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.     

The combined effects of salinity and temperature on larvae of the mussel Mytilus edulis

The combined effects of salinity and temperature on survival and growth of larvae of the mussel Mytilus edulis (L.) were studied. The effects of salinity and temperature are significantly related only as the limits of tolerance of either factor are approached. Survival of larvae at salinities from 15 to 40 is uniformly good (70% or better) at temperatures from 5° to 20°C, but is reduced drastically at 25 °C, particularly at high (40) and low (20) salinities. Larval growth is rapid at a temperature of 15 °C in salinities from 25 to 35, at 20 °C in salinities from 20 to 35. Optimum growth occurs at 20 °C in salinities from 25 to 30. Growth decreases both at 25° and 10 °C; the decline is most drastic at high (40) and low (20) salinities.Part of a study completed at the Bureau of Commercial Fisheries, Biological Laboratory, Milford, Connecticut, USA, while on a UNESCO Fellowship.     

Effects of temperature and salinity on larval development ofNecora puber (Brachyura: Portunidae)

Temperature and salinity affected both length of larval development and mortality inNecora puber collected in the Ría de A Coruña during December 1984 and January 1985. Development time decreased considerably with increased temperature. This decrease was sharper when temperature increased from 15° to 20°C than when it increased from 20° to 25°C. At 35S, average development took 48, 32 and 28 d at 15°, 20° and 25°C, respectively. At the three salinities tested (25, 30 and 35), larval development was completed only at 15°C, at 20°C/30 and 35S, and at 25°C/35S. Development times at 15° and 20°C were highly significantly different at both 35 and 30S (P 0.01). However, there were no significant differences between development times at 20° and 25°C (P > 0.05). Within any one specific temperature series, no significant difference was observed between the salinity values tested (P > 0.05). The duration of each of the five zoeal stages was similar within each and the same temperature/salinity combination, whereas the duration of the megalop was twice as long as any of the zoeal stages. The combination of the lowest temperature (15°C) and the highest salinity (35) tested resulted in the greatest larval survival of 28%. Highest mortality occurred at 25°C, at which temperature development was completed only at 35S. A sharp drop in larval survival was observed in the transition period Zoea V — megalop in all combinations of temperature and salinity tested. Within the limits of tolerance to temperature and salinity, the former effected more pronounced differences in the duration of larval development, while salinity appeared to constitute a limiting factor for survival.     

The effect of temperature-salinity combinations on survival and growth of juvenile Patiriella pseudoexigua (Echinodermata: Asteroidea)

Adult Patiriella pseudoexigua were collected in October 1989 from Wanlitung, Taiwan and then induced to spawn in the laboratory. Post-metamorphosed juvenile P. pseudoexigua were reared on a diet of benthic algae Navicula sp. at 25°C and salinity (34). Six weeks after metamorphosis, juvenile P. pseudoexigua at ca. 400 m in radius were reared on a diet of benthic algae Navicula sp. at different combinations of temperatures (20, 25, 30°C) and salinities (26, 30, 34) for 40 d. Both temperature and salinity had a significant effect on juvenile survival and growth. Juveniles survived best (>90%) at 25°C and 34 and grew best (to ca. 750 m in radius) at 30°C and 34. Variation in juvenile size was small immediately after metamorphosis and increased with time.     

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.     

Individual effects and interactions of salinity,temperature, and zinc on larval development of the grass shrimp Palaemonetes pugio. I. Survival and developmental duration through metamorphosis

Larvae of the estuarine grass shrimp Palaemonetes pugio (Holthuis) were reared from hatch through successful completion of metamorphosis in 80 combinations of salinity (3 to 31%), temperature (20° to 35°C), and zinc (0.00 to 1.00 ppm Zn⁺⁺). Response-surface methodology was employed to depict the individual effects and interactions of the three factors on survival and developmental duration through total larval development. Outside the optimal salinity-temperature conditions of 17 to 27 S and 20° to 27°C, viability of larvae was reduced by both the individual effects of salinity and temperature and interactions between the two factors. Survival capacity of larvae and resistance adaptations to salinity and temperature were progresively reduced by zinc concentrations from 0.25 to 1.00 ppm Zn⁺⁺. Response-surface analysis of the data suggested that the duration of total larval development of P. pugio was least at salinities from 18 to 23 and at temperatures from 30° to 32°C. At both higher and lower salinity-temperature conditions and in increasing zinc concentrations from 0.25 to 1.00 ppm Zn⁺⁺, developmental rates were retarded. A significant zinc-temperature interaction existed, whereby increasing zinc concentrations reduced both survival and developmental rates of larvae more at suboptimal temperatures. Larval resistance to zinc toxicity was least at supraoptimal salinities, indicative of a significant zinc-salinity interaction. The reduced viability, restricted euryplasticity, and retarded developmental rates of P. pugio larvae developing in media with low-level zinc contamination would limit the distributive properties of the pelagic phase in the life cycle of the species and reduce recruitment both into and out of the parent estuarine population.     

Calcification in the maerl coralline alga Phymatolithon calcareum: Effects of salinity and temperature

The coralline alga Phymatolithon calcareum was dredged from 13 m in the Kattegatt, Baltic Sea, in December, 1980, and its rate of calcification was measured by ⁴⁵Ca⁺⁺-uptake methods. Light-saturated calcification rates at 5°C ranged from 15.8 g CaCO₃ g^-1 dry wt h^-1 for the basal parts of the plants to 38.7 g CaCO₃ g^-1 dry wt h^-1 for the tips. These age gradients were not apparent when calcification rates were expressed on the basis of surface area. Experiments with salinity (10, 20, 30) and temperature (0°, 5°, 10°, 20°C) indicated that optimum conditions for calcification were at 30 S and at temperatures above 10°C. Salinity had a greater influence on calcification rate than did temperature, and there was a positive relationship between salinity and calcification rate at all temperatures. In 6 mo old cultures, salinity was again the important factor, with all plants remaining healthy at 30 except those at the highest temperature (20°C). These trends, and the low calcification rates at 10S (4.6 g CaCO₃ g^-1 dry wt h^-1 at 5°C to 8.6 g CaCO₃g^-1 dry wt h^-1 at 20°C) suggest that low salinity may be the explanation for the general absence of P. calcareum from the brackish waters of the Baltic Sea. Short-term experiments in which salinity was kept constant while Ca⁺⁺ concentration was altered, and experiments in which salinity was varied and Ca⁺⁺ concentration kept constant, suggest that it is the calcium ion concentration and not salinity per se which affects calcification rates.     

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.     

Temperature,salinity and ultraviolet irradiation effects on the growth of strains of Nitzschia ovalis

Three strains of Nitzschia ovalis Arnott grew at temperatures from 15°–36°C and at salinities from 5–40 S Optimum growth occurred at combinations of 25°, 27.5° and 30°C and 25, 30 and 35S. This estuarine benthic diatom tolerates wide salinity and temperature conditions while demonstrating resistance to ultraviolet irradiation at 350 nm.     

The respiratory metabolism of Tilapia mossambica (Teleostei)

Tilapia mossambica (Teleostei) weighing 5 to 80 g were acclimated at 30°C to salinities of 0.4 (tap water), 12.5 (50% sea water) and 30.5 (100% sea water). Their respiration was measured at routine activity and the partial pressure of ambient oxygen gradually reduced from 250 to 50 mm Hg. Respiration is salinity-dependent; the proportionate ability to use oxygen in any one salinity is — above the critical pO₂ —the same in all experimental groups. This ability is a function of temperature and increases from 15° to 30°C, becoming temperature independent from 30° to 40°C as long as the pO₂ remains above 150 mm Hg. At 50 mm Hg pO₂, the limiting effect of oxygen causes a decrease in metabolic rate. This limiting effect is minimal in 80 g fish kept in an isotonic medium (12.5 S), allowing greater scope for activity and a higher rate of oxygen uptake.     

Combined effects of temperature and salinity on the complete development ofEurytemora velox (Crustacea: Calanoidea)

The calanoid copepodEurytemora velox was collected from rock pools at Castletown, Isle of Man, UK. Its optimum environmental requirements, particularly temperature and salinity, were determined, with a view to its possible future use as living food in intensive fish and shellfish farming. The species was cultured in 21 different temperature and salinity combinations. Investigations covered a period of two years from December 1983 to December 1985. Complete development from hatching to adult stage was followed in 21 temperature and salinity combinations. Nauplii suffered relatively high mortalities, indicating the sensitivity of this development stage to variations in temperature and salinity. Highest nauplii survival was observed in the combinations 15°C with 25 and 20 S and 20°C with 20 S, the highest copepodite survival at 10°C and 20 S. Lower salinities were tolerated better at higher temperatures and higher salinities at lower temperatures. Development time varied with the temperature and salinity combinations. Lower salinities at the lower temperatures of 10° and 15°C and both lower and higher salinities at 20°C prolonged development, particularly of the naupliar stage. Highest Q₅ values (i.e., rate of change of development with a 5 C° increase in temperature) were recorded for the naupliar stage. Statistical analysis indicated that salinity influences the survival of both nauplii and copepodites; however, this effect is not linear.     

Autecology and clonal variability of the marine centric diatom Thalassiosira rotula (Bacillariophyceae) in response to light,temperature and salinity

The influence of 49 combinations of salinity (10–40 S, at 5 S intervals) and temperature (0°–30°C, at 5C° intervals) on the maximum daily division rate (K) and 18 combinations of light intensity (six levels) and temperature (5°, 15°, and 25°C) on photosynthesis, cell division, and chlorophyll a was examined using two clones of Thalassiosira rotula Meunier isolated from the upwelling area of Baja California (clone C8) and from Narragansett Bay, Rhode Islands (clone A8). Physiological differences appear to characterize these to clones with regard to their temperature tolerance (C8 5°–30°C, A8 0°–25°C), maximum growth rate (C8 K=2.9, A8 K=2.4), chlorophyll a content, and in the rates of growth and photosynthesis in response to light intensity and temperature. Optimum salinity for both clones (25–30 S) was generally independent of temperature, while chlorophyll a content decreased with temperature. T. rotula is a cosmopolitan paractic species; experimental studies indicate that it is eurythermal and moderately euryhaline. Comparison of five additional Narragansett Bay isolates of T. rotula reveal minimal spacial or temporal variability in genetically determined physiological characteristics within this local population.     

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 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.     

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.     

The respiratory metabolism of Tilapia mossambica (Teleostei)

In a series of experiments 174, 120 and 139 individuals of the teleost Tilapia mossambica (Peters), were acclimated to 30°C and to salinities of 0.4, 12.5 and 30.5, respectively. The effect of temperature and salinity upon oxygen consumption was studied by abruptly transferring fish of different wet weights to temperatures from 15° to 40°C at an average initial pO₂ of 250mm Hg. At each salinity, the proportionate response to temperature is size-independent. The metabolic rate increases as a function of temperature at 15° and 30°C but not at 40°C. Oxygen consumption is, however, salinity dependent; maximum rates are obtained at 12.5S. This salinity is isotonic in the 80 g fish and, to a lesser extent, in the 5 g fish. Reduction in osmotic load is suggested as the probable cause for a greater scope for activity and greater rate of oxygen consumption in 12.5 salinity.     

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.     

Effects of temperature and salinity acclimation of adults on larval survival,physiology, and early development of Lytechinus variegatus (Echinodermata: Echinoidea)

Larval survival and developmental rates of Lytechinus variegatus (Lamarck) were determined as a function of temperature and salinity in two experiments by: (1) directly transferring fertilized eggs to 35, 30, 27.5, 25, 20, 15, and 10S seawater at 18 and 23°C, and (2) acclimation of adult sea urchins to the conditions described above for 1 to 4 wk prior to spawning. Developmental rates and percent survival of larvae prior to metamorphosis decreased at salinities below 35 (Q₁₀ values for metamorphosis=0.380 to 0.384). Temperature and salinity significantly (P<0.05) affected metabolic rates of L. variegatus plutei. These results show that L. variegatus larvae are stenohaline when compared to larvae of other echinoderm species. LC₅₀ values (S), developmental rates, and survival to metamorphosis indicate that acclimation of adult sea urchins to lower salinity prior to spawing and fertilization does not enhance development or survival of embryos exposed to low salinity.     

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     

Combined effects of temperature and salinity on fed and starved larvae of the mediterranean mussel Mytilus galloprovincialis and the Japanese oyster Crassostrea gigas

The combined effects of temperature, salinity and nutrition on survival and growth of larvae of the Mediterranean mussel Mytilus galloprovincialis and the Japanese oyster Crassostrea gigas were studied over a period of 7 d in the laboratory. Ripe adults, collected in spring and summer 1987 from natural populations in the Bay of Arcachon, France, were induced to spawn. Larvae of both species were cultured at four temperatures (15°, 20°, 25° and 30°C), four salinities (20, 25, 30 and 35S) per temperature, and two levels of nutrition (fed and unfed) per temperature/salinity combination. The fed larvae received a mixed algal diet of 50 cells each of Isochrysis galbana and Chaetoceros calcitrans forma pumilum per microlitre. In both bivalve species, larvae survived over a wide range of temperature and salinity, with the exception of mussel larvae, which died at 30°C. Statistical analysis indicated that nutrition had the greatest effect on larval development, explaining 64 to 75% of the variance in growth of M. galloprovincialis and 54 to 70% in growth of Crassostrea gigas. Unfed mussel larvae displayed little growth. Compared with temperature, the effect of salinity was very slight. M. galloprovincialis larvae exhibited best growth at 20°C and 35S and C. gigas at 30°C and 30S.