Hi Sasha, "Ebb and flow" refers to the recurring movement of water, such as the waves that roll up the shore before retreating into the sea, or the high and low tides . "Ebb and flow" can also be used figuratively to describe the ups and downs, or rise and fall of something which tends to be variable or follows some pattern. An example would be "fortune" which means the wealth and assets that one has. The better the sales of a magazine, the greater the fortune of its publisher. In your example, the sales of magazines are often at the mercy of changing consumer trends or lifestyles. Therefore, a magazine that used to be a hot seller may face dwindling sales in the future: the fortunes of its publisher ebb and flows. I hope this helps.

In this context, "fortunes" means monetary wealth, although sometimes when used this way it could mean general luck. "Ebb and flow" means to come and go in a cycle, as the ocean tides. If your fortunes ebb and flow, you are sometimes rich and sometimes not.