Essay on Achieving Ionic Equilitbrium in Marine Fish

This report presents the physiological changes in the heart rate of a fresh water crustacean Daphnia magna when exposed to caffeine and alcohol. Different Daphnia magnas were placed in a depression slide containing fresh water and later exposed to solutions of caffeine and alcohol. Each Daphnia magna had different responses. These data suggest there is an increase in heart rate when a Daphnia magna is exposed to caffeine and a decrease in heart rate when it is in a solution of alcohol.

Temperature had a direct effect on oxygen consumption of crayfish, Orconectes propinquus. Crayfish acclimated to warm temperature (20 to 25 C) had a mean mass of 8.25g +/- 1.05. Crayfish acclimated to cold temperature (3 to 5 C) had a mean mass of 10.61g +/- 0.77. Oxygen consumption rates of 30-60 minute treatments were used and there was no significant difference between the two different treatments (t=0.48, df=58, P=0.70). The data from 0-30 minutes were not used because the crayfish were disrupted by transportation and the data were not normally distributed. The Q10 value was 1.05, representing that there was full compensation for oxygen consumption for the crayfish at two different acclimated temperatures. The oxygen consumption of crayfish was not affected significantly by two different temperatures (Figure 1).

Osmosis is the passive movement of water from an area of low solute concentration to an area of high solute concentration, normally across a membrane which prevents the movement of solvent. This is a process by which materials may move into, out of, or within cells. Osmosis doesn’t depend on energy provided by living organisms but is affected by the properties of the cell membrane. The rate of osmosis is dependent on such factors as temperature, pressure, molecular properties such as size and mass, and the concentration gradient. In osmosis, the relationship between a solute’s concentration outside of cell and inside of a cell is described in terms of the tonicity of the solution outside of the cell. A cell is in a hypotonic solution when the solute is more concentrated inside the cell and therefore water moves into the cell. In this solution the cell swells as water enters, this may continue until it ruptures or hemolyzes. In the reverse condition, the cell is in a hypertonic solution

“Since the beginning of the industrial era, the ocean has absorbed some 525 billion tons of CO2 from the atmosphere, presently around 22 million tons per day” (Ocean Portal, n.d). This number is expected to increase forevermore as atmospheric carbon dioxide levels increase and the effects of Climate Change worsen. At first, the idea of our oceans absorbing carbon dioxide from the atmosphere may sound great, however, scientists have been quick to learn otherwise. High concentrations of carbon dioxide in oceans can have detrimental effects on the ocean chemistry and marine ecosystems (Hardt; Safina, 2008). Marine ecosystems are greatly complex and depend on every marine organism to function properly, any change can put the whole ecosystem at risk. For example, the increase of carbon dioxide in our oceans is responsible for the dissolving of “brittle star” skeletal parts, which has in effect caused food scarcity for many fish, crabs, shrimp, and other starfish (Leu, 2013). Furthermore, these marine ecosystems are very important to humans- being the primary food source for millions around the world and having an economic market worth trillions of dollars (Hardt; Safina, 2008). Part of keeping these ecosystems safe is to understand how they work and how projected changes can harm marine organisms.

By pumping sodium through the daphnias’ epithelial cytoplasm and passing to the hemolyph, is the organism’s major method for osmoregulation. The process of ion homeostasis ensures the survival of these osmoregulating aquatic organisms. These organisms maintain high body ion concentrations in freshwater and low concentrations in salt water; however, remain restricted to freshwater environments with concentrations lower than 1gL-1 due to the organisms body size determining the sensitivity of freshwater

After passing through the esophagus, which absorbs much of the salt ions in the swallowed saltwater, and the gut the luminal fluid is isosmotic with the plasma. The intestines continue to absorb salt (sodium through chloride co-transport proteins and the chloride through the sodium co transport proteins and anion exchange protinis) which is followed by an uptake of water. More chloride is absorbed than sodium which creates an electrogradient in the cell (the cell being more positive and the plasma more negative). The anion exchanger intakes chloride all while excreting HCO3- into the intestinal lumen. The intestinal fluid is highly alkaline, high in HcO3- and high in calcium (from the environment), this allows for CaCo3 to be precipitated in the

distal tubule adjusts the ionic balance of the body by changing the amount of sodium

In many cells antiporters move calcium out of the cell while sodium drifts in. This sustains the low calcium concentration in the cytosol.

The map above shows a depiction of aragonite saturation, a form of calcium carbonate that many marine species also rely on to build their protective shells. It is anticipated that a high volume of species relying on carbonate ions to form outer layers and exoskeletons will be negatively affected by the changing chemistry of seawater. Even a slight drop in pH levels will mean higher concentrations of hydrogen ions will be available to bond with carbonate ions, forming more bicarbonate than normal. Marine calcifying species are this put at a higher risk for predation. Ocean researchers and marine biologists are hopeful that some marine species that calcify for survival will be able to adapt to the changing pH levels in the oceans. Others are not so optimistic, and expect that an acidic oceanic environment may result in mass extinction and serious disruptions to aquatic food chains.

Redistribution of blood flow between outer cortex and medulla alters salt and water excretion. The majority of Na+ ion is reabsorbed by the thick ascending loop of Henley, the length of loop of Henley effects the amount of Na+ reabsorbed.

Na+ , K+ and Cl- cotransporter is envolved in electroneutral transport at apical surface, which is driven by low concentration of these ions. This low concentration of ions is achieved by basolateral Na+ and K+ contertransporter (sodium-potassium adenosine triphosphatase) and basolateral chloride ion channel by facilitated diffusion (CLC-kb). Potassium ion is capable of diffusing back to lumen through apical potassium channel (ROMK) and returns net positive charge to lumen, this is important for reabsorption of calcium and magnesium

The fact that potassium is indeed the most influential determinant of crayfish resting membrane potential can be seen through the analysis of Figure 2. This table shows that the obtained resting membrane potential follows the same trajectory as the Nernst calculated one. The initial concentration elicited a resting membrane potential that was significantly more positive than

The concentration of solutes in the bodily fluids of most marine invertebrates is roughly isosmotic to their environment (Raven, 2008). Because there is no osmotic gradient there is no tendency for the net diffusion of water away from the animal’s cells to occur. When a change in salinity occurs some organisms have the ability to maintain a constant internal homeostasis despite these external changes and are known as osmoregulators (Oxford, 2008). Other animals lack this ability and as such are called osmoconformers; their internal osmolarity matches that of their

Being a freshwater dwelling organism, the obvious source of the hydrostatic fluid in the gastro vascular cavity for the hydra is from its surroundings

Two crab species, Plagusia and Cyclograpsus, were collected from a local estuary in the littoral and deep water zone for osmoregulation studies. To examine differences in osmoregulatory mechanisms among the species, haemolymph of the specimens was extracted once they were acclimated to varying concentrations of seawater. Using the comparative melting-point, capillary tubes were filled with small samples of seawater and blood then frozen and melted in a -15˚C ethanol bath. The melting time of each was observed thereafter. Subject’s time range fell over 17 minutes of which the majority of the most salinated samples melted