Effects of salinity on metabolism and life history characteristics of Daphnia magna

In the Baltic Sea area, the cladoceran Daphnia magna is commonly found in brackish water rockpools and it has been suggested that salinity is one of the niche dimensions that affects the distribution of the species. The salinity tolerance of D. magna was studied both in physiological and life history experiments. The experimental salinities were freshwater, 4S and 8S. The highest respiration and ammonium excretion rates were measured in the freshwater treatment with decreasing respiration and ammonium excretion rates at higher salinities. The lowest O/N ratio (oxygen consumption to ammonium excretion), describing the metabolic status of an organism, was obtained at 8S, although the only significant differences were detected when comparing to 4S treatments. Individual growth rate, reproductive output and population growth rate were highest at 4S. At 8S growth and reproduction were reduced as compared to freshwater and 4S. The life history parameters in the performed experiments indicated higher fitness (expressed as r) as well as more favourable conditions for growth and reproduction at 4S, whereas the O/N ratio was more difficult to interpret and, in this case, gave a less clear picture of the salinity influence.     

Acclimation of the Sea Cucumber Apostichopus japonicus to Decreased Salinity at the Blastula and Gastrula Stages: Its Effect on the Desalination Resistance of Larvae at Subsequent Stages of Development

Apostichopus (= Stichopus) japonicus blastulae and gastrulae were acclimated for 18 h to salinities of 32 (control), 24 and 22 (the lower limit of the range of tolerance), and 20 (below the range of tolerance). Acclimation to 20 resulted in the appearance of teratic larvae, most of which subsequently died. Acclimation to 24, 22, and 20 led to a shift in the range of tolerance of the larvae at further stages of development. With a decrease in salinity, acclimated larvae developed more successfully than unacclimated larvae. Acclimated larvae attained the pentactula stage and settled at a salinity range of 32–20; unacclimated larvae, at 32–22. At different stages of development, acclimated larvae survived greater decreases in salinity than unacclimated larvae. The acclimation effects could be traced up to metamorphosis and settling, i.e., two weeks after the end of the acclimation process.     

The Reaction of the Starfish Asterias amurensisand Patiria pectinifera (Asteroidea) from Vostok Bay (Sea of Japan) to a Salinity Decrease

The reactions of the starfish Asterias amurensis and Patiria pectinifera that live in Vostok Bay at the salinity of 32–33 to a salinity decrease were studied under laboratory conditions. The lower limits of the desalination tolerance range of A. amurensis and P. pectinifera were, respectively, 24 and 20. A. amurensis proved to be less resistant to desalination. Under experimental conditions, all specimens of this species survived the salinity of 22, while those of P. pectinifera tolerated 18. At the same time, A. amurensis responded more actively than P. pectinifera to unfavorable changes in the environment. Turned to their dorsal side and exposed to a salinity of 16 to 32, the former reverted to the normal position within a shorter time than the latter. Being a more euryhaline species, P. pectinifera endured a salinity decrease to 6 or 8 over, respectively, 21 or 28 h. However, only 30–40% of all specimens could recover locomotory activity 12 or 8.5 h after being placed into water of normal salinity.     

Experimental effects of elevated salinity on three benthic invertebrates in Pyramid Lake,Nevada

Salinity of Pyramid Lake increased from 3.7 to 5.5 between 1933 and 1980. Concern over future reductions in overall species richness prompted experiments to assess responses of dominant lake organisms to elevated salinity. Salinity tolerances of three important benthic invertebrates, Hyalella aztecta, Chironomus utahensis, and Heterocypris sp., were tested in controlled laboratory bioassays and also in a semi-natural environment consisting of large (47 m³) mesocosms.Densities of H. azteca in mesocosms were significantly lower at salinities of 8.0 and 11.0 compared with 5.6 controls in year one, but not in 8.5 salinity mesocosms in year two. The 96-h LC₅₀ for H. azteca was high at 19.5. Short-term mortalities of C. utahensis were 100% at salinities of 13.3 and greater. Fifty-seven percent fewer larvae matured from third to fourth instar at 8.9 than at 5.5 salinity in 17 day subacute bioassays. Furthermore, larval chironomid densities and emergence of adults from mesocosms were significantly reduced at salinities of 8.0 and higher compared with controls. Mortality of Heterocypris sp. was 50% at a salinity of 18.6 in laboratory bioassays and populations in mesocosms ranged between 40 and 100% lower at salinities of 8.0 and 11.0 than in controls.Multiple generation mesocosm experiments indicated all three invertebrates were more sensitive to elevated salinity than results of short-term bioassays. Our studies suggest populations of these invertebrates may be reduced from present levels if Pyramid Lake's salinity were to double, although none are expected to be extirpated. Food habit shifts and reduced production of lake fishes are likely consequences of salinity-induced disruption in the benthic invertebrate forage base.     

Osmoregulation in two aquatic oligochaetes from habitats with different salinity and comparison to other annelids

The osmoregulatory capacity of two oligochaete species, Enchytraeus albidus Henle, 1837, and Heterochaeta costata (Claparède, 1863), was investigated by direct measurements of the osmolality of the coelomic fluid. Terrestrial and marine (28 S) populations of Enchytraeus albidus and a brackish water population (14 S) of H. costata were used in the study. The range of salinity acclimation investigated was 0–40. The response to osmotic stress was measured (a) after a long-term maintenance (>14 days) in various salinities (E. albidus only), and (b) after a hyperosmotic shock as a short-term time-course sequence. The rate of water loss following a hyperosmotic shock was measured for E. albidus. Long-term acclimation. E. albidus maintained a hyperosmotic coelomic fluid over all salinities tested. In low salinities the osmolality of the coelomic fluid of the marine population was significantly higher than that of the terrestrial population. Possible genetic discrepancies or long-term acclimation may account for this difference. The coelomic fluid of H. costata was hyperosmotic at 15%. S and isoosmotic at 30 S. Short-term acclimation (hyperosmotic shock). Both species investigated, kept at 15 S and then exposed to a salinity of 30, showed fast responses: within the first two hours the internal concentrations were adjusted to the new external condition with only small subsequent changes. Regulation of the body-water content after an exposure to a hyperosmotic shock was much slower: individuals of terrestrial E. albidus, acclimated for two weeks to either 0 or 15 S, had the same water content; hence, they showed a 100% regulation. However, after exposure to 30 S, a 100% regulation was still not attained 4 days after the hyperosmotic shock. Enchytraeus albidus is capable of actively reducing water loss following the hyperosmotic shock: the observed loss of water was only 40% of that expected for a passive osmotic flow. The observed reactions are compared with those in other annelids. It seems that an active transport of ions combined with a changeable permeability of the body wall play a major role in the regulation of body fluids.     

Influence of external salinity on the osmolality of xylem sap,leaf tissue and leaf gland secretion of the mangrove<Emphasis Type="Italic"> Laguncularia racemosa</Emphasis> (L.) Gaertn

This study assessed if mature leaves of Laguncularia racemosa were able to demonstrate salt secretion, and if the magnitude of secretion was a function of soil salinity. Thus, salinity influence on the osmolality of leaf tissue, xylem sap and leaf secretion was assessed in field and glasshouse experiments. As salinity increased, solutes were accumulated in sufficient quantity to decrease osmotic potential over the whole range of water potential. In the field, xylem osmolality (mol m^–3) increased with salinity from 32.4±2.9 at 17 to 38.2±0.6 at 28. Similarly, in the glasshouse, xylem sap osmolality (mol m^–3) increased from 33.4±1.8 (15) to 40.6±1.5 (30). Changes in Na⁺ concentration explained about 51–58% of increase in xylem osmolality. Rates of secretion (mmol m^–2 day^–1) in the field increased from 0.80±0.12 (17) to 1.16±0.14 (28), and in the glasshouse the secretion increased from 0.73±0.07 (15) to 1.25±0.07 (30). The Na⁺ accounted for 40–53% of total secretion. This study presented evidence of the capability of mature leaves of L. racemosa to secrete salt for the first time, and that the rates of secretion were enhanced as soil salinity increased.     

Combined Effects of Seawater Temperature and Salinity on Development of the Larvae of the Rhizocephalan Peltogaster reticulatus (Crustacea: Cirripedia)

The effects of seawater temperature (12, 16, 20, 22, and 25°C) and salinity (of 8 to 34) in different combinations on the larvae of the rhizocephalan Peltogaster reticulatus (Crustacea: Cirripedia), a parasite of the hermit crab Pagurus proximus, were examined. The development of P. reticulatus is comprised of five naupliar stages and one cypris stage. Nauplii have a specific structure, the flotation collar encircling the dorsal side of the larval body. Larvae lack the pigmented nauplius eye, and they show no positive phototaxis. Successful naupliar development occurred in temperature and salinity ranges of 16–25°C and 20 to 34, respectively; but all nauplii died at 12°C and 16. The duration of each naupliar stage increased under lowering of the seawater temperature. At 22–25°C and 26–28, the entire development cycle was completed in 72–80 h; and at 16°C and 20 it lasted 153 h. The cypris larvae showed a greater resistance to decreased salinity in comparison with the nauplii. At temperatures of 16–25°C and salinities of 14 to 34, the lifespan of cyprids was 6 to 12 days, and it decreased at increasing temperature.     

Adaptive Responses of the Larvae of Cirripede Barnacle Peltogasterella gracilis to Changes in Seawater Temperature and Salinity

The responses of the larvae of the cirripede barnacle Peltogasterella gracilis (Crustacea: Cirripedia: Rhizocephala) that parasitizes the hermit crab Pagurus pectinatus to different combinations of seawater temperature (25, 22, 20, 16, and 12°C) and salinity (from 34 to 8) were studied in a laboratory. The nauplii of P. gracilis completed the entire cycle of development at 22 to 12°C in a narrow range of salinity (from 34 to 28), which agrees well with the environmental conditions of the crab hosts' habitat. At favorable temperatures (22–20°C) and salinity (34–28), the nauplii reached the cypris stage in 88 ± 2 h, while at 12°C and 34–30, the naupliar development took 156 ± 5 h. The cypris larvae appeared more resistant compared with the nauplii, in terms of changes in both the temperature and salinity of seawater. They actively swam at all experimental temperatures and in the salinity range of 34–18. At temperatures (22–16°C) and salinities (34–24) favorable for the cyprids, their longevity in plankton equaled 6–10 days. Thus, the nauplii of P. gracilis is the more vulnerable stage of development in the life cycle of this parasitic barnacle. The tolerance against changes in environmental factors is due to the adaptive capabilities of parasitic larvae and the environmental conditions in the habitats of its host, a typical marine crustacean. The insignificant parasitization rate of the hermit crab by its rhizocephalan parasite may be explained by the death of the nauplii of P. gracilis, which occurs when they enter to the surface water layer.     

Use of15N/14N rations to evaluate the food source of the mysid,Neomysis intermedia Czerniawsky,in a eutrophic lake in Japan

The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in ¹⁵N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in ¹⁵N was found in the mysid. The annual averages of ¹⁵N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of¹⁵N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of ¹⁵N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.     

Über den Einfluß des Salzgehaltes auf die photosynthetische Leistung verschiedener Standortformen vonDelesseria sanguinea undFucus serratus

Zusammenfassung 1. Es wurde untersucht, welchen Einfluß kurzfristige und langfristige Salzgehaltsveränderungen auf verschiedene Standortformen der RotalgeDelesseria sanguinea und der BraunalgeFucus serratus haben. Als Kriterium des Lebenszustandes wurde die photosynthetische Leistung gewählt. Die Algen wurden folgenden Salzgehaltskonzentrationen ausgesetzt: 0, 5, 10, 15, 20, 30, 40, 50 S.2. Die Versuche ergaben, daß kurzfristige Konzentrationsveränderungen (30 min) — sowohl Erniedrigung als auch Erhöhung des Salzgehaltes — die photosynthetische Leistung stimulieren. Ein langfristiger Aufenthalt (24 Std) unter den veränderten Bedingungen bewirkt, sofern diese innerhalb der Toleranzgrenzen der Algen liegen, einen Ausgleich der anfänglichen Stimulation. Außerhalb der Toleranzgrenzen liegende Konzentrationen rufen nach der Stimulation eine Leistungsdepression hervor. Bei Rückübertragung in den Ausgangssalzgehalt sind die Depressionen teilweise reversibel.3. Im hypotonischen Milieu verhalten sich die Delesserien der verschiedenen Standorte (Helgoland, Kattegat, Kieler Bucht) gleich: in 5 S treten starke Depressionen auf. Nordsee-Delesserien sind im hypertonischen Milieu weniger empfindlich, sie zeigen noch bei 50 S eine gesteigerte photosynthetische Leistung. In diesem Bereich sind die Ostseeformen schon schwer geschädigt. Am empfindlichsten gegenüber allen Konzentrationsänderungen ist die BrackwasserformDelesseria sanguinea formalanceolata aus der Kieler Bucht.4.Fucus serratus aus dem Litoral von Helgoland zeichnet sich im Gegensatz zu der submers lebenden Form der Ostsee, die sich ähnlich wieDelesseria verhält, in allen untersuchten Konzentrationsbereichen durch eine unveränderte photosynthetische Leistung aus. Die beiden Standortformen vonFucus entsprechen gemäß der Einteilung vonMontfort (1931) dem resistenten Typ und dem Stimulations-Depressionstyp.

---

On the influence of salinity on photosynthetic performance of various ecotypes ofDelesseria sanguinea andFucus serratus

The phaeophyceanF. serratus and the rhodophyceanD. sanguinea came from the North Sea (30 S) and the Baltic Sea (15 S). The activity of photosynthesis was taken as a criterion of algae vitality. Experiments were made in salinity concentrations of 0, 5, 10, 15, 20, 30, 40 and 50 S. Thirty-minute exposures to sub- or supranormal salinities stimulate photosynthesis. Within their physiological salinity ranges the algae assume normal photosynthetic rates within 24 hours. Extreme salinities cause a reduction in photosynthetic activity; this reduction mostly disappears, however, after re-transfer into normal salinity conditions. At 5 S all test individuals ofDelesseria from different locations exhibit a reduction of photosynthetic rates. At 50 SDelesseria from the North Sea still show increased activity, whileDelesseria from the Baltic are already severely damaged. The brackish-water formD. sanguinea (formalanceolata) is most sensitive to salinity variations. The photosynthetic activity ofF. serratus from Helgoland does not vary in all salinities employed. The range of test salinities corresponds to that of the habitat in the littoral zone, where high salinities occur during air exposure, and low salinities, during rainfall. By contrast, inF. serratus from the Baltic Sea occurring only in the sublittoral zone, photosynthetic rates are similarly affected by salinity as inDelesseria.

     

Growth and reproduction as a function of temperature and salinity inClava multicornis (Cnidaria,Hydrozoa)

Summary 1. Rates of growth (length increase of stolons) and of asexual reproduction (increase in number of polyps) were determined in secondaryClava multicornis colonies of a clone exposed to 12 different combinations of water temperature and salinity (12°, 17°, 22° C; 16 , 24 , 32 , 40 S). Sexual reproduction (via gonophores) has been observed only at 12° and 17° C; temperature and salinity ranges are narrower for sexual than for asexual reproduction.2. The data obtained are insufficient for a detailed analysis; they provide, however, interesting insights into the variability of growth and reproduction ofC. multicornis caused by different intensities of temperature and salinity.3. It appears that temperature requirements for maximum colony increase are reduced as the colony grows older.4. One feeding period per 24 hours seems insufficient for maximum growth and reproduction at the higher temperature levels, especially at 22° C.5. The different degrees of environmental stress endured during the initial period of transfer into the test combinations of temperature and salinity have affected the resulting colony size at least up to an age of 39 days. More appropriate criteria for assessment of rates of growth and reproduction are therefore the doubling times (number of days within which stolon length and polyp numbers taken 20 days after initiation of experiments have doubled).6. On the basis of doubling time values, increase in stolon length is progressively reduced with increasing water temperature (12°, 17°, 22° C). At 12° and 17° C stolons grow fastest in 32 , followed by 24 , 16 and 40 S; at 22° C stolon growth rates are identical in 32 and 24 S.7. Doubling times of polyp numbers per colony show a less obvious trend. In 56-day-old colonies, however, stolon length and polyp number are modified to similar degrees by the various temperatures and salinities offered. The sequence of temperatures causing fastest increase in polyp number is 12°>17°>22° C; the respective sequence of salinities reads: 24 , 32 , 16 , 40 S.8. Stolon length and polyp number per colony increase exponentially; most curves obtained exhibit undulations indicating endogenous growth rhythms.9. During the initial period of transfer into the final test media, asexual reproduction via budding seems to have been stimulated by a reduction in salinity.10. The doubling times obtained forC. multicornis are considerably longer than those found forCordylophora caspia and indicate that our culture conditions may have been suboptimal.

---

Wachstum und Reproduktion als Funktion von Temperatur und Salzgehalt beiClava multicornis (Cnidaria, Hydrozoa)

Kurzfassung Einzelpolypen eines Klons vonC. multicornis Forskål wurden schrittweise in 12 verschiedene Temperatur-Salzgehalts-Kombinationen überführt und — während sie zu neuen Kolonien heranwuchsen — das Längenwachstum ihrer Stolonen, die Geschwindigkeit ihrer asexuellen Vermehrung durch Knospung neuer Hydranthen sowie die Gonophorenausbildung (sexuelle Fortpflanzung) registriert. Die erhaltenen Daten sind unzureichend für eine detaillierte Analyse, gewähren jedoch interessante Einblicke in die Bedeutung der verschiedenen Temperatur- und Salzgehaltsbedingungen für Wachstum und Vermehrung. Die anfängliche, schrittweise Überführung in die Testmedien verursacht per se Leistungsunterschiede, deren Auswirkungen sich mindestens bis zu einem Alter von 39 Tagen verfolgen lassen. Doubling times stellen daher objektivere Kriterien dar als absolute Zuwachswerte. Die doubling times von Kolonien, welche länger als 20 Tage in den Testmedien gewachsen waren, zeigen eine Verringerung der Stolonenzuwachsrate mit steigender Temperatur (12°, 17°, 22° C). Die Reihenfolge der fördernden Wirkung der einzelnen Salzgehaltsstufen ergibt sich zu 32 , 24 , 16 , 40 S. Im Prinzip ähnliche Verhältnisse liegen hinsichtlich der asexuellen Vermehrungsrate vor. Bemessen an den getesteten Kriterien scheinen die Temperaturansprüche mit zunehmendem Koloniealter abzunehmen. Die errechneten doubling times sind wesentlich länger als beiCordylophora; möglicherweise deutet dieser Unterschied auf inadäquate Kulturbedingungen (Fütterung, Wasserbewegung) hin.

     

Distribution and abundance of littoral benthic fauna in Canadian prairie saline lakes

The littoral benthos of 18 lakes in Alberta and Saskatchewan ranging in salinity from 3 to 126 (g1^–1 TDS) were investigated twice, in the spring and in the summer of 1986. Multiple Ekman dredge samples were taken at water depths of about 0.5, 1.0 and 2 metres in each transect. Two to three transects were used in each lake according to its estimated limnological diversity for a total of 114 stations. A total of 76 species was present varying from 29–31 species in the three lakes of lowest salinity (means of 3.1–5.55) to only 2 species in lakes exceeding 100. Species richness decreased rapidly in salinities greater than 15.Biomass maximum mean of 10.91 g m^–2 dry weight (maximum 63.0 g m^–2) occurred in culturally eutrophic Humboldt Lake (3.1) but one third as great in other low salinity lakes. However, biomass again increased to about 4.5 gm^–2 in two lakes of 15 As the salinity increased still further biomass declined steadily until a minimum of 0.0212 g m^–2 was recorded in most saline Aroma Lake (mean 119). Summer biomass (11 lakes) was greater than spring biomass (4 lakes) because some groups such as amphipods, corixids and ostracods became more abundant in summer. Wet weight biomass averaged 15.8 of dry weight biomass.Seasonality (spring or summer), sediment texture and organic matter content, water depth, pH, salinity (TDS) and the presence of aquatic plants ( plant cover) were considered in the matrix involving species dry weight biomass at each of 117 stations. TWINSPAN classification of the samples yielded a dendrogram with 18 indicator species. Successive dichotomies divided these indicator species into four main lake groups based on salinity, i.e., Group I: 3–10 (Gammarus, Glyptotendipes I, Chironomus cf. plumosus), Group II: 10–38%. (Hyalella, Enallagma,Bezzia), Group III: 38–63 (Hygrotus salinarius, Cricotopus ornatus), Group IV: >63 (Dolichopodidae, Ephydra hians). Each of these main groups was subdivided into smaller groups of lakes based on factors such as pH, seasonality (spring or summer species dominance), organic matter and plant cover. Depth of samples played no apparent role.     

A pond for edible Spirulina production and its hydraulic studies

Morphometric variation in three clones of Brachionus plicatilis cultured at 20°C, 25°C and 30°C, and 9, 12 and 24 salinity was analysed. Size appeared to be largely under genetic control and this defined the narrow limits within which variation due to abiotic factors could occur. Temperature had a significant effect on size, but affected the three clones differently. The most general effect of temperature was a reduction in size which levelled off as the temperature rose. Of the measurements taken, only distance between the median spines was affected by salinity. An important inter-relationship between the effects of temperature and salinity was also detected.     

Life cycle of Porphyra vietnamensis Tanaka & Pham-Hoang Ho from Thailand

Porphyra vietnamensis Tanaka & Pham-Hoang Ho is a tropical species of high potential for farming. Studies of the life cycle have been conducted for many years but have not been successful until recently. Mature thalli were collected from Songkhla, in the southern part of Thailand, and were used to obtain Conchocelis in the laboratory in Bangkok. Conchocelis in shells as well as free-floating filaments could be observed after one week of incubation at 25 °C, 25 salinity and 350–500 lux light intensity, and covered the culture shell surface within 2 months. Conchosporangia were formed after being incubated for 10 days at 30 °C, 20 salinity under light intensities of 350–500 lux with a photoperiod of 12 hours a day. Induction of conchospore release was achieved by lowering the temperature to 25 °C and the salinity to 10–15 and increasing the light intensity to 800–1000 lux. Liberated conchospores germinated into young thalli which became mature after 70 days.     

Effects of tumor promoters and diacylglycerol on the transdifferentiation of striated muscle cells of the medusa Podocoryne carnea to RF-amide positive nerve cells

Artemia sp (Tuticorin strain) was cultured at a density of 250 individuals 1^–1 at 35, 45, 60, 75 salinity using five combinations of groundnut oil cake, decayed cabbage leaves, single superphosphate and Baker's yeast as feed. Effects on survival, growth, and fecundity were noted.     

Effects of Salinity on the Growth Rate and Survival of Juvenile Littorina saxatilis Gastropods from Habitats with Different Salinity Regimes

The effects of salinity on the growth rate and survival of juvenile Littorina saxatilis gastropods reared in the laboratory from the young of progenic females collected in estuarine, intermediate, and marine habitats were studied. The optimum growth conditions of juveniles were dependent on the salinity regime in their original habitat. The progeny of females from the marine site showed maximum survival at a salinity of 23, the value corresponding to the normal salinity in their native habitat during the breeding period, while at 14, the growth of juveniles from this population was strongly suppressed. Juveniles originating from the estuarine habitat were able to maintain equally high growth rates at 23 and 14; however, at 14, they grew significantly faster than juveniles from the marine site. The progeny of females from the intermediate habitat showed intermediate growth rates at 14. Fluctuating salinity (23–8–23) had an adverse effect on the growth of juvenile Littorina, irrespective of the parental habitat. The differences in survival, size, and growth rates of the progeny of L. saxatilis in habitats with different salinity regimes are discussed in relation to their potential adaptive significance to life in estuaries.     

Salinity-temperature tolerance of two closely related triclad species,Dugesia lugubris and D. polychroa (Turbellaria), in relation to their distribution in The Netherlands

The tolerance of adult specimens of Dugesia lugubris and D. polychroa for 13 different chlorinities ranging from 15.0–3.8 and for two temperatures, viz. 4 and 23 °C, was tested.At chlorinities of 7.5 and lower, the survival time of both species was considerably longer than at higher chlorinities (a few hours at 7.5, one to several days at 6.6 and lower concentrations). It is assumed that this is determined by the osmoregulatory capacity of the planarians.It was found that at low chlorinities combined with a high temperature D. polychroa survived longer than D. lugubris, while at the same chlorinities the opposite was true for a low temperature. The effect of temperature on survival at low chlorinities was more drastic for D. lugubris than for D. polychroa.The results correlate with data on the distribution of both species in The Netherlands. Outside areas with an average chlorinity below 2 the two species were rarely found.     

Changes in Resistance to Salinity and Temperature in Some Species of Polychaetes from the White Sea in Early Ontogenesis

We studied the effects of different salinities on plankton larvae of some polychaetes in the White Sea. It has been found that the salinity resistance of Alitta virens (Nereidae) increases during ontogenesis. Successful fertilization and further larval development in this species occur at the salinity of 22 to 34; embryos taken into the experiment at the stage of 32 blastomeres, trochophores, and early nektochaetes could survive and normally develop at the salinity of 16–32, 14–45, and 12–45 respectively. The rate of settling and metamorphosis in late nektochaetes of A. virens at normal or lowered (down to 14) salinity is dependent on temperature in the range of 5 to 23°C. It is found that the larvae of Harmothoe imbricata (Polynoidae) show the greatest salinity resistance at the stage of nektochaeta, whose lower limit of salinity is 14. Later larval stages of these species can survive in a wide range of salinity due to the development of a provisory nephridial system. The eurybionty of larvae of Spirorbis spirorbis ready for metamorphosis was higher than that in the larvae of Circeus spirillum (Spirorbidae). Under salinity reduced down to 10 the larvae of S. spirorbis die in 8–14 days, whereas more stenohaline larvae of C. spirillum die by the 3-rd day of the experiment. At water temperatures under 5°C the survival of S. spirorbis was the highest at three examined values of salinity, whereas C. spirillum showed the highest survival only under normal salinity.     

Effects of temperature and salinity on larval development ofElminius modestus (Crustacea,Cirripedia) from Helgoland (North Sea) and New Zealand

Larvae ofElminius modestus (Darwin) from four different populations (Portobello, Leigh, Doubtless Bay [New Zealand] and Helgoland [North Sea]) were reared at different salinity and temperature combinations. The larvae ofE. modestus from Helgoland developed successfully at a wide range of temperature (6° to 24 °C) and salinity (20 to 50 S). Mortality was highest at 10 S; only at 12° and 18 °C did a small percentage develop to the cypris. The larvae from New Zealand were reared at a temperature range of 12°–24 °C at 20, 30 and 40 S; mortality increased in all populations at all salinities with decreasing temperature and was extremely high at 12 °C and 40 S. The temperature influence on larval duration could be described in all cases by a power function. No significant differences in temperature influences on developmental times between the tested salinities were found, except for the Portobello population at 20 S. Significant differences were found in the temperature influence on larval development between the populations from Helgoland and the North Island of New Zealand (Leigh, Doubtless Bay). No differences were found between the Helgoland and Portobello population. The pooled data for the temperature influence on the larval development of the three tested New Zealand populations at 20, 30 and 40 S and the pooled Helgoland data at 20, 30 and 40 S show highly significant differences.Larval size (stage VI) was influenced by experimental conditions. The larvae grew bigger at low temperatures and attained their maximum size at 30 S (Helgoland). There was a strong reduction in larval size at temperatures from 18° to 24 °C. The larvae of the New Zealand populations were smaller than those from Helgoland. The greatest difference in size existed between the larvae from Portobello and Helgoland.     

The Influence of Salinity on the Rate of Dark Respiration and Structure of the Cells of Brown Algae Thalli from the Barents Sea Littoral

We studied the changes in the rate of dark respiration (DR) and structure of the cells in Ascophyllum nodosum and Fucus vesiculosus thalli during the incubation at 40, 34, 20, 10, and 2 salinity for 14 days. The changes in salinity affected the rate of DR and the structure of the thallus apical cells: the organelles swollen and were destroyed later. The effect of hyposalinity on the algae was more pronounced as compared to hypersalinity. The stress intensity directly increased with the degree of desalination. Further adaptation of the algae to low salinity enhanced DR and, hence, was an energy-dependent process. Despite higher DR rates (during the stress and adaptation) in F. vesiculosus as compared to A. nodosum, the seaweeds had similar pattern of adaptation to the variation of salinity. Different primary response of the seaweeds to 20 salinity was an important exception; apparently, the salinity around 20 is the limit of these species distribution in desalination zones.