Towards the co‐ordination of terrestrial ecosystem protocols across European research infrastructures

The study of ecosystem processes over multiple scales of space and time is often best achieved using comparable data from multiple sites. Yet, long‐term ecological observatories have often developed their own data collection protocols. Here, we address this problem by proposing a set of ecological protocols suitable for widespread adoption by the ecological community. Scientists from the European ecological research community prioritized terrestrial ecosystem parameters that could benefit from a more consistent approach to data collection within the resources available at most long‐term ecological observatories. Parameters for which standard methods are in widespread use, or for which methods are evolving rapidly, were not selected. Protocols were developed by domain experts, building on existing methods where possible, and refined through a process of field testing and training. They address above‐ground plant biomass; decomposition; land use and management; leaf area index; soil mesofaunal diversity; soil C and N stocks, and greenhouse gas emissions from soils. These complement existing methods to provide a complete assessment of ecological integrity. These protocols offer integrated approaches to ecological data collection that are low cost and are starting to be used across the European Long Term Ecological Research community.     

The impact of simulated chronic nitrogen deposition on the biomass and N2-fixation activity of two boreal feather moss–cyanobacteria associations

Bryophytes achieve substantial biomass and play several key functional roles in boreal forests that can influence how carbon (C) and nitrogen (N) cycling respond to atmospheric deposition of reactive nitrogen (N_r). They associate with cyanobacteria that fix atmospheric N₂, and downregulation of this process may offset anthropogenic N_r inputs to boreal systems. Bryophytes also promote soil C accumulation by thermally insulating soils, and changes in their biomass influence soil C dynamics. Using a unique large-scale (0.1 ha forested plots), long-term experiment (16 years) in northern Sweden where we simulated anthropogenic N_r deposition, we measured the biomass and N₂-fixation response of two bryophyte species, the feather mosses Hylocomium splendens and Pleurozium schreberi. Our data show that the biomass declined for both species; however, N₂-fixation rates per unit mass and per unit area declined only for H. splendens. The low and high treatments resulted in a 29% and 54% reduction in total feather moss biomass, and a 58% and 97% reduction in total N₂-fixation rate per unit area, respectively. These results help to quantify the sensitivity of feather moss biomass and N₂ fixation to chronic N_r deposition, which is relevant for modelling ecosystem C and N balances in boreal ecosystems.     

Effectiveness of entropy-based functions in the analysis of ecosystem state and development

Following the advances in the field of the thermodynamics of far-from-equilibrium systems, several ecological orientors (indicators able to describe the stage and orientation of ecosystem development) incorporating entropy terms have been proposed. Although most of the proposed functions have a good theoretical basis and have proved to perform adequately as ecological indicators, their suitability as ecological orientors has yet to receive a full confirmation in real case studies. The aim of the present contribution is to examine how several entropy-based indicators (exergy, structural information, entropy production, specific entropy production and the Eco-exergy index) perform as orientors when applied to a special case of ecological succession, i.e. eutrophication, in a homogeneous set of shallow lakes lying along a trophic gradient, from oligotrophy to hyper-eutrophy. The results show that a coherent pattern of response emerge, which is also consistent with the classical ecological theory. In particular, the maximisation of storage and the minimisation of specific entropy production are confirmed as the most reliable principles of ecosystem development, whereas the maximisation of dissipation (as entropy production) appears as a debatable criterion of development.     

塔里木盆地南缘旱生芦苇生态特征与水盐因子关系

选择位于塔里木盆地南缘极端干旱区的克里雅河流域于田绿洲为靶区,结合经典统计学和冗余分析技术,研究了旱生芦苇生态特征与水盐因子的分布规律及相互关系。统计学分析显示:芦苇沿河岸至荒漠方向株高、盖度和地上生物量减少、地下生物量增加,水分与土壤盐分也呈现一定的梯度变化规律。冗余分析结果表明:水分为芦苇生态特征变化的关键驱动因子,地下水埋深和土壤水分与芦苇的生态特征呈现极显著的相关关系,钠吸附比、全盐与芦苇的生态特征呈现显著的相关关系,其他指标与芦苇生态特征的相关性均不显著。水盐因子对芦苇生态特征影响的重要性排序为地下水埋深土壤水分钠吸附比全盐HCO-3pH值Cl-/SO2-4。综合水盐要素,水分对芦苇生态特征的影响大于盐分。     

社会-经济-自然复合生态系统生态位评价模型——以四川省为例

在深入分析区域资源、环境、社会、经济综合系统基础上,建立了四川省2001—2010年社会-经济-自然复合生态系统生态位评价指标体系,复合生态系统综合生态位包括资源、环境、经济和社会4个子系统生态位。将耦合投影寻踪模型应用于复合生态系统生态位评价,其中,采用并行模拟退火算法对评价模型参数进行优化。研究结果表明:2001年—2010年四川省复合生态位呈现先降后升的趋势,复合生态位评价值从2001年3.1325下降到2005年的2.8499,从2005年开始,复合生态位逐渐增加,到2010年增加到3.3304。表明环境重视程度的提高,环保意识的加强,促进了复合生态位的提高,区域自然生态和环境得以改善。最佳投影方向各分量的大小反映了各评价指标对生态位评价等级的影响程度,值越大则对应的评价指标对生态位评价等级的影响程度越大。区域生态位评价等级指标的影响程度最大的10项中有4项是环境生态位子系统指标,表明环境生态位子系统对综合生态位影响最大。发展过程中经济生态位子系统和社会生态位子系统指标值相关系数为0.9957,表明两子系统基本上是保持同步发展。而经济生态位和环境生态位子系统指标值相关系数为-0.9346,呈现明显的负相关关系。资源子系统呈现上升趋势。模拟退火优化的投影寻踪耦合模型应用于复合生态位评价,具有实用性和可行性,为区域生态管理科学决策提供重要依据。     

Ecological indicators to capture the effects of fishing on biodiversity and conservation status of marine ecosystems

IndiSeas (“Indicators for the Seas”) is a collaborative international working group that was established in 2005 to evaluate the status of exploited marine ecosystems using a suite of indicators in a comparative framework. An initial shortlist of seven ecological indicators was selected to quantify the effects of fishing on the broader ecosystem using several criteria (i.e., ecological meaning, sensitivity to fishing, data availability, management objectives and public awareness). The suite comprised: (i) the inverse coefficient of variation of total biomass of surveyed species, (ii) mean fish length in the surveyed community, (iii) mean maximum life span of surveyed fish species, (iv) proportion of predatory fish in the surveyed community, (v) proportion of under and moderately exploited stocks, (vi) total biomass of surveyed species, and (vii) mean trophic level of the landed catch. In line with the Nagoya Strategic Plan of the Convention on Biological Diversity (2011–2020), we extended this suite to emphasize the broader biodiversity and conservation risks in exploited marine ecosystems. We selected a subset of indicators from a list of empirically based candidate biodiversity indicators initially established based on ecological significance to complement the original IndiSeas indicators. The additional selected indicators were: (viii) mean intrinsic vulnerability index of the fish landed catch, (ix) proportion of non-declining exploited species in the surveyed community, (x) catch-based marine trophic index, and (xi) mean trophic level of the surveyed community. Despite the lack of data in some ecosystems, we also selected (xii) mean trophic level of the modelled community, and (xiii) proportion of discards in the fishery as extra indicators. These additional indicators were examined, along with the initial set of IndiSeas ecological indicators, to evaluate whether adding new biodiversity indicators provided useful additional information to refine our understanding of the status evaluation of 29 exploited marine ecosystems. We used state and trend analyses, and we performed correlation, redundancy and multivariate tests. Existing developments in ecosystem-based fisheries management have largely focused on exploited species. Our study, using mostly fisheries independent survey-based indicators, highlights that biodiversity and conservation-based indicators are complementary to ecological indicators of fishing pressure. Thus, they should be used to provide additional information to evaluate the overall impact of fishing on exploited marine ecosystems.     

Ecological impacts of water transfers on Lake Taihu from the Yangtze River,China

As an ecosystem responds to external environmental changes slowly due to its reorganization compared with the water quality and it has great influence on lake ecosystems, it is indispensable to evaluate ecological impacts from water transfers for the security of the water source in Lake Taihu. Evaluations were conducted by comparing the indicators exergy (Ex), structural exergy (Ex_st) and phytoplankton buffer capacity (β_((TP)/(Phy))) changes after water transfers from 2002 to 2007 with those reference statuses where the water transfers were not implemented from 1998 to 2001. Besides those three ecological indicators, affiliated indicators such as ratio of zooplankton biomass to phytoplankton biomass, diversity index and trophic state index were also involved in the evaluation. The results showed the water transfers altered the ecosystem status and had positive effects on Lake Taihu and most of its sub-zones, such as Gonghu Bay, Northwest Zone, Southwest Zone and Centre Zone in the post-transfer period. The seasonable trends indicated that the ecosystem health with environmental influences excluded in November and February was better than that in May and August during the water transfers from 2002 to 2007 and there were significant differences in the ecosystem health of the first and second stages during water transfers. The ecosystem health in May and August was better than in November and February during the first stage of the water transfers (from 2002 to 2004), while the opposite obtained during the second stage from 2005 to 2007 in Dongtaihu Bay and East Epigeal Zone. On the whole, water transfers serve to deter algal congregation in Lake Taihu.     

National ecosystem services mapping at multiple scales ⿿ The German exemplar

The EU Biodiversity Strategy 2020 requires the Member States of the European Union to map and assess ecosystem services. This paper presents a procedure for developing a national framework of ecosystem service indicators for Germany that is applicable at different scales and is transferable to other countries. The framework was set up to use existing indicators or datasets and to be compatible with international typologies of ecosystem services and their indicators. Starting with an evaluation of the importance of different ecosystem services for Germany and an analysis of existing monitoring systems, we define suitable indicators for mapping ecosystem services nationwide. We demonstrate how both the supply of and demand for ecosystem services can be mapped with different indicators and datasets and how these indicators have to be adapted for use at different scales. Subsequently, we analyze the resulting maps to draw conclusions about the suitability of the different indicators and their complementarity. Furthermore, we show synergies and trade-offs between ecosystem services in Germany and discuss the applicability of the ecosystem services concept for decision making and spatial planning.     

基于生态系统服务功能和生态敏感性的生态空间划定研究——以南宁市为例

生态空间管制是我国国土空间管制的重要内容。针对目前国内对生态空间认知有差异,对其划定技术方法还处于探索阶段的情况下,以生态系统服务功能和生态敏感性技术评价方法为手段,以广西壮族自治区南宁市为研究对象,开展了基于生态系统服务功能重要性和生态敏感性的生态空间划定方法的探索研究。结果表明:(1)研究区域内主导的生态系统服务功能主要为生物多样性维护功能和水土保持功能,其次为水源涵养功能。生态系统综合服务功能重要性类型以一般重要为主,约占研究区总面积的42.32%。(2)研究区生态敏感性以水土流失敏感性为主,其次为石漠化敏感类型。生态环境综合敏感类型以敏感为主,约占总面积的85.44%。(3)研究区内初步划定生态空间总面积约9325.27 km~2,占研究区总面积的42.19%,占研究区内生态用地面积的76.59%。土地利用类型以林地为主,约占生态空间面积的83.65%。划定的生态空间范围涵盖了绝大部分生态用地。本研究在一定程度上丰富了生态空间的内涵,可为进一步理解和划定生态空间提供参考与借鉴。     

基于能值分析和生态用地分类的中国生态系统生产总值核算研究

生态系统生产总值是生态系统为人类提供的产品与服务价值的总和,研究与建立一个独立的核算一个国家或地区的生态系统生产总值的方法与体系,对科学评价与合理利用自然资源、助推生态文明建设等具有重要意义。将生态系统生产总值分为供给价值、文化价值、承载价值与调节价值等四大类,基于能值分析方法和生态用地分类体系,计算得出全国及各地区生态系统生产总值,并将其与国内生产总值进行比较,为自然资源资产负债核算和综合生态系统管理等研究提供理论和方法借鉴。研究结果表明:(1)生态用地分类体系包括湿地、森林、草地和其他生态土地4个一级类型、19个二级类型。其中,湿地、森林、草地可统称为基础性生态用地。2008年,中国生态用地总量为763.95万km2,约占陆域国土面积的80%,其中基础性生态用地约为530.8万km2。(2)2008年,中国国土生态系统生产总值约为19万亿美元,是当年国内生产总值4.71万亿美元的4倍,人均生态系统总值约为1.45万美元/人。从生态系统生产总值来看,广东、山东、河南位居前三,西藏最低;从人均生态系统生产总值来看,西藏和内蒙古居前,甘肃最低。     

粤港澳大湾区城市群生态保护优先区识别研究

生态保护优先区识别对于城市群的整体性生态保护和区域生态安全具有重要意义。基于生态保护重要性评价识别城市群生态保护优先区,有助于保障生态系统服务的供给水平和维持生态系统的稳定性。以粤港澳大湾区(以下简称“大湾区”)为研究对象,首先通过增加粮食供给等生态系统服务指标和土地利用强度等生态脆弱性指标构建新的生态保护重要性评价指标体系,以弥补原指标体系忽略部分生态系统服务价值或者关乎生态脆弱性的重要因素所导致的评价结果片面性问题;然后运用结合空间主成分分析法和有序加权平均算子(Ordered Weighted Averaged, OWA)的主客观结合赋权法进行生态保护重要性评价的多情景模拟,并基于保护效率和权衡度进行多情景择优,由此所得最优情景的生态保护优先区的整体生态保护价值相对最高,且一定程度上减小了指标间权衡问题可能导致的评价误差;最终大湾区生态保护优先区面积为26406.04 km²,占大湾区陆域国土总面积的47.69%,主要分布在大湾区中部以外的肇庆、惠州、香港、广州北部、江门外环以及深圳东部沿海,同时优先区识别结果基本覆盖现有生态保护红线和周边大部分一般生态空间...     

基于生态系统服务理论的生态福祉内涵表征与评价

当前中国积极倡导生态文明建设,深入研究生态系统服务与人类福祉的关系具有理论和实践意义.本文界定了基于生态系统服务理论的生态福祉概念及其内涵,参考有关国民经济核算理论及相关研究成果构建了生态福祉供给与消费的评价指标,借鉴区位熵理论提出了区域生态福祉红线的刻画方法,在此基础上以2012年中国大陆省区生态福祉评价为例进行实证.结果表明: 2012年,中国大陆地区耕地、林地、牧草地、湿地、水域以及未利用地等6类生态系统生产净值分别为14819.25、81948.06、41762.77、42457.60、31770.84和1337.62亿元;省际生态系统生产净值的空间异质性明显;从供给水平来看,东部和中部省区林地、牧草地、湿地、耕地以及未利用地等5类人均生态福祉多在红线之下,整体低于全国平均水平;从消费水平来看,人均9种生态福祉的空间分布以“胡焕庸线”为界呈现“西北高-东南低”的分布格局.人口密度因素、土地资源禀赋共同导致中国大陆生态福祉的空间分布不均衡特征.     

A method for lake ecosystem health assessment: an Ecological Modeling Method (EMM) and its application

Ecosystem health is a newly proposed concept that sets new goals for environmental management. Its definition, indexing and assessment methods are still being perfected. An Ecological Modeling Method (EMM) for lake ecosystem health assessment is proposed in this paper. The EMM's procedures are: (1) to analyze the ecosystem structure of a lake in order to determine the structure and complexity of the lake's ecological model; (2) to develop a model having ecological health indicators, by designing a conceptual diagram, establishing model equations, estimating model parameters and being integrated with ecological indicators; (3) to compare the simulated and observed values of important state variables and process rates (i.e. model calibration) in order to evaluate the applicability of the model to lake ecosystem health assessment; (4) to calculate ecosystem health indicators based on the developed model; and (5) to assess lake ecosystem health according to the values of the ecosystem health indicators. The EMM was applied, as a case study, to the ecosystem health assessment of a eutrophic Chinese lake (Lake Chao) between April 1987 and March 1988. A relative order of health states from poor to good was determined as follows: August–October 1987 > April–May 1987 > June–July 1987 > November–December 1987 > January–March 1988. These results compared quite favourably with the actual current conditions at Lake Chao. The EMM method, therefore, was suitable in assessing lake ecosystem health at Lake Chao.     

Ecological thresholds: Concept,Methods and research outlooks

The concept of ecological thresholds was raised in the 1970s. However, it was subsequently given different definitions and interpretations depending on research fields or disciplines. For most scientists, ecological thresholds refer to the points or zones that link abrupt changes between alternative stable states of an ecosystem. The measurement and quantification of ecological thresholds have great theoretical and practical significance in ecological research for clarifying the structure and function of ecosystems, for planning sustainable development modes, and for delimiting ecological red lines in managing the ecosystems of a region. By reviewing the existing concepts and classifications of ecological thresholds, we propose a new concept and definition at two different levels: the ecological threshold points, i.e. the turning points of quantitative changes to qualitative changes, which can be considered as ecological red lines; the ecological threshold zones, i.e. the regime shifts of the quantitative changes among different stable states, which can be considered as the yellow and/or orange warning boundaries of the gradual ecological changes. The yellow thresholds mean that an ecosystem can return to a stable state by its self-adjustment, the orange thresholds indicate that the ecosystem will stay in the equilibrium state after interference factors being removed, whereas the red thresholds, as the critical threshold points, indicate that the ecosystem will undergo irreversible degradation or even collapse beyond those points. We also summarizes two types of popular Methods in determining ecological thresholds: statistical analysis and modeling based on data of field observations. The applications of ecological thresholds in ecosystem service, biodiversity conservation and ecosystem management research are also reviewed. Future research on ecological thresholds should focus on the following aspects: (1) methodological development for measurement and quantification of ecological thresholds; (2) emphasizing the scaling effect of ecological thresholds and establishment of national-scale observation system and network; and (3) implementation of ecological thresholds as early warning tools in ecosystem management and delimiting ecological red lines.     

Ecosystem water fluxes for two grasslands in elevated CO2: a modeling analysis

The need to combine data from CO₂ field experiments with climate data remains urgent, particularly because each CO₂ experiment cannot run for decades to centuries. Furthermore, predictions for a given biome need to take into account differences in productivity and leaf area index (LAI) independent of CO₂-derived changes. In this study, we use long-term weather records and field data from the Jasper Ridge CO₂ experiment in Palo Alto, California, to model the effects of CO₂ and climate variability on ecosystem water fluxes. The sandstone and serpentine grasslands at Jasper Ridge provide a range of primary productivity and LAI, with the sandstone as the more productive system. Modeled soil water availability agreed well with published observations of time-domain reflectometry in the CO₂ experiment. Simulated water fluxes based on 10-year weather data (January 1985–December 1994) showed that the sandstone grassland had a much greater proportion of water movement through plants than did the serpentine; transpiration accounted for approximately 30% of annual fluxes in the sandstone and only 10% in the serpentine. Although simulated physiological and biomass changes were similar in both grasslands, the consequences of elevated CO₂ were greater for the sandstone water budget. Elevated CO₂ increased soil drainage by 20% in the sandstone, despite an approximately one-fifth increase in plant biomass; in the serpentine, drainage increased by <10% and soil evaporation was unchanged for the same simulated biomass change. Phenological changes, simulated by a 15-day lengthening of the growing season, had minimal impacts on the water budget. Annual variation in the timing and amount of rainfall was important for water fluxes in both grasslands. Elevated CO₂ increased sandstone drainage >50 mm in seven of ten years, but the relative increase in drainage varied from 10% to 300% depending on the year. Early-season transpiration in the sandstone decreased between 26% and 41%, with elevated CO₂ resulting in a simulated water savings of 54–76 mm. Even in years when precipitation was similar (e.g., 505 and 479 mm in years 3 and 4), the effect of CO₂ varied dramatically. The response of grassland water budgets to CO₂ depends on the productivity and structure of the grassland, the amount and timing of rainfall, and CO₂-induced changes in physiology. In systems with low LAI, large physiological changes may not necessarily alter total ecosystem water budgets dramatically. Received: 11 March 1997 / Accepted: 23 September 1997     

基于地面调查的植被生态质量综合评估指标体系构建

植被是陆地生态系统的主体,是保障生态质量的基础,也是基于自然的生态系统增汇、实现“碳中和”的重要利器。植被是生态质量评价的核心要素,但目前的生态质量评价研究中所用到的植被指标多是通过遥感反演或者气象指数模型计算得到的,而基于典型生态系统尺度地面调查的植被观测数据更直接、更准确,数据也很丰富,却很少用于生态质量评价,也缺乏系统的评价指标体系。通过文献研究、专家研讨和问卷调查,并借鉴群落退化演替和生态系统长期监测研究的理论基础,构建基于地面调查的植被生态质量综合评估指标体系。该指标体系整体分为三级,一级综合指数由群落结构指数、物质生产指数、生物多样性指数、群落发展或者演替趋势4个二级分项指标构成,二级分项指标由12—14个三级指标组成,不同植被类型各有其特征指标。该体系将完善我国多尺度陆地生态系统的生态质量评价指标体系,为新时期国家生态质量评价提供科学建议,为我国生态文明建设提供技术支撑。     

Scaling nitrogen and carbon interactions: what are the consequences of biological buffering?

Understanding the consequences of elevated CO₂ (eCO₂; 800 ppm) on terrestrial ecosystems is a central theme in global change biology, but relatively little is known about how altered plant C and N metabolism influences higher levels of biological organization. Here, we investigate the consequences of C and N interactions by genetically modifying the N-assimilation pathway in Arabidopsis and initiating growth chamber and mesocosm competition studies at current CO₂ (cCO₂; 400 ppm) and eCO₂ over multiple generations. Using a suite of ecological, physiological, and molecular genomic tools, we show that a single-gene mutant of a key enzyme (nia2) elicited a highly orchestrated buffering response starting with a fivefold increase in the expression of a gene paralog (nia1) and a 63% increase in the expression of gene network module enriched for N-assimilation genes. The genetic perturbation reduced amino acids, protein, and TCA-cycle intermediate concentrations in the nia2 mutant compared to the wild-type, while eCO₂ mainly increased carbohydrate concentrations. The mutant had reduced net photosynthetic rates due to a 27% decrease in carboxylation capacity and an 18% decrease in electron transport rates. The expression of these buffering mechanisms resulted in a penalty that negatively correlated with fitness and population dynamics yet showed only minor alterations in our estimates of population function, including total per unit area biomass, ground cover, and leaf area index. This study provides insight into the consequences of buffering mechanisms that occur post-genetic perturbations in the N pathway and the associated outcomes these buffering systems have on plant populations relative to eCO₂.     

基于生态系统服务和农户福祉的生态补偿效果评估研究进展

生态补偿是以经济手段为主调节相关者利益关系的制度安排,最终实现区域生态系统服务和居民福祉"双赢"。尽管我国在生态补偿效果评估方面已开展了大量的研究,但更多关注的是生态系统服务功能的提升,忽略了生态补偿对社区居民福祉的影响及其反馈关系,影响了生态补偿政策的成效和可持续性。围绕生态补偿效果评估中涉及到的主要内容和关键的科学问题,对相关研究进行了归纳总结,认为:生态补偿、农户福祉、生态系统服务三者之间的耦合关系是生态补偿效果评估研究的重要科学问题;生态系统服务、农户生计、成本效益是评估生态补偿效果的3个核心指标;综合自然、人文两个因素统一的生态补偿评估与调控模型与方法体系,是亟待研究探索的重要方向。     

流域生态空间与生态保护红线规划方法——以长江流域为例

生态空间是指以提供生态系统服务为主要目标的地域范围,确定生态空间范围是协调保护与发展、保障生态服务持续供给的基础。长江流域是中华民族的摇篮与中国文化发祥地之一,是中国经济发展的重要增长极,以及具有全球意义的生物多样性热点区。以长江流域为对象,探讨面向流域生态空间规划的方法与管理对策。研究中,选择生态系统服务指标(水源涵养、洪水调蓄、水质净化、水土保持和生物多样性维护)和生态敏感性指标(水土流失、石漠化和土地沙化),基于流域水文路径分析和与其关联的生态系统服务的受益人口,提出一种流域尺度的生态空间规划方法。研究结果显示,长江流域生态空间面积为102.25万km^2,占长江流域总面积的57.42%,森林占52.87%,灌丛占19.51%,草地占18.96%,湿地占4.26%,保护了79.47%的水源涵养功能,86.99%的洪水调蓄功能,78.09%的水质净化功能,80.60%的水土保持功能,以及86.49%的自然栖息地。在生态空间规划的基础上,进一步探讨了长江流域生态保护红线的格局,现阶段生态保护红线面积为59.25万km^2,占长江流域总面积的33.27%,其中上游占比59.24%,中游和下游分别占比38.05%和2.71%。本文提出的规划方法与研究结果,不仅可以为长江流域生态空间规划、保障流域生态安全和促进流域经济社会可持续发展提供依据,还可以为其他流域的生态空间的规划提供参考。     

Global Patterns in Ecological Indicators of Marine Food Webs: A Modelling Approach

Background

Ecological attributes estimated from food web models have the potential to be indicators of good environmental status given their capabilities to describe redundancy, food web changes, and sensitivity to fishing. They can be used as a baseline to show how they might be modified in the future with human impacts such as climate change, acidification, eutrophication, or overfishing.

Methodology

In this study ecological network analysis indicators of 105 marine food web models were tested for variation with traits such as ecosystem type, latitude, ocean basin, depth, size, time period, and exploitation state, whilst also considering structural properties of the models such as number of linkages, number of living functional groups or total number of functional groups as covariate factors.

Principal findings

Eight indicators were robust to model construction: relative ascendency; relative overhead; redundancy; total systems throughput (TST); primary production/TST; consumption/TST; export/TST; and total biomass of the community. Large-scale differences were seen in the ecosystems of the Atlantic and Pacific Oceans, with the Western Atlantic being more complex with an increased ability to mitigate impacts, while the Eastern Atlantic showed lower internal complexity. In addition, the Eastern Pacific was less organised than the Eastern Atlantic although both of these systems had increased primary production as eastern boundary current systems. Differences by ecosystem type highlighted coral reefs as having the largest energy flow and total biomass per unit of surface, while lagoons, estuaries, and bays had lower transfer efficiencies and higher recycling. These differences prevailed over time, although some traits changed with fishing intensity. Keystone groups were mainly higher trophic level species with mostly top-down effects, while structural/dominant groups were mainly lower trophic level groups (benthic primary producers such as seagrass and macroalgae, and invertebrates). Keystone groups were prevalent in estuarine or small/shallow systems, and in systems with reduced fishing pressure. Changes to the abundance of key functional groups might have significant implications for the functioning of ecosystems and should be avoided through management.

Conclusion/significance

Our results provide additional understanding of patterns of structural and functional indicators in different ecosystems. Ecosystem traits such as type, size, depth, and location need to be accounted for when setting reference levels as these affect absolute values of ecological indicators. Therefore, establishing absolute reference values for ecosystem indicators may not be suitable to the ecosystem-based, precautionary approach. Reference levels for ecosystem indicators should be developed for individual ecosystems or ecosystems with the same typologies (similar location, ecosystem type, etc.) and not benchmarked against all other ecosystems.