Since humans eat McDonalds burgers and consume copious amounts of soft drink, it must be OK.
Feeding wild animals is a regular habit in ecotourism worldwide with poorly known consequences for ecosystem functioning. This study investigates how effecti...
www.frontiersin.org
Bread feeding was shown to decrease taxonomical diversity in areas where controlled bread feeding occurred, Attracting more of the limited number of species that ate it. Those species then stayed more local to the area to continue natural feeding, driving away other species.
Add that to the fact that fish are not naturally exposed to gluten, they can't actually digest and process it.
Leave nothing but bubbles, take nothing but pictures. Especially in a marine sanctuary and/or national park.
Control things that are in your control, do your bit when you can.