Raising CO2 levels in the oceans are going to benefit species of small farming fish

Learning to farm essentially changed the course of the entire human history. People settled down, stopped migrating seasonally and could form complex communities with specialized labour. However, humans are not the only animals that farm. There are several species of fish that farm their own patches of seaweed, but they are forced to change these practices with raising CO2 levels.

Damselfish don’t just graze the bottom of the ocean – they actually maintain little patches of seaweed – they are farming. Image credit: Brian Gratwicke via Wikimedia (CC BY 2.0)

There are several species of animals that farm, but damselfish are known for their farming. Damselfish are herbivorous, but they don’t just graze seaweed everywhere. They select small patches of land and start farming there. They weed out unwanted plants, they push out intruders and fertilize that seaweed by defecating around the area. This is adorable and very interesting behaviour, but it is likely to change dramatically in the near future. The problem is that CO2 levels in the ocean are rising at an unprecedented pace and seaweed is adapting to these new conditions.

CO2 levels are rising globally because of human activity. This, together with increasing acidity, is forecasted to decrease biological diversity in the oceans. But that doesn’t mean that there will be less of all the animals – some species can probably increase in number. Scientists say that those herbivorous fish that weed their territories could actually experience growth in population as food sources become more easily abundant. And so damselfish will enjoy seeing their primary food sources, turf algae, grow quicker as a result of raising CO2 levels. This means that one fish will be able to survive on a smaller patch of seaweed and more fish will fit in the same area. This will result in a population growth of damselfish at undersea volcanic seeps in New Zealand, where they’ve been researched.

Scientists found that in high-CO2 environments damselfish change their farming practices. For example, they spent twice as much time on weeding their crops than under control conditions. Professor Sean Connell, one of the researchers from the study, said: “This study shows that some populations of fish species might actually benefit from climate change. Nevertheless, there are still strong predictions of declines in other species, likely leading to an overall decrease in species richness.”

Climate change is still to be controlled. While some species may benefit, ocean life in general is going to suffer – there is no other possible outcome.


Source: University of Adelaide


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