The most common debating point and area for disagreement is "Is a cooler essential" for the well being of native marine fish?
The answer is "well it depends".
Not very helpful I know, but there are some things that make this a bit of a grey area.
There are two categories of rock pool fish. There are fish which make their permanent home in the intertidal zone and are well adapted to being there and there are fish which live in the shallow sea and are often found trapped in the rock pools of the lower shore. These fish although often found in rock pools are less well adapted to the extreme conditions found there through the different seasons. This group of fish would probably fail to thrive in warmer water and so a cooler would be essential if they were being kept.
Then of course there are other factors to consider, if the tank is in an unheated north facing room it is quite different to a tank in a warm south facing room. Lighting can make a huge difference too.
So in short it is easily possible to keep some native marine fish without a cooler but for others a cooler is essential.
Most rock pool fish will readily accept dead prey with just one or two exceptions. But most will refuse dried food such as flake or pellets especially in the early stages.
It is possible to buy blister packs of sterilised and frozen food for marine fish. The range includes:
Lobster eggs, krill, lance fish, cockles, mussels, mysis shrimps, brine shrimps, red plankton, green seaweed and others. If stored correctly they will last for about 18 months in the freezer.