High temperature acclimation alters the emersion behavior in the crab Neohelice granulata

An increase in environmental temperature can deleteriously affect organisms. This study investigated whether the semiterrestrial estuarine crab Neohelice granulata uses emersion behavior as a resource to avoid thermal stress and survive higher aquatic temperatures. We also examined whether this behavior is modulated by exposure to high temperature; whether, during the period of emersion, the animal loses heat from the carapace to the medium; and whether this behavior is altered by the temperature at which the animal has been acclimated. The lethal temperature for 50% of the population (LT₅₀) was determined through 96-h mortality curves in animals acclimated at 20 °C and 30 °C. The behavioral profile of N. granulata during thermal stress was based on monitoring crab movement in aerial, intermediary, and aquatic zones. Acclimation at a higher temperature and the possibility of emersion increased the thermotolerance of the crabs and the synergistic effect of acclimation temperature. The possibility of leaving the hot water further increased the resistance of these animals to thermal stress. We observed that when the crab was subjected to thermal stress conditions, it spent more time in the aerial environment, unlike under control conditions. Under the experimental conditions, it made small incursions into the aquatic environment and stayed in the aerial environment for a longer time in order to cool its body temperature. The animals acclimated at 20 °C and placed into water at 35 °C remained in the aerial zone. The animals acclimated and maintained at 30 °C (control) that were placed in water at 35 °C with the possibility of emerging into hot air transited more frequently between the aquatic and aerial zones than did the animals that were put in water at 35 °C with the possibility of emerging into a cooler air environment. We conclude that emergence behavior allows N. granulata to survive high temperatures and that this behavior is influenced by acclimation temperature.     

Aerial and underwater metabolism of <Emphasis Type="Italic">Patella vulgata</Emphasis> L.: comparison of three intertidal levels

Intertidal molluscs are known to possess specific respiratory organs that permit aerial breathing during emersion. Patella vulgata is a widely distributed intertidal species found from low-water spring tide to high-water neap tidal level. In order to determine metabolic adaptations to habitat, carbon fluxes associated with respiration and calcification of P. vulgata living at high-shore, middle-shore and low-shore levels were compared. Seasonal aerial respiration was measured using an infrared gas analyser; seasonal underwater respiration and calcification were calculated from dissolved inorganic carbon and total alkalinity. P. vulgata showed net CaCO₃ deposition at all seasons, although the high-shore level limpet annual calcification rate was relatively low due to longer air exposure. Both aerial and underwater respiration rates were highly correlated with seasonal temperature variations and followed the vertical shore gradient, with stronger fluxes for low-shore tidal level limpets and lower fluxes for high-shore level limpets that must limit energy expenditure. P. vulgata appears to be well adapted to aerial exposure, with average hourly respiration fluxes stronger in air than in water. This study demonstrates that P. vulgata calcification and respiration are reduced in upper shore levels and are important factors determining the upper distribution limit of the species.     

The influence of mantle cavity fluid on the aerial oxygen consumption of some intertidal gastropods

The intertidal gastropods Gibbula cineraria (L.), Nucella lapillus (L.), and Littorina littorea (L.) have been investigated. Animals that had attached to a plastic surface under sea water were exposed to air and rapidly frozen. Fluid was found to be retained within the mantle cavity in contact with the gill. For each species the weight of the mantle cavity fluid retained in air was related to the whole weight of the animal. There was no significant difference between the weight of fluid held by animals in the laboratory and that held by animals on the shore 2 h after aerial exposure. The oxygen consumption of inactive individuals in air was measured by two techniques which did not produce significantly different results. The aerial oxygen consumption of all three species was lowered by the loss of mantle cavity fluid. This also reduced the temperature coefficient. A correlation is suggested between a large weight of mantle cavity fluid, the presence of a gill in the mantle cavity and a large reduction in oxygen consumption upon the loss of fluid.     

Some factors affecting survival and oxygen uptake in a subtropical beach flea

The survival and oxygen uptake of the supralittoral amphipod Chroestia lota Marsden & Fenwick were investigated in humid air and sea water between 15 and 35°C. Seven-day exposure experiments were made on three size groups of amphipods at 6 constant temperatures (15, 20, 25, 30, 35, 40 °C) and three cyclic temperatures (15–25, 20–30, 25–35°C) in air and in sea water at 34 and 17%. salinity. Neither size, treatment nor temperature affected survival between 15 and 30°C. Mortality increased > 30°C with large individuals being consistently less tolerant than medium and small amphipods. While amphipods exposed to cyclic temperatures during submersion had reduced survival compared with constant temperatures, those individuals exposed to cyclic conditions in humid air showed the greatest resistance. Oxygen uptake of Chroestia increased with dry body wt and, over the range 15–35°C, this semi-terrestrial beach flea could maintain its aerial VO₂ following submersion. Oxygen uptake increased directly in proportion to gill area and the weight specific gill area was low, consistent with the need to reduce desiccation. It is suggested that total gill area does not limit oxygen uptake in Chroestia and that cutaneous respiration may be important especially in aquatic conditions.     

Zur fortpflanzungsbiologie von mesostoma ehrenbergii (Focke, 1836) (Turbellaria)

1. At temperature levels from 10 to 25°C animals from resting eggs produce subitaneous eggs independent on temperature. In contrast animals from subitaneous eggs produce subitaneous eggs dependent on temperature. At a high rate subitaneous eggs are only formed at temperature levels above 20°C.
2. Below 10°C no development occurs in the juveniles. At temperatures of 30/22°C (24.7°C) the first subitaneous eggs are formed after 6–9 days, at 14/9°C (10.7°C) they are formed after 34 days. At different temperature levels the developmental rate of the young is from 10.5 to 42 days. One generation extends over 16.5 (30/22°C) to 75 days (14/9°C). The average egg production is 10–20 subitaneous eggs or 30–60 resting eggs. The maximum egg production of one individual is 50 subitaneous eggs or 84 resting eggs. 50% of the animals have just formed resting eggs, before the juveniles are hatched. Resting eggs in the first egg-batch are formed 6–20 days later than subitaneous eggs. The duration of life is between 65 (30/22°C) and 140 days (19/13°C).
3. Young worms in resting eggs have a dormance period of at least 15–30 days.

At room temperatures (20°C) no juvenile in resting eggs hatches from water. By combining room and refrigerator (3.5°C) temperatures the hatching rate increases to a maximum of 85%. To reach a hatching rate of 50–65% the influence of low temperatures must be at least 30 days. At room temperatures 60% of the young in resting eggs hatch from mud covered with water. Combining high and low temperatures the hatching success is between 67 and 81%, where the highest percentage of the young may hatch at room temperature. Up to 90 days low temperatures cause a maximum hatching rate of 79%. It decreases to approximately 30% after 180 days. At high temperatures resting eggs preserved in 100% moist mud, survive for two months. By adding a period of low temperatures the hatching rate increases to a maximum of 52%. Low temperatures are survived for more than 6 months. Up to 30 days preservation at 3.5°C causes a maximum hatching rate of 61%, up to 12o days it decreases to 30%. At room temperature the young in resting eggs are not resistant against air-dried mud (30–40% rel. air moisture). Combining high and low temperatures air-dried mud is endured 1 month (hatching rate 5–14%). Preservation of 30–120 days at 3.5°C and 70% rel. air moisture result in a hatching rate of 43–61%. li]4. In the open air in Middle-Europe there occur 5–6 generations of M. ehrenbergii per life-cycle. The first generation hatches from resting eggs in May, where the production of subitaneous eggs is independent on temperature. All other generations up to October hatch from subitaneous eggs. The egg-production of those worms is dependent on environmental factors. In summer subitaneous egg production prevails, in autumn resting egg production. The abundance during the life-cycle is dependent on the number of animals which produce subitaneous eggs. Resting eggs are predestinated to endure periods of dryness and cold. The life-cycles of the species M. lingua and M. productum are different from those of M. ehrenbergii in length and in the number of generations. In both species 7 generations occur over 8 to 8.5 respectively 5.5 months. M. nigrirostrum only forms resting eggs. The life-cycle consists of one generation from February/March to May/June.     

The combined effects of temperature,salinity, and declining oxygen tension on oxygen consumption in the marine pulmonate Amphibola crenata (Gmelin, 1791)

Oxygen consumption of Amphibola crenata (Gmelin) was measured in various salinity-temperature combinations (< 0.1‰ to 41‰ salinity and 5 to 30°C) in air, and following exposure to declining oxygen tensions. In all experimental conditions, respiration varied with the 0.44 power of the body weight (sd = 0.14). The aquatic rate was consistently higher than the aerial rate of oxygen consumption, although at 30 °C the two rates were similar. Oxygen consumption increased with temperature up to 25 °C in all salinities; the lowest values were recorded at temperatures below 10 °C and at 30 °C in the most dilute medium. At all exposure temperatures, the oxygen consumption of Amphibola decreased regularly with salinity down to 0.1 ‰, and following exposure to concentrated sea water (41‰). Salinity had the least effect at 15 °C which was the acclimation temperature. In general, all of the temperature coefficients (Q₁₀ values) were low, < 1.65. However, Q₁₀ values above 2.8 were recorded at a salinity of 17.8‰ between 10 and 15 °C. Oxygen consumption of all size classes of Amphibola was more temperature dependent in air than in water and small individuals show a greater difference between their aerial and aquatic rates than larger snails. The rates of oxygen consumption in declining oxygen tensions were expressed as fractions of the rates in air saturated sea water at each experimental salinity-temperature combination. The quadratic coefficient B₂ becomes increasingly more negative with both decreasing salinity and temperatures up to 20 °C. At higher temperatures (25 and 30 °C) the response is reversed such that O₂ uptake in snails becomes increasingly independent of declining oxygen tensions at higher salinities. On exposure to a salinity of 4‰, Amphibola showed no systematic response to declining oxygen tension with respect to temperature. The ability of Amphibola to maintain its rate of oxygen consumption in a wide range of environmental conditions is discussed in relation to its potential for invading terrestrial habitats and its widespread distribution on New Zealand's intertidal mudflats.     

COMPARATIVE PHOTOSYNTHESIS OF TWO SPECIES OF INTERTIDAL EPIPHYTIC MACROALGAE ON MANGROVE ROOTS DURING SUBMERSION AND EMERSION

Photosynthesis and dark respiration rates were measured in water and in air, and the capacity to recover photosynthetic activity from emersion stress was examined for two species of intertidal, epiphytic macroalgae—Bostrychia calliptera (Montagne) Montagne and Caloglossa leprieurii (Montagne) J. Agardh—collected on prop roots of the red mangrove Rhizophora mangle L. in Buenaventura Bay, Pacific coast of Colombia. In both species, net photosynthetic rates were significantly higher under submersed conditions. Maximum photosynthetic rates (P_max) in water and in air were highest in B. calliptera, 126 ± 4 versus 52 ± 9 μmol O₂·mg chl a⁻¹·h⁻¹, respectively. In C. leprieurii, P_max of submerged plants in water and in air were 98 ± 9 versus 30 ± 11 μmol O₂·mg chla⁻¹·h⁻¹. The photoinhibition model of Platt et al. (1980) was used to fit the experimental data in both water and air for both species. Photoinhibition occurred at irradiance as low as 200 μmol·m⁻²·s⁻¹. The photosynthesis–light response curves demonstrated an adaptation to shaded habitats for both species, as light compensation points in water and air for both species were below 17 ± 5 μmol·m⁻²·s⁻¹. The rate of dehydration was significantly lower in thalli of B. calliptera compared to C. leprieurii. An increase of photosynthetic activity in B. calliptera was evident between 5% and 15% water loss, but rates decreased thereafter with declining water content. In C. leprieurii, desiccation negatively influenced photosynthetic rates that significantly decreased linearly with declining water content. In B. calliptera, net photosynthesis reached zero only at a water content between 29% and 35%, whereas in C. leprieurii no net photosynthesis occurred in plants containing less than about 50% of their relative water content. Resubmerged plants ofB. calliptera exhibited 100% photosynthetic recovery after 45 min, whereas C. leprieurii recovered 100% at about 120 min. On the basis of the comparison of rates of light-saturated net photosynthesis for B. calliptera in air versus in water, aerial photosynthetic activity ranged from 35% to 42% of that in water, whereas the emersed photosynthetic capacity of C. leprieurii ranged from 24% to 29% of that in water. Using tidal predictions and the emersed photosynthetic rates, a carbon balance model was constructed for both species over a single daylight period. The calculations indicated that emersed photosynthesis increased average daily carbon production of B. calliptera by 17% and C. leprieuri by 12%. The physiological responses to desiccation stress and the photosynthetic recovery capacities between species correlated with, and may determine, their vertical distribution in the mangrove habitats of Buenaventura Bay.     

Effects of thermal acclimation on water loss rate and tolerance in the collembolan Pogonognathellus flavescens

A few days of thermal acclimation (to 5 °C versus 15 °C) may strongly affect tolerance to drought stress in Collembola. To better understand this phenomenon, the effect of acclimation on water loss rate and its consequence for survival in the species Pogonognathellus flavescens Tullberg (Tomoceridae) is investigated. Acclimation does not affect the water content of hydrated animals but animals exposed to 15 °C and 76% relative humidity lose water much faster after having been acclimated to 5 °C rather than 15 °C. Tolerance to water loss is not affected; in both treatment groups, animals survive up to 40% loss of the water content recorded when fully hydrated. The percentage water content of hydrated animals decreases with size, which may explain why the proportion of initial water lost appears to be a better predictor for survival than the amount of remaining water. The proportion of initial water lost per unit time is little influenced by size in animals acclimated to 15 °C but increases with decreasing size in the group at 5 °C, indicating that acclimation affects a physiological protection against water loss.     

Underwater survival in the dog tick Dermacentor variabilis (Acari:Ixodidae)

Ticks are blood-feeding arthropods known for their long survivability off the host. Although ticks are terrestrial, they can survive extended periods of time submerged underwater. A plastron is an alternative respiration system that can absorb oxygen from water via a thin layer of air trapped by hydrophobic hairs or other cuticular projections. The complex spiracular plate of ticks has been postulated to serve as a plastron but that function has not been verified. This study provides evidence of plastron respiration in the American dog tick, Dermacentor variabilis, and for the first time confirmed the existence of plastron respiration in Ixodidae. Longer survival rates in oxygenated water indicate that underwater respiration requires oxygen. Wetting the spiracular plate with alcohol debilitates any potential plastron function and lowers the survival rate. Survival underwater may also be enhanced by metabolic depression and possibly anaerobic respiration. This study describes the first example of plastron respiration in the Ixodidae.     

Eretmoptera murphyi: pre‐adapted to survive a colder climate

During the late 1960s, larvae of the flightless midge Eretmoptera murphyi Schaeffer were accidentally transferred from the sub‐Antarctic island of South Georgia to Signy Island in the maritime Antarctic. Higher insects are rare in the Antarctic and the introduction and establishment of a new species is an unusual event. The fly has overcome the two major barriers to colonization of the Antarctic by new species: the geographical isolation of the region and its severe climate. Larvae of the flightless midge overwinter in the surface layers of soil on Signy Island where the temperature may fall to below ?10 °C, compared with as little as ?1.5 °C on South Georgia. This suggests the possession of a level of pre‐adaption to colder conditions. Summer‐collected larvae have a supercooling point (SCP or whole body freezing point) of approximately ?5.0 °C but survive experimental exposure to ?13 °C, giving them a level of freeze tolerance. After acclimation at ?4 °C for 4 days, the SCP changes little but the temperature at which 50% of the population would die decreases to lower than ?19 °C. Larvae are also resistant to dehydration. Under experimental conditions of 88% relative humidity at 5 °C, larvae lose water linearly (0.42% h^?1) over the first 30 h but resist further water loss once their water content decreases to approximately 1.4 g g^?1 dry weight. All larvae survive these conditions for the duration of the experiment (55 h). Eretmoptera murphyi is well adapted to survive on Signy Island, and these studies suggest that it has the ability to survive at more extreme locations at higher latitudes if it were to be inadvertently transferred to a suitable habitat.     

A COMPARISON OF AIR AND WATER AS ENVIRONMENTS FOR PHOTOSYNTHESIS BY THE INTERTIDAL ALGA FUCUS SPIRALIS (PHAEOPHYTA)1

The response of photosynthesis and respiration of the intertidal brown alga Fucus spiralis L. to light and temperature at ambient and elevated concentrations of inorganic carbon was investigated. The light-saturated rate of photosynthesis was greater in air at 15° C and 20° C, but greater in water at 10° C. Light compensation point and I_k was about 50% lower under submerged relative to emerged conditions, whereas the initial slope of photosynthesis versus irradiance was higher, except at 20° C. Under both submerged and emerged conditions light-saturated photosynthesis was limited to a similar degree (78%, and 65%, respectively) by the availability of inorganic carbon at naturally occuring concentrations. In air, slight desiccation at tissue water contents of about 96% to 92% caused a stimulation in the rate of net photosynthesis to 110–148% of fully hydrated fronds. At lower water contents the rate of net photosynthesis declined linearly with decreasing water content and became zero at a water content of about 15%. Dark respiration declined linearly with tissue water content and remained positive to a water content of 8%. Upon reimmersion the fronds showed a complete recovery within 35 min following desiccation to a water content of 20–30%. Thus F. spiralis seems to be very tolerant to desiccation. Since F. spiralis photosynthesizes effectively in air, even at a higher rate than in water as long as it has not lost a large proportion of its water in desiccation, the alternating exposure to air may be beneficial by increasing the daily carbon gain compared to a fully submerged situation.     

The effects of temperature and moisture on survival capacity,cuticular permeability,hemolymph osmoregulation and metabolism in the scorpion,Centruroides hentzi (banks) (scorpiones,buthidae)

• 1.1. The temperature and water relations of Centruroides hentzi females were investigated. At 12 and 72% relative humidity (RH), the lower and upper Lt₅₀ were -4.5 and 43.7°C, and -4.7 and 45.1°C, respectively. When exposed to high temperature stress, survivorship was significantly greater under mesic conditions.
• 2.2. Cuticular water loss was higher under xeric conditions (12% RH), ranging from 0.061 mg/cm²/hr at 30°C to 0.211 at 41°C.
• 3.3. Exposure to dry air (0–5% RH) resulted in a significant increase in hemolymph osmolality: from 441 to 688 mOsm over a 5 day period.
• 4.4. Mean oxygen consumption rates increased from 161.7 mm³/g/hr at 34°C to 541.6 at 44°C. ATPase activity was significantly higher in animals acclimated and tested at 35°C.

     

Light,Temperature, and Desiccation Effects on Photosynthetic Activity,and Drought-Induced Ultrastructural Changes in the Green Alga <Emphasis Type="Italic">Klebsormidium dissectum</Emphasis> (Streptophyta) from a High Alpine Soil Crust

Members of the cosmopolitan green algal genus Klebsormidium (Klebsormidiales, Streptophyta) are typical components of terrestrial microbiotic communities such as biological soil crusts, which have many important ecological functions. In the present study, Klebsormidium dissectum (Gay) Ettl &; Gärtner was isolated from a high alpine soil crust in the Tyrolean Alps, Austria. Physiological performance in terms of growth and photosynthesis was investigated under different controlled abiotic conditions and compared with ultrastructural changes under the treatments applied. K. dissectum showed very low light requirements as reflected in growth patterns and photosynthetic efficiency. Increasing temperatures from 5°C to 40°C led to different effects on respiratory oxygen consumption and photosynthetic oxygen evolution. While at low temperatures (5–10°C), respiration was not detectable or on a very low level, photosynthesis was relatively high, Reversely, at the highest temperature, respiration was unaffected, and photosynthesis strongly inhibited pointing to strong differences in temperature sensitivity between both physiological processes. Although photosynthetic performance of K. dissectum was strongly affected under short-term desiccation and recovered only partly after rehydration, this species was capable to survive even 3 weeks at 5% relative air humidity. K. dissectum cells have a cell width of 5.6?±?0.3 μm and a cell length of 8.4?±?2.0 μm. Desiccated cells showed a strongly reduced cell width (46% of control) and cell length (65% of control). In addition, in desiccated cells, fewer mitochondria were stained by DIOC₆, and damaged plasma membranes were detected by FM 1–43 staining. High-pressure freeze fixation as well as chemical fixation allowed visualizing ultrastructural changes caused by desiccation. In such cells, the nucleus and chloroplast were still visibly intact, but the extremely thin cell walls (75–180 nm) were substantially deformed. The cytoplasm appeared electron dense and mitochondria were altered. Although K. dissectum can be characterized as euryoecious species, all ecophysiological and ultrastructural data indicate susceptibility to desiccation. However, the steadily occurring fragmentation of filaments into smaller units leads to improved self protection and thus may represent a life strategy to better survive longer periods of drought in exposed alpine soil crusts.     

PHOTOSYNTHESIS OF THE RED ALGA GASTROCLONIUM COULTERI (RHODOPHYTA) IN RESPONSE TO CHANGES IN TEMPERATURE,LIGHT INTENSITY,AND DESICCATION1

Previously reported transplantation experiments in the field showed that Gastroclonium coulteri (Harvey) Kylin could survive above its normal intertidal range (0.0–0.5 m above MLLW), except during periods of daytime low tides in spring. Net photosynthetic rate measurements in the laboratory were performed to determine which physical factors might determine the upper boundary for this species in the intertidal zone. Maximum net photosynthesis occurred between 15 and 20° C, but remained positive between 4 and 35° C. The air temperature extremes observed in the field were 2° C (only seen once) and 26° C. Net photosynthesis increased as expected with light intensity to the highest value obtainable in the laboratory, 1400 μEin m^?2 s^?1. Plants collected from the field under higher light intensity (up to 2000 μEin m^?2 s^?2) also showed high rates of photosynthesis. Neither the temperature nor light levels observed in the field were directly damaging to photosynthesis. Desiccation, however, resulted in a sharp decrease in both photosynthesis and respiration. G. coulteri fully recovered from successive daily treatments of about 35% desiccation, but not from successive treatments of 50% desiccation. One exposure to 70% desiccation allowed no recovery of photosynthetic capacity.     

Ecological physiology of arctic marine invertebrates. Temperature and salinity relationships of the amphipod Onisimus affinis H. J. Hansen

Effects of temperature and salinity upon the survival, locomotion and metabolism of the Arctic marine amphipod Onisimus affinis H. J. Hansen have been investigated. The LD₅₀ for temperature is ≈ 18.7 °C. The metabolic rate-temperature curve shows a distinct plateau of relative temperature insensitivity the position of which varies seasonally to include a lower temperature range in winter than in summer. Similar shifts in the plateau can be induced in the laboratory by acclimating the animals at summer- and winter-like temperatures.Optimal locomotory activity was between 5° and 8 °C and included a combination of swimming and crawling. Above 12 °C the swimming component was increasingly inhibited.Onisimus is euryhaline and appears to be most successful in brackish water habitats. It tolerates elevated salinities better at low temperatures. The metabolic rate varies inversely with salinity during short-term exposures, but, if the animals are pre-adapted to the experimental salinities for 10 days, the metabolic rate is essentially independent of salinity between 10%. and 25%.The significance of these physiological responses in relation to the general ecology of the species is discussed.     

Distinct responses of growth and respiration to growth temperatures in two mangrove species

Background and AimsMangrove plants are mostly found in tropical and sub-tropical tidal flats, and their limited distribution may be related to their responses to growth temperatures. However, the mechanisms underlying these responses have not been clarified. Here, we measured the dependencies of the growth parameters and respiration rates of leaves and roots on growth temperatures in typical mangrove species.MethodsWe grew two typical species of Indo-Pacific mangroves, Bruguiera gymnorrhiza and Rhizophora stylosa, at four different temperatures (15, 20, 25 and 30 °C) by irrigating with fresh water containing nutrients, and we measured growth parameters, chemical composition, and leaf and root O₂ respiration rates. We then estimated the construction costs of leaves and roots and the respiration rates required for maintenance and growth.Key ResultsThe relative growth rates of both species increased with growth temperature due to changes in physiological parameters such as net assimilation rate and respiration rate rather than to changes in structural parameters such as leaf area ratio. Both species required a threshold temperature for growth (12.2 °C in B. gymnorrhiza and 18.1 °C in R. stylosa). At the low growth temperature, root nitrogen uptake rate was lower in R. stylosa than in B. gymnorrhiza, leading to a slower growth rate in R. stylosa. This indicates that R. stylosa is more sensitive than B. gymnorrhiza to low temperature.ConclusionsOur results suggest that the mangrove species require a certain warm temperature to ensure respiration rates sufficient for maintenance and growth, particularly in roots. The underground temperature probably limits their growth under the low-temperature condition. The lower sensitivity of B. gymnorrhiza to low temperature shows its potential to adapt to a wider habitat temperature range than R. stylosa. These growth and respiratory features may explain the distribution patterns of the two mangrove species.     

Influence of frost on nutrient resorption during leaf senescence in a mangrove at its latitudinal limit of distribution

The latitudinal distribution of mangrove species is limited mainly by low temperature. Leaf scorch and massive leaf fall are the predominant symptoms of frost damage. Nutrient resorption during leaf senescence is an important adaptation mechanism of mangroves. Abnormal defoliation disturbs nutrient resorption. We evaluated the effects of frost on nutrient loss of mangroves and the protective effects of warmer seawater inundation on reducing nutrient loss. On January 14, 2009, the most cold-tolerant mangrove Kandelia obovata at its naturally latitudinal limit (Fuding, China, 27°17??N) was exposed to freezing temperature (?2.4°C) for 4 h (minimum ?2.8°C). The freezing air temperature occurred during flood tide, resulting that the flooded shoots were protected by warmer seawater. Frost caused 31.3% and 13.0% defoliation on the exposed shoots and the flooded shoots, respectively. Frost restricted nutrient resorption during leaf senescence. K. obovata resorbed 61% N and 42% P during normal leaf senescence, respectively. However, frost-damaged leaves only resorbed 13% N and 10% P during the course, respectively. Foliar N:P molar ratios were <31, suggesting N limitation. Tidal inundation can partially protect mangroves from frost damage. Reduced nutrient resorption efficiency and massive leaf fall caused by frost add pressure to mangroves under nutrient limitation at their latitudinal limits.     

Combined effects of temperature and salinity on functional responses of haemocytes and survival in air of the clam Ruditapes philippinarum

The combined effects of temperature and salinity on both immune responses and survival in air of the clam, Ruditapes philippinarum, were evaluated for the first time. The animals were kept for 7 days at three differing temperature (5 °C, 15 °C, 30 °C) and salinity values (18 psu, 28 psu, 38 psu), and effects of the resulting 9 experimental conditions on total haemocyte count (THC), Neutral Red uptake (NRU), haemolymph protein concentration, and lysozyme activity in both haemocyte lysate (HL) and cell-free haemolymph (CFH) were evaluated. The survival-in-air test was also performed. Two-way ANOVA analysis revealed that temperature influenced significantly THC and NRU, whereas salinity and temperature/salinity interaction affected NRU only. Temperature and salinity did not influence significantly HL and CFH lysozyme activity, as well as haemolymph total protein content. Survival-in-air test is widely used to evaluate general stress conditions in clams. In the present study, temperature and salinity were shown to influence the resistance to air exposure of R. philippinarum. The highest LT₅₀ (air exposure time resulting in 50% mortality) value was recorded in clams kept at 18 psu and 15 °C, whereas the lowest value was observed in clams kept at 28 psu and 30 °C. Overall, results obtained demonstrated that temperature and salinity can affect some functional responses of haemocytes from R. philippinarum, and suggested a better physiological condition for animals kept at 15 °C temperature and 18 psu salinity.     

The Japanese tree frog (<Emphasis Type="Italic">Hyla japonica</Emphasis>), one of the most cold-resistant species of amphibians

The Japanese tree frog, a representative of the Manchurian fauna, is characterized by an outstanding cold resistance among the anuran amphibian species studied so far. Almost 70% of the specimens from the population inhabiting the middle Amur River withstand the cooling down to–30°C; some animals, down to–35°C. This exceeds more than twofold the cold hardiness of the wood frog (Lithobates sylvaticus LeConte, 1825), which has been considered earlier to be the most cold-resistant species. The ability of H. japonica to survive for four months in the frozen state at low temperatures makes this species independent of the temperature overwintering conditions.