Estuaries and hydrothermal vents constitute two very different ecosystems, but they have a curious characteristic in common: in both, two different kinds of water meet, creating a unique environment. Their peculiar features favor the flourishing of many forms of life, and have therefore become important objects of study for many researchers. Hydrothermal vents, having been discovered in relatively recent years, are attracting the interest of many a scientist, especially since it was previously believed that life could not exist so deep in the oceans, due to the absence of sunlight.
Estuaries are the meeting point of fresh and salt water and they can be found where rivers pour their water into the ocean. Fresh and salt water mix, allowing for a high productivity. In this special environment salinity varies according to the ebb and flow of tides. Estuaries can vary in dimension and water depth, and they are generally protected by surrounding land or barrier islands, acting as nurseries for a large amount of organisms. In fact, many species of animals spend their youth in estuaries, developing in this protected environment, and migrating either to the sea or to the rivers when they reach their maturity.
Hydrothermal vents are very unusual environments found on the bottom of the oceans, where very hot water rich in chemicals springs out of the seafloor. This happens because at rift valleys and hot spots the internal activity of the Earth forms some breaches in the crust, where the water seeps in and comes back out overheated, bringing along many dissolved minerals. Chimneys formed by this water can vary in temperature and mineral content, and their dimension grows until they become too tall and they eventually collapse. Only in 1977, Dr. Robert Ballard and his team discovered that life was thriving at hydrothermal vents.
Whereas life in estuaries relies as customary on photosynthesis – which means that plants transform the energy of sunlight into food, and then animals feed on plants and other animals, in hydrothermal vents all this is not possible, since the sunlight cannot reach the depths of oceans. This is the reason why scientists were really surprised to find life in such an environment. Then they discovered that there are bacteria able to transform energy from chemicals into food, in a process called chemosynthesis. These bacteria are the producers at hydrothermal vents, instead of plants, which are the producers on earth and also in the superficial part of the sea. Animals then feed on bacteria and other animals.
The mixing of salt and fresh water in estuaries and the protected environment give shield to many varieties of organisms. The producers in this ecosystems are represented by algae, sea grasses, and bacteria, while fishes, mollusks, and arthropods are the consumers. There are several animals, including larger fish – like rays, dolphins, sharks, and others – that go back to estuaries to eat and reproduce. We can also find some organisms specific to estuaries, like herons – which are birds with long legs able to walk in the water, and mangrove trees – which are characterized by large aerial roots.
Hydrothermal vents also have some specific forms of life which prosper in the environment. The principal producers here are bacteria able to transform energy from chemicals into food. The consumers are giant tubeworms, anemones, shrimps, crabs, mussels, and clams. It has been noticed that at times one specific kind of animals would decrease in number, while others species would increase. I suppose this might depend on the stages of development of the chimney which provide the chemicals needed for life, and the subsequent increase or decrease in temperature and mineral content of the ecosystem.
While the exploration of hydrothermal vents is reserved to scientists, due to the very hostile environment in which they are situated, estuaries constitute a protected environment around which a large amount of people live, and in which there are touristic and commercial interests. Fishing is a very productive activity in estuaries, where oysters, trouts, crabs, and shrimps are captured. Birdwatching is also a very popular activity carried out in this environment, and can give incommensurable pleasures, because many kinds of birds can be observed, including some that cannot be found elsewhere. It is also possible to set out with a boat and observe marine species in their reproductive stage, and often also some young fish can be seen. This makes of estuaries a resourceful environment, and a touristic attraction as well.