How does Seawater Chemistry affect Marine Life?



Life as we know it on this planet is based on water. The chemical reactions required to maintain life take place in water, either inside or outside of cells. Living organisms either live in water or have specific mechanisms and structures to collect and conserve water within their bodies. Organisms adjust their behavior so as to maximize the availability of water for their needs. Also the balance of chemicals in seawater is very similar to the balance of chemicals found in the fluids of land-dwelling creatures, suggesting a movement from the oceans onto land.

Survival also requires energy input to drive these chemical reactions and environmental conditions suitable to maximize the efficiency of these reactions. Organisms in the oceans and on land have come to develop the required mechanisms to meet these needs. There are many examples of situations where organisms have developed very interesting mechanisms to take advantage of environmental conditions where they can have an edge on the competition: two of these are coral reefs and hydrothermal vents.

Coral reefs are vast structures formed by the skeletons of living and dead coral polyps. They require huge amounts of calcium carbonate in seawater to provide the basis for the structural material of the skeletons. Temperature affects the solubility of calcium carbonate, with larger amounts dissolving in warmer waters. Therefore, corals tend to form reefs in areas with temperatures around 21 degrees celcius, normally between 25 degrees N and 25 degrees S latitude (cold currents in these areas, however, limit the areas of reef development).

Temperature has the opposite effect on the solubility of gases; gases are more soluble in cold water and less so in warm. Therefore, the warm tropical waters favorable to reef development because of the mineral content are unfavorable because of lack of oxygen. However, it is within these waters that reefs exist.

To provide oxygen so the corals can survive in warm waters, an interesting symbiotic relationship developed between the coral polyps and dinoflagellates called zooxanthellae. The zooxanthellae carry out photosynthesis to produce oxygen. Photosynthesis the biochemical process that combines water and carbon dioxide, in the presence of sunlight, to produce sugars and oxygen. Zooanthellae also help in the formation of skeletal material from calcium carbonate. In return, the coral polyps provide a safe haven, carbon dioxide, and a platform near the sunlight for the zooanthellae. This symbiosis, a true mutualistic relationship, helps explain the tremendous productivity of the coral reef.

Hydrothermal vents are found at the opposite end of the oceans; while coral reefs exist mainly in the upper 30 meters of the ocean, hydrothermal vents exist near the bottom at depths in excess of 2800 meters. Vents were first discovered in 1977 by Robert Ballard (the JASON Project man) and J.F. Grassle of Woods Hole while diving near the Galapagos Islands in the submersible Alvin. These hot springs emit water at temperatures in excess of 350 degrees celcius with large quantities of dissolved metals and sulfur. Since then, additional sites have been discovered in the Atlantic and Pacific oceans, and within the freshwater lakes of Lake Baikal in Siberia and Yellowstone Lake in the U.S. More intriguing still was the discovery of vast numbers of organisms living in the vicinity of these vents, despite the fact that there is absolutely no sunlight, which means no photosynthesis. The vent organisms, like the corals, have also developed symbiotic relationships so they can survive in these harsh conditions.

The best known of the vent-dwellers is the vent tube worm, which is approximately 3 meters in length! These worms have a symbiotic relationship with chemosynthetic bacteria. Instead of capturing the sunlight's energy by photosynthesis, chemosynthetic bacteria produce energy by oxidizing hydrogen sulfide gas from the vent water. Other energy-rich compounds used by chemosynthetic bacteria include metals, methane gas, and petroleum. The energy is then used to convert carbon dioxide into carbohydrates, which are food for the worm. The waste products from the worm then nourish the bacteria to complete the symbiotic relationship.

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Thus we see that, while chemistry dictates the environmental conditions of the oceans, organisms have evolved ways of occupying specific, if initially inhospitable, areas and surviving quite successfully.

This completes How does Seawater Chemistry affect Marine Life?


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