The Response of Crayfish to Variation in Temperature and pH - Research Paper Example

The Response of Crayfish to Variation in Temperature and pH Student’s Name Institution Abstract The changing environmental conditions affect invertebrates throughout their life cycles. Changes in temperature and other environmental conditions may distract the life cycles of invertebrates, while constraining their movements. This study evaluated both the specific effects of pH and temperature, and the interaction between them on the bite force and locomotor performance of crayfish. There was no statistical significant effect of decreasing or increasing temperatures and pH on crayfish locomotion (ANOVA, F = 1.839, df = 8, 25, p = 0.117). However, it was evident that swimming speeds were greatest at the higher values of temperatures and pH. There was a statistical significant effect of decreasing or increasing temperatures and pH on crayfish bite force (ANOVA, F = 2.280, df = 8, 25, p = 0.05). Crayfish displayed unusual muscle performance at temperatures of 20˚C and 30˚C. On the other hand, the muscle performance decreased as the pH level increased. There were no study specifically focusing on the effect of pH on the crayfish’s muscle performance and further studies are necessary to shed more light on this field. 1.0 Introduction Although there are few studies concerning the effect of pH on pelagic processes, several studies indicate that pH influence the evolution and growth of marine organisms. Freshwater has a pH of about 6 to 8, whereas seawater has a constant pH of about 8.2 because of high levels of carbon dioxide (CO2)[Han02]. According to him, phytoplankton species have higher growth rates at a pH of about 7.5 to 8, and a pH of 8.5 slows their growth and this growth is completely halted at a pH of 9.6. On the other hand, Ye and Randall (1991) indicated that acidic conditions of pH 4 causes a gross reduced critical velocity of trout as compared to the pH conditions of the freshwater. Lengthy exposure to acidic conditions causes a higher reduction in swimming velocity because if the accumulation of hydrogen ion (H+). On the same note, most of freshwater species are greatly affected by a pH greater than 9; however, some species are not affected by high alkaline pH[YeX91]. One of the reasons that has been identified to cause decreased swimming speed in high alkaline conditions is the buildup of ammonia in the body, which results in toxicity[YeX91]. In similar manner, the effect of temperature on the bite force and locomotion of organisms is significant. A change in temperature is one of the critical environmental conditions that play a significant role in their adaptation to changes in their surroundings. Some species flourish very well in certain temperatures, optimizing enzyme reactivity, fecundity, and metabolism. For instance, Callaghan, Somme, and Sonesson (1993) indicated that mosses thrive well in a warmer wetter environment, whereas they will decrease in a warmer drier environment. Ross et al. (1992) also indicated that the larval development of house crickets is boosted by elevated temperatures. On the other hand, locomotor speed is directly proportional to temperature up to a time that the critical temperature is surpassed[Cla00]. The purpose of this study was to evaluate both the specific effects of pH and temperature, and the interaction between them on the bite force and locomotor performance of crayfish. Previous studies indicate that both pH and temperature separately affect performance levels. It is also evident that increasing temperature leads to the release of additional hydrogen ions, which eventually reduces the pH value of the water[Wel10]. Therefore, the study predicts that crayfish will perform better at their optimum pH and temperatures, whereby the final pH value will be affected by temperature. Factors such as anthropogenic forcing and global warming both have significant impacts upon aquatic environments; hence it is relevant to understand how aquatic organisms cope with this change. 1.1 Aims and Hypotheses The aim of the study is to examine the effect of temperature and pH on the locomotion and bite force of crayfish. It is hypothesized that locomotion will be the fastest at 25˚C and at a pH of 8. It is also predicted that crayfish may display unusual muscle performance at temperatures of 20˚C and 30˚C and pH of 6.5 and 9.5. 2.0 Methods and Materials 2.1 Experimental Design There were two treatment factors used in the experiment: pH and temperature. Each factor had 3 levels. Temperatures of 20˚C, 25˚C and 30˚C, and pH of 6.5, 8 and 9.5 were tested, and each had 4 replicates. The total number of crayfish measured was 34. The 3 levels of each factor resulted to the following 9 treatment combinations as shown in Table 2 below. Table 1 below shows the levels of each factor. Table 1: Levels of pH and Temperature Temperature pH 20˚C 6.5 8 9.5 25˚C 6.5 8 9.5 30˚C 6.5 8 9.5 Table 2: Treatment Combinations Index Treatment Combination 1 20˚C and pH 6.5 2 20˚C and pH 8 3 20˚C and pH 9.5 4 25˚C and pH 6.5 5 25˚C and pH 8 6 25˚C and pH 9.5 7 30˚C and pH 6.5 8 30˚C and pH 8 9 30˚C and pH 9.5 The study aimed for a replication of about 5 but due to time and availability of crayfish, we settled on a replication of 4 as noted above. The data was analyzed using a two way ANOVA. Assumptions of constant variance and normality were checked and where necessary, data was transformed. When results were significant, least significant differences were used to test which levels were different. 2.2 Treatments The study was conducted over three temperatures: 20˚C, 25˚C and 30˚C. The water temperature was maintained using a water heater for fish tanks. This was done to keep the crayfish at the respective temperatures for one week. Temperature of water was checked daily with a thermometer just in case any adjustments to temperatures needed to be made as temperature could fluctuate due to equipment or ambient temperature. The 3 pH levels measured were 6.5, 8 and 9.5, as stated above. These levels were chosen because most species of crayfish prefer harder water that is slightly alkaline at about 7.5 to 8.5 pH. Therefore, a pH of 8 was chosen as the normal, and other pH levels above and below this level were tested. The pH levels were adjusted by adding chemicals or minerals to the water in order to make it more alkaline. Tests were first started at the lowest pH (6.5) because it is easier to gradually increase the pH level. The crayfish were removed from tanks, and baking soda or similar products added to increase the pH. Similar to temperature, the pH levels of the water were checked daily and adjusted accordingly. The hardness of the water was also monitored because it may also affect the pH. 2.3 Responses Measured The responses that were measured in this study were locomotive performance and bite force. Locomotive performance was measured by measuring the sprint speed of the crayfish. This was done by placing the crayfish into a shallow tray that was filled with enough water to keep it submerged. A ruler/tape measure was placed inside the tray to measure the distance travelled by the crayfish. An escape response was then initiated by chasing the crayfish with a long stick. The escape response was observed in the crayfish through a tail flip. The crayfish was filmed before the tail flip and recorder until it reached the end of the tray. This video was analyzed using Tracker Video Analysis to determine the speed of the crayfish. The speed of the crayfish was also determined by timing how long it took to move to the other end of the tray and then calculating velocity using the distance travelled and time. The second method was used when there was no video taken. The bite force of the crayfish was also measured to determine their muscle performance under the given temperature and pH conditions. The bite force measurements were made using a transducer that was placed between a pair of claws of the crayfish. This set-up was used to measure the strength of their claw muscle as an indicator of muscle performance. 3.0 Results The between-subjects factors for the two responses measured in this study were as shown in the table below. As mentioned above, the crayfish measured were 34, and they were distributed in the two treatment factors as indicated in the table below. Table 3: Between-Subjects Factors 3.1 Locomotor Performance Using UNIANOVA, the results for locomotor performance are as shown in the tables and figures (plots) below. Table 5 below indicates the descriptive statistics for the locomotive variable. Levene’s Test of Equality of Error Variances was also performed to test the null hypothesis that the error variance of the dependent variable (locomotion) is equal across groups. The results of this test are as shown in Table 4 below. Table 4: Levene's Test of Equality of Error Variances Tests of Between-Subject effects were also conducted and the results are as shown in Table 6 below. Spread vs. level plots and scatter plots of locomotion were plotted as shown in Figure 1 and 2 below. Table 5: Locomotion Descriptive Statistics Table 6: Tests of Between-Subjects Effects Figure 1: Spread vs. Level Plots of Locomotion Figure 2: Scatter Plots of Locomotion 3.2 Bite Force Using UNIANOVA, the results for muscle performance are as shown in the tables and figures (plots) below. Table 7 below indicates the descriptive statistics for the bite force variable. Table 7: Bite Force Descriptive Statistics Levene’s Test of Equality of Error Variances was also performed to test the null hypothesis that the error variance of the dependent variable (bite force) is equal across groups. The results of this test are as shown in Table 8 below. Table 8: Levene’s Test of Equality of Error Variances Tests of Between-Subject effects were also conducted and the results are as shown in Table 9 below. Scatter plots of bite force was plotted as shown in Figure 3 below. Table 9: Tests of Between-Subjects Effects Figure 3: Scatter Plots of Bite Force 4.0 Discussion Both temperature and pH had significant effect on the locomotion performance and bite force of the crayfish. As shown in Table 4, there was no statistical significant effect of decreasing or increasing temperatures and pH on crayfish locomotion (ANOVA, F = 1.839, df = 8, 25, p = 0.117). This could be as a result of some limitations in the experiment. However, it was evident that swimming speeds were greatest at the higher values of temperatures and pH. The swimming speeds were 13.0455 and 13.611 for 30o C and pH 9.5 respectively. The temperature part is in agreement with the study conducted by Claussen, Hopper, and Sanker (2000). According to their study, swimming speeds were greatest at 25o C and 30o C. On the other hand, Ellis and Morris (1995) indicate that the swimming speed is greatly affected by the pH levels. According to their study higher and lower pH levels depress aerobic and anaerobic metabolism in crayfish; hence, affecting their locomotion. In terms of lower pH levels causing lower swimming speeds, Ellis and Morris (1995) indicate that alkalinity leads to extensive and rapid depression of metabolism; hence, lower swimming speed (see Table 5). According to their study, cryfish rxposed to higher pH levels (pH 8) had a 53 per cent decrease in oxygen uptake and crayfish exposed to lower pH level (pH 4.5) had a 79 per cent dectrease in oxygen uptake[Ell95]. Oxygen uptake affects their metabolism which in turn affects their locomotion. In regard to bite force, both temperature and pH had significant effect on bite force of the crayfish. As shown in Table 4, there was a statistical significant effect of decreasing or increasing temperatures and pH on crayfish bite force (ANOVA, F = 2.280, df = 8, 25, p = 0.05). As hypothesized, crayfish displayed unusual muscle performance at temperatures of 20˚C and 30˚C. At 20o C the bite force was at 6.1673; this value increased to 9.0017 at 25o C and then reduced to 6.8753 at 30o C. According to Stephens (1985), muscle force generation of crayfish dramatically decreases as temperature increases. This is because an increase in temperature leads to a reduction in the effectiveness of neuromuscular transmission[Ste85]. Seebacher and Wilson (2006) also indicate that raising the temperature alters the properties of the muscles and motor nerves; hence, lowers the muscle performance. On the other hand, the muscle performance decreased as the pH level increased. The bite force was 7.2700 at pH 6.5. This value decreased to 7.2545 and 6.0655 at pH 8.0 and pH 9.5 respectively. There were no study specifically focusing on this area and further studies on this field are necessary to shed more light on the issue. However, studies on some aquatic animals indicate that their muscle performance can be decreased by an increase in pH level[Wel10]. These results may not be conclusive because some of them had no significant effect. For instance, there was no statistical significant effect of decreasing or increasing temperatures and pH on crayfish locomotion possibly because of poor experimental methods. There are a number of things that could be done to improve the future understanding of the subject such as increased time intervals of observations, undertake continuous recording or use a different recording techniques, and possibly increased acclimation time. Conclusion This study extends what previous studies have suggested in regard to the adaption of crayfish to changes in environmental conditions. The effect of temperature and pH on the locomotive performance and bite force of crayfish provides an effective system for evaluating questions regarding the adaptive implication of thermal and pH acclimation, and connecting them with their essential physiological mechanisms. In addition, several species of crayfish experience seasonal variations in environmental conditions. Therefore, it would be a benefit if their physiological capability shows noticeable responses to various changes in environmental conditions. References Han02: , (Hansen , 2002), YeX91: , (Ye & Randall, 1991), Cla00: , (Claussen, Hopper, & Sanker, 2000), Wel10: , (Wells, 2010), Ell95: , (Ellis & Morris, 1995), Ste85: , (Stephens, 1985), Wel10: , (Wells, 2010; Ellis & Morris, 1995), Read More