Carbon and nitrogen stable isotope ratios of deposit-feeding polychaetes in the Nanakita River Estuary, Japan

Two types of deposit-feeding polychaetes, Neanthes japonica and Notomastus sp., and their surrounding sediments were collected from the Nanakita River Estuary and a small brackish lagoon (Gamõ Lagoon) in northeastern Japan. The samples were examined using stable isotope analysis to assess the site specific feeding mode of the animals and their trophic status. N. japonica is a surface deposit-feeder and Notomastus sp. is a subsurface deposit-feeder. In the estuary, the sedimentary ⁵N tended to become isotopically heavier from the upper estuary (2.0 3.9) to the river mouth (4.3 6.2), while sedimentary organic ¹³C constant value (–26.8 –24.4, average –25.6) throughout the river estuary. The ¹³C values of N. japonica were similar to those of the surrounding sediment in the upper estuary, whereas in the lower estuary, N. japonica had a heavier ¹³C value than the surrounding sediment. The ¹³C and dg ¹⁵N values indicated that the carbon, but not the nitrogen, of N. japonica was derived from upland plants in the upper estuary. In the lower estuary, a significant fraction of carbon of N. japonica was derived from phytoplankton. Notomastus sp. exhibited heavier ¹³C values than the surrounding surface sediment throughout the estuary and had heavier ¹³C values than N. japonica in the same location. These results suggest selective utilization of sedimentary carbon by those animals following bacterial processing and subsequent fractionation. The difference in ¹⁵N between sedimentary organics and corresponding polychaetes was 5 ± 1 and rather higher than 3.4 ± 1.1 expected for normal trophic effects in other animals.     

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.     

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.     

Competition between the sibling species Tisbe holothuriae and T. battagliai (Harpacticoida)

The influence of salinity on the performance of the sibling species Tisbe holothuriae and T. battagliai in pure and mixed cultures was studied, using laboratory stocks adapted to 32 for over 175 generations. Cohort studies show that T. holothuriae has higher growth rates (R_o and r) at 32, T. battagliai at 20 The latter's life cycle is much less affected by the difference in salinity. De Wit replacement series were used to study competitive interactions. Without water renewal, T. holothuriae eliminates its sibling species in less than 2 generations, apparently through chemical interference. With water renewal, i.e. when exploitation competition becomes relatively more important, T. holothuriae still proves superior at 27 but the two species are competitively almost equal at 20. The two species cooccur in situ during autumn, but their differential predominance at different sites is not explained by the effect of 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.     

Physiological responses of the early zoeal stages of Palaemon pandaliformis Stimpson and Palaemon northropi (Rankin) to salinity variation

The effect of salinity variation (0, 7, 14, 21, 28 and 35S) on survival, moulting and respiratory metabolism of the early zoeal stages of the shrimps Palaemon pandaliformis and P. northropi from the northern coast of the State of São Paulo, Brazil is investigated. Freshly hatched larvae were maintained at 20 °C, in each salinity for a maximum of seven days. Oxygen consumption measurements were made at 20 °C for each salinity using Cartesian diver microrespirometers. In 0S, all P. northropi zoeae died after 24 h while 24% of the P. pandaliformis zoeae survived until 4 days. Zoeae of both species survived poorly in 7S, the best survival for the two species (90%) being registered in 28%.S. Palaemon northropi zoeae did not survive 35S while 45% survival was recorded for P. pandaliformis zoeae in this medium after seven days. Moulting did not occur in zoeae of either species in 0%.S, nor in P. northropi in 7S. The metabolism-salinity curve for P. pandaliformis zoea I is very stable over the range 0–21S while that for P. northropi exhibits complete salinity independence from 21–35 S. Thus, while the early zoeal stages, at least, are conspecific, both developing in the same environment as part of the coastal zooplankton community, they clearly maintain distinct physiological characteristics. The data presented possibly reflect genetic adaptations to the adult biotope already manifested in the first zoeae.     

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.     

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 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.     

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.     

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.     

Über den Einfluß von Nahrung und Substratsalinität auf Verhalten,Fortpflanzung und Wasserhaushalt von Enchytraeus albidus Henle (Oligochaeta)

Zusammenfassung Enchytraeus albidus aus dem Anwurf mariner Algen an der Kieler Förde (Ostsee) erträgt als Nahrung die folgenden dort vorkommenden Pflanzen (Reihenfolge mit abnehmender Verträglichkeit): Fucus — Grünalgen —Seegras (Zostera) — Rotalgen (Delesseria). Diese Reihenfolge gilt für Nahrungsaufnahme, Fortpflanzungsrate und Überlebensdauer.Mit zunehmender Fäulnis des Nahrungssubstrates steigt die Zahl der Tiere, die aus ihm fliehen. Ihre Anzahl wird außerdem bestimmt durch den Salzgehalt des Substrates: Von 15–45 ist sie proportional der Substratsalinität. Bei 60 ist die Aktivität der Tiere bereits stark eingeschränkt.Bei Fucus-Nahrung ertragen auf Sand gehaltene Tiere eine Salinität von 60–70 länger als 4 Wochen, auf Filtrierpapier dagegen nur 50 für durchschnittlich 1 Woche. Die obere Fortpflanzungsgrenze liegt bei 40 Salzgehalt im Substrat. Bei 5 werden die meisten Kokons abgelegt. Die Sterblichkeit im Kokon ist bei 15 am geringsten. Auf den Substratsalinitäten 0–15 ist die Entwicklungsdauer im Kokon signifikant kürzer als auf Substraten von 30 und 40. Enchytraeus hat sich als Rückwanderer zum Meer mit einer sekundär erweiterten Poikilosmotie an den neuen Lebensraum angepaßt. Er kann eine Binnenkonzentration entsprechend etwa 72 längere Zeit ertragen. Auf niedrigen Salzgehalten besitzt er eine ausgeprägte Hypertonieregulation.

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Summary Enchytraeus albidus was fed with Fucus, green algae, Zostera marina and Delesseria. Judging from absorption of food, rate of reproduction and duration of life, the animals preferred the plants in the sequence given above.As the putrefaction of a Fucus substrate advances, more and more enchytraeids leave it. A changing salinity of the substrate also influences the number of emigrating worms, increasing it from 15–45, but decreasing it towards 60. Fed with Fucus E. albidus tolerates a salinity of 60–70 on sand for more than 4 weeks, on filter paper only 50 for about one week.Reproduction is possible at salinities up to 40. Cocoon production is most frequent at 5. The mortality of young worms within the cocoons is lowest at 15. The incubation period is significantly shorter at salinities of 0–15 than at 30 and 40.As a terrestrial immigrant to the seashore Enchytraeus albidus secondarily enlarged its range of poikilosmosis, tolerating a concentration of 72 in its coelomic fluid for some time. At low salinities it maintains a remarkable degree of hyperosmosis.

     

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.

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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.

     

β-Alanine metabolism and high salinity stress in the sea anemone,Bunodosoma cavernata

Summary During high salinity stress, -alanine accumulates to high levels in the sea anemone,Bunodosoma cavernata. Following a salinity increase from 26 to 40 -alanine increased 28-fold from 1.5 to 41.9 moles/g dry weight. Both whole animal studies and experiments with cell free homogenates indicate that under high salinity conditions an increase in the rate of -alanine synthesis from aspartic acid as well as a decrease in the rate of -alanine oxidation are responsible for the observed accumulation of -alanine. The rate of aspartic acid decarboxylation to -alanine is about 3 times greater in anemones acclimated to 40 than for those in normal salinity water (26). -alanine oxidation to CO₂ and acetyl-CoA proceeds 2.5 to 3 times slower in high salinity adaptedB. cavernata than in those acclimated to normal salinity. There is always a rapid degradation of uracil to -alanine, but this does not change with salinity.Abbreviations CASF cold acid soluble fraction - FAA free amino acids - MES 2(N-morpholino) ethane sulfonic acid - NPS ninhydrin positive substances - PCA perchloric acid - TCA trichloroacetic acid     

Does the impact of nutrients on the biological structure and function of brackish and freshwater lakes differ?

The effects of nutrients on the biological structure of brackish and freshwater lakes were compared. Quantitative analysis of late summer fish, zooplankton, mysid and macrophyte populations was undertaken in 20–36 shallow brackish lakes of various trophic states and the findings compared with a similar analysis of shallow freshwater lakes based on either sampling (fish) or existing data (zooplankton, mysids and macrophytes). Special emphasis was placed on differences in pelagic top-down control. Whereas the fish biomass (CPUE, multiple mesh-size gill nets) rose with increasing P-concentration in freshwater lakes, that of brackish lakes was markedly reduced at P-concentrations above ca. 0.4 mg P l^-1 and there was a concomitant shift to exclusive dominance by the small sticklebacks (Gasterosteus aculeatus and Pungitius pungitius); as a result, fish density remained relatively high. Mysids (Neomysis integer) were found at a salinity greater than 0.5 and increased substantially with increasing P-concentration, reaching levels as high as 13 ind. l^-1. This is in contrast to the carnivorous zooplankton of freshwater lakes, which are most abundant at intermediate P levels. The efficient algal controller, Daphnia was only found at a salinity below 2 and N. integer in lakes with a salinity above 0.5. Above 2 the filter-feeding zooplankton were usually dominated by the less efficient algal controllers Eurytemora and Acartia. In contrast to freshwater lakes, no shift to a clearwater state was found in eutrophic brackish lakes when submerged macrophytes became abundant. We conclude that predation pressure on zooplankton is higher and algal grazing capacity lower in brackish eutrophic-hypertrophic lakes than in comparable freshwater lakes, and that the differences in trophic structure of brackish and freshwater lakes have major implications for the measures available to reduce the recovery period following a reduction in nutrient loading. From the point of view of top-down control, the salinity threshold dividing freshwater and brackish lakes is much lower than the conventionally defined 5.     

Fine-scale movement and assimilation of carbon in saltmarsh and mangrove habitat by resident animals

Despite theories of large-scale movement and assimilation of carbon in estuaries, recent evidence suggests that in some estuaries much more limited exchange occurs. We measured the fine-scale movement and assimilation of carbon by resident macroinvertebrates between adjacent saltmarsh and mangrove habitats in an Australian estuary using ¹³C analysis of animals at different distances into adjacent patches of habitat. ¹³C values of crabs (Parasesarma erythrodactyla –15.7 ± 0.1, Australoplax tridentata –14.7 ± 0.1) and slugs (Onchidina australis –16.2 ± 0.3) in saltmarsh closely matched that of the salt couch grass Sporobolus virginicus (–15.5 ± 0.1). In mangroves, ¹³C values of crabs (P. erythrodactyla –22.0 ± 0.2, A. tridentata –19.2 ± 0.3) and slugs (–19.7 ± 0.3) were enriched relative to those of mangroves (–27.9 ± 0.2) but were more similar to those of microphytobenthos (–23.7 ± 0.3). The ¹³C values of animals across the saltmarsh-mangrove interface fitted a sigmoidal curve, with a transition zone of rapidly changing values at the saltmarsh-mangrove boundary. The width of this transition indicated that the movement and assimilation of carbon is limited to between 5 and 7 m. The ¹³C values of crabs and slugs, especially those in saltmarsh habitat, clearly indicate that the movement and assimilation of carbon between adjacent saltmarsh and mangrove habitat is restricted to just a few metres, although some contribution from unmeasured sources elsewhere in the estuary is possible. Such evidence demonstrating the extent of carbon movement and assimilation by animals in estuarine habitats is useful in determining the spatial arrangement of habitats needed in marine protected areas to capture food web processes.     

Analysis of primary food sources and trophic relationships of aquatic animals in a mangrove-fringed estuary,Khung Krabaen Bay (Thailand) using dual stable isotope techniques

Stable carbon (¹³C) and nitrogen (¹⁵N) isotopes were used to elucidate primary food sources and trophic relationships of organisms in Khung Krabaen Bay and adjacent offshore waters. The three separate sampling sites were mangroves, inner bay and offshore. The ¹³C values of mangrove leaves were –28.2 to –29.4, seagrass –10.5, macroalgae –14.9 to –18.2, plankton –20.0 to –21.8, benthic detritus –15.1 to –26.3, invertebrates –16.5 to –26.0, and fishes –13.4 to –26.3. The ¹⁵N values of mangrove leaves were 4.3 to 5.7, seagrass 4.3, macroalgae 2.2 to 4.4, plankton 5.7 to 6.4 , benthic detritus 5.1 to 5.3, invertebrates 7.2 to 12.2 , and fishes 6.3 to 15.9. The primary producers had distinct ¹³C values. The ¹³C values of animals collected from mangroves were more negative than those of animals collected far from shore. The primary carbon sources that support food webs clearly depended on location. The contribution of mangroves to food webs was confined only to mangroves, but a mixture of macroalgae and plankton was a major carbon source for organisms in the inner bay area. Offshore organisms clearly derived their carbon through the planktonic food web. The ¹⁵N values of consumers were enriched by 3–4 relative to their diets. The ¹⁵N data suggests that some of aquatic animals had capacity to change their feeding habits according to places and availability of foods and as a result, individuals of the same species could be assigned to different trophic levels at different places.     

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.     

Stable isotope and radiocarbon compositions of methane emitted from tropical rice paddies and swamps in Southern Thailand

Stable isotopes (¹³C, D) and radiocarbon weremeasured in methane bubbles emitted from rice paddies and swamps in southernThailand. Methane emitted from the Thai rice paddies was enriched in¹³C (mean ¹³C; –51.5 ±7.1 and–56.5 ± 4.6 for mineral soil and peat soil paddies,respectively)relative to the reported mean value of methane from temperate rice paddies(– 63 ± 5). Large seasonal variation was observed in¹³C(32) in the rice paddies, whereas variationinD was much more smaller (20), indicating that variation in¹³C is due mainly to changes in methane production pathways.Values of ¹³C were lower in swamps (–66.1 ±5.1)than in rice paddies. The calculated contribution of acetate fermentation from¹³C value was greater in rice paddies (mineral soils:62–81%, peat soils: 57–73%) than in swamps (27–42%). Din methane from Thai rice paddies (–324± 7 (n=46)) isrelativelyhigher than those from 14 stations in Japanese rice paddies ranging from–362 ± 5 (Mito: n=2) to –322 ± 8(Okinawa: n=3), due tohigher D in floodwaters. ¹⁴C content in methane produced fromThai rice paddies (127±1 pMC) show higher ¹⁴Cactivity compared with previous work in paddy fields and those from Thai swamps(110±2 pMC).     

Effects of short-term storage of gametes on fertilization of Pacific herring eggs

A method is described whereby arrays of samples ofClupea pallasi eggs may be stored during their preparation. The high fertilization potential retained by the eggs during short-term storage allows them to be fertilized synchronously when sample preparation is complete. A variation of the dry method of storage retained maximum fertilization potential (80–85%) of the eggs for about 1 hr, and of milt dilution (18 with 17 S sea water), about 7 hr. Following dry storage, eggs fertilized in salinities of 0–45 showed maximum rates of fertilization in salinities of 10–20, and fertilization rates 50% in salinities of 4.5–42. Salinities of fertilization influenced egg diameter, median hatching time, and larval length at hatching in egg samples transferred 21/2 hr after fertilization to an incubation salinity of 17 at 7°C. Fertilization rates were higher (90–95%) for eggs stored in 17 S at 7°C prior to fertilization. Under such wet storage conditions, maximum fertilization pontential was retained for about 2 hr. Highest fertilization rates (95–96%) were obtained for eggs stored and fertilized in salinities of 12–15. For the species and the area of origin considered (British Columbia), wet storage of eggs should result in maximum fertilization when the eggs are stored at 4°C for a period not greater than 2 hr prior to fertilization in the 12–15 S storage medium.Prepared under the auspices of the Canadian-German Scientific and Technical Cooperation Agreement.