海草床生态系统固氮微生物研究现状与展望

海草床生态系统是三大典型海洋生态系统之一,具有较高的生产力水平和十分重要的生态意义,其海草附着物中包括许多固氮微生物,通过生物固氮提供该生态系统"新"氮源,在一定程度上缓解了氮对初级生产力的限制.通过对近些年来固氮活性的测定方法、固氮群落组成以及影响因素等的研究进展进行了综合分析,较全面地分析了海草床生态系统的固氮微生物研究现状,并在次基础上对海草床固氮微生物的系统研究进行了展望.     

海草生态学研究进展

海草床生态系统是生物圈中最具生产力的水生生态系统之一,具有重要的生态系统服务功能。作者根据海草生态学及相关领域的最新研究进展,对世界范围内海草床的空间分布、海草床的生态系统服务功能以及外界因素对海草床的影响等研究进展进行了综述。海草床生态系统服务功能主要包括净化水质、护堤减灾、提供栖息地和生态系统营养循环等。对海草床影响较大的外界环境因素包括盐度、温度、营养盐、光照、其他动物摄食、人类活动和气候变化等。海草普查、海草生态功能研究,影响海草床的主要环境因素,海草修复研究等将是我国海草研究的主要方向。     

海草生态系统的固碳机理及贡献

由海草、红树林、盐沼草等植被组成的滨海和海洋生态系统是地球中高效的碳汇热点,它们所固定的碳被称为"蓝碳".作为全球生态服务功能价值最高的生态系统之一,海草生态系统所固定的碳是蓝碳里的重要组成部分.高生产力、高效过滤及高稳定性造就了海草生态系统巨大的固碳能力,进而对全球碳循环具有深刻影响.然而,人为影响以及全球气候变化使全球海草床加速衰退,成为地球生物圈中退化速度最快的生态系统之一.当前,国内外对海草床等滨海生态系统固碳能力的关注、研究深度与广度仍远远不足,对全球海草固碳的评估仍存在诸多不确定性.为了能更准确地评估全球海草床的碳埋存,一些基础性的科学问题应优先考虑:1)全国和全球海草的准确分布面积;2)不同海草优势种类或不同地域的海草床碳汇能力的差异;3)人为干扰和全球气候变化对海草生态系统碳捕获和碳埋存的影响.     

全球变化下海岸带微生物生态研究进展

海岸带地区是元素循环最活跃的自然区域之一,微生物作为地球元素循环的主要驱动者,对该区域生态系统中物质转化与能量流动起着至关重要的作用。本文从典型海岸带生态系统：海岸带湿地、海草床与海藻森林、近岸水体出发,围绕微生物参与的碳、氮循环过程以及其中的温室气体排放情况,综述了在全球气候变化与人为活动干扰的作用下,海岸带地区的微生物群落对外界环境变化的响应机制以及生态功能维持机制,最后对海岸带系统中微生物生态研究进行了初步的展望。     

海草床生态系统的退化及其恢复

海草床是生产力和生物多样性最高的典型海洋生态系统之一,目前全球海草床呈现退化趋势,自然干扰和人类活动的负面影响是其退化原因,以后者为主.海草退化的生理生态机制主要是光合作用速率、光合色素荧光强度和含量、酶活性等生理生态指标在胁迫(高温、光照、盐度、污染物等)下发生显著变化.海草床监测和保护计划已经在局部区域取得成效,使部分海草床得到恢复.中国的海草床恢复研究重点应放在生物多样性保护、海草移植和海草床生态系统服务价值评估.     

海草与其附生藻类之间的相互作用

海草床是滨海湿地中重要的生态系统,近年来世界范围内出现大面积的海草床衰退,水体富营养化引发附生藻类的大量繁殖是其中的一个主要原因。本文综述了近20年来关于海草与其附生藻类之间相互作用的研究进展,包括海草床中附生藻类的地位及其积极作用,附生藻类与海草的物质交换关系,附生藻类对海草的影响（主要是光利用限制和营养物质利用限制）。对海草床中海草-附生藻类群落复杂的生态关系提出了研究展望,包括海草与其附生藻类的物质交换机制,海草与其附生藻类对营养物质利用的竞争关系,附生藻类生物量分别对海草可利用光和光合作用能力的削弱关系,海草与附生藻类对海草床初级生产力的贡献随环境因子的变化关系,通过原位观测数据的积累建立海草生长与生物作用的模型等。     

海草床育幼功能及其机理

海草床是近岸海域中生产力极高的生态系统,是许多海洋水生动物的重要育幼场所。从生物幼体的密度、生长率、存活率和生境迁移4个方面阐述海草床育幼功能,并从食源和捕食压力两个方面探讨海草床育幼功能机理。许多生物幼体在海草床都呈现出较高的密度、生长率和存活率,并且在个体发育到一定阶段从海草床向成体栖息环境迁移。丰富的食物来源或较低的捕食压力可能是海草床具有育幼功能的主要原因,但不同的生物幼体对海草床的利用有差异,海草床育幼功能的机理在不同环境条件下也存在差异。提出未来海草床育幼功能的重点研究方向:(1)量化海草床对成体栖息环境贡献量;(2)全球气候变化和人类活动对海草床育幼功能的影响;(3)海草床育幼功能对海草床斑块效应和边缘效应的响应,以期为促进我国海草床育幼研究和海草床生态系统保护提供依据。     

海草场生态系统及其修复研究进展

海草场能够提供重要的生态系统服务。自20世纪末以来,由于人类活动和自然灾害的影响,全球范围内的海草场出现了急剧衰退,由此也促进了海草场生态系统的研究以及海草场人工修复技术的发展。近年来,针对海草场生境流失的现状,中国也开始开展海草场修复工作。从以下方面进行论述:(1)海草的种类、分布,海草场生态系统功能及其生态系统服务:与陆地系统相比,全球海草物种多样性较低,了解海草的分布特征有助于通过了解海草如何适应当地环境压力,以揭示海草适应环境的能力;海草场提供重要而广泛的自然生态系统服务,特别是在维护近岸生态系统健康和满足人类需求过程中起到重要的作用;(2)海草场的衰退及其原因:认识并缓解人类压力对海草场的危害是促进海草场生态系统可持续发展的重要一环;(3)国内外海草场修复现状:以此阐明海草场修复原理,为海草场修复提供科学的方法;(4)总结与讨论:基于科学研究背景,为中国海草场生态系统保护和修复提出建议。海草场的修复和保护应当相辅相成,并与我国海岸长远规划相结合,以此推动我国海草场生态系统服务的可持续发展。     

海草床恢复研究进展

海草床是热带和温带重要的海洋生态系统,是许多海洋动物的栖息地、生存场所和食物来源地,具有重要的生态系统服务价值。20世纪以来,全世界的海草床衰退严重,仅1993年到2003年间约有2.6×104km2消失,达到15%,开展海草床的生态恢复已迫在眉睫。总结了海草床衰退的原因及恢复的主要方法。海草床衰退的原因包括自然灾害和人类活动的影响。海草床恢复的方法包括生境恢复法、种子法和移植法。移植法是目前最常用的方法,可分为草皮法、草块法和根状茎法。比较了各方法的优缺点,即(1)生境恢复法投入少、代价低,但周期长;(2)种子法破坏小,但种子难收集、易丧失、萌发率低;(3)草块法成活率高,但对原海草床有破坏作用;(4)根状茎法节约种源,但固定困难。因此,海草床恢复的具体方法取决于种源地、移植地及恢复的目标。我国的海草研究与恢复尚处在起始阶段,移植法应是目前我国海草床恢复的首选方法。就未来我国海草恢复的关键技术和研究重点提出了建议。     

营养盐富集和全球温度升高对海草的影响

海草床具有稳定沉积物、净化水质和碳储存等重要的生态系统服务功能。近几十年来,世界范围内海草床衰退严重。在全球近岸水体富营养化和气温升高的背景下,本文对营养盐富集和全球温度升高对海草的影响进行了分析。硝态氮和铵态氮作为海草重要的营养来源,贫营养环境下,会促进海草的生长。由于硝态氮需要转化为亚硝态氮,再通过一系列新陈代谢过程转化为氨基酸,硝态氮富集会影响海草组织的碳平衡,从而对海草床造成负面影响。较高浓度的铵态氮会对海草产生毒性,引起海草床的衰退。有机氮作为海草可选择吸收的氮源,是对海草氮吸收的有效补充。温度是控制全球海草分布和生长的主要因素,春季一定程度的营养盐富集可以提高海草的生产力,而夏季高温和营养盐富集对海草的生长具有抑制作用。营养盐富集和夏季高温还可以通过促进大型海藻爆发性生长,导致光衰减,从而引起海草床向大型海藻生态系统的逆向演替。本文提出了未来海草主要研究方向,主要包括:长时间序列海草床野外观测;有机氮对海草的影响机制;营养盐富集和全球温度升高对海草的协同影响机制;热带海草呼吸作用对全球温度升高的响应。     

Seagrass Restoration Enhances “Blue Carbon” Sequestration in Coastal Waters

Seagrass meadows are highly productive habitats that provide important ecosystem services in the coastal zone, including carbon and nutrient sequestration. Organic carbon in seagrass sediment, known as “blue carbon,” accumulates from both in situ production and sedimentation of particulate carbon from the water column. Using a large-scale restoration (>1700 ha) in the Virginia coastal bays as a model system, we evaluated the role of seagrass, Zostera marina , restoration in carbon storage in sediments of shallow coastal ecosystems. Sediments of replicate seagrass meadows representing different age treatments (as time since seeding: 0, 4, and 10 years), were analyzed for % carbon, % nitrogen, bulk density, organic matter content, and ²¹⁰Pb for dating at 1-cm increments to a depth of 10 cm. Sediment nutrient and organic content, and carbon accumulation rates were higher in 10-year seagrass meadows relative to 4-year and bare sediment. These differences were consistent with higher shoot density in the older meadow. Carbon accumulation rates determined for the 10-year restored seagrass meadows were 36.68 g C m^-2 yr^-1. Within 12 years of seeding, the restored seagrass meadows are expected to accumulate carbon at a rate that is comparable to measured ranges in natural seagrass meadows. This the first study to provide evidence of the potential of seagrass habitat restoration to enhance carbon sequestration in the coastal zone.     

Seagrass‐associated fungal communities show distance decay of similarity that has implications for seagrass management and restoration

Marine fungal biodiversity remains vastly understudied, and even less is known of their biogeography and the processes responsible for driving these distributions in marine environments. We investigated the fungal communities associated with the seagrass Enhalus acoroides collected from Singapore and Peninsular Malaysia to test the hypothesis that fungal communities are homogeneous throughout the study area. Seagrass samples were separated into different structures (leaves, roots, and rhizomes), and a sediment sample was collected next to each plant. Amplicon sequencing of the fungal internal transcribed spacer 1 and subsequent analysis revealed significant differences in fungal communities collected from different locations and different structures. We show a significant pattern of distance decay, with samples collected close to each other having more similar fungal communities in comparison with those that are more distant, indicating dispersal limitations and/or differences in habitat type are contributing to the observed biogeographic patterns. These results add to our understanding of the seagrass ecosystem in an understudied region of the world that is also the global epicenter of seagrass diversity. This work has implications for seagrass management and conservation initiatives, and we recommend that fungal community composition be a consideration for any seagrass transplant or restoration programme.     

Asynchronous local dynamics contributes to stability of a seagrass bed in Tokyo Bay

It is known that asynchronous temporal variations in local populations can contribute to the stability of metapopulations. However, studies evaluating the hierarchical organization of multiple spatial scales are rare for continuous marine landscapes, especially for marine vegetation such as seagrass beds. In this study, long‐term observation (26 yr) of temporal changes and nested spatial analyses were combined for an extensive seagrass meadow in Tokyo Bay, Japan, using remote sensing and geographic information system technologies. We examined how the dynamics at the whole‐bed scale (~1 km²) are related to those at a local scale (0.04 km²), and investigated the relationship between the seagrass dynamics and long‐term changes in environmental conditions using data on oceanography, water quality, and sediment dynamics. The seagrass bed size fluctuated between a maximum of 1.28 km² (in 1987) and a minimum of 0.39 km² (in 2001), with an average of 0.90 km². The temporal variation in seagrass bed size at the whole‐bed scale correlated with sand movement within the seagrass bed related to changes in the position of a sandbar. Seagrass bed size fluctuated asynchronously at a local scale. Multivariate analyses recognized clusters of local areas showing similar patterns of fluctuation. Temporal patterns in the various clusters responded differently to changes in environmental factors, e.g. the position of the sandbar was highly correlated with seagrass bed size in shallow habitats but not in deeper areas. The magnitudes of the temporal variations for the local clusters were greater than that of the entire bed, suggesting that asynchronous fluctuation in different areas of the bed plays an important role in the overall stability of the seagrass bed. The results of the present study also highlight the importance of physical processes in regulating the temporal dynamics of seagrass beds in shallow sedimentary landscapes.     

Microeukaryotic Communities Associated With the Seagrass Zostera marina Are Spatially Structured

Epibiotic microorganisms link seagrass productivity to higher trophic levels, but little is known about the processes structuring these communities, and which taxa consistently associate with seagrass. We investigated epibiotic microeukaryotes on seagrass (Zostera marina) leaves, substrates, and planktonic microeukaryotes in ten meadows in the Northeast Pacific. Seagrass epibiotic communities are distinct from planktonic and substrate communities. We found sixteen core microeukaryotes, including dinoflagellates, diatoms, and saprotrophic stramenopiles. Some likely use seagrass leaves as a substrate, others for grazing, or they may be saprotrophic organisms involved in seagrass decomposition or parasites; their relatives have been previously reported from marine sediments and in association with other hosts such as seaweeds. Core microeukaryotes were spatially structured, and none were ubiquitous across meadows. Seagrass epibiota were more spatially structured than planktonic communities, mostly due to spatial distance and changes in abiotic conditions across space. Seawater communities were relatively more similar in composition across sites and more influenced by the environmental component, but more variable over time. Core and transient taxa were both mostly structured by spatial distance and the abiotic environment, with little effect of host attributes, further indicating that those core taxa would not show a strong specific association with Z. marina.     

Aspects of seagrass ecology along the western Arabian Gulf coast

Results of semi-quantitative observations and quantitative sampling of seagrasses at coastal and offshore sites along the western Arabian Gulf are presented. Overall seagrass cover (all species together) shows significant positive correlation with latitude, but not with salinity, temperature or depth. The same pattern is shown by Halodule uninervis (Forsk.) Aschers., the dominant species. Mean seagrass biomass ranged from 53–235 g m^-2 (dry weight). These values are comparable with biomass estimates from regions in which environmental conditions are generally less extreme than in the Gulf. Seagrass biomass is significantly negatively correlated with depth and sediment grain size. No significant correlation is apparent between seagrass biomass and factors such as season, salinity, or concentrations of nutrients and heavy metals measured. It is pointed out that any correlations observed are not necessarily taken to imply causality.     

Spatiotemporal variability in the structure of seagrass meadows and associated macrofaunal assemblages in southwest England (UK): Using citizen science to benchmark ecological pattern

Seagrass meadows underpin a variety of ecosystem services and are recognized as globally important habitats and a conservation priority. However, seagrass populations are currently impacted by a range of biotic and abiotic stressors, and many are in decline globally. As such, improved understanding of seagrass populations and their associated faunal assemblages is needed to better detect and predict changes in the structure and functioning of these key habitats. Here, we analyzed a large dataset—collected by recreational scuba divers volunteering on a citizen science project—to examine spatiotemporal patterns in ecological structure and to provide a robust and reliable baseline against which to detect future change. Seagrass (Zostera marina) shoot density and the abundance of associated faunal groups were quantified across 2 years at 19 sites nested within three locations in southwest UK, by collecting in situ quadrat samples (2,518 in total) during 328 dives. Seagrass shoot density and meadow fragmentation was comparable across locations but was highly variable among sites. Faunal abundance and assemblage structure varied between areas with or without seagrass shoots; this pattern was largely consistent between locations and years. Overall, increased seagrass density was related to increased faunal abundance and explained shifts in faunal assemblage structure, although individual faunal groups were affected differently. More broadly, our study shows that well‐funded and orchestrated citizen science projects can, to some extent, gather fundamental information needed to benchmark ecological structure in poorly studied nearshore marine habitats.     

Resilience of an isopod population (<Emphasis Type="Italic">Cyathura carinata</Emphasis>) to multiple stress factors in a temperate estuarine system

The Mondego Estuary (Portugal) underwent major modifications in the late 1980s, because of eutrophication, for which it was developed a restoration programme that has been effective in recovering seagrass beds. Recently, this system has been affected by successive weather extremes: floods, droughts, and heat waves. The effect of these multiple stressors on a Cyathura carinata (Isopoda) population has been evaluated, through a long-term data series (16 years) in a seagrass bed, an intermediate area, and a sand flat. A well age-structured and abundant population of C. carinata was observed in the sand flat, in contrast with the seagrass bed and intermediate area. After introducing the restoration measures, C. carinata’s abundance increased even in the stations where it was formerly scarce. This recovery was compromised by successive extreme events. C. carinata declined severely in terms of total abundance and growth production during the 2003 summer heat wave, at the sand flat, also endangering its reproductive success. Floods and droughts affected dispersion of the individuals, which was reflected in the population’s density and production. Nevertheless, this isopod had great resilience, recovering successfully after disturbances. In contrast, the population of C. carinata had less resilience in the seagrass bed and intermediate area, being unable to recover after a succession of disturbances, which may threaten the success of this species in the system. Because the frequency and intensity of weather extremes are expected to continue to increase in a scenario of global climate change, their repercussions will affect such populations, which will have difficulty surviving. This will have severe implications on the functioning of the whole ecosystem.     

Seagrass bed patchiness: effects on epifaunal communities in San Diego Bay, USA

Seagrass habitat structure influences epifaunal density, diversity, community composition and survival, but covariation of structural elements at multiple scales (e.g., shoot density or biomass per unit area, patch size, and patch configuration) can confound studies attempting to correlate habitat structure with ecological patterns and processes. In this study, we standardized simulated seagrass shoot density and bed area among artificial seagrass beds in San Diego Bay, California, USA to evaluate the singular effect of seagrass bed configuration (“patchiness”) on the density and diversity of seagrass epifauna. Artificial seagrass beds all were 1 m², but were composed of a single large patch (“continuous” treatment), four smaller patches (“patchy” treatment), or 16 very small patches (“very patchy” treatment). We allowed epifauna to colonize beds for 1 month, and then sampled beds monthly over the next 3 months. Effects of seagrass bed patchiness on total epifaunal density and species-specific densities were highly variable among sampling dates, and there was no general trend for the effects of fragmentation on epifaunal densities to be positive or negative. Epifaunal diversity (measured as Simpson's index of diversity) was highest in very patchy or patchy beds on two out of the three sampling dates. Very patchy beds exhibited the highest dissimilarity in community composition in the first two sampling periods (August and September), but patchy beds exhibited the highest dissimilarity in the third sampling period (October). Our results indicate that seagrass patch configuration affects patterns of epifaunal density, diversity, and community composition in the absence of covarying bed area or structural complexity, and that patchy seagrass beds may be no less valuable as a habitat than are continuous seagrass beds. The spatial pattern employed when harvesting or planting seagrass may influence epifaunal habitat use and should be a key consideration in restoration plans.