Response of cold-acclimated,farmed South African abalone (Haliotis midae) to short-term and long-term changes in temperature

In its natural environment, the South African abalone, Haliotis midae, occurs at average monthly water temperatures between 12 and 21 °C. In the present study we aimed to describe selected physiological and molecular responses of winter acclimated, cultured H. midae after acute and chronic exposure to 16, 19 and 22 °C.     

The potential threat of algal blooms to the abalone (Haliotis midae) mariculture industry situated around the South African coast

Toxic algal blooms are common world-wide and pose a serious problem to the aquaculture and fishing industries. Dinoflagellate species such as Karenia brevis, Karenia mikimotoi, Heterosigma akashiwo and Chatonella cf. antiqua are recognised toxic species implicated in various faunal mortalities. Toxic blooms of Karenia cristata were observed on the south coast of South Africa for the first time in 1988 and were responsible for mortalities of wild and farmed abalone. K. cristata and various other dinoflagellate species common along the South African coast, as well as K. mikimotoi (Isolation site: Norway, Univ. of Copenhagen) and K. brevis (Isolation site: Florida, BIGELOW), were tested for toxicity by means of a bioassay involving Artemia larvae as well as abalone larvae and spat. K. cristata, like K. brevis, contains an aerosol toxin; however, the toxin present in K. cristata has not yet been isolated and remains unknown. K. brevis was, therefore, used to determine which developmental phase of the bloom would affect abalone farms most, and whether ozone could be used as an effective mitigating agent. Of the 17 dinoflagellate species tested, K. cristata, Akashiwo sanguinea, K. mikimotoi and K. brevis pose the greatest threat to the abalone mariculture industry. K. brevis was most toxic during its exponential and stationary phases. Results suggest that ozone is an effective mitigation agent but its economic viability for use on abalone farms must still be investigated.     

Metabolic consequences of living in a wave-swept environment: Effects of simulated wave forces on oxygen consumption, heart rate, and activity of the shell adductor muscle of the abalone Haliotis iris

Animals in wave-exposed habitats must constantly contend with the hydrodynamic forces of lift and drag. In this study, we investigated aspects of the metabolic response of Haliotis iris to simulated wave forces varying in magnitude up to 9.6 N applied to the shell at 69° to horizontal, alternately from anterior and posterior directions, with a period of 10s. Shell adductor muscle activity (electromyogram, EMG), heart rate, and oxygen consumption were monitored during force application and during extended recovery. EMG spiking was absent at zero force, but increased markedly with increasing force, in synchrony with the wave cycle. In contrast, heart rate was unaffected by wave forces and varied by only 5% over the whole range of applied forces. During force application, oxygen consumption increased by 10-25% above resting rates and remained elevated throughout a 5-hour recovery period, indicating a switch to anaerobic metabolism. It is concluded that living in a wave-swept environment is metabolically costly for abalone although this may be compensated by improved food availability and more efficient ventilation induced by external flow.     

Genetic structure of natural populations of the California black abalone (Haliotis cracherodii Leach, 1814), a candidate for endangered species status

The black abalone (Haliotis cracherodii) has been severely depleted across much of its historic range by a combination of overexploitation and disease. Natural recovery of extirpated populations along the southern California coast will depend on the extent to which remnant populations can serve as larval sources to geographic locations formerly supporting abalone populations. Population genetic analyses of mitochondrial cytochrome oxidase subunit one (COI) DNA sequences, four nuclear microsatellites, and 142 amplified fragment length polymorphisms (AFLPs) were used to evaluate connectivity among populations of H. cracherodii sampled from the central California coast and four islands in the Southern California Bight. Global divergence among populations was significant at COI and the AFLP loci. The Hka28 microsatellite locus and AFLP data showed significant divergence in multiple pairwise population comparisons and exhibited a signal of isolation by distance. Although estimates of gene flow based on genetic analyses must be interpreted with caution, the observed level of interpopulation genetic divergence suggests that larval dispersal is restricted, and natural recovery of decimated H. cracherodii populations along the coast of California is unlikely to occur in the near future.     

Age determination and estimation of larval period in field caught abalone (Haliotis discus hannai Ino 1953) larvae and newly metamorphosed post-larvae by counts of radular teeth rows

We developed an age determination method for larval and newly metamorphosed post-larval abalone Haliotis discus hannai in a laboratory experiment and determined the age of field caught individuals. Laboratory experiments showed that competent veliger larvae (4 days after fertilization) had a radula and regularly added rows of radular teeth with age in the absence of metamorphosis. Under environmentally relevant temperatures (17-22 °C), the number of rows of radular teeth increased linearly with age, but slopes of the regression lines were different among temperatures. Rows of radular teeth were added more slowly at lower temperatures. The effect of temperature on the development rate of the radula was quantified by the regression and the temperature coefficient, Q₁₀. The radular development of newly metamorphosed post-larvae, which had not acquired a peristomal shell (adult shell), was comparable with that of veliger larvae, although older post-larvae had a larger number of rows of radula than those of the same age of veliger larvae. From these results, an age determination method of veliger larvae and newly metamorphosed post-larvae was established, using the number of rows of radular teeth. The age of veliger larvae and newly metamorphosed post-larvae was determined by the age determination method for samples collected in August to October of 2003 and 2004 for which the thermal history of the coastal water of Miyagi Prefecture Japan was available. Only 9.1% of veliger larvae (n = 8) captured in the field had formed a radula and these were estimated to be 4-6 days old. The remaining 90.9% of larvae (n = 80) that had not formed a radula were classified as younger than 4 days old. All newly metamorphosed post-larvae (n = 24) that had metamorphosed on substrata were estimated to be 4-6 days old. Results of the field study indicate that these abalone metamorphosed within a few days after the acquisition of competence (4 days after fertilization) at this site, which has suitable crustose algal habitat.     

Metabolic tolerance of the cold-water coral Lophelia pertusa (Scleractinia) to temperature and dissolved oxygen change

Lophelia pertusa is the world's most common and widespread framework-forming cold-water coral. It forms deep-water coral reefs and carbonate mounds supporting diverse animal communities on the continental shelf and on seamounts. These recently discovered ecosystems have been damaged by deep-sea fishing and are threatened by predicted shallowing of the aragonite saturation horizon. Despite this, very little is known about the ecophysiology of L. pertusa and its likely response to environmental changes. Here we describe the first study of the respiratory physiology of L. pertusa and the effects of altered temperature and oxygen level. This study shows that L. pertusa can maintain respiratory independence over a range of PO₂ illustrated by a high regulation value (R = 78%). The critical PO₂ value of 9-10 kPa is very similar to the lower values of oxygen concentration recorded in the field. This suggests that oxygen level may be a limiting factor in the distribution of this cold-water coral. L. pertusa survived periods of anoxia (1 h), hypoxia (up to 96 h), but high Q₁₀ values revealed sensitivity to short-term temperature changes (6.5-11 °C). For the first time vital data have been gathered on the physiology of this species that is essential to understand distribution and underpin future climate change studies.     

Prey selection and the functional response of sea stars (Asterias vulgaris Verrill) and rock crabs (Cancer irroratus Say) preying on juvenile sea scallops (Placopecten magellanicus (Gmelin)) and blue mussels (Mytilus edulis Linnaeus)

Predators in nature include an array of prey types in their diet, and often select certain types over others. We examined (i) prey selection by sea stars (Asterias vulgaris) and rock crabs (Cancer irroratus) when offered two prey types, juvenile sea scallops (Placopecten magellanicus) and blue mussels (Mytilus edulis), and (ii) the effect of prey density on predation, prey selection, and component behaviours. We quantified predation rates, behavioural components (proportion of time spent searching for prey, encounter probabilities) and various prey characteristics (shell strength, energy content per prey, handling time per prey) to identify mechanisms underlying predation patterns and to assess the contribution of active and passive prey selection to observed selection of prey. Sea stars strongly selected mussels over scallops, resulting from both active and passive selection. Active selection was associated with the probability of attack upon encounter; it was higher on mussels than on scallops. The probability of capture upon attack, associated with passive selection, was higher for mussels than for scallops, since mussels can not swim to escape predators. Sea stars consumed few scallops when mussels were present, and so did not have a functional response on scallops (the target prey). Rock crabs exhibited prey switching: they selected mussels when scallop density was very low, did not select a certain prey type when scallop density was intermediate, and selected scallops when scallop density was high relative to mussel density. The interplay between encounter rate (associated with passive selection) and probability of consumption upon capture (associated with both active and passive selection) explained observed selection by crabs. Scallops were encountered by crabs relatively more often and/or mussels less often than expected from random movements of animals at all scallop densities. However, the probability of consumption varied with scallop density: it was lower for scallops than mussels at low and intermediate scallop densities, but tended to be higher for scallops than mussels at high scallop densities. When mussels were absent, crabs did not have a functional response on scallops, but rather were at the plateau of the response. When mussels were present with scallops at relatively low density, crabs exhibited a type II functional response on scallops. Our results have implications for the provision of protective refuges for species of interest (i.e., scallops) released onto the sea bed, such as in population enhancement operations and bottom aquaculture.     

Physiological and biochemical thermoregulatory responses of Chinese bulbuls Pycnonotus sinensis to warm temperature: Phenotypic flexibility in a small passerine

Temperature is an important environmental cue for the regulation of thermogenesis in small birds. We tested the hypothesis that a small passerine, the Chinese bulbul Pycnonotus sinensis can decrease thermogenesis in response to warmer temperatures by decreasing body mass, the organ mass and changing physiological and biochemical processes in the liver and muscle. Captive Chinese bulbuls decreased in body mass and basal metabolic rate (BMR) during 4 weeks of acclimation to 30±1 °C. They also showed a decrease in liver, kidney and small intestine mass and reduced mitochondrial state-4 respiration and cytochrome C oxidase (COX) activity in the liver and muscle compared to 10±1 °C. Furthermore, BMR was positively correlated with body mass, organ mass (liver, kidney, small intestine and entire digestive tract), and mitochondrial state-4 respiration and cytochrome C oxidase (COX) activity in the liver and muscle. These results indicate that changes in body mass, organ mass and respiratory enzyme activity are mechanisms by which Chinese bulbuls adapt to warmer temperatures. The data support the hypothesis that such physiological flexibility is ubiquitous in birds.     

Growth and IGF-I response of juvenile Nile tilapia (Oreochromis niloticus) to changes in water temperature and dietary protein level

Water temperature and dietary protein level play an important role in influencing the growth and insulin-like growth factor I (IGF-I) in Nile tilapia juveniles. The combined effect of temperature (20–34 °C) and dietary protein level (25–50%) on the specific growth rate (SGR), feed efficiency (FE), serum IGF-I level and hepatic IGF-I mRNA level was examined under laboratory conditions by employing central composite design and response surface method. Results showed that the linear effects of temperature and dietary protein level on the SGR, FE, serum IGF-I and hepatic IGF-I mRNA level were significant (P<0.05); the quadratic effects of temperature and dietary protein level on the FE and serum IGF-I were significant (P<0.05). The interaction of temperature and dietary protein level on the FE, serum IGF-I and hepatic IGF-I mRNA level all proved significant (P<0.05). The optimal temperature/dietary protein level combination was determined, i.e., 29.9 °C/40.3%, at which the greatest SGR (2.748%/d) and FE (0.775) were simultaneously arrived. Both SGR and FE were linearly correlated with serum IGF-I or hepatic IGF-I mRNA level. These results suggested that optimum combination of temperature and dietary protein level would enhance tilapia growth efficiency and IGF-I would regulate growth and FE.     

Influence of oxygen and temperature on growth and metabolic performance of Paralichthys lethostigma (Pleuronectiformes: Paralichthyidae)

In this study, we apply Fry's classification of environmental factors to demonstrate the limiting effects of oxygen and its interaction with temperature on the growth of juvenile P. lethostigma. We also evaluated the properties of two metabolic indices, marginal metabolic scope (MMS) and limiting oxygen concentration (LOC), as indicators of metabolic scope. We found that oxygen limitation has its greatest impact near the optimum temperature for growth of the species. At 29 °C a reduction from 6.00 mg/L to 4.00 mg/L caused a 50% reduction in growth rate while at 27 °C the reduction had no significant effect on growth rate. The results are particularly relevant because these temperatures and oxygen concentrations are commonly observed in nursery areas during summer months. At all temperatures fish from the lowest oxygen treatment (1.75 mg/L) had negative growth rates. Comparisons between daily oscillating oxygen treatments and constant treatments failed to demonstrate significant effects. At temperatures past the optimum, growth rates between the 6.00 mg/L and 4.00 mg/L treatments were not statistically different. LOC was significantly affected by temperature, oxygen, and their interaction. Estimates were positively correlated with oxygen treatment (R² > 0.71) and negatively correlated with temperature at moderate and low oxygen concentrations (R² > − 0.84). MMS was significantly affected by temperature and oxygen and was significantly correlated with oxygen treatment (R² > − 0.91), but correlations with temperature were not as clear. In conclusion, oxygen and temperature interactions have significant effects on metabolic scope and growth rates of fish, well above the accepted hypoxia threshold of 2.00 mg/L and MMS has proved a useful estimator of the metabolic scope of the organism within an environment.     

Thermal adaptability and disease association in common carp (Cyprinus carpio communis) acclimated to different (four) temperatures

The present study was designed to investigate the effect of temperature (20 °C, 24 °C, 28 °C and 32 °C) on the heamato-biochemical and histological alterations of Cyprinus carpio communis. Increase in the temperature showed significant decrease in the serum protein, while a reduced level of blood glucose at high temperature of 32 °C was observed leading to hypoglycemic conditions in the experimental fishes. A significant correlation (P<0.01) was observed between cholesterol (Cho) and triglycerides (TG) for different temperature treatments. Elevated blood urea nitrogen (BUN) at high temperatures was a good indicator of gill osmoregulatory failure. A variation of 86.40% and 38.33%, respectively, was noticed in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) at 32 °C over minimum experimental temperature of 20 °C. The increase in red blood cell (RBC) and Heamoglobin (Hb) concentration is associated with the decrease of mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC), could be the reason for observed poikilo-anisocytosis. Histological studies of different organs of experimental fishes showed accumulation of MMC's (melanomacrophagic centers) and atrophy of the interrenal tissue on exposure to various levels of temperature. These changes were related to severity of thermal stress, being most marked when high temperature was prolonged during acclimatization. Some fishes were found infested by protozoan parasite at elevated temperature of 32 °C. Increased levels of certain biochemical and haemotological parameters studied were strongly correlated with disease in the Cyprinus carpio communis species.     

Combined effect of temperature and salinity on the Thermotolerance and osmotic pressure of juvenile white shrimp litopenaeus vannamei (Boone)

Thermotolerance (CTMax) was determined in L. vannamei in three salinities and five acclimation temperatures 20, 23, 26, 29 and 32 °C. In white shrimp, the CTMax was not significantly affected by salinity (P>0.05). A direct relationship was obtained between CTMax and acclimation temperature. The end point of the CTMax in L. vannamei exposed to different combinations of temperature and salinity was defined as the loss of the righting response (LRR). The acclimation response ratio (ARR) for the juveniles of white shrimp ranged from 0.42 to 0.49; values in agreement with other crustaceans from tropical and sub tropical climates. The osmotic pressure of the hemolymph was measured in control organisms and in organisms exposed to CTMax; significant differences were found in organisms maintained in 10 and 40 psu, but there were no significant differences in hemolymph osmotic pressure in those that were acclimated to 26 psu.     

Effect of allozyme heterozygosity on basal and induced levels of heat shock protein (Hsp70), in juvenile Concholepas concholepas (Mollusca)

Organisms cope physiologically with extreme temperature by producing heat shock proteins (HSPs). Expression of Hsp70 enhances thermal tolerance and represents a key strategy for ectotherms to tolerate elevated temperature in nature. Synthesis of these proteins, together with other physiological responses to elevated temperatures, increases energy demands. A positive association between multiple and single locus heterozygosity (MLH and SLH, respectively) and individual fitness has been widely demonstrated. In molluscs, MLH can decrease routine metabolic rates and improve energetic status. Juvenile Concholepas concholepas live in the intertidal zone and are constantly exposed to temperature fluctuations. Thus, these young individuals are exposed both to thermal risks and the large metabolic costs required to cope with thermal stress. We evaluated the effects of allozyme MLH and SLH on basal (control animals) and induced (stressed animals) levels of the Hsp70 in juveniles C. concholepas. Juveniles (n = 400) were acclimated at 16 °C for 2 weeks; then 100 animals were exposed to 24 °C (stress) and 100 were kept at 16 °C (control) for 2 and 7 days. The variability of 20 loci was analyzed by starch gel electrophoresis. For SLH effects we used 7 polymorphic loci. We quantified expression of Hsp70 by Western blot analyses. Hsp70 expression increased markedly (~ 90%) with temperature. We found a positive association between MLH and basal and induced levels of Hsp70 in the 2-day exposure experiment. Regardless of temperature, Hsp70 levels increased with MLH (r² = 0.7 and 0.9, for basal and induced levels, respectively) reaching maximal levels in juveniles with intermediate and high MLH levels (2 and 3 loci), and decreasing slightly (but not significantly) in juveniles with highest MLH (≥ 4 heterozygous loci). However, after 7 days of exposure to thermal stress, less heterozygous juveniles attained the same levels of Hsp70 than more heterozygous juveniles. Given the faster increment of Hsp70 in C. concholepas juveniles with intermediate-high levels of MLH, these individuals could be less affected by thermal stress in the intertidal zone. We found an association between specific loci genotype and higher Hsp70 levels (basal or induced). In comparison to homozygous juveniles, heterozygous juveniles for several loci showed higher Hsp70. However, these associations were not for the same loci in juveniles exposed to high temperature for 2 and 7 days. This suggests genotypic variation at some allozyme loci could be more important in the period of initial response to high temperature and others can be more important in the response to the chronic temperature stress.     

Respiratory responses to temperature and hypoxia in the nonindigenous Brown Mussel, Perna perna (Bivalvia: Mytilidae), from the Gulf of Mexico

The respiratory responses to increasing temperature and progressive hypoxia were examined relative to temperature acclimation in the nonindigenous, brown mussel, Perna perna (Mytilidae) from the Gulf of Mexico. When oxygen uptake rate (V?_O2) was recorded at near full air O₂ saturation, rate-temperature curves for Texas specimens of P. perna were sigmoidal, V?_O2 generally increasing with increasing temperature but becoming suppressed as temperatures approached 10 and 30 °C, corresponding closely to this species' incipient thermal limits. At each tested temperature, V?_O2 did not differ among individuals acclimated to 15, 20, or 25 °C. Lack of thermal acclimation was also reflected in acclimatory Q₁₀ values>1.0 (range=1.34-2.14) recorded across acclimation groups at test temperatures equivalent to acclimation temperature. Low acute respiratory Q₁₀ values in all acclimation groups across 15-20 °C indicated a limited capacity for thermal regulation of V?_O2 within this temperature range. The ability of P. perna to regulate O₂ uptake with progressive hypoxia was temperature-dependent, increasing from poor O₂ regulation at 10 °C to good regulation at 30 °C. The O₂ regulatory ability of P. perna and other open-water mytilids in declining O₂ concentrations does not greatly differ from that of estuarine heterodont bivalves, suggesting that it is not a major factor preventing open-water species, such as P. perna, from invading estuarine environments. However, P. perna's inability to regulate O₂ uptake at temperatures>25 °C combined with its relatively low upper thermal limit of 30 °C will likely prevent it from establishing permanent estuarine populations on Gulf of Mexico shores.     

Seasonal regulations of resting metabolic rate and thermogenesis in striped hamster (Cricetulus barabensis)

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Resting metabolic rate (RMR), nonshivering thermogenesis (NST) and mitochondria cytochrome c oxydase (COX) activity of brown adipose tissue (BAT), as well as weight of skin and fur were measured in striped hamsters (Cricetulus barabensis) that were live-trapped in the summer, autumn, winter and spring.     

Effect of age and body size on selected temperature by juvenile wood turtles (Glyptemys insculpta)

In an aquatic thermal gradient of 15–30 °C, 3-, 6-, and 12-month-old juvenile wood turtles (Glyptemys insculpta) acclimated to 20 °C selected the warmest temperature available (30 °C) and avoided the coldest temperatures available (15 and 18 °C). Mean selection of chambers differed between control and gradient tests across all temperatures except 27 °C. Turtles of all age classes relocated between chambers less often when the gradient was present than during control tests. Six- and 12-month-old turtles selected 30 °C more frequently, and selected colder temperatures less frequently, than 3-month-old turtles, suggesting that the ability to select preferred temperatures is better developed in older hatchlings.     

Metabolic responses of Glossina pallidipes (Diptera: Glossinidae) puparia exposed to oxygen and temperature variation: Implications for population dynamics and subterranean life

Understanding the factors affecting insect gas exchange in subterranean environments is critical to understanding energy budgets and predicting mortality under field conditions. Here, we examine the metabolic rate (MR) responses of tsetse puparia, which remain underground for ca. 1 month in this life-stage, to varying oxygen and temperature. First, the effects of temperature and oxygen on puparial MR were investigated by ramping temperature from 15 to 35 °C under 10, 21 or 40% O₂. Overall, temperature was the dominant effect on puparial MR although O₂ had small but significant impacts. Second, critical O₂ concentration (P_CRIT) for MR of puparia was examined across a range of oxygen concentrations (0-40%). P_CRIT was 6% O₂ which is similar to P_CRIT in other basal arthropods but relatively high for inactive or subterranean insects. Third, we asked if puparia exposed to anoxia might experience oxygen debt, potentially indicative of anaerobic metabolism or cellular repair. Metabolic responses to anoxia were limited or insignificant, but MR was marginally elevated (∼15%) in anoxia-exposed (4 h) puparia by 12 h post-anoxia. Finally, we examined the ability of puparia to withstand water submersion, thus simulating flooding conditions frequently experienced in tropical soil habitats. Puparia were unable to survive submersion for >24 h suggesting limited flooding tolerance. These novel results suggest that soil conditions experienced by puparia should not be limiting for MR, except possibly under high temperature-low O₂ conditions. Due to a large safety margin between P_CRIT and soil oxygen levels and limited effects of oxygen on metabolism during temperature ramping experiments, we suggest that Glossina pallidipes puparia are not particularly susceptible to oxygen availability in their natural environment. However, soil flooding associated with tropical rainfall likely imposes strong selection on tsetse populations and may have had important effects for tsetse energy budgets and evolution.     

Thermal preference,tolerance and oxygen consumption of adult white shrimp Litopenaeus vannamei (Boone) exposed to different acclimation temperatures

Final temperature preferendum of white shrimp adults were determined with acute and gravitation methods. The final preferendum was similar, independent of method (26.2–25.6 °C). A direct relationship was determined between the critical thermal maxima values and the acclimation temperatures (P<0.05). The end point of Critical Thermal Maxima (CTMax) for adults was defined as the loss of righting response (LRR). The acclimation response ratio (ARR) for adults of white shrimp had an interval of 0.36–0.76, values that agreed with others obtained for crustaceans from tropical and subtropical climates. The oxygen consumption rates increased significantly (P<0.05) from 39.6 up to 90.0 mg O₂ kg⁻¹ h⁻¹ wet weight (w.w.) as the acclimation temperature increased from 20 to 32 °C. The range of temperature coefficient (Q₁₀) of the white shrimp between 23 and 26 °C was the lower 1.60. The results obtained in this work are discussed in relation to the species importance in the reproductive scope and maintenance of breeders.