NIWA's Dr Ashley Rowden describes how a community of organisms develops around a cold-seep site. Forming the base of such a community are specialised bacteria that use methane gas present in the seep water as their energy source. Other organisms such as clams, mussels and tubeworms use these chemosynthetic bacteria by developing symbiotic relationships with them.
DR ASHLEY ROWDEN
So when a seepage first occurs, the bacteria are the first group of organisms which are going to exploit that seepage. They’re a special type of bacteria, so it’s not any sort of bacteria that can set up this chemosynthetic process.
Thereafter, other organisms will arrive who can tolerate the conditions at the seep and also particularly those organisms which can utilise those bacteria themselves. So that would include bivalves like mussels and clams, and those special sort of mussels and clams can take the bacteria into their own tissues on the gills, and then they can use the sugars that are made by the chemosynthetic process of the bacteria for their own food. So the clams and mussels get established and then, over time, due to for instance a reaction between the chemicals, the seawater, you get a precipitation of calcium carbonate that builds up a rocky structure. And that rocky structure then can be colonised by other groups of organisms which can use the bacteria in their bodies, and those include tubeworms. So the bacteria are then housed again in symbiosis within those tubeworms, and they become established. And as time goes on, a series of other organisms then come into this area and can use the whole environment to survive and can potentially even live off the tubeworms and the mussels themselves.
Symbiosis is the relationship between two organisms which is of mutual benefit, and they have evolved over time a relationship by which they perhaps might gain food from one another or shelter from one another. In the case of a seep community and something like a mussel or a tubeworm, the bacteria which reside within the mussel, for instance on the gills where they live, are gaining some sort of shelter by being within the body of the mussels.
They’re also gaining from the amount of fluid which the mussel can draw through its body bringing with it the methane and the other chemicals which the bacteria are going to rely upon to produce energy. The mussel itself is going to gain from this relationship because the energy which the bacteria creates, those sugars which it creates through chemosynthesis will be available also for the mussel to rely upon for its own food source.
National Institute of Water and Atmospheric Research (NIWA)
Dr Kareen Schnabel