© John Turnbull
In 1847 Carl Bergmann observed that animals often grow larger toward the poles; this is evident in many animals both warm and cold blooded. I have certainly found this week that several marine species that are common to both subtropical NSW and temperate Tasmania appear to grow considerably larger in the colder waters. Take the purple urchin for example - in Sydney they're about 5 cm across, whereas in the waters around Hobart they grow to double that. This is known as Bergmann's rule.
Photo taken on 29 Oct 2015
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