Branches Accommodate Algae

photograph of pink and orange sea slug captured underwater

Biological Strategy

Sea slug

AskNature Team

Image: Klaus Stiefel / Flickr / Some rights reserved

Optimize Shape/Materials

Resources are limited and the simple act of retaining them requires resources, especially energy. Living systems must constantly balance the value of resources obtained with the costs of resources expended; failure to do so can result in death or prevent reproduction. Living systems therefore optimize, rather than maximize, resource use. Optimizing shape ultimately optimizes materials and energy. An example of such optimization can be seen in the dolphin’s body shape. It’s streamlined to reduce drag in the water due to an optimal ratio of length to diameter, as well as features on its surface that lie flat, reducing turbulence.

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Gastropods

Class Gastropoda (“stomach-foot”): Snails and slugs

There are at least 40,000 known species of gastropod, with many more yet to be discovered, making it the largest class of mollusks. These animals exhibit torsion, meaning their internal organs are twisted 180° during development. The majority of gastropods have shells, and most open up on the right side. The largest gastropods are the size of a small child (3 feet, or 1 meter) while the smallest are barely visible to the naked eye.

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The gut of one sea slug accommodates the algae it farms for nutrition by branching into leaf-like tentacles for increased housing space.

“One sea-slug common on the Great Barrier Reef in Australia has taken this practice even further. It is able to stimulate its captive algae so that they proliferate to an unusual degree. To accommodate the greater numbers produced in this way, it develops branches in its gut which extend into leaf-like tentacles along its flanks. Having stocked its tentacles with plants, the sea-slug moves away from the feeding grounds among the coral where it first acquired the algae. It seldom if ever feeds on coral again. It is sustained entirely, it seems, by its internal gardens.” (Attenborough 1995:204-205)