Did you intentionally remove the first part of the paragraph ? They are talking about the environmental impact of octopus farming which creates artificial strain on the environment.

> The amount of feed needed to sustain and grow an octpus is three times the weight of the animal itself and, given that octopuses are carnivorous and live on fish oils and protein, rearing them risks putting further pressure on an already over-exploited marine ecoystem.

The calories spent on raising and consuming animals higher in the food chain is exponentially more than consuming those lower in the food chain. This is the point they are trying to make. It wasnt about the ethics of eating Octopus itself, but the means in which they are being raised / procured.