The octopus is a sea-faring creature. Like camels of the desert and snow leopards living in snow-peaked mountains, adapted to live in specific surroundings and climatic conditions, octopuses too have for generations adapted to living in salty waters. What would then happen if you found an octopus all of a sudden living in a freshwater lake? It is this startling discovery of octopuses in the serene backwaters of Kochi that has baffled experts. And because octopuses can’t change their love for salt water in a day, the scientists fear it is actually the water of the backwaters that has turned from sweet to salty.
Oceans and seas around the world have an overdose of minerals dissolved in the water. It is this high mineral content that makes sea water very salty different and from river water. The fish, molluscs and other creatures living in oceans are thus different from the aquatic species found in rivers and freshwater lakes, each only fit to survive in its particular water habitat.
Saline survivors
Recently in Kerala fishermen were stunned to discover octopuses in the water bodies of Champakkara, Panangad and Kumbalanghi near Kochi. Under normal circumstances, if these sea creatures swam into the backwaters by chance they would have perished. But because the eight legged animals have survived, scientists are pondering if something is really wrong with the water quality of the backwaters.
According to K Sunilkumar Muhammad, head of the Molluscan Fisheries Division of the Central Marine Fisheries Research Institute, Kochi, the presence of marine species in coastal waters is due to the increased salinity of the area. He believes the level of salinity has reached 35 ppt (parts per thousand) by now, equivalent to seawater. He adds that sardines, another marine fish, were earlier reported from Champakkara and are proof enough that the water is changing.
Usually the salinity variation in water between high and low tides deter marine organisms from coming to the backwaters for feeding. But strong tidal actions and absence of rain and freshwater influx has changed the situation. It is not just the octopuses who now find the backwaters to be a new home. The less competition for food here, more prey and more space can attract other sea creatures too, including bigger predators like sharks.
Jumbled habitats
It is one of nature’s survival techniques, that makes marine species and freshwater species similar and yet so different. They are both aquatic creatures but there is a world of difference in the way they breathe, feed and exist. It has a lot to do with the salt content of the water and a process called osmosis.
All living organisms are made up of cells and these cells like to keep the concentration of chemicals on the inside the same as on the outside. Therefore a saltwater fish has a high salt content in its body cells like the water it swims in and a freshwater fish has diluted fluids in its cells.
When a saltwater fish is exposed to fresh water, all of that water floods into their cells in order to dilute the chemicals inside and keep a balance with the surrounding environment. Two things can happen when water floods in. Some cells fill up with so much water that they burst, while others just stop working because the chemicals inside them are too diluted. Both of these things will kill the fish. The same thing happens if you forcefully put a freshwater fish into salty seas or oceans.
The presence of octopuses in the backwaters thus signals another catastrophe. It means that the freshwater species already present in these waters, must be finding it hard to survive because the water is becoming saltier than it is supposed to be for them.
While scientists ponder over the matter, it is a lesson for us to understand how a single environment change can create the difference between life and death for so many living forms.