Normal Seawater Salinity Research Articles

The problem of isolation and freshening of the Jurassic–Early Cretaceous Middle Russian Sea: A new 87Sr/86Sr, δ18O and δ13C record from the Saratov Volga region

We provide the first strontium isotope data on molluscs from the lowermost Bathonian (Besnosovi Zone) and lower Aptian (Tenuicostatus and Volgensis zones) of the Saratov Volga region and some new O- and C-isotope results on early Aptian fossils from this region. Despite minor diagenetic changes in the earliest Bathonian bivalve shells from the Besnosovi Zone, they show 87Sr/86Sr values very close to that (0.70706) of a well-preserved belemnite rostrum from the same zone. New data on the Sr-isotopic composition of the Jurassic and Early Cretaceous (early Aptian) molluscs from the Saratov Volga region, combined with information on the stable isotope content of these molluscs, suggest that the isolation and partial freshening of the Middle Russian Sea occurred both in the late Oxfordian-Kimmeridgian, as has recently been reported, and in the early Aptian (during the Volgensis, to a lesser extent the Tenuicostatus chrons). This information on the lower Aptian is consistent with the available stable isotope, palynological and palaeoecological data. The pronounced early Aptian 87Sr/86Sr value deviation detected in many well-preserved fossils mainly from the Volgensis Zone seems to have contributed to the active input of radiogenic strontium into the basin during a series of repetitive events associated with some episodic isolations and partial freshening of the Middle Russian Sea, starting at the Tenuicostatus Chron and intensifying at the onset of the Volgensis Chron associated with the Oceanic Anoxic Event 1a (OAE 1a). New isotope data, collected from certain molluscs residing in the lower Aptian Tenuicostatus Zone of the Saratov Volga region and living in normal seawater salinity conditions, when combined with literature evidence sourced from other locations such as Ulyanovsk Volga region, Central Pacific and Germany suggest the presence of early Aptian climatic optimum. Further molluscs from the lower Aptian Volgensis Zone of the study area offer insight into the habitat conditions of Mesozoic ammonoids.

Chicken Feather Protein Dispersant for Effective Crude Oil Dispersion in the Marine Environment.

Various studies report that aside from the adverse impact of the crude oil on the marine environment, there is the likelihood that chemical dispersants used on the surface of water as oil-treating agents themselves possess a degree of toxicity, which have additional effects on the environment. To eliminate the subject of toxicity, there exist several materials in nature that have the ability to form good emulsions, and such products include protein molecules. In this study, chicken feathers which are known to contain ≥90% protein were used to formulate a novel dispersant to disperse crude oil in seawater (35 ppt). Protein from chicken feathers was extracted and synthesized into the chicken feather protein (CFP) dispersant using deionized water as a solvent. Emulsions formed from CFP-synthesized dispersants were stable over a considerably long period of time, whereas the droplet sizes of the emulsion formed were on the average very small in diameter, making droplet coalescence very slow. The CFP dispersants exhibited moderate surface and interfacial activity at normal seawater salinity. Using the US EPA's baffled flask test, at 800 and 1000 mg/ml CFP surfactant-to-oil ratios, dispersion effectiveness values of 56.92 and 68.64 vol % were obtained, respectively, which show that CFP has a great potential in crude oil dispersion. Moreover, the acute toxicity test performed on Nile tilapia showed that CFP was practically nontoxic with an LC50 value of more than 100 mg/L after 96 h of exposure. The results obtained showed that the CFP dispersant is environmentally friendly.

Paleosalinity of the Nanhua Basin (South China) during the Cambrian Explosion

Similar to marine oxygen level and nutrient supply, seawater salinity has also been suggested as an important control on marine biological evolution. However, the potential links between the seawater salinity and Cambrian Explosion remain unclear. Here, we conducted high-resolution analyses of B/Ga and B/K ratios on four typical sections from different water-depth environments to constrain the paleosalinity in the Nanhua Basin (South China) from late Age 2 to Age 3 (~526–515 Ma). Our new data revealed common hypersaline conditions at shallow-water Meishucun (B/Ga = 13.8 ± 2.3 and B/K = 73.5 ± 15.7) and Wangjiaping (B/Ga = 20.6 ± 2.7 and B/K = 101.1 ± 17.1) locales during most of the period from late Age 2 to Age 3. In contrast, combined with the deep-water data in a recent study, middle- to deep-water environments were dominated by brackish to normal seawater salinity, as documented at Zhijin (B/Ga = 8.0 ± 1.1 and B/K = 48.2 ± 4.5), Daotuo (B/Ga = 6.4 ± 1.6 and B/K = 57.6 ± 12.3), Yuanjia (B/Ga = 4.3 ± 2.7), and Zhalagou (B/Ga = 6.1 ± 1.2) locales. Notably, two transient low-salinity intervals (LS1 and LS2) developed in shallow-water regions at ~526 Ma and ~ 518 Ma, respectively, because of increased freshwater inputs, during which the watermass salinity may be inhabitable for early faunas. Combined with previous redox studies, however, transient shallow-water anoxia at ~525 Ma allowed only the development of hypoxia-tolerant sponge faunas during LS1, indicating redox constrains on the early biological evolution. Additionally, although studies indicated rapid oceanic oxygenation within the hypersaline interval between LS1 and LS2, no important biotas occurred at this hypersaline interval, indicating hypersalinity restriction on metazoan diversification. Instead, when normal seawater salinity and oxic watermass were jointly formed during LS2 (~518 Ma), the Chengjiang and Qingjiang biotas experienced notable explosion. Therefore, the influences of the seawater salinity on early life evolution should be given more attention in the future.

Acclimation and stress response of Prochlorococcus to low salinity.

Prochlorococcus is an obligate marine microorganism and the dominant autotroph in tropical and subtropical open ocean. However, the salinity range for growing and response to low salinity exposure of Prochlorococcus are still unknown. In this study, we found that low-light adapted Prochlorococcus stain NATL1A and high-light adapted strain MED4 could be acclimated in the lowest salinity of 25 and 28 psu, respectively. Analysis of the effective quantum yield of PSII photochemistry (Fv/Fm) indicated that both strains were stressed when growing in salinity lower than 34 psu. We then compared the global transcriptome of low salinity (28 psu) acclimated cells and cells growing in normal seawater salinity (34 psu). The transcriptomic responses of NATL1A and MED4 were approximately different, with more differentially expressed genes in NATL1A (525 genes) than in MED4 (277 genes). To cope with low salinity, NATL1A down-regulated the transcript of genes involved in translation, ribosomal structure and biogenesis and ATP-production, and up-regulated photosynthesis-related genes, while MED4 regulated these genes in an opposite way. In addition, both strains up-regulated an iron ABC transporter gene, idiA, suggesting low salinity acclimated cells could be iron limited. This study demonstrated the growing salinity range of Prochlorococcus cells and their global gene expression changes due to low salinity stress.

Mixed siliciclastic-carbonate-evaporite sedimentation in an arid eolian landscape: The Khor Al Adaid tide-dominated coastal embayment, Qatar

The Khor Al Adaid embayment of southern Qatar represents a unique shallow-water mixed siliciclastic‑carbonate coastal depositional system that developed in a hyper-arid climatic setting over the past 6000 years. The embayment, which was formed during the Flandrian transgression as a result of flooding across a partially fault-controlled incised fluvial drainage, is supplied by quartz-rich sands delivered by wind-blown dunes migrating southward across the surface of Qatar. These offshore-migrating eolian-derived sediments are being redistributed by tidal currents in an otherwise low-energy coastal zone, where in situ formation of carbonate mud and a low-diversity skeletal assemblage is ongoing within salinity-restricted environments. Three depositional sectors are delineated: 1) an energetic, linear, fault-controlled Entrance Channel into which the eolian dunes spill directly; 2) a relatively deep (up to 20 m) Outer Lagoon, interpreted to represent a flooded karst-collapse structure; and 3) a sprawling, low-energy, shallow (<2 m) Inner Lagoon occupying low-lying areas between deflated eolian dunes.Physical oceanographic modeling, integrating multi-seasonal current meter and tidal gage measurements, demonstrates tidal current flow velocities are relatively high in both the Entrance Channel and at the constricted entrance to the Inner Lagoon. Associated flow expansion into less confined areas results in deposition of the eolian-derived sands as flood-tidal deltas, one in the Outer, and two in the Inner Lagoon. A weakly-developed ebb-tidal delta occurs where the Entrance Channel debouches into the Arabian Gulf. Flood-tide dominance is also apparent in Entrance Channel deposits, where sand accumulates in seaward-terminating “ebb barbs” along the margins of the flood-dominant thalweg. Such flood-tide dominance of the thalweg is unusual and likely reflects the absence of river discharge. Evidence of significant inverse estuarine circulation (seaward flow of a brine along the embayment floor) is mostly absent in spite of the landward increase of salinity, where concentrations reach more than double normal seawater salinity in the Inner Lagoon. Modeling results show that seaward-flowing brines formed in the Inner Lagoon are trapped in the relatively deep Outer Lagoon, and that mixing by tidal currents in the energetic Entrance Channel precludes the formation of vertical density gradients there. Because siliciclastic mud is essentially absent, and most of the sediment forming the deltas consists of sand, upper intertidal deltaic deposits that would normally consist of mud are absent, resulting in the flood-tide deltas having a pronounced lobate geometry similar to that of fluvial deltas formed predominantly of sand.Away from tidal deltas, low-energy lagoons are floored by carbonate mud of local production, with minor gypsum precipitating in the Inner Lagoon. Wind-generated waves only locally influence sedimentation, forming complex nearshore bars along some lagoonal shorelines. The overall landward increase in salinity is accompanied by a decrease in the diversity of benthic fauna and their skeletal remains. A fairly diverse faunal assemblage is observed in the Entrance Channel near the Arabian Gulf, including colonial corals, whereas the inner lagoon assemblage is dominated gastropods belonging to Pirenella cingulata. The remnants of large eolian dunes are preserved in the low-energy setting of the Inner Lagoon, segmenting the waterbody, and locally increasing restriction. The sedimentology of the arid-zone coastal Khor Al Adaid embayment may serve as an analogue for environmental settings that were perhaps more commonplace in arid zones of flooded continents during greenhouse times.

Persistence of fecal indicator bacteria associated with zooplankton in a tropical estuary-west coast of India.

In a study carried out during 2014, bacteria associated with zooplankton in the Zuari estuary were three to four orders of magnitude higher in abundance than in seawater. The live zooplankton carried much more bacterial load compared with the carcasses, and the fecal pellets harbored the highest density of bacteria, i.e., 8 × 1013 CFUcm-3. The diversity of bacteria was higher in live zooplankton and also in seawater. But the activity of the zooplankton-associated bacteria was much higher compared with the free-living ones. Most of the associated bacteria belonged to the genus Enterobacter, Pseudomonas, Aeromonas, and Bacillus. In growth experiments, Aeromonas and Bacillus were found to have lower salinity optima than Enterobacter (20psu) and Vibrio and Pseudomonas (normal seawater salinity). Better growth of bacteria was observed in the medium containing the diatom Chaetoceros sp. than Navicula sp. Bacterial isolates were also able to survive in oligotrophic conditions and produce optimum biomass in 2days at salinity 5psu, but in freshwater, the bacteria took a week's time to attain the optima. At salinities 0-35, the bacteria survived even for 3months without nutrient addition, indicating resilience in these bacteria and mechanisms to persist in the estuaries even in adverse conditions.

Facies analysis and depositional environments of the early Eocene Naredi Formation (Nareda locality), Kutch, Western India

The early Eocene Naredi Formation in the southwestern Kutch represents the initial marine sedimentation in Kutch area during Tertiary period. The 22 m thick succession of Naredi Formation, exposed along cliffs (N 23°34′36.8″, E 68°38′38.1″ and N 23°34′3.1″, E 68°39′7.8″) of the tributary of the Kakdi River in and around Nareda village, is dominantly composed of argillaceous member (also known as gypseous shale member) in the lower part and dominantly biochemically precipitated carbonate member, including newly identified algal and coral reef facies, in the upper part. A total of eight lithofacies have been identified based on sedimentological and micropaleontological attributes; those are alternate green- and brown shale facies, comprising the argillaceous member followed by bioclastic wackestone, Assilina packstone, organically bounded framestone (bioherm), clayey limestone, bioclastic packstone–wackestone alternation and ferruginous coralline limestone in ascending order, which constitute the upper carbonate member. The green as well as brown shale facies are splintery in nature and show horizontal interlamination with gypsum layers. Both these facies contain glauconites with circular to elliptical outline and radial fractures, thus suggesting deposition on a mid- to outer-shelf or restricted lagoonal depositional setting. The overlying horizontally bedded wackestone facies and sparitic packstone facies containing fossil shells of larger benthonic foraminifera, including Assilina spinosa, Assilina and Nummulites burdigalensis with some planktonic forms such as Globigerina and Globorotalia in association to rotalids, ostracods, bivalve and gastropod shells, whose presence depict their deposition in mid- to inner-shelf marine realm under normal seawater salinity. The abundance of peloids, calcispheres and limestone fragments are the major non-biogenic allochems in these facies. Replacement of the ostracods, bivalve and gastropod shells by sparry calcite is also the common feature. The overlying organically bounded algal framestone (bioherm) is characterized by slightly undulatory tabular form in the lower part to concentric undulatory mounds in the upper part showing reef growth at outcrop section whereas framework of curvi-radial concentric growth of carbonate layers under thin section indicates reef formation on shallow marine depositional setting in warm and clear tropical water under normal seawater salinity. The thinly bedded brownish white clayey limestone indicates deposition during deepening of the lagoon. The overlying bioclastic packstone–wackestone alternation facies studded with fragments of algal reef and stromatolitic limestone along with various fossil shells like bivalves, echinoids and gastropods, most of them are micritized, resembles its deposition under back-reef lagoonal environments during storm condition which is overlain by an intertidal coralline limestone deposit showing colonial growth and partial to complete replacement of some of the coral shells by ferruginous mineral along with secondary precipitation of the same within the pores during shallowing of the sea and/or due to late diagenetic changes. Based on shale-carbonate wackestone-packstone-reefal-coralline facies association along with the presence of some key minerals such as glauconite, pyrite, siderite and anhydrite and their genetic link to characteristic depositional milieu, authors have proposed fluctuating depositional environments from lagoonal-barrier ridge to lagoonal-tidal flat for the Naredi Formation.

Foraminiferal paleoecology of an upper Cenozoic synorogenic conglomeratic succession in the Zagros basin, Iran

The recently discovered carbonate–siliciclastic intervals within an upper Cenozoic synorogenic conglomeratic succession in the Shalamzar area of the Zagros sedimentary basin in central western Iran contain abundant and diverse assemblages of foraminifera. A total of 32 genera and 34 species of benthic and five genera and eight species of planktic foraminifera representative of Burdigalian age were identified. The foraminifera are classified into four morph groups of: (A) planktic, (B) deep benthic, (C) large benthic (robust hyaline, imperforate agglutinated and porcelaneous foraminifera) and (D) other benthic foraminifera. An outer shelf zone is represented by dominance of planktic and small benthic foraminifera of the morph groups A and B. An inner–middle shelf is indicated by an association of dominant morpho group C and minor morpho group D. Also, a mixed biotic assemblage of abundant morpho group D and sparse morpho group C reflects an inner shelf zone. Based on the biodiversities and morpho groups, the foraminifera were inhabitants of a dysoxic–oxic marine paleoecosystem between ca 120 m depth with low-to-moderate to high water energy in a euphotic to oligophotic zone. Moreover, normal seawater salinity to slightly hypersaline conditions (34 to slightly more than 50 psu) is reflected by the morpho groups.

The influence of salinity on toxicological effects of arsenic in digestive gland of clam Ruditapes philippinarum using metabolomics

Ruditapes philippinarum, a clam that thrives in intertidal zones of various salinities, is a useful biomonitor to marine contaminants. We investigated the influence of dilution to 75% and 50% of normal seawater salinity (31.1) on the responses of the digestive gland of R. philippinarum to arsenic exposure (20 mu g/L), using nuclear magnetic resonance (NMR)-based metabolomics. After acute arsenic exposure for 48 h, salinity-dependent differential metabolic responses were detected. In normal seawater, arsenic exposure increased the concentrations of branched-chain amino acids, and of threonine, proline, phosphocholine and adenosine, and it decreased the levels of alanine, hypotaurine, glucose, glycogen and ATP in the digestive glands. Differential changes in metabolic biomarkers observed at lower salinity (similar to 23.3) included elevation of succinate, taurine and ATP, and depletion of branched-chain amino acids, threonine and glutamine. Unique effects of arsenic at the lowest salinity (similar to 15.6) included down-regulation of glutamate, succinate and ADP, and up-regulation of phosphocholine. We conclude that salinity influences the metabolic responses of this clam to arsenic.

COMPARATIVE BEHAVIOUR OF CORROSION FOR CARBON STEEL IN NHATRANG BAY (VIETNAM) AND VLADIVOSTOK (RUSSIA) SEA WATER

Comparative results of corrosion testing for carbon steel in natural conditions of Nhatrang Bay (East Sea, Vietnam) and Vladivostok (Russian Federation) sea water are presented. It is concluded, that corrosion of carbon mild steel in marine environment of Nhatrang Bay at normal seawater salinity is 1.5 to 2.5 times higher than that in Vladivostoc sea water conditions.

Effects of salinity on multiplication and transmission of an intertidal trematode parasite

Salinity levels vary spatially in coastal areas, depending on proximity to freshwater sources, and may also be slowly decreasing as a result of anthropogenic climatic changes. The impact of salinity on host–parasite interactions is potentially a key regulator of transmission processes in intertidal areas, where trematodes are extremely common parasites of invertebrates and vertebrates. We investigated experimentally the effects of long-term exposure to decreased salinity levels on output of infective stages (cercariae) and their transmission success in the trematode Philophthalmus sp. This parasite uses the snail Zeacumantus subcarinatus as intermediate host, in which it asexually produces cercariae. After leaving the snail, cercariae encyst externally on hard substrates to await accidental ingestion by shorebirds, which serve as definitive hosts. We found that at reduced salinities (25 or 30 psu), the cercarial output of the parasite was lower, the time taken by cercariae to encyst was longer, fewer cercariae successfully encysted and encysted parasites had lower long-term survival than at normal seawater salinity (35 psu). The strong effect of salinity on the replication and transmission of this parasite suggests that there may be sources and sinks of transmission to birds along coastal areas, depending on local salinity conditions. Also, unless it evolves to adapt to changing conditions, the predicted reduction in salinity as a consequence of climate change may have negative impact on the parasite’s abundance.

Evaluation of dike-type causeway impacts on the flow and salinity regimes in Urmia Lake, Iran

Urmia Lake, located in a closed basin in north-west Iran, is the largest lake (5000–6000 km 2) in the Middle East. It is very saline with total dissolved salts reaching 200 g/l compared with a normal seawater salinity of about 35 g/l. The construction of a causeway, which was initiated in 1979 but then abandoned until the early 2000s, is near completion and will provide road access between the western and eastern provinces. The causeway has an opening 1.25 km long and divides Urmia Lake into a northern and southern basin and restricts water exchange. The flow and salinity regimes are affected by the presence of this new causeway, and there are concerns over the well being of the Artemia population. This study investigates the effects of the construction of the causeway on flow and salinity regimes, considers remedial actions, and examines the effects of climatic variability on salinity and flow. Flow and salinity regimes were numerically simulated by using a commercially available two and three-dimensional (2D and 3D) MIKE model. The validity of the numerical model was assessed through sensitivity analysis of the model and comparing the simulated results against field measurements; the 3D model provided the higher correlation between simulated and actual data. Wind input was the main climatic and hydrologic factor influencing flow regime while river discharge, evaporation and rainfall were the key parameters affecting salinity distribution in the lake models. The 3D model was subsequently used to predict lake conditions in typical dry, wet and normal climates, to examine the environmental impacts from the new causeway, and to evaluate possible improvements that some remedial measures may provide.

Influence of an altered salinity regime on the population structure of two infaunal bivalve species

Hydrological alterations in watersheds have changed the flows of freshwater to many nearshore marine environments. The ensuing alterations to the salinity environment of coastal waters may have implications for species distribution. This study describes the response of two common bivalves to a modified salinity environment imposed by freshwater inputs from a hydroelectric power station in Doubtful Sound, New Zealand. Populations of Austrovenus stutchburyi and Paphies australis inhabiting river deltas near the outflow of the power station in inner Doubtful Sound were more than an order of magnitude smaller in abundance than populations in neighbouring Bradshaw Sound where the salinity regime is unaltered. In addition, there was a lack of small size classes of both species in inner Doubtful Sound, suggesting that these populations are unsustainable over the long term (10–20 years). Laboratory experiments demonstrated that sustained exposure (>30 days) to low salinity (<10) significantly decreased bivalve survivorship; however, both species survived periods of exposure to freshwater up to at least 20 days in duration if followed by a period of return to normal seawater salinity. Examination of the extant salinity regime in light of these results indicates the current salinity environment in Doubtful Sound restricts bivalves to deeper waters (5–6 m depth). The observed discrepancy in the total biomass of these active suspension feeders between altered and control sites has potential implications for the flux of organic matter in the food webs of Fiordland's shallow soft sediment communities.

Effects of salinity on leaf growth and survival of the Mediterranean seagrass Posidonia oceanica (L.) Delile

The main aim of this study was to estimate the effects of salinity variation on the Mediterranean seagrass Posidonia oceanica (L.) Delile and its attached epiphytes . Leaf growth and survival of this plant were tested in several short-term (15 days) mesocosms experiments under controlled conditions between February 2001 and November 2001. Plants collected from shallow meadows at Alicante (SE Spain), with an ambient salinity of 36.8–38.0 psu, were placed in tanks of 300 L with an additional overhead light and exposed to different salinity treatments (ranging from 25 to 57 psu) during 15 days. To estimate the mortality and growth recuperation, in some experiments shoots were returned to control salinity (38 psu). Leaf growth was measured in the laboratory where epiphytic fauna and flora were removed from leaves, with a razor blade, to determine their biomass. P. oceanica was negatively influenced by increased salinity. Shoots showed a significant decrease in growth and survival, whereas epiphyte biomass did not show a clear response because of their high variability. Maximum leaf growth occurred between 25 and 39 psu. In addition, plants suffered considerable mortality at salinities above 42 psu and below 29 psu, with 100% mortality at 50 psu. In salinities between 39 and 46 psu, surviving plants were able to regain their original growth rate when returned to normal seawater salinity (38 psu). These results suggest that P. oceanica is one of the most sensitive seagrasses to salinity increments it is more tolerant to salinity reductions (25.0–36.4 psu), perhaps due to the terrestrial origin of seagrasses.

Salinity variation of formation water and diagenesis reaction in abnormal pressure environments

An understanding to the chemistry of formation waters in sedimentary basins is important for many geological processes, such as the fluid-rock interaction, the migrating paths of fluid and the entrapment mechanisms of hydrocarbon. This paper deals with the salinity variation of formation water and diagenesis reaction in the abnormally pressured system. The Shiwu depression of the Songliao basin and the Yinggehai basin are selected for case studies. The studies indicate that there is a distinct difference in the chemistry of subsurface water between hydropressured and abnormally pressured systems. The Shiwu depression of the Songliao basin is composed of terrigeneous clastics in fluvial-lacustrine environments, which contain brackish water with salinity ranging from less than 1000 mg/L to 12000 mg/L. Water composition varies with depth and hydrochemical regions. In the underpressured strata deposited during the rifting period, the formation water is characterized by CaCl2 type water with high salinity. NaHCO3-dominanted water with lower salinity occurs at the hydropressured strata deposited during the post-rifting period. In this halite-free basin, brackish water may be attributed to the condensation of meteoric water and water-rock interaction. In the deeply buried underpressured water, a predominated diagenesis reaction resulting in enrichment of Ca and Cl and reduction of Na may be related to the albitization of plagioclase following the basinal fluid line (BFL). The Yinggehai basin constitutes clastic deposits in nearshore, neritic, shelf environments and contains brackish and saline water with salinity ranging from less than 15000 mg/L to 50000 mg/L. Pore water in these marine deposits must have originated from seawater. In the overpressured system, however, the formation water has much lower salinity and ion concentrations (except bicarbonate and carbonate) than normal seawater. The low salinity indicates that interstitial connate seawater is diluted by the water released from the transformation of smectite to illite. High bicarbonate and carbonate concentrations may contribute to mineral dehydration and kerogen-cracking reactions. Furthermore, low salinity water also occurs near and above the top of the geopressured zone in the diapiric structures, which may indicate that pore water with normal seawater salinity has been mixed by fresher saline water from deeper portions of the overpressured stratigraphic section.

Induction of larval attachment and metamorphosis in the abalone Haliotis diversicolor (Reeve)

The attachment and metamorphic responses of veliger larvae of the abalone, Haliotis diversicolor (Reeve) to potassium chloride (KCl), gamma-aminobutyric acid (GABA) and natural cues were determined. Attachment and metamorphosis of H. diversicolor were two distinctly different responses. Attachment was characterized by larval contact with a substratum followed by crawling with the larval foot firmly attached to the surface of the substratum. This behavior began approximately 48 h post-fertilization at 22°C. Larvae could detach from the substratum and continue to swim for over 96 h after attachment behavior began. Metamorphosis was irreversible and could occur in larvae that were 96 h post-fertilization. The neurotransmitter GABA, stimulated attachment behavior and induced low levels of normal metamorphosis at a concentration of 10 −5 M, but was toxic to larvae at concentrations of 10 −3 and 10 −4 M. KCl at 10, 20 and 30 mM concentrations above normal seawater salinity stimulated attachment behavior, but became toxic at 30 and 40 mM. Low levels of metamorphosis were induced at excess KCl concentrations of 20 and 30 mM. Single films of mucus, diatoms and three species of bacteria were not as stimulatory as a combination film of diatoms and mucus in dish assays. Survival of larvae settled in dishes coated with a film of diatoms and mucus was higher than that in dishes containing either diatom or mucus films alone. The combination of diatom film and conspecific mucus may produce a novel cue that is not present in either film alone. Observations suggest that the condition of the adults may influence cues present in mucus. Moreover, when given a choice of vertical attachment sites, H. diversicolor larvae attached more frequently to slides filmed with both diatoms and mucus than to clean or diatom-filmed slides. A combination film may increase numbers of attached larvae and reduce mortality in commercial aquaculture facilities.

Spatial patterns in estuarine fish faunas in tropical Queensland: a reflection of interaction between long-term physical and biological processes?

Spatial differences in the distribution and abundance of fish faunas of structurally complex habitats in subtidal areas of three tropical estuaries were investigated by using modified Antillean-Z fish traps. The overall species compositions of the three estuaries were similar; however, the distribution and abundance of species differed substantially both within and among estuaries. Although the abundance of most species declined in an upstream direction, the fish assemblages of upstream areas of different estuaries were similar. In contrast, assemblages in seaward regions were quite distinct. Neither temperature nor turbidity were correlated with catch rates of the most abundant species. Although catch rates of some species were significantly correlated with deviation away from normal seawater salinity, in most cases the correlation with maximum deviation in salinity was much stronger. Thus, decreased catches and the absence of some common species from upstream areas may be related to the influence of long-term (months and years) patterns of salinity. Some species were abundant only in one region of a single creek. This may reflect the close proximity of nearby habitats from which recruits may come.

Hydrographic structure of brine-filled deeps in the Red Sea—new results from the Shaban, Kebrit, Atlantis II, and Discovery Deep

Hydrographic profiles with CTD and water samples from four brine-filled deeps in the Red Sea (Shaban, Kebrit, Atlantis II and Discovery Deep) were taken during the Meteor 31/2 expedition in February/March 1995. In the Shaban Deep area two smaller basins containing high saline brine were found in addition to the already known southern basins. Corresponding salinities (150.7%. Cl in the upper brine section) and near equal brine levels (around 1325 m water depth) suggest subbottom connections below the sills separating the northern and southern basins. An insignificant decrease in temperature (to about 24.1 †C) has occurred in the upper brine since detection of the Shaban Deep in 1981 and no changes were found for the brine-seawater level. No significant changes have been observed in the Kebrit Deep over the last 23 years in temperature (24.3 †C), chlorinity (154.0 ± 0.3%. Cl), and brine level (1466 ± 1 m). The transition from high saline brine to normal seawater salinity probably extends over a depth of only a few decimetres or less. Strong changes, however, were registered for the Atlantis II Deep. The temperature increase, known from numerous earlier investigations, continued. The gradient of increase was the steepest during the last 2.5 years and a temperature of 71.7 °C was reached in the lower brine of the SW basin. The structure of the lower transition zone, between about 1990 m water depth and high saline brine, has also changed significantly, now containing two convective layers with nearly constant temperatures (61 and 55 °C, respectively). The neighbouring Discovery Deep also shows evidence of increased hydrothermal activities. While the temperature was nearly constant (near 44.7 °C) until 1977, it has since increased to almost 50 °C and the brine level has risen by about 17 m.

Salinity control of benthic microbial mat community production in a Bahamian hypersaline lagoon

The purpose of this study was to determine the production and N 2 fixation responses of a hypersaline mat community following a reduction in salinity and nutrient enrichment. Cyanobateria-dominated microbial mat samples were collected from hypersaline Storr's Lake and normal seawater salinity Pigeon Creek and preincubated at ambient (90%.) and reduced (45%.) salinities following no nutrient as well as inorganic nutrient (NO 3 −, PO 4 −, trace metals) and dissolved organic carbon (DOC, as mannitol) enrichment. CO 2 and N 2 fixation rates were determined 2 and 4 days later. In addition, DOC (trace concentrations of 3H-labeled glucose and amino acids) uptake was measured in mats under normal and hypersaline conditions. A reduction in salinity from 90 to 45%. significantly enhanced CO 2 and N 2 fixation rates, but inorganic nutrient and DOC additions did not significantly enhance rates compared with the controls. Dissolved organic carbon/dissolved organic nitrogen (DON) uptake was not influenced over the entire range of salinities (45–90%.) used in this study. When salinity-induced osmotic stress was relieved, mats underwent enhanced primary production and nitrogen fixation. Abiotic stress, induced by hypersaline conditions in Bahamian lagoons, results in lower productivity of the microbial mat communities and this stress may outweigh the typical limiting factors regulating phototrophic community primary production.

Growth and Photosynthesis of Nanochlorum eucaryotum, a New and Extremely Small Eucaryotic Green Alga

Nanochlorum eucaryotum is a very small species of unicellular coccoid green algae (1.5 pm). The growth of Nanochlorum under different conditions of salinity, pH and light intensities was studied. Optimal growth rates were observed with normal sea water salinity and low light conditions at pH 7.0. The contents of chlorophylls, carotinoids, soluble proteins and the chlorophyll a to chlorophyll b ratio were measured. The light saturating curves of Nanochlorum cells grown under light intensities of 100 lx, 2000 lx and 10000 lx reveal a very narrow capacity of light adaptation. When cultured under higher light intensities, Nanochlorum was not able to reach high photosynthetic activities but underwent a photoinhibition of photosynthesis. The contents of cytochrome f, P-700 and ribulosebisphosphate carboxylase were low and comparable with those of low light adapted Chlorella cells. The analysis of the chlorophyll-protein complexes shows that about 80% of total chlorophyll is bound in the light harvesting chlorophyll protein complexes. All results indicate that Nanochlorum is a low light adapted marine organism with very narrow ecological flexibility.