How do ecologists select and use indicator species to monitor ecological change? Insights from 14 years of publication in Ecological Indicators

Indicator species (IS) are used to monitor environmental changes, assess the efficacy of management, and provide warning signals for impending ecological shifts. Though widely adopted in recent years by ecologists, conservation biologists, and environmental practitioners, the use of IS has been criticized for several reasons, notably the lack of justification behind the choice of any given indicator. In this review, we assess how ecologists have selected, used, and evaluated the performance of the indicator species. We reviewed all articles published in Ecological Indicators (EI) between January 2001 and December 2014, focusing on the number of indicators used (one or more); common taxa employed; terminology, application, and rationale behind selection criteria; and performance assessment methods. Over the last 14 years, 1914 scientific papers were published in EI, describing studies conducted in 53 countries on six continents; of these, 817 (43%) used biological organisms as indicators. Terms used to describe organisms in IS research included “ecological index”, “environmental index”, “indicator species”, “bioindicator”, and “biomonitor,” but these and other terms often were not clearly defined. Twenty percent of IS publications used only a single species as an indicator; the remainder used groups of species as indicators. Nearly 50% of the taxa used as indicators were animals, 70% of which were invertebrates. The most common applications behind the use of IS were to: monitor ecosystem or environmental health and integrity (42%); assess habitat restoration (18%); and assess effects of pollution and contamination (18%). Indicators were chosen most frequently based on previously cited research (40%), local abundance (5%), ecological significance and/or conservation status (13%), or a combination of two or more of these reasons (25%). Surprisingly, 17% of the reviewed papers cited no clear justification for their choice of indicator. The vast majority (99%) of publications used statistical methods to assess the performance of the selected indicators. This review not only improves our understanding of the current uses and applications of IS, but will also inform practitioners about how to better select and evaluate ecological indicators when conducting future IS research.     

Identifying functional species pool of planktonic protozoa for discriminating water quality status in marine ecosystems

It is cost-effective protocol to identify a functional species pool for marine bioassessment by removing redundant species from a raw dataset. The feasibility of functional species pool for discriminating water quality status was studied based on a dataset of 120 samples of ciliated protozoa. From the full 60-species dataset of the whole ciliate communities, a 35-species subset was identified as a functional species pool, the species number, abundance and biodiversity indices of which were significantly correlated with those of the full species dataset. The spatial pattern of the subset was significantly related to the changes in nutrients soluble reactive phosphates (SRP), nitrate/nitrite nitrogen (NO₃-N/NO₂-N) and ammonium nitrogen (NH₄-N). Four indices of the taxonomic diversity (Δ), taxonomic distinctness (Δ*), average in taxonomic distinctness (Δ⁺) and the variation in taxonomic distinctness (Λ⁺) based on this small species pool were significantly correlated with the changes of nutrients NO₃-N and/or (NH₄-N). The paired indices Δ⁺ and Λ⁺ showed a clear decreasing trend of departure from the expected taxonomic pattern. These findings suggest that the 35-species functional species subset may be used as a feasible functional surrogate of ciliated protozoan assemblages for community-based bioassessment in marine ecosystems.     

Environmental monitoring through functional biodiversity tools

The foundational concept for our research, which is largely shared by statisticians and ecologists, is that biodiversity is one of the most important indicators for environmental assessment. Because this indicator decreases in relation to ecosystem stressors, its measurement is essential for predicting future biological impacts of environmental damages. Although many indices have been proposed, no universally accepted measure for biodiversity has yet been established. In this context, the use of diversity profiles allows the analyst to display a family of indices in a single graph. However, this approach presents two critical limitations: first, a community composition is not always interpretable; second, the diversity profiles could lead to ranking issues when the curves intersect each other. The aim of this paper is to resolve these limitations by introducing functional biodiversity tools. In particular, three functional measures are proposed: the derivatives, the radius of curvature and the curve length. The analysis of derivatives and of the radius of curvature addresses the first limitation and highlights the characteristics, the differences and the similarities among communities. Arc length addresses the second limitation, providing a scalar measure that leads to a unique communities ranking for a given pattern of richness even if profiles intersect. The proposed functional models are applied to a real data set involving lichen biodiversity in the province of Genoa, Italy. Our approach allowed us to analyze the characteristics of lichen communities and to identify the biodiversity ranking. The combined use of these tools provides a useful method for identifying areas of high environmental risk, with the potential to address the monitoring of environmental policies.     

Comparison of boosted regression tree and random forest models for mapping topsoil organic carbon concentration in an alpine ecosystem

Soil organic carbon (SOC) plays an important role in soil fertility and carbon sequestration, and a better understanding of the spatial patterns of SOC is essential for soil resource management. In this study, we used boosted regression tree (BRT) and random forest (RF) models to map the distribution of topsoil organic carbon content at the northeastern edge of the Tibetan Plateau in China. A set of 105 soil samples and 12 environmental variables (including topography, climate and vegetation) were analyzed. The performance of the models was evaluated using a 10-fold cross-validation procedure. Maps of the mean values and standard deviations of SOC were generated to illustrate model variability and uncertainty. The results indicate that the BRT and RF models exhibited very similar performance and yielded similar predicted distributions of SOC. The two models explained approximately 70% of the total SOC variability. The BRT and RF models robustly predicted the SOC at low observed SOC values, whereas they underestimated high observed SOC values. This underestimation may have been caused by biased distributions of soil samples in the SOC space. Vegetation-related variables were assigned the highest importance in both models, followed by climate and topography. Both models produced spatial distribution maps of SOC that were closely related to vegetation cover. The SOC content predicted by the BRT model was clearly higher than that of the RF model in areas with greater vegetation cover because the contributions of vegetation-related variables in the two models (65% and 43%, respectively) differed significantly. The predicted SOC content increased from the northwestern to the southeastern part of the study area, average values produced by the BRT and RF models were 27.3 g kg⁻¹ and 26.6 g kg⁻¹, respectively. We conclude that the BRT and RF methods should be calibrated and compared to obtain the best prediction of SOC spatial distribution in similar regions. In addition, vegetation variables, including those obtained from remote sensing imagery, should be taken as the main environmental indicators and explicitly included when generating SOC maps in Alpine environments.     

The use of environmental DNA of fishes as an efficient method of determining habitat connectivity

This study demonstrated the use of environmental DNA (eDNA) to determine habitat connectivity for migration of fishes between the sea and river. Environmental DNA is DNA fragments released by fishes in water, which can be used as a species-specific marker of the presence/absence of the target species. A year-round water sampling regime at 15 sites on the Yodo River, Japan, was conducted to determine whether three major man-made barriers on the river inhibited the migration of fishes using species-specific detection of DNA fragments from three target migrant species, temperate seabass, Lateolabrax japonicus, flathead grey mullet, Mugil cephalus, and ayu, Plecoglossus altivelis altivelis. The presence/absence of eDNA from target species was consistent with known patterns of species’ seasonal migration. The detection of the DNA of temperate seabass and flathead grey mullet at sites upstream of the dam closest to the river mouth indicated successful upstream migration of these species via a fish ladder bypassing the dam. On the other hand, DNA of these two species was not detected from the upstream side of the two remaining dams, which are not equipped with fish ladders. Ayu is the only species among the three target species with a land-locked population in Lake Biwa located at the headwater of Yodo River. Ayu DNA was detected at most of the sites in the freshwater area during the warm months; however, in the coldest month of February, eDNA was only detected in the uppermost site of Yodo River at the southern tip of Lake Biwa. The eDNA we detected at this site suggests that it was derived from juvenile ayu spending their winter months in the lake. These results suggest that the eDNA analysis presented here can accurately track the seasonal migration of fishes in a river, demonstrating its application as an indicator of habitat connectivity for fishes in association with man-made barriers in a river. The sampling of eDNA involves merely scooping a tank full of water; therefore, it is a simple, rapid, and cost-effective method for long-term monitoring of habitat connectivity associated with the construction of barriers in a river.     

Prescribed moorland burning meets good practice guidelines: A monitoring case study using aerial photography in the Peak District,UK

Upland moors in the UK have been managed for centuries using rotational prescribed-burning, but in recent years there has been contentious debate over its continuing use due to varying effects on moorland ecosystem services. Prescribed-burning should only be carried out using good-practice codes, which include restrictions on the size, location and frequency of burns. Good burning practice is an indicator of management standards and habitat condition in moorland landscapes. However, there has been little attempt to assess management performance with respect to these restrictions. We investigated prescribed-burning on a case-study estate (Howden Moor) in the Peak District National Park from 1988 to 2009 using management maps and aerial photography. The annual area burned (0.9%) was far below recommendations (10%) and patches were in keeping with the target sizes specified (mean ± se: 2370 ± 70 m²). The risk of a large or escaped fire was very low, with less than 1% of fires greater than 15,000 m². However, only 28.9% of the total burnable area was burned, leaving the rest unmanaged and accumulating fuel. Future guidelines might recommend the application of prescribed-burning across the range of Calluna vulgaris growth phases, to reduce fuel load and promote biodiversity at the landscape scale. We show that vegetation mapping and aerial photography are an effective method for monitoring prescribed-burning practice on moorlands. The information derived from such monitoring studies should lead to greater confidence in the standard of prescribed-burning and adherence to good-practice guidelines and requirements imposed by statutory authorities.     

New trophic indicators and target values for an ecosystem-based management of fisheries

In the present study, we tested five trophic indicators and we demonstrated their usefulness to assess the environmental status of marine ecosystems and to implement an ecosystem approach to fisheries management (EAFM). The tested indicators include the slope of the biomass spectrum, the mean trophic level (MTL), the marine trophic index (MTI) and two newly developed indicators, the high trophic level indicator (HTI) and the apex predator indicator (API). Indicators are compared between current state and potential reference situations, using as case studies: the Celtic Sea/Bay of Biscay, North Sea and English Channel ecosystems. Trophic spectra are obtained from Ecopath models while reference situations are estimated, simulating with EcoTroph and Ecosim different fishing pressures including three candidate scenarios for an EAFM. Inter-ecosystems assessments are done using Ecopath models, simulations outputs and scientific surveys data to assess the current states of the studied ecosystems, contrast the reference situations and analyze the responses of all indicators. Sensitivity analyses are also conducted on the main simulation parameters to test the robustness of the chosen indicators. Ecosystems specific targets for EAFM are proposed for the five trophic indicators estimated from whole-ecosystem models, while in the Celtic Sea/Bay of Biscay ecosystem targets are proposed for the MTL (=3.85) and HTI (48%) estimated from standard bottom-trawl surveys. The HTI is proposed to be relevant for survey data and the API is recommended using whole-ecosystem models. We conclude that HTI and API show trends in ecosystems health better than MTI.     

Enhanced Immobilization of Cr(VI) in Soils by the Amendment of Rice Straw Char

This study investigated the effect of rice straw char (RSC) on the immobilization of Cr(VI) in soils. The Cr(VI) sorption experiments on the RSC and RSC-amended soils were conducted using the batch method. RSC exhibited Cr(VI) reduction capacity due to its black carbon content. The addition of RSC to the soils enhanced the overall Cr(VI) immobilization of the soils, which is primarily attributed to the Cr(VI) reduction capacity of RSC. The effects of RSC amendment on the Cr(VI) sorption of the soils increased with increasing RSC content in the soils and decreased with increasing pH or anion contents in the soil solutions. After Cr(VI) was sorbed by the soils, a portion of the Cr(VI) was converted to Cr(III) and the remainder was sorbed onto the soils. The presence of RSC in the soils decreased the portion of sorbed Cr(VI) in the soils and therefore lowered the potential remobilization of Cr(VI) from the soils. The results suggested that RSC amendment can be applied to develop a cost-effective method for immobilizing Cr(VI) in polluted soils, thus lowering the environmental risk from Cr(VI) toxicity.     

Identifying key factors,actors and relevant scales in landscape and conservation planning,management and decision making: Promoting effective citizen involvement

The paper analyses the current limitations of the constraints of decision and action processes in land-use, resource management and conservation policies and approaches, identifying their main factors, proposing alternative strategies to solve the present gaps and limitations. It identifies the need for a new paradigmatic approach based on innovative forms of involvement, commitment and individual and community rewarding systems. This approach is developed based on the characterization of the main drivers of land-use, resource management and conservation policies, namely α-perceptions (immediate and primary satisfaction) and k-perceptions (more mediate and complex consideration of satisfaction, implying long-term perceptions and collective benefits beyond the individual interests). It also analyses the effects of the introduction of new forms of income and incentives (such as trade-offs and payments for environmental services) or management approaches such as Ecological-Based Management or the use of Nature-Based Solutions. The main axioms and instruments necessary to build such a new paradigmatic approach (namely trade-offs, accountability and contractualization) are described. On this basis, it is possible to present a concept for an innovative institutional and social culture and a governance system aimed at an effective land-use, resource management and conservation policies. This governance concept is described and its sustaining individual, social and institutional drivers enunciated.     

Phragmites australis — a helophytic grass — can establish successful partnership with phenol-degrading bacteria in a floating treatment wetland

Helophytic plants contribute significantly in phytoremediation of a variety of pollutants due to their physiological or biochemical mechanisms. Phenol, which is reported to have negative/deleterious effects on plant metabolism at concentrations higher than 500 mg/L, remains hard to be removed from the environmental compartments using conventional phytoremediation procedures. The present study aims to investigate the feasibility of using P. australis (a helophytic grass) in combination with three bacterial strains namely Acinetobacter lwofii ACRH76, Bacillus cereus LORH97, and Pseudomonas sp. LCRH90, in a floating treatment wetland (FTW) for the removal of phenol from contaminated water. The strains were screened based on their phenol degrading and plant growth promoting activities. We found that inoculated bacteria were able to colonize in the roots and shoots of P. australis, suggesting their potential role in the successful removal of phenol from the contaminated water. Pseudomonas sp. LCRH90 dominated the bacterial community structure followed by A. lowfii ACRH76 and B. cereus LORH97. The removal rate was significantly high when compared with the individual partners, i.e., plants and bacteria separately. The plant biomass, which was drastically reduced in the presence of phenol, recovered significantly with the inoculation of bacterial consortia. Likewise, highest reduction in chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total organic carbon (TOC) is achieved when both plants and bacteria were employed. The study, therefore, suggests that P. australis in combination with efficient bacteria can be a suitable choice to FTWs for phenol-degradation in water.