Explanations for results of gorgonian experiment: the most convincing one is highlighted.

Different gorgonians have different growth rates. This is true, but all pieces were taken from colonies living near to one another in the same area of the reef; hence, growth rates would be expected to be similar.

The end portions intercept food items borne in the water currents and deprive the innermost portions of them. Yes, this is the conclusion of the authors. They also note that competition for water-borne resources is often neglected in studies of interactions between reef organisms.

The end portions out-compete the innermost portions for oxygen. Yes, this is possible, and is similar to the idea that the end portions out-compete the innermost ones for food.

The end portions are most advantageously sites with respect to light. Yes, this is true. Light is required by the photosynthesising symbionts found within the tissues of the gorgonians. The authors note that competition for light would increasingly favour the peripheral portions as they grow larger, just like it does for trees in a forest.

Predators selectively feed on the innermost portions owing to their protected location. No, predators play no role here. If they did, they would be more likely to select the end portions owing to their accessibility.

The innermost portions are negatively affected by metabolic and digestive wastes coming from the outmost portions. Yes, this is possible. Such wastes would include carbon dioxide and ammonia, representing end-products of metabolism, and food wastes, representing the end-products of digestion.