That is correct. If starfish have no awareness, no conscious experience, then what is ethically permissible in interacting with starfish is more broad than in the case that starfish are in fact self-aware.
Interesting. Here we have a divergence between us, as I tend to place more emphasis on the doer, rather than the subject. I find that this perspective allows one to more readily create general ethical guidelines, although this is perhaps merely the result of a misunderstanding of your own perspective.
For example, I propose that it is ethical to, in any action, minimize the pain that the action causes to the greatest reasonable extent. This is an ethic that we find fairly well ingrained in society. Ideally, for example, our animals are to be killed as painlessly as possible, regardless of if we're using them for food, science, or companionship, and regardless of this level of cognition. Regardless of if a creature can remember pain, or understand the context of pain, for creatures that can feel pain, it is unpleasant, even if only in the moment. Insofar that it is in our power to minimize that pain, it is our ethical obligation to do so.
Of course, this still does take into consideration the object of the action: I can't cause pain to a rock, so there is no ethical obligation to minimize the pain caused to that rock.
There is, of course, the flipside to this. Lack of cognition in the actor alters the ethics of the action. A cat lacks sufficient awareness to act ethically, and so when it fails to minimize pain by playing with a mouse, it does not act ethically or unethically, but rather "non-ethically."
To return to the rock, for a moment, we could likewise apply a general ethical principle to it as well. We might hold that it is unethical to destroy things without just cause. If so, then we could say that wantonly destroying rocks is unethical, regardless of if other human beings value it as art or not. Not that I expect this specific example to be a point of great significance in an ethical society, but the principle behind it well might be central.