Two different proteases produced by a deep-sea psychrotrophic bacterial strain,<Emphasis Type="Italic"> Pseudoaltermonas</Emphasis> sp. SM9913

A psychrotrophic bacterial strain, Pseudoaltermonas sp. SM9913, was isolated from deep-sea sediment collected at 1,855 m depth. Two proteases produced by Pseudoaltermonas sp. SM9913 were purified, MPC-01 and MCP-02. MCP-01 is a serine protease with a molecular weight of 60.7 kDa. It is cold-adapted with an optimum temperature of 30–35°C. Its K_m and E_a for the hydrolysis of casein were 0.18% and 39.1 kJ mol^–1, respectively. It had low thermostability, and its activity was reduced by 73% after incubation at 40°C for 10 min. MCP-02 is a mesophilic metalloprotease with a molecular weight of 36 kDa. Its optimum temperature for the hydrolysis of casein was 50–55°C. The K_m and E_a of MCP-02 for the hydrolysis of casein were 0.36% and 59.3 kJ mol^–1, respectively. MCP-02 had high thermostability, and its activity was reduced by only 30.5% after incubation at 60°C for 10 min. At low temperatures, Pseudoaltermonas sp. SM9913 mainly produced the psychrophilic protease MCP-01.Communicated by O. Kinne, Oldendorf/Luhe     

Effect of phosphate and ammonium levels on photosynthetic and respiratory responses of the red alga Gracilaria verrucosa

Gracilaria verrucosa (Hudson) Papenfuss exposed to nutrient enriched media (0.1 mM PO₄; 1.0 mM NH ₄ ⁺ ) by pulse feeding 2 h every third day for a period of 5 wk at 20°C and 25–30 salinity showed significantly higher rates of photosynthesis regardless of photon flux density correlated with increased pigment levels. Algae in nonenriched media showed significantly higher levels of soluble carbohydrates and decreased levels of phycoerythrin and chlorophyll a. Photosynthetic and respiratory responses to temperature 15°, 25°, 30°C and salinity (15, 25, 30 S) combinations indicate broad tolerances by both nutrient enriched and non-nutrient enriched algae. Photosynthetic and respiratory rates were highest at the high temperatures. Pulse-fed algae had significantly higher photosynthetic rates than non-nutrient enriched plants at all temperature and salinity combinations. Non-nutrient enriched algae had significantly higher respiratory rates than nutrient enriched algae at only 30°C and 15. The respiratory rates of both nutrient enriched and non-nutrient algae decreased under combinations of higher temperatures and salinities. G. verrucosa, grown without nutrients, has lower tolerances to environmental stresses.     

Respiratory physiology in summer diapause embryos of the neustonic copepodAnomalocera patersoni

The respiratory physiology of summer diapausing eggs of the neustonic copepodAnomalocera patersoni, maintained under constant temperature (13 °C) and light (12 h light:12 h dark) conditions, was characterized by a bell-shaped curve, with low O₂ uptake levels at the beginning of dormancy. This was followed by a steady rise in O₂ consumption with maximum levels of 0.002 l O₂ embryo^–1 h^–1 70 d after spawning. A slow diminution in O₂ uptake then occurred until Day 150 when minimum values of 0.0003 l O₂ embryo^–1 h^–1 were recorded, coinciding with the hatching of the first embryos. Embryos continued to hatch asynchronously up to 360 d from the moment of egg laying. When eggs were subjected to 20 °C, the respiratory activity was almost three times higher than at 13 °C, even though both respiratory curves were similar. The elevated metabolism in eggs kept at 20 °C led to death of the embryos possibly due to a total depletion of metabolic reserves. ATP content also differed at the two temperatures. Diapause eggs kept at 20 °C showed no rapid rise in ATP content as opposed to those kept at 13 °C. The results of temperature shock experiments, in which eggs were first kept at winter temperatures for several weeks, after which the temperature was raised to 20 °C for another number of weeks prior to a second period of chilling at 13 °C, showed that as long as embryos were kept at 20 °C no hatching occurred. By contrast, hatching was observed after 10 d following the resumption of winter temperatures, suggesting that low environmental temperatures are an essential prerequisite for hatching of these eggs. The type of diapause inA. patersoni differs considerably from the one described in insects and in another neustonic copepod,Pontella mediterrana. In this case, there is a U-shaped respiratory curve with greatest O₂ consumption prior to the onset or upon breaking of diapause. Differences in the two types of diapause seem to involve not only differences in O₂ consumption levels but also in the sequence of metabolic changes with time and the metabolic requirements during sommer and winter dormancy.     

Interactions between light and temperature on the physiological ecology ofGracilaria tikvahiae (Gigartinales: Rhodophyta)

Main effects and interactions of light and temperature on rates of growth (), net photosynthesis (P_s), and dark respiration (R) of the red seaweedGracilaria tikvahiae were investigated in outdoor, nutrient-replete continuous-flow seawater culture chambers. Below 15°C,G. tikvahiae did not grow and between 15° and 30°C, both main effects and interactions of light and temperature on and P_s were significant, which explains the occurrence of this alga as a summer annual in its northern range. Temperature interacted with light (I) through its influence on the vs I and P_s vs I curves. The initial slope of the vs I curve, , the light saturation intensity, I_s, and maximum growth rate, _max, were all significantly lowerat 15°C compared to 20°, 25°, or 30°C. Maximum values of _max, the P_s:R ratio and the net photosynthesis:gross photosynthesis ratio (P_s:P_g) all occurred at 25°C, suggesting that this is the best temperature for growth ofG. tikvahiae. Values for P_max increased up to 30°C, indicating that the temperature for maximum growth and net photosynthesis are not the same forG. tikvahiae. Significant photoinhibition of growth and photosynthesis at full incident sunlight (I₀) occurred at 15°C but not at 20°, 25°, or 30°C. Steele's equation fit the 15°C vs I data best, whereas the hyperbolic tangent function fit the 20°, 25°, and 30°C data best. Main effects and interactionof light intensity and temperature on rates of R were also significant (P<0.001). R was highly intercorrelated with and P_s (0.86r0.94), indicating that R inG. tikvahiae is primarily regulated by growth rate and not temperatureper se. Environmental factors that regulate growth, such as light intensity, exert a great influence on R inG. tikvahiae.     

Über den Einfluß der Nahrungskonzentration und anderer Faktoren auf Filtrierleistung und Nahrungsausnutzung der Muscheln Arctica islandica und Modiolus modiolus

Filtration rates and the extent of phagocytosed food particles were determined in the offshore lamellibranchs Artica islandica and Modiolus modiolus in relation to particle concentration, body size and temperature. Pure cultures of the algae Chlamydomonas sp. and Dunaliella sp. were used as food. A new method for determining filtration rates was developed by modifying the classical indirect method. The concentration of the experimental medium (100%) was kept constant to ±1%. Whenever the bivalves removed algae from the medium, additional algae were added and the filtration rate of the bivalves expressed in terms of percentage amount of algae added per unit time. The concentration of the experimental medium was measured continuously by a flow colorimeter. By keeping the concentration constant, filtration rates could be determined even in relation to different definite concentrations and over long periods of time. The amount of phagocytosed food was measured by employing the biuret-method (algae cells ingested minus algae cells in faeces). Filtration rates vary continuously. As a rule, however, during a period of 24 h, two phases of high food consumption alternate with two phases of low food consumption during which the mussels' activities are almost exclusively occupied by food digestion. Filtration rate and amount of phagocytosed algae increase with increasing body size. Specimens of A. islandica with a body length of 33 to 83 mm filter between 0.7 to 71/h (30–280 mg dry weight of algae/24 h) and phagocytose 21 to 122 mg dry weight of algae during a period of 24 h. The extent of food utilization declines from 75 to 43% with increasing body size. In M. modiolus of 40 to 88 mm body length, the corresponding values of filtration rate and amount of phagocytosed algae range between 0.5 and 2.5 l/h (20–100 mg dry weight of algae) and 17 to 90 mg dry weight of algae, respectively; the percentage of food utilization does not vary much and lies near 87%. Filtration rate and amount of phagocytosed algae follow the allometric equation y=a·x ^b. In this equation, y represents the filtration rate (or the amount of phagocytosed algae), a the specific capacity of a mussel of 1 g soft parts (wet weight), x the wet weight of the bivalves' soft parts, and b the specific form of relationship between body size and filtration rate (or the amount of phagocytosed algae). The values obtained for b lie within a range which indicates that the filtration rate (or the amount of phagocytosed algae) is sometimes more or less proportional to body surface area, sometimes to body weight. Temperature coefficients for the filtration rate are in Arctica islandica Q₁₀ (4°–14°C)=2.05 and Q₁₀ (10°–20°C)=1.23, in Modiolus modiolus Q₁₀ (4°–14°C)=2.33 and Q₁₀ (10°–20°C)=1.63. In A. islandica, temperature coefficients for the amount of phagocytosed algae amount to Q₁₀ (4°–14°C)=2.15 and Q₁₀ (10°–20°C)=1.55, in M. modiolus to Q₁₀ (4°–14°C)=2.54 and Q₁₀ (10°–20°C)=1.92. Upon a temperature decrease from 12° to 4°C, filtration rate and amount of phagocytosed algae are reduced to 50%. At the increasing concentrations of 10×10⁶, 20×10⁶ and 40×10⁶ cells of Chlamydomonas/l offered, filtration rates of both mollusc species decrease at the ratios 3:2:1. At 12°C, pseudofaeces production occurs in both species in a suspension of 40×10⁶, at 20°C in 60×10⁶ cells of Chlamydomonas/l. At 12°C and 10–20×10⁶ cells of Chlamydomonas/l, the maximum amount of algae is phagocytosed. At 40×10⁶ cells/l, the amount of phagocytosed cells is reduced by 26% as a consequence of low filtration rates and intensive production of pseudofaeces. At 20°C and 20–50×10⁶ cells of Chlamydomonas/l, the maximum amount of algae is sieved out and phagocytosed; the concentration of 10×10⁶ cells/l is too low and cannot be compensated for by increased activity of the molluscs. With increasing temperatures, the amount of suspended matter, allowing higher rates of filtration and food utilization, shifts toward higher particle concentrations; but at each temperature a threshold exists, above which increase in particle density is not followed by increase in the amount of particles ingested. Based on theoretical considerations and facts known from literature, 7 different levels of food concentration are distinguishable. Experiments with Chlamydomonas sp. and Dunaliella sp. used as food, reveal the combined influence of particle concentration and particle size on filtration rate. Supplementary experiments with Mytilus edulis resulted in filtration rates similar to those obtained for M. modiolus, whereas, experiments with Cardium edule, Mya arenaria, Mya truncata and Venerupis pullastra revealed low filtration rates. These species, inhabiting waters with high seston contents, seem to be adapted to higher food concentrations, and unable to compensate for low concentrations by higher filtration activities. Adaptation to higher food concentrations makes it possible to ingest large amounts of particles even at low filtration rates. Suspension feeding bivalves are subdivided into four groups on the basis of their different food filtration behaviour.     

Influence of high temperature and residual chlorine on marine phytoplankton

Marine phytoplankton forms are frequently exposed to sudden biological changes such as rapid rise in water temperature and chlorine content of their environment, resulting from the use of sea water for cooling purposes by electric generators. The direct influence of these effluents, i.e. inhibitory effects of high temperature and residual chlorine on growth and photosynthesis of Chlamydomonas sp. and Skeletonema costatum, were investigated experimentally. Chlamydomonas sp. and S. costatum exposed to high temperatures were affected in their growth from 43° and 35°C, respectively, by immersion of the respective cultures in a warm bath for 10 min. Treatment at high temperatures of 40 °C and 30° 35°C for 10 min, influenced their photosynthetic activities, which were completely inhibited immediately after 10 min exposure at 42° and 37 °C, respectively. S. costatum was killed by chlorine at a concentration of 1.5 2.3 ppm when exposed for exactly 5 or 10 min, while Chlamydomonas sp. was not irreversibly damaged even at 20 ppm chlorine or more with the same exposure period. These results lead to the conclusion that the high temperature of, and residual chlorine in, effuents from a power plant discharging into the open sea, should not cause great damage to marine phytoplankton in that area.     

Rearing Pandalus borealis larvae in the laboratory

Larvae of the northern shrimp Pandalus borealis (Krøyer) are pelagic. In the Estuary and Gulf of St. Lawrence, Canada, the early stages are found in the upper 25-m of the water column in spring and early summer and are expected to experience a range of water temperatures from as low as 0°C to as high at 6°C. Little is known of the impact of water temperature on metabolic requirements of northern shrimp larvae. In this study, routine respiration (VO₂), maximum respiration (electron transport system activity, ETSA) and metabolic scope for growth (MS, ETSA–VO₂) of northern shrimp larvae were measured as a function of temperature (3, 5 and 8°C), developmental stage (I–V at 3°C, I–VII at 5°C and 8°C) and growth rate in dry mass. After logarithmic transformation, all three metabolic variables were linearly related to dry mass. The increase in VO₂ with body mass was faster at 5°C than at 3 or 8°C, whereas with ETSA this increase was slower. As a result, MS increased more slowly with dry mass at 5°C than at 3 and 8°C. However, MS did not limit growth in this study, since it explained only 39% of the variability in growth. All three metabolic variables as well as growth varied together as a function of temperature and ontogeny. Q₁₀ of all three metabolic variables ranged from 1.6 and 2.2 for stages I–V larvae, except for VO₂ at stage I (3.9) and stage III (2.9).     

Life cycles in marine meiobenthos. Experiments at various temperatures with Monhystera disjuncta and Theristus pertenuis (Nematoda)

Monhystera disjuncta Bastian 1865 and Theristus pertenuis Bresslau and Schuubmans Stekhoven 1935 were cultured on sea-water agar in Boveri dishes at various temperatures. Generation time was measured as the period elapsing in two consecutive generations between the first egg deposit, the first hatching, or the first appearance of sexual characters. M. disjuncta has a generation time of 13 days at 17° to 22°C, 15 days at 13° to 15°C, 17 days at 9° to 12°C, 22 days at 7°C, 77 days at 0° to 2°C, and 135 days at -1° to 1°C. Low temperatures result sometimes in vivipary. T. pertenuis has a generation time of 23 days at 17° to 22°C, 41 days at 13° to 15°C, 47 days at 9° to 12°C, and 71 days at 7°C. M. disjuncta females live for up to 61 days at 17° to 22°C, T. pertenuis females up to 208 days at 7°C. Under North Sea temperature conditions, 17 generations of M. disjuncta and 7 generations of T. pertenuis could occur during the course of 1 year (calculation based upon experiments giving the shortest possible generation time). Females deposit eggs over a couple of days, therefore, the medium generation time is longer, and there will be fewer generations per year in the sea.     

Temperature preference and tolerance,and oxygen consumption of the marbled rockfish,Sebastiscus marmoratus

Behavioral and metabolic responses of the marbled rockfish, Sebastiscus marmoratus (Cuvier), to temperature were measured to define optimal thermal habitat. Preferred temperature was determined by means of a newly developed horizontal temperature-gradient tank. Acclimation temperature had a direct positive effect on critical thermal maxima and minima and upper lethal temperatures but no effect on final preferred temperature. It was indicated that upper temperature tolerance and final preferred temperature of the marbled rockfish were closely connected. Oxygen consumption rate increased with temperature to 23°C but Q ₁₀ (the increase in rate caused by 10°C increase in temperature) declined above 20°C. The maximum Q ₁₀ (4.69) occurred between 15 and 20°C. The final preferred temperature of 20.7 ± 1.5 °C corresponded well to the temperature at which increase in oxygen consumption rate with temperature gradually lessened, approximately 20°C.     

Suitability of estuarine nursery zones for juvenile weakfish (Cynoscion regalis): effects of temperature and salinity on feeding,growth and survival

Juvenile weakfish, Cynoscion regalis (Bloch and Schneider, 1801), exhibit significant spatial diffrences in growth rate and condition factor among estuarine nursery zones in Delaware Bay. The potential influence of temperature and salinity on the suitability of estuarine nursery areas for juvenile weakfish was investigated in laboratory experiments by measuring ad libitum feeding rate, growth rate and gross growth efficiency of juveniles collected in Delaware Bay in 1990 (40 to 50 mm standard length; 1.4 to 2.1 g) in 12 temperature/salinity treatments (temperatures: 20, 24, 28°C; salinities: 5, 12, 19, 26 ppt) representing conditions encountered in different estuarine zones during spring/summer. Feeding rates (FR) increased significantly with temperature at all salinities, ranging from 10 to 15% body wt d^-1 at 20°C to 33–39% body wt d^-1 at 28°C. Specific growth rates (SGR) ranged from 1.4 to 9.4% body wt d^-1 (0.3 to 1.5 mm d^-1) and gross growth efficiencies (K ₁) varied from 13.6 to 26.4% across temperature/salinity combinations. Based on nonlinear multiple regression models, predicted optimal temperatures for SGR and K ₁ were 29 and 27°C, respectively. Salinity effects on SGR and K ₁ were significant at 24 and 28°C where predicted optimal salinity was 20 ppt. At these warmer temperatures, SGR and K ₁ were significantly lower at 5 than at 19 ppt despite higher FR at 5 ppt. Therefore, maximum growth rate and growth efficiency occurred under conditions characteristic of mesohaline nurseries. This finding is consistent with spatial patterns of growth in Delaware Bay, implying that physicochemical gradients influence the value of particular estuarine zones as nurseries for juvenile weakfish by affecting the energetics of feeding and growth. Laboratory results indicate a seasonal shift in the location of physiologically optimal nurseries within estuaries. During late spring/early summer, warmer temperatures in oligohaline areas permit higher feeding rate and faster growth compared to mesohaline areas. By mid-late summer, spatial temperature gradients diminish and mesohaline areas provide more suitable physicochemical conditions for growth rate and growth efficiency whereas oligohaline areas become energetically stressful. Substantial mortality occurred at 5 ppt and 28°C, providing additional evidence that oligohaline conditions are stressful during late summer. Furthermore, juveniles provided a choice among salinities in laboratory trials preferred those salinities which promoted higher growth rates. The extensive use of oligohaline nurseries by juvenile weakfish despite the potential for reduced growth rate and growth efficiency suggests this estuarine zone may provide a substantial refuge from predation.     

Effect of freezing on photosynthesis of intertidal macroalgae: relative tolerance of Chondrus crispus and Mastocarpus stellatus (Rhodophyta)

The effect of freezing on photosynthetic metabolism was studied in the red algae, Chondrus crispus and Mastocarpus stellatus. Plants of both species were collected from the intertidal at Chamberlain or Kresge Point, Maine, USA (43°56N, 69°54W) between February and March 1987. Photosynthetic rates were measured immediately after freezing at-20°C and following recovery periods in seawater. Photosynthesis in C. crispus declined rapidly following freezing, falling to 70% of control values within 1 h and 30% after 3 h exposure. Minimum photosynthetic rates (7 to 9% of controls) occurred following freezing exposures of 12 h or more. Full photosynthetic recovery in C. crispus after 3 h at-20°C required 48 h. Photosynthesis in C. crispus did not fully recover in plants frozen for 6 h or more. In contrast, photosynthesis in M. stellatus was relatively unaffected by freezing exposures of <12 h. Twelve hours or more at-20°C reduced photosynthesis to 55% of controls. Photosynthesis in M. stellatus fully recovered from 24 h at-20°C within 24 h. In both species the reduction of photosynthesis by freezing was associated with damage to the plasma membrane and reduced efficiency of energy transfer from phycobilisomes to chlorophyll a, but did not appear to involve ribulose-1,5-bisphosphate carboxylase oxygenase activity. The freezing tolerance of C. crispus and M. stellatus positively correlates with their respective intertidal distributions, suggesting that freezing may be involved in controlling the distributions of these species on the shore.     

Temperature acclimation of respiration and photosynthesis in the brown algaLaminaria saccharina

Sporophytes of the brown algaLaminaria saccharina (L.) Lamour grown at 15°C contained significantly more chlorophylla (chla) than did similar plants grown at 5°C. The increase in chla in 15°C plants was due to increased numbers of photosystem II reaction centes, and possibly to increased photosynthetic unit size, compared with 5°C plants. These changes were associated with increased values (photosynthetic efficiencies) in 15°C-grownL. saccharina relative to 5°C-grown plants. The changes in together with reduced respiration rates allowed 15°C-grownL. saccharina to achieve net photosynthesis and light-saturated photosynthesis at a lower photon fluence rate (PFR) than 5°C plants when both groups were assayed at the same temperature (15°C). The photon fluence rates necessary to reach the compensation point and achieve light-saturated photosynthesis (I _c andI _k , respectively) increased with increasing incubation temperature inL. saccharina grown at both 5 and 15°C. However, acclimation responses to growth temperature compensated for the short-term effect of temperature onI _c andI _k . Consequently, plants grown at 5 and 15°C were able to achieve similar rates of light-limited photosynthesis, and similarI _c andI _k values at their respective growth temperatures. These responses are undoubtedly important for perennial seaweeds such asL. saccharina, which frequently grow in light-limited habitats and experience pronounced seasonal changes in water temperature.Please address all correspondence and requests for reprints to I.R. Davison     

Plasmatic resistance and rate of respiration and photosynthesis of Zostera marina at different salinities and temperatures

Zostera marina L. was studied at the Izembek Lagoon, Alaska Peninsula. Two morphologically different forms, tidepool and subtidal, can be distinguished. Both show a high tolerance to different salinities and temperatures. The plasmatic resistance was found in a range of distilled H₂O up to 3.0 seawater (24 h) and between-6° and 34°C (12 h). Within these resistance limits, the photosynthesis, which has its maximum in normal (1.0) seawater, decreases nearly to zero not only in distilled H₂O but even in 2.0 seawater, and increases with the temperature in the tidepool form up to 35°C, but in the subtidal form up to 30°C only. At higher temperatures photosynthesis declines sharply in both forms. Respiration has its minimum in distilled H₂O and at 0°C and increases with increasing salinity and temperature.Dedicated to Prof. Dr. Dr. h. c. mult. K. Mothes, Halle, Germany (DDR) on the occasion of his 70th birthday.     

Laboratory studies of the marine copepod Centropages typicus: egg production and development rates

Egg production and development rates of Centropages typicus (Krøyer) were studied in the laboratory under carying food and temperature conditions. Egg production rates in the laboratory ranged from 0 to 124 eggs female^-1 d^-1 and increased with food concentration up to a critical food concentration (P_c) above which egg production was constant. Egg production rates were influenced by temperature, with more eggs being produced at 15°C than at 10°C. Thalassiosira weisflogii and Prorocentrum micans were determined to be equally capable of supporting egg production at concentrations above P_c at 15°C. Rate of egg production was independent of adult female size when food and temperature were constant. Egg production rates of freshly captured females ranged from 0 to 188 eggs female^-1 d^-1 and were higher in April and May than in June or July. Hatching rates of eggs increased with increased temperature; 95% of the eggs at 15°C hatched within 48 h, while only 8% of the eggs at 10°C hatched within 48 h. Development rates, determined at 10°C in excess concentrations of T. weisflogii, were 23.0 d from egg release to copepodid state I, 27.0 d to stage II, 29.5 d to stage III, 32.2 d to stage IV, 38.5 d to stage V and 49 d to adulthood based on the average time required for 50% of the organisms in an experiment to attain a given stage. Adult males were usually observed 2 to 4 d before adult females, and therefore have a slightly faster rate of development. The effects of temperature, food type and food concentration on egg production and the seasonal appearances of diatoms in the New York Bight may account for the observed seasonal cycles in abundance of C. typicus in these coastal waters.     

Feeding energetics and metabolism in demersal fish species from Antarctic,temperate and tropical environments

The energetics of feeding has been investigated in demersal fish with similar sedentary lifestyles from the Antarctic (Notothenia neglecta Nybelin), North Sea (Myoxocephalus scorpius L.) and Indian Ocean (Cirrhitichys bleekeri Bleeker). In general, the metabolic rates of fasting individuals were positively correlated with adaptation temperature: values for a standard 100 g fish (mg O₂/h) were 3.3 for N. neglecta at around 0 °C, 2.7 for winter-acclimatized M. scorpius at 5 °C, 4.3 for summer-acclimatized M. scorpius at 15 °C, and 7.0 for C. bleekeri at 25 °C. In all species, following a single satiating meal, oxygen consumption increased to a peak of 2 to 3.5 times the fasting values. Maximum rates of oxygen consumption after feeding were several-fold higher in the warm-than in the cold-water species. After controlling for the effects of body mass and energy intake by analysis of covariance, the duration of the increase in metabolic rate, referred to as specific dynamic action (SDA), was found to be 3 to 4 times shorter in the warm- than in the cold-water fish, ranging from 57 h in C. bleekeri to 208 h in N. neglecta. In contrast, the SDA was not significantly different in the various species, corresponding to 15 to 23% of the energy ingested. Seasonal influences on metabolism and feeding were also studied in N. neglecta acclimated to simulated winter (-1.0 to-0.5 °C; 3 h light:21 h dark) or summer (0 to 0.9 °C; 21 h light:3 h dark) conditions. The metabolic rates of fasting and fed individuals, and the characteristics of the SDA were found to be independent of acclimation conditions. This suggests that N. neglecta is capable of processing food at similar rates throughout the year. Energy stores and enzyme activities were measured in the swimming muscles and liver of fish fed ad libitum. Summer-acclimated fish had higher concentrations of liver triglyceride stores and elevated activities of some enzymes of intermediary metabolism relative to winter-acclimated fish. The observed changes in intermdiary metabolism are probably related to annual cycles of growth and reproduction. It is suggested that the low aerobic scope for physiological performance in Antarctic fish may necessitate the seasonal switching of energy allocation between growth and reproduction.     

Mass mortality of Strongylocentrotus droebachiensis (Echinodermata: Echinoidea) off Nova Scotia,Canada

A mass mortality of Strongylocentrotus droebachiensis, attributed to disease, was monitored in an echinoiddominated barren ground at Eagle Head on the south-western coast of Nova Scotia, Canada, in 1982. Mortality was 70% in a shallow (3 m) nearshore area, resulting in a loss of echinoid biomass of 2 042 g fresh weight m^-2, and 6% in deeper (7 m, 10 m) offshore areas. Echinoid density, size and nutritional condition (gonad index) were highest in the nearshore area. Survivorship was higher in juveniles (<15 mm diameter) than in adults resulting in the formation of a bimodal size distribution in the nearshore area. Mortality began around early October, near the peak of the annual cycle of seawater temperature (15°C), and was arrested by early December (seawater temperature 7°C) when morbid echinoids appeared to recover. In laboratory experiments, time to morbidity of S. droebachiensis exposed to morbid conspecifics increased exponentially with decreasing temperature (20° to 8°C). There was no survival at 20° and 16°C, 20% survival at 12°C and 100% survival at 8°C after 60 d; suggesting a lower temperature limit (between 12° and 8°C) for possible transmission of a pathogenic agent. Morbid laboratory echinoids from experiments at 16°C, and recovering echinoids collected in the nearshore area in early December, showed 100 and 85% survival respectively at <=8°C, and 0 and 15% survival respectively at 16°C, after 30 d. Time to morbidity was not affected significantly by nutritional condition and was similar for juvenile and adult echinoids. Time to morbidity was greater in echinoids exposed to one or three morbid individuals continuously, or seven morbid individuals for 1 h, relative to higher levels of exposure (up to seven morbid individuals continuously). Recent mass mortalities in S. droebachiensis have occurred in years of record high sea surface temperatures. The extent of mortality is correlated with the magnitude and duration of temperatures above a lower limit.     

Improved survival under heat stress in intertidal embryos (<Emphasis Type="Italic">Fucus</Emphasis> spp.) simultaneously exposed to hypersalinity and the effect of parental thermal history

Intertidal organisms exposed to thermal stress normally experience other stresses simultaneously, but how these combined stresses modify tolerance to heat, especially for embryos, is poorly understood. Tolerance of fucoid algal embryos to heat, with and without acclimation to a sublethal temperature and with simultaneous exposure to hypersaline media, was examined. Embryos of Fucus vesiculosus L. (mid-intertidal zone) were less tolerant than embryos of Fucus spiralis L. (upper intertidal zone); without acclimation and with a growth temperature of 14°C, about half of the embryos survived 3 h exposure to 33°C in F. vesiculosus and of 35°C in F. spiralis. Conditions experienced by parental thalli (4°C versus 14°C storage) significantly affected the heat tolerance of embryos grown for 24 h post-fertilization at 14°C in F. vesiculosus, a result that is important for biologists using fucoid algae as model systems. Acclimation to a sublethal temperature (29°C) or exposure to the LT₅₀ (33°C, F. vesiculosus; 35°C, F. spiralis) in 100 psu seawater (2850 mmol kg^–1 osmolality) resulted in 30–50% higher levels of embryonic survival. Higher levels of HSP60s were found in embryos exposed to 29–33°C than to 14°C; lower levels of HSP60s were present in embryos exposed to the LT₅₀ under hypersaline conditions than in normal seawater. Contemporaneous studies in 1995–1996 of substratum temperature and desiccation levels were made at Schoodic Point, Maine (USA) underneath F. spiralis and F. vesiculosus canopies and in Semibalanus balanoides patches. This study extends the bioindicator utility of heat-shock proteins in studies of intertidal organisms and demonstrates the importance of integrated stress responses in survival of a single stress factor (e.g. temperature).Electronic Supplementary Material Supplementary material is available in the online version of this article at     

Tolerance to freezing and supercooling of interstitial turbellaria and polychaeta from a sandy tidal beach of the island of Sylt (North Sea)

Tolerance experiments on freezing and supercooling (without ice formation) were designed to determine correspondence between tolerance to low temperatures and spatio-temporal distribution of one turbellarian and five polychaete species from sandy beaches of the North Sea island of Sylt. Freezing tolerances are always less than supercooling tolerances. Dinophilus gyrociliatus is significantly more sensitive to freezing (LD₅₀ value after 30 min of freezing:-3°C) than the others, whereas Stygocapitella subterranea is significantly less sensitive (50% mortality at-15.7°C after 30 min). The supercooling tolerances differ considerably among the species. The sequence of tolerances (LD₅₀ values) is as follows: Microphthalmus sczelkowii (-2.9°C after 4 h); D. gyrociliatus (<1 h at-8°C); M. listensis (5.6 h at-8°C); Protodriloides symbioticus (8.2 h at-8°C); Notocaryoplanella glandulosa (66 h at-8°C); S. subterranea (72 h at-8°C). Species of sand flats (d. gyrociliatus, M. listensis, P. symbioticus) have lower tolerances than those of the beach slope (N. glandulosa, S. subterranea). Among the latter, tolerances increase with distance of the distributional area from low tide level. S. subterranea, a species occurring at the uppermost position in the intertidal, proves to be best adapted to both freezing and supercooling. Species preferring deeper regions of the beach (M. sczelkowii) show lower supercooling tolerances than surface dwelling forms. Northern species usually have higher tolerances to cold than southern ones, reaching their distribution limits near the island of Sylt.     

Daily energy requirements and trophic positioning of the sand shrimp<Emphasis Type="Italic"> Crangon septemspinosa</Emphasis>

Sand shrimp, Crangon septemspinosa Say, are important to the trophic dynamics of coastal systems in the northwestern Atlantic. To evaluate predatory impacts of sand shrimp, daily energy requirements (J ind.^–1 day^–1) were calculated for this species from laboratory estimates of energy losses due to routine (R_R), active (R_A), and feeding (R_SDA) oxygen consumption rates (J ind.^–1 h^–1), coupled with measurements of diel motile activity. Shrimp used in this study were collected biweekly from the Niantic River, Connecticut (41°33N; 72°19W) during late spring and summer of 2000 and 2001. The rates of shrimp energy loss due to R_R and R_A increased exponentially with increasing temperature, with the magnitude of increase greater between 6°C and 10°C (Q₁₀=3.01) than between 10°C and 14°C (Q₁₀=2.85). Rates of R_R doubled with a twofold increase in shrimp mass, and R_SDA was 0.130 J h^–1+R_R, irrespective of shrimp body size. Shrimp motile activity was significantly greater during dark periods relative to light periods, indicating nocturnal behavior. Nocturnal activity also increased significantly at higher temperatures, and at 20°C shifted from a unimodal to a bimodal pattern. Laboratory estimates of daily metabolic expenditures (1.7–307.4 J ind.^–1 day^–1 for 0.05 and 1.5 g wet weight shrimp, respectively, between 0°C and 20°C) were combined with results from previous investigations to construct a bioenergetic model and make inferences regarding the trophic positioning of C. septemspinosa. Bioenergetic model estimates indicated that juvenile and adult shrimp could meet daily energy demands via opportunistic omnivory, selectively preying upon items of high energy content (e.g. invertebrate and fish tissue) and compensating for limited prey availability by ingesting readily accessible lower energy food (e.g. detritus and plant material).Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by J.P. Grassle, New Brunswick     

Routine oxygen consumption of Mugil cephalus,Liza dumerili and L. richardsoni at Different temperatures and salinities

Oxygen consumption studies were undertaken with 3 mullet species to determine b, the exponent of w, as well as a, as indices of metabolic rate in the equation M=aw ^bwhere M=metabolic rate, a=the intensity of metabolism, W=body weight, and b=the exponent of w. This was done under 5 experimental temperatures (13°, 18°, 23°, 28°, 33°C) for Mugil cephalus and Liza dumerili at 1 and at 35 S, and for L. richardsoni at 35S only. Mean b values were approximately 0.85. The a values depended on temperature, and increased according to Van't Hoff's law except for L. dumerili (1 S) and L. richardsoni (35 S) for a temperature increase from 23° to 28°C. It was found that handling had a profound influence on metabolic rate and led to considerably increased consumption rates during the first 8 h after introduction into the respiration chambers. Fasting in L. dumerili resulted in a total drop of 27% in oxygen consumption over a period of 6 days, of which 10% occurred over the first 24 h. Oxygen consumption displayed diurnal rhythms during the 6 day period, with lowest consumption rates at midday and midnight and highest just after sunrise and sunset.