Despite the recent reduction in demand for shark fin soup, shark finning is still continuing at a very high level in many areas of the world, and continues to impact severely shark populations. It is important to recognise the negative effects that abuses of ocean ecosystems are having, and to begin to realise that the potential consequences are far more far reaching than just running out of fish to eat. And so by reducing whale populations, we risk increasing carbon dioxide levels, too. This allows iron and other nutrients to come to the surface waters where phytoplankton live – and more phytoplankton means less carbon dioxide. Whales achieve this by transporting essential sources of iron across layers of water that don’t otherwise mix, by feeding at depth and defecating at the surface. There are also studies that demonstrate the potential role of whales in climate change, by providing nutrients for phytoplankton – the “plants” of the sea – to grow, and therefore absorb carbon dioxide. This occurs because predators can control populations or behaviour of other animals, which might prevent the build up of carbon deposits, for example, by disturbing or digging up the sediment, and releasing organic material back into the water column. More recent work has also demonstrated how predators can affect the feeding habits of prey species and how this can result in reductions in the subsequent storage of carbon in marine ecosystems, such as salt marshes. They also showed that carbon production can be increased by removing top predators from the system. While our study is based on a theoretical model, studies on the role of predators in carbon production have been conducted before, in simple systems consisting of only a few species. This results in more respiration occurring, and therefore more carbon dioxide production. Removing the predators, therefore, can result in a large increase in these low level populations – in fact, due to inefficient energy transfer, this increase could be up to 90% more in terms of biomass than the weight of the predators removed. Predators have the potential to reduce the biomass of prey species such as small fish and zooplankton (small animals in the water column). Typically, a predator population will only gain 10% of the biomass of the prey it consumes. The reason for this increase in carbon dioxide production is based on a simple and well-founded ecological principle taught to biology students in schools, that energy and biomass are not efficiently transferred through the food chain.
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