2.5: EFFECTS OF TIDES ON LIFE:

 

2.5.1: Effect of Tides on evolution of life:

What effects do the tides have on the evolution of life on Earth? Isaac Asimov, in his 1972 book, “The Tragedy of the Moon”,  posited how life, having evolved in the sea, could hardly have wanted to come on land. If there were no tides, creatures of the sea would either not have been flung up onto beaches, or if they were, they would not have developed adaptations quick enough to survive without immersion in water. Asimov believed that tidal pools and slopes within the tidal range were nurseries for such life forms to slowly evolve into air-breathing, sun-resistant creatures. They could then slowly develop suitable limbs, scales and other tools needed to venture further inland. Without tides then, Asimov reasoned, rather convincingly that life would have stayed in the Ocean. As in Nick Hoffman’s arguments, no life intelligent enough to produce astronomy would have evolved! 

 

2.5.2: Effects of tides on present life:

Many sea creatures time their spawning to coincide with favourable tidal conditions. Of these, the Grunion, a fish that mates and lays its eggs on beaches must be the most bizarre. They actually time their arrival on the California coast to coincide with the highest possible night Spring tides every year! 

 

Fig 20: Sex on the beach

The horseshoe crab does the same thing and migratory birds, aware of their spawning patterns, actually time their arrivals to coincide with them! It is not known how these creatures do it, but they are actually better at predicting tides than many humans are!

                                                       

Fig 21: The crabs

It is not known how these creatures do it, but they are actually better at predicting tides than many humans are! The Moon is not only a key tool in human time keeping. Animals seem to use it as a natural calendar too!

 

2.5.3: Tides and fishing:

Every fisherman worth his salt knows the importance of the tides to fishing. Fish are abundant at high tide and that is when workers on “kelongs” or “jermal”, platforms in shallow seas built to catch fish, winch up their nets more often. One very special case of a gigantic natural fish trap is the Tonle Sap in Cambodia. During the rainy season from May to October, floodwaters rush downstream to the Sap River, which empties the lake into the sea. The early part of this season coincides with the arrival of snowmelt from the Mekong’s source in the Tibetan Plateau. When these factors meet with a high Spring tide, the famous back flowing of waters into the Tonle Sap is most pronounced. The lake more than doubles in size and fish, caught in the current, flow into the basin. This was one of Cambodia’s richest sources of food, until constant over-fishing depleted stocks severely.

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