Re: Why starfish eat other starfish on the same species?

Dear Mohd Afiq,

Cannibalism in sea stars has been frequently observed and documented. 
Ultimately, the sea star is using his "friend" as a food resource.  It is
possible that this is because there is not enough food in the aquarium, and
the sea stars may eat another for food.  However, in some cases, sea stars
eat each other even when there are sufficient other food resources.  It is
not clear whether this is more common in enclosed aquaria, or whether this
also occurs in the ocean.  Cannibalism in general is not uncommon in
animals as it provides a food resource, and reduced competition within the
species.

The articles referenced below both have some information about cannibalism
in sea stars.

1. http://rparticle.web-p.cisti.nrc.ca/rparticle/AbstractTemplateServlet?journal=cjz&volume=78&year=&issue=&msno=z99-250&calyLang=eng

2. http://www.esajournals.org/esaonline/?request=get-document&issn=0012-9615&volume=073&issue=03&page=0441