The Effects of Pb and Hypoxia on the Oxygen Consumption of Crayfish - Lab Report Example

The Effects of Pb and Hypoxia on the Oxygen Consumption of Crayfish Freshwater and marine invertebrates often encounter reduced oxygen concentrations due to fluctuations in their environment. Such fluctuations such as temperature, salinity, aeration, chemical composition and atmospheric pressure directly either reduce the oxygen in water, or increase it. As a result, these organisms are forced to employ certain physiological mechanisms to compensate for the changes such as the reduction in O2 concentration and increase in Pb. The concomitant effects of Pb and hypoxia on oxygen uptake were tested on the C. destructor, Yabbie, to elicit whether increased Pb and hypoxia have an effect on respitation. There were Yabbies exposed to to 100 mg/L Pb for 7 days. There was also a group subjected to hypoxia with varying oxygen partial pressure without lead intoxication. There was also a group that was subjected to both lead intoxication and hypoxia at varying oxygen concentrations. This paper highlights these mechanisms and attempts to prove that Pb and hypoxia are indeed excluding factors for certain aquatic organisms. The presence of hypoxia alone did not lead to a major change in the amount of oxygen consumed (37.988%), as this would be expected of the crustaceans. When exposed to lead alone, the amount of oxygen consumed rose by 103.43%. This shows that the Pb induced compensatory mechanisms that increased the amount of oxygen taken up by the crayfish. When the crustaceans were exposed to hypoxia and Pb, the amount of oxygen consumed dropped by 45.5461% (12.188% less than those exposed to hypoxia alone). 12.188%. This means that indeed the addition of lead exacerbates the aforementioned hypometabolic state triggered by hypoxic states. This study also shows that the crustacean has a certain ability to cope with lead intoxication. The eventual result would be metabolic derangement of the crustacean leading to death, this exclusion from the environment. Further research into the effects of heavy metals should tus be carried tout to elucidate the exact effect they have on the crustaceans, and the implications. Introduction The organism under study, “Yabby” (Cherax destructor) is a crayfish endemic to the temperate Eastern Australia. Heavy metal contamination, such as lead and cadmium, is present within the industrialized tributaries and feeder channels of the rivers in the urbanized centers of eastern Australia (Birch, 1999). The metal in question, Lead remains within the environment for long periods as it is not biologically degraded. Furthermore, there is the aspect of storm water drainage. Storm water carries chemical substances into the water channel that cause eutrophication. This leads to hypoxic conditions that affect the crustacean. The C. destructor has been shown to occasionally become hypometabolic in response to hypoxic waters thus reducing the oxygen consumption altogether. It may also opt to breathe atmospheric oxygen (Morris S., 1998). All crustaceans generally have the same response to environmental hypoxia. The response to either hypoxic water or inefficient O2 diffusion at the gills is to increase their ventilation frequency. Experiments have shown that the Yabby, C. destructor was able to maintain haemolymph partial oxygen pressures during progressive hypoxia by an increase in ventilation by a factor of four (*4). Other experiments have shown that metals such as copper (Cu) and zinc (Zn) in can lead to or exacerbate the effects of hypoxia in crustaceans. This is probably due to gill damage. Similar effects have been observed and documented in other species of crayfish such as the Procambarus clarkii (A. Torreblanca, 1987). According to the results seen from the experiment, the oxygen consumption with exposure to lead (in hypoxemic conditions) reduces by 23.398%. This indicates a probable metabolic or physiologic change. The Yabby is the example chosen for this paper. It is able to compensate and maintain its O2 consumption until a critical partial pressure of O2 (2.7kPa), below which they cannot maintain normoxic levels of aerobic metabolism (Reiber 1995). The compensatory mechanisms include hyperventilation and increased affinity of their haemocyanin to oxygen. Chemicals such as lead, Pb reduce gill oxidation. This therefore reduces the overall O2 intake leading to hypometabolic conditions at normoxic partial pressures of O2 (Torreblanca et al. 1988). This response may be due to a hypometabolic response to Pb exposure as mentioned above. This may be an evolutionary mechanism allowing the crustacean to endure severe reduction of water quality and consequent impairment of oxygen uptake by its gills. Avoiding anaerobic state via progressive reduction of metabolic activity is energetically conservative. But this is only to a certain level where the crustacean would undergo metabolic derangements such as pH changes that would lead to death. It is thus that Ahern and Morris (1999) suggest that lead contamination would exclude C. destructor from hypoxia- prone waters. This paper focuses on the effect of oxygen concentration and Pb concentration to prove that hypoxia and Pb are excluding factors of aquatic life such as that of the common Yabby. The test organisms were divided into two groups; 1) Crayfish exposed to Pb in normoxic conditions, and 2) Crayfish that have not been exposed to Pb in hypoxic conditions There was also a group that was maintained as a control to ensure that a baseline activity level was achieved. Results In the results displayed by the graphs, it is evident that oxygen consumption in hypoxic conditions is reduced by the presence of lead. In normoxic conditions, the presence of lead leads to an increased amount of oxygen consumption. As seen above, (shown by the trend line), total oxygen consumed by the crayfish exposed to reduced oxygen concentration (H) is reducing. This means that hypoxic conditions reduce oxygen consumption. This may be due to the fact that these crustaceans exhibit physiological mechanisms that lead to reduced metabolism. As seen above, the presence of lead and hypoxia (Hpx/lead) greatly reduces the amount of oxygen taken up by the crayfish. This is as compared to the control (Na/Na). But, it is seen that when the crayfish are exposed to lead alone, their oxygen consumption increases. This reinforces the point that lead has certain effects on the crustaceans that exacerbates their oxygen uptake. The average oxygen consumption by the controls is 58.38337. Those exposed to hypoxia only 36.20445 The average consumption by the crayfish exposed to lead only is 60.3908 The average consumption by the ones exposed to sub lethal hypoxia and lead is 31.792 This data can be compared to show how the different conditions affected the crayfish. Making the assumption the controls are the baseline, The crayfish exposed to lead show a (2.00743/58.38337)*100 =3.4383 increase. This means that the oxygen uptake increased by 103.43% For the ones exposed to hypoxia alone, there was a 37.988% decrease in oxygen consumption. For the ones exposed to hypoxia and lead, there was a 45.5461% decrease in oxygen consumption. This is 12.188% less than that experienced in the hypoxic tests. This means that the crayfish are consuming almost half of the oxygen they would require to be at normal metabolic efficiency. This therefore implies that the presence of lead alone is not enough to cause the exclusion of the species, but also the presence of factors that cause hypoxia. These are factors such as the eutrophication. It is thus true that lead and hypoxia may lead to the exclusion of the Cherax destructor from habitats with Pb poisoning and reduced O2 concentratuons. Bibliography Science direct. (1999). Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. Available: http://www.sciencedirect.com/science/article/pii/S1095643399001014. Last accessed 5/5/2014. Oxford journals. (1995). Physiological Adaptations of Crayfish to the Hypoxic Environment. Available: http://icb.oxfordjournals.org/content/35/1/1.full.pdf+html). Last accessed 5/5/2014. Torreblanca et al. (1988). Cadmium, Mercury, and Lead Effects on Gill Tissue of Freshwater Crayfish Procarnbarusclarkii(Girard). . Biological trace element research. 21 (1), 343-347. Birch G, Taylor S. (1999). Source of heavy metals in sediments of the Port Jackson estuary Australia. Science of the total environment. 227 (1), 123-138. Morris S., Callaghan J.. (1998). The emersion response of the Australian Yabby Cherax destructor to environmental hypoxia and the respiratory and metabolic responses to consequent air breathing. Comp physiol. 168 (2), 389-398. Torreblanca, A., Diaz-Mayans, J., Del Ramo, J., N´u˜nez, A., (1987). Oxygen uptake and gill morphological alterations in Procambarus clarkii (Girard) after sublethal exposure to lead. Comp. Biochem. Physiol. 86C, 219–224. Read More