Biological Assemblages Research Articles

Patterns of benthic mega-invertebrate habitat associations in the Pacific Northwest continental shelf waters

As human impacts and demands for ocean space increase (fisheries, aquaculture, marine reserves, renewable energy), identification of marine habitats hosting sensitive biological assemblages has become a priority. Epifaunal invertebrates, especially the structure-forming species, are an increasing conservation concern as many traditional (bottom-contact fishing) and novel (marine renewable energy) ocean uses have the potential to displace or otherwise impact these slow-growing organisms. The differences in mega-invertebrate species assemblages between high-relief rocks and low-relief sediments are well documented and likely hold for most marine environments. In anticipation of potential development of marine renewable energy faculties off Oregon and Washington (USA), a survey of the benthic invertebrate assemblages and habitats was conducted on the continental shelf of the Pacific Northwest, using video footage collected by ROV, to more finely characterize these assemblage–habitat associations. Four main associations were found: pure mud/sand dominated by sea whips and burrowing brittle stars; mixed mud–rock (which may be further divided based on size of mixed-in rocks) characterized by various taxa at small densities; consolidated rocks characterized by high diversity and density of sessile or motile mega-invertebrates; and rubble rocks showing less diversity and density than the consolidated rocks, possibly due to the disturbance generated by movement of the unconsolidated rocks. The results of this study will help classify and map the seafloor in a way that represents benthic habitats reflective of biological species assemblage distributions, rather than solely geological features, and support conservation and management planning.

Radiocarbon-dating and ancient DNA reveal rapid replacement of extinct prehistoric penguins

Prehistoric faunal extinctions dramatically reshaped biological assemblages around the world. However, the timing of such biotic shifts is often obscured by the fragmentary nature and limited temporal resolution of fossil records. We use radiocarbon-dating and ancient-DNA analysis of prehistoric (ca A.D. 1450–1834) Megadyptes penguin specimens to assess the time-frame of biological turnover in coastal New Zealand following human settlement. These data suggest that the final extirpation of the endemic Megadyptes waitaha, and subsequent replacement by the previously sub-Antarctic-limited Megadyptes antipodes, likely occurred within a narrow temporal window (e.g. a century or less). This transition represents one of the most rapid prehistoric faunal turnover events documented, and is likely linked to human demographic and cultural transitions during the 15th Century. Our results suggest that anthropogenic forces can trigger rapid biogeographic shifts.

Flood disturbance effects on benthic diatom assemblage structure in a semiarid river network

Disturbances such as floods and droughts play a central role in determining the structure of riverine benthic biological assemblages. Extreme disturbances from flash floods are often restricted to part of the river network and the magnitude of the flood disturbance may lessen as floods propagate downstream. The present study aimed to characterize the impact of summer monsoonal floods on the resistance and resilience of the benthic diatom assemblage structure in nine river reaches of increasing drainage size within the Gila River in the southwestern United States. Monsoonal floods had a profound effect on the diatom assemblage in the Gila River, but the effects were not related to drainage size except for the response of algal biomass. During monsoons, algal biomass was effectively reduced in smaller and larger systems, but minor changes were observed in medium systems. Resistance and resilience of the diatom assemblage to floods were related to specific species traits, mainly to growth forms. Tightly adhered, adnate and prostrate species (Achnanthidium spp., Cocconeis spp.) exhibited high resistance to repeated scour disturbance. Loosely attached diatoms, such as Nitzschia spp. and Navicula spp., were most susceptible to drift and scour. However, recovery of the diatom assemblage was very quick indicating a high resilience, especially in terms of biomass and diversity. Regional hydroclimatic models predict greater precipitation variability, which will select for diatoms resilient to bed-mobilizing disturbances. The results of this study may help anticipate future benthic diatom assemblage patterns in the southwestern United States resulting from a more variable climate.

Predicting reference assemblages for freshwater bioassessment with limiting environmental difference analysis

The status of biological assemblages is often inferred by comparing observational assemblage data with reference data generated by a predictive model. Limiting environmental difference analysis (LEDA) applies the ecological concepts of distance decay of similarity and limiting factor theory to model reference data by extrapolation from samples collected at reference sites. I applied LEDA modeling to data sets from the Australian Capital Territory (ACT), Laurentian Great Lakes (GL), and Canadian Yukon Territory (YT) to test its accuracy and precision in predicting the composition of benthic macroinvertebrate samples from reference sites, and its specificity and sensitivity in detecting mathematically simulated human impacts on sample composition. LEDA models were significantly and substantially more accurate than null models for all 3 data sets, but not significantly more precise. They mostly assessed unimpacted samples correctly but seldom detected mild simulated impacts. However, they often detected moderate and usually detected severe impacts. Model performance for the test data sets probably was constrained by limitations of the environmental predictor variables and low taxonomic richness in many samples. The simulated impacts provided insight into model behavior but were limited in their scope and realism. I suggest that future simulations should separately test detection of different kinds of assemblage change, not only different intensities, and should address the consequences of human alteration of predictor variables.

Assessing the biological relevance of aquatic connectivity to stream fish communities

Recent advances in the ability to quantify longitudinal connectivity of riverine systems is enabling a better understanding of how connectivity affects fish assemblages. However, the role of connectivity relative to other factors, such as land use, in structuring biological assemblages is just emerging. We assessed the relevance of a structural connectivity index to stream fish communities at a relatively large scale (across five watersheds of Lake Ontario) while controlling for confounding habitat variables, such as land use, elevation, and stream topology. The results were assessed to determine whether species’ sensitivities to connectivity are in accordance with expectations of life history. Our results indicated that at large scales, structural connectivity explains significant amounts of variation in community structure (1% to 5.4% as measured by Bray–Curtis similarity), but remains secondary to other habitat components. Connectivity also was significantly related to abundance in three of the seven species assessed. The lower explanatory power of our models compared with studies done at smaller scales suggests that the relevance of connectivity to fish communities is scale-dependent and diminishes relative to other environmental factors at larger spatial extents.

Investigating possible causal relations among physical, chemical and biological variables across regions in the Gulf of Maine

We examine potential causal relations between ecosystem variables in four regions of the Gulf of Maine under two major assumptions: (i) a causal cyclic variable will precede, or lead, its effect variable; e.g., a peak (through) in the causal variable will come before a peak (through) in the effect variable. (ii) If physical variables determine regional ecosystem properties, then independent clusters of observations of physical, biological and interaction variables from the same stations will show similar patterns. We use the leading–lagging-strength method to establish leading strength and potential causality, and we use principal component analysis, to establish if regions differ in their ecological characteristics. We found that several relationships for physical and chemical variables were significant, and consistent with “common knowledge” of causal relations. In contrast, relationships that included biological variables differed among regions. In spite of these findings, we found that physical and chemical characteristics of near shore and pelagic regions of the Gulf of Maine translate into unique biological assemblages and unique physical–biological interactions.

Global relationships between beta diversity and latitude after accounting for regional diversity

The latitudinal gradient of beta diversity (i.e. the increase of beta diversity from polar to equatorial regions) has been documented in a number of studies, but the causes of the gradient remain poorly resolved. The latitudinal gradient of beta diversity may result from the latitudinal gradient of regional (gamma) diversity but previous studies have not assessed whether there are relationships between latitude and beta diversity after accounting for regional diversity. The aim of the present study is to test whether there are relationships between latitude and beta diversity for terrestrial vertebrates after accounting for regional diversity. The relationships between beta diversity and latitude were examined for 72 latitudinal gradients of beta diversity (located in 24 longitudinal transects) for amphibians, birds, and mammals from across the globe. Beta diversity was quantified with the Jaccard index of dissimilarity between biological assemblages. We used both linear and non-linear regression analyses to determine the relationship between beta diversity and latitude. Beta diversity generally increases from polar to equatorial regions for all three taxa. Latitude and regional species richness together explain on average 47.6% of the variation in beta diversity across the three taxa. Latitude explains, on average, 20.5% of the variation in beta diversity independently and explains additional 10.0% of the variation in beta diversity jointly with regional species richness. Our study showed that latitude explains a substantial amount of the variation in beta diversity after accounting for regional species richness.

Repeated patterns of trait divergence between closely related dominant and subordinate bird species.

Ecologically similar species often compete aggressively for shared resources. These interactions are frequently asymmetric, with one species behaviorally dominant to another and excluding it from preferred resources. Despite the potential importance of this type of interference competition as a source of selection, we know little about patterns of trait divergence between dominant and subordinate species. We compiled published data on phylogenetically independent, closely related species of North American birds where one species was consistently dominant in aggressive interactions with a congeneric species. We then compared the body size, breeding phenology, life history, ecological breadth, and biogeography of these species. After accounting for body size and phylogeny, we found repeated patterns of trait divergence between subordinate and dominant species within genera. Subordinate species that migrated seasonally arrived 4-7 days later than dominants on their sympatric breeding grounds, and both resident and migratory subordinates initiated breeding 7-8 days later than their dominant, sympatric congeners. Subordinate species had a 5.2% higher annual adult mortality rate and laid eggs that were 0.02 g heavier for their body mass. Dominant and subordinate species used a similar number of different foods, foraging behaviors, nest sites, and habitats, but subordinates were more specialized in their foraging behaviors compared with closely related dominant species. The breeding and wintering ranges of subordinate species were 571 km farther apart than the ranges of dominant species, suggesting that subordinate species migrate greater distances. Range sizes and latitudinal distributions did not consistently differ, although subordinate species tended to breed farther north or winter farther south. These results are consistent with dominant species directly influencing the ecological strategies of subordinate species (via plastic or genetically based changes), either by restricting their access to resources or simply through aggression. Alternatively, these ecological traits may covary with patterns of behavioral dominance, with no direct consequences of interactions. Regardless of the mechanism, recognizing that the relative position of a species within a dominance hierarchy is correlated with a suite of other ecological and fitness related traits has far-reaching implications for the mechanisms underlying species distributions and the structure of biological assemblages.

HABITAT‐ORIENTED SAMPLING OF MACROINVERTEBRATES AFFECTS THE DETERMINATION OF ECOLOGICAL STATUS IN TEMPORARY MEDITERRANEAN RIVER SYSTEMS

ABSTRACTInter‐annual and annual variation in precipitation levels in Mediterranean temporary river systems strongly influence riverine flow regimes and as a result habitat' availability for biological assemblages. Under‐sampling of less well‐presented microhabitats in such changeable, dynamic systems can result in information loss leading to misclassification of Water Framework Directive (WFD) compliant ecological status, with serious consequences for Programmes of Measures in River Basin Management Plans. This paper compares two benthic macroinvertebrate sampling protocols tested in intermittent Mediterranean streams (n = 40) in the Algarve region of southern Portugal. The officially adopted WFD compliant European assessment system for the ecological quality of rivers using benthic macroinvertebrates, a composite sampling protocol, focuses sampling a greater area of the most representative microhabitats at a given sampling site (proportional habitat sampling). A non‐proportional habitat sampling protocol was applied to test the assumption that taxa may have preference for different microhabitats and that this could influence classification of ecological status. Variation was detected in the levels of similarity in the structure and the composition of the benthic macroinvertebrate community within sampling sites and rivers, based on material collected using the two collection methods. Ecological index scores and biotic metrics were higher when the non‐proportional oriented sampling protocol was utilized resulting in a ‘good ecological status’ classification at sites that had been classified as ‘Bad’ using the official WFD, Decision tree analysis results indicated that changes in the area of individual microhabitats sampled among protocols was the principal driver behind differences in ecological status derived. The results indicate that more realistic classifications could be achieved in intermittent Mediterranean rivers when considering and sampling less well‐represented microhabitat types (non‐proportional sampling) rather than distributing sampling effort by the proportion of the dominant habitat present as currently used for the WFD protocol. The application of the non‐proportional microhabitat‐based approach, which accounts for selective preferences of some benthic macroinvertebrate taxa, would ensure that a greater proportion of a given site community contributes to the assessment. Copyright © 2014 John Wiley & Sons, Ltd.

Experimental evaluation of diversity-productivity relationships in a coral reef fish assemblage.

The global decline in biodiversity is causing increasing concern about the effects of biodiversity loss on ecosystem services such as productivity. Biodiversity has been hypothesised to be important in maintaining productivity of biological assemblages because niche complementarity and facilitation among the constituent species can result in more efficient use of resources. However, these conclusions are primarily based on studies with plant communities, and the relationship between diversity and productivity at higher trophic levels is largely unknown, especially in the marine environment. Here, we used a manipulative field experiment to test the effects of species richness and species identity on biomass accumulation in coral reef fish assemblages at Lizard Island. Small patch reefs were stocked with a total of 30 juveniles belonging to three planktivorous damselfish (genus Pomacentrus) according to three different levels of fish species richness (one, two and three species) and seven different combinations of fish species. Species richness had no effect on the relative growth in this assemblage after 18 days, but relative growth differed among individual fish species and the different combinations of species. Patterns of increase in biomass were best explained by species-specific differences and variable effects of intra- and interspecific competition on growth. These results suggest that niche complementarity and facilitation are not the most influential drivers of total productivity within this guild of planktivorous fishes. Total productivity may be resilient to declining reef fish biodiversity, but this will depend on which species are lost and on the life-history traits of remaining species.

Dispersal capacity predicts both population genetic structure and species richness in reef fishes.

Dispersal is a fundamental species characteristic that should directly affect both rates of gene flow among spatially distributed populations and opportunities for speciation. Yet no single trait associated with dispersal has been demonstrated to affect both micro- and macroevolutionary patterns of diversity across a diverse biological assemblage. Here, we examine patterns of genetic differentiation and species richness in reef fishes, an assemblage of over 7,000 species comprising approximately one-third of the extant bony fishes and over one-tenth of living vertebrates. In reef fishes, dispersal occurs primarily during a planktonic larval stage. There are two major reproductive and parental investment syndromes among reef fishes, and the differences between them have implications for dispersal: (1) benthic guarding fishes lay negatively buoyant eggs, typically guarded by the male parent, and from these eggs hatch large, strongly swimming larvae; in contrast, (2) pelagic spawning fishes release small floating eggs directly into the water column, which drift unprotected before small weakly swimming larvae hatch. Using phylogenetic comparative methods, we show that benthic guarders have significantly greater population structure than pelagic spawners and additionally that taxonomic families of benthic guarders are more species rich than families of pelagic spawners. Our findings provide a compelling case for the continuity between micro- and macroevolutionary processes of biological diversification and underscore the importance of dispersal-related traits in influencing the mode and tempo of evolution.

A comparison of top-down and bottom-up approaches to benthic habitat mapping to inform offshore wind energy development

Recent interest in offshore renewable energy within the United States has amplified the need for marine spatial planning to direct management strategies and address competing user demands. To assist this effort in Rhode Island, benthic habitat classification maps were developed for two sites in offshore waters being considered for wind turbine installation. Maps characterizing and representing the distribution and extent of benthic habitats are valuable tools for improving understanding of ecosystem patterns and processes, and promoting scientifically-sound management decisions. This project presented the opportunity to conduct a comparison of the methodologies and resulting map outputs of two classification approaches, “top-down” and “bottom-up” in the two study areas. This comparison was undertaken to improve understanding of mapping methodologies and their applicability, including the bottom-up approach in offshore environments where data density tends to be lower, as well as to provide case studies for scientists and managers to consider for their own areas of interest. Such case studies can offer guidance for future work for assessing methodologies and translating them to other areas.The traditional top-down mapping approach identifies biological community patterns based on communities occurring within geologically defined habitat map units, under the concept that geologic environments contain distinct biological assemblages. Alternatively, the bottom-up approach aims to establish habitat map units centered on biological similarity and then uses statistics to identify relationships with associated environmental parameters and determine habitat boundaries. When applied to the two study areas, both mapping approaches produced habitat classes with distinct macrofaunal assemblages and each established statistically strong and significant biotic–abiotic relationships with geologic features, sediment characteristics, water depth, and/or habitat heterogeneity over various spatial scales. The approaches were also able to integrate various data at differing spatial resolutions. The classification outputs exhibited similar results, including the number of habitat classes generated, the number of species defining the classes, the level of distinction of the biological communities, and dominance by tube-building amphipods. These results indicate that both approaches are able to discern a comparable degree of habitat variability and produce cohesive macrofaunal assemblages. The mapping approaches identify broadly similar benthic habitats at the two study sites and methods were able to distinguish the differing levels of heterogeneity between them.The top-down approach to habitat classification was faster and simpler to accomplish with the data available in this study when compared to the bottom-up approach. Additionally, the top-down approach generated full-coverage habitat classes that are clearly delineated and can easily be interpreted by the map user, which is desirable from a management perspective for providing a more complete assessment of the areas of interest. However, a higher level of biological variability was noted in some of the habitat classes created, indicating that the biological communities present in this area are influenced by factors not captured in the broad-scale geological habitat units used in this approach.The bottom-up approach was valuable in its ability to more clearly define macrofaunal assemblages among habitats, discern finer-scale habitat characteristics, and directly assess the degree of macrofaunal assemblage variability captured by the environmental parameters. From a user perspective, the map is more complex, which may be perceived as a limitation, though likely reflects natural gradations in habitat structure and likely presents a more ecologically realistic portrayal of the study areas. Though more comprehensive, the bottom-up approach in this study was limited by the reliance on full-coverage data to create full-coverage habitat classes. Such classes could only be developed when sediment data was excluded, since this point-sample dataset could not be interpolated due to high spatial heterogeneity of the study areas. Given a higher density of bottom samples, this issue could be rectified.While the top-down approach was more appropriate for this study, both approaches were found to be suitable for mapping and classifying benthic habitats. In the United States, objectives for mapping and classification for renewable energy development have not been well established. Therefore, at this time, the best-suited approach primarily depends on mapping objectives, resource availability, data quality and coverage, and geographical location, as these factors impact the types of data included, the analyses and modeling that can be performed, and the biotic–abiotic relationships identified.

Structural and functional trends indicate fishing pressure on marine fish assemblages

Summary Conservation science increasingly focuses on how ecosystem functioning is affected by anthropogenic pressures, which implies an understanding of the structural and functional changes in biological assemblages and requires indicators to detect such changes within a suitable time frame. A novel approach that combines the spatial analysis of fishing gradients (based on vessel monitoring system records) with distance‐based linear models was used to assess the response of several functional and structural metrics of fish assemblages to gradients of trawling, within four distinct habitat types. In addition, critical thresholds of trawling intensity were identified for the most sensitive metrics through piecewise regression models. Overall, total biomass and dominance (i.e. number of species that make up 90% of the total biomass) metrics as well as metrics representing vulnerable features (such as chondrichthyes, species with very low resilience and sedentary species) were shown to be sensitive to fishing. Our results suggest that decreasing trends in these indicators are likely to be associated with direct and indirect fishing effects acting synergistically on specific features of fish assemblages leading to its homogenization, with likely impacts on ecosystems resilience. Critical thresholds at high, medium and low fishing intensity levels were identified depending on the metric used to assess fishing impacts, suggesting that it is difficult to define a single global target for fishing management as it ultimately will depend on management and conservation objectives (e.g. maintenance of biomass vs. maintenance of structure and function). Synthesis and applications. A key goal of the applied approach was to provide short‐term indicators that are sensitive to gradients of trawling intensity and can be extrapolated to a broader geographical region. The identification of thresholds of fishing pressure that fish assemblages can withstand before ecosystem functioning is altered is key for the development of indicators as warning mechanisms, as well as to assess performance measures for management. Understanding responses to other pressure sources (e.g. pollution, dredging) requires further research, and combining an integrative functional traits approach with a wider range of pressures may help make this achievable.

Habitat Classification of Temperate Marine Macroalgal Communities Using Bathymetric LiDAR

Here, we evaluated the potential of using bathymetric Light Detection and Ranging (LiDAR) to characterise shallow water (<30 m) benthic habitats of high energy subtidal coastal environments. Habitat classification, quantifying benthic substrata and macroalgal communities, was achieved in this study with the application of LiDAR and underwater video groundtruth data using automated classification techniques. Bathymetry and reflectance datasets were used to produce secondary terrain derivative surfaces (e.g., rugosity, aspect) that were assumed to influence benthic patterns observed. An automated decision tree classification approach using the Quick Unbiased Efficient Statistical Tree (QUEST) was applied to produce substrata, biological and canopy structure habitat maps of the study area. Error assessment indicated that habitat maps produced were primarily accurate (>70%), with varying results for the classification of individual habitat classes; for instance, producer accuracy for mixed brown algae and sediment substrata, was 74% and 93%, respectively. LiDAR was also successful for differentiating canopy structure of macroalgae communities (i.e., canopy structure classification), such as canopy forming kelp versus erect fine branching algae. In conclusion, habitat characterisation using bathymetric LiDAR provides a unique potential to collect baseline information about biological assemblages and, hence, potential reef connectivity over large areas beyond the range of direct observation. This research contributes a new perspective for assessing the structure of subtidal coastal ecosystems, providing a novel tool for the research and management of such highly dynamic marine environments.

Does distance between aquatic plant assemblages matter in defining similarity between them during high water‐level periods?

Aquatic environments are subject to natural water-level fluctuations. These fluctuations, in turn, are responsible for causing changes in biota in the aquatic environment, particularly those that colonize floodplains. The flood pulse concept predicts that water-level fluctuations are responsible for the formation of mosaics in biota at a small scale. During high water-level periods, however, there is evidence that the similarity among biological assemblages increases. Within this theoretical context, the present study focuses on determining whether or not the spatial distance between assemblages is a relevant factor for the similarity among them during high water-level periods and, if not, what environmental variables are associated with them? Accordingly, the present study evaluated the association between aquatic plant assemblages and some environmental variables, with emphasis on the spatial distance among assemblages. The study results indicated no association between the similarity of the assemblages and the spatial distances between them. The environmental variables most associated with the assemblages were the total phosphorus and nitrate concentrations. It was concluded that, during high water-level periods, the spatial distance between aquatic plant assemblages was not a relevant factor for greater similarity among them. Rather, the total phosphorus and nitrate concentrations were the environmental factors most associated with the assemblages.

Defining biological assemblages (biotopes) of conservation interest in the submarine canyons of the South West Approaches (offshore United Kingdom) for use in marine habitat mapping

In 2007, the upper part of a submarine canyon system located in water depths between 138 and 1165m in the South West (SW) Approaches (North East Atlantic Ocean) was surveyed over a 2 week period. High-resolution multibeam echosounder data covering 1106km2, and 44 ground-truthing video and image transects were acquired to characterise the biological assemblages of the canyons. The SW Approaches is an area of complex terrain, and intensive ground-truthing revealed the canyons to be dominated by soft sediment assemblages. A combination of multivariate analysis of seabed photographs (184–1059m) and visual assessment of video ground-truthing identified 12 megabenthic assemblages (biotopes) at an appropriate scale to act as mapping units. Of these biotopes, 5 adhered to current definitions of habitats of conservation concern, 4 of which were classed as Vulnerable Marine Ecosystems. Some of the biotopes correspond to descriptions of communities from other megahabitat features (for example the continental shelf and seamounts), although it appears that the canyons host modified versions, possibly due to the inferred high rates of sedimentation in the canyons. Other biotopes described appear to be unique to canyon features, particularly the sea pen biotope consisting of Kophobelemnon stelliferum and cerianthids.

Aquatic Coleoptera assemblages in protected wetlands of North-western Spain

Wetlands are diverse and productive ecosystems endangered by human pressure, which degradation implies a biodiversity loss worldwide. Among the biological assemblages of these habitats, aquatic Coleoptera is one of the most diverse and useful groups when assessing the ecological conditions of the ecosystems they inhabit. The aims of the present study were to analyze the diversity and composition of aquatic Coleoptera assemblages in 24 wetlands protected by the Natura 2000 network of North-western Spain and the influence of environmental variables on the distribution of species, in order to detect differences between the different types of standing water habitats. A total of 11,136 individuals of 105 species belonging to 12 families of aquatic Coleoptera (Gyrinidae, Haliplidae, Noteridae, Paelobiidae, Dytiscidae, Helophoridae, Hydrochidae, Hydrophilidae, Hydraenidae, Scirtidae, Elmidae and Dryopidae) were collected. In general, wetlands presented high richness and diversity values, Dytiscidae and Hydrophilidae having the highest species richness. Most of recorded species have a wide biogeographical distribution and only 12 endemic ones were captured. Cluster and Non-Metric Multi-Dimensional Scaling (NMDS) analyses showed the clustering of the studied ponds and lagoons in four groups based on biological data. In general, the wetlands of each group seem to have distinct aquatic Coleoptera faunas, as showed by the most representative species. A combination of altitude, SST and hydroperiod was the best explaining factor of the distribution of the species throughout the study area. This study shows the high biodiversity of standing water habitats in North-western Spain and the usefulness of water beetles in establishing habitat typologies.

Comparing alternatives for combining invertebrate and diatom assessment in stream quality classification

The present study aimed to determine if a predictive model integrating freshwater assemblages from different trophic levels (macroinvertebrates and diatoms) produces a more sensitive assessment of stream health than single-assemblage assessments combined a posteriori. For this purpose, individual and combined models based on two approaches (BEAST and RIVPACS) were developed for Portuguese streams: two for diatoms; two for macroinvertebrates; and two combining diatoms and macroinvertebrates as a single community. Twenty-three sites affected by organic contamination, industrial effluents and mine drainage were evaluated with the predictive models and also by the official biotic indices used in Portugal. The sensitivity of the RIVPACS assessment to disturbance was improved by the a priori combination of diatoms and macroinvertebrates, whereas for BEAST the a posteriori approaches were slightly more sensitive. Diatom and invertebrate indices combined a posteriori performed better than single-assemblage indices but with lower sensitivity than combined models. We conclude that the a priori combination of the two biological assemblages is valuable (more sensitive to disturbance) for the RIVPACS approach and that the a posteriori combination of assessments for individual biological elements may not always provide the most realistic indication of stream health.

Ecological consequences of global climate change for freshwater ecosystems in South Africa

Freshwater resources in South Africa are under severe pressure from existing anthropogenic impacts and global climate change is likely to exacerbate this stress. This review outlines the abiotic drivers of climate change, focusing on predicted changes in temperature and precipitation. The consequences of global climate change for freshwater ecosystems are reviewed, with effects grouped into those related to water quantity, water quality, habitat and aquatic biological assemblages. Several guiding principles aimed at minimising the potential impact of climate change on freshwater ecosystems are discussed. These guidelines include those focused on water quantity and the maintenance of appropriate environmental flows, integration of global climate change into water quality management, conservation planning for freshwater biodiversity, the promotion of ecosystem resilience, and extending climate change science into policy and public discourse. Proactive assessment and monitoring are seen as key as these will allow for the identification of ecological triggers and thresholds, including thresholds of vulnerability, which may be used to monitor and inform decisions, as well as to improve the ability to forecast based on this knowledge.

Can different biological indicators detect similar trends of marine ecosystem degradation?

Marine ecosystems are typically under the influence of multiple Human activities, which hinders the assessment of the effects of a specific activity upon their biological assemblages. In this context, distance-based linear models were used to analyse the relationships of several structural and functional metrics of both macroinvertebrates and fish assemblages with the specific types of pressure (i.e. fishing, organic, physical and non-point-source) as well as the global pattern of cumulative pressures. Both indicators detected similarly the effects of the global degradation and the analyses of the metrics’ sensitivity (given the expected response trends) suggested that the non-point-source had the strongest contribution to this pattern, followed by organic pollution. The difficulties of assessing single pressure effects in a multiple pressures context are discussed. An approach based on the previous identification of pressure sources, a sampling strategy directed to those sources, together with indicator response is highly recommended, as it could be the only way to accurately predict human-induced changes on broad range ecosystems, with likely implications in the success of marine management plans.