Distribution and community structure of Ostracoda (Crustacea) in shallow waterbodies of southern Kenya

The current study presents the ostracod communities recovered from 26 shallow waterbodies in southern Kenya, combined with an ecological assessment of habitat characteristics. A total of 37 waterbodies were sampled in 2001 and 2003, ranging from small ephemeral pools to large permanent lakes along broad gradients in altitude (700–2 800 m) and salinity (37–67 200 µS cm^?1). Between 0 and 12 species were recorded per site. Lack of ostracods was associated with either hypersaline waters, or the presence of fish in fresh waters. Three of the 32 recovered ostracod taxa, Physocypria sp., Sarscypridopsis cf. elizabethae and Oncocypris mulleri, combined a wide distribution with frequent local dominance. Canonical correspondence analysis on species–environment relationships indicated that littoral vegetation, altitude, surface water temperature and pH best explain the variation in ostracod communities. Presence of fish and water depth also influence species occurrence, with the larger species being more common in shallow waterbodies lacking fish. Based on Chao’s estimator of total regional species richness, this survey recovered about two-thirds (60–68%) of the regional ostracod species pool. Scanning electron micrographs (SEM) of the valve morphology of 14 ostracod taxa are provided, in order to facilitate their application in biodiversity and water-quality assessments and in palaeoenvironmental reconstruction.     

Patagonian ostracods as indicators of climate-related hydrological variables: implications for paleoenvironmental reconstructions in Southern South America

Different precipitation regimes across Patagonia generate an environmental gradient that is expected to reflect upon the solute composition and concentration of lake water through the ensuing differences in water balance. In turn, this hydrochemical gradient could influence the occurrence and distribution of ostracods in the area. A cluster analysis on hydrochemical data of 36 Southern Patagonian waterbodies shows that low salinity, bicarbonate-dominated waters characterize Andean and ecotonal lakes, located in the wetter part of the precipitation gradient, while their steppe counterparts, which receive a much lower precipitation input, are more saline, enriched in all major anions and sodium-dominated. Kruskal–Wallis tests followed by Mann–Whitney pairwise comparisons show statistically significant differences in the ostracod species each water type hosts, with L. patagonica, E. cecryphalium, P. smaragdina and P. incae being found in the more dilute waters characteristic of Andean and ecotonal lakes and Limnocythere rionegroensis in the mesohaline, evaporatively evolved waters typical of steppe lakes. Other species studied do not appear to have such distinct distributions, having been found throughout the range of conditions studied. These findings promote the use of the aforementioned ostracods as semi-quantitative paleohydrological indicators, which could improve paleoclimatic reconstructions in Patagonia.     

The distribution of the freshwater cichlid Sarotherodon mossambicus in estuarine systems

Synopsis The distribution of Sarotherodon mossambicus in south east African estuaries is reviewed. It occurs commonly in closed estuaries and coastal lakes but is absent from open tidal estuaries. When a closed estuary opens to the sea the species usually retreats to the upper reaches. It is euryhaline and eurythermal and can feed on a wide variety of foods but experiments indicate that S. mossambicus avoids areas where current speeds exceed 370 m h^–1. It is concluded that the distribution of S. mossambicus in estuarine systems is governed by an interplay of the following factors: salinity stability, water currents, suitable breeding sites, presence of marginal vegetation, marine competitors and marine piscivorous fish.     

Late Glacial and Holocene Ostracoda of the Gulf of Gdańsk,the Baltic Sea,Poland

To trace environmental changes in water hydrology and salinity in the Late Glacial to Holocene of the Gulf of Gdańsk, a south‐eastern bay of the Baltic Sea within the maritime zone of Poland, the distribution of ostracod valves was studied in 20 sediment cores collected from both the shallow‐ and deep‐water zones (depth 10.9–67.5 m). The studied sediment sequences yielded ca. 3000 valves of 21 ostracod species, of which only five are known to live today in the Gulf, which has a present maximum depth of 118 m and water salinity up to 7–8‰. The majority of the studied sediment layers that contained ostracod valves corresponded to the period of the Late Glacial to Mid‐Holocene and was dominated by non‐marine species, of which the most common were Candona neglecta (present in 17 cores), Cytherissa lacustris (15 cores) and Candona candida (14 cores). By clustering classification five major ostracod assemblage types were recognised in the studied cores. Initial assemblage types dominated mostly by inhabitants of the profundal/sub‐littoral zones of modern oligo‐mesotrophic lakes (C. lacustris and C. neglecta) in some sediment sequences were replaced in stratigraphical order by the assemblages dominated by brackish‐water species (Cyprideis torosa or Cytheromorpha fuscata). The structure and species composition of the distinguished ostracod assemblage types as well as their successional transitions indicate that the studied sediments were deposited initially in the Late Glacial in freshwater lacustrine conditions, and subsequently, during the Holocene marine transgression, covered by marine sands. The present results confirm and consolidate inferences based on previously published data on ostracods from the western part of the Gulf of Gdańsk as well as on other biotic (molluscs, diatoms) and abiotic (seismoacoustic) indices from this area (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Megalocypris ingens Delorme (Ostracoda) in Saskatchewan saline lakes: osmoregulation and abundance

Results of freezing point depression determinations show that the haemolymph of the ostracod, Megalocypris ingens Delorme, remains hyperosmotic to the medium as the concentration of the medium increases. Even though M. ingens is poikilosmotic, the median lethal concentration (LC50) for this species exceeds the LC50 for an insect species living in the same lakes that is capable of hyposmotic regulation. The LC50 for M. ingens occurred in sulphate-saline lake water with a specific conductance of 48 000 µS cm^-1 (at 25 °C). The absence of vegetation may be more important than salinity in limiting the distribution of M. ingens in Saskatchewan saline lakes.     

Biogeography of copepods in lakes and ponds of subarctic Québec,Canada

We aimed to determine whether the copepod assemblages in lakes and ponds of northern Québec, Canada, were closer in composition to those found in southern Québec, or to those reported from the subarctic and arctic. Six calanoid and five cyclopoid species were identified from 37 ponds and lakes located in the region between 55° N and 59° N. Species diversity was generally low, ranging from 0 to 4 species per lake. Dominant species were Leptodiaptomus minutus and Acanthocyclops vernalis. The species assemblages showed high affinity with those found in forested regions of southern Québec. Exceptions were Leptodiaptomus tyrrelli, previously only recorded west of Hudson Bay, and Hesperodiaptomus arcticus, hitherto recorded north of 58° N. Relationships between the lakes, species, and environmental variables were explored using multivariate analysis. Lakes situated along the coast and on two offshore islands clustered together and were characterised by higher conductivity and pH than those lakes located further inland. Leptodiaptomus tyrrelli was common in these coastal lakes. Canonical correspondence analysis revealed statistically significant relationships between copepod distributions and conductivity, dissolved organic carbon and pH. These three variables accounted for 70% of the variation in the species' distribution.     

Anthropogenic disturbance and spatial heterogeneity of macrobenthic invertebrate assemblages in coastal lagoons: the study case of Pialassa Baiona (northern Adriatic Sea)

The distribution patterns of macrobenthic invertebrate assemblages at different spatial scales and in relation to natural and anthropogenic disturbance gradients were investigated in the Pialassa Baiona, a eutrophic and polluted brackish coastal lagoon located along the Italian coast of the northern Adriatic Sea. This coastal lagoon shows a complex physiography with several shallow water ponds and channels separated by discontinuous artificial embankments. Environmental variables and macrobenthic invertebrate assemblages showed higher heterogeneity at small spatial scale (i.e. within channels and ponds). Distinction between channels and ponds is only weakly supported by the distribution patterns of macrobenthic assemblages. Depth was the major factor in structuring benthic communities within ponds, while species distributions along the channels were strongly correlated with the anthropogenic disturbance gradient. Anthropogenic disturbance mainly affected species richness, which was inversely correlated with the organic carbon contents in the sediments and the water surface temperature, which is affected by the input of cooling water from two thermal power plants. Some opportunistic species, like the polychaetes Streblospio shrubsolii and Capitella capitata, were more abundant in the southern polluted areas. In particular, the abundance of S. shrubsolii significantly increased with organic carbon contents in the sediments and water surface temperature, while C. capitata was more abundant in the warmed sites and close to sewages. Conversely, the abundance of the amphipod Corophium insidiosum was inversely related to organic carbon contents.     

Evaporation effects as reflected in freshwaters and ostracod calcite from modern environments in Central and Northeast Yakutia (East Siberia,Russia)

Taxonomical and geochemical investigations on freshwater ostracods from 15 waters in Central and Northeast (NE) Yakutia have been undertaken in order to estimate their potential usefulness in palaeoenvironmental reconstructions based on regional fossil records. Higher variability in environmental factors such as pH, electrical conductivity, and ionic content was observed in thermokarst-affected lakes in Central Yakutia than in NE Yakutia lakes. Species diversity of freshwater ostracods reached up to eight taxa per lake, mostly dominated by Candona weltneri Hartwig 1899, in Central Yakutia, whereas in NE Yakutian waters the diversity was lower and Candona muelleri jakutica Pietrzeniuk 1977 or Fabaeformiscandona inaequivalvis (Sars 1898) had highest frequencies. Coupled analyses of stable isotopes (δ¹⁸O, δ¹³C) and element ratios (Sr/Ca, Mg/Ca) were performed on both host waters and ostracod calcite, aiming to estimate the modern relationships. Correlations between host waters and ostracod calcite of single species were found for δ¹⁸O, δ¹³C and Sr/Ca and Mg/Ca ratios. The relationships between δ¹⁸O, Mg/Ca and Sr/Ca ratios and electrical conductivity (salinity) as an expression of solute concentrations in the waters mainly controlled by evaporation are more complicated but evident, and may be useful in future interpretation of geochemical data from fossil Siberian ostracods. Handling editor: K. Martens     

Ostracoda as bioindicators of anthropogenic impact in salt lakes,saltpans, and a lagoon: A case study from the Gulf of Saros coast (NE Aegean Sea), Turkey

The study area consists of wetlands and semi-wetlands (saltpan and salt lakes) that are separated from the Gulf of Saros in the northeastern Aegean Sea by a littoral cordon. Twenty-four samples were collected from the Enez Salt Lake; Dalyan, Enez Gala, Kuvalak, Isik, and Tasalti Lakes; Vakif and Erikli Saltpans; and Karagol Lagoon. The overall distribution of the sediment sizes reveals that they consist predominantly of mud and sand and a mixture of mud, sand, and gravel. The average proportion of gravel size particles is 8.36%. Feldspar and mica are abundant in sand and gravel-sized materials. Ecological conditions of these coastal areas were assessed on the basis of ostracod assemblages that can be considered as useful bioindicators and depend on water depth, temperature, and salinity. In this context, the effects of physical and chemical properties of the environment, geochemistry of the sediment, and anthropogenic impact on the meiofauna, in particular ostracoda, was here evaluated. Cyprideis torosa Jones, a cosmopolitan species of ostracoda, was found in salt lakes. Other species of ostracoda were shown to be affected by environmental conditions. The toxicity of some heavy metals in the saltpans, salt lakes, and hypersaline lagoons was evaluated. Lake Dalyan and Erikli Saltpan display high toxicity for Cu and Cd levels. The distribution of hydrocarbon pollution of terrestrial origin was determined.     

Transition zones in small lakes: the importance of dilution and biological uptake on lake-wide heterogeneity

Community structure and diversity patterns of pelagic copepods were investigated for the coastal areas and in the marine lakes of the Palau islands in the West Pacific. We conducted field surveys during 2004–2007 and collected zooplankton samples from eight coastal areas and 16 marine lakes. The marine lakes in the islands of Palau are limnologically classified into two types, meromictic and holomictic lakes. Species diversity indices (Margalef’s species richness d′, Shannon–Wiener index H′, and Simpson’s dominance) were measured at each sampling site. The copepod community structure was analyzed using multivariate analyses, hierarchical cluster analysis, and non-metric multidimensional scaling (MDS) from the PRIMER package. A total of 36 copepod taxa were identified to the genus or species level from Calanoida, Cyclopoida, Harpacticoida, and Poecilostomatoida. Multivariate analysis based on the Bray–Curtis similarity index revealed that copepod assemblages could be classified into three different groups according to their habitat: (I) meromictic lakes, (II) holomictic lakes with an exceptionally shallow and flat basin (type A holomictic lakes), (III) holomictic lakes with a deep basin (type B holomictic lakes), and all coastal areas. The meromictic lakes were characterized by markedly decreased species diversity (d′ = 0.15, H′ = 0.41) in which only two brackish-water species, Bestiolina similis and Oithona dissimilis, were dominant. Type A holomictic lakes were characterized by relatively low levels of species diversity (d′ = 1.25, H′ = 1.35). In contrast, type B holomictic lakes were characterized by relatively high levels of species diversity, which was comparable to that of coastal areas. This result indicated that zooplankton assemblages in the type B holomictic lakes were closely related to a coastal community. The present study showed that the species diversity of pelagic copepods varies according to the level of isolation and the local environmental conditions for each marine lake.     

Effect of temperature and salinity on the gastric evacuation of juvenile sole Solea solea and Solea senegalensis

The juveniles of Senegal sole, Solea senegalensis, Kaup 1858, and common sole, Solea solea (Linnaeus 1758) concentrate in estuarine and coastal nurseries of widely differing temperatures and salinities. Yet, little is known about the effect of these physiologically important variables on the gastric evacuation rates of these species. Gastric evacuation experiments were performed on juveniles of S. senegalensis and S. solea. Three temperatures were tested, 26, 20 and 14°C at a salinity of 35‰. A low salinity experiment was also carried out at 15‰, at 26°C. Experimental conditions intended to reflect conditions in estuarine and coastal nurseries where juveniles of these species spend their first years of life. The relation between stomach contents and time was best described by exponential regression models for both species. An analysis of covariance (ancova ) was performed in order to test differences in evacuation rate due to temperature and salinity (slope of evacuation time against stomach contents) for each species. While increasing temperature increased evacuation rates in both species (although not at 26°C in S. solea), the effect of low salinity differed among species, leading to a decrease in gastric evacuation rate in that of S. senegalensis and an increase in S. solea. Differences in gastric evacuation rate between species were related to its metabolic optimums and to its distribution in the nursery area where fish were captured. Implications for the habitat use of estuarine and coastal nurseries are discussed.     

Land use and ostracod community structure

Ostracods are important members of the benthos and littoral communities of lake ecosystems. Ostracods respond to hydrochemistry (water chemistry) which is influenced by climatic factors such as water balance, temperature, and chemicals in rainfall runoff from the land. Thus, at local scales, environmental preferences of ostracods and characteristics of lakes are used to infer changes in climate, hydrology, and erosion of lake catchments. This study addresses potential drivers of ostracod community structure and biodiversity at multiple spatial scales using NMS, CART^?, and multiple regression models. We identified 23 ostracod species from 12 lake sites. Lake area, maximum depth, spring conductivity, chlorophyll a, pH, dissolved oxygen, sedimentary carbonate, and organic matter all influence ostracod community structure based on our NMS. Based on regression analysis, lake depth, chlorophyll a, and total dissolved solids best explained ostracod richness and abundance. Land uses are also important community structuring elements that varied with scale; locally and regionally agriculture, wetlands, and grasslands were important. Nationally, using regression tree analysis of lakes sites in the North American Non-marine ostracod database (NANODe), row-crop agriculture was the most important predictor of biodiversity. Low agriculture corresponded to low species richness but greater landscape heterogeneity produced sites of high ostracod richness.     

Seasonal changes in the abundance and distribution of submerged aquatic vegetation in a highly managed coastal lagoon

The inflow of fresh water into coastal lagoons is a key factor influencing the structure and function of these ecosystems. Biscayne Bay, a coastal lagoon adjacent to the city of Miami, is located downstream of the Everglades ecosystem where the extensive water management system now in place has modified the historical hydrology, replacing groundwater and overland flows with pulsed releases from canals. In areas where canals discharge directly into littoral habitats, an environment with low-mean salinity and high-salinity variability is created. In this study, we characterize the salinity patterns of nearshore habitats (<500 m from shore) and document patterns of seasonal abundance and distribution of submerged aquatic vegetation (SAV) to evaluate the impacts of water management practices. Seagrasses were the principal component of the SAV community during the 2005 dry season (mean cover = 25.5%), while macroalgae dominated during the wet season (mean cover = 33.4%). The distribution and abundance of SAV were directly related to the tolerance of each taxon to salinity patterns. Seagrass species with high tolerance to low and variable salinity such as Halodule wrightii and Ruppia maritima were found only in canal-influenced areas and increased in abundance and spatial distribution in the wet season when freshwater inflow is highest. The dominance of rhizophytic macroalgae during the wet season was determined by the appearance and high abundance of Chara, a taxon commonly associated with freshwater environments. Thalassia testudinum, the most abundant seagrass species, was found throughout the study region, but decreased in abundance in the canal-influenced areas during the wet season when lower, more variable salinity resulted in lowered productivity. The data presented here showed a significant relationship between salinity patterns and the seasonal abundance and distribution of SAV. These findings support the use of SAV as appropriate indicators of changes in water quality resulting from future restoration projects associated with the Everglades Restoration Plan, which will once again modify the delivery of fresh water into littoral habitats with unknown ecological consequences. Handling editor: S. M. Thomaz     

The biogeography of three Boeckella species (Copepoda: Calanoida) in New Zealand

The New Zealand distributions of three species of Boeckella (Copepoda, Calanoida), B. triarticulata, B. dilatata and B. hamata are mapped. B. triarticulata is primarily a pond dweller but is also found in reservoirs and shallow lakes. B. dilatata is mainly found in the deeper glacial lakes and ponds in the central region of the South Island and B. hamata has a more widespread distribution in lakes and ponds in the South Island and lower half of the North Island. Differences in temperature optima, food requirements and dispersal ability among the three Boeckella species are related to vicariant events to explain their distribution in New Zealand.     

A study of benthic communities in some shallow saline lakes of western Victoria,Australia

The summer benthos of 24 lakes ranging from 1–204 g l^-1 salinity contained 27 species of macroinvertebrates. The worm Antipodrilus timmsi, the ostracod Mytilocypris splendida, the amphipod Austrochiltonia subtenuis, the chironomids Procladius spp. and Chironomus duplex aand the snail Coxiella striata were common at lower salinities (3—ca. 30 g l^-1) while the crustaceans Australocypris robusta and Haloniscus searlei, the chironomid Tanytarsus barbitarsis and a ceratopogonid larva dominated in salinities ca. 20–100 g l^-1. Small ostracods were common from 40–150 g l^-1. Diversity changed little with salinity. Mean dry biomass ranged from 0–3.94 g m^-2; distribution between lakes was negatively skewed with a peak around 7 g l^-1 salinity. Within many lakes, there was considerable spatial heterogeneity which in some cases seemed to result from different bottom characteristics or to point source enrichment. Many groups contributed to the standing crop at low to moderate salinities, and at high salinities crustaceans were important. The lakes were grouped into two low salinity associations, an association which comprised the Red Rock Lakes and a cluster of highly saline lakes. This reflects the grouping of species into halobiont, halophilic and salt-tolerant freshwater species.     

Magnesium and strontium in non-marine ostracod shells as indicators of palaeosalinity and palaeotemperature

Measurements of the Ca, Sr, and Mg contents of individual calcitic shells of non-marine ostracods and their host waters, both in lakes and controlled aquaria, permit the calculation of the distribution coefficients of Sr/Ca and Mg/Ca partitioning in ostracod shells. We report new K_D[Sr] for seven genera of non-marine ostracods and K_D[Mg] for Cyprideis at 25°C.Strontium partitioning is virtually temperature-independent, and is related to the Sr/Ca of the host water, and in Ca²⁺-saturated waters, to the salinity of the water. Magnesium partitioning is dependent on both temperature and Mg/Ca of the host water.For simple closed-basin lakes (crater lakes are ideal), the Sr content of ostracods is a sensitive indicator of salinity and thus evaporation/precipitation changes, which in turn, indicate variations in continental climate. A 10000-year continuous palaeosalinity record established by Sr and Mg contents of fossil ostracods for Lake Keilambete, southeastern Australia, is in close agreement with an independent palaeosalinity estimate based on sediment textures.We suggest rules that allow Sr and Mg analyses of suites of individual fossil ostracod shells from lacustrine sediments to be interpreted in terms of palaeosalinity and palaeotemperature variations.     

Vibrio communities along a salinity gradient within a marine saltern hypersaline environment (Saline di Tarquinia,Italy)

Vibrio species are ubiquitous in a number of different aquatic environments and promptly adapting to environmental changes due to high genome plasticity. The presence of these bacteria in marine salterns, in relation to a salinity gradient has been not investigated yet. Moreover, it is not clear if these hypersaline environments could represent a reservoir for Vibrio spp. This work investigated, through a metagenetic approach, the distribution of Vibrio (over 2 years) in different ponds along the salinity gradient within the ‘Saline di Tarquinia’ salterns, considering also the adjacent coastal waters and an isolated brine storage basin (BSB). Vibrio occurrence was higher in the sea than in the ponds and BSB, where it usually represented a rare taxon (abundance <1%). In the sea, it showed abundances in-between 1%–2.6% in 8 months out of 24. Four OTUs were assigned to the Vibrio genus; except for one that was more abundant in BSB, the others were much higher in the sea. Redundancy analysis (RDA) suggested a different distribution of the OTUs in relation to water temperature and salinity. Vibrio was found, even with low abundances, at the highest salinities also, suggesting the salterns as a possible reservoir for the bacterium.     

The biology of the burrowing goby Croilia mossambica Smith (Teleostei,Gobiidae)

Synopsis Croilia mossambica, a burrowing goby endemic to the coastal lakes of south east Africa occurs from L. Poelela (salinity 8%.) to L. Sibaya (freshwater). Since these lakes are isolated from one another its distribution is discontinuous. It is not found in estuaries or the sea. In L. Sibaya C. mossambica is present on sheltered sides from a depth of 1 m to about 16 m. On exposed shores it is not found at less than 3.5 m depth. It is restricted to sandy, quiet water areas and is unable to form burrows where the substrate is disturbed by water movement, is muddy or consists of sand with a particle diameter greater than 0.5 mm. The maximum depth at which it lives is probably determined by light penetration since it is dependent on sight for prey capture. The food consists of slow moving benthic invertebrates such as chironomid larvae, gastropods, bivalves and amphipods. The relative importance of each depends upon its abundance. C. mossambica is a summer breeder with a protracted spawning season. The sticky eggs measure 0.7–0.8 mm when laid. Tolerance experiments show that it is euryhaline and can survive in seawater of 35%. and that its upper temperature limit is between 32 and 35°C. Temperatures in shallow waters of lakes and estuaries of the region frequently exceed 35°C. Thus its local distribution may be limited by temperature. Its lack of tolerance to high temperatures, to marked water movements and its ability to live in seawater indicates that C. mossambica is suited to life in the sea rather than in estuaries. It is suggested that it was present in quiet areas of the sea, such as lagoons, and that it invaded the coastal lakes which were formed as the estuaries and river valleys were inundated during the Pleistocene marine transgression. C. mossambica cannot tolerate estuarine conditions and with the present absence of quiet water in the sea off the south east African coast the species is now confined to deep coastal lakes.Note     

Spanish salt lakes: Their chemistry and biota

A large number of small saline lakes are distributed throughout Spain. Four main lake districts occur from sea level to 1000 m.a.s.l. Most lakes are temporary because of the arid conditions in the Spanish endorheic areas. Many lakes are situated in Tertiary depressions in NE. and S. Spain. Lake basins were formed in karstic areas by hydrologic and aeolian erosion. Saline lakes in NE. Spain occupy areas isolated between river basins. The major ions encountered in these lakes are usually sodium-chloride and magnesium-sulphate; sodium carbonate or sodium-sulphate rich waters also occur.The biota of Spanish salt lakes is related to that of a larger biogeographical region which includes the Mediterranean countries. The main types of salt lakes in Spain include: (1) temporarily mineralized but not highly saline lakes, salinity is less than 7 g l^-1. Chara canescens, C. aspera, Zanichellia palustris, Daphnia atkinsoni, Mixodiaptomus incrassatus and Arctodiaptomus wierzejskii are the most characteristic organisms. (2) Temporary salt lakes, salinity fluctuates between 7 and 300 g l^-1. Chara galioides, Lamprothamnion papulosum, Daphnia mediterranea, Arctodiaptomus salinus and Cletocamptus retrogressus are the most common species. (3) Permanent salt lakes, Ruppia maritima, Najas marina and Artemia salina are the characteristic organisms.     

Complex controls on ostracod palaeoecology in a shallow coastal brackish‐water lake: implications for palaeosalinity reconstruction

1. The low‐Mg calcite shells of Ostracoda (Crustacea) are often well preserved in the sediments of alkaline lakes. In coastal waters that have undergone large temporal changes in salinity, ostracod assemblages preserved in the sediment record have been used to reconstruct palaeosalinity, often assuming that salinity is the only significant control on the faunas. 2. We evaluate the performance of ostracods as palaeosalinity indicators in Hickling Broad, a shallow brackish coastal lake in Norfolk, U.K., by comparing fossil ostracod assemblages covering two centuries with geochemical inferences and instrumental records of past salinity and water composition along with other palaeolimnological indicators. 3. Despite large changes in the salinity of the lake and the supposed salinity sensitivity of ostracods, the fossil ostracod assemblages do not clearly reflect the salinity trends inferred from the other independent data. Rather, a complex series of changes has occurred in the lake over the past 200 years and factors other than salinity, including eutrophication, toxicity and associated complex alterations in habitat availability have probably influenced ostracod assemblages. In contrast, there is a good broad agreement between inferred or measured salinity and the trace‐element chemistry of ostracod shells. 4. We conclude that ostracod faunas may not always provide unambiguous palaeosalinity records and should therefore not be used to reconstruct salinity changes except as part of a multi‐proxy investigation that includes other palaeoecological and/or geochemical indicators.