Recruitment of the infaunal bivalve Soletellina alba (Lamarck, 1818) (Bivalvia: Psammobiidae) in response to different sediment types and water depths within the intermittently open Hopkins River estuary

Studies examining recruitment processes for soft-sediment macroinvertebrate fauna in intermittent estuaries are rare and most studies of active habitat selection have been tested in the laboratory rather than the field. The present field study examined whether recruitment of the infaunal bivalve Soletellina alba was influenced by water depth and sediment particle size in the intermittent Hopkins River estuary, southern Australia. The number of recruits in sediment trays differed between water depths, but active habitat selection was not evident across treatments of varying sediment particle size. The use of sediments with varying particle sizes also provided an opportunity to identify potential discontinuities in body-size distributions of recruits associated with varying habitat architecture. The length (mm) of recruits was converted to the same scale used to express sediment particle size (i.e. phi units: ? = − log₂ of sediment particle size). The size of recruits differed across water depths, but did not differ across treatments with fine (? = 3) versus coarse (? = 1) sediment, and no relationships were apparent between bivalve size and sediments consisting of varying particle size. These patterns of recruitment do not correspond with the distribution of adult S. alba within the Hopkins River estuary. Previous sampling has shown that abundances of juvenile and adult S. alba are variable across time, site and water depth, but are often greater at the deeper water depth (1.05 m below the Australian Height Datum). However, recruitment during the present study was greatest at the shallower water depth (0.05 m below AHD), and the apparent absence of active habitat selection suggests that the distribution of adults is unlikely to be attributable to differences in recruitment associated with sediments of varying particle size.     

Hypoxia, low salinity and lowered temperature reduce embryo survival and hatch rates in black bream Acanthopagrus butcheri (Munro, 1949)

Embryo survival and hatch rates were measured in black bream Acanthopagrus butcheri exposed to different treatments of dissolved oxygen: hypoxic and normoxic, three salinities: 15, 23 and 35 and two temperatures: 16 and 20° C. Hypoxic conditions (50% saturation) reduced 1 day embryo survival by up to 15% ( P < 0·05) compared to embryos held in normoxic (>80% saturation) conditions. Temperature had no effect on the survival of embryos in these treatments, however, lowered salinity significantly reduced embryo survival at 20° C, but not at 16° C. Mean hatch rates were reduced by 10–28% in hypoxic treatments ( P < 0·05) and lowered salinity treatments ( P < 0·05). Hatching was delayed by up to 24 h at 16° C and very low (or zero) hatching occurred in hypoxic treatments at salinities of 15 and 23. These results confirm that environmental conditions in estuaries are important factors in determining spawning success of black bream and are discussed in relation to global warming and climate change that are likely to alter the physical conditions in southern Australian estuaries.     

Effects of salinity on distribution, growth and survival of three neotropical armoured catfishes (Siluriformes—Callichthyidae)

Three species of closely related armoured catfishes, Hoplosternum littorale, H. thoracatum and Callichthys callichtkys , are widely distributed throughout (sub)tropical South America, but a detailed inspection of collection localities in both Suriname and the South American continent reveals a clear pattern. Hoplosternum littorale is not found in rainforest creeks and clear-water rivers draining the Precambrium Guiana and Brazilian Shields. Here, waters are extremely poor in dissolved minerals. In salinity tolerance experiments, 1-week-old larvae of H. littorale were found to be incapable of surviving in rainwater that is also very poor in electrolytes. Probably for the same reason, H. littorale is not collected in black-water rivers like the Rio Negro. Within the Amazon river-system H. litiorale is found in sediment-laden white-water rivers originating in the Andes. Larvae of H. thoracatum and C. caiiichthys are able to survive and develop further in rainwater and consequently have a less restricted distribution than H. littorale . Both species are found in clear water and black water. All three species tolerate salinities up to 2000 mg Cl/1, and show a marked decrease in growth at low salinities.     

The influence of seasonal salinity and turbidity maximum variations on the nursery function of the Loire estuary (France)

In the Loire estuary which is a macrotidal estuary, the river flow and tides induce large seasonal variations in salinity gradients and in location and density of the turbidity maximum. These characteristics influence colonization patterns developed by juveniles of euryhaline fish populations (structure, distribution, density) and the dynamics of benthic communities which constitute their food resources. In some hydrological conditions, the upstream limit of the nursery function may be controlled by the turbidity maximum which induces anoxic conditions: reduction in densities or mass mortalities may be observed.     

The effect of salinity on larval survival and development in the sea urchin Echinometra lucunter

Summary

Reductions in salinity can have adverse effects on larval development and larval survival in some invertebrate taxa but not others. Salinity tolerance of larvae may be particularly important in echinoderms because they are both poor ion regulators and stenohaline. I examined the effect of six levels of salinity (15, 18, 21, 24, 27 and 33 PSU) on survival and rate of development of larvae in the subtropical sea urchin Echinometra lucunter. In the short-term, mortality rate was significantly lower in 33 PSU than in all other salinities except 27 PSU, and it was significantly greater in 15 and 18 PSU than in all higher salinities. In the long-term, daily and cumulative mortality were significantly greater in 15 PSU than in most other salinities over 11 days of development (except for cumulative mortality in 18 PSU). They were significantly greater in 18 PSU than in 21 PSU or 33 PSU over a period of 13 days. Furthermore, daily mortality was significantly greater in 18 PSU than in 24 PSU or 27 PSU at 13 d after fertilization. Daily and cumulative mortality were significantly lower in 33 PSU than in 21, 24 or 27 PSU over a period of 17 days. Although in the control (33 PSU) 75% of larvae completed development to the 8-arm stage at 35 d, no larvae developed further than the 4-arm stage in 18, 21, 24 or 27 PSU; in 15 PSU, ~60% of larvae did not develop further than swimming blastulae. Since prolonged exposure to salinities as high as 27 PSU (frequently recorded in the adult habitat) can result in great larval losses, adaptive behaviours that prevent larvae from entering water layers of low salinity will enhance their chance for survival.     

Adaptability of the amphipod Pontoporeia affinis (Crustacea: Amphipoda) to salinity changes

Salinity tolerance of the amphipod Pontoporeia affinis from the Baltic Sea was examined after acclimation to increased and decreased salinity. There were adaptive shifts in tolerance related to ambient salinity. A sharp change in salinity tolerance of amphipods occurred after acclimation to extremely low salinity.     

Effects of salinity variations on the rates of photosynthesis and respiration of the juvenile giant clam (Tridacna gigas,Bivalvia, Cardiidae)

Giant clams are in symbiotic relationship with the photosynthesizing zooxanthellae and dwell in the shallow coral reefs of the Indo-Pacific region where they may be exposed to fluctuating salinities during high levels of precipitation. This study evaluated the effects of reduced salinities (18, 25, and 35‰ as control) on the rates of photosynthesis and respiration in juvenile Tridacna gigas for 14 days. At 18‰, total mortality was recorded after day 4, so no photosynthetic measurements were subsequently conducted for this treatment. However, results showed no significant differences in the photosynthetic rates among treatments. Respiration rates were significantly increased at both low salinities resulting in low P_g/R ratios. After 14 days of exposure, photosynthetic parameters at 25‰ were not significantly different from the control which suggests that juvenile T. gigas may be able to acclimate to osmotic stress and adjust its photophysiology following reductions in salinity of up to 25‰.     

Biodiversity of aquatic gastropods in the Mont St-Michel basin (France) in relation to salinity and drying of habitats

Seventy-seven polder and marsh stations were sampled for aquatic and riparian gastropods in the terrestrial basin of Mont St-Michel from March 1994–March 1995 and during a drought in 1996. In addition, four ponds with riparian coppice (bocage) were investigated. Twenty-one stations, mostly in polders, lacked snails; high values of conductivity, and by implication salinity, appeared to make the habitats unfavourable. Only the euryhaline hydrobid Potamopyrgus antipodarum and the amphibious lymnaeid Lymnaea truncatula survived in areas of high conductivity. In associated lagoons, the maximum level of salinity tolerated by freshwater gastropods was 35. Of the 14 species of gastropods collected, Lymnaea peregra and Anisus leucostoma were the most abundant. Stations had 1–7 species and the average gastropod species richness was 3.32 (±1.67). The canals that were the most susceptible to drying had a community of desiccation-resistant species including L. truncatula, Aplexa hypnorum, A. leucostoma and L. peregra. It appears that gastropod assemblages in the terrestrial basin of Mont St-Michel have achieved their current diversity by surviving strong ecological constraints.     

Comparing salinity tolerance in embryonic and larval development of two species of water strider,Aquarius paludum and Gerris latiabdominis (Hemiptera: Gerridae)

Water strider Aquarius paludum (Fabricius) is a cosmopolitan species colonizes mainly freshwater but occasionally brackish habitats throughout the Palearctic and Oriental regions. Water strider Gerris latiabdominis (Miyamoto) is a common species in Japan lives in temporary habitats as freshwater paddy fields. These two species often occur syntopically. We investigated differences in the developmental response to brackish water during embryonic and larval stages between the two species. Eggs were exposed to 0–1.8% NaCl solutions within 24 h of oviposition. Larvae of G. latiabdominis were exposed to salinities of 0, 0.5%, and 0.9% from the first instar until adult emergence. Limits of NaCl concentration for hatching were 1.3% and 1.0% for A. paludum and G. latiabdominis, respectively. The hatching rate of G. latiabdominis was lower than that of A. paludum at salinities ≥0.9%. The period of embryonic development of G. latiabdominis was more prolonged than that of A. paludum at a given salinity. Although the salinity tolerance of G. latiabdominis was lower than that of A. paludum, our results suggest G. latiabdominis has the physiological capacity to expand into brackish waters. High and low salinity tolerances of A. paludum and G. latiabdominis, respectively, reflect the relatively wide range of habitat salinities utilized by A. paludum and the relatively restricted habitats preferred by G. latiabdominis. The high salinity tolerance of A. paludum could be an important factor contributing to their cosmopolitan distribution because high tolerance to salinity means the possibility of them to be dispersed via ocean or sea to other continents and islands.     

Effects of salinity on larval and early juvenile growth of an extremely euryhaline crab species,Armases miersii (Decapoda: Grapsidae)

The neotropical crab Armases miersii (Rathbun, 1897) breeds in supratidal rock pools, where great salinity variations occur. In laboratory experiments, all larval stages and the first juveniles were reared at six different salinities (5–55 PSU, intervals of 10 PSU). In five series of experiments, exposure to these conditions began either from hatching (Zoea I) or from the onset of successively later stages (Zoea II, III, Megalopa, Crab I). Growth was measured in terms of dry weight, carbon, nitrogen and hydrogen content. At osmotically extreme conditions (5 and 55 PSU, resp.), all stages showed minimum biomass accumulation; this was consistent with maximum mortality and longest duration of development (data presented in a separate paper). Successively later exposure to these salinities tended to reduce these effects. Lowest mortality and shortest time of development occurred generally at 15–25 PSU, indicating an optimum at moderately reduced salinities. This response pattern, however, was not congruent with that observed in growth. Biomass accumulation was initially maximum within a wide range of salinities (15–45 PSU), but in the Zoea II and III stages, this range tended to narrow and to shift towards higher salinities (35–45 PSU). These trends reversed in the Megalopa and Crab I, where maximum growth occurred again in a wider range and at lower salinities (15–35 PSU). The reduction of zoeal growth in moderately dilute media (15–25 PSU), which were optimal for survival and development, is interpreted as an energetic cost of hyper-osmoregulation, which begins already at hatching. Five PSU caused hypo-osmotic stress, exceeding in the long term the larval capacity for hyper-regulation. Poor zoeal survival and growth at 55 PSU are interpreted as effects of hyper-osmotic stress. In the Megalopa and Crab I, reduced growth at salinities 35 PSU may reflect the energetic costs of hypo-osmoreguation beginning in these stages. Our data suggest that the physiological adaptations of larval and early juvenile A. miersii allowing for survival and development in a physically harsh and unpredictable habitat imply a trade-off with reduced growth, due to energetic costs of osmoregulation.     

温度和盐度对皱肋文蛤幼贝存活与生长的影响

在室内控制条件下,研究了不同海水温度和盐度对皱肋文蛤(Meretrix lyrata)幼贝存活与生长的影响。结果表明:皱肋文蛤幼贝适宜生存温度为12.2-35.6℃,最适生存温度为24-30℃;适宜生长温度为23.5-33.0℃,最适生长温度为27-30℃,属典型的南方滩涂贝类。皱肋文蛤幼贝适宜生存盐度为4.3-40.5,最适生存盐度为11-31;适宜生长盐度为17.1-33.4,最适生长盐度为19-23,属广盐性滩涂贝类。该贝低温和高温敏感起始点分别为21℃和33℃;低盐和高盐敏感起始点分别为9和33。皱肋文蛤幼贝对极端温、盐度具有一定的耐受力:在37℃下仍可保持6d,100%不死亡,在39、41℃下分别在3d和5d内全部死亡;在4、6、8、10、12℃下则可分别100%存活3、4、6、9、11d;在盐度为0、5、7、9时保持100%存活的时间分别为5、8、10、10d;在盐度为33、35、37、39时保持100%存活的时间分别为7、5、3、3d,盐度41时当天即出现死亡。     

Doubly uniparental inheritance (DUI) of mitochondrial DNA in Donax trunculus (Bivalvia: Donacidae) and the problem of its sporadic detection in Bivalvia

Mitochondrial DNA is transmitted maternally in metazoan species. This rule does not hold in several species of bivalves that have two mtDNA types, one that is transmitted maternally and the other paternally. This system of mitochondrial DNA transmission is known as doubly uniparental inheritance (DUI). Here we present evidence of DUI in the clam Donax trunculus making Donacidae the sixth bivalve family in which the phenomenon has been found. In addition, we present the taxonomic affiliation of all species in which DUI is currently known to occur and construct a phylogeny of the maternal and paternal genomes of these species. We use this information to address the question of a single or multiple origins of DUI and to discuss whether failed attempts to demonstrate the presence of DUI in several bivalve species might be due to problems of detection or to genuine absence of the phenomenon.     

Effect of daily salinity fluctuation on the intraspecific interactions of a euhalophyte (Suaeda salsa) along a salinity gradient

每日盐度波动对真盐生植物盐地碱蓬种内相互作用沿盐度梯度的影响 土壤盐度的异质性是河口潮间带的一个突出的环境特征,影响植物的生长和盐沼中生物相互作用的转变。本研究旨在探究盐度梯度和盐度波动对一种真盐生植物的种内相互作用的交互影响。     

Effects of salinity on the survival and aggression of the invasive Rio Grande cichlid (Herichthys cyanoguttatus)

The spread of non-native Rio Grande cichlids (Herichthys cyanoguttatus) in southeast Louisiana includes brackish habitats. We studied the effects of three different salinity levels on the biology of juvenile H. cyanoguttatus for 13 months to determine the potential of this species to spread through local estuaries. The highest salinity tolerated was 30.0 psu, and these fish did not survive acclimation to the 32 psu treatment. Fish in brackish conditions grew slower than fish in freshwater conditions, indicating a potential long-term detriment to juvenile fish living in brackish conditions. Aggression levels were notably higher for fish in brackish (15 psu) vs. freshwater conditions. This persisted through the entire experiment even after acclimation back to freshwater. This study indicates that higher salinity habitats in Louisiana can be tolerated by this species. It also raises a question about the effect of higher salinities on aggressive behavior.     

Gonad morphology and reproductive cycle of the mangrove oyster Crassostrea brasiliana (Lamarck, 1819) in the baía de Guaratuba,Paraná, Brazil

This study aimed to describe the gonadal histology and the reproductive cycle of Crassostrea brasiliana in the mangroves of Guaratuba Bay in southern Brazil. Adults were collected monthly from January 2010 to April 2011 from three sampling sites in intertidal oyster beds. The animals were evaluated using biometric and histological analyses of the gonads. The gonadal tissue samples were processed according to the standard histological procedures, and permanent slides were prepared using Harris' haematoxylin and eosin. The oysters were identified at the species level using a molecular protocol. Females (69%) predominated over males (26%), with 4% indeterminate and 1% hermaphroditic. Mature females were more prevalent in February, March and December 2010 and in March 2011. Mature males were more prevalent in February and April 2010 and in March 2011. The presence of hermaphroditic individuals was sporadic, and oysters in immature stages or sexual repose were observed in only a few collections between the months of May and October 2010. The reproduction of C. brasiliana in Guaratuba Bay occurs intermittently, but with greater intensity during the summer, with a larger number of females produced.     

Influence of changes in salinity and light intensity on growth of phytoplankton communities from the Schelde river and estuary (Belgium/The Netherlands)

In the Schelde continuum, a succession in the phytoplankton community is observed along the transition from the river to the freshwater tidal reaches of the estuary and from the freshwater to brackish reaches of the estuary. The goal of this study was to experimentally evaluate the contribution of changes in salinity and light climate to this succession. In summer 2000 and in spring 2001, phytoplankton communities from the river, the freshwater tidal reaches and the brackish reaches of the estuary were incubated under high or low light intensities and exposed to a change in salinity. HPLC analysis was used to evaluate the response of different algal groups to changes in light intensity and salinity. When incubated at a light intensity corresponding to the mean underwater light intensity of the freshwater tidal reaches, growth of phytoplankton from the river as well as from freshwater tidal reaches was significantly lower than when incubated at a light intensity corresponding to the mean underwater light intensity of the river. The phytoplankton community from the freshwater tidal reaches did not appear to be better adapted to low light intensities than the phytoplankton community from the river. Although diatoms were expected to be less sensitive to a reduction in light intensity than green algae, the opposite response was observed. Freshwater and brackish water phytoplankton were negatively affected by respectively an increase or decrease in salinity. However, the effect of salinity was not strong enough to explain the disappearance of freshwater and brackish water phytoplankton between a salinity of 0.5 and 10 psu, suggesting that other factors also play a role. In the freshwater phytoplankton communities from the river and the freshwater tidal reaches, green algae and diatoms responded in a similar way to an increase in salinity. In the brackish water phytoplankton community, fucoxanthin displayed a different response to salinity than lutein and chlorophyll a.     

Effects of salinity on turgor pressure and fertility in Tolypella (Characeae)

We present the first experimental results on salinity tolerance and regulation mechanisms in the genus Tolypella. The two species investigated, T. nidifica and T. glomerata, regulate turgor pressure with almost complete effectiveness by adjustment of K+ and CT concentrations. Sucrose is also involved. The mechanism is basically identical to the mechanism of turgor pressure regulation previously identified in representatives of the genera Chara and Lamprothamnium. Since Chara and Lamprothamnium on the one hand and Tolypella on the other belong to different phylogenetic branches that separated early in the geological history of the Characeae, the K+ regulation mechanism can be assumed to represent an ancient pattern derived from a salt-tolerant common ancestor. Furthermore, our experiments provide evidence that salinity is a limiting factor for fertility in both T. nidifica and T. glomerata. Although the onset of gametangia covers the whole range of salinities tested here (0–29 psu), 12psu was the inhibitory level for the formation of mature oospores. Fertilization is probably disturbed by an increase in salinity. An inability to reproduce sexually under euryhaline conditions could explain why the distribution of the two species is restricted to oligo- and mesohaline environments, despite the wide range of salinity tolerance of their vegetative apparatus.     

Responses of <Emphasis Type="Italic">Venerupis philippinarum</Emphasis> (Mollusca: Bivalvia) to Predators and Changes in Hydrodynamics

The rate of burrowing into sand by the bivalve mollusk Venerupis philippinarum was studied under laboratory conditions. It is found that an increase in the intensity of water flow to an average of 1000 ml/min stimulates the burrowing of the mollusk, while higher values suppress burrowing; the threshold values are somewhat different for the young and adult specimens. It is shown that the presence of the starfish Asterias amurensis in the experimental environment decreases the rate of burrowing of V. philippinarum by 10–20% depending upon the sizes of the predator and the potential victim, but the depth of penetration of the mollusks into the sediment increases. It is supposed that in V. philippinarum and other species of bivalve mollusks related to the same life form and characterized by a moderate capability to burrow into the ground, the adaptive strategy of threat avoiding (great wave activity, an approach of a predator) is expressed as burrowing into a depth uncommon for usual situations and waiting. This behavior, to a significant degree, provides the capability of some species to inhabit shallow water areas with poor hydrodynamics inhabited by numerous predators.     

Effects of salinity, pH, organic solutes, anaerobic conditions, and the presence of other microbes on production and survival of Lagenidium giganteum (Oomycetes: Lagenidiales) zoospores

The effects of several environmental factors on the production of viable zoospores by Lagenidium giganteum were determined by counts of germlings produced after induction of zoosporogenesis by suspension of mycelium in various substances. NaCl at a concentration of 0.6 g/liter virtually eliminated zoosporogenesis. At 0.2 g/liter NaCl there was a significant reduction in four of the five fungal isolates tested. Transmission of fungus between mosquito larvae at 0.8 g/liter NaCl suggests that estimates of solute effects from in vitro studies are exaggerated. Zoosporogenesis took place from pH 4.5 to 8.4 by three isolates and from 4.5 to 8 by two other isolates (±0.2). Anaerobic conditions halted zoosporogenesis. Reintroduction of oxygen within 7 days allowed the process to resume, but with reduced production for each day under anaerobic conditions. Five species of bacteria inhibited zoosporogenesis at concentrations of 10⁷–10⁸ cells/ml. The yeast, Saccharomyces cerevisiae, was inhibitory at 10⁶ cells/ml. Three sugars, a sugar alcohol, three amino acids, and peptone all reduced zoosporogenesis at levels that generally correlated positively with their nutritional values for the fungus. Peptone, which can support lush vegetative growth of L. giganteum in the absence of other nutrients, was far more effective in inhibiting zoosporogenesis than the other solutes.