1. One biotic factor that affects consumers in an ocean ecosystem is
2. A. number of autotrophs
3. B. temperature variation
4. C. salt content
5. D. pH of water

Any change that might affect a link of the trophic web, will inevitably cause a cascade effect in the whole web. In the exposed example, the number of autotrophs is the biotic factor affecting consumers in an ocean ecosystem.

In oceanic and terrestrial ecosystems, organisms build nets of varying levels of interaction known as the trophic webs.  

The trophic web is a relationship process between different organisms, through which occurs transference of energy. The ones placed at lower levels pass energy to the ones at the higher levels.

Organisms at each level feed on the preceding one and become food for the next one.

As it is a web, all organisms are equilibrated until a change occurs. When the change affects any of the involved links, there can be a cascade effect on the web. A change in a link population size (increasing or decreasing) will affect the superior links and the immediately anterior link.

Also, when two or more species are competing for the same source of food, a change in any of the population sizes will affect the other ones.  

In the exposed example, we need to say which of the options are BIOTIC factors that affect consumers.

Among the options, there are temperature variations, salt content, and pH of water. All of them are significant factors that influence oceanic life. However, they are ABIOTIC factors.

The remaining option is the number of autotrophs. This option is a BIOTIC factor and is also the first link of many trophic chains.

Any change that might occur in this link -increasing or decreasing these populations-, will affect the whole system, beginning with their consumers.

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The right answer is A), number of autotrophs.

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