Quantifying keystone species complexes: Ecosystem-based conservation management in the King George Island (Antarctic Peninsula)

A keystone species complex (KSC) is a small set of interacting species that play an outstandingly important role in community organization. Two KSC indices are suggested and have been calculated in the coastal benthic/pelagic ecosystem of Fildes Bay, King George Island (Antarctica). These indices of keystoneness emerge after considering: (1) functional indices based on steady-state and dynamic quantitative trophic models (using bottom-up, mixed and top-down control flow mechanisms); (2) structural indices including bottom-up and top-down control mechanisms, (3) semi-quantitative (qualitative) keystone indices using loop analysis (under mixed control); and (4) topological key player indices based on the centrality of node sets in the network. The models constructed and analyzed describe the interactions of the most abundant species and functional groups inhabiting the coastal ecological systems of Fildes Bay. Although our results only represent the transient dynamics of these ecological systems, the KSC indices identified the following trophically connected common core of components: the functional groups of Seastars (top-predators), the herbivorous sea urchin species Sterechinus neumayeri and the Phytoplankton (primary producers). The KSC indices for Fildes Bay could facilitate the design and assessment of conservation monitoring, especially when the Antarctic ecosystems are being severely stressed by the direct effects of global warming and UV radiation. A more holistic view of conservation remains difficult because the traditional view is based principally on single species. This imposes an even greater challenge, for global changes accompany the network of interacting species, co-varying with the variables of the natural system.     

Assessment of long-term changes of ecosystem indexes in Tongoy Bay (SE Pacific coast): Based on trophic network analysis

Quantitative macroscopic's indexes have been used to compare three trophic models of the exploited benthic ecosystem of Tongoy Bay. In this system the primary productivity and benthic invertebrates are more important in the cycling of biomass. The models were built with a similar number of compartments for the years 1992, 2002 and 2012, using Ecopath with Ecosim (EwE). Odum and Ulanowicz's frameworks and ecological network analysis were then used to estimate the levels of maturity, growth and development of the system. Likewise, “keystoneness” indexes – at each time – were also estimated for the models. Our results show that Tongoy Bay exhibited an increase in maturity and development (“health”) in 2012 compared to past conditions, which was reflected by (1) an increase in the total system biomass, total system throughput, AMI, and absolute Ascendency, (2) higher flow and increased efficiency of transferred energy and its proportion at higher trophic levels, (3) an increase of recycling (FCI), (4) a reduction of NPP/R and NPP/B ratios of the system, and (5) an increase in the number of compartments trophically linked that comprise the keystone species complex. We argue that these results are a consequence of reduced fishing pressure on this benthic system in recent years. This study shows that the fishing would not only have a direct impact on exploited species, but would also affect the structure and functioning of the ecosystem. The information obtained could help to improve the management of fisheries resources, evaluating surveillance indicators that can show the putative changes of intervened ecosystems.     

Evaluating ecosystem structure and functioning of the East China Sea Shelf ecosystem,China

As China’s second-largest large marine ecosystem, the East China Sea Shelf has suffered from overfishing, eutrophication, and physical disturbance over the last several decades. A trophic mass-balance model of this ecosystem was developed in order to characterize the structure and functioning of its food web, to identify its keystone species, and to quantify the ecological impacts of fishing that it sustained during the early 2000s. Using a multivariate statistical analysis, we identified 38 functional groups for the trophic model, including fish and invertebrate groups targeted and not targeted by fisheries. Pelagic sharks and rays were identified as the keystone species in the ecosystem. Strong benthic–pelagic coupling was indicated in this ecosystem. In particular, this study highlighted the interdependent relationships that exist among plankton, benthic invertebrates, and detritus. Recent fishing activities were characterized by high exploitation rates for various commercially targeted and non-targeted species, leading to the removal of much of the ecosystem’s fishable production. Overall, our findings give a preliminary explanation of the current problems of eutrophication and fishery depletion and other changes in the East China Sea Shelf, and highlight the need for developing ecosystem-based fisheries management.     

Macroscopic network properties and short-term dynamic simulations in coastal ecological systems at Fildes Bay (King George Island,Antarctica)

A trophic mass-balanced of the benthic/pelagic system dominated by large brown macroalgae in Fildes Bay (Antarctica) was constructed by integrating biomass, production, food spectrum, and consumption related information. The resulting trophic model was used to determine the macroscopic (emergent) properties, overall health and propagation of dynamical higher order effects within this complex Antarctic ecological system in response to simulated impacts. The magnitude of the Relative Ascendency, Relative Overhead, and Redundancy values indicates that the coastal benthic/pelagic Fildes Bay system is likely to remain less developed and therefore more resistant to perturbations than other ecological systems dominated by brown macroalgae. In terms of model component contributions to the Ascendency, detritus accounted for ∼33% of the value, followed by the phyto-zooplankton complex (∼26%), macroalgae (∼19%), filter-feeders (∼7%), small epifauna (5%), and top predators (2%). Short-term or transient Ecosim dynamical responses to increase the total mortality of each model component-given mixed and top-down vulnerabilities-revealed that changes in macroalgae levels had a limited impact on the other components of the system. The filter feeder, small epifauna and benthic fishés functional groups had the greatest effects on the remaining Fildes Bay system components. The magnitude of the System Recovery Time indicated that the Nacella concinna and small epifauna components would take the longest time to return to their initial state. Based on the outcomes obtained from the model, we suggest that this preliminary trophic model, including simulated impacts, provides promising possibilities for the determination of macroscopic baseline conditions and the most sensitive components of the Fildes Bay ecological system.     

海州湾5种关键饵料生物的主要捕食者及其捕食压力

为了解海州湾关键饵料生物在食物网中的被捕食压力及自然死亡率波动情况,研究基于2011和2013—2020年在海州湾及其邻近海域进行的渔业资源底拖网调查资料和胃含物分析数据,以物种间的营养联系为基础,选择细螯虾(Leptochela gracilis)、日本鼓虾(Alpheus japonicus)、枪乌贼(Loligo sp.)、小黄鱼(Larimichthys polyactis)和口虾蛄(Oratosquilla oratoria)5种关键饵料生物为研究对象,通过计算捕食压力指数(Predation pressure index, PPI),分析它们在海州湾食物网中的主要捕食者及其捕食压力,并计算了纳入捕食压力指数的自然死亡系数。结果表明,细螯虾的捕食者对其年平均捕食压力指数最高,小黄鱼的捕食者对其年平均捕食压力指数最低。小眼绿鳍鱼(Chelidonichthys kumu)对细螯虾和枪乌贼的年平均捕食压力指数最高,分别为168.89和75.77;(Miichthys miiuy)对日本鼓虾和口虾蛄的年平均捕食压力指数最高,分别为39.41和9.85;海鳗(Muraenesox c...     

Development of an Index of Trophic Completeness for benthic macroinvertebrate communities in flowing waters

The analysis of the trophic structure of benthic macroinvertebrate communities can be used in biological assessments of the condition of river ecosystems. Using the trophic, or functional approach, the Index of Trophic Completeness (ITC) was developed. The goal was to overcome the problems and drawbacks of using conventional diversity or biotic indices in biological assessments of rivers, such as limitation to distinct geographical regions or focus on species richness without regard for ecosystem functioning. Following an extensive review of the literature on the trophic characteristics of benthic macroinvertebrates, a large number of species (±300) were characterized according to a number of trophic criteria: plant:animal ratio in the diet, feeding mechanism, food size, food acquisition behaviour, and energy and substance transfers. On the basis of their trophic characteristics, the species could be divided into 12 trophic groups. After examination of data from geographically diverse rivers, it was concluded that any undisturbed riverine benthic macroinvertebrate community should be represented by members of each of these 12 trophic groups, with each group fulfilling a function in the benthic community. Being a community which plays a central role in the functioning of the aquatic ecosystem, the benthic invertebrates are expected to respond to disturbances to the hydrobiocoenose. The outcome of an ITC assessment is clearly presentable in the form of a pie graph with 12 wedges, each representing one of the 12 defined trophic groups. Functionally complete communities are represented by 12 wedges; a blank wedge indicates that a trophic group is not represented. This paper describes the preliminary developments in the ITC method, its potential as a biological assessment method in rivers in different geographical zones, and presents examples of trial mappings of Russian and European rivers. The application of the ITC to these rivers demonstrated the absence of ITC trophic groups at sites under the influence of anthropogenic activity.     

Spatio-temporal dynamics of multi-trophic communities reveal ecosystem-wide functional reorganization

Large-scale alterations in marine ecosystems as a response to environmental and anthropogenic pressures have been documented worldwide. Yet, these are primarily investigated by assessing abundance fluctuations of a few dominant species, which inadequately reflect ecosystem-wide changes. In addition, it is increasingly recognized that it is not species identity per se, but their traits that determine environmental responses, biological interactions and ecosystem functioning. In this study, we investigated long-term, spatio-temporal variability in trait composition across multiple organism groups to assess whether functional changes occur in a similar way across trophic levels and whether shifts in trait composition link to environmental change. We combined extensive trait datasets with long-term surveys (30–40 yr) of four organism groups (phytoplankton, zooplankton, benthic invertebrates and fish) in three environmentally distinct areas of a large marine ecosystem. We found similar temporal trajectories in the community weighted mean trait time-series of the different trophic groups, revealing ecosystem-wide functional changes. The traits involved and their dynamics differed between areas, concurrent with climate-driven changes in temperature and salinity, as well as more local dynamics in nutrients and oxygen. This finding highlights the importance of considering both global climate, as well as local external drivers when studying ecosystem changes. Using a multi-trophic trait-based approach, our study demonstrates the importance of integrating community functional dynamics across multiple trophic levels to capture ecosystem-wide responses which could, ultimately, help moving towards a holistic understanding, assessment and management of marine ecosystems.     

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.     

基于Ecopath模型的莱州湾中国对虾增殖生态容量

通过增殖放流,增加优质渔业资源、改善种群结构是渔业资源养护的重要手段,而增殖生态容量的研究是科学实施增殖放流的前提.本文根据2009-2010年的渔业资源与生态环境数据,构建了由26个功能群组成的莱州湾生态系统Ecopath模型,利用该模型分析了生态系统的总体特征、营养相互关系与关键种,计算了放流品种中国对虾的增殖生态容量.结果表明：系统的总初级生产量/总呼吸(TPP/TR)为1.53,总初级生产量/总生物量(TPP/B)为24.54,同时具有较低的循环指数(FCI=0.07)、较高的剩余生产量（434.41 t·km^-2·a^-1）和较低的系统连接指数(CI=0.29),该系统目前处于发育的早期阶段.中国对虾目前不是莱州湾生态系统的关键种,当前中国对虾的生物量为0.1143 t·km^-2,有较大的增殖潜力;当生物量增长25.8倍时,仍不会超过增殖生态容量2.9489 t·km^-2.     

山东半岛南部海湾底栖动物群落生态特征及其与水环境的关系

2006-2007年对山东半岛南部4个海湾(荣成湾、桑沟湾、靖海湾和五垒岛湾)19个站位的底栖动物群落结构特征进行了研究,并对14个环境因素和底栖动物群落生态特征分别进行主成分分析和Spearman相关分析。结果显示,荣成湾、桑沟湾和靖海湾的底栖动物种类中,多毛类所占比例最高,而五垒岛湾仅秋、冬季多毛类所占比例最高。根据聚类分析和非度量多维标度方法分析,4季底栖动物群落均可分为2个群落,春、冬季的第一聚群为靖海湾和五垒岛湾,第二聚群为荣成湾和桑沟湾。秋季荣成湾、桑沟湾、靖海湾组成第一聚群,第二聚群由五垒岛湾构成。夏季,底栖动物Shannon-Wiener多样性指数(H')与采样深度和总碱度呈显著正相关,与水温呈极显著的负相关关系。秋季,与硝酸盐呈负相关关系,说明富营养化对山东半岛南部4个海湾大型底栖动物群落产生了一定负面影响。ABC曲线法分析显示,荣成湾和桑沟湾底栖动物的丰度优势度曲线与生物量优势度曲线相交,表明荣成湾和桑沟湾大型底栖动物群落处于中度干扰状态,密集的养殖活动可能对其生态系统带来了巨大影响,加强海水养殖管理,强化生态健康养殖理念,合理利用海洋生物资源,对大型底栖动物群落的稳定性具有重要意义。     

基于Ecopath模型的崂山湾人工鱼礁区生态系统结构和功能研究

基于2014—2016年青岛崂山湾人工鱼礁区的生物资源调查数据,利用Ecopath with Ecosim(EwE)软件构建崂山湾人工鱼礁区生态系统生态通道模型(Ecopath),系统分析了崂山湾人工鱼礁区生态系统的能量流动规律和结构特征,估算了栉孔扇贝的养殖容量。该模型由17个功能组组成,基本涵盖了崂山湾人工鱼礁区生态系统能量流动的主要过程。生态网络分析表明,生态系统各功能组的营养级范围为1.0—4.255,星康吉鳗占据了营养级的最高层。能量流动主要有5级,各营养级平均能量传递效率为10.8%,其中来自初级生产者的能量效率为9.8%,来自碎屑的传递效率为10.9%;系统总流量为14256.510 t km~(-2) a~(-1),其中68%的能量来自碎屑供给;系统的总初级生产量/总呼吸量为1.127,系统联结指数为0.293,杂食指数为0.333,表明崂山湾人工鱼礁区生态系统成熟度较高,食物网结构较复杂,系统内部稳定性较高。关键种指数分析结果显示,许氏平鲉具有较高的关键指数和相对总影响,表明其可能在当前生态系统中扮演重要的生态角色。吊笼养殖栉孔扇贝生态容纳量为189.679 t/km~2,在维持生态系统平衡和稳定的前提下,当前现存量最大可增加18.55%。     

基于SURF指数识别海州湾食物网的关键饵料生物

关键种(keystone species)在生态系统中发挥着不可替代的重要作用,对于群落结构的稳定与演替起着决定性的作用。基于2011年3—12月在海州湾及其邻近海域进行的渔业资源底拖网调查资料以及胃含物分析数据和参考历史文献数据,以物种间的摄食关系作为基础,采用SURF(Supportive Role to Fishery ecosystems)指数识别海州湾食物网中的关键饵料生物。在矩阵中分析每个物种作为饵料生物为捕食者提供的摄食比例及捕食者数量,计算每个物种的关键指标(SURFi)的值,结果表明前五位数值较高的物种是细鳌虾(Leptochela gracilis)、毛虾(Acetessp.)、疣背宽额虾(Latreutes planirostris)、日本鼓虾(Alpheus japonicus)和鳀鱼(Engraulis japonicus),它们是海州湾的关键饵料生物,在整个食物网中起到关键的控制作用,它们的数量波动会对海州湾其他物种产生直接或间接的影响。加强关键饵料生物的保护,对于维持海州湾生态系统的健康和稳定至关重要。     

Species–area relationship within benthic habitat patches of a tropical floodplain river: An experimental test

The curvilinear relationship between species richness and habitat area (species–area relationship (SAR)) is a fundamental ecological pattern. The relationship is often viewed from a long‐term perspective across relatively large spatial scales, reflecting a balance between immigration and extinction dynamics. We explored whether predictions of SAR also manifest over short time periods (days) in benthic habitat patches of a dynamic floodplain river where littoral faunal assemblages are continuously assembled and disassembled with changing water levels. We examined the relationship of patch size with faunal abundance (i.e. fish and aquatic invertebrates), taxonomic richness, trophic group richness and overall assemblage composition. Strong taxa–area relationships emerged despite the relatively short experimental time period (21 days); larger patches had more taxa and trophic groups. For the smallest patches, taxonomic richness was especially sensitive to abundance of individuals; abundance of individuals was a less important predictor of taxonomic and trophic group richness for the largest patches. Despite the relatively short time frame for study within this temporally dynamic ecosystem, our findings indicate a strong SAR for fishes and macroinvertebrates inhabiting patchy habitats in the littoral zone of this tropical river.     

A review of the biology,ecology, behavior and conservation status of the dusky grouper, <Emphasis Type="Italic">Epinephelus marginatus</Emphasis> (Lowe 1834)

The dusky grouper is a large-bodied marine species usually associated with rocky substrates and reefs currently experiencing increasing anthropogenic pressures. Here, we critically evaluate studies conducted during the last few decades on this endangered species, focusing on its biology, ecology, behavior, stock structure and fisheries, and identify future research directions to fill current knowledge gaps. This species plays an important functional role in the rocky bottom habitats in which it lives, usually occupying the highest trophic levels and with the potential role as a keystone species in some ecosystems. It has a complex life cycle characterized by a high longevity, a slow growth rate and a monandric protogynous hermaphroditic mode of reproduction. The species also exhibits spawning aggregation behavior, which makes it more vulnerable to fishing activity. Aside from its ecological importance, this species has high commercial value for professional fishers and is also highly prized by recreational spearfishers. These biological features, associated with increasing fishing pressures throughout most of its geographical distribution, have led to Epinephelus marginatus being included since 2004 in the IUCN Red List of Threatened Species as Endangered. Despite a large amount of research being conducted on this species over the last five decades or so, using a number of different tools and techniques, key questions regarding its biology still remain unanswered. In terms of conservation and management plans designed to safeguard this endangered species, we identified the crucial need to improve fisheries landing statistics for the species and to increase the number of marine protected areas within its distribution beyond the Mediterranean Sea.     

海州湾鱼类群落功能多样性的时空变化

功能多样性是联系物种、生态环境和生态系统功能的基础.从功能多样性的角度研究群落结构,有助于更好地理解生物多样性与生态系统功能之间的关系.本研究根据2011—2017年(除2012年外)春、秋季海州湾渔业资源底拖网调查数据,选取反映鱼类摄食、运动、生态适应性、繁殖行为和种群动态特征的13个功能性状,利用功能丰富度指数、功能均匀度指数、功能离散度指数和群落特征加权平均数指数(CWM),研究了海州湾鱼类群落功能多样性的季节、年际和空间的变化.结果表明: 海州湾鱼类群落功能多样性指数具有显著的季节差异,其中秋季功能丰富度指数显著高于春季,春季功能离散度指数显著高于秋季,鱼类洄游是造成功能多样性指数季节变化的主要原因;CWM分析表明,春季鱼类群落优势种为营养级较高、运动能力较强、生长系数、恢复力和脆弱性较高的冷/暖温性鱼类,秋季则相反,春、秋季鱼类群落均以产浮性卵鱼类为主;鱼类群落功能多样性指数呈现一定的年际变化,其中春、秋季各功能多样性指数在不同年际均呈波动趋势,表明海州湾鱼类群落稳定性较低;鱼类群落功能多样性指数呈现显著的空间差异,其中20 m以深远岸水域功能离散度指数较高.海州湾鱼类群落功能多样性具有明显的时空变化特征,鱼类生态位与其对资源的利用均随季节、年际和空间而变化.     

海南岛霸王岭热带天然林景观中主要木本植物关键种的潜在分布

在较大的空间尺度上生态位模型是预测物种潜在分布的有效途径之一。为了探讨在热带天然林景观中木本植物(限于乔木和灌木)主要关键种的潜在分布,在对海南岛霸王岭的热带天然林进行按公里网格样方调查的基础上,采用演替地位和最大潜在高度两个功能性指标对物种进行了功能群划分,并在功能群框架下运用优势度指数法进行了关键种的确定;采用基于地理信息系统(Geographic information system, GIS)的基于规则集合预测的遗传算法(Algorithm for rule-set prediction, GARP)生态位模型对主要关键种的地理分布进行了预测,并应用受试者工作特征分析进行了模型精度验证;应用多元线性回归分析对影响各关键种潜在分布的关键因子进行了确定。结果表明:除了顶极次林层乔木功能群和顶极主林层乔木功能群外,在先锋种功能群、顶极灌木种功能群和顶极超冠层乔木功能群中采用优势度指数法划分出的关键种较为理想;一般来讲,在进行预测的8个关键种中,除了先锋主林层乔木种海南杨桐(Adinandra hainanensis),其它3个先锋种毛稔(Melastoma sanquiueum)、银柴(Aporosa chinensis)和枫香(Liquidambar formosana) 在研究区北部、西部以及西南部均具有较高的发生概率,而顶极种除了顶极超冠层乔木种南亚松(Pinus merkusii)外,九节(Psychotria rubra)、高脚罗伞(Ardisia quinquegona)和海南椎(Castanopsis hainanensis)具有相似的潜在分布格局,在研究区中部、东南部和南部地区具有较高的发生概率;相关分析表明极端最低温、年均温、极端最高温、年均降水量、海拔和坡向6大因子是影响研究区关键种潜在分布的关键因子;精度检验表明,GARP模型对8个关键种的潜在分布预测效果均较好,而其中又以银柴和海南椎的预测精度最高。     

红树林植被对大型底栖动物群落的影响

大型底栖动物是红树林生态系统的重要组成部分,从红树林大型底栖动物种类、红树林与其周边生境大型底栖动物群落的比较,以及生境变化对动物群落的影响等方面阐述了红树林植被与大型底栖动物群落的关系.从物种数量上看,软体动物和甲壳类动物构成了红树林大型底栖动物的主要部分.影响大型底栖动物分布的环境因素包括海水盐度、潮位和土壤特性等,但在小范围区域,林内动物的分布更多地与红树林植被特性和潮位有关.因此,由于红树林植被破坏或者恢复引起的生境变化,将导致大型底栖动物群落和常见物种种群的变化,尤其对底上动物影响明显;随着人工恢复红树林的发育,林内底栖动物的多样性相应增加,优势种也发生变化.相比位于相同潮位的无植被滩涂,红树林可促进潮间带生物多样性.     

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.     

Feeding repellence of Antarctic and sub-Antarctic benthic invertebrates against the omnivorous sea star Odontaster validus

Antarctic and sub-Antarctic benthic invertebrates are subjected to intense predation by mobile macroinvertebrates. Accordingly, chemical protection as well as other defensive mechanisms are expected to be common in organisms inhabiting these ecosystems. In order to evaluate anti-predation activities and allocation of chemical defenses within the anatomy of marine benthic Antarctic and sub-Antarctic invertebrates, 55 species were tested for feeding repellence against the sea star Odontaster validus, a common eurybathic sympatric predator. The invertebrates tested were collected from the deep waters of two poorly surveyed areas in terms of chemical ecology studies: the eastern Weddell Sea (Antarctica) and the vicinities of Bouvet Island (sub-Antarctica). Experiments were conducted at the Spanish Antarctic Base in Deception Island. In the feeding deterrence experiments, shrimp pieces were treated with crude lipophilic fractions obtained from each species, and were offered to the sea stars. A total of 29 species (53 %) from 7 different phyla (Porifera, Cnidaria, Chordata, Bryozoa, Echinodermata, Mollusca, and Annelida) showed feeding repellence against O. validus, and are therefore chemically protected against this keystone predator. Furthermore, 25 species were dissected into parts to investigate the possible allocation of defensive compounds. Some of the results obtained from these analyses support the prediction that the most exposed/vulnerable tissues concentrate chemical defenses to avoid predation against the sea stars. In summary, the results obtained in our survey support the hypothesis that deep-water Antarctic and sub-Antarctic benthic invertebrates are well protected chemically against sympatric predators, similarly to what has been reported in previous studies investigating shallow-water Antarctic species.     

Lack of Congruence in Species Diversity Indices and Community Structures of Planktonic Groups Based on Local Environmental Factors

The importance of analyzing the determinants of biodiversity and community composition by using multiple trophic levels is well recognized; however, relevant data are lacking. In the present study, we investigated variations in species diversity indices and community structures of the plankton taxonomic groups–zooplankton, rotifers, ciliates, and phytoplankton–under a range of local environmental factors in pond ecosystems. For each planktonic group, we estimated the species diversity index by using linear models and analyzed the community structure by using canonical correspondence analysis. We showed that the species diversity indices and community structures varied among the planktonic groups and according to local environmental factors. The observed lack of congruence among the planktonic groups may have been caused by niche competition between groups with similar trophic guilds or by weak trophic interactions. Our findings highlight the difficulty of predicting total biodiversity within a system, based upon a single taxonomic group. Thus, to conserve the biodiversity of an ecosystem, it is crucial to consider variations in species diversity indices and community structures of different taxonomic groups, under a range of local conditions.