I have a world which is (nearly) a single-biome planet; it is mostly covered in shallow, ice-choked seas. There are few continents, but many archipelagos. Think northern Canada or Alaska as this planet's tropics.
Iceworld was not always this way. It used to be much warmer. In part to give somber historical depth, but also I needed to have land animals evolve. ;D
Here's my problem. I am not sure there is enough food available to support a human civilization. We have the following sources:
The sea is rich. Coastal areas thrive on hunters --- think seal- or walrus-like creatures -- which feed in the sea, then retreat inland to avoid the hotly (ha!) competitive environment of the coast. Smaller secondary ecosystems live off of this resource migration.
There is migration of birds and animals when feasible from the tropics north- and southward. Plant life shows up in the tropics in the summer, creatures eat it, then the creatures disperse.
Some kind of algae or lichen can grow on the open ice even at higher latitudes, supporting grazing and predation.
Even with all this, I'm not sure there's enough sustenance for to support a civilization. I want the main action to be in the bleak, bitter northern areas, not the soft tropics. The need is to support cities of at least 10,000 souls.
So, the actual question: How can I maximize the biomass in a high-arctic archipelago environment?