approaches used may determine the environmental drivers to shape the spatial variations in body-size structure of biofilm-dwelling protozoa in marine ecosystems.     

What is the Value of a Good Map? An Example Using High Spatial Resolution Imagery to Aid Riparian Restoration

Riparian areas contain structurally diverse habitats that are challenging to monitor routinely and accurately over broad areas. As the structural variability within riparian areas is often indiscernible using moderate-scale satellite imagery, new mapping techniques are needed. We used high spatial resolution satellite imagery from the QuickBird satellite to map harvested and intact forests in coastal British Columbia, Canada. We distinguished forest structural classes used in riparian restoration planning, each with different restoration costs. To assess the accuracy of high spatial resolution imagery relative to coarser imagery, we coarsened the pixel resolution of the image, repeated the classifications, and compared results. Accuracy assessments produced individual class accuracies ranging from 70 to 90% for most classes; whilst accuracies obtained using coarser scale imagery were lower. We also examined the implications of map error on riparian restoration budgets derived from our classified maps. To do so, we modified the confusion matrix to create a cost error matrix quantifying costs associated with misclassification. High spatial resolution satellite imagery can be useful for riparian mapping; however, errors in restoration budgets attributable to misclassification error can be significant, even when using highly accurate maps. As the spatial resolution of imagery increases, it will be used more routinely in ecosystem ecology. Thus, our ability to evaluate map accuracy in practical, meaningful ways must develop further. The cost error matrix is one method that can be adapted for conservation and planning decisions in many ecosystems.     

Population Structure and Phylogenetic Characterization of Marine Benthic Archaea in Deep-Sea Sediments

During the past few years Archaea have been recognized as a widespread and significant component of marine picoplankton assemblages and, more recently, the presence of novel archaeal phylogenetic lineages has been reported in coastal marine benthic environments. We investigated the relative abundance, vertical distribution, phylogenetic composition, and spatial variability of Archaea in deep-sea sediments collected from several stations in the Atlantic Ocean. Quantitative oligonucleotide hybridization experiments indicated that the relative abundance of archaeal 16S rRNA in deep-sea sediments (1500 m deep) ranged from about 2.5 to 8% of the total prokaryotic rRNA. Clone libraries of PCR-amplified archaeal rRNA genes (rDNA) were constructed from 10 depth intervals obtained from sediment cores collected at depths of 1,500, 2,600, and 4,500 m. Phylogenetic analysis of rDNA sequences revealed the presence of a complex archaeal population structure, whose members could be grouped into discrete phylogenetic lineages within the two kingdoms, Crenarchaeota and Euryarchaeota. Comparative denaturing gradient gel electrophoresis profile analysis of archaeal 16S rDNA V3 fragments revealed a significant depth-related variability in the composition of the archaeal population.