'Island rule' may apply to pint-sized deep-sea life: study

Animals that live on isolated islands have long followed the "island rule" of evolution, where small species grow larger and large species become smaller over time.

But according to scientists at the Monterey Bay Aquarium Research Institute (MBARI), deep-sea animals may follow the same rule.

The researchers found that deep-sea marine life was significantly smaller or larger than their shallow water relatives. In other words, if you live in shallow water, your deep sea neighbours of the same species are likely much larger or much smaller than you.

The MBARI scientists tested the "island rule" theory on deep-sea animals by observing thousands of marine snails in both deep and shallow levels of the ocean.

The results showed that shallow-water snails smaller than 12 millimetres in length had larger deep-water relatives. In comparison, shallow-water snails larger than 20 mm had smaller deep-water relatives.

But the island rule has been widely debated by scientists over the years. Those who disagree with it say that the size of the animals on isolated islands may depend on other factors, such as food resources. Some say that an animal's size is largely due to how accessible the food is, keeping in mind predation and competition from other animals.

With this in mind, MBARI scientists also say that deep-sea snails may not undergo evolutionary pressures like other animals, such as reduced habitat, predation or competition for food.

Photography: Paradise Found Island Retreat

Source: Discovery Channel Reports, July 11 edition