Salinity Preference Research Articles

Ocean acidification alters temperature and salinity preferences in larval fish.

Ocean acidification alters the way in which animals perceive and respond to their world by affecting a variety of senses such as audition, olfaction, vision and pH sensing. Marine species rely on other senses as well, but we know little of how these might be affected by ocean acidification. We tested whether ocean acidification can alter the preference for physicochemical cues used for dispersal between ocean and estuarine environments. We experimentally assessed the behavioural response of a larval fish (Lates calcarifer) to elevated temperature and reduced salinity, including estuarine water of multiple cues for detecting settlement habitat. Larval fish raised under elevated CO2 concentrations were attracted by warmer water, but temperature had no effect on fish raised in contemporary CO2 concentrations. In contrast, contemporary larvae were deterred by lower salinity water, where CO2-treated fish showed no such response. Natural estuarine water-of higher temperature, lower salinity, and containing estuarine olfactory cues-was only preferred by fish treated under forecasted high CO2 conditions. We show for the first time that attraction by larval fish towards physicochemical cues can be altered by ocean acidification. Such alterations to perception and evaluation of environmental cues during the critical process of dispersal can potentially have implications for ensuing recruitment and population replenishment. Our study not only shows that freshwater species that spend part of their life cycle in the ocean might also be affected by ocean acidification, but that behavioural responses towards key physicochemical cues can also be negated through elevated CO2 from human emissions.

Spatial distribution pattern and physical – biological interactions in the larval notothenioid fish assemblages from the Bransfield Strait and adjacent waters

AbstractThe Bransfield Strait and adjacent waters represent one of the most important areas of larval retention off the Antarctic Peninsula. The species composition of larval fish assemblages has been described in detail in previous surveys carried out in the area, but the role of environmental parameters influencing the spatial distribution of early life stages was poorly known. By applying generalized additive models and multivariate analyses, we evaluated the role of environmental variables in shaping the small‐scale distribution of larval fish and investigated the spatial structure of the larval assemblage. It consisted of a few dominant notothenioid species, such as Champsocephalus gunnari, Lepidonotothen squamifrons, Lepidonotothen larseni, Pleuragramma antarctica and Trematomus scotti, and several other rarely caught species. Sea water temperature, salinity and sampling depth were the most important factors determining the spatial distribution of fish with different relative contributions, together explaining more than 80% of total deviance observed. Species richness was mostly affected by salinity, probably due to the narrow range of salinity preference by the species. Cluster analysis of abundance and presence data identified six and five distinct groups, respectively, each of them with substantial contributions of single or rarely two species. Differences in reproductive strategies of adult populations and spatial distribution of early life stages driven by different larval behaviour in response to environmental factors contribute to maintaining a well‐structured larval fish assemblage, ensuring spatial and food niche partitioning.

Different expression patterns of renal Na+/K+-ATPase α-isoform-like proteins between tilapia and milkfish following salinity challenges.

Euryhaline teleosts can survive in a broad range of salinity via alteration of the molecular mechanisms in certain osmoregulatory organs, including in the gill and kidney. Among these mechanisms, Na+/K+-ATPase (NKA) plays a crucial role in triggering ion-transporting systems. The switch of NKA isoforms in euryhaline fish gills substantially contributes to salinity adaptation. However, there is little information about switches in the kidneys of euryhaline teleosts. Therefore, the responses of the renal NKA α-isoform protein switch to salinity challenge in euryhaline tilapia (Oreochromis mossambicus) and milkfish (Chanos chanos) with different salinity preferences were examined and compared in this study. Immunohistochemical staining in tilapia kidneys revealed the localization of NKA in renal tubules rather than in the glomeruli, similar to our previous findings in milkfish kidneys. Protein abundance in the renal NKA pan α-subunit-like, α1-, and α3-isoform-like proteins in seawater-acclimated tilapia was significantly higher than in the freshwater group, whereas the α2-isoform-like protein exhibited the opposite pattern of expression. In the milkfish, higher protein abundance in the renal NKA pan α-subunit-like and α1-isoform-like proteins was found in freshwater-acclimated fish, whereas no difference was found in the protein abundance of α2- and α3-isoform-like proteins between groups. These findings suggested that switches for renal NKA α-isoforms, especially the α1-isoform, were involved in renal osmoregulatory mechanisms of euryhaline teleosts. Moreover, differences in regulatory responses of the renal NKA α-subunit to salinity acclimation between tilapia and milkfish revealed that divergent mechanisms for maintaining osmotic balance might be employed by euryhaline teleosts with different salinity preferences.

Halocline Behavior and Salinity Preference in the Estuarine Teleost Fish, the Mummichog (Fundulus heteroclitus)

Mummichogs prefer seawater but have wide ability to acclimate to extreme temperatures and salinities and spawn in dilute brackish water. Haloclines are common features of estuaries, but how fish react to them is not known. The objective was to reveal how mummichogs select microhabitats in the estuary and whether haloclines were a major feature affecting behavior. In the field, minnow trapping revealed that mummichogs move progressively into low salinity warmer water during early spring after ice melt and show significant aversion to colder temperatures and high salinity. First appearance in estuarine shallows occurred above 10 ºC and catch increased to 21 ºC over four weeks. Threespine stickleback (Gasterosteus aculeatus) also preferred warmer low salinity locations, but preferred slow moving streams, whereas mummichogs preferred tidal ponds. In the laboratory, artificial haloclines were made to test isothermal salinity preference, between 28 ‰ full strength seawater (SW, below) and 10 % SW (3.0 ‰, above). Mummichogs of both sexes acclimated to 5 ºC in SW strongly preferred SW. Surprisingly, freshwater (0 % SW) acclimated mummichogs at 21 ºC also preferred SW. In sexually mature fish acclimated to 21 ºC SW, only the males preferred SW; the females showed no significant preference for SW, meaning they freely entered low salinity. SW preference was manifested by a stereotypic passive aversion to the dilute upper layer at the halocline. We conclude that the overall movement of mummichogs into summer breeding grounds of low salinity is driven by maturation of females and their preference for warmer water (regardless of salinity) that overcomes the general tendency of the immature and male fish to avoid dilute waters.Support or Funding InformationSupported by NSERC Discovery Grant RGPIN3698‐2009 to WSM and UCR scholarship to JCT.

Trade-offs between salinity preference and antipredator behaviour in the euryhaline sailfin molly Poecilia latipinna.

Salinity preference and responses to predatory chemical cues were examined both separately and simultaneously in freshwater (FW) and saltwater (SW)-acclimated sailfin mollies Poecilia latipinna, a euryhaline species. It was hypothesized that P. latipinna would prefer FW over SW, move away from chemical cues from a crayfish predator, and favour predator avoidance over osmoregulation when presented with both demands. Both FW and SW-acclimated P. latipinna preferred FW and actively avoided predator cues. When presented with FW plus predator cues v. SW with no cues, P. latipinna were more often found in FW plus predator cues. These results raise questions pertaining to the potential osmoregulatory stress of salinity transitions in euryhaline fishes relative to the potential fitness benefits and whether euryhalinity is utilized for predator avoidance. This study sheds light on the potential benefits and consequences of being salt tolerant or intolerant and complicates the understanding of the selection pressures that have favoured the different osmoregulatory mechanisms among fishes.

Salinity Preference in the Estuarine Teleost Fish Mummichog (Fundulus heteroclitus): Halocline Behavior.

Mummichogs prefer seawater (SW) but have wide ability to acclimate to extreme temperatures and salinities. In the field, minnow trapping revealed that mummichogs move progressively into low-salinity warmer water during early spring after ice melt and show significant aversion to colder temperatures and high salinity. First appearance in estuarine shallows occurred above 10°C, and catch increased to 21°C over 4 wk. Three-spine sticklebacks (Gasterosteus aculeatus) also preferred warmer low-salinity locations but preferred slowing streams, whereas mummichogs preferred tidal ponds. In the laboratory, artificial haloclines tested isothermal salinity preference, between 28‰ full-strength SW (below) and 10% SW (3.0‰; above). Mummichogs of both sexes acclimated to 5°C in SW strongly preferred SW. Freshwater (0% SW)-acclimated mummichogs at 21°C also preferred SW, but of sexually mature fish acclimated to 21°C SW, only the males preferred SW; the females showed no significant preference for SW, meaning they freely entered low salinity. SW preference was manifested by a stereotypic passive aversion to the dilute upper layer at the halocline. We conclude that the overall movement of mummichogs into summer breeding grounds of low salinity is driven by maturation of females and their preference for warmer water regardless of salinity.

Physiological preparedness and performance of Atlantic salmon Salmo salar smolts in relation to behavioural salinity preferences and thresholds.

This study investigated the relationships between behavioural responses of Atlantic salmon Salmo salar smolts to saltwater (SW) exposure and physiological characteristics of smolts in laboratory experiments. It concurrently described the behaviour of acoustically tagged smolts with respect to SW and tidal cycles during estuary migration. Salmo salar smolts increased their use of SW relative to fresh water (FW) from April to June in laboratory experiments. Mean preference for SW never exceeded 50% of time in any group. Preference for SW increased throughout the course of smolt development. Maximum continuous time spent in SW was positively related to gill Na(+), K(+)-ATPase (NKA) activity and osmoregulatory performance in full-strength SW (measured as change in gill NKA activity and plasma osmolality). Smolts decreased depth upon reaching areas of the Penobscot Estuary where SW was present, and all fish became more surface oriented during passage from head of tide to the ocean. Acoustically tagged, migrating smolts with low gill NKA activity moved faster in FW reaches of the estuary than those with higher gill NKA activity. There was no difference in movement rate through SW reaches of the estuary based on gill NKA activity. Migrating fish moved with tidal flow during the passage of the lower estuary based on the observed patterns in both vertical and horizontal movements. The results indicate that smolts select low-salinity water during estuary migration and use tidal currents to minimize energetic investment in seaward migration. Seasonal changes in osmoregulatory ability highlight the importance of the timing of stocking and estuary arrival.

Response of gut microbiota to salinity change in two euryhaline aquatic animals with reverse salinity preference

While a digestive tract is known to harbor complex assemblages of microbiota, maintaining a functional, stable microbial community is important to the host's health but can be constantly influenced by various environmental factors. Salinity can lead to stress, including hyposaline or hypersaline stress to aquatic animals, which influence the growth condition of the animals. However, the relationship among the salinity, intestinal microbiota and growth condition of the aquatic animals remains unclear. In this study, two euryhaline species, Oreochromis niloticus (Nile tilapia) and Litopenaeus vannamei (Pacific white shrimp) were reared in water with different salinity and the growth condition verified that Nile tilapia and Pacific white shrimp had reverse salinity preference. The gut microbiota of Nile tilapia and Pacific white shrimp were compared by using 16S rRNA gene Illumina sequencing. Analysis of more than 280,000 quality-filtered sequences obtained from guts of Nile tilapia and Pacific white shrimp reared in different salinities showed that both host phylogeny and water salinity influenced the intestinal microbiota composition. Redundancy analysis combined with the heat map analysis indicated that among the shared operational taxonomy units (OTUs) in both Nile tilapia and Pacific white shrimp, 14 OTUs increased while 10 OTUs decreased in abundance toward to the increase of salt concentration. The proportion of bacteria regarded as opportunists increased while those regarded as commensal or beneficial bacteria decreased when the host facing hyposaline or hypersaline stress. The alteration of intestinal microbiota was likely attributed to the environmental selection for microbes that could grow better under high or low salinity, the host response to the salinity stress and subsequent stress exerting on the gut microbiota, or both. Statement of relevanceThis manuscript studied the correlation between the intestinal microbiota and two euryhaline aquatic animals, Oreochromis niloticus (Nile tilapia) and Litopenaeus vannamei (Pacific white shrimp).

Ecological context determines the choice between prey of different salinities

Food choice has profound implications for the relative intakes of water and salts, and thus for an animal’s physiological state. Discrimination behaviors with respect salt intake have been documented in a number of vertebrate species, but few studies have considered the ecological context in which they occur. Here, we report on the results of a 2-choice experiment designed to examine the influence of dietary salt content and freshwater availability in food discrimination behaviors in red knots Calidris canutus (Aves: Scolopacidae) that feed on mud snails Peringia ulvae (Gastropoda: Hydrobiidae) whose body fluids have either relatively low (25‰) or high (42‰) salinity. Birds ate more and spent longer time foraging on low-salinity mud snails when their salt gland sizes—an indicator of excretory capacity—were relatively small and when they were deprived of freshwater. However, as they enlarged salt glands—following a prolonged exposure to salty diet without access to freshwater—and regained access to freshwater, their preference for low-salinity prey disappeared. Such a change of preference illustrates the context dependency of discrimination. As the birds were able to maintain salt–water balance—inferred from plasma sodium concentration—under all conditions, changes in salinity preferences may occur without measurable physiological signs of osmotic stress. Our results highlight the importance of ecological context for understanding foraging responses. We argue that areas with high salinities could act as refuges for euryhaline invertebrates and fish from top vertebrate predators.

Evolutionary history influences the salinity preference of bacterial taxa in wetland soils.

Salinity is a major driver of bacterial community composition across the globe. Despite growing recognition that different bacterial species are present or active at different salinities, the mechanisms by which salinity structures community composition remain unclear. We tested the hypothesis that these patterns reflect ecological coherence in the salinity preferences of phylogenetic groups using a reciprocal transplant experiment of fresh- and saltwater wetland soils. The salinity of both the origin and host environments affected community composition (16S rRNA gene sequences) and activity (CO2 and CH4 production, and extracellular enzyme activity). These changes in community composition and activity rates were strongly correlated, which suggests the effect of environment on function could be mediated, at least in part, by microbial community composition. Based on their distribution across treatments, each phylotype was categorized as having a salinity preference (freshwater, saltwater, or none) and phylogenetic analyses revealed a significant influence of evolutionary history on these groupings. This finding was corroborated by examining the salinity preferences of high-level taxonomic groups. For instance, we found that the majority of α- and γ-proteobacteria in these wetland soils preferred saltwater, while many β-proteobacteria prefer freshwater. Overall, our results indicate the effect of salinity on bacterial community composition results from phylogenetically-clustered salinity preferences.

Salinity Selection by Juvenile Brown Shrimp (Farfantepenaeus aztecus) and White Shrimp (Litopenaeus setiferus) in a Gradient Tank

Changes in freshwater inflow and salinity patterns may affect the nursery value of estuarine systems for penaeid shrimp, but the relationship between salinity and shrimp abundance is complex and likely confounded by other environmental variables. Laboratory experiments can provide insights into salinity selection, and we designed an experimental gradient tank to examine salinity preferences of juvenile brown shrimp and white shrimp. Our design uses gently flowing water to eliminate various physical constraints often associated with selection experiments. We conducted experiments with juvenile brown shrimp (12 trials) and white shrimp (seven trials), to examine selection for salinities along a gradient from 1 to 42. Data were analyzed using contingency tables and log-linear modeling to examine relationships with salinity and possible interactions with temperature. Both brown shrimp and white shrimp were present in all salinities examined within the experimental range. In general, brown shrimp showed a preference for salinities from 17 to 35 and demonstrated avoidance for the extreme low salinities along the gradient. Results for white shrimp were not statistically significant, and this species did not appear to avoid low salinities. There was no effect of water temperature on the observed selection patterns for brown or white shrimp. Our results suggest that although salinity preferences likely exist for these species, strong distribution trends associated with salinity gradients in estuaries are likely caused by other environmental factors.

Regional variation in energy storage strategies in American glass eels from Eastern Canada

Energy status was analyzed in glass eels captured during two early waves of arrival at the mouths of the Mersey River, Nova Scotia, Canada (MR), and Grande-Rivière-Blanche, Québec, Canada (GRB), and according to their salinity preference (freshwater, brackish, or saltwater). Glass eels captured in the GRB estuary were larger, more pigmented, and exhibited higher whole-body glycogen, phospholipid, and sterol and wax ester contents. Those from MR had a higher condition index and a higher whole-body triacylglycerol content, suggesting different patterns of storage and/or use of energy reserves. Within a river, a delay of two weeks in estuarine arrival was characterized by significantly lower energy reserves. No differences in energy storage were observed according to salinity preference. Thus, the results revealed the occurrence of different energy storage strategies according to glass eel migration distance and duration, but not according to salinity preference.

On the mismatch between salinity tolerance and preference for an invasive fish: A case for incorporating behavioral data into niche modeling

Many estuarine species are euryhaline, tolerating a broad range of salinity conditions, such that data on their salinity tolerances can provide little information about a species' distribution and abundance. This is particularly true for nonnative species, known to be tolerant of a broad range of conditions. Instead, data on a species' abiotic or habitat preferences may improve prediction of a nonnative species' potential range, if introduced or if undergoing range expansion. At minimum, information about abiotic preferences may be telling of areas where the probability of nonnative occurrence or density may be higher, and if present, of areas that confer higher fitness. In this study, the salinity preference of the nonnative African jewelfish (Hemichromis letourneuxi), a recent and rapidly-expanding invader in the Florida Everglades, was quantified in laboratory trials. Despite the broad salinity tolerance of African jewelfish (up to 50), trials show a strong preference for freshwater conditions. When presented with a salinity gradient, over 50% of observations in timed videotaped trials were collected in the lowest salinity chamber (0.3), suggesting an affinity for low salinity, which was unaffected by the sex or body condition of study fish. Fish clearly avoided mid and full salinity conditions. Findings suggest that their distribution may be considerably more limited, and that the species may have higher invasion success in oligohaline habitats, than predicted based on their salinity tolerance. Results have important implications for nonnative species niche modeling, and argue for better integration of behavior along with physiological responses when examining species distributions in dynamic environments.

Effects of salinity gradients on benthic invertebrate and diatom communities in a German lowland river

The Lippe is a lowland river located in the Western part of Germany and has been heavily impacted by coal mining activities ever since. Although mining activities significantly decreased during the last decades, the associated discharge of salt-enriched mine water into the river still poses a persistent threat to the local benthic invertebrate and diatom communities. To analyze the effect of salt pollution on invertebrate and diatom species, biological and chemical data were compiled for this study from a publicly available database. Changes in the community composition due to increased salt concentrations were explored by Non-Metrical-Multidimensional Scaling. Indicator species and salinity thresholds for single species and communities were identified using the method TITAN (Threshold Indicator Taxa Analysis). The method is an analytical approach to detect changes in frequency and abundance of species along an environmental gradient by combining the methods of change point analysis (nCPA) and indicator species analysis. The obtained salinity preferences and individual and community thresholds were compared to the literature and existing salinity classifications. For both diatoms and benthic invertebrates, Non-Metrical-Multidimensional Scaling showed a clear split between samples of high and low salinities. Significant salinity thresholds were determined for 50 invertebrate and 58 diatom species of which 23 respectively 18 species were described as ‘reliable’ indicators according to the specifications given by Baker and King (2010). A majority of salt-tolerant indicator organisms were invasive species. For both organism groups, major changes in community composition were detected at a conductivity value exceeding 900μS/cm. A reduction of the average salinity to below this threshold may have positive effects on the overall species richness and the persistence of sensitive taxa in the river Lippe. Individual and community thresholds may however be data-dependent to a certain degree and subjected to fluctuations considering the potential interdependencies between salinity and additional physico-chemical and environmental parameters (e.g. water temperature, lime content).

How does salinity influence habitat selection and growth in juvenile American eels Anguilla rostrata?

The influence of salinity on habitat selection and growth in juvenile American eels Anguilla rostrata captured in four rivers across eastern Canada was assessed in controlled experiments in 2011 and 2012. Glass eels were first categorized according to their salinity preferences towards fresh (FW), salt (SW) or brackish water (BW) and the growth rate of each group of elvers was subsequently monitored in controlled FW and BW environments for 7 months. Most glass eels (78-89%) did not make a choice, i.e. they remained in BW. Salinity preferences were not influenced by body condition, although a possible role of pigmentation could not be ruled out. Glass eels that did make a choice displayed a similar preference for FW (60-75%) regardless of their geographic origin but glass eels from the St Lawrence Estuary displayed a significantly higher locomotor activity than those from other regions. Neither the salinity preferences showed by glass eels in the first experiment nor the rearing salinities appeared to have much influence on growth during the experiments. Elvers from Nova Scotia, however, reached a significantly higher mass than those from the St Lawrence Estuary thus supporting the hypothesis of genetically (or epigenetically) based differences for growth between A. rostrata from different origins. These results provide important ecological knowledge for the sustained exploitation and conservation of this threatened species.

The effects of salinity on swimming performance of two estuarine fishes, Fundulus heteroclitus and Fundulus majalis.

Prolonged and high-speed swimming performance measurements were used to explore the swimming abilities of two species of estuarine fishes, the mummichog Fundulus heteroclitus and the striped killifish Fundulus majalis, under different salinities. Critical swimming performance was significantly higher for F. majalis in high salinity than in low salinity, but no difference was observed in brief constant acceleration swimming trials in this species; however, the swimming performance of F. heteroclitus was not significantly affected by salinity changes, indicating that this species is well adapted to regular estuarine salinity oscillations. Fundulus majalis displayed higher swimming speeds than F. heteroclitus in both high and low salinities, and while this cannot be explained by their respective salinity preferences, the specific habitat preferences of F. majalis for sandy subtidal habitats and F. heteroclitus for vegetated marshes could explain the better swimming performance of F. majalis.

Estrogen inhibit salt‐overload induced hypernatremia in ovariectomized female rats (683.5)

Since estrogen is controversially implicated on sodium balance, our aim in the present study was to evaluate the estrogen modulations on female rats under basal and salt‐overload conditions. Female Wistar rats were bilaterally ovariectomized (OVX) and randomly divided in two groups to receive estradiol benzoate (EB‐OVX, 10 µg/0.1 mL/animal, s.c.) or vehicle (OVX, 0.1 mL/animal, s.c.). The animals were placed in metabolic cages for adaptation; 7 days after the estradiol or vehicle treatement beggining, two experimental protocols were performed in OVX and EB‐OVX rats: i) basal water or water plus saline (0.075, 0.15 and 0.3 M NaCl) offering and, ii) salt‐overload (0.3 M NaCl offered as only fluids) during 3 or 15 days. OVX and EB‐OVX rats exhibited a decreased 0.3 M saline preference compared to hypotonic and isotonic solutions. Also, salt overloaded rats showed a progressive increase of hypertonic intake, as only fluid offered, with no changes induced by estrogen. However, estrogen induced a inhibition of hypernatremia on EB‐OVX rats induced by high salt ingestion when compared to OVX. Additionally, AVP and OT increasing in response to salt loading was not modulated by estrogen, meanwhile estrogen inhibited and attenuated the decrease on ANP and ANG II plasma concentrations, respectively. Taken together, our present findings suggest that estrogen participates on the control of natremia in salt‐overloaded rats.Grant Funding Source: Supported by FAPERJ and FAPESP

Oviductal-uterine and nursing milieus alter saline preference in normotensive but not in spontaneously hypertensive rats

Oviductal-uterine and nursing milieus alter saline preference in normotensive but not in spontaneously hypertensive rats

Species composition and distribution of microalgae in the Sukhodol River estuary (Ussury Bay, Peter the Great Bay) in autumn. 2. Epiphyton

Epiphyte microalgae from common macrophytes ( Zostera marina, Z. japonica, Ruppia maritima, Ulva prolifera, Gracilaria verrucosa, Cladophora glomerata, Phragmites australis ) were sampled in the Sukhodol estuary in September of 2012. In total, 46 taxa of diatoms are registered, 72 % of them belong to microphytobenthos. The most numerous are mesohaline species and species indifferent to salinity (in sum 71 %). Similarity between species composition of phytoplankton and epiphyton was 57.4 %, by Czekanowski-Sørensen index. Total number of the epiphyton diatoms varied from 12.9 · 10 3 to 2583.9 · 10 3 cells/g wet weight of basiphyte (on average 541.1 · 10 3 ± 111.9 · 10 3 cells/g), their biomass varied from 17.4 to 3099.0 mg/g (on average 595.0 ± 134.7 mg/g). The lowest epiphyton biomass was registered for U. prolifera (33.9 ± 11.7 mg/g) and the highest - for Z. marina (2790.6 ± 166.8 mg/g). Species composition of epiphyton is significantly different between three groups of macrophytes: 1 - seagrass of external estuary ( Z. marina ); 2 - seagrasses ( Z. japonica, R. maritima ), attached bottom macroalgae ( U. prolifera, C. glomerata, G. verrucosa ) and emergent vegetation ( Ph. australis ) of internal estuary; and 3 - drifting macroalgae ( C. glomerata ) of internal estuary. Thus, species structure of epiphyte communities changes between biotopes and between water layers in each biotope that is determined by salinity preferences of the most common epiphytes, on the one hand, and vertical distribution of macrophytes within the water column, on the other hand. Domination of such α -mesosaprobionts as Tabularia tabulata , Melosira lineata and M. moniliformis var. subglobosa indicates eutrophication of the Sukhodol estuary that presumably is maintained by terrigenous biogenic elements supply. The biogenic elements recycled and accumulated in bottom sediments are dispersed in the estuarine waters by tidal and wind-driven turbulence.

Differences of spatial distribution and seasonal succession among Ulva species (Ulvophyceae) across salinity gradients

Ogawa T., Ohki K. and Kamiya M. 2013. Differences of spatial distribution and seasonal succession among Ulva species (Ulvophyceae) across salinity gradients. Phycologia 52: 637–651. DOI: 10.2216/13-199.1Ulva species are common along seashores as well as in brackish lakes and estuaries, and recent molecular phylogenetic examinations have revealed inter- and intraspecific genetic diversity and wide distributions across oceans. However, Ulva species are difficult to identify because of their simple morphologies and high plasticity, and thus ecological properties such as salinity preference and phenology have been reported for a limited number of species. This study examined the genetic diversity, spatial distribution, and seasonal succession of Ulva species collected from various salinity regimes in Mikata-goko and Minami River, Fukui, Japan, during a 2-year period. By analysing the internal transcribed spacer regions of 125 specimens from a marine site and 1169 specimens from seven brackish sites, we detected four marine species (Ulva compressa, U. linza, U. torta, and Ulva sp. 1) and six brackish species (two subspecies of U. flexuosa, U. limnetica, U. prolifera, U. simplex, Ulva sp. 2, and Ulva sp. 3). Two additional species (U. californica and Ulva sp. 4) were found in other brackish lakes. Roughly three distribution patterns (low- and high-salinity brackish, and wide-range) were recognized among the brackish species. Phenological patterns were diverse among Ulva species: some species appeared only for a few months, and others were found at all times of the year. More than one ribotype, including heterozygous ribotypes, were detected within each of the five species (U. linza, U. prolifera, U. simplex, U. torta, and Ulva sp. 1). In the most dominant species U. prolifera, ribotypes pro1, pro2, and pro1/2 were distributed from low- to high-salinity brackish sites; whereas, the other five ribotypes were restricted to the high-salinity brackish sites, suggesting ecotypic differentiation within U. prolifera.