Bottom-up concerns the availability of nutrients or resources. Thus, in the context of a coral reef community, if nutrients are scarce, so that algae can't grow, it is said that there is a bottom-up control on the community. Thus, any effect nutrients have must go up the web, while any effect consumers may have goes down the web. At the same time, certain species of fish are kept in the reef tank expressly to graze on any algae that might start to appear. In the following discussion the word algae is used frequently.
Algae encompasses a large group of organisms.
In a reef tank, as in nature, algae can be grouped into three broad categories. There are encrusting coralline algae that are rarely a problem in a reef tank. The last group is the macroalgae, which includes both fleshy and calcareous forms. While I have used the more generic term algae, the results of the paper discussed below pertain to marcoalgaes. Nutrient thresholds for bottom-up control of macroalgal blooms on coral reefs in Jamaica and southeast Florida.