Salinity tolerance of benthic estuarine diatoms as tested with a rapid polarographic measurement of photosynthesis

Measurements of net photosynthesis of benthic estuarine diatoms were made by polarographic registration of oxygen saturation. A measuring cell was constructed in which media with salinities of 2.0 to 100.7 were pumped over the algae between measurements. Diatoms from unialgal cultures and mixed populations from intertidal flats appeared to be highly tolerant of extreme salinities. During short-term exposures (20 min) the net photosynthesis of the algae did not drop below 70% of the initial values, within the salinity range 4.0 to 60.0. Prolonged exposure (up to 6 h) gave essentially the same results. Populations of benthic diatoms, sampled from field stations with mean salinities of about 30, 12, and below 5, showed only gradual differences in their tolerance of salinities between 2.0 and 33.7. Two species, Navicula arenaria and Nitzschia sigma, were cultured in media ranging in salinity from 8.0 to 45.0 and from 2.0 to 45, respectively. The tolerance to changing salinity was only slightly affected by the salinity of the medium in the preculture. The role of salinity in the production and distribution of intertidal diatoms is discussed.     

Influence of salinity on embryonic development and the distribution ofSepia officinalis in the Delta Area (South Western part of The Netherlands)

The effect of salinity on embryonic development ofSepia officinalis (cuttlefish) in the Delta Area (South Western part of The Netherlands) was investigated in 1988/1989, and compared with data concerning the distribution ofS. officinalis in the three main parts of this area: Oosterschelde, Westerschelde and Grevelingen. Embryos hatched in water collected at Yerseke (Oosterschelde), Vlissingen (Western part of the Westerschelde) and Bommenede (Grevelingen), i.e., at salinity values above 28.1, but not in water sampled at Hoedekenskerke and Hansweert (Middle and Eastern part of the Westerschelde; salinities below 22.0). Under laboratory conditions, using diluted Oosterschelde water, the highest hatching percentages ofS. officinalis were found at salinities above 29.8. Some embryos hatched at a salinity value of 26.5 but no hatching occurred at salinities below 23.9. In embryos exposed to salinity changes during late embryonic development, the developmental rate decreased at salinity values of 28.7 or less. Below 22.4 embryos with morphological malformations were found. It can be concluded that salinity is an important factor limiting the distribution ofS. officinalis in most parts of the Delta Area, with the exception of the Western part of the Westerschelde and the Grevelingen.Contribution no. 489 of the Library of the Delta Institute for Hydrobiological Research     

Effects of salinity on respiration and nitrogen excretion in two species of echinoderms

The 30-d survival limit of Eupentacta quinquesemita and Strongylocentrotus droebachiensis is 12–13 S. The activity coefficient (1 000/righting time in seconds) of stepwise acclimated sea urchins declined from 16.3 at 30 S to 3.5 at 15 S. Oxygen consumption rates (QO₂) of both species held at 30 S and 13°C were highest in June and lowest in December. During the summer, when environmental salinity is most variable in southeastern Alaska, the QO₂ of both species held at 30, 20 and 15 S varied directly with salinity. Perivisceral fluid PO₂ varied directly with acclimation salinity in sea urchins, but not in sea cucumbers. Perivisceral fluid oxygen content of acclimated sea urchins was significantly lower at 15 and 20 S than at 30 S due to reduced PO₂ and extracellular fluid volume at the lower salinities. The QO₂ of both species varied directly with ambient salinity during a 30-10-30. semidiurnal pattern of fluctuating salinity. No change occurred in the average QO₂ of either species over a 15-30-15. semidiurnal pattern of fluctuating salinity. Sea urchin perivisceral fluid PO₂ declined as ambient salinity fluctuated away from the acclimation salinity in both cycles and increased as ambient salinity returned to the acclimation salinity. Total nitrogen excretion of stepwise acclimated sea cucumbers declined significantly from 30 to 15 S, but there was no salinity effect on total nitrogen excretion in sea urchins. Ammonia excretion varied directly with salinity in stepwise acclimated sea cucumbers (67–96% of total nitrogen excreted), but there was no salinity effect on ammonia excretion (89–95% of total nitrogen excreted) of sea urchins. Urea excretion did not vary with salinity in sea cucumbers (2–4% of total nitrogen excreted) or sea urchins (2–9% of total nitrogen excreted). Primary amines varied inversely with salinity in sea cucumbers (2–30% of total nitrogen excreted), but did not vary with salinity in sea urchins (2–4% of total nitrogen excreted). The oxygen: nitrogen ratio of both species indicated that carbohydrate and/or lipid form the primary catabolic substrate. The O:N ratio did not vary as a function of salinity. Both species are more tolerant to reduced salinity than previously reported, however, rates of oxygen consumption and/or nitrogen excretion are modified by salinity as well as season.     

Influence of salinity and temperature on the oxygen consumption in young juveniles of the Indian prawn Penaeus indicus

Routine oxygen consumption of very young juveniles (0.1 g) of Penaeus indicus H. Milne Edwards was significantly influenced by ambient temperature and weight of the animal, but not by ambient salinity, when tested at salinities (7, 21, and 35) to which they had been long-term (over 10 days) acclimated. Standard oxygen consumption of young juvenile prawns (1 to 3 g), subjected to step-wise changes in ambient salinity, from sea water to low salinity waters (2 to 6), and measured after short-term (24 h) salinity acclimation at each step, was lowest at salinities where prawns such as those tested occur naturally (10 to 15). The metabolic rates do not appear to have a direct relation to the osmotic gradient, even when the influence of interfering activity is eliminated. It appears that factors other than osmotic gradient will have to be sought in order to explain the metabolic patterns of P. indicus in relation to salinity.     

Zooplankton of the Bristol Channel and Severn Estuary. The distribution of four copepods in relation to salinity

The seasonal variations in distribution and abundance of the common zooplankton species in the Bristol Channel and Severn Estuary were related to the salinity regimes observed over the period November 1973 to February 1975. The dominant constituents in all regions were the calanoid copepods, which reached maximum densities in July: approximately 100 times their winter levels. Four zooplankton assemblages were recognised using an objective classification program which computed similarity coefficients and used group-average sorting. The assemblages existed along the salinity gradient observed from the Severn Estuary to the Celtic Sea. The assemblages were classified as true estuarine, estuarine and marine, euryhaline marine and stenohaline marine and were characterized by the copepods Eurytemora affinis (Poppe) (<30S), Acartia bifilosa var. inermis (rose) (27 to 33.5S), Centropages hamatus (Lilljeborg) (31 to 35S) and Calanus helgolandicus (Claus) (>33S), respectively.     

The significance of temperature,salinity and zinc as lethal factors for the mussel Mytilus edulis in a polluted estuary

Mussels, Mytilus edulis L., were subjected to high temperatures, low salinities and dissolved zinc in order to investigate possible environmental hazards of a discharge of heated effluent near Newport on the Yarra River estuary, Victoria, Australia. Exposure to zinc at 0.8 mg l^-1 for 14 d in otherwise favourable conditions significantly increased mortality resulting from subsequent exposure to temperatures between 29° to 31°C for 24 h without added zinc. Mussels collected from water of temporarily lowered salinity (8–16 S) showed significantly lower thermal resistance than controls collected from marine salinities (35 S). Mussels taken from a marine environment and exposed to 10 S died at a rate which increased with temperature. Mussels acclimated for 14 d to combinations of 10°, 16° and 22°C and 22 and 35 S, and subsequently exposed to increased zinc concentrations accumulated zinc to levels which were independent of temperature and salinity. The zinc was lethal more quickly at 22°C and 35 S than at the lower temperatures and salinities. The modes of toxic action of the salinity, zinc and temperature factors are discussed and it is argued that zinc which has been found accumulated in mussels near Newport could be reducing their resistance to raised temperatures and perhaps other stresses, probably as a result of effects on lysosomal functioning. The evidence suggests that the heated effluent will accelerate any toxic effects of zinc or low salinities which occur near Newport and so poses a hazard in winter as well as in summer.     

Survival and chloride ion regulation of the porcelain crab Petrolisthes armatus exposed to mercury

Acute toxicity bioassays conducted at various salinities demonstrated that mercury (as mercuric chloride) at low concentrations was lethal to Petrolisthes armatus. Ninety-six hour LC₅₀ values varied from 50 to 64 parts per billion (ppb) of mercury, depending on test salinities. Lower salinities. decreased the time to death of mercuryexposed crabs. Differences in survival after 96 h due to salinity were not statistically significant. Blood chloride concentrations were regulated hyperchloride to the medium at low salinities and hypochloride at high salinities by acclimated crabs. The salinity isochloride to blood was 20 S. Transfer of crabs from 15 S to salinities ranging from 7 to 35 S resulted in new steadystate chloride levels within 12 h. Exposure to 50 ppb mercury did not alter chloride ion regulation of either acclimated crabs or crabs adjusting to new salinities.     

Salinity tolerance,salinity preference and temperature tolerance in the high-shore harpacticoid copepod Tigriopus brevicornis

Tigriopus brevicornis (O. F. Müller) were collected in 1992 from rock pools close to U.M.B.S. Millport, Isle of Cumbrae, U.K. and acclimated to various combinations of salinity and temperature for at least 1 wk prior to laboratory experiments. Higher salinities of acclimation enhanced tolerance to high salinity stress, while tolerance of low salinities was hardly affected by acclimation salinity. Acclimation to low temperature (10°C) extended the survivable salinity range for T. brevicornis. High-salinity acclimation enhanced the survivable temperature range. Copepods acclimated to 60 survived significantly lower and higher temperatures than did 34-acclimated individuals. At high temperature, 75-acclimated female copepods had the highest median lethal temperature, 38.9°C. Females were significantly more resistant to high temperatures than males. The copepods were seen to have a very low median lethal temperature when frozen into solid ice for 2 h; 50% mortality occurred at-16.9°C in 10°C, 34-acclimated T. brevicornis. Salinity preference experiments demonstrated an ability to discriminate between salinities differing by as little as 3. Copepods acclimated to 34 chose salinities near their acclimation salinity; individuals acclimated to 5 favoured slightly higher salinities, while copepods acclimated to 60 chose rather lower salinities.     

Levels of intracellular free amino acids used for salinity tolerance by oysters (Crassostrea virginica) are altered by protozoan (Perkinsus marinus) parasitism

Free amino acid (FAA) levels were measured from May through October 1991 in gill tissues of two groups of juvenile oysters (Crassostrea virginica Gmelin), one transferred from a low salinity field site (8) to a field site of high salinity (20) and high Perkinsus marinus (Mackin, Owen, and Collier) prevalence, the other kept at the low salinity field site. Within 24 h, glycine levels in the oysters transferred to high salinity increased 8-fold, taurine concentrations doubled and the total FAA pool rose from 150 mol g^–1 dry wt to 400 mol g^–1 dry wt. Taurine levels reached a plateau within 20 d after transfer to high salinity and remained at that level until P. marinus infections were detected 85 d after transfer. Taurine and glycine levels declined by 40% in the high salinity population as infection intensity increased between 70 and 105 d. Total FAA declined by approximately 33% over this period. The oysters kept at low salinity were not infected and continued to grow while the infected high salinity oysters showed no increase in shell length after Day 85. FAA levels in the low salinity group remained relatively constant throughout the experiment except for an initial rise triggered by an increase in ambient salinity from 8 to 12. The results suggest that salinity tolerance mechanisms in C. virginica may be impaired by P. marinus infection.     

Stepwise acclimation—a method for estimating the potential euryhalinity of the gastropod Hydrobia ulvae

The White Sea gastropod Hydrobia ulvae (Pennant) was exposed to step-wise lowering or increase of the habitat salinity. The time allowed for acclimatization to the successive salinity levels was sufficient to complete non-genetic adaptation. In this way, the lower and upper salinity limits were extended. The tolerance limits obtained are assumed to be indicative of the capacity for non-genetic adaptation and to serve as a genotypical characteristic. The tolerance of specimens colleced from in situ conditions (mid littoral, 20 S) ranged between 14 and 34 S. After non-genetic adaptation, the lower tolerance value shifted to 6 S (adaptation limit), and the upper value to 76 S (final limit not reached). There is no reason for considering White Sea H. ulvae to represent a special physiological race of specimens from those on the coast of Great Britain.     

Effects of salinity and temperature on Corophium volutator and C. arenarium (Crustacea: Amphipoda), with particular reference to distribution

The responses of the post-embryonic stages of Corophium volutator (Pallas) and C. arenarium Crawford to the combined effects of salinity and temperature show that gravid females have a wider tolerance than nongravid adult females which in turn are more tolerant than adult males. C. volutator is more tolerant of low salinity (2 to 10) than C. arenarium, but the latter is more tolerant of salinities above 45. The embryos of C. volutator develop normally and hatch at lower salinities and temperatures than those of C. arenarium, in which successful development was recorded at higher temperatures. Females undergoing a pre-copulatory moult failed to lay eggs below salinities of 3 (C. volutator) and 10 (C. arenarium), but in both species the lowest salinity at which all females moulted and laid eggs was 20. The results are discussed in relation to the distribution of both species.     

Osmoregulation of the grass shrimp Palaemonetes pugio exposed to polychlorinated biphenyls (PCBs). I. Effecton chloride and osmotic concentrations and chloride-and water-exchange kinetics

Grass shrimp, Palaemonetes pugio, were capable of hypo- and hyper-osmotic regulation of body fluids. Hemolymph chloride and osmotic concentrations were maintained at relatively stable levels over a wide salinity range. Following an abrupt transfer from intermediate (14 and 17) to high (31 and 35) or low (1 and 2) salinities, hemolymph chloride levels exhibited initial overshoot and undershoot, respectively, of new steady-state levels. Osmotic concentrations exhibited an initial undershoot at low, but not overshoot at high salinity. Chloride space in salinity-acclimated shrimp was relatively stable at salinities from 1 to 35. Changes in chloride space following salinity transfer paralleled those of hemolymph chloride levels, and are discussed in the light of alterations in intracellular sodium concentrations reported earlier. Rate constants for chloride turnover indicated independent exchanges of sodium and chloride ions. Water-turnover measurements showed that permeability of P. pugio was greatest at the isosmotic salinity (17) and reduced at salinities which were associated with active osmoregulation. Exposure to sublethal and 96-h LC₅₀ levels of Aroclor^® 1254 did not seriously alter hemolymph chloride and osmotic concentrations, chloride space or chloride-exchange kinetics in adult shrimp. Disruption of hemolymph chloride regulation in juvenile shrimp was associated with large mortalities not observed in adults. Shrimp exposed to Aroclor 1254 at 17 S exhibited reduced water permeability similar to levels previously observed in controls at high and low salinities in response to osmotic or ionic gradients. Exposure to PCBs did not result in further reduction in permeability at the latter salinities.     

Salinity dependence of sexual and asexual reproduction in the rotifer Brachionus plicatilis

A salinity dependent mictic response was observed in a clone of Brachionus plicatilis cultured in the 2 to 4 salinity range. This response was related to asexual exponential reproduction rates (G) and could be divided into three categories: (a) no mixis occurred at a salinity of 35 S and above, where G values were lower than 0.30 d^-1, (b) low mictic levels in rotifers cultured at 2 and 30 S, where G values ranged between 0.40 to 0.50 d^-1, and (c) high mictic levels in rotifers cultured at salinities ranging between 4 and 20 S, where G values ranged between 0.50 to 0.85 d^-1. Fluctuations in mictic levels varied with time during the course of the experiments. Results suggest that salinity conditions leading to optimal parthenogenic reproduction also support mixis.     

Effect of temperature and salinity on larval development of southern king crab (Lithodes antarcticus)

Larvae of Lithodes antarcticus Jacquinot were reared in October, 1981 from hatching to the glaucothoe stage at 16 temperature/salinity combinations (5.5°; 7.5°; 9.5° and 13.5°C; 26, 29, 32 and 35 S) to determine optimal environmental conditions for larval development. The highest survival percentage was obtained in the culture at 7.5°C and diminished according to temperature increase or decrease. High temperature cultures significantly shorten the larval life duration, but produce large mortalities. At 5.5°C mortality occurred almost exclusively during the moult to glaucothoe stage. Higher survival percentages were obtained as salinity was increased. In the lowest salinity culture (26 S) no zoea reached the post-larvae stage at culture temperatures. The best T/S combination was obtained at 7.5°C and 35 S, with a survival percentage of 29%. The shortest zoeal developments were obtained at 32 S in all culture temperatures. Salinity also affects larvae coloration: there is a pigment concentration on erythrophores, which causes a color decrease.     

The effect of salinity and cyclic temperature on larval development of the mud-crab Rhithropanopeus harrisii (Brachyura: Xanthidae) reared in the laboratory

Larvae of Rhithropanopeus harrisii (Gould) were reared from hatching to the first or second crab stages in 11 combinations of salinities and cyclic temperatures (5, 20, and 35 S at 20° to 25°C, 25° to 30°C, and 30° to 35°C; 25 S at 20° to 25°C and 30° to 35°C). The larvae survived to the megalops and first crab stages in all salinities and cycles of temperature other than 5 S at 30° to 35°C. The best survival to the megalops (94%) and first crab (90%) stages occurred in 20 S, 20° to 25°C. In all other combinations of salinities and temperatures there was a reduction in survival to the first crab stage. The duration of the larval stages was affected significantly by temperature, whereas the effect of salinity on the mean days from hatching to the first crab stage was not consistent at the different temperature cycles. Development to the first crab stage required the shortest time in 20 S, 30° to 35°C (mean 12.3 days), and the longest time in 5 and 35 S, 20° to 25°C (mean 22.6 days and 21.6 days, respectively). Megalops larvae reared in 35 S at all cycles of temperature, as well as larvae in 20 and 25 S, 30° to 35°C, showed a high percentage of abnormality, with the highest percentage occurring in 35 S, 30° to 35°C. It appears that larval development of R. harrisii is strongly influenced by environmental factors and not solely related to genetic differences.This research was supported by grants from the Nordic Council for Marine Biology and the U.S. Atomic Energy Commission [Grant No. At-(40-1)-4377].Contribution No. 116, Zoological Museum, University of Oslo, Norway.     

Acute toxicity and sublethal behavioral effects of copper on barnacle nauplii (Balanus improvisus)

This study documents the effects of short-term (24h) sublethal copper exposures on undirected swimming activity and photobehavior of Balanus improvisus stage II nauplii. All Cu treatments were static, with temperature and salinity conditions at 20°C and 15 or 30. The 24h LC 50 estimate for Cu is 88 ppb at 15 and >200 ppb at 30. Sub-lethal Cu concentrations cause reductions in swimming speed, which decrease progressively with increasing Cu dose. At 50 ppb Cu, this was significant primarily at light intensities below the phototactic threshold. At higher Cu concentrations, significant reductions in mean linear velocity occurred at most light intensities tested. At 30, 50 and 100 ppb Cu also reduce the positive phototactic response and 150 ppb Cu causes reversal of phototaxis at optimal intensities. Photokinesis is reduced at 100 ppb Cu and disappears at 150 ppb Cu. At 15, the behavioral effects of 50 ppb Cu resemble those occurring with 150 ppb Cu at 30. Swimming speed and photobehavior show promise as sensitive behavioral indicators of copper toxicity. Additional research is required to determine if these responses apply to a broad range of pollutants and to other planktonic organisms. There is also a need to further evaluate the significance of these behavioral effects ecologically.Contribution No. 181 from the EPA Environmental Research Laboratory, Narragansett, RI 02882, USA     

Effects of salinity and calcium concentration on arm regeneration byOphiothrix angulata (Echinodermata: Ophiuroidea)

At 33 salinity a tissue stump formed 2 to 3 d after autotomy and developing ossicles were present by the fourth day inOphiothrix angulata (Say). Regeneration proceeded rapidly from the sixth day until the thirteenth day, when the rate decreased greatly. The length of the regenerated arm and the number of ossicles formed did not vary over a salinity range of 28 to 38 S, but were significantly less at 23 S. The number of ossicles regenerated increased linearly (y=1.9 x-7.7;r=0.9089) with the calcium concentrations ranging from 3.8 to 9.5 mM. No ossicle formation occurred at 3.8 mM calcium concentration. Rate of net uptake of calcium-45 into the ossicles of intact individuals in salinities of 28 and 33 was significantly greater than that in 23 and 38 S. However, net uptake rate of calcium into the soft tissues of the arms was significantly higher at 18S than at the lower two salinities.     

Initiation of feeding and salinity tolerance in the pacific lamprey Lampetra tridentata

Changes in salinity tolerance were determined during metamorphosis in Lampetra tridentata. Lampreys in Phase 5 of metamorphosis were unable to withstand salinities>13.4S, while those in Phase 6 survived direct transfer to sea water (30S). This abrupt change in tolerance coincided with the opening of the foregut lumen. Parasitic feeding began at the end of Phase 7 of metamorphosis following the completion of tooth development.     

Responses of Leptasterias hexactis (Echinodermata: Asteroidea) to low salinity

The six-rayed starfish Leptasterias hexactis (Stimpson, 1862) is seasonally exposed to low salinities in southeastern Alaska. Individuals that were gradually exposed to reduced salinities in the laboratory had a 28-d TLm of 12.9 S. The activity of L. hexactis, as measured by its activity coefficient, varied directly with salinity. Individual feeding rates of the starfish on similarly exposed Mytilus edulis, measured daily for 21 d at salinities of 30, 20 and 15 S, also varied directly with salinity. The dry weight of mussel tissue consumed was 8.84, 8.49 and 0.58 mg ·starfish^-1·d^-1 at 20, 20 and 15 S. Expressed as percent of dry starfish weight, the daily feeding rate was 1.35, 0.76 and 0.10% at 30, 20 and 15 S. Absorption efficiency decreased from 64% at 30 S to 49% at 20 S, further reducing the energy available for metabolism. Growth, measured in terms of changes in total dry weight or dry weight of soft tissues, also varied directly with salinity. Although exposure to hyposmotic conditions did induce stress responses, as indicated by reductions in activity, feeding, absorption efficiency and growth rates, L. hexactis maintained positive growth for at least a 3-wk period in the laboratory at 20 S and 13°CC. The population of L. hexactis investigated must be considered euryhaline and brief periods of exposure to hyposmotic conditions should not limit its distribution.     

On the ecology of Heterocypris salinus,H. incongruens and Cypridopsis aculeata (Crustacea: Ostracoda) from Baltic brackish-water rockpools

The ostracod fauna of Baltic brackish-water rockpools is made up of two groups: permanent members of the pools, and occasional guests from the littoral zone. The former group consists of Heterocypris salinus, H. incongruens and Cypridopsis aculeata. These species are characterized by rapid development (which starts when the water temperature approaches 15°C), a short life span, and 2 or 3 separate generations during the summer and autumn. The number of generations is determined by water temperature. Hibernation always takes place as eggs. Hatching and development during the late spring or early summer has been found to be mostly simultaneous. The spawning of the 3 species always starts epidemically. Reproduction is entirely parthenogenetic in the investigated area. Under natural conditions, C. aculeata may be found with either H. salinus or H. incongruens, but these two latter species have never been recorded together. H. incongruens is less tolerant to high salinities than the other 2 species and, even after successive adaptation, it does not resist salinities higher than 16. H. salinus has been found in 35.2 S in the field, and has been kept in 30 S in the laboratory after successive adaptation. The optimum salinity-temperature range for this species is 5 to 10 S and 15°C, when both survival and development are considered. Corresponding figures for C. aculeata are 0.5 to 20 S and 15°C, although this species, like H. salinus, survives longest at 5°C. The very rapid development, parthenogenetic reproduction and short life span of these species must be considered as favourable adaptations to the variable and unstable environment of the rockpool ecosystems.