Is all salinity the same? I. The effect of ionic compositions on the salinity tolerance of five species of freshwater invertebrates

Salts of marine origin, predominantly consisting of Na+ and Cl- ions, are dominant in most Australian inland saline waters. The proportions of other ions, Ca2+, Mg2+, SO42-, HCO3- and CO32-, in the water may influence salinity tolerance of freshwater organisms and thus the effect of increasing salinity may vary with difference in ionic proportions. We exposed freshwater invertebrates to different concentrations of four ionic compositions and compared them with commercial sea salt ( Ocean Nature). They were: synthetic Ocean Nature (ONS) and three saline water types (ONS but without: SO42-, HCO3- and CO32- (S1); Ca2+, HCO3- and CO32- (S2); and Ca2+ and Mg2+ (S3)), which are considered to be the predominant saline water types in south-eastern Australia and the Western Australian wheatbelt. The 96-h LC50 values for the five media were determined for six invertebrate species and sub-lethal responses were observed for two species. There were no differences between responses of invertebrates to various ionic compositions in acute toxicity tests. However, in prolonged sub-lethal tests, animals reacted differently to the various ionic compositions. The greatest effect was observed in water types lacking Ca, for which plausible physiological mechanisms exist. Variation in ionic proportions should be taken into account when considering sub-lethal effects of salinity on freshwater invertebrates

Maintenance of daphnia carinata cultures for use in toxicity testing

A growing concern for use of local species for toxicity testing leads to the need to create toxicity data banks for these species. In order to have healthy animals to conduct the tests, procedures for maintenance of stock cultures of these species should be developed. The most widespread daphnid in Australia, Daphnia carinata, is considered to be one of the most suitable for toxicity testing of contaminants entering Australian freshwaters. However very little data are available on the culture requirements of the species. In this study different types of food were tested: Chlorella vulgaris cultured in two different media - Keating and Tamiya, Chlorella pyrenoidosa cultured in the same two media, and a suspension of trout pellets. Intrinsic rates of natural increase of individual cultures of D. carinata were determined from "life tables". The best food from among those tested were C. pyrenoidosa cultured in either Keating or Tamiya medium. Two different procedures of individual cultures are proposed for the maintenance of D. carinata for use in toxicity testing, based on tests conducted using different culture volume

Roundup biactive modifies cadmium toxicity to Daphnia carinata

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Growth of the damselfly Ischnura heterosticta is better in saline water than freshwater

Increasing salinity has the potential to affect freshwater organisms. Yet sub-lethal effects of salinity on macro invertebrates are poorly understood. Growth and development of Ischnura heterosticta (Odonata: Coenagrionidae) was experimentally shown to be faster in 5-20 mS/cm than 0.1-1 mS/cm, while in 35 mS/cm all individuals died. In 30 mS/cm about half died and growth was similar to the 0.1 mS/cm treatment. The salinity-growth relationship cannot be explained indirectly, that is salinity affecting the survival of their prey. Tissue content and concentration of Ca, Mg, Na and K in emerged adults showed no evidence of deficiencies at low salinity. Heart beat rate was similar across treatments, except at 35 mS/cm, where it was slower. Respiration and feeding were similar at 0.1, 10 and 30 mS/cm. While there are similarities in I. heterosticta and other species' salinity response, there are differences and studies on more species are urgently needed

Effects of pH on salinity tolerance of selected freshwater invertebrates

Salinization of freshwaters often co-occurs with other changes in the environment, including pH. We investigate the effect of pH on salinity tolerance in selected macroinvertebrates (Notalina fulva, Centroptilum sp. and Physa acuta--lethal effects only) and microinvertebrates (Paramecium caudatum and Hydra oligactis--lethal and sublethal effects). Despite seemingly plausible physiological arguments, no difference in salinity tolerance over 96-h period was detected between low (5 or 6 nominal) pH and circumneutral (7-8.2 nominal) pH. P. caudatum was more salt sensitive in pH 11 than in pH 5, 7, and 10 in terms of mortality, and in terms of a sublethal endpoint, number of individuals produced and survived over 72 h, more sensitive to salinity in pH 10 than in pH 5 and 7. No other effects of pH on salinity tolerance were detected. Acidification will likely have effects on freshwater organisms on its own, however, when combined with salinization (from saline waters approximating seawater) acidification level tested did not modify the direct effects of salinity on the sample of freshwater invertebrates tested from a range of taxonomic groups. Thus the risk of low (5 or 6) pH modifying the effect of salinity on freshwater invertebrates is not high. Logically, lower pH values might have modified the effect of salinity, but there is a limited scope for lower pH values that would keep the species studied alive. In contrast, alkaline pH may increase the effect of salinity in some freshwater invertebrates. It is possible that the effect of pH on salinity tolerance may, however, be increased in saline waters with low calcium concentrations

Colonisation and succession of marine biofilm-dwelling ciliates in response to environmental variation

Protozoan assemblages and successional dynamics are important components of biofouling that require better understanding. We studied marine ciliates in temperate Australia as they colonised artificial substrates for 21 d during 2 different seasons, with 2 different aspects of orientation. Sessile and planktonic taxa established within 7 d, whereas vagile taxa colonised throughout the period. Abundances reached 366 ciliates cm-2. Colonies of the peritrichs Zoothamnium and Vorticella, and the hypotrichs Aspidisca and Euplotes were the most abundant. The north aspect received more light than the south aspect during summer, but assemblages did not differ significantly. Assemblage structure was different between seasons, and it developed more quickly and reached greater abundances during summer. A storm late in summer abruptly reduced abundances and affected functional groups differently, but diversity was largely unaffected. Thus, diversity of an established assemblage can be maintained through disturbances, despite abundances being subject to great fluctuation

Colonisation and succession of marine biofilm-dwelling ciliate assemblages on biocidal antifouling and fouling-release coatings in temperate Australia

Ciliate assemblages are often overlooked, but ubiquitous components of microbial biofilms which require a better understanding. Ciliate, diatom and bacterial colonisation were evaluated on two fouling-release (FR) coatings, viz. Intersleek 970 and Hempasil X3, and two biocidal antifouling (AF) coatings, viz. Intersmooth 360 and Interspeed 5640, in Port Phillip Bay, Australia. A total of 15 genera were identified during the 10 week deployment. Intersleek 970 displayed the most rapid fouling by ciliates, reaching 63.3(± 5.9) cells cm-2. After 10 weeks, all four coatings were extensively fouled. However, the toxicity of the AF coatings still significantly inhibited microbial fouling compared to the FR coatings. On all treatments, colonies of sessile peritrichs dominated the ciliate assemblage in the early stage of succession, but as the biofilm matured, vagile ciliates exerted more influence on the assemblage structure. The AF coatings showed selective toxic effects, causing significant differences in the ciliate species assemblages among the treatments

Is the integration of hormesis and essentiality into ecotoxicology now opening Pandora's Box?

Hormesis and essentiality are likely real and common effects at the level of the individual. However, the widespread incorporation of stimulatory effects into applications of ecotoxicology requires the acceptance of assumptions, value judgements and possibly lowering of water/sediment quality standards. There is also currently little data appropriate for considering hormetic effects in the ecotoxicological context. Except perhaps in the case of fitting concentration-response curves, it is not clear that incorporation of hormetic and essentiality type responses into ecotoxicology is necessary. Furthermore, its incorporation presents considerable intellectual and practical changes for ecotoxicology and could have unanticipated consequences. The acceptance of hormesis and essentiality in ecotoxicology requires major conceptual changes and considerable new data

How are macroinvertebrates of slow flowing lotic systems directly affected by suspended and deposited sediments?

The effects of suspended and deposited sediments on the macroinvertebrates are well documented in upland streams but not in slower flowing lowland rivers. Using species found in lowland lotic environments, we experimentally evaluate mechanisms for sediments to affect macroinvertebrates, and in one experiment whether salinity alters the effect of suspended sediments. Suspended kaolin clay reduced feeding of Ischnura heterosticta (Odonata: Coenagrionidae) at high turbidity (1000-1500 NTU) but had no effects on feeding of Hemianax papuensis (Odonata: Aeshnidae) and Micronecta australiensis (Hemiptera: Corixidae). In freshwater (0.1 mS/cm), survival of Ischnura aurora was poor in clear water, but improved with suspended kaolin. Growth and feeding of I. aurora were unaffected by suspended sediments and salinity. Burial (1-5 mm) of eggs with kaolin or sand reduced hatching in Physa acuta (Gastropoda: Physidae), Gyraulus tasmanica (Gastropoda: Planorbidae) and Chironomus cloacalis (Diptera: Chironomidae). Settling sediments may pose greater risk to lowland lotic invertebrates than suspended sediments

Development of a larval-settlement assay protocol for the serpulid polychaete, Galeolaria caespitosa

Static settlement assays are considered the standard tool for determining the settlement preferences of marine invertebrates. Often used to assess and evaluate the properties of a given substrate or biofilm cues for coloni- sation, the static assay format is technically simple, rapid, and inexpensive. Galeolaria caespitosa is a sessile, filter-feeding polychaete worm that inhabits mid to low intertidal regions of exposed rocky shores. Mature adults of G. caespitosa are fertile throughout the year, easy to spawn and rear to settlement competency, and their gregarious settlement behaviour enables easy collection making them an ideal test species. Here we report an optimised protocol for larval settlement assays with G. caespitosa. Unlike other serpulid polychaetes, a bacterial biofilm alone was not sufficient to consistently induce settlement. Instead, a conspecific cue was required for reliable settlement under assay conditions. Yet empty tubes and a homogenate of crushed adult worms had no significant impact on settlement compared to a control, and both treatments showed high variance, indu- cing < 5% of larvae to settle. Only the presence of live conspecific worms consistently induced settlement to the extent necessary for useful assays. In this case, after 48 h the proportion of larvae to have successfully settled reached 44%. On average, live conspecific worms increased settlement by 87% compared to the presence of a biofilm alone. The static settlement assay protocol developed in this study provides a reproducible tool for assessing invertebrate settlement with G. caespitosa. Guidelines are provided for adapting this approach to other species