Euryhaline Species Research Articles

Synergistic climatic and anthropogenic effects on marine species turnover in estuarine waters

Climate and anthropogenic stressors are frequent in coastal systems, affecting biological communities in different intensities and directions. When acting synergistically, their effects may be intensified. ENSO strongly affects the climate globally, being responsible for increased rainfall in the Atlantic Southwestern during El Niño and droughts during La Niña phases. Contrasting, human-made breakwaters have static influence in decreasing estuarine salinity. Using a 23-year of fish abundance dataset, we identified that intense El Niño events and breakwater extension decreased the marine fish abundance, with potential additive synergistic effects, whereas La Niña showed no influence. Species composition changes were observed after the breakwater extension, probably related to opportunistic habits of euryhaline species. Anthropogenic and natural climatic disturbances affect habitat use, and their synergic effects must be considered to evaluate ecosystem responses in the current climate change scenario, and constant human modification of coastal zones.

Salinity Tolerance, Seasonal and Multiyear Dynamics of Biting Midges (Diptera, Ceratopogonidae) in Macrozoobenthos Communities of Saline Rivers (the Lake Elton Basin, Russia)

The results of long-term studies of biting midges (Diptera, Ceratopogonidae) in macrozoobenthos communities of five saline rivers of the hyperhaline Lake Elton basin are presented. The fauna of Ceratopogonidae includes 5 halophilic and euryhaline species, among which representatives of the tribe Palpomyiinae predominate. Taxonomic composition of the family differs in rivers with different levels of salinity. Species Sphaeromias miricornis and Culicoides riethi are widely distributed in mesohaline the Khara, the Lantsug and the Bolshaya Samoroda rivers, and P. schmidti widely distributed in polyhaline the Chernavka and the Solyanka rivers. Two generations of S. miricornis and three generations of P. schmidti were recorded. Departure of the first generation of P. schmidti occurs in mid-May, S. miricornis in late May–early June. There is an increase in mean annual abundance and biomass of biting midges in polyhaline rivers compared to mesohaline rivers.

Molecular evidence for the adaptive evolution in euryhaline bivalves

Marine bivalves inhabiting intertidal and estuarine areas are frequently exposed to salinity stress due to persistent rainfall and drought. Through prolonged adaptive evolution, numerous bivalves have developed eurysalinity, which are capable of tolerating a wide range of salinity fluctuations through the sophisticated regulation of physiological metabolism. Current research has predominantly focused on investigating the physiological responses of bivalves to salinity stress, leaving a significant gap in our understanding of the adaptive evolutionary characteristics in euryhaline bivalves. Here, comparative genomics analyses were performed in two groups of bivalve species, including 7 euryhaline species and 5 stenohaline species. We identified 24 significantly expanded gene families and 659 positively selected genes in euryhaline bivalves. A significant co-expansion of solute carrier family 23 (SLC23) facilitates the transmembrane transport of ascorbic acids in euryhaline bivalves. Positive selection of antioxidant genes, such as GST and TXNRD, augments the capacity of active oxygen species (ROS) scavenging under salinity stress. Additionally, we found that the positively selected genes were significantly enriched in KEGG pathways associated with carbohydrates, lipids and amino acids metabolism (ALDH, ADH, and GLS), as well as GO terms related to transmembrane transport and inorganic anion transport (SLC22, CLCND, and VDCC). Positive selection of MCT might contribute to prevent excessive accumulation of intracellular lactic acids during anaerobic metabolism. Positive selection of PLA2 potentially promote the removal of damaged membranes lipids under salinity stress. Our findings suggest that adaptive evolution has occurred in osmoregulation, ROS scavenging, energy metabolism, and membrane lipids adjustments in euryhaline bivalves. This study enhances our understanding of the molecular mechanisms underlying the remarkable salinity adaption of euryhaline bivalves.

Gastrochaenolites as Palaeoenvironmental Information Traps: The Case of the Tholos of La Pastora (Valencina de la Concepción, SW Spain)

ABSTRACT In the Mio-Pliocene calcareous sandstone slabs used as capstones at La Pastora tholos in the Copper Age megasite of Valencina de la Concepción-Castilleja de Guzmán (SW Spain), marine bioerosion structures produced in the 3rd millennium BCE were recognised. In this work, we focus on the perforations made by the lithophage bivalve Petricola lithophaga, called Gastrochaenolites, specifically on its functionality as a ‘trap’ of sediment of the environment where they were produced and of which there are no observable outcrops. The microfaunal content consisting of planktonic and benthic foraminifera as well as ostracods was studied. It was possible to infer the palaeoenvironmental conditions of the place where the slabs were quarried, c. 4700–4600 years ago, which correspond to a wide marine bay. The presence of benthic foraminifera like Astrononium stelligerum, Elphidum crispum, Ammonia beccarii and ostracods like Loxoconcha elliptica and Cytherois fischeri implies that the sector of the bay had a water temperature of no more than 20°C, a bathymetry between 0 and 25 m of depth. Also, episodes of fluvial influence caused a variation in water salinity between 30 and 35‰, attested by the presence of euryhaline species of ostracods from low energy environments and clay substrates, thus confirming estuarine conditions.

Isolation of euryhaline microalgal strains from tropical waters of Brunei Darussalam for potential biomass production

Abstract. Roseli W, Tanaka Y, Taha H. 2023. Isolation of euryhaline microalgal strains from tropical waters of Brunei Darussalam for potential biomass production. Biodiversitas 24: 4651-4660. Rapid urbanization has increased the accumulation of excess nitrogen (N) and phosphorus (P) in natural water bodies (eutrophication). Microalgae are seen as a viable candidate to resolve the problem due to their ability to absorb nutrients from the eutrophicated water (phycoremediation). Euryhaline microalgae could significantly benefit because they can tolerate various salinities while maintaining high biomass productivity. This study aimed to isolate euryhaline microalgae from tropical waters and evaluate the algae's potential to produce biomass and absorb nutrients in a wide range of salinities. Three strains labeled W1, W2, and W3 were isolated from Brunei waters and confirmed by DNA barcoding as Desmodesmus sp., Micractinium sp., and Chlorococcum sp., respectively. These strains were screened for salinity tolerance by exposing them to eight conditions (salinity 0, 5, 10, 15, 20, 25, 30, and 35) and evaluated for their high growth performance based on optical density. While the growth of Desmodesmus sp. and Chlorococcum sp. decreased from its highest value by 51% and 45%, respectively, the growth of Micractinium sp. was only reduced by 30%, and therefore, Micractinium sp. was considered to be the most euryhaline species and studied further in the next scale-up experiment. Micractinium sp. was cultivated at salinities of 0, 15, and 30 and recorded the highest biomass production of 54.1 ± 6.0 mg L?1 d?1 at salinity 15. Furthermore, they produced high amounts of N and P in their biomass, indicating that they are suitable for the phycoremediation of eutrophic water bodies. Therefore, Micractinium sp. is a potential candidate for open-pond cultivation because of its tolerance to a wide range of salinities and high biomass productivity.

First Knowledge on Data Poor Stock: LWR and Condition Factor of a Recently Established Population of Atherina boyeri in Atikhisar Reservoir, Turkiye

Fisheries management practices require reliable data for the assessment of data poor stocks. This paper reported the first knowledge on length-weight relationship (LWR) and condition factor of Atherina boyeri in Atikhisar Reservoir, Çanakkale, Türkiye. A total of 1103 individuals of which 132 were immature was captured in June 2021. The sex ratio male to female was 1:1.75. The relationship between weight (W) and total length (TL), standard length (SL), and fork length (FL) were estimated as W=9E-06TL2.9212, W=1E-05SL2.9082, and W=9E-06FL2.9495. A. boyeri exhibited a negative allometric growth. The mean of Fulton`s condition factor of A. boyeri population in Atikhisar Reservoir was determined as 0.619±0.061. The mean Fulton`s condition factor for female individuals were higher than the males` condition factor and the difference between sexes was statistically significant. The present study made available valuable information on the data poor stock by providing LWR and condition factor of A. boyeri in Atikhisar Reservoir, a new freshwater system for the very euryhaline amphidromous species. The findings of the present study will substantially contribute to the knowledge of the population dynamics of the commercially important species for fisheries managers and decision-makers to maintain sustainable population levels.

Size estimation based on Genidens barbus and Micropogonias furnieri otoliths. Exploring Late Holocene euryhaline fish capture techniques in the eastern Pampa–Patagonia transition, Argentina

Sea catfish (Genidens barbus) and whitemouth croaker (Micropogonias furnieri) were the most marine euryhaline species exploited by hunter-gatherers during the final Late Holocene along the coastal fringe of the eastern Pampa–Patagonia transition (Argentina). In the lower basin of the Colorado River, zooarchaeological evidence recovered from the San Antonio archaeological locality indicates prevalent fish consumption. However, no specific technology related to fishing has been recovered as part of the archaeological assemblages, hence strategies and techniques of fish capture remain unknown. The aim of this paper is to estimate the size of both species through archaeological otolith measurements to evaluate possible fish capture techniques. The analyzed sample is made up of 117 otoliths of whitemouth croaker and 863 of sea catfish. The estimated size of G. barbus individuals is between ca. 240 and 730 mm, which indicates the presence of juveniles and adults. In the case of M. furnieri, the estimated size range of individuals is ca. 350–750 mm, which indicates the representation of adult specimens. Based on the diversity of sizes represented in both species, their ethology, and the geomorphological characteristics of the study area, it is proposed that the fish could have been caught with either nets or bare hands through nonselective mass trapping strategies during the spring–summer season.

Effects of Estuarine Environmental Heterogeneity on the Habitat of Gobiidea Species Larvae

AbstractIn aquatic ecosystems around the world, gobies comprise one of the most diverse groups of fishes in estuaries. The Yangtze River estuary, the biggest estuary in the western Pacific, is a major habitat for larval gobies, with the peak spawning and breeding season occurring during late spring and summer. To investigate the adaptation mechanism of larval gobies to environmental factors, three models (a global generalized linear model, a generalized additive model, and a geographically weighted Poisson regression) were used to simulate and forecast the major habitat distributions of larval gobies based on the survey data from 2018 to 2020. Six species of gobies were studied:Rhinogobius giurinu,Odontamblyopus rubicundus,Tridentiger barbatus,Parachaeturichthys polynema,Tridentiger trigonocephalus,andTrypauchen vagina. The habitats for brackish speciesT. barbatuswere mainly in freshwater (where, using the practical salinity scale, salinity is 0–1) of the south branch, whereas the marine speciesP. polynemawas mainly caught in oligohaline waters (where salinity is 1–5) of the north branch. The other euryhaline species were near the exit of the north branch or dispersed throughout the surveyed region. Year, season, salinity, and sample location had significant effects (P < 0.001) on determining the habitat distributions of larval gobies. The geographically weighted Poisson regression identified that the temperature, depth, distance from the coast, and chlorophyllahad a significant effect (P < 0.001) on the local distribution of habitats. This work supplements information about the distribution of major habitats and their interactions with the environment for the ecologically important species of goby in the Yangtze estuary during the larval stage, and the conclusions provide a basis for the management of aquatic ecosystems and biological habitats.

First records of ratan goby Ponticola ratan in the Kaniv Reservoir and Desna River (Ukraine): A discreet invader of rip-raps

Monitoring of nearshore fish communities carried out in 2019 and 2022 in the Kaniv Reservoir and lower Desna River (Dnieper River basin, Ukraine) showed the presence of the ratan goby (Ponticola ratan), which has never been observed in these water bodies before and naturally inhabited marine and brackish waters of the Black and Azov Sea basins. The ratan goby was detected only on rip-rap structures and not on any other surveyed substrates including sand, mud, clay, and gravel which suggests a narrow habitat preference for this species. In all instances, the ratan goby co-occurred with the round goby (Neogobius melanostomus). Occurrence on all surveyed rip-raps, high abundances and the presence of a variety of size classes of the ratan goby in samples suggest that this species penetrated the Kaniv Reservoir quite long ago and successfully established there and has become a common component of the local fish fauna. Based on the obtained data, this gobiid should be listed among freshwater fishes of Europe as a euryhaline species that can potentially colonize other rivers flowing into the Black Sea including the Danube.

Macro-invertebrates response to acute salinity changes in the Shatt Al-Arab River system, Southern Iraq

The stress of acute salinity increase on the life of macro-invertebrates in Shatt Al-Arab River system were investigated based on their abundance estimation acute salinity increase during the year 2018,where the salinity of the River at central, Basrah City became above 5 ppt and reached up to 25 ppt. Review work was done to determine the sizes and densities of the species during the normal conditions in past decades (1975-1995). The results of observations, photography and semi-quantitative sampling which were taken during many visits in the years 2012, 2015, 2016, 2016, 2017, 2018, 2019 and 2020 at Al-Salhia, Abo Al-Kassib, Al-Garmma and Al-Gurnah, were expressed in an ordinal six abundant scales (SACFOR), modified for species sizes and densities. All the species were have superabundance or common scale during the period 1975-1995, whereas at 2018-2020 the abundance of all species except M. affinis, were declined in general, 7 species were absent and 3 more were rare. The amphipods Parhyale basrensis, Platorchestia monodi, the isopod Sphaeroma annandalei and the annelid Namalycastis indica were commonly or frequently found at good state indicating their ability to resist the mesohaline conditions, the euryhaline species M. affinis and B. amphitrite weren’t affected. The study concluded that, in case of long term mesohaline conditions, most of the estuarine macro-invertebrates will be unable to persist and may be shifting to the upper reaches of the River.

Freshwater transfer affected intestinal microbiota with correlation to cytokine gene expression in Asian sea bass.

As a catadromous fish, Asian sea bass (Lates calcarifer) juveniles migrate from seawater (SW) to freshwater (FW) for growth and development. During migration, they undergo physiological changes to acclimate to environmental salinity. Thus, it is crucial to understand how SW-to-FW migration affects the gut microbiota of catadromous fish. To the best of our knowledge, no study has revealed the effects of transfer to hypotonic environments on a catadromous fish microbiota. In this study, we aimed to determine the effects of FW transfer on the microbiota and cytokine gene expression in the intestines of juvenile catadromous Asian sea bass. The relationship between the water and the gut microbiota of this euryhaline species was also examined. We found that FW transfer affected both mucosa- and digesta-associated microbiota of Asian sea bass. Plesiomonas and Cetobacterium were dominant in both the mucosa- and digesta-associated microbiota of FW-acclimated sea bass. The pathogenic genera Vibrio, Staphylococcus, and Acinetobacter were dominant in the SW group. Although dominant fish microbes were present in the water, fish had their own unique microbes. Vitamin B6 metabolism was highly expressed in the FW fish microbiota, whereas arginine, proline, and lipid metabolism were highly expressed in the SW fish microbiota. Additionally, the correlation between cytokine gene expression and microbiota was found to be affected by FW transfer. Taken together, our results demonstrated that FW transfer altered the composition and functions of mucosa- and digesta-associated microbiota of catadromous Asian sea bass intestines, which correlated with cytokine gene expression.

Morphological and Molecular Identification of Mullet Helminth Parasite Fauna from Ganzirri Lagoon (Sicily, Southern Italy)

Mullets (Osteichthyes: Mugilidae) are a euryhaline species widely distributed all over the world, thus representing an excellent study model for host-parasite interactions. From March to June 2022, 150 mullets, belonging to Chelon labrosus (n = 99), Chelon auratus (n = 37), and Oedalechilus labeo (n = 14) species, were caught to identify the helminth parasite fauna of the different mullet species present in the Ganzirri Lagoon (Messina, Sicily, Italy). A parasitological evaluation of the gastrointestinal tract (GIT) was carried out with a total worm count technique (TWC) to detect helminth presence. All collected parasites were stored in 70% ethanol until morphological evaluation, and frozen at -80 °C for subsequent molecular analysis, using 28S, ITS-2, 18S primers. The morphological evaluation allowed for the identification Acanthocephalan parasites (Neoechinorhynchus agilis) from two C. labrosus specimens. Sixty-six samples were positive for adult digenean trematodes (C. labrosus, 49.5 %; C. auratus, 27%, and O. labeo, 50%), molecularly identified as Haploporus benedeni. This study represents the first survey of helminthic parasite fauna of mullets from the south of Italy. The presence of Hydrobia sp. in the stomach contents of mullets allowed us to infer the H. benedeni life cycle in the Ganzirri lagoon.

The environmental significance and low-oxygen indicator potential of benthic foraminiferal assemblages in surface sediments off the Changjiang River (Yangtze River) Estuary, China

86 surface sediment samples and a core (CDZS38) from the Changjiang River Estuary (CRE) and its adjacent area were collected to investigate the environmental significance of foraminifera, and determine a microfaunal index for coastal hypoxia to be used for paleoenvironmental studies. Benthic foraminifera and their relationship with environmental parameters including grain size composition and total organic carbon in surface sediment samples were studied. The benthic foraminiferal assemblages were dominated by littoral species in the study area. R-mode cluster analysis identified three clusters based on the percentage of benthic foraminifera. Cluster 1 covers the transitional area between the Radial Sand Ridges of the South Yellow Sea and the CRE. The dominant foraminiferal assemblage is Ammonia beccarii vars.–Ammonia compressiuscula–Quinqueloculina spp., which is a good environmental indicator of an oligotrophic near-shore condition with a strong hydrodynamic force. Cluster 2 covers the inner-shelf off the CRE. The dominant foraminiferal assemblage of Cluster 2 is Epistominella naraensis–Bolivina cochei–Bulimina marginata, which can be used to represent a eutrophic, hypoxic inner-shelf environment. Cluster 3 covers the Hangzhou Bay, which is a typical macro-tidal river mouth. The dominant foraminiferal assemblage of Cluster 3 is A. beccarii vars.–E. naraensis–Ammonia convexidorsa, which is indicative of an environment that is strongly disturbed by tidal currents and influenced by substances from the Changjiang River. The occurrence of E. naraensis, B. marginata and B. cochei is always associated with the hypoxic region. With the correlation analysis with environmental parameters, these species can be considered low-oxygen foraminiferal assemblages (LOFA). We generated a low-oxygen foraminiferal index (the ratio of LOFA to the sum of LOFA and Euryhaline species) to explore the development of hypoxia at the inner-shelf off the CRE, and applied this index to the short core CDZS38. The result indicated that high LOFI values found for CDZS38 is consistent with the recorded trends in hypoxia and harmful algae bloom (HAB) for this area over the past 59 years, and reflect an increase in the hypoxic conditions over this time period.

Relationship between phytoplankton distribution and salinity in the giant artificial brackish Lake Saemangeum

In 2021, an abundance of phytoplankton species was observed in Lake Saemangeum. We analyzed the relationship between phytoplankton abundance and salinity by comparing the distribution of salinity that changed because of freshwater inflow and drainage sluice gate operation. Thirteen field surveys were conducted: monthly basic surveys from January to November 2021 and additional surveys after rainfall in August and September at seven sites. During the survey period, 46–94 species were recorded. Pearson correlation coefficients were used to analyze the relationship between salinity and abundance of the dominant phytoplankton species. The result showed that Cyclotella atomus, Stephanodiscus hantzschii, Phormidium tenue, and Chaetoceros spp. were correlated with salinity. Chaetoceros spp. was significantly positively correlated (p < 0.001), whereas all other species were negatively correlated. Moreover, the correlation coefficient between seven species and salinity was close to zero. Compared with the general correlation coefficient of salinity and abundance, the point-biserial correlation coefficient showed a higher overall absolute value. Four species (Skeletonema spp., Cyclotella atomus, Phormidium tenue, Chaetoceros spp.) exhibited p < 0.001. Particularly, the correlation coefficient of Cyclotella atomus changed significantly from -0.237 to -0.451, whereas that of Phormidium tenue changed from -0.207 to -0.431. The results imply that salinity can affect the distribution and survival of euryhaline species. Therefore, high salinity may inhibit some freshwater and euryhaline species in the lake. However, further research is required to validate our findings.

Euryhalinity and Geographical Origin Aid Global Alien Crayfish Invasions

Salinity tolerance is a determinant of a narrow or wide distribution range of organisms. Crayfishes are important key species in many aquatic environments so require a better understanding of their ability to live in different saline regimes. We identified all alien crayfish and examined their habitats (freshwater and/or saline) and origins to test whether these factors predict their dispersal. We used contingency tables populated with raw frequency data with χ2—tests and assessed statistical significance at α of 0.05. We identified 21 alien crayfishes and we found that alien crayfish species were disproportionately freshwater (71%), with significantly lower proportions of euryhaline crayfishes inhabiting freshwater to saline environments (29%). Alien crayfishes also significantly disproportionally originate from America (67% of these taxa) when compared to all ‘other’ grouped regions (33%). In total, 36% of American crayfishes represent euryhaline species inhabiting freshwater to saline habitats against only 14% of crayfishes from all “other” grouped regions. This suggests that binomial euryhalinity/origin can help understand the potential of spread. We discussed obtained results with known experimental data on salinity tolerance, osmoregulation, growth, and reproduction of American alien crayfish. The paper will help in the management of crayfish spread.

Effects of prior acclimation on the survival, feed intake and salinity preference of a freshwater-adapted euryhaline crab

Abstract In estuarine systems, salinity changes by freshwater inflows and tides affect the survival and behaviour of euryhaline species. Juvenile Chinese mitten crabs, Eriocheir sinensis, are considered to live in fresh water during their complex life history, whilst some are found in coastal wetlands. To understand how juveniles disperse in estuarine residence, we investigated their survival, feed intake and salinity preference after acclimating in three different water situations (i.e., fresh water, salt water and alternation between fresh water and salt water). We supposed that behavioural alternation and salinity preference would play an essential role in their acclimation. Results showed no significant difference in survival and feed intake amongst the three groups of juveniles () in acclimation trials. However, the feed intake of crabs in each group was declining after changing water every three days. In the salinity preference experiment, crabs from fresh water preferred 0 and 12, whereas those from salinity and alternation treatments showed no preference. The salinity preference seemed to be modified by prior acclimation as well, and juvenile crabs could therefore survive and disperse in the different salinities. Our study helps to explain the complex distribution of juveniles in estuaries and provides arguments for the feasibility of Chinese mitten crabs being reared in low salinity waters.

Molluscs along a salinity gradient in a hypersaline coastal lagoon, southern Gulf of Mexico

Abstract Molluscs are a diverse phylum in coastal lagoons because the numerous taxa collectively display broad ranges of optima and tolerance with respect to ambient conditions. We report on the taxonomic composition, habitat preferences and feeding guilds of molluscs from Río Lagartos coastal lagoon, Mexico. Molluscs were collected in the rainy season (September/October 2017), during the winter (Nortes) season (February 2018) and at the end of the warm, dry season (May 2018). Samples were taken using a Ponar dredge, a cylindrical PVC core barrel, or a beach seine. We studied the abiotic characteristics (sediment grain-size distributions, submersed aquatic vegetation abundance and salinity) to explore assemblage differences across the broad salinity gradient that characterizes the system (~30–78 PSU). Molluscs were represented by 39 species, 34 genera, 23 families and two classes. Stenohaline species were more numerous overall than euryhaline species, but their occurrence in samples was low (&lt;20% of the samples). Stenohaline taxa lived primarily in environments characterized by marine salinity, and few were found under hypersaline conditions. We collected a smaller number of species than did studies carried out in the lagoon &gt;35 years ago. Species accumulation curves revealed that the full species richness was not captured in our study. Euhaline environments displayed greater mollusc species richness and had a larger proportion of amount (mass) of submersed aquatic vegetation. In the hypersaline environments, species richness may be favoured by the lower dominance of sands. Suspension feeders were the most diverse group in both the euhaline and hyperhaline environments.

Morphology of Coscinodiscus radiatus Ehrenberg (Bacillariophyta) from Kara-Bogaz-Gol Bay (Caspian Sea)

The study of morphology of Coscinodiscus radiatus from Kara-Bogaz-Gol Bay (the Caspian Sea) revealed that among the investigated parameters, the valve diameter was the most variable (variation coefficient CV = 21.2%) at a salinity of 50 to 262‰. The number of areolae in 10 µm on the valve mantle was the least variable characters (CV = 9.6%). The variability of the aforementioned quantitative traits, in comparison with the literature data was revealed. An increase in the valve diameter of C. radiatus at a salinity of 60‰ was noted and a decrease – at a salinity of 216–262‰. Calculation of correlation coefficient between the analyzed morphometric characters revealed a stable positive correlation between the valve diameter and the number of areolae in 10 μm on the valve. Mass development in the Bay conditions allows to characterize C. radiatus not only as a marine euryhaline species occurring in desalinated sea areas, but also as a halophile capable of tolerating wide fluctuations in salinity.

Characterization of a Pseudokeronopsis Strain (Ciliophora, Urostylida) and Its Bacterial Endosymbiont “Candidatus Trichorickettsia” (Alphaproteobacteria, Rickettsiales)

Symbiotic associations between bacteria and ciliate protists are rather common. In particular, several cases were reported involving bacteria of the alphaproteobacterial lineage Rickettsiales, but the diversity, features, and interactions in these associations are still poorly understood. In this work, we characterized a novel ciliate protist strain originating from Brazil and its associated Rickettsiales endosymbiont by means of live and ultrastructural observations, as well as molecular phylogeny. Though with few morphological peculiarities, the ciliate was found to be phylogenetically affiliated with Pseudokeronopsis erythrina, a euryhaline species, which is consistent with its origin from a lagoon with significant spatial and seasonal salinity variations. The bacterial symbiont was assigned to “Candidatus Trichorickettsia mobilis subsp. hyperinfectiva”, being the first documented case of a Rickettsiales associated with urostylid ciliates. It resided in the host cytoplasm and bore flagella, similarly to many, but not all, conspecifics in other host species. These findings highlight the ability of “Candidatus Trichorickettsia” to infect multiple distinct host species and underline the importance of further studies on this system, in particular on flagella and their regulation, from a functional and also an evolutionary perspective, considering the phylogenetic proximity with the well-studied and non-flagellated Rickettsia.

Early to mid-Holocene sedimentary environmental evolution in the palaeo-Ningbo Bay, East China and its implications for Neolithic coastal settlement

The Ningbo Plain on the East China coast is an important center of Neolithic culture, and associated settlements were influenced by changing sea levels and the geomorphological and hydrological environments of the palaeo-Ningbo Bay, the details of which are still subject to debate. This study is based on two well-dated sediment cores obtained from the Ningbo Plain, and here we report analyses of their sedimentology and foraminifera to reveal the infilling history of the palaeo-Ningbo Bay and its association with Neolithic occupation. The lithology of the largely muddy sediments and the dominance of euryhaline and brackish water foraminiferal species are indicative of an intertidal to a subtidal environment in the palaeo-bay during the early to mid-Holocene. Abrupt coarsening of sediment grain size and a corresponding increase in the abundance of foraminiferal species of inner and middle shelf environments occurred at ca. 8.8 cal. kyr BP and 7.6 cal. kyr BP, reflecting two major events of strengthened marine transgression that correspond to the rapid global sea-level rise events of Meltwater pulses (MWPs) 1C and 1D, respectively. A marked increase in the relative abundance of Ammonia annectens and Ammonia compressiuscula during ca. 7.5–7.1 cal. kyr BP further indicates frequent storm surges at that time. Between the two rapid transgression events, aggradation of tidal flats prevailed after ca. 8.0 cal. kyr BP, which provided a suitable setting for Neolithic settlements, as indicated by the recently discovered Jingtoushan site. However, the transgression sequence associated with the latter, the MWP-1D event, caused a regional cultural interruption at ca. 7.6 cal. kyr BP. Infilling and coastal marsh development in the palaeo-Ningbo Bay occurred progressively after ca. 7.0 cal. kyr BP and are associated with the emergence of the Hemudu culture.