The correct answer is option 2 - always upright.

In an aquatic ecosystem, the pyramid of numbers represents the number of organisms at each trophic level. It shows the flow of energy and the relationship between different organisms in the ecosystem.

An upright pyramid of numbers means that the number of organisms decreases as you move up the trophic levels. This is because at each higher level, there are fewer organisms that can be supported by the available energy and resources.

In some cases, the pyramid of numbers can be partially inverted, where the number of organisms at a higher trophic level is greater than the number at the lower level. However, this is not common in aquatic ecosystems.

Therefore, an upright pyramid of numbers is the most common and expected pattern in an aquatic ecosystem.