Carolyn G. Palmer

What is Meant by “95% of Species”? An Argument for the Inclusion of Rapid Tolerance Testing

ABSTRACT It is increasingly common for water quality guidelines and risk assessments to consider the proportion of species at risk from a particular toxicant, based on the species sensitivity distribution (SSD) for that toxicant. There is a premise that the sensitivity data from species included in the SSD are sufficient to predict the effect on species for which there are no data. We discuss and review assumptions that follow this premise and find that for most toxicant SSDs include too few species, and that component species are biased toward particular taxonomic groups, common species and species from North America and western Europe. Consequently, protecting a given percentage, for example, 95%, of species in an SSD will likely protect more or less than 95% of species in nature, by an unknown amount. For the assumptions of SSDs to be better met, there is a need for tolerance data on more species, from more taxonomic and other groups, including rare species and those from widespread localities. In order to achieve this, we argue for the inclusion of rapid tests, which we define as toxicity tests designed to require less effort to conduct, relative to traditional tests, so sensitivity can be quickly and approximately determine in many species. Their use will allow for more species, more representative of natural communities, to be tested and therefore allow the construction of less biased SSDs and thus more accurate guidelines and assessments of risk.

Relative salinity tolerance of freshwater macroinvertebrates from the south-east Eastern Cape, South Africa compared with the Barwon Catchment, Victoria, Australia

Salinity is rising in many southern African and Australian rivers with unknown effects on aquatic organisms. The extent of spatial variation, at any scale, in salt tolerances of aquatic organisms is unknown, so whether data from one location is applicable elsewhere is also unknown. The acute tolerances (72-h median lethal concentration (LC50)) to sea salt of 49 macroinvertebrate taxa from the south-east Eastern Cape (SEEC), South Africa were compared with those of 57 species from the Barwon Catchment, Victoria, Australia. The mean LC50 values from both locations were similar (Barwon: 31 and SEEC: 32 mS cm −1 ) and less abundant (rare) taxa tended to be more tolerant than more abundant (common) taxa. There was, however, a greater range of LC50 values (5.5-76 mS cm −1 ) in the Barwon Catchment than in the SEEC (11-47 mS cm −1 ). The species sensitivity distribution (SSD) for SEEC taxa was bimodal whereas the Barwon Catchments SSD had a single peak. With few exceptions, members of an order had similar tolerances in both locations. The differences in SSD between locations were related to crustacean, odonate and non-arthropod relative richness. Although it is not ideal to extrapolate SSDs from one location to another, it may be reasonable to assume similar salinity tolerances among related taxa.

Global scale variation in the salinity sensitivity of riverine macroinvertebrates: Eastern Australia, France, Israel and South Africa

Salinity is a key abiotic property of inland waters; it has a major influence on biotic communities and is affected by many natural and anthropogenic processes. Salinity of inland waters tends to increase with aridity, and biota of inland waters may have evolved greater salt tolerance in more arid regions. Here we compare the sensitivity of stream macroinvertebrate species to salinity from a relatively wet region in France (Lorraine and Brittany) to that in three relatively arid regions eastern Australia (Victoria, Queensland and Tasmania), South Africa (south-east of the Eastern Cape Province) and Israel using the identical experimental method in all locations. The species whose salinity tolerance was tested, were somewhat more salt tolerant in eastern Australia and South Africa than France, with those in Israel being intermediate. However, by far the greatest source of variation in species sensitivity was between taxonomic groups (Order and Class) and not between the regions. We used a Bayesian statistical model to estimate the species sensitivity distributions (SSDs) for salinity in eastern Australia and France adjusting for the assemblages of species in these regions. The assemblage in France was slightly more salinity sensitive than that in eastern Australia. We therefore suggest that regional salinity sensitivity is therefore likely to depend most on the taxonomic composition of respective macroinvertebrate assemblages. On this basis it would be possible to screen rivers globally for risk from salinisation.

Are Macroinvertebrate Assemblages in the Buffalo River, Southern Africa, Associated with Particular Biotopes?

Stream biotopes (habitat types) have commonly been defined using subjective recognition of hydraulic and substrate conditions. In this study the relationship between groups of macroinvertebrates and subjectively defined biotopes was examined at three sites in the upper, middle, and lower reaches of the Buffalo River. Biotopes which were recognised included riffles, leaf packs in riffles, and a waterfall (erosional biotopes); and stony backwaters, marginal vegetation and sediments (depositional biotopes). Over 100 taxa were identified from the three sites, and an hierarchical classification of 138 samples was prepared using TWINSPAN. The first division distinguished between the invertebrate assemblages of the upper reaches and those of the middle/lower reaches. In the upper reaches, the waterfall was differentiated from all the other stream biotopes. In addition, seasonal changes in assemblage composition were recognised. Divisions in the middle/lower reaches differentiated between biotopes. Of the 27 most common taxa, 13 occurred in a single biotope in more than 50% of the samples in which they had been collected. Clearest species-biotope associations were riffle-dwelling mayflies and caddisflies, and stone-dwelling planaria and ancylid gastropods. Invertebrate assemblages were not always associated with subjectively identified biotopes, particularly in the narrow headwaters, where different biotopes tended to be smaller and less distinct. However, associations of assemblages with biotopes were found in the middle/lower reaches. This study shows that stratified random sampling regimes can be useful tools in stream research if the scale at which biotopes are recognised is clearly defined.

An assessment of macroinvertebrate functional feeding groups as water quality indicators in the Buffalo River, eastern Cape Province, South Africa

The aim of this paper was to investigate the potential for using functional feeding groups (FFGs) as indicators of water quality conditions in rivers, using the Buffalo River, South Africa, as a specific example. Multivariate classification and ordination techniques were used to investigate species and FFG distributions in relation to a number of physico-chemical variables at 16 sites from the headwaters to the estuary of the Buffalo River.Two-way indicator species analysis (TWINSPAN) of species composition ranked most of the sites sequentially down the river, irrespective of water quality conditions. Ordination of FFGs from a set of riffle samples collected in mid-late summer showed only weak relationships between FFG distribution and water quality changes, except where variables changed sequentially down the river (e.g. pH and temperature). Individual species responses to water quality gradients were examined for nine riffle-dwelling species representing diverse FFGs. Following correspondence analysis of a matrix of environmental variables and species frequencies, some species showed strong associations with defined ranges of some variables. In particular, Adenophlebia auriculata (Leptophlebiidae, Ephemeroptera) from the headwater sampling site, was associated with low pH and low temperature. Simulium damnosum occurred under conditions of high turbidity, while Afronurus harrisoni was found under high concentrations of potassium, ammonium and nitrite ions.We conclude that although there was a distinct headwaters fauna in the Buffalo River, and sequential downstream changes in species composition, most FFGs (apart from shredders) were represented down the whole length of the river. FFG classifications are therefore unlikely to provide useful indications of water quality conditions in the Buffalo River.Using a categorical approach to classifying water quality variables, and by applying correspondence analysis to the resulting matrix, we recognised nine species that could be used to define water quality. These indicator species can be used to define tolerance ranges of the fauna for water quality conditions in different parts of the Buffalo river.

Risk assessment using the species sensitivity distribution method: Data quality versus data quantity

Species sensitivity distributions (SSDs) are cumulative distributions of measures of species sensitivity to a stressor or toxicant, and are used to estimate concentrations that will protect p% of a community (PCp ). There is conflict between the desire to use high-quality sensitivity data in SSDs, and to construct them with a large number of species forming a representative sample. Trade-offs between data quality and quantity were investigated using the effects of increasing salinity on the macroinvertebrate community from the Hunter River catchment, in eastern Australia. Five SSDs were constructed, representing five points along a continuum of data quality versus data quantity and representativeness. This continuum was achieved by the various inclusion/exclusion of censored data, nonmodeled data, and extrapolation from related species. Protective concentrations were estimated using the Burr type III distribution, Kaplan-Meier survival function, and two Bayesian statistical models. The dominant taxonomic group was the prime determinant of protective concentrations, with an increase in PC95 values resulting from a decrease in the proportion of Ephemeropteran species included in the SSD. In addition, decreases in data quantity in a SSD decreased community representativeness. The authors suggest, at least for salinity, that the inclusion of right censored data provides a more representative sample of species that reflects the natural biotic assemblage of an area to be protected, and will therefore improve risk assessment.

The impact of water quality deterioration on macroinvertebrate communities in the Swartkops River, South Africa: a multimetric approach

A multimetric approach, using 21 metrics representing five categories — abundance, composition, richness, diversity and biotic indices — was applied to investigate the impacts of water quality deterioration on macro-invertebrate communities in the Swartkops River. Macroinvertebrates were sampled seasonally between August 2009 and July 2010 using the South African Scoring System version 5 (SASS5) protocol at one reference site upstream of Uitenhage and three downstream sites. Assessment of water quality impacts on macroinvertebrates was based on the discriminatory ability of metrics between the reference and impaired sites, and on their correlation with the physico-chemical variables. The metrics’ discriminatory ability was explored using box plots, and their relationships with water chemistry variables elucidated with Pearsons correlation. Trichoptera abundance, %Chironomidae + Oligochaeta, %Ephemeroptera–Trichoptera–Odonata–Coleoptera (ETOC), %Trichoptera, Ephemeroptera–Plecoptera–Trichoptera (EPT) richness, ETOC richness, Margalefs family richness index, equitability, Shannon and Simpson diversity indices, SASS5 score and average score per taxon (ASPT) discriminated between the reference and impacted sites, and also exhibited significant correlations (p < 0.05) with water chemistry variables. Conversely, Gastropoda abundance, EPT abundance, ETOC abundance, EPT:Chironomidae ratio, %EPT, %Corixidae, %Oligochaeta + Hirudinae, Chironomidae + Oligochaeta abundance and Hemiptera + Diptera richness did not discriminate between the reference and impacted sites.

Feeding patterns of four macroinvertebrate taxa in the headwaters of the Buffalo River, eastern Cape

Gut content analysis, field and laboratory observations, and food choice experiments were used to assign four abundant macroinvertebrate taxa in the headwaters of the Buffalo River, eastern Cape, to functional feeding groups. The mayfly Adenophlebia auriculata (Leptophlebiidae) was classified as a collector: brusher; while the caddisflies, Dyschimus ensifer (Pisuliidae) and Goerodes caffrariae (Lepidostomatidae), and stoneflies Afronemoura spp. (Notonemouridae) were classified as shredders. The effects of organism size, season and biotope on dietary composition were tested, with size accounting for most of the dietary variability within each taxon. Larger individuals consumed more material, larger items, and, in the case of A. auriculata, a wider variety of food-types. There was little variation in the feeding of the taxa in different seasons or biotopes. Shredders ingested mainly leaf fragments, and this, rather than the size of particles in the gut, is a more useful basis for the shredder designation. A. auriculata was the most opportunistic feeder, and items in its diet additional to fine detritus varied seasonally and in the various biotopes. Of the shredders, Afronemoura spp. and D. ensifer were more varied in their diet, augmenting the staple intake of leaf material with other items. G. caffrariae was the most specialised feeder, being exclusively a shredder, regardless of biotope or season. Despite criticisms of the applicability of the FFG concept in the literature, we conclude that these taxa can reasonably be accommodated in functional feeding classes, and that the results are useful in describing the functions performed by the organisms in the river. The relationship between feeding function and river process is emphasised: we suggest that collectors contribute primarily to organic particle retention, while shredders facilitate organic particle size reduction and mobilisation, and the enhancement of substrates for microbial colonisation. An emphasis on river function is a useful context within which to view the FFG concept.

Defining an exposure–response relationship for suspended kaolin clay particulates and aquatic organisms: Work toward defining a water quality guideline for suspended solids

Water quality guidelines for suspended solids generally rely on the percentage departure from reference condition, an approach that has been criticized. Attempts to develop a biological effects-base guideline have, however, been confounded by low data availability. Furthermore, the high biological response variability to suspended solids exposure suggests that organisms are responding not only to exposure concentration and duration but also to other mechanisms of effect associated with suspended particles (e.g., size, shape, and geochemical composition). An alternative option is to develop more situation and site specific guidelines by generating biological effects data to suspended particles of a particular geochemistry and restricted size range. With this in mind, aquatic organism responses to kaolin clay particle exposure were collated from the literature and incorporated into 2 exposure-response relationship approaches. The species sensitivity distribution approach produced a hazardous concentration affecting 5% of species estimate of 58 mg/L for mortality responses, and 36 mg/L for sublethal data. The severity-of-ill-effect approach produced similar estimates for lethal and sublethal data. These results suggest that aquatic organisms are slightly more tolerant of kaolin clay particles than particles from barite or bentonite clays, based on results from previous studies on these clay types. This type of information can enable better estimates of the risk faced by aquatic organisms exposed to suspended solids. For example, when the sediments of a particular water body are dominated by a particular type of clay particle, then the most appropriate exposure-response relationship can be applied.

A chronic toxicity test protocol using Caridina nilotica (Decapoda: Atyidae) and the generation of salinity toxicity data

Salinization of freshwater resources is an increasing global problem, yet there is a paucity of chronic salinity tolerance data linked to very few chronic toxicity test protocols. This research aimed to generate a chronic toxicity test protocol and protective salinity tolerance data for the indigenous South African freshwater shrimp Caridina nilotica. In addition, the theory that LC5s (concentration causing 5% lethality) are indicative of No Observed Effect Concentrations (NOECs) was tested. NaCl and Na2SO4 were used as toxicants as they are indicative of natural and industrial salinization, respectively. NOEC values of 1.9 g l–1 were calculated for both salts. Within the chronic toxicity tests, LC5s that were calculated using regression methods approximated the calculated NOEC values for both salts. Chronic NOECs calculated here are lower, by a factor of 3, than the acute LC50s calculated for the same species and salts. Although evidence exists to suggest that C. nilotica is generally sensitive to toxicants, it was found to be not particularly sensitive to salinity. However, the species was found to be a good chronic toxicity test organism for partial life-cycle toxicity tests where growth was measured as the test endpoint, and may yield valuable chronic toxicity data for other toxicants.