Low-salinity Ponds Research Articles

Impact of Water Quality and Phytoplankton on Juvenile Vannamei Shrimp Growth in Low-Salinity Ponds

The Vannamei shrimp (Litopenaeus vannamei) is a key species in global aquaculture, with its growth influenced by various environmental factors and nutritional quality. This study aimed to analyze water quality parameters and phytoplankton density, as well as assess the growth of juvenile Vannamei shrimp in circular ponds with low salinity (5-6 ppt). Shrimp were stocked at a density of 80 individuals per square meter in 5-ton capacity tanks and fed four times daily over a 30-day period. Water quality parameters, including temperature, dissolved oxygen, pH, and light intensity, were monitored bi-daily, revealing fluctuations that impacted shrimp health. Notably, plankton density assessments showed Cyclotella present on day 14 but absent on day 28, while Microcystis and Rhizosolenia were detected on day 28, indicating shifts in the phytoplankton community. The specific growth rate (SGR) of shrimp was measured at 18.69% per day, with initial and final weights recorded at 0.01 ± 0.00 g and 2.72 ± 0.23 g, respectively. This study highlights the importance of maintaining optimal water quality and understanding phytoplankton dynamics for enhancing shrimp growth. Additionally, it explores the potential benefits of alginate supplementation and the effects of low salinity on the growth of juvenile Vannamei shrimp, contributing valuable insights for sustainable aquaculture practices.

Influence of Water Quality and Phytoplankton Community on the Growth of Litopenaeus vannamei in Low-Salinity Semi-Mass Circular Ponds

This study examines the dynamics of vannamei shrimp (Litopenaeus vannamei) cultivation in low salinity aquaculture systems, focusing on water quality parameters, plankton diversity, and shrimp growth rates. Vannamei shrimp are favored in aquaculture due to their disease resistance, rapid growth, and high survival rates. Key water quality parameters, including dissolved oxygen (DO), temperature, light intensity, pH, and salinity, were monitored over a 30-day period in low salinity ponds. The results showed significant fluctuations in these parameters, influencing shrimp health and growth. DO levels varied from 5.8 to 8.39 ppm in the morning and from 5.14 to 7.8 ppm in the afternoon. Water temperature ranged from 27.3°C to 32.3°C, light intensity from 3,170 to 66,300 lux, pH from 7.72 to 8.73, and salinity from 5 to 6 ppt. Plankton diversity and density, including species like Microcystis, Cyclotella, and Rhizosolenia, were also assessed, highlighting their role in the aquatic ecosystem. The specific growth rate (SGR) of the shrimp was calculated, showing a favorable growth rate of 2.32% per day. These findings indicate that maintaining stable water quality and diverse plankton populations is crucial for optimizing shrimp growth in low salinity aquaculture systems. This research provides valuable insights into the environmental conditions necessary for successful vannamei shrimp cultivation, emphasizing the importance of regular monitoring and management to ensure sustainable aquaculture

Growth of Litopenaeus vannamei using Synbiotics Supplementation Diet in Outdoor Low-Salinity Ponds Concerning Water Quality Parameters and Phytoplankton Communities

This study aimed to evaluate the influence of probiotic supplementation using L. bulgaricus FNCC-004 and prebiotics sodium alginate on the growth of Litopenaeus vannamei shrimp, as well as water quality parameters and plankton density in a five tons circle outdoor pond for 30 days of rearing. Assessment was conducted on specific pathogen-resistant (SPR) shrimp. Shrimp weight, plankton density, and water quality, with samples collected from circular ponds. The probiotic L. bulgaricus FNCC–004 was prepared as feed supplementation by adding 2% sodium alginate into the incubated bacterial media. One kg of feed was mixed with 200 mL of media containing the alginate-probiotic mixture. Feeding frequency was four times a day. Water quality sampling involved temperature, salinity, pH, dissolved oxygen (DO), and light intensity, measured twice daily. Plankton density was determined using a haemocytometer under microscope. Specific growth rate (SGR) of shrimp was calculated based on initial and final weights. Results showed variations in water quality parameters throughout the day, indicating the dynamic nature of the aquatic environment. Plankton density analysis revealed variations in species and abundance over the study period. The specific growth rate of Litopenaeus vannamei shrimp was recorded at 17.44% per day. This study enhances understanding of the effects of synbiotics supplementation in the diet on shrimp growth and environmental conditions in aquaculture systems

Enhancement of aquaculture performance of cobia, Rachycentron canadum (Linnaeus 1766): A review

Cobia, Rachycentron canadum, is a marine fish with recognized potential for aquaculture due to its fast growth rate, high fecundity, disease resistance, and quality flesh. However, much progress has been made to overcome problems associated with aspects of cobia production, including broodstock management, fingerling production, larval-rearing, grow-out, and disease management, though, an effort is needed to ensure its sustainability. Broodstock conditioning protocols for continuous spawning as well as induced spawning via hormonal injection resulted in all-year-round seed production in cobia, but detailed information on the cost-effective dosages of various spawning hormones for maximum fecundity and larval survival needs to be investigated. Selective breeding, the application of genetics in trait selection, and the use of molecular markers could produce more viable strains to mitigate high mortality, particularly in colder climates. In addition, considering the fact cobia are carnivorous fish with a high protein requirement, it will be necessary to investigate fishmeal alternatives to reduce feeding costs. Low salinity pond culture may become a reality in the future if the cobia metabolism-physiology of nutrition at various levels of salinity is well understood. The present paper provides information on some of the options for optimizing the aquaculture performance of Rachycentron canadum.

A Three-Phase Approach to Production of Shedding Crabs (Callinectes sapidus) in Low Salinity Ponds in Mississippi

The ability to reliably produce small blue crabs through aquaculture allows for expanded development of the soft crab industry in the United States with little or no impact to the wild fishery. Research on soft crab aquaculture in Mississippi is based on a three-phase approach: hatchery production of megalopae, salinity acclimation and grow-out of early juveniles in raceways, and final growth to shedding crabs in shallow ponds. Limited access to quality salt water or to hard water aquifers in Mississippi, coupled with the high cost associated with salting ponds led to the development of techniques to produce peeler crabs in reduced salinities. Hatchery success has been variable (average 14%) with significantly lower production following the Deepwater Horizon Oil disaster in 2011. Protocols for hatching and rearing of larvae and methods developed for intermediate grow-out and salinity acclimation of juveniles are reviewed as well as the adaptation of a folk-fishing technique to harvest peelers from the ponds. Economic studies defined production parameters necessary to reduce costs and attain profitability in low salinity (1) pond culture. Increased survivorship of larvae and juveniles during the hatchery, intermediate grow-out and pond phases and stocking density in ponds were key determinants of profitability. Simulation results at various stocking densities indicated that production of shedding crabs could be economically feasible. Although individual culture runs in the current research approached survival rates that would ensure profitability, routine survivorship is currently below the projected estimates necessary to achieve that goal.

Proteomic analysis of the effects of low salinity stress on liver of Naked carp (Gymnocyprinus przewalskii)

Naked carp is only distributed widely in Lake Qinghai. A unique feature of this species is its resistance to high salinity, which enables it to survive and adapt to the extreme environment of Lake Qinghai. Since Naked carp is an endangered species, we considered increasing its resources by reproduction and domestication measures in low salinity ponds. To investigate the molecular biological mechanism of the effects of low salinity stress on the liver of the cultured Naked carp, TMT markers combined with high-performance liquid chromatography-mass spectrometry (TMT-LC-MS/MS) were used to compare and analyze the difference in the expression of liver tissue protein between the cultured population (JH) and wild population (QH) in this study. Proteomic analysis results showed that 107 differential proteins were significantly expressed, and 102 of them were up-regulated. Functional and pathway enrichment analysis results found those differential proteins participate in molecular functions such as pyruvate kinase activity, alkali metal ion binding and potassium ion binding, and various biological processes of energy metabolism including glucose metabolism and lipid metabolism. Differential proteins were mainly concentrated in glycolysis and gluconeogenesis, retinol metabolism, linoleic acid metabolism, and steroid biosynthesis and lipid metabolism pathways.

Consequences of access to water from managed aquifer recharge systems for blood pressure and proteinuria in south-west coastal Bangladesh: a stepped-wedge cluster-randomized trial.

BackgroundDrinking-water salinity has been associated with high blood pressure (BP) among communities in south-west coastal Bangladesh. We evaluated whether access to water from managed aquifer recharge (MAR)—a hydrogeological intervention to lower groundwater salinity by infiltrating rainwater into the aquifers—can reduce community BP.MethodsWe conducted a stepped-wedge cluster-randomized trial with five monthly visits between December 2016 and April 2017 in 16 communities. At each visit following baseline, four communities were randomized to access MAR water. Systolic BP was the primary outcome, measured during each visit using Omron® HEM–907 devices. We also measured participants’ 24-hour urinary sodium and households’ drinking- and cooking-water salinity each visit. We used multilevel regression models to estimate the effects of MAR-water access on participants’ BP. The primary analysis was intention-to-treat.ResultsIn total, 2911 person-visits were conducted in communities randomized to have MAR-water access and 2834 in communities without MAR-water access. Households without MAR-water access predominantly used low-salinity pond water and 42% (range: 26–50% across visits) of households exclusively consumed MAR water when access was provided. Communities randomized to MAR-water access had 10.34 [95% confidence interval (CI): 1.11, 19.58] mmol/day higher mean urinary sodium, 1.96 (95% CI: 0.66, 3.26; p = 0.004) mmHg higher mean systolic BP and 1.44 (95% CI: 0.40, 2.48; p = 0.007) mmHg higher mean diastolic BP than communities without MAR-water access.ConclusionsOur findings do not support the scale-up of MAR systems as a routine drinking-water source, since communities that shifted to MAR water from the lower-salinity pond-water source had higher urinary sodium and BP.

The effect of tilapia Oreochromis niloticus addition on the sediment of brackish low-salinity ponds to white shrimp Penaeus vannamei farming system during the wet and dry season

The present study was carried out to determine the effect of tilapia Oreochromis niloticus on the physical and chemical sediment parameters on an earthen pond in monoculture (shrimp Penaeus vannamei) and co-culture (tilapia-shrimp) during the dry and wet seasons in a commercial farm during the period from mid-September to end-December 2017 and February to mid-May 2018. Chemical and physical analyses were realized on sediment samples from brackish water ponds representing shrimp farms in San Blas Nayarit, Mexico. Concentrations of organic carbon, nitrogen, potassium, magnesium and calcium were higher in co-culture ponds, and there was a tendency to a higher concentration of phosphorus and sodium in the sediment of monoculture ponds. The texture of the ponds showed a tendency in the dry season to increase the percentage of clay in co-culture due to the effect of bioturbation caused by tilapia. There was no evidence of poor development of sediment quality in any treatment. It was found that tilapia was a factor that affected sediment quality, differences in growth between shrimp monoculture and tilapia-shrimp co-culture can be explained, at least in part, by differences in their sediment.

Eco-immunology of native and invasive water bugs in response to water mite parasites: insights from phenoloxidase activity

Biological invasions provide an opportunity for ecological and evolutionary exploration of immune function in host–parasite interactions. Studying parasite-induced immune response in native and invasive species can provide novel insights into mechanisms underlying invasion success. We aimed to establish the influence of mite ectoparasites on the invasion of the alien water boatman Trichocorixa verticalis (Corixidae) originating from North America. We examined the variation in a key component of insect immune function (phenoloxidase activity), and condition (fat storage) of T. verticalis and four species of native water boatmen in relation to water mites, combining field and laboratory observations in southern Spain. Mite infection was associated with a general decrease in corixid immune function (but not of fat stores), but to a varying extent in different host species. Immunosuppression was particularly high in the alien species, which also had a particularly high prevalence of mites in both field and laboratory infections. Mite infections may therefore explain the low abundance of the alien corixid in low salinity ponds, where native corixids dominated and mites were abundant. Uninfected T. verticalis had a lower immune function than three native corixid species, probably because the alien is adapted to higher salinities where ectoparasites are absent, supporting the “cost of immunity hypothesis”. This study shows that higher immunocompetence in invasive species is not the rule as previously assumed, and highlights the need to better integrate immunology into invasion biology.

Coastal saltpans as foraging grounds for migrating shorebirds: an experimentally drained fish pond in Portugal

Worldwide, low-salinity ponds of coastal saltpans are often drained for artisanal fishing, at which time shorebirds feed opportunistically on the drained ponds. This case study sought to examine how shorebirds exploit this food supply after experimentally draining a large pond (9.1 ha) used for artisanal fishing at the Tagus estuary, Portugal. Shorebirds rapidly increased after draining (reaching 156 birds ha−1), and the pond provided a suitable foraging ground for a high density of shorebirds during 6–12 days after the study site was drained, supporting up to 6% of the total population using the estuary. The benthic invertebrate community was dominated by polychaete worms, and their high density (2215.0 ± 329.9 ind m−2) apparently explained the relatively large percentage of feeding birds in the pond. Most shorebirds fed on polychaete worms at high intake rates throughout the experiment, probably because they increased their searching effort. Bird predation contributed to the food supply decrease during the first 3–6 days, and desiccation was presumably the major factor in 8–15 days. The drainage of low-salinity ponds by artisanal fishing is a traditional activity in coastal saltpans that might play a significant role in providing suitable foraging grounds for migrating shorebirds.

Archaeal and bacterial tetraether lipids in tropical ponds with contrasting salinity (Guadeloupe, French West Indies): Implications for tetraether-based environmental proxies

The occurrence and distribution of archaeal and bacterial glycerol dialkyl glycerol tetraether lipids (GDGTs) in continental saline environments have been rarely investigated. Here, the abundance and distribution of archaeal isoprenoid GDGTs (iGDGTs) and archaeol, and of bacterial branched GDGTs (brGDGTs) in four tropical water ponds of contrasting salinity in two islands from the French West Indies, Grande-Terre and La Désirade, have been determined. The sedimentary distribution of the GDGTs strongly differed between the two islands. Caldarchaeol was largely predominant among iGDGTs in the (hyper)saline ponds from Grande-Terre, suggesting a substantial contribution of iGDGTs derived from methanogenic Archaea. In contrast, both caldarchaeol and crenarchaeol were present in high relative abundance in the low salinity ponds from La Désirade, suggesting that iGDGTs were derived from mixed archaeal communities. In addition, the relative proportion of the most methylated brGDGTs was much higher in Grande-Terre ponds than in La Désirade ponds. The applicability of different proxies based on GDGTs and archaeol was tested for these specific environments. The relative abundance of archaeol vs. caldarchaeol (ACE index) was comparable for the four ponds, independent of salinity, showing that the ACE index might not necessarily track salinity change. Moreover, the relative proportion of caldarchaeol vs. total iGDGTs was unexpectedly observed to increase with salinity, suggesting production of this compound by halophilic Archaea. The supposed high abundance of methanogenic Archaea in Grande-Terre ponds prevented the application of TEX86 as a temperature proxy, whereas TEX86 could be successfully used for local temperature reconstruction in La Désirade ponds. BrGDGTs seem to be produced predominantly in situ (water column and/or sediment) in hypersaline ponds from Grande-Terre, but in La Désirade ponds likely result from a mixture of soil and aquatic sources. In Grande-Terre ponds, brGDGT-derived temperature estimates generated using either soil or lacustrine calibrations were much lower than expected. The mismatch between expected and estimated temperature might be explained by the presence of halophilic microbial communities producing specific brGDGT distributions in the saline ponds from Grande-Terre. The study shows that the sources of brGDGTs, iGDGTs and archaeol (i) may strongly differ in aquatic environments of varying salinity, even at a regional scale, and (ii) have to be constrained before tetraether-derived proxies in such settings can be confidently applied.

Occurrence, molecular characterization, and antimicrobial susceptibility of Aeromonas spp. in marine species of shrimps cultured at inland low salinity ponds

We aimed to document the risk of Aeromonas spp. in marine shrimp species cultured in inland low salinity ponds in Thailand. In 14 of 18 shrimp samples retrieved from inland grow-up ponds, Aeromonas spp. were detected at ranges from 4667 to 1,500,000 CFU/g body weight. The phylogenetic tree constructed with the gyrB and cpn60 concatenated sequences indicated that the 87 isolates consisted of Aeromonas veronii (70%), Aeromonas aquariorum (18%), Aeromonas caviae (7%), Aeromonas jandaei (2%), and Aeromonas schubertii (2%). The potential virulence of the isolates was examined by phenotypic and PCR assays. Hemolytic activity and the extracellular activity of lipase, DNase, and gelatinase were observed in most isolates (94–99%). PCR revealed the presence of 9 genes related to virulence in the 87 isolates: act (75%), aer (74%), alt (30%), ast (1%), ascV (34%), aexT (24%), fla (92%), ela (34%), and lip (24%). The susceptibility profiles to 14 antimicrobial agents of isolates were typical for the genus, but resistance to cefotaxime, a third-generation cephalosporin, and imipenem were found in two A. aquariorum and in three A. veronii isolates, respectively. These resistances were confirmed by determining minimum inhibitory concentrations. Our results indicate that the microbiological risk posed by Aeromonas should be considered for marine shrimp species that are cultured in low-salinity ponds. These shrimps may also be a vehicle for the transfer of different genotypes of Aeromonas and antibiotic-resistant determinants to regions worldwide through trade.

Prevalence and antimicrobial susceptibility of Vibrio species related to food safety isolated from shrimp cultured at inland ponds in Thailand

Inland farming of marine shrimp species is a relatively recent development, in response to increasing demand for the products. This study aimed to investigate the prevalence and antimicrobial resistance of potentially pathogenic Vibrio species in shrimps cultured at inland ponds with low salinity in Thailand. Of 16 shrimp samples (white-leg shrimps and black-tiger shrimps) from ponds with water temperatures from 29 to 32 °C, and salinities from 1 to 5 parts per trillion, 15 contained Vibrio cholerae (densities: 62–252,000 MPN/g). Vibrio parahaemolyticus was present in six samples (370–6,300,000 MPN/g), and Vibrio vulnificus was present in two samples (16–1300 MPN/g). V. parahaemolyticus has higher affinity for non-native white-leg shrimp than for native black-tiger shrimp. The minimum inhibitory concentrations were then measured for 12 common antimicrobial agents. Resistance to ampicillin and oxytetracycline (8% and 2% of the isolates) was documented in V. cholerae isolates, resistance to ampicillin and oxytetracycline (72% and 3%) was found in V. parahaemolyticus isolates, and resistance to nalidixic acid (20%) was detected in V. vulnificus isolates. β-lactamase and tetracycline resistance genes were detected in the resistant Vibrio isolates. The oxytetracycline-resistance phenotype was eliminated by plasmid curing, suggesting that the resistance was related to R-plasmids. Our results show that shrimps cultured even in low salinity ponds are potentially contaminated with pathogenic Vibrio species, and that shrimp are a vehicle for transfer of species with antimicrobial resistance genes to the public.

Phytoplankton and macrofauna in the low salinity ponds of a productive solar saltworks: Spatial variability of community structure and its major abiotic determinants

This paper focuses on the structure of the phytoplankton and macrobenthic invertebrates communities in a productive solar saltworks, as well as the major abiotic determinants of the observed biotic patterns. The observed patterns in the structure of the biotic communities attest that the ecosystem of the low salinity ponds of Kalloni Saltworks is similar to a productive coastal lagoon. Major abiotic determinants include the salinity and confinement gradients, as well as inorganic nutrients loads. The episodic enrichment of the water column in the ponds with either new nutrients from the incoming seawater, or regenerated nutrients released from the sediment, was shown to stimulate the growth to bloom levels of phytoplankton species indicative of organic enrichment and coastal eutrophication. Algal biomass and the accumulated detritus and organic matter on and within the sediment are exploited by opportunistic herbivores and deposit feeders tolerant to organic enrichment. Management measures are needed for the mitigation of the productiveness of the low salinity ponds, e.g. lower water residence times, a shallower water column, facilitation of the oxygenation of the sediment, sediment removal in winter and culture and harvesting of the naturally occuring, edible Cerastoderma glaucum bivalves.

Swimming of Xenopus laevis Sperm Exhibits Multiple Gears and Its Duration Is Extended by Egg Jelly Constituents

The motility of Xenopus sperm is initiated by the osmotic shock experienced when these cells are ejaculated into low-salinity pond water. Motility is brief and is required for the sperm to penetrate the jelly layers and fertilize the egg. In this study we demonstrate that extracts of egg jelly contain factors that extend the period of sperm motility as well as providing a chemoattractant activity as previously reported. Both activities are partially dependent on extracellular calcium. Time-lapse and video microscopy show that after activation of motility the number of motile sperm decreases rapidly, with a half-time of about 2 min. Addition of 10% v/v egg jelly extract ("egg water") increased the number of motile sperm 2-fold over controls at 20 s and about 4- to 10-fold over controls at 10 min after initiation of motility. Extension of motility lifetime was not mediated by a nonspecific protein or by allurin, the egg-water protein that has chemoattractant activity. The helical path of Xenopus sperm exhibited tight coupling between rotational and forward velocities in egg jelly, but coupling changed rapidly from moment to moment in low-salinity buffer. Our observations suggest that jelly-derived factors regulate both the longevity and directionality of sperm propulsion.

High diversity of Ruppia meadows in saline ponds and lakes of the western Mediterranean

Saline inland and coastal waterbodies are valuable habitats that deserve attention for the protection of their unique submerged macrophyte beds that render the water clear, stabilize sediments and provide a habitat for high biomasses of invertebrates as food for waterfowl. The ‘continental seagrass’ Ruppia has the widest salinity tolerance among the submerged macrophytes and occurs in a wide variety of saline saltmarsh pond and lagoon systems. Although two cosmopolitan species Ruppia maritima and Ruppia cirrhosa are recognized in Europe and Ruppia drepanensis in the western Mediterranean, their diversity and distribution are not well known. This previously held traditional idea that there are only two widespread Ruppia species suggests a uniform and very homogenized population structure following the hypothesis of long-distance-dispersal through strong bird-mediated dispersal events. Therefore, the Ruppia chloroplast DNA diversity was investigated along a more than 1,000 km transect of the Iberian Peninsula. We studied 492 individuals from 11 wetland areas (17 ponds) and sequenced a 1,753-bp length of seven chloroplast introns. Eight haplotypes represented at least four distinct groups or taxa which is higher than commonly accepted. Six wetland areas contained more than one haplotype and within-pond diversity occurred within distances as small as 30 m (5 out of 17 cases). This underlines the importance of single waterbodies for harbouring haplotypic diversity in Ruppia. Unique haplotypes were observed in four wetland areas and R. maritima was detected only from a low salinity pond, suggesting the species might be more rare than previously accepted. The present results tend to minimize an overall effect of strong bird-mediated dispersal. This emphasizes the role of regional pond habitat diversity for the preservation of Ruppia taxa and their unique haplotype diversity in extreme saline habitats.

Nutrient limitation of phytoplankton in solar salt ponds in Shark Bay, Western Australia

The aim of this research was to examine nutrient limitation of phytoplankton in solar salt ponds of varying salinity at Useless Inlet in Western Australia. These ponds use solar energy to evaporate seawater for the purpose of commercial salt production. A combination of techniques involving water column nutrient ratios, comparisons of nutrient concentrations to concentration of magnesium ions and bioassays were used in the investigation. Comparisons of changes in dissolved inorganic nitrogen to phosphorus ratios and concentrations of dissolved inorganic nutrients against changes in concentrations of the conservative cation Mg2+ indicated that phytoplankton biomass was potentially nitrogen limited along the entire pond salinity gradient. Nutrient addition bioassays indicated that in low salinity ponds, phytoplankton was nitrogen limited but in high salinity ponds, phosphorus limited. This may be due to isolation of phytoplankton in bioassay bottles from in situ conditions as well as to changes in phytoplankton species composition between ponds, and the variable availability of inorganic and organic nutrient sources. The differences in limiting nutrient between methods indicate that phytoplankton cells may be proximally limited by nutrients that are not theoretically limiting at the pond scale. Dissolved organic nutrients constituted a large proportion of total nutrients, with concentrations increasing through the pond sequence of increasing salinity. From the change in nutrient concentrations in bioassay bottles, sufficient dissolved organic nitrogen may be available for phytoplankton uptake in low salinity ponds, potentially alleviating the dissolved inorganic nitrogen limitation of phytoplankton biomass.

Temporal and spatial variation of an aquatic invertebrate community subjected to avian predation at the Odiel salt pans (SW Spain)

We studied the temporal variation in abundance and distribution of inverte- brates in the water column in both traditional and industrial salt pans in the Odiel marshes, south-west Spain, in 2001. We selected 12 ponds that were representative of different salinities and stages of salt production. Every two months, invertebrates were sampled within the 0 - 20 cm depth range used by foraging waders. We identified 40 taxa, including 30 aquatic and eight terrestrial metazoan invertebrates. Aquatic inverte- brate taxa richness and diversity decreased significantly with increasing pond salinity, whereas total biomass showed a non-significant increase. Overall, Artemia partheno- genetica constituted 67.6 % of invertebrates by number, and 95.5 % of the biomass. The copepod Cletocamptus retrogressus represented 31.1 % of invertebrates by num- ber, and 0.6 % of the biomass. Invertebrate biomass and dominance of A. parthenogen- etica was highest in September and lowest in November. There was significant spatial and temporal variation in abundance for all aquatic taxa, and for a given pond and month, the depth, distance to shoreline and fetch (wind effects) all had important par- tial effects on invertebrate distribution. Ordination methods showed a strong relation- ship between community structure and water chemistry (salinity, pH and redox poten- tial), with the salinity gradient being the most important. There was a clear separation between low salinity ponds with fish and submerged macrophytes and other ponds. The more intensively managed industrial salines held lower densities and biomass of invertebrates than traditional salines, perhaps owing to greater protection from wind or greater inputs of detritus. The beetle Ochthebius corrugatus was abundant in the tradi-

Seasonal study on ectoenzyme activities, carbohydrate concentrations, prokaryotic abundance and production in a solar saltern in Korea

Solar salterns in temperate climates commercially produce salt in the summer. To deter- mine whether prokaryotic growth-related variables vary seasonally along the salinity gradient, ectoenzyme activities, prokaryotic abundance (PA), prokaryotic heterotrophic production (PHP) and environmental variables were measured in a solar saltern in 1999 and 2001. In low-salinity (i.e. <120‰) ponds, where marine bacteria are known to dominate the prokaryotic community, posi- tive relationships of ectoenzyme activities with PA (aminopeptidase: r 2 = 0.51, p < 0.01, n = 16; β-glucosidase: r 2 = 0.57, p < 0.01, n = 17), temperature (β-glucosidase: r 2 = 0.56, p < 0.01, n = 17) and PHP (aminopeptidase: r 2 = 0.25, p < 0.05, n = 16) were observed, as also reported for ordinary marine environments. However, in high-salinity (i.e. ≥120‰) ponds, the relationships became insignificant or weak, and a strongly negative relationship between aminopeptidase activity and salinity (r 2 = 0.71, p < 0.01, n = 19) was found. Thus, the high salinity seems to significantly reduce ectoenzyme activi- ties. In high-salinity ponds (120 to 390‰) per-cell ectoenzyme activities decreased by as much as 2 to 3 orders of magnitude. Furthermore, substrate-addition and temperature-treatment experiments indicated that limiting factors for PHP vary seasonally in the saltern. PHP was limited by organic com- pounds (i.e. glucose and an amino acid mixture) in the spring at a salinity of 120‰ and by osmoreg- ulatory substances (i.e. betaine) in the summer at salinities of 260 to 390‰, and temperature in the autumn at 29 to 213‰. Despite the dominant influence of high salinity on prokaryotic activities, rela- tionships between prokaryotic parameters varied seasonally both in low-salinity and in high-salinity ponds. Thus, it seems that prokaryotic variables along the salinity gradient in the saltern are con- trolled by different factors over seasonal cycles.

Salinity controls on trophic interactions among invertebrates and algae of solar evaporation ponds in the Mojave Desert and relation to shorebird foraging and selenium risk

Three saline evaporation ponds formed by wastewater from a solar energy-generating facility near Harper Dry Lake in the Mojave Desert of California, USA were compared for differences in the communities of benthic and planktonic invertebrates and algae present along with avian visitation and foraging activity. Salinity of the ponds ranged from near 90 to over 200 g L 1 total dissolved solids. During the period of study (1997-1999), the lowest salinity pond averaged 98 g L . Differences in the biological communities, abundance of invertebrates and algae, and avian foraging were examined in relation to these differences in salinity. Only three aquatic invertebrate species were present in substantial numbers, a water boatman (Trichocorixa reticulata), a brine shrimp (Artemia franciscana), and a brine fly (Ephydra gracilis). An abundance of the predator Trichocorixa under low salinity conditions appeared to reduce algae-grazing Artemia, and so released phytoplankton growth, but this was observed only in surveys later in the growth season when populations were mature and had greatest potential for efficient consumption of resources. Brine fly larvae were also fed upon by Tricho- corixa and were least abundant in the low salinity pond. At highest salinities where Trichocorixa could not survive, Artemia were abundant and waters were usually clear, becoming dense with phytoplankton only during the winter dormancy of brine shrimp. Intermediate salinity levels supported some water boatmen, often coexisting with dense brine shrimp and phytoplankton populations, and the greatest dry mass of benthic brine fly larvae and pupae. The high salinity pond produced abundant but small Ephydra larvae and pupae, accompanied by reduced emergence success of adult flies. Birds appeared to forage primarily on benthic brine fly larvae and were most successful in the intermediate salinity pond, possibly because lower salinity resulted in loss of this preferred prey to water boatman predation, and high salinity produced prey of poor quality. These observations suggest that reduced salinity may at times mediate a trophic cascade within a simple food chain, where an invertebrate predator may reduce primary consumers and permit enhanced algal density, but the predation control becomes uncoupled as salinity increases. In the case of the ponds studied here, there appeared to be minimal risk associated with selenium poisoning of water birds because Se was not detected in brine fly larvae or pupae and was found only occasionally in low content in the brine shrimp and corixids and mostly in locales where few birds were found feeding.