Low Salinity Seawater Research Articles

Comparative transcriptomic analysis reveals mechanisms of divergence in osmotic regulation of the turbot Scophthalmus maximus.

The turbot Scophthalmus maximus has evolved extensive physiological ability to adapt to multiple environmental salinities. The morphological changes of the kidney indicated the adaptability difference and similarity of turbot to salinity stress. Identify transcriptome-wide differences between low-salinity seawater (LSW, salinity 5)- and high-salinity seawater (HSW, salinity 50)-acclimated kidneys of turbot to decipher the osmotic regulation mechanism. We identified 688 differentially expressed genes (DEGs) in the LSW-acclimated kidneys and 2441 DEGs in the HSW-acclimated kidneys of turbot compared with seawater-acclimated kidneys, respectively. We investigated three patterns of gene regulation to salinity stress that involved in ion channels and transporters, functions of calcium regulation, organic osmolytes, energy demand, cell cycle regulation, and cell protection. Additionally, protein-protein interaction (PPI) analysis of DEGs suggested the presence of a frequent functional interaction pattern and that crucial genes in the PPI network are involved in hyper-osmotic regulation. Based on the analysis of comparative transcriptome data and related literature reports, we conclude that the mechanisms responsible for osmotic regulation and its divergence in turbot are related to various genes that are involved in canonical physiological functions. These findings provide insight into the divergence in osmoregulation of turbot and valuable information about osmoregulation mechanisms that will benefit other studies in this field.

Oil Recovery Efficiency and Mechanism of Low Salinity-Enhanced Oil Recovery for Light Crude Oil with a Low Acid Number.

Low salinity waterflooding (low salinity-EOR) has attracted great interest from many giant oil producers and is currently under trial in some of the oil fields of the United States, Middle Eastern countries, and North Sea reservoirs. Most of the reported studies on this process were carried out for medium to relatively heavy oil with significant polar contents. In this work, we have investigated low salinity waterflooding performance for light paraffinic crude oil with a low acid number. This study has been performed using crude oil from an Indian offshore oilfield and Indian offshore seawater. Oil recovery efficiencies of seawater and its diluted versions (low salinity seawater) were evaluated through core-flooding experiments performed on a silica sand pack containing small amounts (2 wt %) of bentonite clay saturated with crude oil. Interfacial tension and wettability studies were performed to understand the associated low salinity effects on the crude oil/brine/rock properties. Effluent brine produced during the flooding experiments was also analyzed to obtain a clearer insight into the low salinity-enhanced oil recovery (EOR) mechanism. The results showed that injection of low salinity seawater can significantly increase the waterflood recovery in comparison with high salinity seawater injection. Interfacial tension and contact angle studies revealed that there is an optimum dilution level at which the interfacial tension and wettability are the most favorable for enhanced oil recovery even in the case of light paraffinic crude. These results are in line with the results obtained from the core-flooding experiments. The possible reason behind recovery improvement based on the interfacial tension and wettability studies in conjugation with the effluent brine analysis has been discussed in detail. In this study, we have observed that the enhanced oil recovery efficiency could be achieved by applying low salinity seawater flooding even in the case of light paraffinic oil with a low acid number.

Developmental Consequences of Temperature and Salinity Stress in the Sand Dollar Dendraster excentricus.

Animals that reside, reproduce, and develop in nearshore habitats are often exposed to strong fluctuations in abiotic conditions, including temperature and salinity. We studied the developmental response of the sand dollar Dendraster excentricus to increased temperature and reduced salinity at levels comparable to those induced by summer freshwater input into the San Juan Archipelago, Washington. We observed that embryos exposed to temperature and salinity stress exhibited polyembryony (the splitting of one embryo into multiple independent individuals), and we subsequently tested the competency of twin and normal embryos to reach metamorphosis. We found that twin embryos generated from a single egg are each capable of reaching metamorphosis. To begin investigating the mechanisms underlying polyembryony, we tested whether osmotic stress caused swelling of the fertilization envelope, thus allowing embryos the physical space to produce multiples within a single envelope. We also tested whether reduced calcium levels in low-salinity seawater reduced cell-cell adhesion and allowed cells to separate and develop as multiple embryos within a fertilization envelope. However, neither osmotic stress nor reduced calcium levels alone appear sufficient to induce polyembryony. We hypothesize that changes in the properties of the hyaline layer that lies beneath the fertilization envelope facilitate polyembryony.

The role of salinity and aging time on carbonate reservoir in low salinity seawater and smart seawater flooding

Although the terms Low Salinity Sea Water and Smart Sea Water have been used interchangeably as one of Enhanced Oil Recovery methods in recent years, the present study shows that there are some differences between these two. To prove the claim, the role of salinity and aging time on interfacial tension reduction and contact angle alteration of a crude oil/brine/rock system is investigated using both smart sea water and low salinity sea water. Moreover, the governing mechanisms of the IFT variation and wettability alteration are discussed. For this purpose, the seawater solution is diluted with distilled water and at the optimal salinity NaCl, CaCl2, and Na2SO4 salts are added to the solution. Next, the IFT of brine and oil, and the CA of the oil drop are measured on the carbonate surface in the presence of brine. The results showed that IFT between low salinity sea water and oil was decreased with increasing salinity and then increased. In this regard, similar results were observed by adding NaCl, CaCl2, and Na2SO4 to a low salinity seawater (LSSW) solution. Additionally, reducing seawater salinity improved the wettability from oil-wet to neutral wet such that the optimum wettability range was achieved by adding Na2SO4 to the LSSW solution. The effect of aging time in the low salinity sea water solution and smart sea water resulted in a reduction in the interfacial tension and the contact angle, as well as improving the crude oil/brine/rock interface. The mechanisms governing the reduction of the interfacial tension of low salinity sea water and smart sea water were surface excess concentration, salting in effect, and boiling point reduction, while the dominant mechanism for changing the wettability of low salinity water and smart sea water were the pH rise, pseudo-alkaline behavior, double layer increase, carbonate surface dissolution and salting in effect.

Epiphytic bacterial community composition on the surface of the submerged macrophyte Myriophyllum spicatum in a low-salinity sea area of Hangzhou Bay

Abstract In this study, we conducted a comparative analysis of the abundance and diversity of bacteria on the surface of the submerged macrophyte Myriophyllum spicatum, as well as in the surrounding water column and sediment in the low-salinity area of Hangzhou Bay, China. Bacterial clones from three clone libraries were classified into 2089 operational taxonomic units (OTUs), most of which affiliated with bacterial divisions commonly found in marine ecosystems. Alphaproteobacteria, Cyanobacteria and Gammaproteobacteria were the most abundant groups of bacteria on the surface of plants, in the water column and sediment, respectively. Epiphytic bacterial communities were more closely related to those in the sediment than bacterioplankton, and some species of epiphytic bacteria were found only on the surface of M. spicatum. The relative abundance of epiphytic bacterial genera associated with breakdown of organic compounds and with cellulose digestion was higher in October than that in July. These results suggested that bacterial communities on the surface of M. spicatum may originate from sediment bacterial communities and their specific structure was gradually formed on the surface of M. spicatum after being cultivated in low-salinity seawater.

Effects of the post-operative care with low salinity seawater on the pearl quality of pearl oysters Pinctada fucata inserted with two or four small nuclei

真珠核を2個（直径4.27-4.51 mm）あるいは4個（直径2.50-2.67 mm）挿入した貝（2個挿核貝，4個挿核貝）を低塩分海水養生と海上養生させ，低塩分海水養生による無キズ珠率向上効果を評価した。その結果，2個挿核貝では低塩分海水区の無キズ珠率が海上区よりも顕著に高く，試験区間に有意差が認められた。一方，4個挿核貝では試験区間に有意差は認められなかった。以上の結果から，直径4.27 mm以上の真珠核を1個あるいは2個挿入した貝では，低塩分海水養生効果を得られることが明らかになった。

Transcriptomic responses to extreme low salinity among locally adapted populations of Olympia oyster (Ostrea lurida).

The Olympia oyster (Ostrea lurida) is a foundation species inhabiting estuaries along the North American west coast. In California estuaries, O.lurida is adapted to local salinity regimes and populations differ in low salinity tolerance. In this study, oysters from three California populations were reared for two generations in a laboratory common garden and subsequently exposed to low salinity seawater. Comparative transcriptomics was then used to understand species-level responses to hyposmotic stress and population-level mechanisms underlying divergent salinity tolerances. Gene expression patterns indicate Olympia oysters are sensitive to hyposmotic stress: All populations respond to low salinity by up-regulating transcripts indicative of protein unfolding, DNA damage and cell cycle arrest after sub-lethal exposure. Among O.lurida populations, transcriptomic profiles differed constitutively and in response to low salinity. Despite two generations in common-garden conditions, transcripts encoding apoptosis modulators were constitutively expressed at significantly different levels in the most tolerant population. Expression of cell death regulators may facilitate cell fate decisions when salinity declines. Following low salinity exposure, oysters from the more tolerant population expressed a small number of mRNAs at significantly higher levels than less tolerant populations. Proteins encoded by these transcripts regulate ciliary activity within the mantle cavity and may function to prolong valve closure and reduce mortality in low salinity seawater. Collectively, gene expression patterns suggest sub-lethal impacts of hyposmotic stress in Olympia oysters are considerable and that even oysters with greater low salinity tolerance may be vulnerable to future freshwater flooding events.

Expression of Na+/K+-ATPase Was Affected by Salinity Change in Pacific abalone Haliotis discus hannai.

Na+/K+-ATPase (NKA) belongs to the P-type ATPase family, whose members are located in the cell membrane and are distributed in diverse tissues and cells. The main function of the NKA is to regulate osmotic pressure. To better understand the role of NKA in osmoregulation, we first cloned and characterized the full-length cDNAs of NKA α subunit and β subunit from Pacific abalone Haliotis discus hannai in the current study. The predicted protein sequence of the NKA α subunit, as the catalytic subunit, was well conserved. In contrast, the protein sequence of the β subunit had low similarity with those of other species. Phylogenetic analysis revealed that both the α and β subunits of the NKA protein of Pacific abalone were clustered with those of the Gastropoda. Then, the relationship between salinity changes and the NKA was investigated. Sudden salinity changes (with low-salinity seawater (LSW) or high-salinity seawater (HSW)) led to clear changes in ion concentration (Na+ and K+) in hemolymph; however, the relative stability of ion concentrations in tissue revealed that Pacific abalone has a strong osmotic pressure regulation ability when faced with these salinity changes. Meanwhile, the expression and activity of the NKA was significantly decreased (in LSW group) or increased (in HSW group) during the ion concentration re-establishing stages, which was consistent with the coordinated regulation of ion concentration in hemolymph. Moreover, a positive correlation between cyclic adenosine monophosphate (cAMP) concentrations and NKA mRNA expression (NKA activity) was observed in mantle and gill. Therefore, the sudden salinity changes may affect NKA transcription activation, translation and enzyme activity via a cAMP-mediated pathway.

Exploring the potential of providing and feeding pikeperch larvae (Sander lucioperca L.) with euryhaline copepod nauplii: A zoo technical trial

ABSTRACTEgg hatching and nauplii success from three euryhaline calanoid copepod species at low salinities suggest a promising alternative initial live feed for pikeperch (Sander lucioperca L.) to the conventional live feed. Acartia bifilosa and Eurytemora affinis are viable candidates with egg hatching down to zero salinity, and Acartia tonsa nauplii survive up to 2 h at zero salinity after transfer from low-salinity seawater. When offered A. tonsa and Artemia, pikeperch larvae equally consumed both prey types. We suggest that euryhaline copepods can be a supplement to or even a substitute for the normal live feed currently used as larval feed for pikeperch.

An integrated experimental approach to quantify the oil recovery potential of seawater and low-salinity seawater injection in North Sea chalk oil reservoirs

In this study, the oil recovery potential of seawater (SW), SW with different ion compositions, low-salinity seawater (LSSW), and formation water (FW), is investigated, using chalk reservoir cores and crude oil from the North Sea. Furthermore, the impact of temperature on SW flooding performance is addressed.A series of flooding experiments were conducted at reservoir conditions (2800 psi and 60 °C), followed by spontaneous imbibition tests. Secondary SW and FW flooding led to the same oil recovery. Tertiary SW injections, performed after secondary FW flooding and secondary LSSW injection, did not lead to any extra oil recovery at 60 °C. Injecting SW at 100 °C did not lead to additional recovery either. Spiking the SO4−2 content of SW by four times, at 60 °C, did not show any additional oil production as well as increasing the concentration of Ca+2 and the Ca+2/Mg+2 ratio at 60 °C. Conversely, tertiary LSSW injection, after secondary SW injection, led to 2.5% OOIP additional oil recovery. More importantly, secondary LSSW injection, compared to the secondary SW and FW injection, led to around 8% OOIP extra oil recovery. Consistently, the results of the imbibition test showed the same trend: tertiary LSSW imbibition, after secondary SW imbibition, led to 4.25% OOIP extra oil recovery.This study, through employing chalk reservoir cores and crude oil, reveals that LSSW flooding in examples of silica containing chalk reservoirs in the North Sea, has a better oil recovery potential compared to both SW and FW flooding. This is in contrast to other published results as it will be discussed in the paper.

Comparison of PCL degradation in different aquatic environments: Effects of bacteria and inorganic salts

Six different water bodies of different salinities and bacteria were set up to study the effects of microorganisms and salts on the degradation process of biodegradable polycaprolactone (PCL) spline. The experimental data for a 52-week period consistently indicate that both microorganisms and salts have an impact on the degradation process. PCL shows slow bulk hydrolysis in aseptic water and relatively rapid interfacial enzymatic degradation in bacteria-containing water however. The degradation rate of PCL in lab-prepared high-salinity seawater was noticeably higher than that in distilled water and low-salinity seawater, indicating a salt-driven acceleration of PCL hydrolysis. Because of the combined effects of factors such as the presence of bacteria, salinity, and external forces in the sea, PCL degrades fastest in natural seawater, losing 29.8% of its original weight in 52 weeks.

Growth performance, blood health, antioxidant status and immune response in red sea bream (Pagrus major) fed Aspergillus oryzae fermented rapeseed meal (RM-Koji)

This study evaluated the effects of dietary substitution of fishmeal by graded levels of a blend composed of Aspergillus oryzae fermented rapeseed meal [0% (RM0), 25% (RM25), 50% (RM50), 75% (RM75) and 100% (RM100)] on growth performance, haemato-immunological responses and antioxidative status of Pagrus major (average weight 5.5 ± 0.02 g). After 56 days, growth performances were significantly improved in fish fed RM25 diet compared to control (P < 0.05). Meanwhile, up to 50% replacement of fishmeal did not affect growth performance, feed conversion efficiency, protein efficiency ratio, protein apparent digestibility, protease activity, fish somatic indices and survival compared to control. While blood hematocrit and plasma protein were significantly enhanced in groups fed RM0 and RM25 diets, most of the hematological parameters did not change through the trial except glutamic pyruvate transaminase which was significantly increased in RM75 and RM100 groups and blood cholesterol which was gradually decreased with the increasing level of the blend. Interestingly, feeding fish with RM25 and RM50 diets significantly showed enhanced lysozyme, bactericidal and peroxidase activities and fish fed the same diets showed high resistance against oxidative stress (biological antioxidant potential and reactive oxygen metabolites). Additionally, catalase activity and tolerance against low salinity seawater were higher in fish fed RM25 diet. These findings suggested that, at a moderate level (25% and 50%), substitution of fishmeal by the fermented rapeseed meal promoted growth, nutrient utilization, and exerted immune responses and anti-oxidative effects in red sea bream.

Treatment effects during the post-operative care on the rate of pearl-sac formation in the pearl oyster Pinctada fucata

The pearl culture industry using the Akoya pearl oyster Pinctada fucata in Japan has been suffering from low productivity due to the proportion of low-quality pearls, which are not round in shape and have blemishes on the surface, is fairly high with over 70% of pearls effected. Recent studies indicate that the immersion treatment of oysters in low salinity seawater (25psu) in a tank for 8days just after the implantation of nuclei has a positive effect on the production of high-quality pearls compared to the suspension of oysters in the sea (33psu), so-called the “conventional method”, throughout two weeks of the post-operative care. However, a mechanism to increase the proportion of high-quality pearls in low salinity seawater is not fully known. In this study, we compared the periods from the implantation of nuclei to the completion of pearl-sac formation among implanted pearl oysters nursed in tanks containing low salinity (25psu) or normal salinity (33psu) seawater in tanks and in the sea (33psu). After the immersion of the implanted oysters in 25 or 33psu seawater in the tanks for 8days, animals were suspended from a raft in an inland bay for the remainder of post-operative care period. The implanted oysters treated with the conventional method were all fastened from the raft throughout the post-operative care period. The oysters from the three treatments were 10% formalin-fixed at periodic intervals and thin slices of the nucleus-implanted part of body were prepared for the examination of the process of pearl-sac formation. The oysters suspended from the raft in the sea throughout the post-operative care period showed the shortest interval from the implantation to the pearl-sac formation, followed by those in normal salinity and low salinity treatments, respectively. This trend corresponds well to that in the proportion of high-quality pearls among the three treatments. The results of the present study suggest that the delay of pearl-sac formation is most likely one of the important factors in preventing deformities and blemishes of pearls in future culture production.

Effect of low salinity on the expression profile of Na+/K+-ATPase and the growth of juvenile chub mackerel (Scomber japonicusHouttuyn)

Chub mackerel (Scomber japonicus Houttuyn) is one of the most commercially important scombroid fish used as a food resource. Recently, there has been a demand for efficient rearing methods of this fish for a full-life cycle aquaculture. In the present study, we evaluated the physiological responses in the juvenile S. japonicus to different ambient salinities. A significantly higher gain of the body mass was observed in the juveniles reared in 24 g/L and 13 g/L seawater than in those reared in natural seawater (34 g/L) within 40 days of the experimental period without affecting mortality. A principal enzyme for osmoregulation, Na+/K+-ATPase, was expressed in the ionocytes located in the gill filaments of the juveniles. The number and the cell size of ionocytes and the enzymatic activity of Na+/K+-ATPase in the gills decreased within 10 days after the low-salinity challenge, which implies the reduction of the energy-consuming active ion secretion under the low-salinity environment. The physiological capacity for adaptation to low-salinity seawater in chub mackerel could be basic knowledge to carry out culturing of these fish in coastal sea pens where ambient salinity fluctuates. The improvement of the growth performance by rearing in low-salinity seawater will contribute to the efficient production of the seed juveniles for aquaculture.

The influence of the Sunda Strait opening on paleoenvironmental changes in the eastern Indian Ocean

With sea level rise in the early Holocene, the warm and low-salinity sea water from the Java Sea was transported into the eastern Indian Ocean after the opening of the Sunda Strait. However, the impact of this process on sediment provenance and paleoproductivity is rarely known. In this study, we analyzed the grain size, Sr-Nd-Pb isotopic compositions and biogenic elements of core CJ01-185 (1538m water depth) in the eastern Indian Ocean off the Sunda Strait. Our new results reveal a large volcanic eruption in the west of Java at 2.1ka, and the Krakatau eruption at 1883 CE. On the basis of the Pb isotopic compositions, 87Sr/86Sr ratios, and εNd values, we infer that sediments from core CJ01-185 were derived primarily from Java Island. There is a distinct change in Sr-Nd-Pb isotopic compositions of the sediments from the last glacial period to the Holocene, indicating less radiogenic Nd isotopes from the Java Sea into the eastern Indian Ocean after the opening of the Sunda Strait at ∼10ka. Moreover, the sedimentation rate increased significantly from 6.5cmkyr−1 during the last glacial period to 20cmkyr−1 in the Holocene. The input of additional terrigenous nutrients from the Java Sea induced paleoproductivity with higher TOC and TN concentrations after the opening of the Sunda Strait. Our results thus suggest that the paleoproductivity was mainly influenced by terrigenous materials input in the Holocene, other than southeast monsoon or upwelling in the last glacial period.

Using high- and low-salinity seawater injection to maintain the oil reservoir pressure without damage

The oil reservoir pressure declines due to oil production, and this decline will lead to reduction in the oil productivity. The reservoir pressure maintenance is a practice in the oil industry in which seawater is injected into the aquifer zone below the oil zone to support the reservoir pressure. Calcium sulfate scale is one of the most serious oilfield problems that could be formed in sandstone and carbonate reservoirs. Calcium sulfate may precipitate during the injection of seawater with high sulfate content into formation brine with high calcium content. Mixing seawater and formation water may cause precipitation of calcium sulfate, barium sulfate, and/or strontium sulfate. Seawater treatment does not remove the entire sulfate ions from the injected water. Low sulfate concentrations may cause damage. Enhanced oil recovery processes such as smart water injection, which originally is diluted seawater, may cause calcium sulfate precipitation as the reduction of water salinity will increase the sulfate precipitation and decrease its solubility. This study was conducted to investigate the damage caused by the deposition of calcium sulfate precipitation. A solution is proposed to prevent the damage due to calcium sulfate by using chelating agents. Several coreflooding experiments were conducted using Berea sandstone and Indiana limestone cores at reservoir conditions of pressure and temperature using seawater (high and low salinity) and formation water. Chelating agents used in this study are: EDTA (ethylenediaminetetraacetic acid), HEDTA (hydroxyethylenediaminetriacetic acid), and HEIDA (hydroxyethyliminodiacetic acid). HEDTA and HEIDA chelating gents are environmentally friendly and can be used in marine environment. High-salinity water injection caused severe formation damage, and the injectivity will decline faster compared to the low-salinity water injection. HEDTA and EDTA chelating agents at low concentrations performed better than HEIDA chelating agents in both Berea sandstone and Indiana limestone cores. HEDTA and EDTA chelating agents were able to prevent the damage due to calcium sulfate precipitation and enhanced the core permeability.

Origin and characteristics of brackish groundwater in Abu Madi coastal area, Northern Nile Delta, Egypt

Hydrogeochemical and geoelectrical resistivity investigations were carried out to assess the origin and characteristics of a brackish groundwater in Abu Madi coastal area. Twenty six surface water, shallow and deep groundwater samples were collected and analyzed for various ionic concentrations as well as oxygen and hydrogen stable isotopic contents. In addition, a total of 20 vertical electrical sounding sites were conducted to investigate layers’ thicknesses, resistivities, and to detect the water-bearing layers. Then, 2-D Electrical Resistivity Tomography (ERT) along two profiles in the study area was conducted to get information about the surface water effect on recharge. The stable isotopic composition and the chloride concentrations strongly suggest that the deep groundwater in Abu Madi area is dominated by inland freshwater with a minor seawater component. This groundwater was recharged during the first and the third Holocene humid climatic cycles where the sea surface was about 125 and 25 m below the current sea level, respectively. The brackish nature and higher piezometric surface of the groundwater, as well as the occurrence of vertical low-salinity seawater zone in front of the study area, support the possibility of submarine groundwater discharge. The geoelectrical resistivity surveying, on the other hand, revealed a number of geoelectrical groundwater-bearing layers. The main water-bearing layer in the study area is represented by the sixth geoelectrical layer, which has relatively high resistivity and a considerable thickness being consistent with the hydrogeochemical observations. ERT results point to the presence of shallow water-bearing layers recharged from the surface water drains with low resistivity and surface rain water of moderate resistivity. Results from the hydrogeochemical analyses and the different hydrogeological data are consistent with the high resistivity values of this geoelectrical layer. However, the overall high specific conductance and high sodium hazards indicate that the groundwater in the study area should be carefully treated before irrigation and domestic uses through mixing it with surface irrigation water.

Influence of the commensal gastropod Crepidula plana on shell choice by the marine hermit crab Pagurus longicarpus, with an assessment of the degree of stress caused by different eviction techniques

Hermit crabs are notoriously choosy about the gastropod shells they live in. Many periwinkle shells at Nahant, Massachusetts, U.S.A. contain the gastropod Crepidula plana, which forms a thin flat shell inside the periwinkle shell. This study examined how the presence of C. plana affected shell selection behavior by the hermit crab Pagurus longicarpus: naked hermit crabs were offered different combinations of shells, including some containing C. plana and some that had been drilled by naticid gastropods, and their choices were recorded. Because we had to evict hermit crabs from their shells before conducting our choice tests, we also determined rates of recovery from five commonly used shell eviction techniques. No hermit crabs were successfully evicted using low salinity seawater. For the other techniques used, hermit crabs took significantly longer to recover after being removed by gentle but continuous pulling on the carapace and appendages than after being removed by immersion in heated seawater, cracking the shell using a vise, or prodding the hermit crab in the abdomen through a hole drilled in the shell. Even so, most hermit crabs recovered from all of the stresses tested within 20h, and from at least some stresses within 2–6h. If shells are to be re-used for experiments, heating seawater is the best technique for evicting P. longicarpus; otherwise, cracking the shell using a vise is recommended. When provided with intact shells and similarly-sized shells containing adult C. plana, all of the hermit crabs chose shells without C. plana, and did so within only about 30min. However, given a choice between shells housing C. plana and those bearing drill holes–shells which they normally avoid–the hermit crabs were about evenly divided in their choice of shells, and many of the hermit crabs never made a final decision even after 18 or 19h, suggesting that the presence of C. plana greatly reduces shell attractiveness and suitability. The presence of C. plana increased total shell weight and reduced internal shell volume considerably, and also weakened the shell substantially, likely making the hermit crabs more vulnerable to predators; all of these factors may play a role in selecting for the intense avoidance behavior exhibited by this species for periwinkle shells bearing C. plana.

Genetic responses of the marine copepod Acartia tonsa (Dana) to heat shock and epibiont infestation

Expression of stress-related genes was investigated in the marine copepod Acartia tonsa in relation to heat shock at two different salinities (10 and 32‰), and it was furthermore investigated whether experimentally induced epibiont infestation led to elevated expression of stress-related genes. Expression of the genes ferritin, Hsp90 and Hsp70 were analyzed in adult copepods by conducting reverse transcription-quantitative real time PCR (RT-qPCR). The expression of Hsp70 and Hsp90 was significantly up-regulated after heat shock and the expression levels were higher in copepods cultivated at 10‰ salinity seawater than in copepods cultivated at 32‰. Significant up-regulation of ferritin (3.3 fold increase) was observed as a response to infestation with the epibiotic euglenid Colacium vesiculosum. Results suggest that (i) A. tonsa responds more pronounced to thermal shock when cultivated in low salinity seawater (10‰) as compared to optimal salinity seawater (32‰) and (ii) epibiont infestation does cause a measureable physiological response in the host.

Effects of salinity changes on coastal Antarctic phytoplankton physiology and assemblage composition

A natural marine phytoplankton assemblage from a coastal environment of Antarctica was experimentally exposed to low salinity sea water (30 vs 34 in the control) during 8days in order to study their physiological and community responses to hypoosmotic stress conditions. Hypoosmotic conditions favour water influx into the cells, which results in increased turgor pressure and increased oxidative stress. This stress is linked to a number of other cellular toxic processes, including damages to proteins, enzyme inactivation and DNA breakage. Inhibition of the instantaneous growth rate started after 48h exposure to low salinity, but at the end of experiment, growth was significantly higher in the low than in the normal (control) salinity treatment. Hypoosmotic conditions prevented phytoplankton biomass accumulation, as evidenced by reduced Chlorophyll-a concentrations as compared to the control treatment. However, in terms of cell numbers and species composition, we observed a gradual replacement of big centric by small pennate diatoms, which became dominant by the end of the experiment. In addition, the content of reactive oxygen species (ROS) and 2-thiobarbituric acid-reactive substances (TBARS), which are indicative of oxidative stress, were studied. In the low salinity treatments, ROS concentrations were significantly higher than control values on days 4 and 6, decreasing thereafter to nearly initial values. TBARS content increased during the first 48h and then decreased until around day 0 values. This coincided with significant increased values of the antioxidants α-tocopherol and β-carotene in low salinity treatments over the control. These results suggest the existence of protection mechanisms against lipid peroxidation, and lead to the conclusion that the response to stress is species-specific, so that at the community level a change in the relative abundance of phytoplankton taxa appears as a response to hypoosmotic conditions. This could have important consequences for the trophic food web dynamics in areas influenced by high fresh water inputs.