Effect of acclimation temperature and substrate type on selected temperature,movement and activity of juvenile spiny softshell turtles (Apalone spinifera) in an aquatic thermal gradient

In some turtle species, temperature selection may be influenced by environmental conditions, including acclimation temperature and substrate quality. These factors may be particularly important for softshell turtles that are highly aquatic and often thermoregulate by burying in the substrate in shallow water microhabitats. We tested for effects of acclimation temperature (22 °C or 27 °C) and substrate type (sand or gravel) on the selected temperature and movement patterns of 20 juvenile spiny softhshell turtles (Apalone spinifera; Reptilia: Trionychidae) in an aquatic thermal gradient of 14–34 °C. Among 7–11 month old juvenile softshell turtles, acclimation temperature and substrate type did not influence temperature selection, nor alter activity and movement patterns. During thermal gradient tests, both 22- and 27 °C-acclimated turtles selected the warmest temperature (34 °C) available most frequently, regardless of substrate type (sand or gravel). Similarly, acclimation temperature and substrate type did not influence movement patterns of turtles, nor the number of chambers used in the gradient tests. These results suggest that juvenile Apalone spinifera are capable of detecting small temperature increments and prefer warm temperatures that may positively influence growth and metabolism, and that thermal factors more significantly influence aquatic thermoregulation in this species than does substrate type.     

Embryonic temperature affects metabolic compensation and thyroid hormones in hatchling snapping turtles.

Temperature acclimation of adult vertebrates typically induces changes in metabolic physiology. During early development, such metabolic compensation might have profound consequences, yet acclimation of metabolism is little studied in early life stages. We measured the effect of egg incubation temperature on resting metabolic rate (RMR) and blood thyroid hormone levels of hatchling snapping turtles (Chelydra serpentina). Like many reptiles, snapping turtles have temperature-dependent sex determination (TSD), in which embryonic temperature determines sex. Therefore, we designed the experiments to separately measure effects of temperature and of sex on the response variables. We incubated eggs in the laboratory at 21. 5 degrees, 24.5 degrees, 27.5 degrees, and 30.5 degrees C, producing both sexes, all males, both sexes, and all females, respectively. Hatchling RMR, when measured at a common temperature (either 25 degrees or 31 degrees C), was negatively correlated with egg temperature in both males and females, such that RMR of turtles from 21.5 degrees C-incubated eggs averaged 160% that of turtles from 30.5 degrees C-incubated eggs. These results indicate that egg temperatures induced positive metabolic compensation in both sexes. Thyroid hormone levels of hatchlings showed similar correlations with egg temperature; thyroxine level of turtles from 21.5 degrees C-incubated eggs averaged 220% that of turtles from 30.5 degrees C-incubated eggs. To examine the possibility that thyroid hormones contribute to positive metabolic compensation, we added triiodothyronine to eggs during mid-incubation. RMR of hatchlings from these treated eggs averaged 131% that of controls, consistent with the previous possibility. Moreover, the effects of embryonic temperature on metabolic physiology, in combination with effects on sex, can result in differences in RMR and thyroid hormone levels between male and female hatchling turtles. Such differences may be important to the ecology and evolution of TSD.     

EXPERIMENTAL EVIDENCE FOR THE EVOLUTIONARY SIGNIFICANCE OF TEMPERATURE-DEPENDENT SEX DETERMINATION

The evolutionary significance of sex-determining mechanisms, particularly temperature-dependent sex determination (TSD) in reptiles, has remained unresolved despite extensive theoretical work. To investigate the evolutionary significance of this unusual sex-determining mechanism, I incubated eggs of the common snapping turtle (Chelydra serpentina) at a male-producing temperature (26°C), a female-producing temperature (30°C), and an intermediate temperature that produced both sexes about equally (28°C). Laboratory experiments indicated that two performance variables, but no morphological measurements, were significantly influenced by incubation temperature (P ≤ 0.05): hatchlings from cooler incubation treatments swam faster than turtles from warmer incubation treatments, and hatchlings from 28°C exhibited a greater propensity to run than did individuals from 26°C and 30°C. In the field, hatchlings from the all-male and all-female producing temperatures had significantly higher first-year survivorship than did consexuals from the incubation temperature that produced both sexes (G = 6.622, P = 0.03). Significant directional selection was detected on propensity of hatchlings to run (β′ = –0.758, P = 0.05): turtles that tended to remain immobile had a higher probability of first-year survivorship than did individuals that moved readily. Thus, the effects of the gender × incubation temperature interaction on survivorship of hatchling turtles observed in the field experiment may have been mediated by temperature-dependent antipredator behavior. These results provide a possible functional explanation for the evolutionary significance of TSD in turtles that is consistent with predictions of theoretical models.     

Thermoconformity strategy in the freshwater turtle Hydromedusa tectifera (Testudines,Chelidae) in its southern distribution area

Ectotherm species are not capable of generating metabolic heat; therefore, they present different strategies for regulating their body temperatures, ranging from a precise degree of thermoregulation to a passive thermoconformity with ambient temperatures. In reptiles, aerial basking is the most common mechanism for gaining heat. However, among aquatic reptiles, such as freshwater turtles, aquatic basking is also frequent. Hydromedusa tectifera is a turtle of exclusively aquatic and nocturnal habits widely distributed in South America. We studied the relationship between body temperature (Tb) of H. tectifera and its habitat, and explored the effects of sex, life stage and body size and mass on Tb. Fieldwork was conducted in two streams of a mountain area of central Argentina. We recorded cloacal temperature, size and mass of 84 turtles. We also determined individuals’ sex and life stage (adult/juvenile). Regarding ambient temperatures, we measured water temperature on the surface (Tsurf) and at depth of turtle capture (Tdepth) and air temperature. Mean Tb was 18.58 °C (Min = 10.20 °C; Max = 25.70 °C). Tsurf and Tdepth were highly correlated. Multi-model analysis using Akaike criterion indicated that Tb was strongly associated with water temperature, whereas air temperature and body size and mass did not show a significant effect. There was also no effect of turtle sex or life stage on Tb. Our results indicate that H. tectifera is a thermoconformer and eurythermal species. A nocturnal pattern of activity and a fully aquatic lifestyle are suggested as determinant factors.     

Behavioral responses of hatchling painted turtles (Chrysemys picta) and snapping turtles (Chelydra serpentina) at subzero temperatures

We monitored behavioral responses of cold-acclimated hatchling painted turtles (Chrysemys picta) indigenous to Nebraska and hatchling snapping turtles (Chelydra serpentina) indigenous to Nebraska and Arkansas during cooling (0.1°C/min) to temperatures as low as −19°C. All turtles made exploratory movements during cooling and locomotion occurred at temperatures as low as −2 to −4°C, but C. picta maintained relatively higher levels of locomotor activity than C. serpentina, and no differences in motility occurred between northern and southern groups of C. serpentina. Slow movements of the head and limbs were observed in supercooled hatchling C. picta at temperatures as low as −10°C, whereas at about −5°C, C. serpentina exhibited an increase in spontaneous motor activity followed by muscle contracture, immobility, and spontaneous freezing. C. picta spontaneously froze at about −16°C without exhibiting cold contracture, suggesting that they are better adapted to survive exposure to extreme cold.     

Effects of constant and fluctuating incubation temperatures on hatching success and hatchling traits in the diamondback terrapin (Malaclemys terrapin) in the context of the warming climate

As global temperatures continue to rise, so too will the nest temperatures of many species of turtles. Yet for most turtle species, including the estuarine diamondback terrapin (Malaclemys terrapin), there is limited information on embryonic sensitivity to elevated temperature. We incubated eggs of M. terrapin at three, mean temperatures (31, 34, 37 °C) under two thermal exposure regimes (constant or semi-naturally fluctuating temperature) and measured hatching success, developmental rate, and hatchling size. Hatching success was 100% at 31 °C and 67% at 34 °C, respectively; at 37 °C, all eggs failed early in the incubation period. These values were unaffected by exposure regime. The modeled LT₅₀ (temperature that was lethal to 50% of the test population) was 34.0 °C in the constant and 34.2 °C in the fluctuating thermal regime, reflecting a steep decline in survival between 33 and 35 °C. Hatchlings having been incubated at a constant 34 °C hatched sooner than those incubated at 31 °C under either constant or fluctuating temperature. Hatchlings were smaller in straight carapace length (CL) and width after having been incubated at 34 °C compared to 31 °C. Larger (CL) hatchlings resulted from fluctuating temperature conditions relative to constant temperature conditions, regardless of mean temperature. Based upon recent temperatures in natural nests, the M. terrapin population studied here appears to possess resiliency to several degrees of elevated mean nest temperatures, beyond which, embryonic mortality will likely sharply increase. When considered within the mosaic of challenges that Maryland's M. terrapin face as the climate warms, including ongoing habitat losses due to sea level rise and impending thermal impacts on bioenergetics and offspring sex ratios, a future increase in embryonic mortality could be a critical factor for a population already experiencing ecological and physiological challenges due to climate change.     

Temperature selection by juvenile tuatara (Sphenodon punctatus) is not influenced by temperatures experienced as embryos

Most reptiles thermoregulate to achieve body temperatures needed for biological processes, such as digestion and growth. Temperatures experienced during embryogenesis may also influence post-hatching growth rate, potentially through influencing post-hatching choice of temperatures. We investigated in laboratory settings whether embryonic temperatures (constant 18 °C, 21 °C and 22 °C) influence selected body temperatures (T_sel) of juvenile tuatara (Sphenodon punctatus), providing a possible mechanism for differences in growth rates. We found that incubation temperature does not influence T_sel. Although the average daily mean T_sel was 21.6 ± 0.3 °C, we recorded individual T_sel values up to 33.5 °C in juvenile tuatara, which is higher than expected and above the panting threshold of 31–33 °C reported for adults. We found diel patterns of T_sel of juvenile tuatara, observing a general pattern of two apparent peaks and troughs per day, with T_sel being significantly lower around dawn and at 1500 h than any other time. When comparing our results with other studies on tuatara there is a remarkable consistency in mean T_sel of ~ 21 °C across tuatara of different ages, sizes and acclimatization histories. The ability of juvenile tuatara to withstand a wide range of temperatures supports their former widespread distribution throughout New Zealand and warrants further investigation into their plasticity to withstand climate warming, particularly where they have choices of habitat and the ability to thermoregulate.     

Combined effects of seawater temperature and nutrient condition on growth and survival of juvenile sporophytes of the kelp Undaria pinnatifida (Laminariales; Phaeophyta) cultivated in northern Honshu, Japan

Recently, withering of farmed juvenile sporophytes of the kelp Undaria pinnatifida (Harvey) Suringar has led to reduced production of this species in northern Japan, possibly because of the high water temperature and low nutrient concentration in cultivation areas. This problem may be solved by introducing parental plants with greater tolerance to high temperature and low nutrient conditions. We examined the combined effects of various temperatures (15, 20, 24, and 27 °C) and nutrient availabilities (seawater enriched with 25 % PESI medium and non-enriched seawater) on the growth and survival of cultivated juvenile sporophytes (1–2 cm) collected from Matsushima Bay, Miyagi Prefecture in northern Japan and Naruto, Tokushima Prefecture in southern Japan. The relative growth rates of juvenile sporophytes from both locations were significantly greater at 15 and 20 °C than at 24 and 27 °C. The juvenile sporophytes cultured in enriched medium had significantly higher relative growth rates than those cultivated in non-enriched seawater. Dead juveniles were observed in non-enriched seawater at all temperatures and the survival percentage decreased with increasing seawater temperatures. Compared to the juvenile sporophytes from Matsushima Bay, those from Naruto showed greater tolerance to high temperature even under the low nutrient condition. These results suggest that the withering of juvenile sporophytes is caused by the combined effects of low nutrient availability and high temperature. A potential solution to this problem is to introduce ecotypes with greater tolerance to high temperature and low nutrient conditions from a warmer region of Japan.     

Heart rate during development in the turtle embryo: effect of temperature

 Growth and development can occur over a wide range of physical conditions in reptiles. Cardiovascular function must be critical to this ability. However, information on cardiovascular function in developing reptiles is lacking. Previous work indicated that in reptiles the effects of temperature on growth and metabolism are largely restricted to early development. This study examined whether the previously observed effects of temperature and different perinatal patterns of metabolism observed in amniotic vertebrates are correlated with cardiovascular function. Embryonic and hatchling carcass mass, heart mass and heart rate (HR) were compared for snapping turtle eggs (Chelydra serpentina) incubated at 24 ° and 29 °C. Incubation time was shorter at 29 °C (56.2 days) than at 24 °C (71.1 days). Carcass and heart growth showed a sigmoidal pattern at both temperatures. However, cardiac growth showed a relative decrease as incubation proceeded. Incubation temperature significantly affected the HR pattern during development. The HR of embryos incubated at 24 °C was constant for most of incubation (51.8±4.8 min^-1). A small decrease was observed just prior to and a large decrease immediately following hatching (posthatch, 22.3±4.1 min^-1). At 29 °C embryonic HR was greater than at 24 °C early in development (72.3±3 min^-1). The HR steadily decreased to values equivalent to those at 24 °C. The HRs of 24 °C and 29 °C hatchlings were not different. Cardiac output (estimated as the product of heart mass and HR) increased rapidly during early development and then slowed dramatically at both temperatures. These data are consistent with the suggestion that temperature exerts its effects primarily early in development. Furthermore, the changes in cardiovascular function are correlated with metabolic changes in hatching vertebrates. Accepted:12 June 1996     

Effects of temperature on embryonic and early larval growth and development in the rough-skinned newt (Taricha granulosa)

We investigated the effects of temperature on the growth and development of embryonic and early larval stages of a western North American amphibian, the rough-skinned newt (Taricha granulosa). We assigned newt eggs to different temperatures (7, 14, or 21 °C); after hatching, we re-assigned the newt larvae into the three different temperatures. Over the course of three to four weeks, we measured total length and developmental stage of the larvae. Our results indicated a strong positive relationship over time between temperature and both length and developmental stage. Importantly, individuals assigned to cooler embryonic temperatures did not achieve the larval sizes of individuals from the warmer embryonic treatments, regardless of larval temperature. Our investigation of growth and development at different temperatures demonstrates carry-over effects and provides a more comprehensive understanding of how organisms respond to temperature changes during early development.     

Early thermal history significantly affects the seasonal hyperplastic process occurring in the myotomal white muscle of <Emphasis Type="Italic">Dicentrarchus labrax</Emphasis> juveniles

The effect of early (embryonic and larval) thermal history on subsequent (juvenile) white muscle hyperplasia was studied in a teleost fish, the European sea bass (Dicentrarchus labrax L.). D. labrax, incubated and reared at constant temperatures of 13°C, 15°C or 20°C from the embryonic stage of half epiboly up to 18–19 mm in total length, were transferred to ambient seawater temperature and reared for the subsequent 14 months on commercial feed. The somatic growth of juveniles was linked to annual variations of ambient seawater temperature and inversely related to early rearing temperature, so that, after 14 months, the juveniles originally reared at low temperatures had compensated for the growth retardation experienced during early life. The white muscle growth process of juveniles was quantified after two periods of growth opportunity at ambient seawater temperature (100 and 400 days post-transfer) as well as, in order to follow total-length-dependent effects of early temperature and to discriminate total-length-independent effects of early temperature, on juveniles from the three batches sampled at six successive equivalent total lengths (31–33, 84–88, 141–145, 166–172, 196–206 and 211–220 mm). Our data demonstrate the existence of a seasonal recruitment of new white muscle fibres when seawater temperature increases and of a shrinkage of the largest white muscle fibres during the winter months. The seasonal recruitment of new white muscle fibres occurring in juveniles is linked to their early rearing temperature. Juveniles originating from low temperatures have a higher and longer capacity to recruit new white muscle fibres when seawater temperature increases, supporting their better somatic growth. This finding is discussed in relation to the early (embryonic and larval) myogenic processes of the three populations and is related to their sex ratio. This work was financed by the European Commission, FAIR Program no. PL96–1941 “Muscle Ontogeny in Sea bass and Trout”.     

Postembryonic growth in two species of freshwater Ostracoda (Crustacea) shows a size-age sigmoid model fit and temperature effects on development time, but no clear temperature-size rule (TSR) pattern

Although the temperature-size rule is a widespread phenomenon that describes the impact of temperature on the intraspecific size of ectotherms, what determines the wide intrinsic variation in moult increment and the intermoult period within and between Crustacea species remains unknown. This work characterizes the growth of freshwater ostracods Chlamydotheca incisa and Strandesia bicuspis under different controlled temperatures and identifies growth patterns. Animals were collected from temporary ponds in Argentina. The experiment was done at two constant temperatures: 17 and 23 °C. The intermoult time and the time from hatching to the final moult were calculated. Three different growth regression equations were tested: von Bertalanffy and two sigmoidal models (Sigmoid and Gompertz). For both species, significant differences in the duration of each instar were found by comparing individuals grown at 17 and at 23 °C. A strong temperature effect was noted on intermoult time but not on growth factors. The best model selected for the size-age relationship was a sigmoid growth type, indicating accelerated growth in the earliest juvenile instars. These results challenge the widely-accepted application of nonsigmoidal growth models and are in agreement with recent analyses of growth patterns in aquatic invertebrates when early juvenile instars are considered.     

Genetic differentiation of high-temperature tolerance in the kelp Undaria pinnatifida sporophytes from geographically separated populations along the Pacific coast of Japan

The kelp Undaria pinnatifida has a widespread latitudinal range in Japan, with populations exposed to very different temperature regimes. To test the hypothesis that U. pinnatifida exhibits genetic differentiation in its temperature response, juvenile sporophytes from a warmer location (Naruto, southern Japan) and two colder locations (Okirai Bay and Matsushima Bay, northern Japan) were collected and transplanted to long lines, cultivated under the environmental conditions in Matsushima Bay. These plants were bred using successive self-crossing methods for three generations and the characteristics of photosynthesis, growth, survival, and nitrogen contents of the third-generation juvenile sporophytes (2–3 cm) then were measured and compared. The plants from Naruto showed significantly higher photosynthetic activities and respiration than those from the northern populations at warmer temperatures of 20–35°C. The juvenile sporophytes from all three locations had similar growth rates below 18°C, but significant differences were observed at 18–24°C. The optimum temperatures for growth were 14–16°C in plants that originated from Okirai Bay and Matsushima Bay and 18°C in plants that originated from Naruto. These results reflected the differences in latitude. Dead plants were observed at high temperatures of 22 and 24°C in the northern population plants, whereas no plants from Naruto died. Juvenile sporophytes from Naruto exhibited the greatest capacity to accumulate high nitrogen reserves. These results suggest that the differences in high-temperature tolerance in juvenile U. pinnatifida sporophytes from geographically separated populations are due to genetic differentiation rather than phenotypic plasticity.     

Too cold is better than too hot: Preferred temperatures and basking behaviour in a tropical freshwater turtle

Thermoregulation is critical to the survival of animals. Tropical environments can be particularly thermally challenging as they reach very high, even lethal, temperatures. The thermoregulatory responses of tropical freshwater turtles to these challenges are poorly known. One common thermoregulatory behaviour is diurnal basking, which, for many species, facilitates heat gain. Recently, however, a north-eastern Australian population of Krefft's river turtles (Emydura macquarii krefftii) has been observed basking nocturnally, possibly to allow cooling. To test this, we determined the thermal preference (central 50% of temperatures selected) of E. m. krefftii in an aquatic thermal gradient in the laboratory. We then conducted a manipulative experiment to test the effects of water temperatures, both lower and higher than preferred temperature, on diurnal and nocturnal basking. The preferred temperature range fell between 25.3°C (±SD: 1.5) and 27.6°C (±1.4) during the day, and 25.3°C (±2.4) and 26.8°C (±2.5) at night. Based on this, we exposed turtles to three 24 h water temperature treatments (‘cool’ [23°C], ‘preferred’ [26°C] and ‘warm’ [29°C]) while air temperature remained constant at 26°C. Turtles basked more frequently and for longer periods during both the day and night when water temperatures were above their preferred range (the ‘warm’ treatment). This population frequently encounters aquatic temperatures above the preferred thermal range, and our results support the hypothesis that nocturnal basking is a mechanism for escaping unfavourably warm water. Targeted field studies would be a valuable next step in understanding the seasonal scope of this behaviour in a natural environment.     

A potential tool to mitigate the impacts of climate change to the caribbean leatherback sea turtle

It is now well understood that climate change has the potential to dramatically affect biodiversity, with effects on spatio‐temporal distribution patterns, trophic relationships and survivorship. In the marine turtles, sex is determined by incubation temperature, such that warming temperatures could lead to a higher production of female hatchlings. By measuring nest temperature, and using a model to relate the incubation temperature to sex ratio, we estimate that Caribbean Colombian leatherback sea turtles currently produce approximately 92% female hatchlings. We modelled the relationship between incubation, sand and air temperature, and under all future climate change scenarios (0.4–6.0 °C warming over the next 100 years), complete feminization could occur, as soon as the next decade. However, male producing refugia exist in the periphery of smaller nests (0.7 °C cooler at the bottom than at the centre), within beaches (0.3 °C cooler in the vegetation line and inter‐tidal zone) and between beaches (0.4 °C higher on dark beaches), and these natural refugia could be assigned preferential conservation status. However, there exists a need to develop strategies that may ameliorate deleterious effects of climate‐induced temperature changes in the future. We experimentally shaded clutches using screening material, and found that it was effective in reducing nest temperature, producing a higher proportion of male hatchlings, without compromising the fitness or hatching success. Artificial shade in hatcheries is a very useful and simple tool in years or periods of high environmental temperatures. Nevertheless, this is only an emergency response to the severe impacts that will eventually have to be reversed if we are to guarantee the stability of the populations.     

Effects of different thermal treatments during embryonic development on the artificial incubation efficiency of crayfish (Austropotamobius pallipes Lereboullet) eggs. Control of the embryogenetic duration and implications for commercial production

Summary

The development and improvement of artificial incubation techniques for freshwater crayfish eggs and their incorporation into the working schedule of breeding centres is of great interest for commercial production. Factors such as the water circulation system, flow rate, thermal treatment, etc., could strongly influence the success of the process. The present study attempts to test the possible influence of one of these variables, the thermal regime, on both the duration of embryonic development and the efficiency rates obtained in the artificial incubation of white-clawed crayfish (Austropotamobius pallipes) eggs. Four different thermal treatments were tested (three of them included a period at low temperature: 4°-5°C). Survival rates to juvenile stage 2 were similar in the four cases, ranging between 66.7 and 72.7%. We conclude that water cooling (an expensive management procedure) is not necessary in astacid breeding centres provided that egg development takes place at moderately low temperatures (8°-10°C) with a subsequent increase of up to 15°C from the eyed stage. However, the inclusion of periods at low temperature (4°-5°C) allows the staggered production of juvenile batches throughout a 3-week period without adverse effects on efficiency rates. This could be useful to breeding centres in meeting seasonal market requirements. In our study, egg and juvenile losses (mortality rate: 15–20%) were concentrated during the last phases of embryogenesis, particularly from the eyed stage to juvenile stage 2, during which they amounted to more than 90% of the overall mortality which took place during the artificial incubation process.     

Climate change and sea turtles: a 150-year reconstruction of incubation temperatures at a major marine turtle rookery

Sea turtles show temperature dependent sex determination. Using an empirical relationship between sand and air temperature, we reconstructed the nest temperatures since 1855 at Ascension Island, a major green turtle (Chelonia mydas) rookery. Our results show that inter‐beach thermal variations, previously ascribed to the albedo of the sand, which varies hugely from one beach to another, have persisted for the last century. Reconstructed nest temperatures varied by only 0.5 °C on individual beaches over the course of the nesting season, while the temperature difference between two key nesting beaches was always around 3 °C. Hence inter‐beach thermal variations are the main factor causing a large range of incubation temperatures at this rookery. There was a general warming trend for nests, with a mean increase in reconstructed nest temperatures for different months of between 0.36 and 0.49 °C for the last 100 years.     

Effect of rearing temperature on growth and thermal tolerance of Schizothorax (Racoma) kozlovi larvae and juveniles

Effect of rearing temperature on growth and thermal tolerance of Schizothorax (Racoma) kozlovi Nikolsky larvae and juveniles was investigated. The fish (start at 12 d post hatch) were reared for nearly 6 months at five constant temperatures of 10, 14, 18, 22 and 26 °C. Then juvenile fish being acclimated at three temperatures of 14, 18 and 22 °C were chosen to determine their critical thermal maximum (CTMax) and lethal thermal maximum (LTMax) by using the dynamic method. Growth rate of S. kozlovi larvae and juveniles was significantly influenced by temperature and fish size, exhibiting an increase with increased rearing temperature, but a decline with increased fish size. A significant ontogenetic variation in the optimal temperatures for maximum growth were estimated to be 24.7 °C and 20.6 °C for larvae and juveniles of S. kozlovi, respectively. The results also demonstrated that acclimation temperature had marked effects on their CTMax and LTMax, which ranged from 32.86 °C to 34.54 °C and from 33.79 °C to 34.80 °C, respectively. It is suggested that rearing temperature must never rise above 32 °C for its successful aquaculture. Significant temperature effects on the growth rate and thermal tolerance both exhibit a plasticity pattern. Determination of critical heat tolerance and optima temperature for maximum growth of S. kozlovi is of ecological significance in the conservation and aquaculture of this species.     

Growth and Survival of Early Juveniles of the Marine Sponge Hymeniacidon perlevis (Demospongiae) Under Controlled Conditions

To resolve “the supply problem” in sponge-derived drug development and other biotechnological applications, current research is exploring the possibility of obtaining an alternative sustainable supply of sponge biomass through intensive aquaculture of sponges utilizing artificial seed rearing. This study aimed to investigate the technology of early juvenile sponge cultivation under controlled conditions. The effects of food, temperature, water flow, and light on the growth and survival of early juveniles of the marine sponge Hymeniacidon perlevis were examined. The concentrations of four types of food elements [microalgae (Isochrysis galbana), photosynthetic bacteria (Rhodopseudomonas), Fe³⁺ (FeCl₃), and Si (Na₂SiO₃)] were investigated for early H. perlevis juvenile growth. Interestingly, temperature changes have striking effects on juvenile growth. Juvenile sponges grow faster when they are shifted to higher temperatures (18°C to 23°C) than when they are shifted to lower temperatures (18°C to 4°C to 23°C) or kept at a constant temperature (18°C). Periodic water flow and light cycles favor early juvenile sponge growth. Light was found to be a key factor in the color loss of early H. perlevis juveniles. Overall, size (area) increased as much as 29 times for H. perlevis juveniles under the tested controlled conditions.     

The influence of temperature and salinity on the duration of embryonic development,fecundity and growth of the amphipod Echinogammarus marinus Leach (Gammaridae)

The effects of salinity and temperature on the duration of embryonic development, fecundity and growth of the amphipod Echinogammarus marinus Leach from the Mondego estuary (Portugal) were studied in laboratory experiments. Combinations of three temperatures (10, 15 and 20 °C) and four salinities (10, 15, 20 and 25 ‰) were used. The duration of embryonic development was 33 ± 0.7 d (mean ± S.E.) at 10 °C, 32 ± 0.5 d at 15 °C, and 17 ± 0.3 d at 20 °C. Analysis of variance demonstrated that the duration of E. marinus embryonic development, reared under different combinations of salinity and temperature, was significantly affected only by temperature (P < 0.001). A positive correlation between the number of newborn juveniles and the size of E. marinus females (as head length) was observed. The number of juveniles released per female was higher at 10 °C and lower at 20 °C. Analysis of variance showed that only temperature significantly affected the number of juveniles released per female (P < 0.001). Experimental data were used to calibrate the von Bertalanffy growth model. Results showed that growth was continuous throughout life under all laboratory conditions. Intrinsic growth rates were higher at 20 °C and lower at 10 °C. Analysis of covariance applied over the initial 90 d after hatching showed significant differences between growth rates of E. marinus under different salinity and temperature conditions. Extrapolation of laboratory data to the field scenario suggests that E. marinus in the Mondego estuary have a multivoltine life cycle.